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Sensors, Volume 13, Issue 3 (March 2013) – 80 articles , Pages 2700-3997

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748 KiB  
Article
A Silver Nanoparticle-Modified Evanescent Field Optical Fiber Sensor for Methylene Blue Detection
by Ji Luo, Jun Yao, Yonggang Lu, Wenying Ma and Xuye Zhuang
Sensors 2013, 13(3), 3986-3997; https://doi.org/10.3390/s130303986 - 21 Mar 2013
Cited by 31 | Viewed by 9553
Abstract
A silver nanoparticle-modified evanescent field optical fiber sensor based on a MEMS microchannel chip has been successfully fabricated. Experimental results show that the sensor response decreases linearly with increasing concentration of analyte. Over a range of methylene blue concentrations from 0 to 0.4 [...] Read more.
A silver nanoparticle-modified evanescent field optical fiber sensor based on a MEMS microchannel chip has been successfully fabricated. Experimental results show that the sensor response decreases linearly with increasing concentration of analyte. Over a range of methylene blue concentrations from 0 to 0.4 μmol/mL, the sensor response is linear (R = 0.9496). A concentration variation of 0.1 μmol/mL can cause an absorbance change of 0.402 dB. Moreover, the optical responses of the same sensing fiber without decoration and modified with silver nanoparticles have also been compared. It can be observed that the output intensity of the Ag nanoparticle-modified sensor is enhanced and the sensitivity is higher. Meanwhile, the absorbance spectra are found to be more sensitive to concentration changes compared to the spectra of the peak wavelength. Full article
(This article belongs to the Section Chemical Sensors)
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<p>Schematic representation of the light path in optical fibers.</p> Full article ">
<p>Fabrication process sequence and the mask pattern.</p> Full article ">
<p>(<b>a</b>) Front-side photograph of the MEMS microchannel chip; (<b>b</b>) Completed sensing fiber picture.</p> Full article ">
<p>The SEM images of the as-prepared silver nanoparticles.</p> Full article ">
<p>(<b>a</b>) Schematic of sensing fiber surface silanization and the silver nanoparticles modification processing procedure; (<b>b</b>) Image of the sensing fiber modified with the silver nanoparticles.</p> Full article ">
<p>Schematic representation of the experimental system.</p> Full article ">
<p>Spectra of varying concentrations of methylene blue under (<b>a</b>) visible light; (<b>b</b>) red light.</p> Full article ">
<p>(<b>a</b>) The curves of the peak absorption intensity and wavelength changing with different concentrations of the analytes; (<b>b</b>) The plot of absorbance <span class="html-italic">versus</span> concentration.</p> Full article ">
<p>(<b>a</b>) Spectra of six different concentrations of methylene blue; (<b>b</b>) Test curve of absorbance <span class="html-italic">versus</span> corresponding concentration and plot of absorbance <span class="html-italic">versus</span> concentration of the silver nanoparticle-modified optical fiber sensor.</p> Full article ">
431 KiB  
Article
Piper nigrum, Piper betle and Gnetum gnemon- Natural Food Sourcewith Anti-Quorum Sensing Properties
by Li Ying Tan, Wai-Fong Yin and Kok-Gan Chan
Sensors 2013, 13(3), 3975-3985; https://doi.org/10.3390/s130303975 - 20 Mar 2013
Cited by 47 | Viewed by 9230
Abstract
Various parts of Piper nigrum, Piper betle and Gnetum gnemon are used as food sources by Malaysians. The purpose of this study is to examine the anti-quorum sensing (anti-QS) properties of P. nigrum, P. betle and G. gnemon extracts. The hexane, chloroform [...] Read more.
Various parts of Piper nigrum, Piper betle and Gnetum gnemon are used as food sources by Malaysians. The purpose of this study is to examine the anti-quorum sensing (anti-QS) properties of P. nigrum, P. betle and G. gnemon extracts. The hexane, chloroform and methanol extracts of these plants were assessed in bioassays involving Pseudomonas aeruginosa PA01, Escherichia coli [pSB401], E. coli [pSB1075] and Chromobacterium violaceum CV026. It was found that the extracts of these three plants have anti-QS ability. Interestingly, the hexane, chloroform and methanol extracts from P. betle showed the most potent anti-QS activity as judged by the bioassays. Since there is a variety of plants that serve as food sources in Malaysia that have yet to be tested for anti-QS activity, future work should focus on identification of these plants and isolation of the anti-QS compounds. Full article
(This article belongs to the Section Biosensors)
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<p>Violacein inhibition by (<b>a</b>) <span class="html-italic">P. nigrum</span> (chloroform) extract; (<b>b</b>) <span class="html-italic">P. nigrum</span> (Methanol) extract.</p> Full article ">
<p><span class="html-italic">P. aeruginosa</span> PA01 pyocyanin formed after addition of (<b>a</b>) <span class="html-italic">P. betle</span> (hexane extract); (<b>b</b>) <span class="html-italic">P. Betle</span> (chloroform extract).</p> Full article ">
<p>Effect of <span class="html-italic">P. betle</span> methanolic extract against <span class="html-italic">P. aeruginosa</span> PA01 swarming motility; (<b>a</b>) swarming agar with the addition of (<b>b</b>) solvent (DMSO 30%); (<b>c</b>) <span class="html-italic">P. betle</span> methanolic extract (1 mg/mL); (<b>d</b>) <span class="html-italic">P. betle</span> Methanolic extract (2 mg/mL); (<b>e</b>) <span class="html-italic">P. betle</span> Methanolic extract (3 mg/mL).</p> Full article ">
<p>Growth of (<b>a</b>) <span class="html-italic">P. aeruginosa</span> PA01 in the presence of <span class="html-italic">P. betle</span> (hexane extract); (<b>b</b>) <span class="html-italic">P. aeruginosa</span> PA01 in the presence of <span class="html-italic">P. betle</span> (chloroform extract); (<b>c</b>) <span class="html-italic">E. coli</span> [pSB 1075] in the presence of <span class="html-italic">G. gnemon</span> (hexane extract); (<b>d</b>) <span class="html-italic">E. coli</span> [pSB 1075] in the presence of <span class="html-italic">G. gnemon</span> (chloroform extract).</p> Full article ">
991 KiB  
Article
A Transmission Power Optimization with a Minimum Node Degree for Energy-Efficient Wireless Sensor Networks with Full-Reachability
by Yi-Ting Chen, Mong-Fong Horng, Chih-Cheng Lo, Shu-Chuan Chu, Jeng-Shyang Pan and Bin-Yih Liao
Sensors 2013, 13(3), 3951-3974; https://doi.org/10.3390/s130303951 - 20 Mar 2013
Cited by 16 | Viewed by 9447
Abstract
Transmission power optimization is the most significant factor in prolonging the lifetime and maintaining the connection quality of wireless sensor networks. Un-optimized transmission power of nodes either interferes with or fails to link neighboring nodes. The optimization of transmission power depends on the [...] Read more.
Transmission power optimization is the most significant factor in prolonging the lifetime and maintaining the connection quality of wireless sensor networks. Un-optimized transmission power of nodes either interferes with or fails to link neighboring nodes. The optimization of transmission power depends on the expected node degree and node distribution. In this study, an optimization approach to an energy-efficient and full reachability wireless sensor network is proposed. In the proposed approach, an adjustment model of the transmission range with a minimum node degree is proposed that focuses on topology control and optimization of the transmission range according to node degree and node density. The model adjusts the tradeoff between energy efficiency and full reachability to obtain an ideal transmission range. In addition, connectivity and reachability are used as performance indices to evaluate the connection quality of a network. The two indices are compared to demonstrate the practicability of framework through simulation results. Furthermore, the relationship between the indices under the conditions of various node degrees is analyzed to generalize the characteristics of node densities. The research results on the reliability and feasibility of the proposed approach will benefit the future real deployments. Full article
(This article belongs to the Section Sensor Networks)
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<p>A graph of wireless sensor network.</p> Full article ">
<p>Three-tier network model.</p> Full article ">
<p>The flowchart of an adaptive optimization transmission with a minimum node degree.</p> Full article ">
<p>The corresponding relationship of network evaluations with a node density of 0.0005 nodes/m<sup>2</sup>.</p> Full article ">
<p>The corresponding relationship of network evaluations with a node density of 0.005 nodes/m<sup>2</sup>.</p> Full article ">
<p>A comparison of the simulation results for connectivity and reachability with different node densities.(<b>a</b>) density = 0.0005 nodes/m<sup>2</sup>; (<b>b</b>) density = 0.001 nodes/m<sup>2</sup>; (<b>c</b>) density = 0.005 nodes/m<sup>2</sup>; (<b>d</b>) density = 0.01 nodes/m<sup>2</sup>.</p> Full article ">
<p>A comparison of the simulation results for connectivity with node degrees ranging from 1 to 8 with different node densities.</p> Full article ">
<p>A comparison of the simulation results for energy savings and reachability with different node densities. (<b>a</b>) density = 0.0005 nodes/m<sup>2</sup>; (<b>b</b>) density = 0.001 nodes/m<sup>2</sup>; (<b>c</b>) density = 0.005 nodes/m<sup>2</sup>; (<b>d</b>) density = 0.01 nodes/m<sup>2</sup>.</p> Full article ">
<p>A comparison of the simulation results for energy savings and reachability with different node densities. (<b>a</b>) density = 0.0005 nodes/m<sup>2</sup>; (<b>b</b>) density = 0.001 nodes/m<sup>2</sup>; (<b>c</b>) density = 0.005 nodes/m<sup>2</sup>; (<b>d</b>) density = 0.01 nodes/m<sup>2</sup>.</p> Full article ">
<p>A comparison of simulation results for the transmission range with node degrees ranging from 1 to 8 with different node densities.</p> Full article ">
429 KiB  
Article
Simple Fabrication Process for 2D ZnO Nanowalls and Their Potential Application as a Methane Sensor
by Tse-Pu Chen, Sheng-Po Chang, Fei-Yi Hung, Shoou-Jinn Chang, Zhan-Shuo Hu and Kuan-Jen Chen
Sensors 2013, 13(3), 3941-3950; https://doi.org/10.3390/s130303941 - 20 Mar 2013
Cited by 61 | Viewed by 8288
Abstract
Two-dimensional (2D) ZnO nanowalls were prepared on a glass substrate by a low-temperature thermal evaporation method, in which the fabrication process did not use a metal catalyst or the pre-deposition of a ZnO seed layer on the substrate. The nanowalls were characterized for [...] Read more.
Two-dimensional (2D) ZnO nanowalls were prepared on a glass substrate by a low-temperature thermal evaporation method, in which the fabrication process did not use a metal catalyst or the pre-deposition of a ZnO seed layer on the substrate. The nanowalls were characterized for their surface morphology, and the structural and optical properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence (PL). The fabricated ZnO nanowalls have many advantages, such as low growth temperature and good crystal quality, while being fast, low cost, and easy to fabricate. Methane sensor measurements of the ZnO nanowalls show a high sensitivity to methane gas, and rapid response and recovery times. These unique characteristics are attributed to the high surface-to-volume ratio of the ZnO nanowalls. Thus, the ZnO nanowall methane sensor is a potential gas sensor candidate owing to its good performance. Full article
(This article belongs to the Special Issue Nanotube and Nanowire Sensors)
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<p>SEM images of ZnO nanowalls grown on a glass substrate by thermal evaporation: (<b>a</b>) top view, (<b>b</b>) cross-section, and high-magnification of the (<b>c</b>) nanowall and (<b>d</b>) tube-like structure.</p> Full article ">
<p>XRD spectrum of the nanowall structure.</p> Full article ">
<p>(<b>a</b>) Low-magnification TEM image of a nanowall. (<b>b</b>) High-resolution TEM image taken from a single ZnO nanowall. (<b>c</b>) SAED pattern taken along the (0001) axis of orientation. (<b>d</b>) EDS analysis of the ZnO nanowalls.</p> Full article ">
<p>Room temperature PL spectrum of the ZnO nanowalls.</p> Full article ">
<p>Relative sensitivity ratio <span class="html-italic">versus</span> temperature curves of the ZnO nanowall methane sensor.</p> Full article ">
<p>Transient response curves of the ZnO nanowalls at 300 °C and 3 V applied bias.</p> Full article ">
514 KiB  
Article
Measurements of Tropospheric NO2 in Romania Using a Zenith-Sky Mobile DOAS System and Comparisons with Satellite Observations
by Daniel-Eduard Constantin, Alexis Merlaud, Michel Van Roozendael, Mirela Voiculescu, Caroline Fayt, François Hendrick, Gaia Pinardi and Lucian Georgescu
Sensors 2013, 13(3), 3922-3940; https://doi.org/10.3390/s130303922 - 20 Mar 2013
Cited by 26 | Viewed by 8797
Abstract
In this paper we present a new method for retrieving tropospheric NO2 Vertical Column Density (VCD) from zenith-sky Differential Optical Absorption Spectroscopy (DOAS) measurements using mobile observations. This method was used during three days in the summer of 2011 in Romania, being [...] Read more.
In this paper we present a new method for retrieving tropospheric NO2 Vertical Column Density (VCD) from zenith-sky Differential Optical Absorption Spectroscopy (DOAS) measurements using mobile observations. This method was used during three days in the summer of 2011 in Romania, being to our knowledge the first mobile DOAS measurements peformed in this country. The measurements were carried out over large and different areas using a mobile DOAS system installed in a car. We present here a step-by-step retrieval of tropospheric VCD using complementary observations from ground and space which take into account the stratospheric contribution, which is a step forward compared to other similar studies. The detailed error budget indicates that the typical uncertainty on the retrieved NO2tropospheric VCD is less than 25%. The resulting ground-based data set is compared to satellite measurements from the Ozone Monitoring Instrument (OMI) and the Global Ozone Monitoring Experiment-2 (GOME-2). For instance, on 18 July 2011, in an industrial area located at 47.03°N, 22.45°E, GOME-2 observes a tropospheric VCD value of (3.4 ± 1.9) × 1015 molec./cm2, while average mobile measurements in the same area give a value of (3.4 ± 0.7) × 1015 molec./cm2. On 22 August 2011, around Ploiesti city (44.99°N, 26.1°E), the tropospheric VCD observed by satellites is (3.3 ± 1.9) × 1015 molec./cm2 (GOME-2) and (3.2 ± 3.2) × 1015 molec./cm2 (OMI), while average mobile measurements give (3.8 ± 0.8) × 1015 molec./cm2. Average ground measurements over “clean areas”, on 18 July 2011, give (2.5 ± 0.6) × 1015 molec./cm2 while the satellite observes a value of (1.8 ± 1.3) × 1015 molec./cm2. Full article
(This article belongs to the Section Remote Sensors)
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<p>The tracks of mobile DOAS measurements performed in Romania.</p> Full article ">
<p>The mobile DOAS system.</p> Full article ">
<p>The Langley-plot for SZA 90°–80° of measurements on 6 October 2011 with respect to a reference spectrum measured on 18 July 2011.</p> Full article ">
<p>Comparison of the stratospheric NO<sub>2</sub> between ground-based measurements and derived from OMI on 6 October 2011. The AM diurnal variation was simulated using the PSCBOX model.</p> Full article ">
<p>The tropospheric AMFs simulations for the three days of road measurements.</p> Full article ">
<p>Time series of (<b>a</b>) DSCD and Total SCD; (<b>b</b>) Stratospheric SCD and VCD and; (<b>c</b>) Tropospheric SCD and VCD for 22 August 2011.</p> Full article ">
<p>Diurnal variations of O<sub>4</sub> DSCDs absorptions for clear sky or mostly clear sky conditions on (<b>a</b>) 18 July 2011; (<b>b</b>) 28 July 2011 and (<b>c</b>) 22 August 2011.</p> Full article ">
<p>Color coded tropospheric NO<sub>2</sub> VCD for the Oradea-Cluj Napoca road measurements on 18 July 2011 (line) and GOME-2 tropospheric NO<sub>2</sub> VCDs for the same day (rectangles).</p> Full article ">
<p>Comparison of tropospheric NO<sub>2</sub> VCD obtained from mobile DOAS zenith-sky measurements with GOME-2 observations (18 July 2011) and corresponding error bars.</p> Full article ">
4117 KiB  
Communication
Rank Awareness in Group-Sparse Recovery of Multi-Echo MR Images
by Angshul Majumdar and Rabab Ward
Sensors 2013, 13(3), 3902-3921; https://doi.org/10.3390/s130303902 - 20 Mar 2013
Cited by 10 | Viewed by 6317
Abstract
This work addresses the problem of recovering multi-echo T1 or T2 weighted images from their partial K-space scans. Recent studies have shown that the best results are obtained when all the multi-echo images are reconstructed by simultaneously exploiting their intra-image spatial redundancy and [...] Read more.
This work addresses the problem of recovering multi-echo T1 or T2 weighted images from their partial K-space scans. Recent studies have shown that the best results are obtained when all the multi-echo images are reconstructed by simultaneously exploiting their intra-image spatial redundancy and inter-echo correlation. The aforesaid studies either stack the vectorised images (formed by row or columns concatenation) as columns of a Multiple Measurement Vector (MMV) matrix or concatenate them as a long vector. Owing to the inter-image correlation, the thus formed MMV matrix or the long concatenated vector is row-sparse or group-sparse respectively in a transform domain (wavelets). Consequently the reconstruction problem was formulated as a row-sparse MMV recovery or a group-sparse vector recovery. In this work we show that when the multi-echo images are arranged in the MMV form, the thus formed matrix is low-rank. We show that better reconstruction accuracy can be obtained when the information about rank-deficiency is incorporated into the row/group sparse recovery problem. Mathematically, this leads to a constrained optimization problem where the objective function promotes the signal’s groups-sparsity as well as its rank-deficiency; the objective function is minimized subject to data fidelity constraints. The experiments were carried out on ex vivo and in vivo T2 weighted images of a rat's spinal cord. Results show that this method yields considerably superior results than state-of-the-art reconstruction techniques. Full article
(This article belongs to the Special Issue Medical & Biological Imaging)
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<p>Row structure in MMV matrix.</p> Full article ">
<p>Grouping according to positions.</p> Full article ">
<p>Images from <span class="html-italic">ex vivo</span> reconstruction. Top row—groundtruth; 2nd row—same sampling pattern, row-sparse recovery; 3rd row—same sampling pattern, rank-deficient row-sparse recovery; 4th row—different sampling pattern, group-sparse recovery; 5th row—different sampling pattern, rank-deficient group-sparse recovery.</p> Full article ">
<p>Images from <span class="html-italic">in vivo</span> reconstruction. Top row—groundtruth; 2nd row—same sampling pattern, row-sparse recovery; 3rd row—same sampling pattern, rank-deficient row-sparse recovery; 4th row—different sampling pattern, group-sparse recovery; 5th row—different sampling pattern, rank-deficient group-sparse recovery.</p> Full article ">
<p>Difference Images from <span class="html-italic">ex vivo</span> reconstruction. Top row—same sampling pattern, row-sparse recovery; 2nd row—same sampling pattern, rank-deficient row-sparse recovery; 3rd row—different sampling pattern, group-sparse recovery; 4th row—different sampling pattern, rank-deficient group-sparse recovery.</p> Full article ">
<p>Difference Images from <span class="html-italic">In vivo</span> Reconstruction. Top row—same sampling pattern, row-sparse recovery; 2nd row—same sampling pattern, rank-deficient row-sparse recovery; 3rd row—different sampling pattern, group-sparse recovery; 4th row—different sampling pattern, rank-deficient group-sparse recovery.</p> Full article ">
<p>T2 maps for <span class="html-italic">Ex vivo</span> (top) and <span class="html-italic">In Vivo</span> (bottom) data; from left to right—Groundtruth, same sampling mask row-sparse recovery; same sampling mask, proposed rank-deficient row-sparse recovery; different sampling masks, group-sparse recovery; different sampling masks, proposed rank-deficient group-sparse recovery.</p> Full article ">
<p>T2 difference maps for <span class="html-italic">Ex vivo</span> (top) and <span class="html-italic">In Vivo</span> (bottom) data; from left to right—same sampling mask row-sparse recovery; same sampling mask, proposed rank-deficient row-sparse recovery; different sampling masks, group-sparse recovery; different sampling masks, proposed rank-deficient group-sparse recovery.</p> Full article ">
837 KiB  
Article
Improvement of H2S Sensing Properties of SnO2-Based Thick Film Gas Sensors Promoted with MoO3 and NiO
by Soo Chool Lee, Seong Yeol Kim, Byung Wook Hwang, Suk Yong Jung, Dhanusuraman Ragupathy, In Sung Son, Duk Dong Lee and Jae Chang Kim
Sensors 2013, 13(3), 3889-3901; https://doi.org/10.3390/s130303889 - 19 Mar 2013
Cited by 35 | Viewed by 8324
Abstract
The effects of the SnO2 pore size and metal oxide promoters on the sensing properties of SnO2-based thick film gas sensors were investigated to improve the detection of very low H2S concentrations (<1 ppm). SnO2 sensors and [...] Read more.
The effects of the SnO2 pore size and metal oxide promoters on the sensing properties of SnO2-based thick film gas sensors were investigated to improve the detection of very low H2S concentrations (<1 ppm). SnO2 sensors and SnO2-based thick-film gas sensors promoted with NiO, ZnO, MoO3, CuO or Fe2O3 were prepared, and their sensing properties were examined in a flow system. The SnO2 materials were prepared by calcining SnO2 at 600, 800, 1,000 and 1,200 °C to give materials identified as SnO2(600), SnO2(800), SnO2(1000), and SnO2(1200), respectively. The Sn(12)Mo5Ni3 sensor, which was prepared by physically mixing 5 wt% MoO3 (Mo5), 3 wt% NiO (Ni3) and SnO2(1200) with a large pore size of 312 nm, exhibited a high sensor response of approximately 75% for the detection of 1 ppm H2S at 350 °C with excellent recovery properties. Unlike the SnO2 sensors, its response was maintained during multiple cycles without deactivation. This was attributed to the promoter effect of MoO3. In particular, the Sn(12)Mo5Ni3 sensor developed in this study showed twice the response of the Sn(6)Mo5Ni3 sensor, which was prepared by SnO2(600) with the smaller pore size than SnO2(1200). The excellent sensor response and recovery properties of Sn(12)Mo5Ni3 are believed to be due to the combined promoter effects of MoO3 and NiO and the diffusion effect of H2S as a result of the large pore size of SnO2. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
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<p>XRD patterns of SnO<sub>2</sub> materials calcined at (<b>a</b>) 600; (<b>b</b>) 800; (<b>c</b>) 1,000; and (<b>d</b>) 1,200 °C; (◆) SnO<sub>2</sub>.</p> Full article ">
<p>(<b>I</b>) Response curves, (<b>II</b>) responses, and (II) 80% response times of SnO<sub>2</sub>-based gas sensors, such as (a) SnO<sub>2</sub>(600); (b) SnO<sub>2</sub>(800); (c) SnO<sub>2</sub>(1000); and (d) SnO<sub>2</sub>(1200) at a H<sub>2</sub>S concentration of 1.0 ppm at 350 °C.</p> Full article ">
<p>SEM images of the SnO<sub>2</sub> thick-film sensors: (<b>a</b>) SnO<sub>2</sub>(600); (<b>b</b>) SnO<sub>2</sub>(800); (<b>c</b>) SnO<sub>2</sub>(1000); and (<b>d</b>) SnO<sub>2</sub>(1200).</p> Full article ">
<p>Response curves of the SnO<sub>2</sub>-based gas sensors promoted with various metal oxides at a H<sub>2</sub>S concentration of 1.0 ppm at 350 °C.</p> Full article ">
<p>Responses and recoveries of the SnO<sub>2</sub>-based gas sensors promoted with various amounts of metal oxides at a H<sub>2</sub>S concentration of 1.0 ppm at 350 °C; (a) SnO<sub>2</sub>(1200); (b) Sn(12)Mo1; (c) Sn(12)Mo3; (d) Sn(12)Mo5; (e) Sn(12)Mo5Ni1; (f) Sn(12)Mo5Ni3; (g) Sn(12)Mo5Ni5; (h) Sn(12)Mo5Zn3; and (i) Sn(6)Mo5Ni3.</p> Full article ">
<p>Responses and recovery of the Sn(12)Mo5Ni3 sensor as a function of the detection temperature at a H<sub>2</sub>S concentration of 1.0 ppm.</p> Full article ">
<p>Response of the Sn(12)Mo5Ni3 sensor as a function of the H<sub>2</sub>S concentration.</p> Full article ">
<p>Repeatabilities of the (a) SnO<sub>2</sub>(1200); (b) Sn(12)Mo5Ni3; and (c) Sn(6)MoNi3 sensors.</p> Full article ">
<p>XRD patterns of the (<b>a</b>) Sn(6)Mo5Ni3 and (<b>b</b>) Sn(12)Mo5Ni3 materials; (◆); SnO<sub>2</sub>, (nO MoO<sub>3</sub>, and (nd NiO.</p> Full article ">
652 KiB  
Article
Electrical Characterization and Hydrogen Peroxide Sensing Properties of Gold/Nafion:Polypyrrole/MWCNTs Electrochemical Devices
by Graziella Scandurra, Antonella Arena, Carmine Ciofi and Gaetano Saitta
Sensors 2013, 13(3), 3878-3888; https://doi.org/10.3390/s130303878 - 19 Mar 2013
Cited by 36 | Viewed by 7534
Abstract
Electrochemical devices using as substrates copier grade transparency sheets are developed by using ion conducting Nafion:polypyrrole mixtures, deposited between gold bottom electrodes and upper electrodes based on Multi Walled Carbon Nanotubes (MWCNTs). The electrical properties of the Nafion:polypyrrole blends and of the gold/Nafion:polypyrrole/MWCNTs [...] Read more.
Electrochemical devices using as substrates copier grade transparency sheets are developed by using ion conducting Nafion:polypyrrole mixtures, deposited between gold bottom electrodes and upper electrodes based on Multi Walled Carbon Nanotubes (MWCNTs). The electrical properties of the Nafion:polypyrrole blends and of the gold/Nafion:polypyrrole/MWCNTs devices are investigated under dry conditions and in deionized water by means of frequency dependent impedance measurements and time domain electrical characterization. According to current-voltage measurements carried out in deionized water, the steady state current forms cycles characterized by redox peaks, the intensity and position of which reversibly change in response to H2O2, with a lower detection limit in the micromolar range. The sensitivity that is obtained is comparable with that of other electrochemical sensors that however, unlike our devices, require supporting electrolytes. Full article
(This article belongs to the Section Chemical Sensors)
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<p>Components of the conducting inks used to develop the top electrode MWCNT (<b>a</b>), and PEDOT:PSS (<b>b</b>).</p> Full article ">
<p>Schematic view of process steps for the realization of the sensors: (<b>a</b>) Linearly shaped gold electrodes applied onto the copier grade transparency sheets, developed by thermal evaporation in vacuum; (<b>b</b>) deposition of the ion conducting (Nafion:polypyrrole) film; (<b>c</b>) deposition of the conducting ink over the Nafion:polypyrrole film, in correspondence of one of the underlying gold electrodes.</p> Full article ">
<p>(<b>a</b>) Magnified image of a film deposited on silicon from the dispersion of MWCNTs in PEDOT; (<b>b</b>) SEM micrograph of Nafion:polypyrrole deposited on a silicon substrate, evidencing the layered structure of the ion conducting film.</p> Full article ">
<p>(<b>a</b>) Frequency dependence of the complex impedance of a typical Nafion:polypyrrole film; (<b>b</b>) Cole Cole plot reporting the opposite of the imaginary part of the impedance versus the real part.</p> Full article ">
<p>(<b>a</b>) Steady state current-voltage cycles of a typical gold/Nafion:polypyrrole/gold device, measured in distilled deionized water (black line), and in the presence of increasing amounts of H<sub>2</sub>O<sub>2</sub>; (<b>b</b>) Current-voltage cycle of a typical gold/Nafion:polypyrrole/gold cell, compared to the I–V cycle of a typical gold/Nafion:polypyrrole/MWCNTs cell. Both the curves are measured in steady state, in deionized water. The inset in the right bottom of the figure shows the schematic view of the gold/Nafion:polypyrrole/MWCNTs cell and the voltage polarity.</p> Full article ">
<p>(<b>a</b>) Steady state current-voltage cycles of a typical gold/Nafion:polypyrrole/MWCNTs, measured over the same voltage range in pure deionized water, evidencing the shift of the current peaks as a function of the voltage change rate; (<b>b</b>) Current-voltage cycle of a typical gold/Nafion:polypyrrole/MWCNTs device, measured in distilled deionized water (black line), and in the presence of increasing amounts of H<sub>2</sub>O<sub>2</sub>. Scan speed is 50 mV/s.</p> Full article ">
<p>(<b>a</b>) Forward current peak position of a gold/Nafion:polypyrrole/MWCNTs device and (<b>b</b>) its forward current intensity measured at 0.7 V as a function of H<sub>2</sub>O<sub>2</sub> concentration. Data are extracted from the results of the measurements shown in <a href="#f5-sensors-13-03878" class="html-fig">Figure 5(b)</a>.</p> Full article ">
<p>(<b>a</b>) Time evolution of the current measured at constant voltage on a gold/Nafion:polypyrrole/MWCNT cell in deionized water, in response to H<sub>2</sub>O<sub>2</sub> subsequent injections in steps of 20 μM; (<b>b</b>) plateau values of the current as function of the hydrogen peroxide concentration.</p> Full article ">
7704 KiB  
Article
Efficient VLSI Architecture for Training Radial Basis Function Networks
by Zhe-Cheng Fan and Wen-Jyi Hwang
Sensors 2013, 13(3), 3848-3877; https://doi.org/10.3390/s130303848 - 19 Mar 2013
Cited by 11 | Viewed by 6621
Abstract
This paper presents a novel VLSI architecture for the training of radial basis function (RBF) networks. The architecture contains the circuits for fuzzy C-means (FCM) and the recursive Least Mean Square (LMS) operations. The FCM circuit is designed for the training of centers [...] Read more.
This paper presents a novel VLSI architecture for the training of radial basis function (RBF) networks. The architecture contains the circuits for fuzzy C-means (FCM) and the recursive Least Mean Square (LMS) operations. The FCM circuit is designed for the training of centers in the hidden layer of the RBF network. The recursive LMS circuit is adopted for the training of connecting weights in the output layer. The architecture is implemented by the field programmable gate array (FPGA). It is used as a hardware accelerator in a system on programmable chip (SOPC) for real-time training and classification. Experimental results reveal that the proposed RBF architecture is an effective alternative for applications where fast and efficient RBF training is desired. Full article
(This article belongs to the Section Physical Sensors)
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<p>A typical RBF network.</p> Full article ">
<p>The proposed RBF architecture.</p> Full article ">
<p>The FCM architecture.</p> Full article ">
<p>The architecture of pre-computation unit.</p> Full article ">
<p>The architecture of membership coefficients computation unit.</p> Full article ">
<p>The architecture of center updating unit.</p> Full article ">
<p>The architecture of cost function computation unit.</p> Full article ">
<p>The proposed recursive LMS architecture.</p> Full article ">
<p>The architecture of kernel Gaussian computation unit.</p> Full article ">
489 KiB  
Article
A New Adaptive Self-Tuning Fourier Coefficients Algorithm for Periodic Torque Ripple Minimization in Permanent Magnet Synchronous Motors (PMSM)
by Alfonso Gómez-Espinosa, Víctor M. Hernández-Guzmán, Manuel Bandala-Sánchez, Hugo Jiménez-Hernández, Edgar A. Rivas-Araiza, Juvenal Rodríguez-Reséndiz and Gilberto Herrera-Ruíz
Sensors 2013, 13(3), 3831-3847; https://doi.org/10.3390/s130303831 - 19 Mar 2013
Cited by 24 | Viewed by 10383
Abstract
A New Adaptive Self-Tuning Fourier Coefficients Algorithm for Periodic Torque Ripple Minimization in Permanent Magnet Synchronous Motors (PMSM) Torque ripple occurs in Permanent Magnet Synchronous Motors (PMSMs) due to the non-sinusoidal flux density distribution around the air-gap and variable magnetic reluctance of the [...] Read more.
A New Adaptive Self-Tuning Fourier Coefficients Algorithm for Periodic Torque Ripple Minimization in Permanent Magnet Synchronous Motors (PMSM) Torque ripple occurs in Permanent Magnet Synchronous Motors (PMSMs) due to the non-sinusoidal flux density distribution around the air-gap and variable magnetic reluctance of the air-gap due to the stator slots distribution. These torque ripples change periodically with rotor position and are apparent as speed variations, which degrade the PMSM drive performance, particularly at low speeds, because of low inertial filtering. In this paper, a new self-tuning algorithm is developed for determining the Fourier Series Controller coefficients with the aim of reducing the torque ripple in a PMSM, thus allowing for a smoother operation. This algorithm adjusts the controller parameters based on the component’s harmonic distortion in time domain of the compensation signal. Experimental evaluation is performed on a DSP-controlled PMSM evaluation platform. Test results obtained validate the effectiveness of the proposed self-tuning algorithm, with the Fourier series expansion scheme, in reducing the torque ripple. Full article
(This article belongs to the Section Physical Sensors)
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<p>Block diagram of the Fourier series controller applied to the Field Oriented Control.</p> Full article ">
<p>Experimental setup including the TMDSHVMTRPF development and EMJ-04APB22 PMSM.</p> Full article ">
<p>Angular position of the motor, at 273 rpm, controlled by Field Oriented Control.</p> Full article ">
<p>Fundamental cosine term, distorted by speed ripple, for Field Oriented Control.</p> Full article ">
<p>Speed ripple, at 273 rpm, controlled by Field Oriented Control.</p> Full article ">
<p>Angular position of the motor, at 273 rpm, controlled by the proposed scheme, for the first two terms.</p> Full article ">
<p>Fundamental cosine term, corrected by the proposed scheme, for the first two terms.</p> Full article ">
<p>Speed ripple, at 273 rpm, controlled by the proposed scheme, for the first two terms.</p> Full article ">
<p>Control signal u(θ), of the proposed scheme, for the first two terms.</p> Full article ">
314 KiB  
Article
J3Gen: A PRNG for Low-Cost Passive RFID
by Joan Melià-Seguí, Joaquin Garcia-Alfaro and Jordi Herrera-Joancomartí
Sensors 2013, 13(3), 3816-3830; https://doi.org/10.3390/s130303816 - 19 Mar 2013
Cited by 41 | Viewed by 8714
Abstract
Pseudorandom number generation (PRNG) is the main security tool in low-cost passive radio-frequency identification (RFID) technologies, such as EPC Gen2. We present a lightweight PRNG design for low-cost passive RFID tags, named J3Gen. J3Gen is based on a linear feedback shift register (LFSR) [...] Read more.
Pseudorandom number generation (PRNG) is the main security tool in low-cost passive radio-frequency identification (RFID) technologies, such as EPC Gen2. We present a lightweight PRNG design for low-cost passive RFID tags, named J3Gen. J3Gen is based on a linear feedback shift register (LFSR) configured with multiple feedback polynomials. The polynomials are alternated during the generation of sequences via a physical source of randomness. J3Gen successfully handles the inherent linearity of LFSR based PRNGs and satisfies the statistical requirements imposed by the EPC Gen2 standard. A hardware implementation of J3Gen is presented and evaluated with regard to different design parameters, defining the key-equivalence security and nonlinearity of the design. The results of a SPICE simulation confirm the power-consumption suitability of the proposal. Full article
(This article belongs to the Section Physical Sensors)
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<p>Block diagram of J3Gen.</p> Full article ">
<p>Different combinations present suitable trade-offs between security and implementation area.</p> Full article ">
<p>EPC Gen2 first randomness property test, achieving similar statistical results than <span class="html-italic">Random.org</span> true random sequences.</p> Full article ">
<p>LTSpice power consumption simulation. Power dissipation is concentrated around the internal clock cycles.</p> Full article ">
1332 KiB  
Article
Sliding Window-Based Region of Interest Extraction for Finger Vein Images
by Lu Yang, Gongping Yang, Yilong Yin and Rongyang Xiao
Sensors 2013, 13(3), 3799-3815; https://doi.org/10.3390/s130303799 - 18 Mar 2013
Cited by 88 | Viewed by 8110
Abstract
Region of Interest (ROI) extraction is a crucial step in an automatic finger vein recognition system. The aim of ROI extraction is to decide which part of the image is suitable for finger vein feature extraction. This paper proposes a finger vein ROI [...] Read more.
Region of Interest (ROI) extraction is a crucial step in an automatic finger vein recognition system. The aim of ROI extraction is to decide which part of the image is suitable for finger vein feature extraction. This paper proposes a finger vein ROI extraction method which is robust to finger displacement and rotation. First, we determine the middle line of the finger, which will be used to correct the image skew. Then, a sliding window is used to detect the phalangeal joints and further to ascertain the height of ROI. Last, for the corrective image with certain height, we will obtain the ROI by using the internal tangents of finger edges as the left and right boundary. The experimental results show that the proposed method can extract ROI more accurately and effectively compared with other methods, and thus improve the performance of finger vein identification system. Besides, to acquire the high quality finger vein image during the capture process, we propose eight criteria for finger vein capture from different aspects and these criteria should be helpful to some extent for finger vein capture. Full article
(This article belongs to the Section Physical Sensors)
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<p>The block diagram of primary steps employed in ROI extraction.</p> Full article ">
<p>Skew image detection and correction. (<b>a</b>) A predefined window in red; (<b>b</b>) The finger vein candidate region; (<b>c</b>) The finger edges; (<b>d</b>) The corrected finger vein image.</p> Full article ">
<p>Locations of the distal inter-phalangeal joint in different images of one finger.</p> Full article ">
<p>Phalangeal joint. (<b>a</b>) The structure of a phalangeal joint; (<b>b</b>) Phalanx structure; (<b>c</b>) Two phalangeal joint regions in finger vein image.</p> Full article ">
<p>The height of ROI. (<b>a</b>) The corrective finger vein image. (<b>b</b>) The binary finger edge image with internal tangents. (<b>c</b>) The key area. (<b>d</b>) The detected positions of two phalangeal joints. (<b>e</b>)The ROI with defined height.</p> Full article ">
<p>The width of the ROI. (<b>a</b>) The ROI with defined height. (<b>b</b>) The binary finger edge image with internal tangents. (<b>c</b>) The ROI of a finger vein image.</p> Full article ">
<p>The imaging device.</p> Full article ">
<p>The positions of two phalangeal joints in the finger vein image. (<b>a</b>) The original finger vein image. (<b>b</b>) The positions of two phalangeal joints detected by the method in [<a href="#b6-sensors-13-03799" class="html-bibr">6</a>] (<b>c</b>) The positions of two phalangeal joints detected by our method.</p> Full article ">
<p>The effect of skewed image correction. (<b>a</b>) The skewed finger vein images. (<b>b</b>) The corrected finger vein images. (<b>c</b>) ROIs extracted by [<a href="#b5-sensors-13-03799" class="html-bibr">5</a>]. (<b>d</b>) ROIs extracted by [<a href="#b6-sensors-13-03799" class="html-bibr">6</a>]. (<b>e</b>) ROIs extracted by our method.</p> Full article ">
961 KiB  
Article
Identifying Rhodamine Dye Plume Sources in Near-Shore Oceanic Environments by Integration of Chemical and Visual Sensors
by Yu Tian, Xiaodong Kang, Yunyi Li, Wei Li, Aiqun Zhang, Jiangchen Yu and Yiping Li
Sensors 2013, 13(3), 3776-3798; https://doi.org/10.3390/s130303776 - 18 Mar 2013
Cited by 11 | Viewed by 6994
Abstract
This article presents a strategy for identifying the source location of a chemical plume in near-shore oceanic environments where the plume is developed under the influence of turbulence, tides and waves. This strategy includes two modules: source declaration (or identification) and source verification [...] Read more.
This article presents a strategy for identifying the source location of a chemical plume in near-shore oceanic environments where the plume is developed under the influence of turbulence, tides and waves. This strategy includes two modules: source declaration (or identification) and source verification embedded in a subsumption architecture. Algorithms for source identification are derived from the moth-inspired plume tracing strategies based on a chemical sensor. The in-water test missions, conducted in November 2002 at San Clemente Island (California, USA) in June 2003 in Duck (North Carolina, USA) and in October 2010 at Dalian Bay (China), successfully identified the source locations after autonomous underwater vehicles tracked the rhodamine dye plumes with a significant meander over 100 meters. The objective of the verification module is to verify the declared plume source using a visual sensor. Because images taken in near shore oceanic environments are very vague and colors in the images are not well-defined, we adopt a fuzzy color extractor to segment the color components and recognize the chemical plume and its source by measuring color similarity. The source verification module is tested by images taken during the CPT missions. Full article
(This article belongs to the Section Chemical Sensors)
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<p>Identify the chemical source using the SIZ_T algorithm. (<b>a</b>) The first successful CPT in a near-shore ocean environment was conducted in November 2002 on San Clemente Island (California, USA). The mission MSN007r2 documented over distance of 411 meters from the first detection point to the identified source location. (<b>b</b>) The MSN003 mission at Duck (North Carolina, USA) in June 2003 tracked a chemical plume with the longest distance over 975 meters between the first point of chemical detection and the identified source location.</p> Full article ">
<p>Identify the chemical source using the SIZ_F algorithm. The mission MSN171639 Dalai Bay (China) in October 2010 traveled over 60 meters from the home location to identify the source location.</p> Full article ">
<p>Subsumption architecture for chemical plume tracing.</p> Full article ">
<p>Derive source identification algorithms from moth-inspired plume tracing strategies. (<b>a</b>) An AUV records (<span class="html-italic">x<sub>last</sub></span>, <span class="html-italic">y<sub>last</sub></span>) as a last chemical detection point (LCDP), if it cannot re-catch the plume within λ seconds during Track-Out activity. (<b>b</b>) The AUV generates most of the LCDPs in the vicinity of the source location, when it overshoots the source and reacquires the lost plume.</p> Full article ">
<p>Derive source identification algorithms from moth-inspired plume tracing strategies. (<b>a</b>) An AUV records (<span class="html-italic">x<sub>last</sub></span>, <span class="html-italic">y<sub>last</sub></span>) as a last chemical detection point (LCDP), if it cannot re-catch the plume within λ seconds during Track-Out activity. (<b>b</b>) The AUV generates most of the LCDPs in the vicinity of the source location, when it overshoots the source and reacquires the lost plume.</p> Full article ">
<p>Rhodamine dye plume in the vincity of its source location (November 2002 at San Clemente Island, California, USA)</p> Full article ">
<p>The AUV for the field experiments conducted in October 2010, developed by the Shenyang Institute of Automation, Chinese Academy of Sciences.</p> Full article ">
<p>Cyclops-7 underwater fluorometer. For the in-water tests, the sampling rate of the fluorometer is set as 10 Hz, and the 0–10 μg/L measurement scale in which the fluorometer outputs 5 VDC corresponding to a rhodamine dye concentration of 10 μg/L is chosen.</p> Full article ">
<p>Workhorse navigator 1200K DVL.</p> Full article ">
<p>A rhodamine plume generated by a release rate of 1–2 g/min is observed about 350 meters far away from the source. This distance is calculated based on GPS signals.</p> Full article ">
381 KiB  
Article
A Dibutyl Phthalate Sensor Based on a Nanofiber Polyaniline Coated Quartz Crystal Monitor
by You Wang, Pengfei Ding, Ruifen Hu, Jianming Zhang, Xingfa Ma, Zhiyuan Luo and Guang Li
Sensors 2013, 13(3), 3765-3775; https://doi.org/10.3390/s130303765 - 18 Mar 2013
Cited by 24 | Viewed by 7505
Abstract
Dibutyl phthalate (DBP) is a commonly used plasticizer and additive to adhesives, printing inks and nail polishes. Because it has been found to be a powerful reproductive and developmental toxicant, a sensor to monitor DBP in some working spaces and the environment is [...] Read more.
Dibutyl phthalate (DBP) is a commonly used plasticizer and additive to adhesives, printing inks and nail polishes. Because it has been found to be a powerful reproductive and developmental toxicant, a sensor to monitor DBP in some working spaces and the environment is required. In this work polyaniline nanofibers were deposited on the electrode of a quartz crystal oscillator to form a Quartz Crystal Microbalance gas sensor. The coated quartz crystal and a non-coated quartz crystal were mounted in a sealed chamber, and their frequency difference was monitored. When DBP vapor was injected into the chamber, gas adsorption decreased the frequency of the coated quartz crystal oscillator and thereby caused an increase in the frequency difference between the two crystals. The change of the frequency difference was recorded as the sensor response. The sensor was extremely sensitive to DBP and could be easily recovered by N2 purging. A low measurement limit of 20 ppb was achieved. The morphologies of the polyaniline films prepared by different approaches have been studied by SEM and BET. How the nanofiber-structure can improve the sensitivity and stability is discussed, while its selectivity and long-term stability were investigated. Full article
(This article belongs to the Section Chemical Sensors)
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<p>SEM images of the nanofiber-structured (<b>a</b>) and non-nanofiber (<b>b</b>) polyaniline film on a quartz crystal electrode.</p> Full article ">
<p>Responses of QCM sensors to 0.2 ppm DBP with different thickness of sensing film.</p> Full article ">
<p>Response cycles of a nanofiber-structured polyaniline film based QCM sensor to different concentrations of DBP purged by high-purity N<sub>2</sub> at room temperature.</p> Full article ">
<p>Calibration curve of the nanofiber-structured polyaniline based QCM sensor response to DBP, the inset indicates calibration curve obtained for the linear range.</p> Full article ">
<p>Comparison of the responses of the sensor to different analytes while the concentration of acetone, ethanol and acetaldehyde was 8 ppm and the concentration of DBP was 0.8 ppm.</p> Full article ">
<p>Response cycles to 0.8 ppm DBP. The dashed line represents the response of the immediately fabricated sensor, while the solid line shows the response of the sensor stored in a dry cabinet at room temperature for 60 days.</p> Full article ">
<p>Response cycles to 0.4 ppm DBP of the polyaniline film based sensors with (solid line) and without (dashed line) nanofiber-structure.</p> Full article ">
2782 KiB  
Article
Eye-Tracker-Guided Non-Mechanical Excimer Laser Assisted Penetrating Keratoplasty
by Edgar Janunts, Frank Schirra, Nora Szentmáry, Berthold Seitz and Achim Langenbucher
Sensors 2013, 13(3), 3753-3764; https://doi.org/10.3390/s130303753 - 18 Mar 2013
Cited by 2 | Viewed by 6829
Abstract
Purpose: The purpose of the study was to implement a new eye tracking mask which could be used to guide the laser beam in automated non-mechanical excimer laser assisted penetrating keratoplasty. Materials and methods: A new trephination mask design with an [...] Read more.
Purpose: The purpose of the study was to implement a new eye tracking mask which could be used to guide the laser beam in automated non-mechanical excimer laser assisted penetrating keratoplasty. Materials and methods: A new trephination mask design with an elevated surface geometry has been proposed with a step formation between conical and flat interfaces. Two recipient masks of 7.5/8.0 mm have been manufactured and tested. The masks have outer diameter of 12.5 mm, step formation at 10.5 mm, and slope of conical surfaces 15°. Its functionality has been tested in different lateral positions and tilts on a planar surface, and pig eye experiments. After successful validation on porcine eyes, new masks have been produced and tested on two patients. Results: The build-in eye tracking software of the MEL 70 was always able to capture the masks. It has been shown that the unwanted pigmentation/pattern induced by the laser pulses on the mask surface does not influence the eye-tracking efficiency. The masks could be tracked within the 18 × 14 mm lateral displacement and up to 12° tilt. Two patient cases are demonstrated. No complications were observed during the surgery, although it needs some attention for aligning the mask horizontally before trephination. Stability of eye tracking masks is emphasized by inducing on purpose movements of the patient head. Conclusion: Eye-tracking-guided penetrating keratoplasty was successfully applied in clinical practice, which enables robust tracking criteria within an extended range. It facilitates the automated trephination procedure of excimer laser-assisted penetrating keratoplasty. Full article
(This article belongs to the Section Biosensors)
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<p>Schematic overview of current approaches in penetrating keratoplasty (PKP) with respect to eye tracking necessity and availability.</p> Full article ">
<p>Two different eye-tracking mask designs: (<b>a</b>) tracking is reached at the inner-most aperture, (<b>b</b>) tracking is achieved in the middle ring. The tracking outlines where the IR contrast changes from bright to dark are highlighted. The white arrows show the circular regions where the mask appears dark in the IR reflected image due to the surface tilt.</p> Full article ">
<p>Technical specifications of the eye-tracking-guided trephination mask.</p> Full article ">
<p>Pop-up diagram in the MEL 70 excimer laser for managing the eye-tracking features. It allows enabling as well as disabling the active eye-tracking by “On” and “Off” buttons, fine alignment of the tracking outlines, and adjusting the threshold value of the IR illumination.</p> Full article ">
<p>Eye tracking mask with 8 mm inner diameter according to design in <a href="#f2-sensors-13-03753" class="html-fig">Figure 2(a)</a>. Laser pulses induce pigmentation on the flat surface of the mask which may interfere with the eye tracking function.</p> Full article ">
<p>Eye tracking for the conventional <span class="html-italic">vs.</span> newly proposed trephination masks. The masks bear eight orientation notches.</p> Full article ">
<p>Eye-tracking masks of 6.0 mm and 8.0 mm before and after the first time laser ablation. It is seen that the patterns do not exceed the dark region of the IR reflected image.</p> Full article ">
<p>(<b>a</b>) depicts the camera view of the porcine eye without any tracking mask. Eye-tracking on the porcine eye using the new trephination masks of 6.0 mm (<b>b</b>) and 8.0 mm (<b>c</b>).</p> Full article ">
<p>Demonstration of the eye tracker by using the new trephination mask for various lateral displacements on planar surface. The 7.5 mm mask was tracked in horizontal and vertical directions (X-Y). The mask was captured by the eye tracker as far as its center (see yellow arrow) was still in the hot zone (blue rectangle, see blue arrow).</p> Full article ">
745 KiB  
Article
Design and Application of a Field Sensing System for Ground Anchors in Slopes
by Se Woon Choi, Jihoon Lee, Jong Moon Kim and Hyo Seon Park
Sensors 2013, 13(3), 3739-3752; https://doi.org/10.3390/s130303739 - 18 Mar 2013
Cited by 14 | Viewed by 8519
Abstract
In a ground anchor system, cables or tendons connected to a bearing plate are used for stabilization of slopes. Then, the stability of a slope is dependent on maintaining the tension levels in the cables. So far, no research on a strain-based field [...] Read more.
In a ground anchor system, cables or tendons connected to a bearing plate are used for stabilization of slopes. Then, the stability of a slope is dependent on maintaining the tension levels in the cables. So far, no research on a strain-based field sensing system for ground anchors has been reported. Therefore, in this study, a practical monitoring system for long-term sensing of tension levels in tendons for anchor-reinforced slopes is proposed. The system for anchor-reinforced slopes is composed of: (1) load cells based on vibrating wire strain gauges (VWSGs), (2) wireless sensor nodes which receive and process the signals from load cells and then transmit the result to a master node through local area communication, (3) master nodes which transmit the data sent from sensor nodes to the server through mobile communication, and (4) a server located at the base station. The system was applied to field sensing of ground anchors in the 62 m-long and 26 m-high slope at the side of the highway. Based on the long-term monitoring, the safety of the anchor-reinforced slope can be secured by the timely applications of re-tensioning processes in tendons. Full article
(This article belongs to the Section Sensor Networks)
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<p>Components of ground anchor system.</p> Full article ">
<p>Field sensing system for anchor-reinforced slopes.</p> Full article ">
<p>System topology for the monitoring of tendons in anchor slopes.</p> Full article ">
<p>Sensor node and receiver module of the master node.</p> Full article ">
<p>Sensor network configuration based on sensor nodes and master nodes deployed at field.</p> Full article ">
<p>Screen capture showing measured data and the time history graph for residual forces.</p> Full article ">
<p>The target slope for field sensing of residual forces in ground anchors. (<b>a</b>) Perspective view of the slope. (<b>b</b>) Installation of a load cell for sensing of residual forces.</p> Full article ">
<p>Master and sensor nodes for the field sensing of ground anchors at field.</p> Full article ">
<p>Sensor network system for the field monitoring of tensile forces in ground anchors.</p> Full article ">
2308 KiB  
Article
Multipass Active Contours for an Adaptive Contour Map
by Jeong Heon Kim, Bo-Young Park, Farhan Akram, Byung-Woo Hong and Kwang Nam Choi
Sensors 2013, 13(3), 3724-3738; https://doi.org/10.3390/s130303724 - 15 Mar 2013
Cited by 15 | Viewed by 6744
Abstract
Isocontour mapping is efficient for extracting meaningful information from a biomedical image in a topographic analysis. Isocontour extraction from real world medical images is difficult due to noise and other factors. As such, adaptive selection of contour generation parameters is needed. This paper [...] Read more.
Isocontour mapping is efficient for extracting meaningful information from a biomedical image in a topographic analysis. Isocontour extraction from real world medical images is difficult due to noise and other factors. As such, adaptive selection of contour generation parameters is needed. This paper proposes an algorithm for generating an adaptive contour map that is spatially adjusted. It is based on the modified active contour model, which imposes successive spatial constraints on the image domain. The adaptability of the proposed algorithm is governed by the energy term of the model. This work focuses on mammograms and the analysis of their intensity. Our algorithm employs the Mumford-Shah energy functional, which considers an image’s intensity distribution. In mammograms, the brighter regions generally contain significant information. Our approach exploits this characteristic to address the initialization and local optimum problems of the active contour model. Our algorithm starts from the darkest region; therefore, local optima encountered during the evolution of contours are populated in less important regions, and the important brighter regions are reserved for later stages. For an unrestricted initial contour, our algorithm adopts an existing technique without re-initialization. To assess its effectiveness and robustness, the proposed algorithm was tested on a set of mammograms. Full article
(This article belongs to the Special Issue Medical & Biological Imaging)
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<p>Multiscale approach for isocontour maps [<a href="#b1-sensors-13-03724" class="html-bibr">1</a>]: (<b>a</b>) Mammogram, (<b>b</b>) Coarsescale isocontour map, (<b>c</b>) Intermediate-scale isocontour map, (<b>d</b>) Fine-scale isocontour map.</p> Full article ">
<p>Partition by the curve <span class="html-italic">C</span> = {<span class="html-italic">x: ϕ</span>(<span class="html-italic">x</span>) =0} with the level set function <span class="html-italic">ϕ</span> restricted by a <span class="html-italic">k</span><sup>th</sup> sub-region <span class="html-italic">w<sub>k</sub></span> in an image domain Ω with evolving of <span class="html-italic">C</span> to normal vector N.</p> Full article ">
<p>(<b>a</b>) Calculated adaptive contour map from a given image <span class="html-italic">w<sub>0</sub></span>, (<b>b</b>) Inclusion tree from the adaptive contour map.</p> Full article ">
<p>The mini-MIAS database of mammogram number 028. (<b>a</b>) The approximated region of abnormality from the database. (<b>b</b>) Contour 1 after 9 iterations of (14). (<b>c</b>) Contour 2 after 7 iterations. (<b>d</b>) Contour 3 after 7 iterations. (<b>e</b>) Contour 4 after 12 iterations. (<b>f</b>) Last contour 5 after 17 iterations. (<b>g</b>) Final contour map.</p> Full article ">
<p>The mini-MIAS database of mammogram number 063 (<b>a</b>) The approximated region of abnormality from the database. (<b>b</b>) Contour 1 after 8 iterations of (14). (<b>c</b>) Contour 2 after 12 iterations. (<b>d</b>) Contour 3 after 9 iterations. (<b>e</b>) Contour 4 after 11 iterations. (<b>f</b>) Last contour 5 after 12 iterations. (<b>g</b>) Final contour map.</p> Full article ">
<p>Results of a synthetic image with 5% uniform noise. (<b>a</b>) Contour 1 after 3 iterations of (14). (<b>b</b>) Contour 2 after 7 iterations. (<b>c</b>) Contour 3 after 7 iterations. (<b>d</b>) Contour 4 after 7 iterations.</p> Full article ">
261 KiB  
Article
Assessing Herbivore Foraging Behavior with GPS Collars in a Semiarid Grassland
by David J. Augustine and Justin D. Derner
Sensors 2013, 13(3), 3711-3723; https://doi.org/10.3390/s130303711 - 15 Mar 2013
Cited by 82 | Viewed by 8635
Abstract
Advances in global positioning system (GPS) technology have dramatically enhanced the ability to track and study distributions of free-ranging livestock. Understanding factors controlling the distribution of free-ranging livestock requires the ability to assess when and where they are foraging. For four years (2008–2011), [...] Read more.
Advances in global positioning system (GPS) technology have dramatically enhanced the ability to track and study distributions of free-ranging livestock. Understanding factors controlling the distribution of free-ranging livestock requires the ability to assess when and where they are foraging. For four years (2008–2011), we periodically collected GPS and activity sensor data together with direct observations of collared cattle grazing semiarid rangeland in eastern Colorado. From these data, we developed classification tree models that allowed us to discriminate between grazing and non-grazing activities. We evaluated: (1) which activity sensor measurements from the GPS collars were most valuable in predicting cattle foraging behavior, (2) the accuracy of binary (grazing, non-grazing) activity models vs. models with multiple activity categories (grazing, resting, traveling, mixed), and (3) the accuracy of models that are robust across years vs. models specific to a given year. A binary classification tree correctly removed 86.5% of the non-grazing locations, while correctly retaining 87.8% of the locations where the animal was grazing, for an overall misclassification rate of 12.9%. A classification tree that separated activity into four different categories yielded a greater misclassification rate of 16.0%. Distance travelled in a 5 minute interval and the proportion of the interval with the sensor indicating a head down position were the two most important variables predicting grazing activity. Fitting annual models of cattle foraging activity did not improve model accuracy compared to a single model based on all four years combined. This suggests that increased sample size was more valuable than accounting for interannual variation in foraging behavior associated with variation in forage production. Our models differ from previous assessments in semiarid rangeland of Israel and mesic pastures in the United States in terms of the value of different activity sensor measurements for identifying grazing activity, suggesting that the use of GPS collars to classify cattle grazing behavior will require calibrations specific to the environment and vegetation being studied. Full article
(This article belongs to the Section Physical Sensors)
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<p>Frequency distributions of movement distances and activity sensor measurements collected at 5 minute intervals using Lotek 3300LR GPS collars on yearling steers in eastern Colorado, for each of four activity categories. The “mixed” category refers to 5 minute intervals where neither grazing, resting, nor traveling occurred for 50% or more of the interval. Red lines show thresholds identified by the final selected classification tree discriminating among the four activity categories (see <a href="#f3-sensors-13-03711" class="html-fig">Figure 3</a>).</p> Full article ">
<p>Selected binary classification tree differentiating cattle grazing <span class="html-italic">vs.</span> non-grazing activities based upon movement distances and activity sensor data collected at 5-minute intervals with Lotek 3300LR GPS collars on yearling steers in eastern Colorado. Misclassification rates for this model for both the training and validation datasets are shown in bold in <a href="#t1-sensors-13-03711" class="html-table">Table 1</a>. Number of observations refers to the training dataset. Variables in the classification tree are DIST = Distance in meters between GPS fixes over a 5-minute interval, Xact = number of movements in the horizontal direction (head movement left to right or right to left) detected by the activity sensor, Yact = number of movements in the vertical direction (head movement up and down) detected by the activity sensor, XYsum = Xact + Yact, and Headdown = percent of the 5-minute interval in which the Y-axis sensor was in the head down position. See text for a definition of the LogWorth statistic.</p> Full article ">
<p>Selected four-category classification tree for cattle activity predicted by movement distances and activity sensor data collected at 5-minute intervals using Lotek 3300LR GPS collars on yearling steers in eastern Colorado. Counts of observations in each box refer to the training dataset used to fit the model. Variables in the classification tree are DIST = Distance in meters between GPS fixes over a 5-minute interval, Xact = number of movements in the X direction detected by the activity sensor, Yact = number of movements in the Y direction detected by the activity sensor, XYsum = Xact + Yact, and Headdown = percent of the 5-minute interval in which the Y-axis sensor was in the head down position. See text for a definition of the LogWorth statistic.</p> Full article ">
1509 KiB  
Review
Slotted Photonic Crystal Sensors
by Mark G. Scullion, Thomas F. Krauss and Andrea Di Falco
Sensors 2013, 13(3), 3675-3710; https://doi.org/10.3390/s130303675 - 15 Mar 2013
Cited by 89 | Viewed by 16057
Abstract
Optical biosensors are increasingly being considered for lab-on-a-chip applications due to their benefits such as small size, biocompatibility, passive behaviour and lack of the need for fluorescent labels. The light guiding mechanisms used by many of them results in poor overlap of the [...] Read more.
Optical biosensors are increasingly being considered for lab-on-a-chip applications due to their benefits such as small size, biocompatibility, passive behaviour and lack of the need for fluorescent labels. The light guiding mechanisms used by many of them results in poor overlap of the optical field with the target molecules, reducing the maximum sensitivity achievable. This review article presents a new platform for optical biosensors, namely slotted photonic crystals, which provide higher sensitivities due to their ability to confine, spatially and temporally, the optical mode peak within the analyte itself. Loss measurements showed values comparable to standard photonic crystals, confirming their ability to be used in real devices. A novel resonant coupler was designed, simulated, and experimentally tested, and was found to perform better than other solutions within the literature. Combining with cavities, microfluidics and biological functionalization allowed proof-of-principle demonstrations of protein binding to be carried out. Higher sensitivities were observed in smaller structures than possible with most competing devices reported in the literature. This body of work presents slotted photonic crystals as a realistic platform for complete on-chip biosensing; addressing key design, performance and application issues, whilst also opening up exciting new ideas for future study. Full article
(This article belongs to the Special Issue Photonic Crystal Sensors)
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<p>(<b>a</b>) Slot waveguide geometry. A narrow air slot is introduced into a ridge waveguide. Alternatively, this can be viewed as two separate waveguides separated by a small region of air. Light is guided mostly in air; (<b>b</b>) Field distribution of a slot mode.</p> Full article ">
<p>(<b>a</b>) Schematic of a 2-D slab photonic crystal, with a W1 defect. Light is delivered to and from a photonic crystal via access waveguides. The defect consists of a single row of holes being removed, which allows normally forbidden frequencies to exist within the crystal. Holes on either side of the line defect behave as very efficient mirrors for forbidden frequencies, and thus can be used to guide light; (<b>b</b>) Corresponding photonic band diagram of 2D photonic crystal with W1 defect. Even and odd defect guided modes shown.</p> Full article ">
<p>Sketch of slotted photonic crystal geometry. Slot waveguide defect introduced to guiding region of W1 photonic crystal.</p> Full article ">
<p>(<b>a</b>) Photonic band diagram of 2-D slot photonic crystal; (<b>b</b>) Mode profile.</p> Full article ">
<p>Photonic crystal membrane fabrication steps. (<b>a</b>) ZEP e-beam resist coated SOI substrate exposed to electrons in electron beam writer; (<b>b</b>) Sample developed exposing surface in pattern of design. Silicon etched using plasma of reactive ions; (<b>c</b>) Silica under photonic crystals removed using hydrofluoric acid through an S1818 photoresist patterned window. d) S1818 removed and final membrane sample cleaved.</p> Full article ">
<p>SEM image of slotted photonic crystal fabricated in SOI.</p> Full article ">
<p>Optical endfire setup for transmission measurements. TE polarised light from broadband ASE source focused onto sample edge facet using aspheric lenses. Light collected from back facet split between OSA and photodetector. Sample using photodetector signal and camera as reference.</p> Full article ">
<p>Coupling between slot waveguide and slotted photonic crystal. (<b>a</b>,<b>c</b>) Coupling in 1st Brillouin zone using narrow slot rails (196 nm wide) results in good transmission due to group velocity and phase matching. (<b>b</b>,<b>d</b>) Coupling in 2nd Brillouin zone using wide slot rails (294 nm wide) results in poor transmission due to group velocity mismatch. (Copyright © IEEE. All rights reserved. Adapted with the permission from [<a href="#b70-sensors-13-03675" class="html-bibr">70</a>]).</p> Full article ">
<p>SEM image of slotted photonic crystal with resonant defect couplers and access waveguides, fabricated in SOI.</p> Full article ">
1070 KiB  
Article
A Zirconium Dioxide Ammonia Microsensor Integrated with a Readout Circuit Manufactured Using the 0.18 μm CMOS Process
by Guan-Ming Lin, Ching-Liang Dai and Ming-Zhi Yang
Sensors 2013, 13(3), 3664-3674; https://doi.org/10.3390/s130303664 - 15 Mar 2013
Cited by 2 | Viewed by 6429
Abstract
The study presents an ammonia microsensor integrated with a readout circuit on-a-chip fabricated using the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process. The integrated sensor chip consists of a heater, an ammonia sensor and a readout circuit. The ammonia sensor is [...] Read more.
The study presents an ammonia microsensor integrated with a readout circuit on-a-chip fabricated using the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process. The integrated sensor chip consists of a heater, an ammonia sensor and a readout circuit. The ammonia sensor is constructed by a sensitive film and the interdigitated electrodes. The sensitive film is zirconium dioxide that is coated on the interdigitated electrodes. The heater is used to provide a working temperature to the sensitive film. A post-process is employed to remove the sacrificial layer and to coat zirconium dioxide on the sensor. When the sensitive film adsorbs or desorbs ammonia gas, the sensor produces a change in resistance. The readout circuit converts the resistance variation of the sensor into the output voltage. The experiments show that the integrated ammonia sensor has a sensitivity of 4.1 mV/ppm. Full article
(This article belongs to the Special Issue Gas Sensors - 2013)
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<p>Schematic of the integrated ammonia sensor.</p> Full article ">
<p>The readout circuit for the ammonia sensor.</p> Full article ">
<p>Simulated readout of the output voltage for the readout circuit.</p> Full article ">
<p>Relation between the output voltage and temperature for the circuit.</p> Full article ">
<p>SEM image of the zirconium dioxide film.</p> Full article ">
<p>Fabrication process of the integrated ammonia sensor: (<b>a</b>) after the CMOS process, (<b>b</b>) etching the sacrificial layer, (<b>c</b>) the sensitive film coated.</p> Full article ">
<p>SEM image of the ammonia microsensor after the wet etching.</p> Full article ">
<p>Optical image of the integrated ammonia sensor after the post-process.</p> Full article ">
<p>Measured results of the working temperature generated by the heater.</p> Full article ">
497 KiB  
Communication
A Small and Slim Coaxial Probe for Single Rice Grain Moisture Sensing
by Kok Yeow You, Hou Kit Mun, Li Ling You, Jamaliah Salleh and Zulkifly Abbas
Sensors 2013, 13(3), 3652-3663; https://doi.org/10.3390/s130303652 - 14 Mar 2013
Cited by 29 | Viewed by 8739
Abstract
A moisture detection of single rice grains using a slim and small open-ended coaxial probe is presented. The coaxial probe is suitable for the nondestructive measurement of moisture values in the rice grains ranging from from 9.5% to 26%. Empirical polynomial models are [...] Read more.
A moisture detection of single rice grains using a slim and small open-ended coaxial probe is presented. The coaxial probe is suitable for the nondestructive measurement of moisture values in the rice grains ranging from from 9.5% to 26%. Empirical polynomial models are developed to predict the gravimetric moisture content of rice based on measured reflection coefficients using a vector network analyzer. The relationship between the reflection coefficient and relative permittivity were also created using a regression method and expressed in a polynomial model, whose model coefficients were obtained by fitting the data from Finite Element-based simulation. Besides, the designed single rice grain sample holder and experimental set-up were shown. The measurement of single rice grains in this study is more precise compared to the measurement in conventional bulk rice grains, as the random air gap present in the bulk rice grains is excluded. Full article
(This article belongs to the Special Issue Sensor-Based Technologies and Processes in Agriculture and Forestry)
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<p>The side sectional view and front sectional view.</p> Full article ">
<p>The Cross-sectional View.</p> Full article ">
<p>Variation in real and imaginary parts of reflection coefficient, ((image)e (Γ<sub><span class="html-italic">BB’</span></sub>) and ℑm (Γ<sub><span class="html-italic">BB’</span></sub>)) at plane <span class="html-italic">BB’</span> with frequency, <span class="html-italic">f</span> at (25 ± 1) °C.</p> Full article ">
<p>Variation in dielectric constant, <math display="inline"> <semantics id="sm15"> <mrow> <msubsup> <mi>ɛ</mi> <mi>r</mi> <mo>′</mo></msubsup></mrow></semantics></math> with frequency, <span class="html-italic">f</span> for Teflon and liquid methanol at (25 ± 1) °C.</p> Full article ">
<p>Experimental Set-up.</p> Full article ">
<p>The relationship between reflection coefficient (magnitude, Γ<sub><span class="html-italic">BB’</span></sub> and phase, <span class="html-italic">ø</span>) and the moisture content, <span class="html-italic">m.c</span> at 2.44 GHz, 5.81 GHz and 10.02 GHz, respectively.</p> Full article ">
<p>The relationship between reflection coefficient (magnitude, Γ<sub><span class="html-italic">BB’</span></sub> and phase, <span class="html-italic">ø</span>) and the moisture content, <span class="html-italic">m.c</span> at 2.44 GHz, 5.81 GHz and 10.02 GHz, respectively.</p> Full article ">
<p>(<b>a</b>) The variations in <math display="inline"> <semantics id="sm16"> <mrow> <msubsup> <mi>ɛ</mi> <mi>r</mi> <mo>′</mo></msubsup></mrow></semantics></math> of single rice grain with its bulk moisture content, <span class="html-italic">m.c.</span> at 2.44 GHz, 5.81 GHz and 10.02 GHz, respectively. (<b>b</b>) The absolute deviation, <math display="inline"> <semantics id="sm17"> <mo>|</mo> <mi>Δ</mi> <msubsup> <mi>ɛ</mi> <mi>r</mi> <mo>′</mo></msubsup> <mo>|</mo></semantics></math> of dielectric constant prediction between the use of studied inversion technique and the Agilent 85070E software computation.</p> Full article ">
1207 KiB  
Article
Fabrication and Characterisation of the Graphene Ring Micro Electrode (GRiME) with an Integrated, Concentric Ag/AgCl Reference Electrode
by James W. Dickinson, Michael Bromley, Fabrice P. L. Andrieux and Colin Boxall
Sensors 2013, 13(3), 3635-3651; https://doi.org/10.3390/s130303635 - 14 Mar 2013
Cited by 20 | Viewed by 9068
Abstract
Abstract: We report the fabrication and characterisation of the first graphene ring micro electrodes with the addition of a miniature concentric Ag/AgCl reference electrode. The graphene ring electrode is formed by dip coating fibre optics with graphene produced by a modified Hummers method. [...] Read more.
Abstract: We report the fabrication and characterisation of the first graphene ring micro electrodes with the addition of a miniature concentric Ag/AgCl reference electrode. The graphene ring electrode is formed by dip coating fibre optics with graphene produced by a modified Hummers method. The reference electrode is formed using an established photocatalytically initiated electroless deposition (PIED) plating method. The performance of the so-formed graphene ring micro electrodes (GRiMEs) and associated reference electrode is studied using the probe redox system ferricyanide and electrode thicknesses assessed using established electrochemical methods. Using 220 µm diameter fibre optics, a ~15 nm thick graphene ring electrode is obtained corresponding to an inner to outer radius ratio of >0.999, so allowing for use of extant analytical descriptions of very thin ring microelectrodes in data analysis. GRiMEs are highly reliable (current response invariant over >3,000 scans), with the concentric reference electrode showing comparable stability (current response invariant over >300 scans). Furthermore the micro-ring design allows for efficient use of electrochemically active graphene edge sites and the associated nA scale currents obtained neatly obviate issues relating to the high resistivity of undoped graphene. Thus, the use of graphene in ring microelectrodes improves the reliability of existing micro-electrode designs and expands the range of use of graphene-based electrochemical devices. Full article
(This article belongs to the Special Issue Novel Tools in Electrochemical Sensing)
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<p>PIED Experimental Setup.</p> Full article ">
<p>Stages of fabrication of the GRiME and concentric Ag/AgCl reference electrode. (<b>a</b>) Bare copper wire attached to the Ag/AgCl layer present on the capillary tube using Ag loaded epoxy. (<b>b</b>) Un-potted GRiME. (<b>c</b>) Un-potted assembly comprised of the Ag/AgCl reference, the GRiME and relevant wire connections. (<b>d</b>) Side view of the completed assembly. (<b>e</b>) End view of the completed assembly. (<b>f</b>) Optical microscopy image of the tip of the GRiME and Ag/AgCl reference electrode.</p> Full article ">
<p>(<b>a</b>) GO layer. (<b>b</b>) GO EDX analysis. (<b>c</b>) Hydrazine reduced HG layer. (<b>d</b>) HG EDX analysis. (<b>e</b>) Hydrazine and thermally reduced, graphene layer. (<b>f</b>) Graphene EDX analysis.</p> Full article ">
<p>Raman spectra of graphene prepared on a quartz substrate.</p> Full article ">
<p>XRD spectra of (A) as prepared GO and (B) reduced GO/graphene.</p> Full article ">
<p>(<b>a</b>) Topographical contact mode AFM image of the graphene layer shown in <a href="#f3-sensors-13-03635" class="html-fig">Figure 3(e)</a>. (<b>b</b>) 2D, aerial view, of the same area. (<b>c</b>) Profile analysis of same, showing step heights of 1.97 and 0.74 nm, for arrow sets 1 and 2 respectively.</p> Full article ">
<p>Comparison of CV's recorded in aqueous background at pH 7 for a glassy carbon disk electrode (4 mm dia.) and a GRiME. CV's were recorded over a potential range from −2 to 2.5 V at a scan rate of 150 mV/s <span class="html-italic">vs.</span> SCE.</p> Full article ">
<p>(<b>a</b>) CVs recorded at a GRiME at a range of sweep rates in a solution of 5 mmol/L Fe(CN)<sub>6</sub><sup>3−</sup> and 1 mmol/L KCl<sub>,</sub> pH 2. The starting potential was +0.3 V <span class="html-italic">vs.</span> SCE scanning in the positive direction at onset. The solution was deoxygenated using an N<sub>2</sub> stream for 10 min prior to data acquisition. (<b>b</b>) anodic and cathodic peak currents of <a href="#f8-sensors-13-03635" class="html-fig"> Figure 8(a)</a> plotted as a function of the square root of the scan rate. (<b>c</b>) 3,000 scan overlay recorded at 500mV/s.</p> Full article ">
<p>(<b>a</b>) Mesoporous structure of anatase TiO<sub>2</sub> layer. (<b>b</b>) AFM topography of the silver metal grains within a silver layer deposited on a TiO<sub>2</sub> sensitised microscope slide. (<b>c</b>) AFM image of the silver layer/glass slide fringe. (<b>d</b>) AFM topography step height measurement over a distance of 9.10 μm and a height change of 104.8 nm.</p> Full article ">
637 KiB  
Article
Fluorescent Imaging for Assessment of the Effect of Combined Application of Electroporation and Rifampicin on HaCaT Cells as a New Therapeutic Approach for Psoriasis
by Biliana Nikolova, Anelia Kostadinova, Borislav Dimitrov, Zhivko Zhelev, Rumiana Bakalova, Ichio Aoki, Tsuneo Saga and Iana Tsoneva
Sensors 2013, 13(3), 3625-3634; https://doi.org/10.3390/s130303625 - 14 Mar 2013
Cited by 5 | Viewed by 7005
Abstract
The study aimed to clarify the role of electric pulses in combination with chemotherapy on the viability of keratinocyte cell line HaCaT, in the context of its application as a new therapeutic approach for psoriasis. The data show that electroporation of HaCaT cells [...] Read more.
The study aimed to clarify the role of electric pulses in combination with chemotherapy on the viability of keratinocyte cell line HaCaT, in the context of its application as a new therapeutic approach for psoriasis. The data show that electroporation of HaCaT cells in combination with rifampicin induces cytoskeleton disruption and increases permeability of cell monolayer due to cell-cell junctions’ interruption, visualized by fluorescent imaging of E-cadherin and actin integrity. This was accompanied with synergistic reduction of cell viability. The study proposes a new opportunity for more effective skin treatment than chemotherapy. The future application of this electrochemotherapeutic approach for combined local treatment of psoriasis may have serous benefits because of a high possibility to avoid side-effects of conventional chemotherapy. Full article
(This article belongs to the Special Issue Medical & Biological Imaging)
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<p>Viability of HaCaT keratinocytes after treatment with high voltage electric pulses alone (black columns) or in combination with rifampicin (white columns). Bars—SD (Standard Deviation); * p &lt; 0.05 <span class="html-italic">versus</span> control groups; ** p &lt; 0.01, significant difference between electroporated cells in the absence of rifampicin and electroporated cells in the presence of 20 μg·mL<sup>−1</sup> rifampicin.</p> Full article ">
<p>Fluorescent imaging of E-cadherin (Cy2-labelled; immunostaining) after treatment of HaCaT cells with electrical pulses and/or 20 μg·mL<sup>−1</sup> rifampicin. (<b>A</b>) Untreated control HaCaT cells; (<b>B</b>) HaCaT cells, treated with 20 μg·mL<sup>−1</sup> rifampicin alone; (<b>C</b>) HaCaT cells 24 h after electroporation with 1,000 V, only. (<b>D</b>–<b>F</b>) HaCaT cells treated with 20 μg·mL<sup>−1</sup> rifampicin plus 200 V, 500 V, 1,000 V, respectively. Magnification—63×.</p> Full article ">
<p>Fluorescent imaging of actin (BODIPY<sup>558/568</sup> phalloidin-labelled) after treatment of HaCaT cells with electrical pulses and/or 20 μg·mL<sup>−1</sup> rifampicin. (<b>A</b>) Untreated control HaCaT cells; (<b>B</b>) HaCaT cells, treated with 20 μg·mL<sup>−1</sup> rifampicin alone; (<b>C</b>) HaCaT cells 24 h after electroporation with 1,000 V, only. (<b>D</b>–<b>F</b>) HaCaT cells treated with 20 μg·mL<sup>−1</sup> rifampicin plus 200 V, 500 V, 1,000 V, respectively. Magnification—63×.</p> Full article ">
964 KiB  
Article
A Humidity Sensing Organic-Inorganic Composite for Environmental Monitoring
by Zubair Ahmad, Qayyum Zafar, Khaulah Sulaiman, Rizwan Akram and Khasan S. Karimov
Sensors 2013, 13(3), 3615-3624; https://doi.org/10.3390/s130303615 - 14 Mar 2013
Cited by 81 | Viewed by 9085
Abstract
In this paper, we present the effect of varying humidity levels on the electrical parameters and the multi frequency response of the electrical parameters of an organic-inorganic composite (PEPC+NiPc+Cu2O)-based humidity sensor. Silver thin films (thickness ~200 nm) were primarily deposited on [...] Read more.
In this paper, we present the effect of varying humidity levels on the electrical parameters and the multi frequency response of the electrical parameters of an organic-inorganic composite (PEPC+NiPc+Cu2O)-based humidity sensor. Silver thin films (thickness ~200 nm) were primarily deposited on plasma cleaned glass substrates by the physical vapor deposition (PVD) technique. A pair of rectangular silver electrodes was formed by patterning silver film through standard optical lithography technique. An active layer of organic-inorganic composite for humidity sensing was later spun coated to cover the separation between the silver electrodes. The electrical characterization of the sensor was performed as a function of relative humidity levels and frequency of the AC input signal. The sensor showed reversible changes in its capacitance with variations in humidity level. The maximum sensitivity ~31.6 pF/%RH at 100 Hz in capacitive mode of operation has been attained. The aim of this study was to increase the sensitivity of the previously reported humidity sensors using PEPC and NiPc, which has been successfully achieved. Full article
(This article belongs to the Section Chemical Sensors)
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<p>(<b>a</b>) Molecular structure of nickel phthalocyanine (NiPc); (<b>b</b>) molecular structure of poly-N-epoxypropylcarbazole (PEPC).</p> Full article ">
<p>(<b>a</b>) and (<b>b</b>) represent SEM micrographs of Cu<sub>2</sub>O-PEPC-NiPC thin film at 1K and 3K magnification, respectively.</p> Full article ">
<p>EDX compositional analysis of organic-inorganic composite film.</p> Full article ">
<p>Schematic view of Ag/Cu<sub>2</sub>O-PEPC-NiPC/Ag humidity sensor.</p> Full article ">
<p>Characterization setup for electrical characterization of the humidity sensor.</p> Full article ">
<p>3D AFM micrograph of organic-inorganic composite film.</p> Full article ">
<p>Capacitance-relative humidity relationship of the Ag/Cu<sub>2</sub>O-PEPC-NiPC/Ag sensor at 100 Hz, 1 kHz and 10 kHz.</p> Full article ">
<p>Response and recovery time (40% RH-97% RH level) of the Ag/Cu<sub>2</sub>O-PEPC-NiPC/Ag humidity sensors at 100 Hz.</p> Full article ">
<p>Hysteresis-relative humidity relationship for Ag/Cu<sub>2</sub>O-PEPC-NiPC/Ag.</p> Full article ">
928 KiB  
Article
Utilizing Joint Routing and Capacity Assignment Algorithms to Achieve Inter- and Intra-Group Delay Fairness in Multi-Rate Multicast Wireless Sensor Networks
by Frank Yeong-Sung Lin, Chiu-Han Hsiao, Leo Shih-Chang Lin and Yean-Fu Wen
Sensors 2013, 13(3), 3588-3614; https://doi.org/10.3390/s130303588 - 14 Mar 2013
Viewed by 6034
Abstract
Recent advance in wireless sensor network (WSN) applications such as the Internet of Things (IoT) have attracted a lot of attention. Sensor nodes have to monitor and cooperatively pass their data, such as temperature, sound, pressure, etc. through the network under constrained physical [...] Read more.
Recent advance in wireless sensor network (WSN) applications such as the Internet of Things (IoT) have attracted a lot of attention. Sensor nodes have to monitor and cooperatively pass their data, such as temperature, sound, pressure, etc. through the network under constrained physical or environmental conditions. The Quality of Service (QoS) is very sensitive to network delays. When resources are constrained and when the number of receivers increases rapidly, how the sensor network can provide good QoS (measured as end-to-end delay) becomes a very critical problem. In this paper; a solution to the wireless sensor network multicasting problem is proposed in which a mathematical model that provides services to accommodate delay fairness for each subscriber is constructed. Granting equal consideration to both network link capacity assignment and routing strategies for each multicast group guarantees the intra-group and inter-group delay fairness of end-to-end delay. Minimizing delay and achieving fairness is ultimately achieved through the Lagrangean Relaxation method and Subgradient Optimization Technique. Test results indicate that the new system runs with greater effectiveness and efficiency. Full article
(This article belongs to the Section Sensor Networks)
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<p>Scenario of unicast and multicast.</p> Full article ">
<p>Max-min fairness.</p> Full article ">
<p>Minimum spanning tree.</p> Full article ">
<p>Multi-rate multicast wireless sensor network.</p> Full article ">
<p>Multicast sensor networks.</p> Full article ">
<p>Solution of a general non-linear programming problem.</p> Full article ">
<p>State diagram of Lagrangean Relaxation method.</p> Full article ">
<p>Procedures of Lagrangean Relaxation method.</p> Full article ">
<p>An example of Subproblem 3 considering <span class="html-italic">c<sub>sl</sub></span>.</p> Full article ">
880 KiB  
Article
A Novel Offset Cancellation Based on Parasitic-Insensitive Switched-Capacitor Sensing Circuit for the Out-of-Plane Single-Gimbaled Decoupled CMOS-MEMS Gyroscope
by Ming-Hui Chang and Han-Pang Huang
Sensors 2013, 13(3), 3568-3587; https://doi.org/10.3390/s130303568 - 14 Mar 2013
Cited by 3 | Viewed by 7600
Abstract
This paper presents a novel parasitic-insensitive switched-capacitor (PISC) sensing circuit design in order to obtain high sensitivity and ultra linearity and reduce the parasitic effect for the out-of-plane single-gimbaled decoupled CMOS-MEMS gyroscope (SGDG). According to the simulation results, the proposed PISC circuit has [...] Read more.
This paper presents a novel parasitic-insensitive switched-capacitor (PISC) sensing circuit design in order to obtain high sensitivity and ultra linearity and reduce the parasitic effect for the out-of-plane single-gimbaled decoupled CMOS-MEMS gyroscope (SGDG). According to the simulation results, the proposed PISC circuit has better sensitivity and high linearity in a wide dynamic range. Experimental results also show a better performance. In addition, the PISC circuit can use signal processing to cancel the offset and noise. Thus, this circuit is very suitable for gyroscope measurement. Full article
(This article belongs to the Section Physical Sensors)
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<p>The PISC sensing circuit.</p> Full article ">
<p>The PISC sensing circuit for the two operations: (<b>a</b>) sampling mode; (<b>b</b>) amplification mode.</p> Full article ">
<p>The PISC sensing circuit with parasitic capacitances shown.</p> Full article ">
<p>Schematic of the OP-amp circuit.</p> Full article ">
<p>Transmission gate.</p> Full article ">
<p>Schematic of the non-overlapping clock circuit.</p> Full article ">
<p>ΣΔ modulator behavior simulation.</p> Full article ">
<p>One-bit ΣΔ modulator circuit design.</p> Full article ">
<p>Comparator circuit design.</p> Full article ">
1165 KiB  
Article
Continuous Transmission Frequency Modulation Detection under Variable Sonar-Target Speed Conditions
by Yang Wang and Jun Yang
Sensors 2013, 13(3), 3549-3567; https://doi.org/10.3390/s130303549 - 13 Mar 2013
Cited by 9 | Viewed by 6987
Abstract
As a ranging sensor, a continuous transmission frequency modulation (CTFM) sonar with its ability for range finding and range profile formation works effectively under stationary conditions. When a relative velocity exists between the target and the sonar, the echo signal is Doppler-shifted. This [...] Read more.
As a ranging sensor, a continuous transmission frequency modulation (CTFM) sonar with its ability for range finding and range profile formation works effectively under stationary conditions. When a relative velocity exists between the target and the sonar, the echo signal is Doppler-shifted. This situation causes the output of the sensor to deviate from the actual target range, thus limiting its applications to stationary conditions only. This work presents an approach for correcting such a deviation. By analyzing the Doppler effect during the propagation process, the sensor output can be corrected by a Doppler factor. To obtain this factor, a conventional CTFM system is slightly modified by adding a single tone signal with a frequency that locates out-of-sweep range of the transmitted signal. The Doppler factor can be extracted from the echo. Both verification experiments and performance tests are carried out. Results indicate the validity of the proposed approach. Moreover, ranging precision under different processing setups is discussed. For adjacent multiple targets, the discrimination ability is influenced by displacement and velocity. A discrimination boundary is provided through an analysis. Full article
(This article belongs to the Section Physical Sensors)
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<p>The signal spectrogram of the demodulation procedure.</p> Full article ">
<p>Signal spectrogram of a dual demodulation system.</p> Full article ">
<p>Output signal spectrum under echo SNR of (<b>a</b>) 0 dB; (<b>b</b>) 3 dB; (<b>c</b>) 10 dB; and (<b>d</b>) 20 dB.</p> Full article ">
<p>The propagation of the ultrasonic signal.</p> Full article ">
<p>The CTFM output <span class="html-italic">vs</span>. the actual target distance. (<b>a</b>) A target approaching the sonar at 1 m·s<sup>−1</sup>; (<b>b</b>) A target accelerating away from the sonar at 1.5 m·s<sup>−2</sup>.</p> Full article ">
<p>Pictures of the experimental apparatus. (<b>a</b>) The entire motion system; (<b>b</b>) The sonar head.</p> Full article ">
<p>The control diagram of the experimental apparatus.</p> Full article ">
<p>A block diagram of the system.</p> Full article ">
<p>The setup for the two tested conditions. (<b>a</b>) The sonar head is moving while the target remains still; (<b>b</b>) Both the sonar head and the target are moving.</p> Full article ">
1159 KiB  
Article
Deployment of a Fully-Automated Green Fluorescent Protein Imaging System in a High Arctic Autonomous Greenhouse
by Talal Abboud, Matthew Bamsey, Anna-Lisa Paul, Thomas Graham, Stephen Braham, Rita Noumeir, Alain Berinstain and Robert Ferl
Sensors 2013, 13(3), 3530-3548; https://doi.org/10.3390/s130303530 - 13 Mar 2013
Cited by 4 | Viewed by 7761
Abstract
Higher plants are an integral part of strategies for sustained human presence in space. Space-based greenhouses have the potential to provide closed-loop recycling of oxygen, water and food. Plant monitoring systems with the capacity to remotely observe the condition of crops in real-time [...] Read more.
Higher plants are an integral part of strategies for sustained human presence in space. Space-based greenhouses have the potential to provide closed-loop recycling of oxygen, water and food. Plant monitoring systems with the capacity to remotely observe the condition of crops in real-time within these systems would permit operators to take immediate action to ensure optimum system yield and reliability. One such plant health monitoring technique involves the use of reporter genes driving fluorescent proteins as biological sensors of plant stress. In 2006 an initial prototype green fluorescent protein imager system was deployed at the Arthur Clarke Mars Greenhouse located in the Canadian High Arctic. This prototype demonstrated the advantageous of this biosensor technology and underscored the challenges in collecting and managing telemetric data from exigent environments. We present here the design and deployment of a second prototype imaging system deployed within and connected to the infrastructure of the Arthur Clarke Mars Greenhouse. This is the first imager to run autonomously for one year in the un-crewed greenhouse with command and control conducted through the greenhouse satellite control system. Images were saved locally in high resolution and sent telemetrically in low resolution. Imager hardware is described, including the custom designed LED growth light and fluorescent excitation light boards, filters, data acquisition and control system, and basic sensing and environmental control. Several critical lessons learned related to the hardware of small plant growth payloads are also elaborated. Full article
(This article belongs to the Section Biosensors)
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<p>The controller setup as deployed within the ACMG on Devon Island. Shown are cFP-2120 (<b>1</b>); cFP-PWM-520 (<b>2</b>); cFP-RLY-421 (<b>3</b>) and cFP-CB-1 connector blocks (<b>4</b>).</p> Full article ">
<p>Side view of the TIS-III as installed. Grow lights and fan inputs (<b>1</b>); camera Ethernet connection (<b>2</b>); camera power cable (<b>3</b>); cooling pipe (<b>4</b>).</p> Full article ">
<p>Top view of the installed TIS-III NI-1744 Camera (<b>1</b>); Computer M1214-MP lens (<b>2</b>); camera guide bracket (<b>3</b>); camera Light control connector (<b>4</b>); excitation light board (<b>5</b>); cooling fan (<b>6</b>).</p> Full article ">
<p>LabVIEW TIS-III control panel.</p> Full article ">
<p>VBAI Inspection State Diagram (TIS-III capture sequence logic).</p> Full article ">
<p>Grow lights boards and positioning within the TIS-III.</p> Full article ">
<p>Grow light distribution pattern, size and installation angle.</p> Full article ">
<p>TIS-III excitation LEDs behind a band-pass filter.</p> Full article ">
<p>ACMG (<b>A</b>) and the CSA development greenhouse (<b>B</b>).</p> Full article ">
131 KiB  
Comment
Comments and Reply to: Foot Plantar Pressure Measurement System: A Review. Sensors 2012, 12, 9884-9912
by Nachiappan Chockalingam, Aoife Healy, Roozbeh Naemi, Philip Burgess-Walker, Abdul Hadi Abdul Razak, Aladin Zayegh, Rezaul K. Begg and Yufridin Wahab
Sensors 2013, 13(3), 3527-3529; https://doi.org/10.3390/s130303527 - 13 Mar 2013
Cited by 2 | Viewed by 6675
Abstract
We would like to comment on a recent review article published in Sensors by Razak et al. [1]. The authors provided a review of plantar pressure measurement systems which included the discussion of the recently developed WalkinSense® system. While the authors correctly [...] Read more.
We would like to comment on a recent review article published in Sensors by Razak et al. [1]. The authors provided a review of plantar pressure measurement systems which included the discussion of the recently developed WalkinSense® system. While the authors correctly identified that our group completed research using this system [2], they have inaccurately reported the manufacturer of the system and our research findings. Full article
2164 KiB  
Article
Ultrasound Indoor Positioning System Based on a Low-Power Wireless Sensor Network Providing Sub-Centimeter Accuracy
by Carlos Medina, José Carlos Segura and Ángel De la Torre
Sensors 2013, 13(3), 3501-3526; https://doi.org/10.3390/s130303501 - 13 Mar 2013
Cited by 136 | Viewed by 20618
Abstract
This paper describes the TELIAMADE system, a new indoor positioning system based on time-of-flight (TOF) of ultrasonic signal to estimate the distance between a receiver node and a transmitter node. TELIAMADE system consists of a set of wireless nodes equipped with a radio [...] Read more.
This paper describes the TELIAMADE system, a new indoor positioning system based on time-of-flight (TOF) of ultrasonic signal to estimate the distance between a receiver node and a transmitter node. TELIAMADE system consists of a set of wireless nodes equipped with a radio module for communication and a module for the transmission and reception of ultrasound. The access to the ultrasonic channel is managed by applying a synchronization algorithm based on a time-division multiplexing (TDMA) scheme. The ultrasonic signal is transmitted using a carrier frequency of 40 kHz and the TOF measurement is estimated by applying a quadrature detector to the signal obtained at the A/D converter output. Low sampling frequencies of 17.78 kHz or even 12.31 kHz are possible using quadrature sampling in order to optimize memory requirements and to reduce the computational cost in signal processing. The distance is calculated from the TOF taking into account the speed of sound. An excellent accuracy in the estimation of the TOF is achieved using parabolic interpolation to detect of maximum of the signal envelope at the matched filter output. The signal phase information is also used for enhancing the TOF measurement accuracy. Experimental results show a root mean square error (rmse) less than 2 mm and a standard deviation less than 0.3 mm for pseudorange measurements in the range of distances between 2 and 6 m. The system location accuracy is also evaluated by applying multilateration. A sub-centimeter location accuracy is achieved with an average rmse of 9.6 mm. Full article
(This article belongs to the Special Issue Last Trends in Acoustic Sensing)
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<p>Illustration of the connection between nodes in the TELIAMADE system based on a master-slave topology. A coordinator node connected to a PC is operating as master and allows synchronization, configuration and control of the network end nodes. The end nodes operate as slaves. These can send information about their configuration and also data about TOF measurements of the ultrasound signal when they are operating as ultrasonic receivers, which are processed on a PC. The communication between nodes is based on the exchange of radio packets using the ZigBee Protocol.</p> Full article ">
<p>Hardware design of the TELIAMADE nodes. In transmission, the ultrasound signal is amplified before being driven to the transducer, in order to increase the signal power and improve the range of the system. In reception, the signal is amplified and band-pass filtered before being sampled and digitized using the A/D converter of the microcontroller.</p> Full article ">
<p>Picture of a TELIAMADE node. The regions identified by dashed line show the hardware components of the radio module and the signal conditioning modules for transmission and reception of ultrasonic signal.</p> Full article ">
<p>The typical configuration of the TELIAMADE system. A coordinator node is connected to a PC through which all other nodes of the network are managed. A set of fixed nodes work as ultrasonic transmitters (Tx) and are placed on known positions (typically at the ceiling). The mobile node operates as ultrasonic receiver. Its position is determined by applying multilateration using the estimated distances to the transmitter nodes.</p> Full article ">
<p>The normalized frequency response of the filters using a value of M = 5 (<span class="html-italic">F<sub>s</sub></span> =17.78 kHz). (Above) Magnitude response of the low-pass prototype filter (<span class="html-italic">h</span>) and the band-pass in-phase (<span class="html-italic">h<sub>i</sub></span>) and quadrature (<span class="html-italic">h<sub>q</sub></span>) filters derived from it. (Below) Phase response of the band-pass in-phase and quadrature filters.</p> Full article ">
<p>Reception of an ultrasonic pulse emitted by a transmitter node located at a distance of 3 m from the receiver node. The thin continuous line represents the received sampled signal using a sampling frequency of <span class="html-italic">F<sub>s</sub></span> = 32.00 <span class="html-italic">kHz</span> (<span class="html-italic">M</span> = 3). The curves of filled and empty points correspond respectively to the in-phase (<span class="html-italic">C<sub>i</sub></span>) and quadrature (<span class="html-italic">C<sub>q</sub></span>) components obtained at the output of the matched filter. Finally, the thick continuous line represents the signal envelope (<span class="html-italic">C</span><sub>e</sub>).</p> Full article ">
<p>Parabolic interpolation using a buffer size of 3 samples to obtain the maximum of the signal envelope.</p> Full article ">
<p>Illustration of the test-bed used in the distance measurements. A transmitter node and a receiver node are placed one in front of the other using a pair of tripods at a height of 1.6 m above the ground. Different distances in the range of 2–6 m are considered. The distance between nodes is set by using a commercial laser rangefinder of precision ±1.5 mm. The transmitter node sends periodically an ultrasound pulse of 1 ms by allowing 8 TOF measurements every 3.2 seconds. The receiver node is configured to use the sampling frequencies of 32 kHz, 17.78 kHz and 12.31 kHz. A total of 500 TOF measurements were taken for each distance and each sampling frequency.</p> Full article ">
<p>Calibration procedure for a pair of nodes. A linear regression of the distance measurements is used in order to compensate the group delay in the TOF measurements. The distances measured with the laser rangefinder are plotted on the Y-axis, while the averaged distances obtained from the TOF measurements are plotted on the X-axis. The thin line shows the linear regression of the plotted dots before the group delay compensation. Here a distance error of 22.41 cm is observed. The thick line shows the regression line obtained after calibration of the nodes.</p> Full article ">
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