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10 pages, 2747 KiB

Open AccessArticle

Quartz Enhanced Photoacoustic Spectroscopy Based on a Custom Quartz Tuning Fork

by Maxime Duquesnoy, Guillaume Aoust, Jean-Michel Melkonian, Raphaël Lévy, Myriam Raybaut and Antoine Godard

Sensors 2019, 19(6), 1362; https://doi.org/10.3390/s19061362 - 19 Mar 2019

Cited by 43 | Viewed by 4051

Abstract

We have designed and fabricated a custom quartz tuning fork (QTF) with a reduced fundamental frequency; a larger gap between the prongs; and the best quality factor in air at atmospheric conditions ever reported, to our knowledge. Acoustic microresonators have been added to [...] Read more.

We have designed and fabricated a custom quartz tuning fork (QTF) with a reduced fundamental frequency; a larger gap between the prongs; and the best quality factor in air at atmospheric conditions ever reported, to our knowledge. Acoustic microresonators have been added to the QTF in order to enhance the sensor sensitivity. We demonstrate a normalized noise equivalent absorption (NNEA) of 3.7 × 10⁻⁹ W.cm⁻¹.Hz^−1/2 for CO₂ detection at atmospheric pressure. The influence of the inner diameter and length of the microresonators has been studied, as well as the penetration depth between the QTF’s prongs. We investigated the acoustic isolation of our system and measured the Allan deviation of the sensor. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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(a) Picture of the custom quartz tuning fork used for our experiment. The quartz tuning fork (QTF) presents a 2 mm gap between the prongs. (b) Picture of a commercial fork. Full article ">Figure 2
(a) Acoustic radiation of our QTF simulated by finite element modeling (FEM). The QTF was excited by applying a pressure force on the QTF prongs. (b) Principle scheme of acoustic recovery—firstly, emission of acoustic waves by the QTF; and secondly, reflection thanks to the acoustic recovery device. Full article ">Figure 3
(a) Picture of the QTF within its acoustic cavity: the microresonators for acoustic amplification and the surrounding cylinder for acoustic recovery. (b) Schematic of our QTF used with its acoustic recovery cavity and acoustic microresonators, with a laser beam passing through (in red). Full article ">Figure 4
Normalized sensitivity to the external sound, for the bare C2 QTF (red) and for C2 with its acoustic recovery cavity without microresonators (blue). Full article ">Figure 5
(a) Quality factor of the system (QTF + microresonators) as a function of the length of the tubes, for two different diameters of the tubes and a penetration depth of the tubes of −0.8 mm with respect to the face of the prongs. (b) Same as (a) for tubes of same length and diameter, depending on the depth of penetration of the tubes within the gap between the QTF’s prongs. The quality factor is measured with an impedance-meter. (c) Schematic of the penetration depth. Full article ">Figure 6
Calculated absorption spectra of CO2 (red) and H2O (blue) at atmospheric conditions (P = 101,325 Pa, T = 300K) using the HITRAN database. Full article ">Figure 7
Detection scheme for quartz enhanced photoacoustic spectroscopy (QEPAS) CO2 detection. Full article ">Figure 8
Allan deviation of the measured absorption of 2.7% of CO2 at 6490.05 cm−1. Full article ">

13 pages, 4108 KiB

Open AccessArticle

Dual-Gas Sensor of CH₄/C₂H₆ Based on Wavelength Modulation Spectroscopy Coupled to a Home-Made Compact Dense-Pattern Multipass Cell

by Xing Tian, Yuan Cao, Jiajin Chen, Kun Liu, Guishi Wang, Tu Tan, Jiaoxu Mei, Weidong Chen and Xiaoming Gao

Sensors 2019, 19(4), 820; https://doi.org/10.3390/s19040820 - 17 Feb 2019

Cited by 30 | Viewed by 5749

Abstract

A sensitive dual-gas sensor for the detection of CH₄ and C₂H₆ is demonstrated. Two tunable semiconductor lasers operating at 1.653 μm (for CH₄ monitoring) and 1.684 μm (for C₂H₆) were used as the light [...] Read more.

A sensitive dual-gas sensor for the detection of CH₄ and C₂H₆ is demonstrated. Two tunable semiconductor lasers operating at 1.653 μm (for CH₄ monitoring) and 1.684 μm (for C₂H₆) were used as the light source for spectroscopic measurements of CH₄ and C₂H₆. Long-path absorption in a home-made compact dense-pattern multipass cell (L_eff = 29.37 m) was employed, combined with wavelength modulation and second harmonic detection. Simultaneous detection of CH₄ and C₂H₆ was achieved by separated wavelength modulations of the two lasers. Modulation frequencies and amplitudes were optimized for sensitivity detection of CH₄ and C₂H₆ simultaneously. The dual-gas sensor exhibits 1σ detection limits of 1.5 ppbv for CH₄ in 140 s averaging time and 100 ppbv for C₂H₆ in 200 s. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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14 pages, 5538 KiB

Open AccessArticle

SWIR AOTF Imaging Spectrometer Based on Single-pixel Imaging

by Huijie Zhao, Zefu Xu, Hongzhi Jiang and Guorui Jia

Sensors 2019, 19(2), 390; https://doi.org/10.3390/s19020390 - 18 Jan 2019

Cited by 4 | Viewed by 4123

Abstract

An acousto-optic tunable filter (AOTF) is a new type of mono-wavelength generator, and an AOTF imaging spectrometer can obtain spectral images of interest. However, due to the limitation of AOTF aperture and acceptance angle, the light passing through the AOTF imaging spectrometer is [...] Read more.

An acousto-optic tunable filter (AOTF) is a new type of mono-wavelength generator, and an AOTF imaging spectrometer can obtain spectral images of interest. However, due to the limitation of AOTF aperture and acceptance angle, the light passing through the AOTF imaging spectrometer is weak, especially in the short-wave infrared (SWIR) region. In weak light conditions, the noise of a non-deep cooling mercury cadmium telluride (MCT) detector is high compared to the camera response. Thus, effective spectral images cannot be obtained. In this study, the single-pixel imaging (SPI) technique was applied to the AOTF imaging spectrometer, which can obtain spectral images due to the short-focus lens that collects light into a small area. In our experiment, we proved that the irradiance of a short-focus system is much higher than that of a long-focus system in relation to the AOTF imaging spectrometer. Then, an SPI experimental setup was built to obtain spectral images in which traditional systems cannot obtain. This work provides an efficient way to detect spectral images from 1000 to 2200 nm. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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13 pages, 3807 KiB

Open AccessArticle

An Optical Fiber Sensor Based on La₂O₂S:Eu Scintillator for Detecting Ultraviolet Radiation in Real-Time

by Yongji Yan, Xu Zhang, Haopeng Li, Yu Ma, Tianci Xie, Zhuang Qin, Shuangqiang Liu, Weimin Sun and Elfed Lewis

Sensors 2018, 18(11), 3754; https://doi.org/10.3390/s18113754 - 2 Nov 2018

Cited by 15 | Viewed by 4124

Abstract

A novel ultraviolet (UV) optical fiber sensor (UVOFS) based on the scintillating material La₂O₂S:Eu has been designed, tested, and its performance compared with other scintillating materials and other conventional UV detectors. The UVOFS is based on PMMA (polymethyl methacrylate) [...] Read more.

A novel ultraviolet (UV) optical fiber sensor (UVOFS) based on the scintillating material La₂O₂S:Eu has been designed, tested, and its performance compared with other scintillating materials and other conventional UV detectors. The UVOFS is based on PMMA (polymethyl methacrylate) optical fiber which includes a scintillating material. Scintillating materials provide a unique opportunity to measure UV light intensity even in the presence of strong electromagnetic interference. Five scintillating materials were compared in order to select the most appropriate one for the UVOFS. The characteristics of the sensor are reported, including a highly linear response to radiation intensity, reproducibility, temperature response, and response time (to pulsed light) based on emission from a UV source (UV fluorescence tube) centered on a wavelength of 308 nm. A direct comparison with the commercially available semiconductor-based UV sensor proves the UVOFS of this investigation shows superior performance in terms of accuracy, long-term reliability, response time and linearity. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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14 pages, 3177 KiB

Open AccessArticle

Sub-Diffraction Visible Imaging Using Macroscopic Fourier Ptychography and Regularization by Denoising

by Zhixin Li, Desheng Wen, Zongxi Song, Gang Liu, Weikang Zhang and Xin Wei

Sensors 2018, 18(9), 3154; https://doi.org/10.3390/s18093154 - 18 Sep 2018

Cited by 7 | Viewed by 4515

Abstract

Imaging past the diffraction limit is of significance to an optical system. Fourier ptychography (FP) is a novel coherent imaging technique that can achieve this goal and it is widely used in microscopic imaging. Most phase retrieval algorithms for FP reconstruction are based [...] Read more.

Imaging past the diffraction limit is of significance to an optical system. Fourier ptychography (FP) is a novel coherent imaging technique that can achieve this goal and it is widely used in microscopic imaging. Most phase retrieval algorithms for FP reconstruction are based on Gaussian measurements which cannot extend straightforwardly to long range, sub-diffraction imaging setup because of laser speckle noise corruption. In this work, a new FP reconstruction framework is proposed for macroscopic visible imaging. When compared with existing research, the reweighted amplitude flow algorithm is adopted for better signal modeling, and the Regularization by Denoising (RED) scheme is introduced to reduce the effects of speckle. Experiments demonstrate that the proposed method can obtain state-of-the-art recovered results on both visual and quantitative metrics without increasing computation cost, and it is flexible for real imaging applications. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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Transfer functions of the imaging system with incoherent illumination, coherent illumination and macroscopic Fourier ptychography, respectively. Full article ">Figure 2
The imaging process of Fourier ptychography. Full article ">Figure 3
Peak signal to noise ratio (PSNR) for Reweighted Amplitude Flow for Fourier Ptychography (RAFP) algorithm with different weights. Full article ">Figure 4
Block scheme of the simulation experiments. Full article ">Figure 5
Quantitative comparison of the reconstruction results by different methods under Gaussian noise and speckle noise. Full article ">Figure 5 Cont.
Quantitative comparison of the reconstruction results by different methods under Gaussian noise and speckle noise. Full article ">Figure 6
Visual comparison of the reconstruction results by different methods under Gaussian noise and speckle noise. Full article ">Figure 6 Cont.
Visual comparison of the reconstruction results by different methods under Gaussian noise and speckle noise. Full article ">

22 pages, 10933 KiB

Open AccessArticle

New Digital Plug and Imaging Sensor for a Proton Therapy Monitoring System Based on Positron Emission Tomography

by Nicola D’Ascenzo, Min Gao, Emanuele Antonecchia, Paolo Gnudi, Hsien-Hsin Chen, Fang-Hsin Chen, Ji-Hong Hong, Ing-Tsung Hsiao, Tzu-Chen Yen, Weidong Wang, Daoming Xi, Bo Zhang and Qingguo Xie

Sensors 2018, 18(9), 3006; https://doi.org/10.3390/s18093006 - 8 Sep 2018

Cited by 22 | Viewed by 5286

Abstract

One of the most challenging areas of sensor development for nuclear medicine is the design of proton therapy monitoring systems. Sensors are operated in a high detection rate regime in beam-on conditions. We realized a prototype of a monitoring system for proton therapy [...] Read more.

One of the most challenging areas of sensor development for nuclear medicine is the design of proton therapy monitoring systems. Sensors are operated in a high detection rate regime in beam-on conditions. We realized a prototype of a monitoring system for proton therapy based on the technique of positron emission tomography. We used the Plug and Imaging (P&I) technology in this application. This sensing system includes LYSO/silicon photomultiplier (SiPM) detection elements, fast digital multi voltage threshold (MVT) readout electronics and dedicated image reconstruction algorithms. In this paper, we show that the P&I sensor system has a uniform response and is controllable in the experimental conditions of the proton therapy room. The prototype of PET monitoring device based on the P&I sensor system has an intrinsic experimental spatial resolution of approximately 3 mm (FWHM), obtained operating the prototype both during the beam irradiation and right after it. The count-rate performance of the P&I sensor approaches 5 Mcps and allows the collection of relevant statistics for the nuclide analysis. The measurement of both the half life and the relative abundance of the positron emitters generated in the target volume through irradiation of

10^{10}

protons in approximately 15 s is performed with 0.5% and

5 %

accuracy, respectively. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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9 pages, 3293 KiB

Open AccessArticle

Quartz-Enhanced Photoacoustic Spectroscopy Sensor with a Small-Gap Quartz Tuning Fork

by Yu-Fei Ma, Yao Tong, Ying He, Jin-Hu Long and Xin Yu

Sensors 2018, 18(7), 2047; https://doi.org/10.3390/s18072047 - 27 Jun 2018

Cited by 16 | Viewed by 4162

Abstract

A highly sensitive quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor based on a custom quartz tuning fork (QTF) with a small-gap of 200 μm was demonstrated. With the help of the finite element modeling (FEM) simulation software COMSOL, the change tendency of the QEPAS signal [...] Read more.

A highly sensitive quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor based on a custom quartz tuning fork (QTF) with a small-gap of 200 μm was demonstrated. With the help of the finite element modeling (FEM) simulation software COMSOL, the change tendency of the QEPAS signal under the influence of the laser beam vertical position and the length of the micro-resonator (mR) were calculated theoretically. Water vapor (H₂O) was selected as the target analyte. The experimental results agreed well with those of the simulation, which verified the correctness of the theoretical model. An 11-fold signal enhancement was achieved with the addition of an mR with an optimal length of 5 mm in comparison to the bare QTF. Finally, the H₂O-QEPAS sensor, which was based on a small-gap QTF, achieved a minimum detection limit (MDL) of 1.3 ppm, indicating an improvement of the sensor performance when compared to the standard QTF that has a gap of 300 μm. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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12 pages, 4402 KiB

Open AccessArticle

Flash Smelting Copper Concentrates Spectral Emission Measurements

by Luis Arias, Sergio Torres, Carlos Toro, Eduardo Balladares, Roberto Parra, Claudia Loeza, Camilo Villagrán and Pablo Coelho

Sensors 2018, 18(7), 2009; https://doi.org/10.3390/s18072009 - 22 Jun 2018

Cited by 26 | Viewed by 4266

Abstract

In this paper, we report on spectral features emitted by a reaction shaft occurring in flash smelting of copper concentrates containing sulfide copper minerals such as chalcopyrite (CuFeS₂), bornite (Cu₅FeS₄) and pyrite (FeS₂). Different combustion [...] Read more.

In this paper, we report on spectral features emitted by a reaction shaft occurring in flash smelting of copper concentrates containing sulfide copper minerals such as chalcopyrite (CuFeS₂), bornite (Cu₅FeS₄) and pyrite (FeS₂). Different combustion conditions are addressed, such as sulfur-copper ratio and oxygen excess. Temperature and spectral emissivity features are estimated for each case by using the two wavelength method and radiometric models. The most relevant results have shown an increasing intensity behavior for higher sulfur-copper ratios and oxygen contents, where emissivity is almost constant along the visible spectrum range for all cases, which validates the gray body assumption. CuO and FeO emission line features along the visible spectrum appear to be a sensing alternative for describing the combustion reactions. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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Experimental setup: (a) Experimental setup picture depicting main components; (b) Optical setup of a constructed pinhole to shaft spectra access. Full article ">Figure 2
Emitted spectra during the flash smelting process, for three different copper concentrates with a: (a) S/Cu ratio of 1.07; (b) S/Cu ratio of 1.27 and (c) S/Cu of 1.85. Full article ">Figure 3
Industrial measurement setup: (a) smelter top peephole; (b) steel cooled protecting probe and cooled optical fiber; (c) mounted probe. Full article ">Figure 4
Emitted spectra during the flash smelting process in a flash smelter (real plant): (a) Uncalibrated spectra; (b) Calibrated spectra. Full article ">Figure 5
Mean estimated temperature by using two wavelength method and standard deviation as a function of wavelength interval Δλ. Full article ">Figure 6
Spectral emissivity during the flash smelting process, for three different copper concentrates of a: (a) S/Cu ratio of 1.07; (b) S/Cu ratio of 1.27 and (c) S/Cu of 1.85. Full article ">Figure 7
Spectral emissivity during the industrial flash smelting process, for two measurements. Full article ">

17 pages, 4734 KiB

Open AccessArticle

Filter Selection for Optimizing the Spectral Sensitivity of Broadband Multispectral Cameras Based on Maximum Linear Independence

by Sui-Xian Li

Sensors 2018, 18(5), 1455; https://doi.org/10.3390/s18051455 - 7 May 2018

Cited by 14 | Viewed by 4342

Abstract

Previous research has shown that the effectiveness of selecting filter sets from among a large set of commercial broadband filters by a vector analysis method based on maximum linear independence (MLI). However, the traditional MLI approach is suboptimal due to the need to [...] Read more.

Previous research has shown that the effectiveness of selecting filter sets from among a large set of commercial broadband filters by a vector analysis method based on maximum linear independence (MLI). However, the traditional MLI approach is suboptimal due to the need to predefine the first filter of the selected filter set to be the maximum ℓ₂ norm among all available filters. An exhaustive imaging simulation with every single filter serving as the first filter is conducted to investigate the features of the most competent filter set. From the simulation, the characteristics of the most competent filter set are discovered. Besides minimization of the condition number, the geometric features of the best-performed filter set comprise a distinct transmittance peak along the wavelength axis of the first filter, a generally uniform distribution for the peaks of the filters and substantial overlaps of the transmittance curves of the adjacent filters. Therefore, the best-performed filter sets can be recognized intuitively by simple vector analysis and just a few experimental verifications. A practical two-step framework for selecting optimal filter set is recommended, which guarantees a significant enhancement of the performance of the systems. This work should be useful for optimizing the spectral sensitivity of broadband multispectral imaging sensors. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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The data sets used for simulation are visualized above: (a) transmittances of 45 single filters; (b) all 1035 transmittances of single filters and two single filter combinations; (c) camera sensitivity of a Basler 302f camera sensor; (d) CIE standard illuminant D65; (e) The first eigenvectors of spectral data of the Macbeth ColorChecker; (f) CIE standard illuminant A and (g) color display of spectral data cubic of the Macbeth Color Checker. Full article ">Figure 1 Cont.
The data sets used for simulation are visualized above: (a) transmittances of 45 single filters; (b) all 1035 transmittances of single filters and two single filter combinations; (c) camera sensitivity of a Basler 302f camera sensor; (d) CIE standard illuminant D65; (e) The first eigenvectors of spectral data of the Macbeth ColorChecker; (f) CIE standard illuminant A and (g) color display of spectral data cubic of the Macbeth Color Checker. Full article ">Figure 2
Overall performances of the 45 series of filter sets in terms of GFC, where the upper round marker denotes the maximum value; the middle square denotes the mean; and the lower round denotes the minimum (some of the minimums with negative value less than −2 are not be displayed). Full article ">Figure 3
Overall performances of the 45 series of filter sets for 6 channels in terms of GFC, where the upper round marker denotes the maximum value; the middle square denotes the mean; and the lower round denotes the minimum (some of the minimums with negative value less than −2 are not be displayed). Full article ">Figure 4
Statistics of the top 20% best-performed filter set series in terms of the four indices, PSNR, GFC, MSE and CIEDE2000: (a) frequency and (b) cumulative scores. Full article ">Figure 5
Radar charts of the condition numbers versus the corresponding filter sets in terms of several channel numbers. The radical coordinates denote condition numbers and the angular coordinates denote the No. of the filter sets, therefore the markers denote the position of condition number of the corresponding filter sets. In the radar charts at seven and eight channels, some of the condition numbers cannot be seen because they are too large to be displayed, however only the filter sets with the smaller ones deserve for consideration. Full article ">Figure 6
Transmittance curves of the verified best-performed filter sets under CIE standard illuminant D65 at 4, 5, 6, 7and 8 channels (No. 45, 44 and 38) and the filter set series with maximum <math display="inline"> <semantics> <mrow> <mo> </mo> <msub> <mo>ℓ</mo> <mn>2</mn> </msub> </mrow> </semantics> </math> norm first filter (No. 2), where the first filter of the filter sets is graphed in bold line with solid round markers. The filter sets are selected the same way as the traditional MLI algorithm charted in <a href="#sec2-sensors-18-01455" class="html-sec">Section 2</a> by minimizing condition number at each channel with the designated filter as the first filter of the corresponding filter set. The notation, for example, No. 38 (5 channels) denotes the No. 38 filter set is superior to others when the number of channels is 5, and the No. of the first filter of the filter set is 38. Full article ">Figure 7
Transmittances of the best-performed filter sets, No. 16 (5), under CIE standard illuminant A according to the cumulative scores listed in <a href="#sensors-18-01455-t006" class="html-table">Table 6</a>. Full article ">

14 pages, 960 KiB

Open AccessArticle

Classification and Discrimination of Different Fungal Diseases of Three Infection Levels on Peaches Using Hyperspectral Reflectance Imaging Analysis

by Ye Sun, Kangli Wei, Qiang Liu, Leiqing Pan and Kang Tu

Sensors 2018, 18(4), 1295; https://doi.org/10.3390/s18041295 - 23 Apr 2018

Cited by 40 | Viewed by 7349

Abstract

Peaches are susceptible to infection from several postharvest diseases. In order to control disease and avoid potential health risks, it is important to identify suitable treatments for each disease type. In this study, the spectral and imaging information from hyperspectral reflectance (400~1000 nm) [...] Read more.

Peaches are susceptible to infection from several postharvest diseases. In order to control disease and avoid potential health risks, it is important to identify suitable treatments for each disease type. In this study, the spectral and imaging information from hyperspectral reflectance (400~1000 nm) was used to evaluate and classify three kinds of common peach disease. To reduce the large dimensionality of the hyperspectral imaging, principal component analysis (PCA) was applied to analyse each wavelength image as a whole, and the first principal component was selected to extract the imaging features. A total of 54 parameters were extracted as imaging features for one sample. Three decayed stages (slight, moderate and severe decayed peaches) were considered for classification by deep belief network (DBN) and partial least squares discriminant analysis (PLSDA) in this study. The results showed that the DBN model has better classification results than the classification accuracy of the PLSDA model. The DBN model based on integrated information (494 features) showed the highest classification results for the three diseases, with accuracies of 82.5%, 92.5%, and 100% for slightly-decayed, moderately-decayed and severely-decayed samples, respectively. The successive projections algorithm (SPA) was used to select the optimal features from the integrated information; then, six optimal features were selected from a total of 494 features to establish the simple model. The SPA-PLSDA model showed better results which were more feasible for industrial application. The results showed that the hyperspectral reflectance imaging technique is feasible for detecting different kinds of diseased peaches, especially at the moderately- and severely-decayed levels. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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Review

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15 pages, 2033 KiB

Open AccessReview

Acoustic Detection Module Design of a Quartz-Enhanced Photoacoustic Sensor

by Tingting Wei, Hongpeng Wu, Lei Dong and Frank K. Tittel

Sensors 2019, 19(5), 1093; https://doi.org/10.3390/s19051093 - 4 Mar 2019

Cited by 11 | Viewed by 4463

Abstract

This review aims to discuss the latest advancements of an acoustic detection module (ADM) based on quartz-enhanced photoacoustic spectroscopy (QEPAS). Starting from guidelines for the design of an ADM, the ADM design philosophy is described. This is followed by a review of the [...] Read more.

This review aims to discuss the latest advancements of an acoustic detection module (ADM) based on quartz-enhanced photoacoustic spectroscopy (QEPAS). Starting from guidelines for the design of an ADM, the ADM design philosophy is described. This is followed by a review of the earliest standard quartz tuning fork (QTF)-based ADM for laboratory applications. Subsequently, the design of industrial fiber-coupled and free-space ADMs based on a standard QTF for near-infrared and mid-infrared laser sources respectively are described. Furthermore, an overview of the latest development of a QEPAS ADM employing a custom QTF is reported. Numerous application examples of four QEPAS ADMs are described in order to demonstrate their reliability and robustness. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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Different gas detection techniques are compared in terms of the sensitivity, complexity, and robustness of the sensor. The font sizes stand for their current importance for trace gases detection. DAS: direct absorption spectroscopy, WMAS: wavelength modulation absorption spectroscopy, MPAS: multi-pass absorption spectroscopy, FMS: frequency modulation spectroscopy, ICOS: integrated cavity output spectroscopy, OA-ICOS: off-integrated cavity output spectroscopy axis, CRDS: cavity ring-down spectroscopy, OFCEAS: optical-feedback cavity-enhanced absorption spectroscopy, DCEAS: direct cavity-enhanced absorption spectroscopy and NICE-OHMS: noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. Full article ">Figure 2
Comparison of transmission ranges for different window materials. Full article ">Figure 3
(a) A supporter to hold the AmR; (b) The length L, the thickness T, the width W and the prong spacing g of a standard QTF. Full article ">Figure 4
(a) CAD image of the KF25 vacuum cap; (b) CAD image of the KF25 vacuum base; (c) Photo of the KF25 cap; (d) Photo of the KF25 base. Full article ">Figure 5
(a) CAD image of single-mode fiber-coupled ADM; (b) Photo of single-mode fiber-coupled ADM. Full article ">Figure 6
(a) CAD image of the free space MIR ADM; (b) photo of the top cap with spectrophone; (c) photo of the free space MIR ADM. Full article ">Figure 7
(a) CAD image of the KF40 vacuum cap; (b) CAD image of the KF40 vacuum base; (c) Photo of the KF40 vacuum cap; (d) Photo of the KF40 vacuum base. Full article ">

32 pages, 3516 KiB

Open AccessReview

Recent Applications of Multispectral Imaging in Seed Phenotyping and Quality Monitoring—An Overview

by Gamal ElMasry, Nasser Mandour, Salim Al-Rejaie, Etienne Belin and David Rousseau

Sensors 2019, 19(5), 1090; https://doi.org/10.3390/s19051090 - 4 Mar 2019

Cited by 132 | Viewed by 18631

Abstract

As a synergistic integration between spectroscopy and imaging technologies, spectral imaging modalities have been emerged to tackle quality evaluation dilemmas by proposing different designs with effective and practical applications in food and agriculture. With the advantage of acquiring spatio-spectral data across a wide [...] Read more.

As a synergistic integration between spectroscopy and imaging technologies, spectral imaging modalities have been emerged to tackle quality evaluation dilemmas by proposing different designs with effective and practical applications in food and agriculture. With the advantage of acquiring spatio-spectral data across a wide range of the electromagnetic spectrum, the state-of-the-art multispectral imaging in tandem with different multivariate chemometric analysis scenarios has been successfully implemented not only for food quality and safety control purposes, but also in dealing with critical research challenges in seed science and technology. This paper will shed some light on the fundamental configuration of the systems and give a birds-eye view of all recent approaches in the acquisition, processing and reproduction of multispectral images for various applications in seed quality assessment and seed phenotyping issues. This review article continues from where earlier review papers stopped but it only focused on fully-operated multispectral imaging systems for quality assessment of different sorts of seeds. Thence, the review comprehensively highlights research attempts devoted to real implementations of only fully-operated multispectral imaging systems and does not consider those ones that just utilized some key wavelengths extracted from hyperspectral data analyses without building independent multispectral imaging systems. This makes this article the first attempt in briefing all published papers in multispectral imaging applications in seed phenotyping and quality monitoring by providing some examples and research results in characterizing physicochemical quality traits, predicting physiological parameters, detection of defect, pest infestation and seed health. Full article

(This article belongs to the Special Issue Optical Sensing and Imaging, from UV to THz Range)

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