A Novel Power-Efficient Wireless Multi-channel Recording System for the Telemonitoring of Electroencephalography (EEG)

This research introduces the development of a novel EEG recording system that is modular, batteryless, and wireless (untethered) with the supporting theoretical foundation in wireless communications and related design elements and circuitry. Its modular construct overcomes the EEG scaling problem and makes it easier for reconfiguring the hardware design in terms of the number and placement of electrodes and type of standard EEG system contemplated for use. In this development, portability, lightweight, and applicability to other clinical applications that rely on EEG data are sought. Due to printer tolerance, the 3D printed cap consists of 61 electrode placements. This recording capacity can however extend from 21 (as in the international 10-20 systems) up to 61 EEG channels at sample rates ranging from 250 to 1000 Hz and the transfer of the raw EEG signal using a standard allocated frequency as a data carrier. The main objectives of this dissertation are to (1) eliminate the need for heavy mounted batteries, (2) overcome the requirement for bulky power systems, and (3) avoid the use of data cables to untether the EEG system from the subject for a more practical and less restrictive setting. Unpredictability and temporal variations of the EEG input make developing a battery-free and cable-free EEG reading device challenging. Professional high-quality and high-resolution analog front ends are required to capture non-stationary EEG signals at microvolt levels. The primary components of the proposed setup are the wireless power transmission unit, which consists of a power amplifier, highly efficient resonant-inductive link, rectification, regulation, and power management units, as well as the analog front end, which consists of an analog to digital converter, pre-amplification unit, filtering unit, host microprocessor, and the wireless communication unit. These must all be compatible with the rest of the system and must use the least amount of power possible while minimizing the presence of noise and the attenuation of the recorded signal A highly efficient resonant-inductive coupling link is developed to decrease power transmission dissipation. Magnetized materials were utilized to steer electromagnetic flux and decrease route and medium loss while transmitting the required energy with low dissipation. Signal pre-amplification is handled by the front-end active electrodes. Standard bio-amplifier design approaches are combined to accomplish this purpose, and a thorough investigation of the optimum ADC, microcontroller, and transceiver units has been carried out. We can minimize overall system weight and power consumption by employing battery-less and cable-free EEG readout system designs, consequently giving patients more comfort and freedom of movement. Similarly, the solutions are designed to match the performance of medical-grade equipment. The captured electrical impulses using the proposed setup can be stored for various uses, including classification, prediction, 3D source localization, and for monitoring and diagnosing different brain disorders. All the proposed designs and supporting mathematical derivations were validated through empirical and software-simulated experiments. Many of the proposed designs, including the 3D head cap, the wireless power transmission unit, and the pre-amplification unit, are already fabricated, and the schematic circuits and simulation results were based on Spice, Altium, and high-frequency structure simulator (HFSS) software. The fully integrated head cap to be fabricated would require embedding the active electrodes into the 3D headset and applying current technological advances to miniaturize some of the design elements developed in this dissertation

Wireless Power Transfer For Biomedical Applications

In this research wireless power transfer using near-field inductive coupling is studied and investigated. The focus is on delivering power to implantable biomedical devices. The objective of this research is to optimize the size and performance of the implanted wireless biomedical sensors by: (1) proposing a hybrid multiband communication system for implantable devices that combines wireless communication link and power transfer, and (2) optimizing the wireless power delivery system. Wireless data and power links are necessary for many implanted biomedical devices such as biosensors, neural recording and stimulation devices, and drug delivery and monitoring systems. The contributions from this research work are summarized as follows: 1. Development of a combination of inductive power transfer and antenna system. 2. Design and optimization of novel microstrip antenna that may resonate at different ultra-high frequency bands including 415 MHz, 905 MHz, and 1300MHz. These antennas may be used to transfer power through radiation or send/receive data. 3. Design of high-frequency coil (13.56 MHz) to transfer power and optimization of the parameters for best efficiency. 4. Study of the performance of the hybrid antenna/coil system at various depths inside a body tissue model. 5. Minimizing the coupling effect between the coil and the antenna through addressed by optimizing their dimensions. 6. Study of the effects of lateral and angular misalignment on a hybrid compact system consisting of coil and antenna, as well as design and optimize the coilâs geometry which can provide maximum power efficiency under misalignment conditions. 7. Address the effects of receiver bending of a hybrid power transfer and communication system on the communication link budget and the transmitted power. 8. Study the wireless power transfer safety and security systems

Multi-frequency microwave energy harvesting receivers: theory and applications

Mención Internacional en el título de doctorEmissions across the electromagnetic spectrum are not only used for communications, but they can also be used for powering electronic devices. This resource has been made more and more abundant in the last years thanks to the recent deployment of 4G and 5G, and the popularization of broadband wireless networks such as WiFi, including traditional services such as TV and radio broadcasting. In order to take advantage of the energy (currently wasted), rectennas (a rectifier integrated with an antenna) are used. This thesis has the objective of studying these rectifying elements, to reduce or eliminate the use of batteries that are employed in millions of low-power devices and sensor networks planned for deployment in the near future. To do this, a self-supply system in situ is required. This could be achieved with photovoltaics or piezoelectrics, but they require the presence of light or vibration. However, the electromagnetic energy produced by mobile communications, TV base stations and radar is noticeable inside a large coverage area, 24 hours a day. This includes difficult access areas where it is nearly impossible to provide appropriate maintenance to replace batteries. As explained through the thesis, energy harvesting applications have a severe limitation on the available levels of power density to scavenge, constraining the RF-DC power conversion effciencies. Therefore, the amount of DC power to feed a sensor is limited and some techniques must be applied to improve the performance. This thesis proposes an alternative for improving the RF-DC power conversion efficiency based on the multiple-tone scenario (the electromagnetic spectrum). Previous studies have been published about an empirical improvement in the power efficiency when working with high Peak to Average Power Ratio (PAPR) multiple-tone signals, compared to a CW signal with the same average power, although the theoretical proof was not accurate enough. A mathematical model that predicts the expected DC current of the diode when excited with multiple tones is proposed along the thesis, having good agreement with simulations and measurements, demonstrating the good performance of the theoretical model. With this mathematical approach, convergence problems in simulation software can be avoided. This document comprises six chapters and it is organized as follows: In the first chapter a brief introduction on the evolution of wireless power transfer is presented, including all the different approaches that compose it, emphasizing the far-filed non-directional powering or harvesting, which is the topic of this thesis. In addition, an analysis of the state of the art is presented with the most signifficant values of conversion effciency, as well as the main characteristics of various designs. In the second chapter, the performance of the diode is explored theoretically. For very low incident power densities (those present in the environment), the diode works in a non-linear region, where a power effciency improvement is obtained when using high PAPR multiple-tone signal instead of a single tone with the same average power. This fact has been empirically tested but an accurate theoretical model has not been accomplished. Therefore, this chapter deals with this issue, showing a novel mathematical analysis of the diode operation in that region for multiple input tones, varying their relative amplitude and frequency. In Chapter 3, the theoretical analysis is compared with simulations and experiments for multiple input tones with a large resulting PAPR using three different rectifier circuits. To properly compare the results, it is necessary to use an accurate Spice diode model (including parasitics) and an appropriate measurement setup. Otherwise, results will differ due to an inadequate characterization of the non-linear device. This chapter addresses those issues. The analysis shows that the relative frequency and amplitude of multiple simultaneous signals impacts the amount of efficiency improvement. Once the recti er element is studied, Chapter 4 deals with the antenna design, which is part of the rectenna deployment. It is seen that different design criteria must be used when working with a WPT directive beaming application or a non-directive harvesting one, as happens in this thesis. The integration between the antenna and the recti er is analyzed, showing possible alternatives. Finally, a rectenna design is built and tested through indoor and outdoor measurements. An analysis of the electromagnetic spectrum is included to demonstrate the feasibility of the rectenna model. In Chapter 5 a wearable rectenna application is shown, with a broadband 2 to 5 GHz rectenna array, implemented on a cotton shirt. This application allows to collect enough energy to power energy-efficient devices. Different rectenna array sizes were tested at different power densities. The single element is a self-complementary tightly-coupled bow-tie. Simulations and measurements were performed over a phantom and over body tissues taking into account the electrical properties of the torso. The thickness of each layer was varied analyzing its influence in the antenna performance, to check what happens under different body compositions (people with more adipose tissue or on the contrary more brous). Finally, Chapter 6 collects the conclusions of the work shown in this thesis and ideas for future work. Some ideas are proposed about Chapter 2 to reduce the error of the mathematical approach when working in the non-linear region. Also, some possible improvements to the printed antenna of Chapter 5 are included such as adding a dual linear polarization.Las emisiones a lo largo de todo el espectro electromagnético no sólo se pueden utilizar para las comunicaciones, sino que también pueden emplearse para la alimentación de dispositivos electr onicos. Este recurso se ha hecho cada vez más abundante en los ultimos años gracias a los recientes despliegues en telefonía móvil de 4G y 5G y a la popularización de las redes inalámbricas de banda ancha (WiFi), sin olvidar las comunicaciones de difusión ya existentes como la radio o televisión. Para poder aprovechar este recurso (actualmente desaprovechado), se utilizan las llamadas rectenas, que son antenas con un elemento rectificador integrado. Esta tesis tiene por objetivo el estudio de estos elementos rectificadores, para desarrollar aplicaciones capaces de reducir o eliminar el uso de baterías en los millones de dispositivos y redes de sensores de bajo consumo existentes hoy día, mediante el autoabastecimiento de energía. Este proceso podría llevarse a cabo con paneles fotovoltaicos o sistemas piezoeléctricos, pero estos requieren de la presencia continua de la fuente que los origina (vibraciones, horas de sol). Sin embargo, la energía electromagnética producida por las estaciones base, de telefonía o televisión, está presente bajo su zona de cobertura las 24 horas del día, lo cual incluye zonas de difícil acceso, en las que es complicado el recambio o mantenimiento de las baterías. Además, estas emisiones tienen como principal limitación la baja densidad de potencia, obteniéndose valores de eficiencia de conversión RF-DC muy bajos. Esto conlleva que los valores de corriente DC para alimentar al sensor sean muy pequeños, de nA o uA, y por tanto, deben emplearse técnicas para la mejora del rendimiento. Esta tesis propone una alternativa para mejorar la eficiencia de conversión, basada en la probada mejora de eficiencia cuando se trabaja con señales con un Peak to Average Power Ratio (PAPR) grande. Esto se da en escenarios multitonales como puede ser el espectro electromagnético. Esta mejora no ha sido abordada teóricamente con resultados precisos en trabajos previos, por lo que en esta tesis se desarrolla un modelo matemático que predice la componente DC de la corriente del diodo, cuando se excita con múltiples tonos. Los resultados obtenidos han sido validados en el laboratorio, demostrándose la mejora en la eficiencia de conversión y el buen comportamiento del modelo teórico. De esta forma, se pueden agilizar los cálculos cuando no se tiene un software de simulación disponible, o cuando este arroja problemas de convergencia. Esta tesis consta de seis capítulos y está organizada de la siguiente manera: En el primer capítulo se expone una breve introducción sobre la evolución de la transferencia inalámbrica de potencia y sobre las diferentes tecnologías que la componen, haciéndose hincapié en la transferencia de potencia no directiva en campo lejano, puesto que se corresponde a la recolección de la energía electromagnética ambiental. Además, se incluye un análisis del estado del arte con los valores más significativos de eficiencia de conversión, así como las principales características de varios diseños (como por ejemplo la potencia o las bandas de trabajo empleadas). En el segundo capítulo se explora el comportamiento del diodo desde el punto de vista matemático. Bajo densidades de potencia pequeñas, como las presentes en este entorno, el diodo opera en su región no lineal, produciendo un incremento de eficiencia cuando se trabaja con señales con gran PAPR, respecto a un tono con la misma potencia media. Este hecho ha sido probado empíricamente pero ningún modelo teórico preciso ha sido realizado. En este capítulo se incluye un novedoso análisis matemático del funcionamiento del diodo en esa región para múltiples tonos de entrada, variando la amplitud y frecuencia de estos. En el capítulo 3 se muestra la comparativa entre el modelo teórico, las simulaciones y las medidas en el laboratorio, usando múltiples tonos entrada en tres rectificadores. Para comparar adecuadamente todos los resultados, es necesario utilizar un modelo Spice del diodo preciso (incluyendo los parásitos del encapsulado) y un correcto setup de medida. De lo contrario, existiría un error en los resultados debido a una caracterización inadecuada del dispositivo no lineal. Este capítulo aborda esos problemas. El análisis muestra que la frecuencia y amplitud relativa de múltiples señales simultáneas afectan a la eficiencia. Una vez estudiado el rectificador, el capítulo 4 de la tesis aborda el diseño de la antena. Para ello, se analizan los diferentes criterios de diseño que deben emplearse cuando se trabaja con una transmisión de potencia inalámbrica directiva o no directiva, como es en caso bajo estudio, así como las técnicas de integración entre rectificador y antena. Para concluir, se diseña y mide una rectena tanto en laboratorio como en espacio abierto, usando la energía ambiental, previamente caracterizada con medidas espectrales. Los resultados demuestran que es posible recolectar y rectificar la energía ambiental. En el capítulo 5 se muestra una posible aplicación al integrarse una rectena impresa en una camiseta para alimentar sensores biológicos o \wearable". Se trata de un diseño de banda ancha que opera en el rango de 2 a 5 GHz, que permite recolectar suficiente energía para alimentar sensores de bajo consumo. Se analiza el funcionamiento de dos tamaños distintos de arrays con diferentes densidades de potencia. Al ser un diseño \wearable", la aplicación ha sido diseñada y probada sobre un maniquí y un cuerpo humano, analizándose el comportamiento de la antena impresa sobre distintas composiciones corporales (personas con más tejido adiposo o por el contrario más fibrosas). Finalmente, el capítulo 6 recopila las conclusiones del trabajo que se muestra en esta tesis e ideas para trabajos futuros, proponiéndose desde enfoques para reducir más el error en la aproximación del comportamiento no lineal del diodo en el capítulo 2, a posibles mejoras en la antena impresa del capítulo 5, incluyendo la doble polarización lineal.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: Carlos Martín Pascual.- Secretario: Simon Jacques Hemour.- Vocal: Nuno Miguel G. Borges De Carvalh

Environment insensitive mobile terminal antennas

Tämän lisensiaatintutkimuksen pääpaino on tutkia ja kehittää uudenlaisia matkapuhelinantenneja, joilla on mahdollisimman hyvä suorituskyky vaihtelevissa käyttöolosuhteissa. Matkapuhelinantennin tulee toimia tehokkaasti riippumatta siitä onko käyttäjä matkapuhelinantennin läheisyydessä vai ei. Lisäksi käyttäjään kohdistuvan sähkömagneettinen säteilyn tulisi olla mahdollisimman pieni. Aluksi työssä tutkitaan käyttäjän käden vaikutusta antennin suorituskykyyn sekä esitetään uudentyyppinen antennirakenne, jolla on voitu vähentää käden ja pään vaikutusta antennin suorituskykyyn. Tällä rakenteella päähän kohdistuvaa ominaisabsorptiota (SAR) voidaan pienentää 81 % sekä parantaa säteilyhyötysuhdetta 2.8 dB 900 MHz:n taajuudella verrattuna perinteiseen antennirakenteeseen. Lisäksi työssä on tutkittu balansoitujen antennien soveltuvuutta matkapuhelimiin. Balansoituja antenneja voidaan käyttää kohteissa, jotka tarvitsevat suurta antennien välistä sähkömagneettista isolaatiota. Lisäksi joissain tapauksissa balansoituja antenneja voidaan käyttää pienentämään antennin ja käyttäjän välistä vuorovaikutusta. Balansoitujen antennien käyttö rajoittuu kuitenkin korkeahkoille, yli 2 GHz taajuuksille kaistanleveysrajoitusten takia. Lopuksi työssä esitetään uudentyyppinen aaltoloukkuihin perustuva rakenne, jolla voidaan pienentää merkittävästi sähkö- ja magneettikenttiä puhelimen rungon päädyssä ja siten parantaa kuulolaiteyhteensopivuutta.The main emphasis of this licentiate thesis is in investigating and developing novel mobile terminal antennas having optimal performance in different operating environments. The mobile terminal antenna should work efficiently regardless whether the user is in the vicinity of the antenna or not. In addition, the electromagnetic radiation absorbed by the user should be as small as possible. First, the effect of the user's hand on the antenna performance is studied, and a novel antenna shielding method to decrease the effect of the hand and head is developed. It is shown that the shielding structure can decrease specific absorption rate (SAR) in the head by 81% at 900 MHz and the corresponding improvement in radiation efficiency is 2.8 dB compared to the tradiational antenna. Secondly, the feasibility of balanced antenna structures in mobile terminals is investigated. The balanced antennas can be used in applications requiring high electromagnetic isolation between multiple antenna elements. It is also shown that in some cases the electromagnetic interaction between the antenna and the user can be decreased by using a balanced antenna instead of an unbalanced one. However, the use of balanced antennas is typically limited to higher UHF frequencies, over 2 GHz. Finally, a novel method to control the electromagnetic near fields of a mobile terminal by using wavetraps is introduced. Wavetraps can be used to significantly decrease the electric and magnetic fields at the open end of the chassis of the terminal and thus improve the hearing-aid combitibility

Study to investigate and evaluate means of optimizing the radar function for the space shuttle

Results are discussed of a study to define a radar and antenna system which best suits the space shuttle rendezvous requirements. Topics considered include antenna characteristics and antenna size tradeoffs, fundamental sources of measurement errors inherent in the target itself, backscattering crosssection models of the target and three basic candidate radar types. Antennas up to 1.5 meters in diameter are within specified installation constraints, however, a 1 meter diameter paraboloid and a folding, four slot backfeed on a two gimbal mount implemented for a spiral acquisition scan is recommended. The candidate radar types discussed are: (1) noncoherent pulse radar (2) coherent pulse radar and (3) pulse Doppler radar with linear FM ranging. The radar type recommended is a pulse Doppler with linear FM ranging. Block diagrams of each radar system are shown

Microwave Front-End Component Codesign: Filter-Amplifiers, Integrated Passives and Rectifying-Radiators

The ever-growing need for improved wireless communications motivates innovation in miniaturization and integration of microwave front-end components. This thesis addresses miniaturization by co-design methods that enable simultaneous size reduction, improved efficiency, diverse technology integration, and enhanced safety. First, a new theoretical treatment for simple design of narrowband filters with arbitrary complex impedance ports is introduced and validated through 2.4GHz designs with 2nd-order all-pole and 4th-order elliptical response. The theory is then extended to filters with port impedance tuning capabilities and validated with a 2nd-order Chebyshev filter with varactor-tunable input impedance over a pre-defined impedance range with maintained filter response. The theory is also applied to impedance-matching filters for power amplifiers (PAs) with the goal of improving efficiency and reducing footprint. A high-efficiency 4.7GHz single-stage 4-W hybrid GaN filter-PA (FPA) shows a measured gain of 15dB and PAE=55% with a pre-specified 9% fractional bandwidth. The approach is further validated on a GaAs MMIC FPA at 28GHz with a measured saturated gain of 8dB, 200mW of output power and PAE=30%. For further integration of components with miniaturized footprint, a heterogeneous integration process called metal-embedded chip assembly (MECA), developed by HRL, is exploited to combine ceramic passive circuits, surface-mount capacitors and GaN MMICs with a unique interconnect network. The interconnects outperform standard wirebonds and are also used to implement transmission lines, referred to as bridge-lines, with reduced loss and higher possible characteristic impedances compared to microstrip. Various couplers in the 8-10GHz range are designed and characterized to demonstrate the additional design capabilities provided by the MECA process. Thermal performance improvement of PAs is shown, and increased gain and efficiency for an X-band GaN MMIC is reported. Finally, the FPA design approach from the first part of the thesis is used to design a quasi-MMIC FPA with a predicted gain of 7.4dB, peak PAE of 23% and output power above 30dBm from 23.65 to 24.4GHz. Additionally, a 20-GHz dual-mode rectangular cavity resonator filter with insertion loss under 0.25dB is designed in the MECA process, and is in fabrication at the time of writing of this thesis. Wireless systems rely on batteries or wired charging, which limits the operational time. In the second part of the thesis, co-design and integration of wireless charging and harvesting is researched. Another application of wireless charging is for electric vehicles, where methods analogous to microwave antenna arrays, amplifiers and rectifiers can be used to provide a means for charging batteries of stationary or moving vehicles at lower frequencies and high power levels. A new method for reducing fringing fields in a capacitive wireless power transfer (CWPT) system using a near-field phased array is demonstrated using a multi-module approach on a 1.1kW system at 13.67MHz at a 25-cm energy-transfer distance with over 80% efficiency. To meet safety standards, a fringing field reduction of 24% with a two-module system and 43% with a four-module system, is demonstrated at 7, 14 and 29MHz. This system applied co-design of capacitor arrays with matching networks for the high-power inverters and rectifiers on the circuit side, and energy-transfer and fringing fields on the free-space side. In the low-power regime, co-design of both narrowband and broadband rectifiers and antennas for harvesting ambient power for wireless devices is demonstrated.Harvesting power from airplane altimeter radar antenna sidebands with a rectifier-antenna (rectenna) for aircraft health monitoring sensors demonstrates the possibility of charging a storage device at incident power levels below 2 W/cm2 at 4.3GHz. The narrowband harvesting device applies co-design to the antenna, rectifier and maximum power point tracking power-management circuit to provide a usable voltage level. For wideband energy harvesting from unknown and variable sources, wearable rectenna arrays screen-printed on clothing are demonstrated for harvesting 4-130W/cm2 power densities over more than an octave bandwidth in the sub-6GHz frequency range. Measurements on 36 and 64-element arrays show up to PDC=32W for incident power densities of 4W/cm2. For low incident power densities, the efficiency is in the 5-10% range, and reaches 32% for 100W/cm2. In these arrays, the rectifiers and tightly-coupled antennas are co-designed for broadband performance.</p

Near Earth asteroid rendezvous

The Spacecraft Design Course is the capstone design class for the M.S. in astronautics at the Naval Postgraduate School. The Fall 92 class designed a spacecraft for the Near Earth Asteroid Rendezvous Mission (NEAR). The NEAR mission uses a robotic spacecraft to conduct up-close reconnaissance of a near-earth asteroid. Such a mission will provide information on Solar System formation and possible space resources. The spacecraft is intended to complete a NEAR mission as a relatively low-budget program while striving to gather as much information about the target asteroid as possible. A complete mission analysis and detailed spacecraft design were completed. Mission analysis includes orbit comparison and selection, payload and telemetry requirements, spacecraft configuration, and launch vehicle selection. Spacecraft design includes all major subsystems: structure, electrical power, attitude control, propulsion, payload integration, and thermal control. The resulting spacecraft demonstrates the possibility to meet the NEAR mission requirements using existing technology, 'off-the-shelf' components, and a relatively low-cost launch vehicle

Implantable antennas for biomedical applications

Recently, the interest in implantable devices for biomedical telemetry has significantly increased. Amongst the different components of the implantable device, the antenna plays the most significant role in the wireless data transmission. However, the human body around the antenna alters its overall characteristics and absorbs most of its radiation. Therefore, this thesis is mainly focused on improving the antenna characteristics (bandwidth and radiation efficiency) to overcome the human body effect and investigating new structures that reduce the power absorption by the human body tissues. A novel antenna design methodology is developed and used to design new flexible implantable antennas of much lighter weight, larger radiation efficiency, and wider bandwidth than existing embedded antennas. These antennas work for multiple ((401-406 MHz) MedRadio, 433 MHz and 2.45 GHz ISM) bands which satisfy the requirements of low power consumption and wireless power transfer. This has been combined with thorough investigations of the antenna performance in the anatomical human body. New effective evaluation parameters such as the antenna orientation are investigated for the first time. New structures inspired by complementary and multiple split ring resonators (CSRRs and MSRRs) are designed. The structures are found to reduce the electric near field and hence the absorbed power which increases the radiated power accordingly. This new promising function of metamaterial based structures for implantable applications is investigated for the first time. The path loss (between pacemaker and glucose monitoring implantable antennas inside the anatomical body model) and (between an implantable and external antennas for a wireless power channel at 433 MHz) are estimated. Moreover, the optimum antenna type for on-in body communication is investigated. Loop antennas are found to outperform patch antennas in close proximity to the human body