Miniaturized Microwave Devices and Antennas for Wearable, Implantable and Wireless Applications

This thesis presents a number of microwave devices and antennas that maintain high operational efficiency and are compact in size at the same time. One goal of this thesis is to address several miniaturization challenges of antennas and microwave components by using the theoretical principles of metamaterials, Metasurface coupling resonators and stacked radiators, in combination with the elementary antenna and transmission line theory. While innovating novel solutions, standards and specifications of next generation wireless and bio-medical applications were considered to ensure advancement in the respective scientific fields. Compact reconfigurable phase-shifter and a microwave cross-over based on negative-refractive-index transmission-line (NRI-TL) materialist unit cells is presented. A Metasurface based wearable sensor architecture is proposed, containing an electromagnetic band-gap (EBG) structure backed monopole antenna for off-body communication and a fork shaped antenna for efficient radiation towards the human body. A fully parametrized solution for an implantable antenna is proposed using metallic coated stacked substrate layers. Challenges and possible solutions for off-body, on-body, through-body and across-body communication have been investigated with an aid of computationally extensive simulations and experimental verification. Next, miniaturization and implementation of a UWB antenna along with an analytical model to predict the resonance is presented. Lastly, several miniaturized rectifiers designed specifically for efficient wireless power transfer are proposed, experimentally verified, and discussed. The study answered several research questions of applied electromagnetic in the field of bio-medicine and wireless communication.Comment: A thesis submitted for the degree of Ph

In-body to On-body Experimental UWB Channel Characterization for the Human Gastrointestinal Area

[ES] La población mundial en países desarrollados está envejeciendo y con ello existe un aumento de enfermedades en gran medida causadas por la edad. Las nuevas tecnologías médicas pueden ayudar a detectar, diagnosticar y tratar estas enfermedades y con ello ahorrar dinero, tiempo y recursos de los sistemas sanitarios. Las tecnologías inalámbricas implantables han abierto un nuevo panorama para la próxima generación de tecnologías médicas. Frecuencias como la Ultra Wide-Band (UWB) de 3.1 a 10.6 GHz están siendo consideradas para la nueva generación de dispositivos inalámbricos para dentro del cuerpo humano. Las características como el reducido tamaño de las antenas, la baja potencia de transmisión y la alta velocidad de datos son las más buscadas en este tipo de dispositivos. El problema surge porque el cuerpo humano depende de la frecuencia de modo que a mayores frecuencias, mayores son las pérdidas por propagación. Conociendo el canal de transmisión se puede solventar el problema de las altas pérdidas. Esta tesis tiene como objetivo caracterizar el canal de radio frecuencia (RF) para la nueva generación de dispositivos médicos implantables. Para caracterizar el canal se han empleado tres diferentes metodologías: simulaciones numéricas, medidas en phantom y experimentos en animales vivos. Las medidas en phantom fueron realizadas en un nuevo sistema de medidas expresamente disen¿ados para medidas de dentro a fuera del cuerpo humano en la banda de frecuencias UWB. Además, se utilizó un novedoso recipiente con dos capas de phantom imitando la zona gastrointestinal del cuerpo. Estos phantoms fueron creados para este tipo de medidas y son extremadamente precisos a las frecuencias UWB. Para los experimentos en animales se utilizaron cerdos y se intentó reproducir en ellos las medidas previamente realizadas en phantom. Las simulaciones software se realizaron con la intención de replicar ambas metodologías. Una vez realizados los experimentos se realizó un extensivo estudio del canal en dominio frecuencial y temporal. Mas en detalle, se compararon las antenas usadas en la recepción y transmisión, el efecto de la grasa en el canal, la formas del recipiente contenedor de phantom y las componentesmulticamino. Como resultado se ha propuesto un modelo de propagación del canal para la banda baja de las frecuencias UWB (3.1 -5.1 GHz) para la zona gastrointestinal del cuerpo humano. Este modelo de propagación ha sido validado utilizando las tres metodologías previamente descritas y comparada con otros estudios existentes en literatura. Finalmente, se midió el canal de propagación para una determinada aplicación a bajas frecuencias con señales UWB. También se realizaron medidas del canal de propagación en la zona cardíaca del cuerpo humano desde un punto de vista de seguridad de datos. Los resultados obtenidos en esta tesis confirman los beneficios que tendría la utilización de frecuencias UWB para las futuras generaciones de dispositivos médicos implantables.[CA] La població mundial a països desenvolupats està envellint-se i enfrontant-se a un augment d'infermetats principalment causades per la edat. Les noves tecnologies mèdiques poden ajudar a detectar, diagnosticar i tractar aquestes malalties, estalviant diners, temps i recursos sanitaris. Els dispositius implantables sense fils han generat un nou panorama per a les noves generacions de dispositius mèdics. Les freqüències com la banda de UWB estan sent considerades per a les futures tecnologies implantables. La reduïda grandària de les antenes, la baixa potència de transmissió i les altes velocitats de dades son característiques buscades per als dispositius implantables. Per contra, els éssers humans depenen de la freqüència en el sentit que a majors freqüències, majors les pèrdues per propagació quan el senyal travessa el cos humà d'interior a exterior. Per solventar aquestes pèrdues el canal de propagació s'ha d'entendre i conèixer de la millor manera possible. Aquesta tesi doctoral te com a objectiu caracteritzar el canal de radio freqüència (RF) per a la nova generació de dispositius mèdics implantables. S'han emprat tres metodologies diferents per a realitzar aquesta caracterització: simulacions software, mesures amb fantomes i experiments amb animals vius. Els experiments amb fantomes es van realitzar a un sistema de mesures dissenyat expressament per a les transmissions de dins a fora del cos humà a les freqüències UWB. També es van utilitzar un contenidor per als fantomes de dues capes, imitant l'area gastrointestinal dels humans. Per als experiments a animals es van emprar porcs, replicant els experiments al laboratori en fantomes de la forma més semblant possible. Les simulacions software foren dissenyades per a imitar les experiments amb fantomes i animals. Després dels experiments el canal de propagació es va investigar exhaustivament des del domini freqüèncial i temporal. S'ha observat com les antenes en transmissió i recepció afecten al senyal, la influència de la grassa, la forma del contenidor de fantoma i les possibles contribucions multicamí. Finalment es proposa un nou model de propagació per a les baixes freqüències UWB (3.1 a 5.1 GHz) per a la zona GI del cos humà. El model es va validar utilitzant les tres metodologies abans esmentades i també foren comparades amb model ja existents a la literature. Finalment des d'un punt de vista aplicat, el canal es va avaluar per al senyal UWB a baixes freqüències (60 MHz). A més a més, per a la nova generació de marcapassos sense fil es va investigar el canal des d'un punt de vista de seguretat de dades. Els resultats obtinguts a aquesta tesi confirmen els avantatges d'emprar la banda de freqüències UWB per a la nova generació de dispositius médics implantables.[EN] The current global population in developed countries is becoming older and facing an increase in diseases mainly caused by age. New medical technologies can help to detect, diagnose and treat illness, saving money, time, and resources of physicians. Wireless in-body devices opened a new scenario for the next generation of medical devices. Frequencies like the Ultra Wide-band (UWB) frequency band (3.1 - 10.6 GHz) are being considered for the next generation of in-body wireless devices. The small size of the antennas, the low power transmission, and the higher data rate are desirable characteristics for in-body devices. However, the human body is frequency ependent, which means higher losses of the radio frequency (RF) signal from in- to out-side the body as the frequency increases. To overcome this, the propagation channel has to be understood and known as much possible to process the signal accordingly. This dissertation aims to characterize the (RF) channel for the future of in-body medical devices. Three different methodologies have been used to characterize the channel: numerical simulations, phantom measurements, and living animals experiments. The phantom measurements were performed in a novel testbed designed for the purpose of in-body measurements at the UWB frequency band. Moreover, multi-layer high accurate phantoms mimicking the gastrointesintal (GI) area were employed. The animal experiments were conducted in living pigs, replicating in the fairest way as possible the phantom measurement campaigns. Lastly, the software simulations were designed to replicate the experimental measurements. An in-depth and detail analysis of the channel was performed in both, frequency and time domain. Concretely, the performance of the receiving and transmitting antennas, the effect of the fat, the shape of the phantom container, and the multipath components were evaluated. Finally, a novel path loss model was obtained for the low UWB frequency band (3.1 - 5.1 GHz) at GI scenarios. The model was validated using the three methodologies and compared with previous models in literature. Finally, from a practical case point of view, the channel was also evaluated for UWB signals at lower frequencies (60 MHz) for the GI area. In addition, for the next generation of leadless pacemakers the security link between the heart and an external device was also evaluated. The results obtained in this dissertation reaffirm the benefits of using the UWB frequency band for the next generation of wireless in-body medical devices.Pérez Simbor, S. (2019). In-body to On-body Experimental UWB Channel Characterization for the Human Gastrointestinal Area [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/133034TESI

Compact Antenna with Artificial Magnetic Conductor for Noninvasive Continuous Blood Glucose Monitoring

A non-invasive technique for real-time continuous monitoring of blood glucose has been under development by Venkataraman’s research group in the ETA lab at RIT [16]-[18]. The methodology involves placing an antenna on the arm and monitoring changes in the resonant frequency, which is attributed to changes in the blood glucose level. This is because the blood’s permittivity depends on the glucose levels, and in turn, affects the antenna’s resonant frequency. In order to correlate the antenna’s resonant frequency shift with the real-time blood glucose change, glucose estimation was also modeled using the antenna’s input impedance. The antennas designed could successfully track the rise and fall of blood glucose using the glucose estimation model for both diabetic and non-diabetic patients. However, the antennas being used in this research are too large in size and not flexible. Additionally, the antenna’s radiation pattern was omnidirectional as it is a monopole antenna where the radiation is into the arm as well as away from the arm (back radiation). As a result, during the test procedure, the arm must be in a steady position throughout the time of the resonant frequency measurement. While it worked very well to prove the feasibility of continuous glucose monitoring, a better antenna is required for the next phase of research that involves clinical testing in a hospital environment. My goal in this thesis is to take the research further by designing antennas that are unidirectional, flexible and small in size. The unidirectional property can be achieved by using PEC (Perfect Electric Conductors) or PMC (Perfect Magnetic Conductors) over the antenna that can suppress the back radiation. Unlike the presence of infinite electric charges on an electric conductor, magnetic charges don’t exist. Therefore magnetic conductors are modeled artificially to achieve magnetic properties commonly known as Artificial Magnetic Conductors (AMC). The antenna used in this thesis is a monopole antenna with AMC as a ground plane. The advantage of using AMC over a perfect metal conductor as a ground plane to the antenna is that the AMC reflects the incident wave in phase and not out of phase like a regular metal conductor. Moreover, AMC layers not only suppresses the back radiation but also enhances the gain of the antenna into the arm. Using the AMC layer as the ground plane has also helped in miniaturizing the antenna. The different artificial magnetic conductors designed in this thesis are Rectangular Patch, Rectangular Ring, I-shaped, and Jerusalem Cross. The antennas were fabricated and tested in the unlicensed ISM band (2.4GHz – 2.5GHz) and are within the SAR standards laid out by FCC. The fabricated antenna was strapped to the arm and measurements of resonant frequency similar to those made previously were conducted with respect to time [16]-[18]. Two types of measurements were compared, that is, when the arm was held steady and when the arm had some movement. No significant change or fluctuations in the resonant frequency was observed with arm movement. Whereas the same type of measurements conducted on the monopole antenna in [18] showed significant fluctuations in the resonant frequency with arm movement. This experiment shows the significant advantage of the antenna with AMC layer as compared to the monopole antenna. Also demonstrated in the present work, is the ability of the designed antenna in tracking the increase and decrease of glucose level with changes in the resonant frequency, similar to [16]. This has been demonstrated with two non-diabetic subjects. Further, no back radiation was noted, when a hand above the setup is moved. Additionally, the effect of creeping waves was negligible. The antenna designed in this work will conform well to clinical studies of the ETA Lab research

Ultra Wideband

Ultra wideband (UWB) has advanced and merged as a technology, and many more people are aware of the potential for this exciting technology. The current UWB field is changing rapidly with new techniques and ideas where several issues are involved in developing the systems. Among UWB system design, the UWB RF transceiver and UWB antenna are the key components. Recently, a considerable amount of researches has been devoted to the development of the UWB RF transceiver and antenna for its enabling high data transmission rates and low power consumption. Our book attempts to present current and emerging trends in-research and development of UWB systems as well as future expectations

Wide Band Embedded Slot Antennas for Biomedical, Harsh Environment, and Rescue Applications

For many designers, embedded antenna design is a very challenging task when designing embedded systems. Designing Antennas to given set of specifications is typically tailored to efficiently radiate the energy to free space with a certain radiation pattern and operating frequency range, but its design becomes even harder when embedded in multi-layer environment, being conformal to a surface, or matched to a wide range of loads (environments). In an effort to clarify the design process, we took a closer look at the key considerations for designing an embedded antenna. The design could be geared towards wireless/mobile platforms, wearable antennas, or body area network. Our group at UT has been involved in developing portable and embedded systems for multi-band operation for cell phones or laptops. The design of these antennas addressed single band/narrowband to multiband/wideband operation and provided over 7 bands within the cellular bands (850 MHz to 2 GHz). Typically the challenge is: many applications require ultra wide band operation, or operate at low frequency. Low frequency operation is very challenging if size is a constraint, and there is a need for demonstrating positive antenna gain

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Antennas and Propagation

This Special Issue gathers topics of utmost interest in the field of antennas and propagation, such as: new directions and challenges in antenna design and propagation; innovative antenna technologies for space applications; metamaterial, metasurface and other periodic structures; antennas for 5G; electromagnetic field measurements and remote sensing applications

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Wireless body area networks for intra-spacesuit communications: modeling, measurements and wearable antennas

Doctor of PhilosophyDepartment of Electrical and Computer EngineeringWilliam B. KuhnBalasubramaniam NatarajanWireless body area networks (WBANs) are an important part of the developing internet of things (IOT). NASA currently uses space suits with wired sensors to collect limited biomedical data. Continuous monitoring and collecting more extensive body vital signs is important to assess astronaut health. This dissertation investigates wireless biomedical sensor systems that can be easily incorporated into future space suits to enable real time astronaut health monitoring. The focus of the work is on the radio-wave channel and associated antennas. We show that the space suit forms a unique propagation environment where the outer layers of the suit’s thermal micrometeoroid garment are largely radio opaque. This environment can be modeled as a coaxial one in which the body itself plays the role of the coax center conductor while the space suit shielding materials play the role of the outer shield. This model is then validated through simulations and experiments. Selecting the best frequency of operation is a complex mixture of requirements, including frequency allocations, attenuation in propagation, and antenna size. We investigate the propagation characteristics for various frequency bands from 315 MHz to 5.2 GHz. Signal attenuation is analyzed as a function of frequency for various communication pathways through 3D simulations and laboratory experiments. Small-scale radio channel results indicate that using lower frequency results in minimal path loss. On the other hand, measurements conducted on a full-scale model suggest that 433 MHz and 2400 MHz yield acceptable path loss values. Propagation between the left wrist and left ankle yielded the worst overall path loss, but signals were still above –100 dBm in raw measurements for a 0dBm transmission indicating that the intra-suit environment is conducive to wireless propagation. Our findings suggest that the UHF bands are best candidate bands since there is interplay between the body conductivity favoring lower frequencies, and the difficulty of coupling RF energy into and out of the channel using suitably sized antennas favoring higher frequencies. Finally, a new self-shielded folded bow-tie antenna is proposed that can be a promising choice for the general area of WBAN technologies as well as potential new space suit environments