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RFID and Wireless Sensors using Ultra-Wideband Technology
 Remote Identification Beyond RFID Set
coordinated by
Etienne Perret

RFID and Wireless Sensors

using Ultra-Wideband
Technology

Angel Ramos
Antonio Lazaro
David Girbau
Ramon Villarino
First published 2016 in Great Britain and the United States by ISTE Press Ltd and Elsevier Ltd

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as
permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced,
stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers,
or in the case of reprographic reproduction in accordance with the terms and licenses issued by the
CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the
undermentioned address:

ISTE Press Ltd Elsevier Ltd

27-37 St George’s Road The Boulevard, Langford Lane
London SW19 4EU Kidlington, Oxford, OX5 1GB
UK UK
www.iste.co.uk www.elsevier.com

Notices
Knowledge and best practice in this field are constantly changing. As new research and experience
broaden our understanding, changes in research methods, professional practices, or medical treatment
may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and
using any information, methods, compounds, or experiments described herein. In using such information
or methods they should be mindful of their own safety and the safety of others, including parties for
whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any
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© ISTE Press Ltd 2016

The rights of Angel Ramos, Antonio Lazaro, David Girbau and Ramon Villarino to be identified as the
authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents
Act 1988.

British Library Cataloguing-in-Publication Data

A CIP record for this book is available from the British Library
Library of Congress Cataloging in Publication Data
A catalog record for this book is available from the Library of Congress
ISBN 978-1-78548-098-0

Printed and bound in the UK and US

 Pre ace

Wireless sensor networks WSNs for smart cities, smart homes

and Internet of Things IoT applications require low-power, low-cost
and simple radio interfaces for a very large number of scattered
sensors. UWB in time domain is used here as an enabling radio
communications technology.

A comprehensive circuit model is explained for time-coded UWB

RFID. Reader setups based on commercial impulse radars are
combined with signal processing techniques. As a starting point,
several chipless time-coded RFID tag designs are shown as examples.
Then, the tags’ performance is shown in terms of a number of possible
IDs, maximum reading distance, polarization, influence of attached
materials, angular behavior and bending for tags on flexible
substrates .

Chipless wireless sensors are derived based on these tag designs.

Specifically, for temperature and concrete composition the latter
enabled by permittivity sensing chipless sensors are shown as
possible options.

In order to have more complex, more robust, and longer read range
solutions, two chip-based semi-passive sensing platforms are inferred
from the chipless tag designs. A wake-up link is used to save energy
when the sensor is not being read.
 RFID and Wireless Sensors Using Ultra-Wideband Technology

Using an analog semi-passive UWB platform, a wireless

temperature sensor powered by solar energy and a wireless nitrogen
dioxide sensor enabled with carbon nanotubes and powered by a
small battery are explained. Using a digital with a low-power
microcontroller semi-passive UWB platform, a multi-sensor tag
capable of measuring temperature, humidity, pressure and acceleration
is analyzed.

In order to even further increase the read range, two active time-
coded RFID systems are illustrated, based on the use of signal
amplifiers within the tag.

Finally, a smart floor application for indoor localization is

introduced, by joining the proposed designs with ground penetrating
radar technology.

Angel RA OS
Antonio LA ARO
David GIRBAU,
Ramon VILLARINO
February 2016
 Ac no ledgements

The authors would like to acknowledge the Spanish Government

Projects TEC2008-06758-C02-02 and TEC2011-28357-C02-01, the
Universitat Rovirai Virgili grant 2011BRDI-06-08, the AGAUR Grant
FI-DGR 2012 and the 2020 Grant Agreement 645771
E ERGENT. The authors would also like to acknowledge the
undergraduate students Sergi Rima, Xavier Domenech, Eduard Ibars
and Cristian ernandez.
 Introduction to RFID
and hi less RFID

Automatic identification ID of goods is widely used in industry,

logistics, medicine and other fields. The aim is to obtain the ID
information of a good in transit. Giant electronic commerce platforms
such as Amazon, Alibaba or eBay are becoming the main choice for
buyers worldwide LOE 14 . Instead of buying from a small retailer,
final customers are directly in contact with a wholesaler or distributor.
In this context, accurate tracking of each good to its final customer is a
major concern in a massive and growing logistics market. An
efficient, automatic organization of the stock in large warehouses
both sellers’ and logistics companies’ is also crucial to reduce costs
and delivery times.

Nowadays, the barcode see Figure 1.1 is the most used automatic
ID solution PAL 07 . It consists of a reader that optically reads a tag.
The tag is created by printing black stripes on a white background.
Depending on the number, width and separation of stripes, a unique
ID is generated. In order to code more information in a smaller space,
variations such as R codes DEN 14 have recently arisen. The cost
of each barcode tag is extremely cheap because it only requires paper
and ink. In addition, barcode readers are cheap, and even low-cost
compact mobile phone cameras can provide high-resolution images to
read barcodes O B 04 . owever, it requires a direct line of sight
 RFID and Wireless Sensors Using Ultra-Wideband Technology

between the reader and the tag. A specific positioning of the object is
required in order to orientate the barcode toward the reader, and
normally only one tag can be read at a time. Barcode storage capacity
is also limited, and they cannot be reprogrammed. Another common
problem with barcodes is misreading due to a low-resolution printing
of the tag, or ink wearing away in harsh environments.

Figure Photograph of a barcode system

RFID state of the art

Introduction to RFID

In order to overcome barcode limitations, radio frequency

identification RFID technologies have been developed in recent
years FIN 10 . RFID systems are used to remotely retrieve data from
target objects tags without the need for physical contact or line of
sight by using magnetic or electromagnetic E waves. With some
RFID systems, it is also possible to measure several tags at the same
time and rewrite the tag information.

Figure 1.2 shows a basic scheme of an RFID system. There are two
main families: near-field RFID Figure 1.2 a and far-field RFID
Figure 1.2 b WAN 06 . Near-field RFID is based on Faraday’s
principle of magnetic induction magnetic coupling . Both the reader
and the tag have coils. The reader powers up the tag’s transponder
chip, which can be rewritten. Near-field RFID based on this inductive
communication is used for small distances, typically below / 2
where is the wavelength WAN 06 . ISO 15693 and 14443 standards
 Introduction to RFID and hi less RFID

set frequencies below 14 z, which results in a range of a few

centimeters. Near-field RFID is widely used for cards and access
control, but not for goods management due to its limited range.
Far-field RFID uses E waves propagated through antennas
both in the reader and the tag. A reader can be monostatic if it only
has an antenna that acts for transmission Tx and reception Rx .
On the contrary, if the reader has separate Tx and Rx antennas,
it is bistatic. The reader sends an E wave that is captured by the
tag’s antenna at a distance of several meters. There are several
standards for far-field RFID, with the Electronic Product Code EPC
Gen2 standard, at the Ultra igh Frequency U F 868 z in
Europe or 915 z in the United States band, being the most used.

Figure Scheme of an RFID system; a) near-field and b) far-field

Even though the barcode is still the de facto standard, RFID is one
of the fastest growing sectors of the radio technology. As of 2014,
nearly every commercially available smartphone integrates near-field
RFID with the Near Field Communication NFC forum’s standards
AR 14 . Wal- art and Tesco, some of the largest retailers in
the United States the and the United Kingdom, respectively, are
adopting RFID WAN 06 . Furthermore, wireless ID has developed
 RFID and Wireless Sensors Using Ultra-Wideband Technology

into an interdisciplinary field. Radio frequency RF technology,

semiconductor technology, data protection and cryptography,
telecommunications and related areas come together to develop cheap,
secure, reliable, long-range and self-powered RFID tags.

Far-field RFID systems can be classified depending on how the

tags get the necessary energy to respond to the readers. Active tags are
the most expensive tags, since they need their own power supply i.e.
batteries not only to power their own chip but also to generate the
radio signal with the response to the reader. Semi-passive tags are less
expensive than active tags, since they need batteries, but only to
power their own logic circuitry, not a transmitter. The response is
achieved by changing the reflected signal from the reader in a process
called backscattering. This means that the batteries can be smaller and
have longer life times usually years . Finally, passive tags are the
cheapest ones and have the largest commercial potential for large-
scale spreading VIT 05, COL 04 . Passive tags use the reader’s RF
signal to harvest the necessary power for themselves VIT 05 .
Specifically, passive U F EPC tags are the type of RFID tags most
widely used for large-scale applications. Depending on the region,
there are different frequency bands and maximum allowed powers
allocated for RFID applications GS1 14 . In Europe, the most used
band is 865.6 867.6 z, with a maximum transmitted power of
2 W of effective radiated power ERP , or, equivalently, 3.28 W of
effective isotropic radiated power EIRP . Similarly, in the United
States the allowed RFID band is 902 928 z, with a maximum
transmitted power of 4 W EIRP, or, equivalently, 2.44 W of ERP. It
can be observed that American regulations permit more transmitted
power than European regulations, allowing for longer read ranges.
ost manufacturers provide U F RFID tags and readers compatible
with both European and American bands. Figure 1.3 shows an
example of a typical commercial U F EPC Gen2 reader and tag from
Alien Technology ALI 16 . These types of tags have a sensitivity of
about −20 dBm I P 14, ALI 14 , and read ranges between 6 and 10
m depending on the region EXT 10 . Recent research has increased
the read range to about 25 m by assisting the tag with a battery
battery-assisted passive tags E 14 .
 Introduction to RFID and hi less RFID

There have also been recent developments in millimeter wave

bands. illimeter wave identification ID has been presented in
PUR 08 as a concept of RFID operating at 60 G z. ID is not a
replacement of RFID, since its read range is much shorter a few
centimeters . ID, however, permits high data rate communications
even gigabit . Directive antennas at millimeter wave frequencies are
also very small compared to U F, permitting the possibility of
selecting a tag by pointing toward it. The use of nonlinear devices for
RFID tags has also been studied recently. Tags based on the
inter-modulation distortion of devices have been presented in
CAR 07 using a diode for localization applications, and in VII 09
using the micro electromechanical system.

a b

Figure a) Alien ALR-9900 UHF EPC Gen2 RFID reader;

b) Alien ALN9740 UHF RFID tag

Chipless RFID

Chipless tags are a specific type of passive RFID tags. In these

tags, instead of storing the ID in a digital IC, it is stored in physical
permanent modifications when the tag is fabricated. These
modifications change from one tag to another. A notable reduction in
costs for passive U F tags has been achieved recently VIT 05 due to
the popularization in using RFID technology. owever, each U F tag
price is fixed by the chip and by the process of connecting it to the tag
antenna. Consequently, using chip-based tags is non-viable for
identifying large volumes of paper or plastic documents such as
banknotes, postage stamps, tickets or envelopes, since the price of the
tag is larger than the document itself COL 04 . U F RFID
technology also presents some weaknesses. U F frequency-band
 RFID and Wireless Sensors Using Ultra-Wideband Technology

allocation depends on the region, as well as the readers’ output signal

power, which directly affects the read range the more power allowed,
the longer the read distance . U F tags are affected by multipath
propagation LA 09a , interference between readers LA 09b and
frequency detuning due to different materials used as the tag physical
support LOR 11 , factors that can lead to smaller read ranges. It is
also necessary to consider special tags, used when attached to metal
surfaces, which increase the total price.

Figure a) Scheme of a chipless RFID system. b) Classification

of chipless RFID tags [KAR 10]. For a color version of
the figure, see www.iste.co.uk/ramos/rfid.zip

Chipless tags can be a promising low-cost alternative for RFID

systems, since they do not need an IC to work KAR 10, TED 13 . In
chipless tags, the ID is stored in physical permanent modifications in a
scattering antenna. The modifications are unique for each tag, and
change its RF backscattered response, or signature. Figure 1.4 a
shows a scheme of a chipless RFID system. It is important to note that
 Introduction to RFID and hi less RFID

chipless tags cannot change their information once they have been
fabricated, since their physical characteristics are permanent.
owever, chipless RFID can provide a low-cost alternative, which
could increase the capabilities of barcodes. Since a standard for
chipless RFID does not exist, there are several types of approaches
undergoing active research to achieve chipless RFID tags.
Figure 1.4 b shows a classification of chipless RFID tags given in
KAR 10 . One drawback with chipless RFID tags compared with
chip-based tags is the small number of possible IDs KAR 10, TED
13 . owever, this drawback is not very important if the chipless tag
integrates additional capabilities beyond ID such as sensing.

Time-domain based time-coded tags encode the ID in the time

delay of a reflected peak. Surface acoustic wave SAW technology
offers a nonprintable alternative for chipless RFID AR 02, REI 98,
REI 01 . SAW RFID is usually based on passive RFID systems,
where the signal from the reader is converted into an acoustic wave. A
scheme of a SAW tag is shown in Figure 1.5. The acoustic wave hits
the tag substrate. Then, multiple reflections occurring at different time
instants modify the wave. Then, it is reconverted to an RF signal and
sent to the reader. These types of systems have great immunity to
temperature changes, have high data transfer rates, can integrate
sensors, and have a high read range AR 02 . owever, SAW tags
are expensive and cannot be made easily due to their piezoelectric
nature. Therefore, SAW chipless RFID cannot be used with low-cost
products COL 04 . Thin film transistor circuit TFTC tags can be
printed at high speeds on low-cost films DAS 06 . They are small in
size and have low power consumption. owever, manufacturing
TFTCs is not a low-cost process, and they are limited to several
megahertz. Delay line-based chipless tags consist of an antenna
followed by a delay line. Similar to SAW tags, delay line-based tags
code the ID in reflections introduced by the delay line. Delay
line-based tags can operate either at a narrowband S R 07 or
wideband DOU 10 frequencies, but their ID capacity number of bits
for a given tag size is small. owever, the read range of these types
of tags is larger than frequency-coded or amplitude/phase backscatter
modulation, as will be detailed next. Delay line-based chipless tags at
wideband frequencies are studied in detail in this book.
 RFID and Wireless Sensors Using Ultra-Wideband Technology

Figure Scheme of a SAW tag. For a color version

of the figure, see www.iste.co.uk/ramos/rfid.zip

Spectral signature based frequency-coded chipless tags encode

the ID using resonant structures. Each bit state corresponds to a
presence or absence of a resonance at a given frequency. Frequency-
coded tags are printable, robust, have a moderate ID capacity and are
low cost. owever, a large spectrum is often required in order to
encode a large number of IDs, which may not be under regulation at
all frequencies. Frequency-coded tags are more sensitive to orientation
and distance than delay line based tags, and their read range is shorter.
Chemical tags are designed from a deposition of resonating fibers or
special electronic ink COL 06 . In COL 06 , tags fabricated from
particles of chemicals that resonate at specific frequencies when
illuminated by E waves are presented. Ink-tattoo chipless tags use
electronic ink patterns printed on the surface of the object being
tagged: no actual substrate is required ON 07 . Planar circuit
frequency-coded chipless RFID has been the subject of research by
several groups. In AL 05 , a tag consisting of an array of vertically
polarized identical dipoles, capacitive tuned, is presented. Each dipole
is tuned at different frequencies to code a data bit. In CV 06 , a
frequency-coded tag based on space-filling curves at 900 z is
presented. Space-filling curves can create resonances with very small
footprints compared to the frequencies they are resonating. The main
drawback with these types of tags is the difficulty in creating the
appropriate layouts to achieve the required resonant frequencies. LC
resonant chipless tags consist of a magnetic resonant coil at a
particular frequency. Instead of working at a predetermined frequency,
as with NFC standards, the reader sweeps a frequency band searching
for a resonant frequency peak, which corresponds to the unique tag
frequency ID . Commercial LC resonant chipless tags are widely
 Introduction to RFID and hi less RFID

used for surveillance portals and antitheft purposes at supermarkets

and retail stores FLE 02 . One interesting type of multi resonator-
based frequency-coded tag consists of a structure with two antennas in
cross-polarization KAR 10 . The antennas are connected with a
transmission line, loaded by resonators at different frequencies. The
backscattered response codes the information in the presence or
absence of the resonant peaks, determined by the resonators loading
the transmission line in the tag. Finally, in TED 13 , another type of
multi-resonant structure is presented. In this case, the structure is
created by several dipoles that backscatter the incident wave in its
orthogonal polarization. Each dipole is tuned at a predetermined
frequency, and its presence or absence codes the corresponding bit
state. The use of orthogonal polarization mitigates the clutter
reflections and coupling between the reader’s antennas, allowing a
better detection of the tags.

Amplitude-phase backscatter modulation-based chipless RFID tags

operate at narrower bandwidths compared with time- or frequency-
coded tags. These types of tags encode the ID varying the amplitude
or phase of the backscattered signal due to the load connected to an
antenna. Left-hand L delay line based tags consist of a narrowband
antenna connected to a series of cascaded L delay lines SC 09 .
Each L section produces a discontinuity in the phase of an incident
wave. The reader interrogates the L -based tag using a modulated
signal, such as quadrature phase shift keying. Each tag produces a
unique phase variation on the carrier signal. Remote complex
impedance-based chipless tags UK 07 are formed by a printable
scattering antenna for instance a patch antenna loaded with a lossless
reactance. Each tag has a unique reactance that generates a unique
inductive loading. The backscattered signal thus has a different phase
for each tag. Stub-loaded patch antenna based tags BAL 09a are
similar to remote complex impedance-based tags, with increased
robustness. In this case, a stub loads a patch antenna. The ID is coded
in the cross-polarized phase difference between electric E and
magnetic planes. Finally, carbon nanotube CNT loaded chipless
tags consist of RFID antennas loaded by CNTs, which modify the
scattering signature depending on their state. In AN 09 , a
 RFID and Wireless Sensors Using Ultra-Wideband Technology

conformal U F RFID antenna is loaded with single-walled CNTs to

realize a chipless RFID gas sensor.

In summary, chipless RFID is a field of interest in RFID. There is

not a common standard as in passive U F RFID. Therefore, chipless
RFID is still the subject of active research. There are advantages and
disadvantages between each approach, and the final application will
decide which approach is chosen. ost of the published work on
chipless RFID relies on using high-cost laboratory instruments as
readers to demonstrate the feasibility of the proposed tags. owever,
there is an increasing interest in developing custom readers TED 13 ,
which would reduce costs and enable the adoption of chipless RFID
for specific market niches.

tending RFID ca abilities from ID to sensing

There have been many advances in the miniaturization and cost

reduction of advanced sensors IC 08 . A large number of
applications can benefit from the information about their environment
these sensors can obtain. Smart homes EL 05 or smart cities
EL 05 are concepts that have flourished recently. In both cases,
one of the main ideas is to fill an area either houses or cities with
small, self-autonomous and low-cost sensors. These sensors are
connected creating so-called sensor networks IC 08 . For large-
scale applications, wiring each sensor is not viable. Also, some
sensors can be placed in areas difficult to access. Therefore, wireless
radio technologies that enable the sensors to be read remotely,
creating a sensor node, are desired. The association of these wirelessly
readable sensor nodes is called a wireless sensor network WSN .
Apart from smart homes or smart cities, WSNs also have a great
potential in a large number of applications such as IC 08 military
target tracking and surveillance, natural disaster relief, biomedical
health monitoring, hazardous environment exploration and seismic
sensing. Low-power communication technologies are required to
achieve years of lifetime for wireless sensors. Careful design for these
technologies, based on small data rates for small amounts of
information, only sensor readings , has to be taken into account.
 Introduction to RFID and hi less RFID

Sensor nodes and readers or reading points RP can be

associated in several ways. A direct wireless link between each sensor
and RP see Figure 1.6 a , centralized star topology is a solution
that requires high RF power transmitters if distances are long, with a
consequent impact on battery lifetime or the need for a power supply
to each sensor. A second possibility is to link the sensors in what is
called a wireless network. In this way, the sensors also act as a bridge
for other sensors see Figure 1.6 b , mesh topology . A third solution
might be the use of a mobile link between sensors and RP see Figure
1.6 c , mobile topology . This means taking advantage of the mobility
of vehicles inside a city, by using them to also transport information.
For instance see Figure 1.6 d , buses can be good candidates. A bus
always performs the same route, and stops periodically and repeatedly
in bus stops. If a wireless sensor is installed in a bus stop and the
reader at the bus, the sensor can be read every time the bus stops there.
The information recorded in each trajectory can be downloaded at a
point normally another bus stop , which is connected to the data
management point. The main advantage of this solution is that low-
power consumption wireless sensors can be used, since read ranges
are in the order of few meters,

a b c

Figure Sensors: green points. Reader point (RP): red point.

a) Centralized topology, b) mesh topology, c) mobile RP topology and
d) scheme of transmission between the bus and the bus station. For a
color version of the figure, see www.iste.co.uk/ramos/rfid.zip
 RFID and Wireless Sensors Using Ultra-Wideband Technology

Existing technologies for WSNs

There are several commercial low-power solutions on the market

for WSNs NAP 11, S I 11, GUN 09, TEX 14, DE 13 . Some of
the most popular solutions are now compared in terms of cost, power
consumption, speed and range. Table 1.1 summarizes typical values of
these parameters for bluetooth low-energy LE , ANT and igBee
technologies. Other technologies such as Wi-Fi IEEE 802.11 , NFC
or infrared IrDA S I 11 were discarded in this comparison
because they are not intended for wireless sensor applications either
their power consumption is extremely high for miniaturized portable
devices Wi-Fi or their read range is very short for a wireless sensor
NFC or IrDA .
Bluetooth LE: although its original aim was for mobile devices
and accessories, the latest specification version 4.0 LE in 2010 takes
into account low-power devices. Wearable devices, such as cardiac
sensors or pedometers, companions for smartphones, are enabled with
bluetooth LE WAN 13 .
ANT: a proprietary technology by Dynastream, working at 2.4
G z as bluetooth. It is aimed towards wearable devices in
combination with smartphones D N 15 .
ZigBee: a specification given by the IEEE 802.15.4 standard,
which is specifically intended for home automation and larger areas
than bluetooth LE or ANT W E 07 .

Approximate Power Peak

cost per unit Sensitivity Speed Approximate
Technology consumption current
dBm kbps range m
US W/bit mA

Bluetooth LE 2.95 −87 0.153 12.5 305 100

0 dBm Tx

ANT 3.95 −85 0.71 17 20 30

0 dBm Tx

igBee 3.20 −100 185.9 40 205 100

1 dBm Tx

Table Comparison between existing

technologies for WSNs with typical values
 Introduction to RFID and hi less RFID

As can be observed, bluetooth LE has very low average power

consumption however, its peak current is very large for battery-less
devices, which rely on external sources PAR 05 . These external
sources can be the reader’s RF signal, solar energy or movement, for
instance KI 13 . As introduced in section 1.1, passive RFID tags
are powered from the reader’s signal.

RFID-enabled wireless sensors

The RFID reader uses a wireless communication link when it

retrieves the ID from one or several tags. This link can also be
exploited to collect data from a sensor connected to or embedded into
the tag KI 13, WAN 04 . Adding sensing capabilities to RFID
permits possibilities beyond what barcode systems offer. In addition,
RFID systems have less complicated protocols and data frames than
igBee or Bluetooth, for instance. Also, even though igBee or
bluetooth can offer faster absolute data rates, the communication with
RFID is established faster because the tag does not need to associate
and authenticate with the reader at the beginning. One typical
application for RFID-enabled wireless sensors is monitoring the cold
chain in perishable products. The customer, as well as the seller and
logistics companies, can determine the temperature range of the item
from its production to its final destination. Accelerometers can also be
used in fragile products in order to detect hits or bad package
handling. As an example, in GON 14 , an RFID-enabled sensor tag is
embedded in cork wine bottle stoppers to monitor their temperature.

RFID systems also have a several advantages for WSNs in smart

homes or smart cities applications. The cost of RFID tags can be very
low when using low-cost substrates and inkjet printing technology
OL 03 . The architecture of RFID systems is also simpler than
other systems such as bluetooth LE or igBee see section 1.2.1 ,
because the sensor tags do not require dedicated transceivers. It is also
possible to integrate RFID systems in conventional WSNs, as shown
in LIU 08 . RFID-enabled sensors are integrated with materials that
are sensitive to physical parameters, for instance water-absorbing
materials for humidity sensors and carbon nanostructures for gas
sensors VEN 13a . The electrical parameters of the materials such as
 RFID and Wireless Sensors Using Ultra-Wideband Technology

permittivity and conductivity are changed by the physical parameters.

These electrical changes are translated in changes in the RFID signal.
In the last few years, some platforms based on microcontrollers that
emulate the behavior of passive U F EPC Gen2 tags have been
presented. The best known example is the wireless ID and sensing
platform SA 08 from Intel Research Seattle. A photograph is
shown in Figure 1.7. Other similar platforms based on inkjet printing
on paper substrates have been presented V K 09 .

Figure Photograph of the wireless identification and sensing

platform (WISP) RFID-enabled sensing platform

Ultra- ideband technology for RFID a lications

Introduction to ultra-wideband technology

Ultra-wideband UWB radio technology uses very short

nanosecond order time domain pulses FCC 03, OS 04 . Using
these kinds of pulses widens the signal in the frequency domain to be
much wider than traditional communications that use narrowband
frequency-multiplexed signals. A UWB signal is defined as a signal
with a bandwidth higher than 20 of its center frequency, or a signal
with a bandwidth higher than 0.5 G z.

The American Federal Communications Commission FCC

specified a band of operation for UWB signals from 3.1 to 10.6 G z
in 2002 FCC 03 . This band can be used freely, with the only
limitation of radiated power. Therefore, UWB signals cannot affect
traditional narrowband communications. In Europe, the European
Telecommunications Standard Institute ETSI and the European
Conference of Postal and Telecommunications Administrations
specified a slightly different power mask for UWB communications
ETS 08, AST 09 . Figure 1.8 shows the maximum allowed indoor
 Introduction to RFID and hi less RFID

and outdoor levels by both ETSI and FCC. Evidently, European

regulations are more restrictive than American regulations. The FCC
also allowed operation of UWB in 2002 while Europe did in 2005.
Since the ETSI does not regulate a single country as the FCC does,
approving the standard is slower and the final mask is more restrictive,
to comply with all countries’ existing narrowband systems A 11 .
From Figure 1.8, there is a band below 1 G z that is intended for
ground penetrating radar GPR systems. GPR systems point the radar
antenna s toward the ground floor, and therefore are not likely to
cause interference on other systems DAN 05 . Figure 1.9 compares
the transmitted power of a UWB signal and a narrowband signal as a
function of frequency. It can be clearly seen that UWB signals require
less power than narrowband signals, but their bandwidth is much
higher than narrowband systems.

Figure Maximum indoor and outdoor levels of power spectral

density (PSD) as a function of frequency for ETSI and FCC regulations.
For a color version of the figure, see www.iste.co.uk/ramos/rfid.zip

Figure Comparison between power levels and frequency

bandwidth of a narrowband and a UWB signal
 RFID and Wireless Sensors Using Ultra-Wideband Technology

Since UWB pulses have this large bandwidth, a UWB system

permits better immunity to multipath propagation and narrowband
interferences, because these kinds of interferences only affect a part of
the complete spectrum. UWB also has good penetration in materials.
Another advantage of UWB technology for RFID resides in the size of
the antennas, which is usually smaller than traditional narrowband
RFID due to the increase in the operating frequency. There exists
rising demand for new antenna designs to have small dimensions. The
higher frequencies of UWB enable compact hand readers and an
increase in resolution position for localization systems. RF circuitry
can be simpler with UWB, and data transfer rates can be higher.
Therefore, an interest in UWB technology has arisen in industry and
research fields FON 04 .

UWB-based RFID

UWB technology can be a promising solution for next-generation

RFID systems due to the advantages inherent to its large bandwidth.
any frequency bands from 9 k z to 24 G z are theoretically
capable of being used in RFID. Some of these allocated bands are
denominated industrial, scientific and medical IS , and they are
usually free to use without any license in many countries. In front of
the U F band for RFID, IS bands, especially the most popular one
at 2.4 G z, is saturated because of wireless LAN and bluetooth
applications, leading to a poor performance when using it for RFID.
owever, UWB presents a frequency band that is much higher than
allocated narrowband frequencies.

Additionally, even though IS bands do not need licenses, their

emitting power is limited to avoid interferences, leading to a majority
of active-only RFID tags in these bands, and the highest power
consumption is precisely in the RF transmission part. UWB impulses
need less power than narrowband signals, which means that UWB can
be used to develop low-power active and semi-passive tags in the
future. oreover, UWB is able to resolve the growing demand for
higher data transmission speeds. The bandwidth with U F and IS
bands is usually not sufficient for the resolution required in indoor
localization applications. One of the most important commercial
 Introduction to RFID and hi less RFID

applications of UWB and GPR is indoor localization due to their

large bandwidth.

Despite all these potential advantages, it is still necessary to

improve certain aspects such as cost reduction, tag tracking precision
regardless of its speed or read rate and reading reliability. Recently,
UWB-based chipless RFID systems have been proposed in the
literature BAL 09b, A 06 . The number of IDs that chipless
frequency-coded RFID can encode depends on the allowed
bandwidth. Thus, the UWB is often used in these tags. In BAL 09b ,
chipless printable RFID tags are proposed by using several resonators
in frequency domain. In SC 09, DOW 09 , sensors are integrated
with chipless RFID tags to remotely read the sensor. In chipless
passive RFID UWB tags, the read range is not limited by the power
threshold to activate the chip, which is the main limitation for read
distance of passive U F tags LA 09b .

oreover, multipath interferences can positively or negatively

affect the read when working with U F RFID tags. The tag may not
be readable even though it is inside the read range due to multipath
LA 09b . This situation can be resolved using UWB technology,
since different responses originated by the multipath interference can
be minimized by using signal-windowing techniques in time domain.

An alternative method of using several resonators in the frequency

domain consists of coding the information in the time delay
DOU 10, DAR 08 . ere, the simplest way to code information is by
varying the physical length of an open-ended transmission line
connected to a scattering UWB antenna. The length of the
transmission line changes the time delay of the reflection due to the
tag antenna, and therefore different states can be coded. Although this
idea has been proposed by some authors DOU 10, DAR 08 , there are
few experimental results, which have been obtained by means of high-
cost instruments such as vector network analyzers. Future
implementations of commercial readers should be based on low-cost
equipment, such as impulse radio UWB radars.
 RFID and Wireless Sensors Using Ultra-Wideband Technology

rgani ation of this boo

The book is organized as follows. Chapter 2 describes the chipless

time-coded UWB RFID theory, signal processing techniques and
reader alternatives. Several designs of chipless tags are shown and
characterized. A study and discussion on read range, resolution,
number of bits, influence of angle, polarization, materials and tag
bending are presented. Chapter 3 uses foundations and tags shown in
Chapter 2 to design chipless sensors. Amplitude-based continuous
and threshold temperature and delay-based permittivity for concrete
composition detection chipless sensors are presented as examples.
Chapter 4 describes semi-passive sensing platforms based on time-
coded UWB RFID. Two topologies based on analog and digital
approaches are explained. Chapter 5 integrates sensors in the semi-
passive sensing platforms from Chapter 4, and a temperature and a gas
sensor this later based on CNTs are shown as examples. Chapter 6
shows a smart floor application where chipless Chapter 2 and semi-
passive Chapter 4 tags are combined with GPR techniques. Finally,
Chapter 7 presents active long-range platforms based on time-coded
UWB RFID intended for localization applications.
 hi less Time-coded
UW RFID Reader Signal
Processing and Tag Design

Introduction

Chipless time-coded UWB RFID could be an alternative for RFID

systems. The tag’s ID is coded in the physical length of an open-ended
transmission line connected to a scattering UWB antenna. Although
this idea has been proposed by some authors U 07, U 08,
U 10, DAR 08 , there are few experimental results, which have been
obtained by means of expensive instruments such as vector network
analyzers VNAs . Future implementations of commercial readers
should be based on low-cost equipment, such as impulse radio IR
UWB radars GEO 14, NOV 12, TI 14 . Due to their large
bandwidth, a small signal-to-noise ratio SNR is expected with these
systems. Therefore, signal processing techniques should be considered
in order to detect the tag in a real scenario with noise. Finally, the
realization integrating a UWB antenna with a long delay and
characterization of chipless time-coded UWB tags should be studied
in detail. In this chapter, the following fields are addressed:
section 2.2 presents the theoretical foundations
section 2.3 compares two reader approaches
Another random document with
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We saw Katinka first when we were all about the table—Cousin
Diantha, Miss Waitie who was her spinster sister, Pelleas and I, and
Andy, who worked for his board. I shall not soon forget the picture
that she made as she passed the corn cakes,—Katinka, little maid-
of-all-work, in a patched black frock and a red rubber ring and a red
rubber bracelet. Her face was round and polished and rosy with
health, and she was always breathless and clothed with a pretty fear
that she was doing everything wrong. Moreover, she had her ideas
about serving—she afterward told me that she had worked for a
week at the minister’s in Paddington where every one at breakfast,
she added in an awed voice, “had a finger bowl to themself.” Cousin
Diantha, good soul, cared very little how her dainties were served so
that the table was kept groaning, and Katinka had therefore
undertaken a series of reforms to impress which she moved in a
mysterious way. For example, as she handed the corn cakes and
just as I raised my hand to take one, steaming, moist, yellow and
quite beneath my touch, the plate was suddenly sharply withdrawn, a
spirited revolution of Katinka’s hands ensued, and the cakes
reappeared upon my other side.
“We got the table set longways o’ the room to-night,” she explained
frankly, “and I can’t hardly tell which is left till I look at my ring.”
Conversation with Katinka while she served was, I perceived, a habit
of the house; and indeed Katinka’s accounts of kitchen happenings
were only second in charm to Katinka’s comments upon the table
talk. It was to this informality that I was indebted for chancing on a
radiant mystery on that very night of our arrival.
“Mis’ Grocer Helman,” said Cousin Diantha to me at this first supper
—every woman in Paddington has her husband’s occupation for a
surname—“wants to come to see you about making over her silk.
She’s heard you was from the city an’ she says Mis’ Photographer
Bronson’s used up the only way she—Mis’ Grocer—knew on a
cheap taffeta. Mis’ Grocer Helman won’t copy. She’s got a sinful
pride.”
Katinka set down the bread plate.
“I got some loaf sugar sent up from Helman’s to-day,” she
contributed, “because I just had to get that new delivery wagon up
here to this house somehow. It’d been in front o’ Mis’ Lawyer More’s
twict in one forenoon.”
And at this Miss Waitie, who was always a little hoarse and very
playful, shook her head at Katinka.
“Now, new delivery wagon nothin’,” she said skeptically; “it’s that
curly-headed delivery boy, I’ll be bound.”
So it was in my very first hour in Cousin Diantha’s house that I saw
what those two good souls had never suspected. For at Miss
Waitie’s words Andy, who worked for his board, suddenly flushed
one agonizing red and spilled the preserves on the tablecloth. What
more did any sane woman need on which to base the whole
pleasant matter? Andy was in love with Katinka.
I sat up very straight and refused the fish balls in my preoccupation.
My entire visit to Paddington quickly resolved itself into one
momentous inquiry: Was Katinka in love with Andy?
“Is Katinka in love with Andy?” I put it to Pelleas excitedly, when at
last we were upstairs.
“Katinka? Andy? Andy? Katinka?” responded Pelleas politely.
“Now, one would think you were never in love yourself,” I chided him,
and fell planning what on earth they would live on. Why are so many
little people with nothing at all to live on always in love—when every
one knows spinster after spinster with an income apiece?
I was not long in doubt about Katinka. The very next morning I came
upon her in the hall, her arms filled with kindling for the parlour fire. I
followed her. Her dear, bright little face and yellow braids reminded
me of the kind of doll that they never make any more.
“Katinka,” said I, lingering shamelessly, “do you put the sticks in
across or up and down?”
For it may very well be upon this nice question as well as Angora
cats that Pelleas and I will have our final disagreement, which let no
one suppose that we will really ever have.
She looked up to answer me. The gingham bib of her apron fell
down. And there, pinned to her tight little waist, I beheld—a button-
picture of Andy! Never tell me that there does not abide in the air a
race of little creatures whose sole duty it is to unveil all such secrets
to make glad the gray world. Never tell me that it is such a very gray
world either, if you wish my real opinion.
She looked down and espied the exposed mystery. She cast a
frightened glance at me and I suppose that she saw me, who am a
very foolish old woman, smiling with all my sympathetic might. At all
events she gasped and sat down among the kindling, and said:—
“Oh, ma’am, we’re agoin’ to be marrit to-morrow. An’ Mis’ Bethune—
I’m so scairt to tell ’er.”
I sat down too and caught my breath. This blessed generation. I had
been wondering if these two were in love and on what they could live
when at last they should make up their minds and lo, they were to be
married to-morrow.
“Why, Katinka!” said I; “where?”
The little maid-of-all-work sobbed in her apron.
“I do’ know, ma’am,” she said. “Andy, he’s boardin’ so, an’ I’m a
orphing. I t’ought,” mentioned Katinka, still sobbing, “maybe Mis’
Bethune’d let us stand up by the dinin’-room windy. The hangin’ lamp
there looks some like a weddin’ bell, Andy t’ought.”
The hanging lamp had an orange shade and was done in dragons.
“When I see you an’ him las’ night,” Katinka went on, motioning with
her stubby thumb toward the absent Pelleas, “I t’ought maybe you’d
sign fer seein’ it done. I tol’ Andy so. Mis’ Bethune, I guess she’ll be
rarin’. I wanted it to be in the kitchen, but Andy, he’s so proud. His pa
was in dry goods,” said Katinka, wiping her eyes at the mere
thought.
Here was a most delicious business thrown, as it were, fairly in my
arms. I hailed it with delight, and sat holding my elbows and planning
with all my might.
“Katinka,” said I portentously, “you leave where you are to be
married to me.”
“Oh, ma’am!” said Katinka.
I never had more earnest appreciation.
Cousin Diantha Bethune was heard calling her at that moment, and
Katinka went off with the coals quite as if the next day were not to
see her a bride, married in the parlour.
For I was determined that the wedding should be in the parlour, and I
spent a most feverish day. I made repeated visits to the kitchen and
held consultations with the little maid, whose cheeks grew rosy and
whose eyes grew bright at the heaven of having some one in the
world interested in her.
While she washed the dishes she told me that she and Andy had
saved enough to live for three months at Mis’ Slocum’s boarding
house. After that the future was a pleasant but indefeasible mystery.
While she cleaned the knives I slipped down to find whether Andy
had remembered to engage the parson; and he had done so, but at
the risk of having the ceremony performed in the scullery as the only
available apartment. Andy, it appeared, objected to being married at
the parson’s house; and Katinka seemed to think that this also was
because his father had been “in dry goods.” At our last conference,
during lamp cleaning, I advised Katinka to break the news to Cousin
Diantha Bethune immediately after supper when we were still at
table. Katinka promised and her mouth quivered at the thought.
“She’ll never hev us in the parlour, not in this world, ma’am,” she said
to me hopelessly, “not with that new three-ply ingrain on the floor.”
Meanwhile I had told Pelleas who, though he is sometimes disposed
to pretend to scoff at romance which he does not himself discover,
was yet adequately sympathetic. At supper we were both absurdly
excited, and Pelleas heaped little attentions on Andy who ate nothing
and kept brushing imaginary flies from before his face to show how
much at ease he was. And after the last plate of hot bread had been
brought in I wonder now at my own self-possession; for I knew
thereafter that little Katinka, by the crack in the pantry door, was
waiting the self-imposed signal of Cousin Diantha’s folded napkin.
When this came she popped into the room like a kind of toy and
stood directly back of Cousin Diantha’s chair.
“Please, ma’am,” she said, “Andy an’ me’s goin’ to get marrit.”
Andy, one blush, rose and shambled spryly to her side and caught at
her hand and stood with glazing eyes.
Cousin Diantha wheeled in her chair and her plate danced on the
table. My heart was in my mouth and I confess that I was prepared
for a dudgeon such as only mistresses know when maids have the
temerity to wish to marry. In that moment I found, to my misery, that I
had forgotten every one of my arguments about young love and the
way of the world and the durability of three-ply ingrain carpets, and I
did nothing but sit trembling and fluttering for all the world as if it
were my own wedding at stake. I looked beseechingly at Pelleas,
and he nodded and smiled and rubbed his hands under the
tablecloth—O, I could not have loved a man who would look either
judicious or doubtful as do too many at the very mention of any one’s
marriage but their own.
Dimly I saw Cousin Diantha look over her spectacles; I heard her
amazed “Bless us, Katinka! What are you talking about?” And I half
heard the little maid add “To-morrow” quite without expression as
she turned to leave the room, loyally followed by Andy. And then,
being an old woman and no longer able to mask my desire to
interfere in everything, I was about to have the last word when
Cousin Diantha turned to me and spoke:—
“Listen at that!” she cried; “listen at that! To-morrow—an’ not a scrap
o’ cake in this house! An’ a real good fruit cake had ought to be three
months old at the least. I declare, it don’t seem as if a wedding could
be legal on sponge cake!”
I could hardly believe my ears. Not a word against the parlour, no
mention of the three-ply ingrain nor any protest at all. Cousin
Diantha’s one apprehension was concerning the legality of weddings
not solemnized in the presence of a three-months-old fruit cake. The
mince-pie-and-plum-pudding branch of our family had risen to the
occasion as nobly as if she had been steeped in sentiment.
Upstairs Pelleas and I laughed and well-nigh cried about it.
“And Pelleas,” I told him, “Pelleas, you see it doesn’t matter in the
least whether it’s romance or cooking that’s accountable so long as
your heart is right.”
So it was settled; and I lay long awake that night and planned which
door they should come in and what flowers I could manage and what
I could find for a little present. Here at last, I thought triumphantly as I
was dropping asleep, was a chance to overcome Nichola by the
news that I had actually found another wedding at which to wear my
white lady’s-cloth gown.
With that I sat suddenly erect, fairly startled from my sleep.
What was Katinka to wear?
Alas, I have never been so firmly convinced that I am really seventy
as when I think how I remembered even the parson and yet could
forget Katinka’s wedding gown.
Immediately I roused Pelleas.
“Pelleas!” I cried, “what do you suppose that dear child can be
married in?”
Pelleas awoke with a logical mind.
“In the parlour, I thought,” said he.
“But what will she wear, Pelleas?” I inquired feverishly; “what can
she wear? I don’t suppose the poor child—”
“I thought she looked very well to-night,” he submitted sleepily;
“couldn’t she wear that?” And drifted into dreams.
Wear that! The little tight black frock in which she served. Really, for
a man who is adorable, Pelleas at times can seem stupid enough,
though he never really is stupid.
I lay for a little while looking out the high window at the Paddington
stars which some way seemed unlike town stars. And on a sudden I
smiled back at them, and lay smiling at them for a long time. For little
Katinka was very nearly my size and I knew what she was to wear at
her wedding. My white lady’s-cloth gown.
As soon as her work was done next morning I called her to my room.
It was eleven o’clock and she was to be married at twelve.
“Katinka,” said I solemnly, “what are you going to wear, child, to be
married in?”
She looked down at the tight little black gown.
“I t’ought o’ that,” said the poor little thing uncertainly, “but I haven’t
got nothink nicer than what this is.”
She had thought of that. The tears were in my eyes as I turned to the
cretonne curtain and pulled it aside.
“Look, Katinka,” I said; “you are going to wear this.”
There hung the white lady’s-cloth in all its bravery of chiffon and fichu
and silver buttons. Katinka looked once at that splendour and smiled
patiently, as one who is wonted to everything but surprises.
“La, ma’am,” she humoured me, pretending to appreciate my jest.
When at last she understood, the poor little soul broke down and
cried on the foot of the bed. I know of no sadder sight than the tears
of one to whom they are the only means of self-expression.
Never did gown fit so beautifully. Never was one of so nearly the
proper length. Never was such elegance. When she was quite ready,
the red ring and red bracelet having been added at her request,
Katinka stood on a chair to have a better view in the little mirror
above my washbasin, and she stepped down awe-struck.
“O, ma’am,” she said in a whisper, “I look like I was ready to be laid
out.”
Then she went to the poor, tawdry things of her own which she had
brought to my room, and selected something. It was a shabby plush
book decorated with silk flowers and showing dog-eared gilt leaves.
“I t’ought I’d carry this here,” she said shyly.
I opened the book. And my eye fell on these words written in letters
which looked as if they had been dropped on the page from a sieve:
—

There may be sugar and there may be spice

But you are the one I shall ever call nice.

It was an autograph album.

“Why, Katinka,” I said, “what for?”
“Well,” she explained, “I know in the fashion pictures brides allus
carries books. I ain’t got no other book than what this is. An’ this was
mother’s book—it’s all of hers I’ve got—and I t’ought—”
“Carry it, child,” I said, and little Katinka went down the stairs with the
album for a prayer-book.
And lo! as the door opened my heart was set beating. For there was
music; the reed organ in the parlour was played furiously; and I at
once realized that Pelleas was presiding, performing the one tune
that he knows: The long-meter doxology.
The parlour blinds were open, the geraniums had been brought up
from the cellar to grace the sills, and as crowning symbol of festivity
Cousin Diantha had shaken about the room a handkerchief wet with
cologne. Miss Waitie had contributed the presence of her best dress.
Andy, blushing, waited by the window under the transferred wedding
bell of dragons, pretending to talk with the parson and continually
brushing imaginary flies from before his face. When he saw Katinka
he changed countenance and fairly joined in the amazed “Ah!” of the
others. Indeed the parson began the ceremony with Andy’s honest
eyes still reverently fixed on Katinka’s gown.
There was but one break in the proceedings. Pelleas, at Cousin
Diantha’s urgent request attempting to play softly through the
ceremony, reckoned without one of the keys which stuck fast with a
long, buzzing sound and could not be released though every one
had a hand at it. And finally Katinka herself, who had dusted the
keyboard for so long that she understood it, had to come to the
rescue while the parson waited for her “I will.”
As for me, by the time that it was all over I was crying softly behind
the stove with as much enjoyment as if I had been Katinka’s mother.
And not until I bent my head to hide a tear did I perceive that I had
not changed my gown that morning. As if because one is seventy
that is reason for losing one’s self-respect!
Pelleas put the rest in my head.
“Etarre,” he said, while we were having cherry sauce and seedcakes
after the ceremony, “you’ve got your gray gown, haven’t you?”
“Why, yes,” said I, not understanding.
“And you don’t really need that white one....” He hesitated.
I saw what he meant. We looked across at the little bride,
speechlessly happy in my old woman’s finery.
“Not a bit,” I said, loving Pelleas for his thought.
We smiled at each other with the tidings of a new secret.
That is why, when we reached home three nights later, we permitted
Nichola to unpack our trunk and had no fear. The white lady’s-cloth
gown was not there.
 XI
THE CHRISTENING
The christening of Enid’s baby, delayed until David’s return from
Washington, was to be at our house because Enid and her little son
had already come to us, but we, being past seventy, could not so
easily go up in Connecticut to Enid. At all events that was what they
told us, though Pelleas and I smiled somewhat sadly as we
permitted our age to bear the burden of our indolence. Besides, I
would always be hostess rather than guest, for the hostess seems
essentially creative and the guest pathetically the commodity.
Therefore on a day in May we rose early and found our shabby
drawing-room a kind of temple of hyacinths, and every one in the
room—by whom I mean its permanent inhabitants—rejoicing. The
marble Ariadne, on a pedestal in a dark corner, guided her panther
on a field of jonquils which they two must have preferred to
asphodel; the Lady Hamilton who lived over the low shelves folded
her hands above a very home of Spring; and once, having for a
moment turned away, I could have been certain that the blindfold
Hope above the mantel smote her harp softly, just loud enough, say,
for a daffodil to hear.
“Ah, Pelleas,” I cried, “one would almost say that this is The Day—
you know, the day that one is expecting all one’s life and that never
comes precisely as one planned.”
“Only,” Pelleas supplemented positively, “this is much nicer than that
day.”
“Much,” I agreed, and we both laughed like children waiting to be
christened ourselves.
Pelleas was to be godfather—I said by virtue of his age, but Enid,
whose words said backward I prefer to those of many others in their
proper order, insisted that it was by office of his virtue. There were to
be present only the Chartres’ and the Cleatams, Miss Lillieblade and
Lisa and Hobart Eddy and a handful besides—all our nearest and
dearest and no one else; although, “Ah, me,” cried Madame Sally
Chartres while we waited, “haven’t you invited every one who has
lately invited you to a christening?” And on, so to speak, our positive
negative, she added: “Really, I would have said that in these social
days no one is even asked to a funeral who has not very recently
had a sumptuous funeral of her own.”
“Who was my godfather?” Pelleas asked morosely. “I don’t think I
ever had a godfather. I don’t know that I ever was christened. Have I
any proof that I was named what I was named? I only know it by
hearsay. And how glaringly unscientific.”
“You are only wanting,” cried Madame Polly Cleatam, shaking her
curls, “to be fashionably doubtful!”
“Religions have been thrown away by persons who had no more
authentic doubts,” Pelleas gravely maintained.
“I dare say,” Miss Lillieblade piped. “In these days if a man has an
old coat he puts on a new doubt, and society is satisfied.”
Thereafter the baby arrived, a mere collection of hand embroidery
and lace, with an angel in the midst of these soft billows. The baby
looked quite like a photograph made by the new school, with the
high lights on long sweeping skirts and away up at the top of the
picture a vague, delicious face. Our grandniece Enid is an adorable
little mother, looking no less like a mermaid than does Lisa, but with
a light in her eyes as if still more of the mystery of the sea were
come upon her. And, as a mer-mother should, she had conversation
not exclusively confined to the mer-child. I heard her on the subject
of prints with the bishop’s lady, and the mer-child was not three
months old.
The christening was to have been at eleven o’clock, and at twelve
Pelleas had an appointment which it was impossible to delay, or so
he thought, having a most masculine regard for hours, facts, and the
like. Therefore when, at fifteen after eleven, the bishop had not yet
arrived, Pelleas began uneasily suggesting taking leave. Enid looked
at him with a kind of deep-sea-cave reproach before which every
one else would have been helpless; but Pelleas, whose nature is
built on straight lines, patted her and kissed the baby at large upon
the chest and, benign, was still inexorable.
“But who will be godfather?” Enid cried disconsolately, and, young-
wife-like, looked reproachfully at her young husband.
At that moment the hall door, as if it had been an attentive listener as
long as it could and must now give the true answer, opened and
admitted Hobart Eddy, come late to the christening and arrived with
that vague air of asking why he was where he was which lent to him
all the charm of ennui without its bad taste.
“Hobart,” Enid cried ecstatically, “you shall be godfather!”
Hobart Eddy continued to bend to kiss my hand and then sought the
hand of Madame Sally and next the hand of Madame Polly Cleatam.
Finally he bowed before Enid and fixed his monocle on the baby.
“It opens and shuts its eyes,” he earnestly observed; “how these
baby people imitate the doll factories. It’s disgraceful.”
“Kiss him!” the mer-mother commanded, as if she were the prompter.
Hobart Eddy obediently kissed the baby’s thumb.
“Man and brother,” he greeted him solemnly; “Lord, to think I’ll take it
to luncheon sometime and hear it know more about the town than I
do.”
“At all events,” Madame Sally Chartres begged gravely, “don’t ask
him to lunch until he’s been christened. In Society you have to have
a name.”
“But,” Enid settled it with pretty peremptoriness, “you must be
godfather even if he never lunches. Hobart—you will?”
“Its godfather?” said Hobart Eddy. “I? But yes, with all pleasure.
What do I have to do? Is there more than one figure?”
When at length the arrival of the bishop followed close on the
departure of Pelleas, regretful but absurdly firm, we were in a merry
clamour of instruction. The situation had caught our fancy and this
was no great marvel. For assuredly Hobart Eddy was not the typical
godfather.
“On my honour,” he said, “I never was even ‘among those’ at a
christening, in my life, and I would go a great distance to be
godfather. It’s about the only ambition I’ve never had and lost.”
The service of the christening holds for me a poignant solemnity.
And because this was Enid’s baby and because I remembered that
hour in which he had seemed to be Pelleas’ dream and mine come
back, my heart was overflowingly full. But I missed Pelleas absurdly,
for this was one of the hours in which we listen best together; and to
have learned to listen with some one brings, in that other’s absence,
a silence. But it was a happy hour, for the sun streamed gayly across
the window-boxes, there were the dear faces of our friends, the mer-
mother and her young husband were near to joyful tears and the
bishop’s voice was like an organ chord in finer, fluttering melody.
Through the saying of prayer and collects I stood with uplifting heart;
and then Enid’s husband gave the baby’s name with a boyish
tremble in his voice; and after the baptism and its formalities the
bishop read the words that were the heart of the whole matter; and
the heart of a matter does not always beat in the moment’s uplift.
“‘And thou, Child,’ the bishop read, ‘shalt be called the prophet of the
Highest; for thou shalt go before the face of the Lord to prepare His
ways.
“‘Through the tender mercy of our Lord, whereby the day spring from
on high hath visited us.
“‘To give light to them that sit in darkness and in the shadow of
death, to guide our feet into the way of peace.’”
As he read a hush fell upon us. It seemed suddenly as if our
conventional impulse to see Enid’s baby christened was an affair of
more radiant import than we had meant. From the words of
exhortation that followed I was roused by a touching of garments,
and I looked up to see a trim, embroidered maid holding the baby
toward Hobart Eddy. The moment for his service as godfather was
come. As he held out his arms he questioned Enid briefly with his
eyes, and then earnestly gave himself to establishing the little man
and brother in a curve of elbow. It was after all, I suppose him to
have been reflecting, as sternly required of a man that he be an
efficient godfather as that he perfectly fill all the other offices of a
man of the world. I even suspected him of a downward glance to be
assured that the soft skirts were gracefully in place, quite as if he
were arranging tableaux vivants. Thereafter he stood erect, with his
complaisant passivity of look, as perfectly the social automaton as if
the baby were a cup of tea. Really, to accept dear Hobart Eddy as
godfather was rather like filling a champagne glass with cream.
“What shall be the name of this child?” once more demanded the
bishop.
“Philip Wentworth,” prompted the young father a second time,
presenting a serious, young-father profile to the world.
The bishop waited.
“Philip Wentworth,” obediently repeated Hobart Eddy with, I dare be
sworn, the little deferential stooping of the shoulders with which I had
seen him return many and many a fan.
The bishop, his face filled with that shining which even in gravity
seemed sweeter than the smile of another, fixed his deep eyes upon
the godfather, and when he spoke it was as if he were saying the
words for the first time, to the guardian of the first child:—
“‘Dost thou, in the name of this Child, renounce ... the vain pomp and
glory of this world, with all covetous desires of the same, and the
sinful desires of the flesh, so that thou wilt not follow nor be led by
them?’”
Hobart, his eyes fixed on the open prayer-book which he held, read
the response quickly and clearly:
“‘I renounce them all, and by God’s help I will endeavour not to follow
or be led by them.’”
“‘Wilt thou, then,’” pursued the bishop benignly, “‘obediently keep
God’s holy will and commandments and walk in the same all the
days of thy life?’”
“‘I will,’” said Hobart Eddy, “‘by God’s help.’”
There was no slightest hesitation, no thought, or so it seemed to me;
only the old urbane readiness to say what was required of him. What
had he said, what had he done, this young lion of the social moment,
beau, gallant, dilettante, and was it possible that he did not
understand what he had promised? Or was I a stupid and exacting
old woman taking with convulsive literalness that which all the world
perhaps recognizes as a form of promise for the mere civilized
upbringing of a child? I tried to remember other godfathers and I
could remember only those who, like Pelleas, had indeed served, as
Enid had said in jest, by office of their virtue. And yet Hobart Eddy—
after all I told myself he was a fine, upright young fellow who paid his
debts, kept his engagements, whose name was untouched by a
breath of scandal, who lived clear of gossip; so I went through the
world’s dreary catalogue of the primal virtues. But what had these to
do with that solemn “I renounce them all”?
By the time that the service was well over I could have found it in my
heart to proclaim to our guests that, as the world construed it, a
christening seemed to me hardly more vital than the breakfast which
would follow.
This however I forbore; and at the end every one pressed forward in
quite the conventional way and besieged the baby and Hobart and
showered congratulations upon them both and kissed Enid and was
as merry as possible. And as for Hobart, he stood in their midst,
bowing a little this way and that, giving his graceful flatteries as
another man gives the commonplaces, complaisant, urbane, heavy-
lidded....
I omitted the baby and looked straight at the godfather.
“How do you like the office?” I asked somewhat dryly.
He met my eyes with his level look.
“Dear friend,” he said softly, “you see how inefficient I am. Even to
describe your charming christening toilet is my despair.”
“Hobart Eddy,” said I sharply, “take Enid in to breakfast.”
While May was still stepping about the fields loath to leave her
business of violets and ladywort, Madame Sally Chartres sent
pleasant word from Long Island that a dozen or more of her friends
were to spend a day with her, and no one would willingly disregard
the summons. The Chartres’ lived on the edge of an orchard and
another edge of field. I dare say they lived in a house although what I
chiefly remember is a colonnade of white pillars, a library shelved to
the ceiling, and a sprinkling of mighty cushioned window seats
whereon the sun forever streamed through lattices. Perhaps
Madame Sally and Wilfred had assembled these things near an
orchard and considered that to be house enough. At all events there
could have been no fairer place for a Spring holiday.
Pelleas and I went down by train, and the morning was so golden
that I wholly expected to divine a procession of nymphs defiling
faintly across the fields in a cloud of blossoms rooted in air. I have
often wondered why goblins, dryads and the like do not more
frequently appear to folk on railway trains. These shy ones would be
quite safe, for by the time the bell rope should have been pulled and
the conductor told why the train must be stopped and the engine and
cars brought effectually to a standstill, the little shadowy things could
have vanished safely against the blue. Perhaps they do not
understand how sadly long it takes a spirit to influence the wheels of
civilization.
The others coached down to the Chartres’ with Hobart Eddy,
although there must be made one important exception: Madame
Sally had insisted that Enid bring the baby; and Enid and her
husband, who since the christening were lingering on in town, had
given the baby and his new nurse to the charge of Pelleas and me.
We arrived ahead of the coach and stood on the veranda to
welcome the others.
Lisa was among these, with Eric at her side; and Madame Polly and
Horace Cleatam and Miss Lillieblade, all three in spite of their white
hair and anxiety about draughts stoutly refusing to ride inside. There
were four or five others, and from the box seat beside Hobart Eddy I
saw descending with what I am bound to call picturesque
deliberation a figure whom I did not remember.
“Pray who is that?” there was time for me to ask Madame Sally.
“My dear,” she answered hurriedly, “she is a Mrs. Trempleau. I used
to love her mother. And Hobart wanted her here.”
“Hobart!” I exclaimed. “That Mrs. Trempleau?” I comprehended. “You
don’t think ...” I intimated.
Madame Sally’s eyebrows were more expressive than the eyes of
many.
“Who knows?” she said only, and made of her eyebrows a positive
welcome to our friends.
Mrs. Trempleau came toward us flickering prettily—I protest that she
reminded me of a thin flame, luminous, agile, seeking. She had hair
like the lights in agate, and for its sake her gown and hat were of
something coloured like the reflection of the sun in a shield of
copper. She had a fashion of threading her way through an hour of
talk, lighting a jest here, burning a bit of irony there, smouldering
dangerously near the line of daring. And that day as she moved from
group to group on the veranda the eyes of us all, of whom Hobart
Eddy was chief, were following her. I think it may have been because
her soul was of some alien element like the intense, avid spirit of the
flames, though when I told Pelleas he argued that it was merely the
way she lifted her eyes.
“Where is Mr. Trempleau?” Pelleas added, his nature as I have said
being built on straight lines.
“There may be one,” I answered, “but I think he lives on some other
continent.”
Pelleas reflected.
“Hobart Eddy and Pelham and Clox look in love with her,” he said; “if
she doesn’t take care there won’t be enough continents.”
In no small amusement during luncheon we watched Hobart Eddy,
especially Pelleas and I who, however, besides being amused, were
also a little sad. Mrs. Trempleau’s appropriation of him was insistent
but very pretty. Indeed, if she had on a night of stars appropriated
Sirius I dare say the constellations would have sung approval. She
had the usual gift of attractive faults. But above Mrs. Trempleau’s
shoulders and beyond the brightness of her hair I had, at luncheon,
glimpses which effectually besought my attention from the drama
within. The long windows overlooked the May orchards, white and
sweet and made like youth, and I was impatient to be free of the
woman’s little darting laughs and away to the fields. Some way, in
her presence it was not like May.
Therefore, when Pelleas had been borne to the stables by his host
and when the others had wandered back to the veranda, I went
away down what I think must have been a corridor, though all that I
remember is a long open window leading to the Spring, as if one
were to unlatch an airy door and reveal a diviner prospect than our
air infolds. A lawn, cut by a gravel walk bounded by tulips, sloped
away from this window to the orchard and I crossed the green in the
frank hope that the others would not seek me out. But when I turned
the corner by the dial I came fairly on two other wanderers. There,
with the white-embroidered nurse-maid, sat, like another way of
expressing the Spring, Enid’s baby. Was ever such happy chance
befallen at the gate of any May orchard whatever?
“Ah,” I cried to the little nurse, “Bonnie! Come quickly. I see a place—
there—or there—or there—where you must bring the baby at once—
at once! Leave the perambulator here—so. He is awake? Then
quickly—this way—to the pink crab apple-tree.”
I sometimes believe that in certain happy case I find every one
beautiful; but I recall that Bonnie—of whom I shall have more to tell
hereafter—that day seemed to me so charming that I suspected her
of being Persephone, with an inherited trick of caring for the baby as
her mother cared for Demophoön.
To the pink crab apple-tree! What a destination. It had for me all the
delight of running toward, say, the plane tree in the meadow of
Buyukdere. I remember old branches looking like the arms of Pan,
wreath-wound, and rooms of sun through which petals drifted ... who
could distinctly recall the raiment of such an hour? But at length by
many aisles we came to a little hollow where the grass was
greenest, hard by the orchard arbour, and we stood before the giant
pink crab apple-tree. Has any one ever wondered that Sicilian
courtiers went out a-shepherding and that the Round Table, warned
to green gowns, fared forth a-Maying?
“Spread the baby’s rug!” I cried to Bonnie; “here is a little seat made
in the roots for this very day. Pull him a branch of apple blossoms—
so. And now run away, child, and amuse yourself. The baby and I
are going to make an apple-blossom pie.”
Bonnie, hesitating, at my more peremptory bidding went away. I
have no idea whether she was caught up among the branches by
friendly hands or whether the nearest tree trunk hospitably opened to
receive her. But there, in May, with the world gone off in another
direction, the baby and I sat alone.
“O—o-o-o-o—” said the baby, in a kind of lyric understanding of the
situation.
I held him close. These hours of Arcady are hard to win for the
sheltering of dreams.

Voices, sounding beyond a momentary rain of petals, roused me.

Enid’s baby smiled up in my eyes but I saw no one, though the
voices murmured on as if the dryads had forgotten me and were idly
speaking from tree to tree. Then I caught from the orchard arbour
Mrs. Trempleau’s darting laugh. It was as if some one had kindled
among the apple blossoms a torch of perfumed wood.
“I am sailing on Wednesday,” I heard her saying in a voice abruptly
brought to sadness. “Ah, my friend, if I might believe you. Would
there indeed be happiness for you there with me, counting the cost?”
It was of course Hobart Eddy who answered quite, I will be bound,
as I would have said that Hobart Eddy would speak of love: with fine
deliberation, as another man would speak the commonplaces,
possibly with his little half bow over the lady’s hand, a very courtier of
Love’s plaisance.
She replied with that perpetual little snare of her laughter laid like a
spider web from one situation to the next.
“Come with me then,” she challenged him; “let us find this land
where it is always Spring.”
“Do you mean it?” asked Hobart Eddy.
I do not know what she may have said to this, for the new note in his
voice terrified me. Neither do I know what his next words were, but
their deliberation had vanished and in its stead had come something,
a pulse, a tremor....
I remember thinking that I must do something, that it was impossible
that I should not do anything. I looked helplessly about the great
empty orchard with its mock-sentinel trees, and down into Enid’s
baby’s eyes. And on a sudden I caught him in my arms and lifted him
high until his head was within the sweetness of the lowest boughs.
He did what any baby in the world would have done in that
circumstance; he laughed aloud with a little coo and crow at the end
so that anybody in that part of the orchard, for example, must have
heard him with delight.
The two in the orchard arbour did hear. Mrs. Trempleau leaned from
the window.
“Ah,” she cried, in her pretty soaring emphasis, “what a picture!”
“Is he not?” I answered, and held the baby high. On which she said
some supreme nonsense about Elizabeth and the little John and
“Hobart—see!” she cried.
The two came out of the arbour, and Mrs. Trempleau made little
dabs at the baby and then went picturesquely about filling her arms
with blossoms. Hobart Eddy threw himself on the grass beside me
and watched her. I looked at them all: at the woman who was like
thin flame, at the man who watched her, indolent, confident, plainly
allured, and at Enid’s baby. And,
“There,” said I, abruptly to the baby, “is your godfather.”