774 research outputs found
Wireless Moisture Sensor Using a Microstrip Antenna
A wireless moisture sensor has been developed on the basis of the backscatter characteristic of the microstrip antenna, which works in the far field without a battery. This study aims to develop a wireless sensor with a long communication distance and to apply the wireless applications, such as monitoring the moisture in the wrapped products and surface adsorption of hydrogen peroxide in the biological isolation systems. The dropwise addition of the distilled water on the cleaning tissue is clearly detected by the measurement of the backscattered power from the sensor at the frequencies of 0.954 GHz and 2.45 GHz. The ratio of the backscattered power in two frequency bands can be used as an index to measure moisture
Development of impedance spectroscopy based in-situ, self-calibrating, on-board wireless sensor with inbuilt metamaterial inspired small antenna for constituent detection in multi-phase mixtures like soil
Real time and accurate measurement of sub-surface soil moisture and nutrients is critical for agricultural and environmental studies. This work presents a novel on-board solution for a robust, accurate and self-calibrating soil moisture and nutrient sensor with inbuilt wireless transmission and reception capability that makes it ideally suited to act as a node in a network spread over a large area. The sensor works on the principle of soil impedance measurement by comparing the amplitude and phase of signals incident on and reflected from the soil in proximity of the sensor. The permittivity of the soil dielectric mixture which is calculated from these impedance measurements is used as input parameter to the dielectric mixing models which are used to estimate the ionic concentration in soil. The inbuilt wireless transceiver system is connected to a specially designed metamaterial inspired small antenna in order to reduce the sensor size while keeping the path losses to a minimum by using a low frequency. This composite right-left handed (CRLH) antenna for wireless transmission at 433 MHz doubles up as an underground, sensing element (external capacitor) and integrates with the on-board sensor for soil moisture and nutrient determination. The input impedance of the CRLH sensor, surrounded by the soil containing moisture and nutrient and other ions, is measured at multiple frequencies. It is shown that the change in moisture and ioinic-concentration can be successfully detected using the sensor. The inbuilt self-calibrating mechanism makes the sensor reliable at different environmental conditions and also useful for remote, underground and hand-held applications. A multi-power mode transceiver system has been designed to
support the implementation of an energy efficient medium-access-control
Microwave antennas for infrastructure health monitoring
Infrastructure health monitoring (IHM) is a technology that has been developed for the detection and evaluation of changes that affect the performance of built infrastructure systems such as bridges and buildings. One of the employed methods for IHM is wireless sensors method which is based on sensors embedded in concrete or mounted on surface of structure during or after the construction to collect and report valuable monitoring data such as temperature, displacement, pressure, strain and moisture content, and information about defects such as cracks, voids, honeycombs, impact damages and delamination. The data and information can then be used to access the health of a structure during and/or after construction. Wireless embedded sensor technique is also a promising solution for decreasing the high installation and maintenance cost of the conventional wire based monitoring systems. However, several issues should be resolved at research and development stage in order to apply them widely in practice. One of these issues is that wireless sensors cannot operate for a long time due to limited lifetime of batteries. Once the sensors are embedded within a structure, they may not be easily accessible physically without damaging the structure.
The main aim of this research is to develop effective antennas for IHM applications such as detection of defects such as gaps representing cracks and delaminations, and wireless powering of embeddable sensors or recharging their batteries. For this purpose, modelling of antennas based on conventional antipodal Vivaldi antennas (CAVA) and parametric studies are performed using a computational tool CST Studio (Studio 2015) including CST Microwave Studio and CST Design Studio, and experimental measurements are conducted using a performance network analyser. Firstly, modified antipodal Vivaldi antenna (MAVA) at frequency range of 0.65 GHz – 6 GHz is designed and applied for numerical and experimental investigations of the reflection and transmission properties of concrete-based samples possessing air gap or rebars. The results of gap detection demonstrate ability of the developed MAVA for detection of air gaps and delivery of power to embeddable antennas and sensors placed at any depth inside 350-mm thick concrete samples. The investigation into the influence of rebars show that the rebar cell can act as a shield for microwaves if mesh period parameter is less than the electrical half wavelength. At higher frequencies of the frequency range, microwaves can penetrate through the reinforced concrete samples. These results are used for the investigating the transmission of microwaves at the single frequency of 2.45 GHz between the MAVA and a microstrip patch antenna embedded inside reinforced concrete samples at the location of the rebar cell. It is shown that -15 dB coupling between the antennas can be achieved for the samples with rebar cell parameters used in practice. Secondly, a relatively small and high-gain resonant antipodal Vivaldi antenna (RAVA) as a transmitting antenna and modified microstrip patch antenna as an embeddable receiving antenna are designed to operate at 2.45 GHz for powering the sensors or recharging their batteries embedded in reinforced concrete members. These members included reinforced dry and saturated concrete slabs and columns with different values of mesh period of rebars and steel ratio, respectively. Parametric study on the most critical parameters, which affect electromagnetic (EM) wave propagation in these members, is performed. It is shown that there is a critical value of mesh period of rebars with respect to reflection and transmission properties of the slabs, which is related to a half wavelength in concrete. The maximum coupling between antennas can be achieved at this value. The investigation into reinforced concrete columns demonstrates that polarisation configuration of the two-antenna setup with respect to rebars and steel ratios as well as losses in concrete are important parameters. It is observed that the coupling between the antennas reduces faster by increasing the value of steel ratio in parallel than in vertical configuration due to the increase of the interaction between electromagnetic waves and the rebars. This effect is more pronounced in the saturated than in dry reinforced concrete columns.
Finally, a relatively high gain 4-element RAVA array with a Wilkinson power divider, feeding network and an embeddable rectenna consisting of the microstrip patch antenna and a rectified circuit are developed. Two wireless power transmission systems, one with a single RAVA and another with the RAVA array, are designed for recharging batteries of sensors embedded inside reinforced concrete slabs and columns with different configurations and moisture content. Comparison between these systems shows that the DC output voltage for recharging commonly used batteries can be provided by the systems with the single RAVA and the system with the RAVA array at the distance between the transmitting antenna and the surface of reinforced concrete members of 0.12 m and 0.6 m, respectively, i.e. the distance achieved when the array is 5 times longer that the distance achieved with a single antenna
Antenna integration for wireless and sensing applications
As integrated circuits become smaller in size, antenna design has become the size limiting factor for RF front ends. The size reduction of an antenna is limited due to tradeoffs between its size and its performance. Thus, combining antenna designs with other system components can reutilize parts of the system and significantly reduce its overall size. The biggest challenge is in minimizing the interference between the antenna and other components so that the radiation performance is not compromised. This is especially true for antenna arrays where the radiation pattern is important.
Antenna size reduction is also desired for wireless sensors where the devices need to be unnoticeable to the subjects being monitored. In addition to reducing the interference between components, the environmental effect on the antenna needs to be considered based on sensors' deployment.
This dissertation focuses on solving the two challenges: 1) designing compact multi-frequency arrays that maintain directive radiation across their operating bands and 2) developing integrated antennas for sensors that are protected against hazardous environmental conditions.
The first part of the dissertation addresses various multi-frequency directive antennas arrays that can be used for base stations, aerospace/satellite applications. A cognitive radio base station antenna that maintains a consistent radiation pattern across the operating frequencies is introduced. This is followed by multi-frequency phased array designs that emphasize light-weight and compactness for aerospace applications. The size and weight of the antenna element is reduced by using paper-based electronics and internal cavity structures.
The second part of the dissertation addresses antenna designs for sensor systems such as wireless sensor networks and RFID-based sensors. Solar cell integrated antennas for wireless sensor nodes are introduced to overcome the mechanical weakness posed by conventional monopole designs. This can significantly improve the sturdiness of the sensor from environmental hazards. The dissertation also introduces RFID-based strain sensors as a low-cost solution to massive sensor deployments. With an antenna acting as both the sensing device as well as the communication medium, the cost of an RFID sensor is dramatically reduced. Sensors' strain sensitivities are measured and theoretically derived. Their environmental sensitivities are also investigated to calibrate them for real world applications.Ph.D.Committee Chair: Tentzeris, Emmanouil; Committee Member: Akyildiz, Ian; Committee Member: Allen, Mark; Committee Member: Naishadham, Krishna; Committee Member: Peterson, Andrew; Committee Member: Wang, Yan
Wireless Power Transmission to a Buried Sensor in Concrete
The feasibility of sending wireless power to a buried sensor antenna within concrete was studied. a receive patch rectenna with 75.8% conversion efficiency was designed for operation at 5.7 GHz. The received DC power at the rectenna was measured within dry and wet concrete samples with various cover thicknesses and air-gaps. For the rectenna buried within 30 mm of the concrete, the received DC power was 10.37 mW, which was, about 70% of the received DC power in free-space
Evaluation of antenna design and energy harvesting system of passive tag in UHF RFID applications
Backscattering communication-based Radio Frequency Identification (RFID) has been essential to the rapid advancement of IoT devices. However, most RFID applications only utilize relatively simple antenna designs. This work contributes in two ways: we investigate the impact of different antenna configurations on a passive network using backscattering technology. In addition, we evaluate the designs of power harvesting technologies valid for Ultra-High-Frequency (UHF) RFID applications. Our evaluations demonstrate that tailored antenna designs can more efficiently achieve application requirements when compared to a simple universal antenna. In addition, we give recommendations on energy harvesters for applications operating in different scenarios
Wideband and UWB antennas for wireless applications. A comprehensive review
A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems
Development of Textile Antennas for Energy Harvesting
The current socio-economic developments and lifestyle trends indicate an increasing
consumption of technological products and processes, powered by emergent concepts, such as
Internet of Things (IoT) and smart environments, where everything is connected in a single
network. For this reason, wearable technology has been addressed to make the person, mainly
through his clothes, able to communicate with and be part of this technological network.
Wireless communication systems are made up of several electronic components, which over
the years have been miniaturized and made more flexible, such as batteries, sensors, actuators,
data processing units, interconnectors and antennas. Turning these systems into wearable
systems is a demanding research subject. Specifically, the development of wearable antennas
has been challenging, because they are conventionally built on rigid substrates, hindering their
integration into the garment. That is why, considering the flexibility and the dielectric
properties of textile materials, making antennas in textile materials will allow expanding the
interaction of the user with some electronic devices, by interacting through the clothes. The
electronic devices may thus become less invasive and more discrete.
Textile antennas combine the traditional textile materials with new technologies. They emerge
as a potential interface of the human-technology-environment relationship. They are becoming
an active part in the wireless communication systems, aiming applications such as tracking and
navigation, mobile computing, health monitoring and others. Moreover, wearable antennas
have to be thin, lightweight, of easy maintenance, robust, and of low cost for mass production
and commercialization.
In this way, planar antennas, the microstrip patch type, have been proposed for garment
applications, because this type of antenna presents all these characteristics, and are also
adaptable to any surface. Such antennas are usually formed by assembling conductive (patch
and ground plane) and dielectric (substrate) layers. Furthermore, the microstrip patch
antennas, radiate perpendicularly to a ground plane, which shields the antenna radiation,
ensuring that the human body is exposed only to a very small fraction of the radiation.
To develop this type of antenna, the knowledge of the properties of textile materials is crucial
as well as the knowledge of the manufacturing techniques for connecting the layers with glue,
seam, adhesive sheets and others. Several properties of the materials influence the behaviour
of the antenna. For instance, the bandwidth and the efficiency of a planar antenna are mainly
determined by the permittivity and the thickness of the substrate. The use of textiles in
wearable antennas requires thus the characterization of their properties. Specific electrical
conductive textiles are available on the market and have been successfully used. Ordinary
textile fabrics have been used as substrates. In general, textiles present a very low dielectric constant, εr, that reduces the surface wave
losses and increases the impedance bandwidth of the antenna. However, textile materials are
constantly exchanging water molecules with the surroundings, which affects their
electromagnetic properties. In addition, textile fabrics are porous, anisotropic and
compressible materials whose thickness and density might change with low pressures.
Therefore, it is important to know how these characteristics influence the behaviour of the
antenna in order to minimize unwanted effects.
To explain some influences of the textile material on the performance of the wearable
antennas, this PhD Thesis starts presenting a survey of the key points for the design and
development of textile antennas, from the choice of the textile materials to the framing of the
antenna. An analysis of the textile materials that have been used is also presented. Further,
manufacturing techniques of the textile antennas are described.
The accurate characterization of textile materials to use as a dielectric substrate in wearable
systems is fundamental. However, little information can be found on the electromagnetic
properties of the regular textiles. Woven, knits and nonwovens are inhomogeneous, highly
porous, compressible and easily influenced by the environmental hygrometric conditions,
making their electromagnetic characterization difficult. Despite there are no standard
methods, several authors have been adapting techniques for the dielectric characterization of
textiles. This PhD Thesis focuses on the dielectric characterization of the textile materials,
surveying the resonant and non-resonant methods that have been proposed to characterize the
textile and leather materials. Also, this PhD Thesis summarizes the characterization of textile
materials made through these methods, which were validated by testing antennas that
performed well.
Further a Resonant-Based Experimental Technique is presented. This new method is based on
the theory of resonance-perturbation, extracting the permittivity and loss tangent values based
on the shifts caused by the introduction of a superstrate on the patch of a microstrip antenna.
The results obtained using this method have shown that when positioning the roughest face of
the material under test (MUT) in contact with the resonator board, the extracted dielectric
constant value is lower than the one extracted with this face positioned upside-down. Based
on this observation, superficial properties of textiles were investigated and their influence on
the performance of antennas was analysed.
Thus, this PhD Thesis relates the results of the dielectric characterization to some structural
parameters of textiles, such as surface roughness, superficial and bulk porosities. The results
show that both roughness and superficial porosity of the samples influence the measurements,
through the positioning of the probes. Further, the influence of the positioning of the dielectric
material on the performance of textile microstrip antennas was analysed. For this, twelve
prototypes of microstrip patch antennas were developed and tested. The results show that,
despite the differences obtained on the characterization when placing the face or reverse-sides of the MUT in contact with the resonator board, the obtained average result of εr is well suited
to design antennas ensuring a good performance.
According to the European Commission Report in 2009, “Internet of Things — An action plan for
Europe”, in the next years, the IoT will be able to improve the quality of life, especially in the
health monitoring field. In the Wireless Body Sensor Network (WBSN) context, the integration
of textile antennas for energy harvesting into smart clothing is a particularly interesting
solution for a continuous wirelessly feed of the devices. Indeed, in the context of wearable
devices the replacement of batteries is not easy to practice. A specific goal of this PhD Thesis
is thus to describe the concept of the energy harvesting and then presents a survey of textile
antennas for RF energy harvesting. Further, a dual-band printed monopole textile antenna for
electromagnetic energy harvesting, operating at GSM 900 and DCS 1800 bands, is also proposed.
The antenna aims to harvest energy to feed sensor nodes of a wearable health monitoring
system. The gains of the antenna are around 1.8 dBi and 2.06 dBi allied with a radiation
efficiency of 82% and 77.6% for the lowest and highest frequency bands, respectively.
To understand and improve the performance of the proposed printed monopole textile antenna,
several manufacturing techniques are tested through preliminary tests, to identify promising
techniques and to discard inefficient ones, such as the gluing technique. Then, the influence
of several parameters of the manufacturing techniques on the performance of the antenna are
analysed, such as the use of steam during lamination, the type of adhesive sheet, the
orientation of the conductive elements and others. For this, seven prototypes of the printed
monopole textile antenna were manufactured by laminating and embroidering techniques.
The measurement of the electrical surface resistance, Rs, has shown that the presence of the
adhesive sheet used on the laminating process may reduce the conductivity of the conductive
materials. Despite that, when measuring the return loss of printed monopole antennas
produced by lamination, the results show the antennas have a good performance. The results
also show that the orientation of the conductive fabric does not influence the performance of
the antennas. However, when testing embroidered antennas, the results show that the
direction and number of the stitches in the embroidery may influence the performance of the
antenna and should thus be considered during manufacturing.
The textile antennas perform well and their results support and give rise to the new concept
of a continuous substrate to improve the integration of textile antennas into clothing, in a more
comfortable and pleasure way. A demonstrating prototype, the E-Caption: Smart and
Sustainable Coat, is thus presented. In this prototype of smart coat, the printed antenna is fully
integrated, as its dielectric is the textile material composing the coat itself. The E-Caption
illustrates the innovative concept of textile antennas that can be manipulated as simple
emblems. The results obtained testing the antenna before and after its integration into cloth,
show that the integration does not affect the behaviour of the antenna. Even on the presence
of the human body the antenna is able to cover the proposed resonance frequencies (GSM 900
and DCS 1800 bands) with the radiation pattern still being omnidirectional. At last, the exponential growth in the wearable market boost the industrialization process of
manufacturing textile antennas. As this research shows, the patch of the antennas can be easily
and efficiently cut, embroidered or screen printed by industrial machines. However, the
conception of a good industrial substrate that meets all the mechanical and electromagnetic
requirements of textile antennas is still a challenge. Following the continuous substrate
concept presented and demonstrated through the E-Caption, a new concept is proposed: the
continuous Substrate Integrating the Ground Plane (SIGP). The SIGP is a novel textile material
that integrates the dielectric substrate and the conductive ground plane in a single material,
eliminating one laminating process. Three SIGP, that are weft knitted spacer fabrics having one
conductive face, were developed in partnership with the Borgstena Textile Portugal Lda,
creating synergy between research in the academy and industry. The results of testing the
performance of the SIGP materials show that the integration of the ground plane on the
substrate changes the dielectric constant of the material, as a consequence of varying the
thickness. Despite this, after the accurate dielectric and electrical characterization, the SIGP
I material has shown a good performance as dielectric substrate of a microstrip patch antenna
for RF energy harvesting. This result is very promising for boosting the industrial fabrication of
microstrip patch textile antennas and their mass production and dissemination into the IoT
network, guiding future developments of smart clothing and wearables.Os atuais desenvolvimentos socioeconómicos e tendências de estilo de vida apontam para um
crescimento do consumo de produtos e processos tecnológicos, impulsionado por conceitos
emergentes como a Internet das Coisas, onde tudo tudo está conectado em uma única rede.
Por esta razão, as tecnologias usáveis (wearable) estão a afirmar-se propondo soluções que
tornam o utilizador possivelmente através das suas roupas, capaz de comunicar com e fazer
parte desta rede.
Os sistemas de comunicações sem fios são constituídos por diversos componentes eletrónicos,
que com o passar dos anos foram sendo miniaturizados e fabricados em materiais flexíveis, tais
como as baterias, os sensores, as unidades de processamento de dados, as interconexões e as
antenas. Tornar os sistemas de comunicações sem fios em sistemas usáveis requer trabalho de
investigação exigente. Nomeadamente, o desenvolvimento de antenas usáveis tem sido um
desafio, devido às antenas serem tradicionalmente desenvolvidas em substratos rígidos, que
dificultam a sua integração no vestuário. Dessa forma, considerando a flexibilidade e as
propriedades dielétricas dos materiais têxteis, as antenas têxteis trazem a promessa de
permitir a interacção dos utilizadores com os dispositivos eletrónicos através da roupa,
tornando os dispositivos menos invasivos e mais discretos.
As antenas têxteis combinam os materiais têxteis tradicionais com novas tecnologias e emergem
assim como uma potencial interface de fronteira entre seres humanos-tecnologias-ambientes.
Expandindo assim a interação entre o utilizador e os dispositivos eletrónicos ao recurso do
vestuário. Assim, através das antenas têxteis, o vestuário torna-se uma parte ativa nos sistemas
de comunicação sem fios, visando aplicações como rastreamento e navegação, computação
móvel, monitorização de saúde, entre outros. Para isto, as antenas para vestir devem ser finas,
leves, de fácil manutenção, robustas e de baixo custo para produção em massa e
comercialização.
Desta forma, as antenas planares do tipo patch microstrip têm sido propostas para aplicações
em vestuário, pois apresentam todas estas características e também são adaptáveis a qualquer
superfície. Estas antenas são geralmente formadas pela sobreposição de camadas condutoras
(elemento radiante e plano de massa) e dielétricas (substrato). Além disso, as antenas patch
microstrip irradiam perpendicularmente ao plano de massa, que bloqueia a radiação da antena,
garantindo que o corpo humano é exposto apenas a uma fração muito pequena da radiação.
Para desenvolver este tipo de antena, é crucial conhecer as propriedades dos materiais têxteis,
bem como as técnicas de fabricação para conectar as camadas, com cola, costuras, folhas
adesivas, entre outros. Diversas propriedades dos materiais influenciam o comportamento da
antena. Por exemplo, a permitividade e a espessura do substrato determinam a largura de banda e a eficiência de uma antena planar. O uso de têxteis em antenas usáveis requer assim
uma caracterização precisa das suas propriedades. Os têxteis condutores elétricos são materiais
específicos que estão disponíveis comercialmente em diversas formas e têm sido utilizados com
sucesso para fabricar o elemento radiante e o plano de massa das antenas. Para fabricar o
substrato dielétrico têm sido utilizados materiais têxteis convencionais.
Geralmente, os materiais têxteis apresentam uma constante dielétrica (εr) muito baixa, o que
reduz as perdas de ondas superficiais e aumenta a largura de banda da antena. No entanto, os
materiais têxteis estão constantemente a trocar moléculas de água com o ambiente em que
estão inseridos, o que afeta as suas propriedades eletromagnéticas. Além disso, os tecidos e os
outros materiais têxteis planares são materiais porosos, anisotrópicos e compressíveis, cuja
espessura e densidade variam sob muito baixas pressões. Portanto, é importante saber como
estas grandezas e características estruturais influenciam o comportamento da antena, de forma
a minimizar os efeitos indesejáveis.
Para explicar algumas das influências do material têxtil no desempenho das antenas usáveis,
esta Tese de Doutoramento começa por fazer o estado da arte sobre os pontos-chave para o
desenvolvimento de antenas têxteis, desde a escolha dos materiais têxteis até ao processo de
fabrico da antena. Além disso, a tese identifica e apresenta uma análise dos materiais têxteis
e técnicas de fabricação que têm sido utilizados e referidos na literatura.
A caracterização rigorosa dos materiais têxteis para usar como substrato dielétrico em sistemas
usáveis é fundamental. No entanto, pouca informação existe sobre a caracterização das
propriedades eletromagnéticas dos têxteis vulgares. Como já referido, os tecidos, malhas e
não-tecidos são materiais heterogéneos, altamente porosos, compressíveis e facilmente
influenciados pelas condições higrométricas ambientais, dificultando a sua caracterização
eletromagnética. Não havendo nenhum método padrão, vários autores têm vindo a adaptar
algumas técnicas para a caracterização dielétrica dos materiais têxteis. Esta Tese de
Doutoramento foca a caracterização dielétrica dos materiais têxteis, revendo os métodos
ressonantes e não ressonantes que foram propostos para caracterizar os materiais têxteis e o
couro. Além disso, esta Tese de Doutoramento resume a caracterização de dieléctricos têxteis
feita através dos métodos revistos e que foi validada testando antenas que apresentaram um
bom desempenho.
No seguimento da revisão, apresenta-se uma Técnica Experimental Baseada em Ressonância.
Esta nova técnica baseia-se na teoria da perturbação de ressonância, sendo a permitividade e
tangente de perda extraídas com base nas mudanças de frequência causadas pela introdução
de um superstrato no elemento radiante de uma antena patch microstrip. Os resultados de
caracterização obtidos através deste método revelam que, ao posicionar a face mais rugosa do
material em teste em contato com a placa de ressonância, o valor da constante dielétrica
extraída é inferior ao valor extraído quando esta face é colocada ao contrário. Com base nesta
observação, as propriedades estruturais da superfície dos materiais têxteis foram investigadas
e a sua influência no desempenho das antenas foi analisada. Assim, esta Tese de Doutoramento relaciona os resultados da caracterização dielétrica com
alguns parâmetros estruturais dos materiais, como rugosidade da superfície, porosidades
superficial e total. Os resultados mostram que tanto a rugosidade como a porosidade superficial
das amostras influenciam os resultados, que dependem assim do posicionamento do material
que está a ser testado. Também foi analisada a influência do posicionamento do material
dielétrico na performance das antenas têxteis tipo patch microstrip. Para isso, foram
desenvolvidos e testados doze protótipos de antenas patch microstrip. Os resultados mostram
que, apesar das diferenças observadas durante o processo de caracterização, o valor médio da
permitividade é adequado para a modelação das antenas, garantindo um bom desempenho.
De acordo com o relatório da Comissão Europeia, “Internet das Coisas - Um plano de ação para
a Europa”, emitido em 2009, nos próximos anos a Internet das Coisas poderá melhorar a
qualidade de vida das pessoas, nomeadamente pela monitorização da saúde. No contexto das
Redes de Sensores Sem Fios do Corpo Humano, a integração de antenas têxteis para recolha de
energia em roupas inteligentes é uma solução particularmente interessante, pois permite uma
alimentação sem fios e contínua dos dispositivos. De fato, nos dispositivos usáveis a substituição
de baterias não é fácil de praticar. Um dos objetivos específicos desta Tese de Doutoramento
é, portanto, descrever o conceito de recolha de energia e apresentar o estado da arte sobre
antenas têxteis para recolha de energia proveniente da Rádio Frequência (RF). Nesta tese, é
também proposta uma antena impressa do tipo monopolo de dupla banda, fabricada em
substrato têxtil, para recolha de energia eletromagnética, operando nas bandas GSM 900 e DCS
1800. A antena visa recolher energia para alimentar os nós de sensores de um sistema usável
para monitorização da saúde. Os ganhos da antena apresentada foram cerca de 1.8 dBi e 2.06
dBi, aliados a uma eficiência de radiação de 82% e 77.6% para as faixas de frequência mais
baixa e alta, respetivamente.
Para entender e melhorar o desempenho da antena impressa tipo monopolo de dupla banda em
substrato têxtil, várias técnicas de fabrico foram testadas através de testes preliminares, de
forma a identificar as técnicas promissoras e a descartar as ineficientes, como é o caso da
técnica de colagem. De seguida, analisou-se a influência de vários parâmetros das técnicas de
fabrico sobre o desempenho da antena, como o uso de vapor durante a laminação, o tipo de
folha adesiva, a orientação dos elementos irradiantes e outros. Para isto, sete protótipos da
antena têxtil monopolar impressa foram fabricados por técnicas de laminação e bordado.
As medições da resistência elétrica superficial, Rs, mostrou que a presença da folha adesiva
usada no processo de laminagem pode reduzir a condutividade dos materiais condutores. Apesar
disso, ao medir o S11 das antenas impressas tipo monopolo produzidas por laminagem, os
resultados mostram que as antenas têm uma boa adaptação da impedância. Os resultados
também mostram que a orientação do tecido condutor, neste caso um tafetá, não influencia o
desempenho das antenas. No entanto, ao testar antenas bordadas, os resultados mostram que
a direção e o número de pontos no bordado podem influenciar o desempenho da antena e,
portanto, estas são características que devem ser consideradas durante a fabricação. De um modo geral, as antenas têxteis funcionam bem e seus resultados suportam e dão origem
ao um novo conceito de substrato contínuo para melhorar a integração de antenas têxteis no
vestuário, de maneira mais confortável e elegante. A tese apresenta um protótipo
demonstrador deste conceito, o E-Caption: A Smart and Sustainable Coat. Neste protótipo de
casaco inteligente, a antena impressa está totalmente integrada, pois o seu substrato dielétrico
é o próprio mat
Active textile antennas in professional garments for sensing, localisation and communication
New wireless wearable monitoring systems integrated in professional garments require a high degree of reliability and autonomy. Active textile antenna systems may serve as platforms for body-centric sensing, localisation, and wireless communication systems, in the meanwhile being comfortable and invisible to the wearer. We present a new dedicated comprehensive design paradigm and combine this with adapted signal-processing techniques that greatly enhance the robustness and the autonomy of these systems. On the one hand, the large amount of real estate available in professional rescue worker garments may be exploited to deploy multiple textile antennas. On the other hand, the size of each radiator may be designed large enough to ensure high radiation efficiency when deployed on the body. This antenna area is then reused by placing active electronics directly underneath and energy harvesters directly on top of the antenna patch. We illustrate this design paradigm by means of recent textile antenna prototypes integrated in professional garments, providing sensing, positioning, and communication capabilities. In particular, a novel wearable active Galileo E1-band antenna is presented and fully characterized, including noise figure, and linearity performance
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