Radio frequency inductive coupling is extensively employed for wireless powering of embedded devices such as low power passive near-field RFID systems and implanted sensors. The efficiency of low power inductive links is typically less than 1%and is characterised by very unfavourable coupling conditions, which can vary significantly due to coil position and geometry. Although, a considerable volume of knowledge is available on this topic, most of the existing research is focused on the circuital modeling of the transformer action between the external and implanted coils. The practical issues of coil misalignment and orientation and their implications on transmission characteristics of RF links have been overlooked by researchers. The aim of this work is to present a novel analytical model for near-field inductive power transfer incorporating misalignment of the RF coil system. In this thesis the influence of coil orientation, position and geometry on the link efficiency is studied by approaching the problem from an electromagnetic perspective. In implanted devices some degree of misalignment is inevitable between external and implanted coils due to anatomical requirements. First two types of realistic misalignments are studied; a lateral displacement of the coils and an angular misalignment described as a tilt of the receiver coil. A loosely coupled system approximation is adopted since, for the coil dimensions and orientations envisaged, the mutual inductance between the transmitter and receiver coils can be neglected. Following this, formulae are derived for the magnetic field at the implanted coil when it is laterally and angularly misaligned from the external coil and a new power transfer function presented. The magnetic field solution is carried out for a number of practical antenna coil geometries currently popular in RFID and biomedical domains, such as planar and printed square, and circular spirals as well as conventional air-cored and ferromagnetic solenoids. In the second phase of this thesis, the results from the electromagnetic modeling are embodied in a near-field loosely coupled equivalent circuit for the inductive link. This allows us to introduce a power transfer formula incorporating for the first time coil characteristics and misalignment factors. This novel power transfer function allows a comparison between different coil structures such as short solenoids, with air or ferromagnetic core, planar and printed spirals with respect to power delivered at the receiver and its relative position to the transmitter. In the final stage of this work, the experimental verification of the model shows close agreement with the theoretical predictions. Using this analysis a formal design procedure is suggested that can be applied on a larger scale compared to existing methods. The main advantage of this technique is that it can be applied to a wide range of implementations without the limitations imposed by numerical modeling and existing circuital methods. Consequently, the designer has the flexibility to identify the optimum coil geometry for maximum power transfer and misalignment tolerance that suit the specifications of the application considered. This thesis concludes by suggesting a new optimisation technique for maximum power transfer with respect to read range, coil orientation, geometry and operating frequency. Finally, the limitations of this model are reiterated and possible future development of this research is discussed.

In an attempt to provide a more secure and amiable living environment in our homes, there has been constant effort to develop more efficient and suitable intelligent sensor technology for household application. Wireless sensors provide an efficient means of sensing without the need for messy wiring, and are ideally suited for the household environment. Although many sensor products have been developed (e.g. temperature, humidity and smoke), automated detection and reporting of an incidence occurring in places hard to observe or reach, such as wetting of diapers or water seepage under carpets, are still not readily available at low cost. Most of the existing technologies consist of complex design architecture and follow specific communication protocols which can be overkill for many simple household applications. In this thesis, we present a new wireless sensor system which is based on the detection of just the ON or OFF state of a condition. This approach overcomes the need for complex architecture and design, but is still able to achieve the functionality that is required for many household applications such as water leakage, food rotting, diaper wetting etc. and thus can be made available very cheaply. The sensor system consisting of an interrogator and a sensor circuit is implemented using inductive coupling. A passive L-C circuit is used for the sensor design and the system is tested using diaper wetting as an example of a simple household application. The testing results shows that the sensor can detect an ON and OFF condition for sensor and tag separation of 10 cm which is enough for applications like water leakage behind walls and under carpets, diaper wetting, food rotting etc.

Crosstalk is defined as an unwanted coupling between the conductors. By this it is meant that signals from one of the signal conductors (a generator in this case) are coupled to another signal conductor (receptor), or conductors (receptors), depending on the number of conductors in the vicinity of the generator. Crosstalk in this way affects the signal level on the receptor and thereby affects the total system performance within the system. This can happen in several ways, one of which is through edge coupling. Edge coupling is a process where two signal conductors are placed beside each other in the same layer while the ground conductor could have been placed either under these conductors, in a separate layer like Mclin (Microstrip coupled lines) and Sclin (Coupled striplines), or beside the signal conductors as in Cpwcpl2 (Coplanar wave guide coupled lines). This then means that edge coupling occurs through the sides where the generator and the receptor are facing each other. Broadside coupling is another way, where it occurs when the signal conductors are broadside faced to each other in different layers with reference planes above and below these signal conductors. Coupling of the signals from the generator to the receptor can occur through capacitive coupling or inductive coupling. Capacitive coupling, also known as electrical coupling, occurs due to the difference in the characteristic impedance of the generator (usually 50 or 100 §Ù) and its heavy load (1 k§Ù or more) which results in high voltage difference between the generator and the reference conductor (ground). This leads to the creation of a charge across the generator and the receptor-facing sides and finally results in the electric field coupling between them. On the other hand, inductive coupling, also known as magnetic coupling, occurs when the load is less than the characteristic impedance of the generator, and this thereby results in a heavy current flow through the generator which in return results in a strong magnetic field around itself and so leads to magnetic coupling to the receptor. The aim in this thesis is to measure both the capacitive and inductive coupling load¡¯s impacts on both the edge coupling and the broadside coupling models through crosstalk on the receptor. This thesis starts with the background and corresponding theory and equations to the crosstalk coupling. Later on it tests both the edge- and broadside coupling models with different physical properties exploitation. Inductive and capacitive loads are used to measure the resulting crosstalk coupling. Particularly to see the effect of capacitive and inductive coupling in reality in multi layered PCB, a Sbclin (Broadside coupled striplines) model has been used with different angular placement of the generator. Finally mclin physical models are compared with the simulated models and corresponding differences are discussed. It can be concluded that crosstalk effect increases or decreases with physical properties exploitation. Crosstalk also increases with the wrong termination of the load.

Wireless powered communication (WPC) is an emerging paradigm where wireless devices are powered over the air while exchanging information with them. This technology is attractive for various wireless applications, including classical radio-frequency identification (RFID) systems, implantable sensors, environmental sensing as found in agriculture and forestry, and simultaneous charging and telemetry communications for electric vehicles. While recent studies have shown that inductive coupling provides a more energy-efficient and robust channel for short and middle-range wireless transmission, most of the previous analyses on WPC have been limited to far-field transmission models. To this end, this work provides a comprehensive framework to design and analyze WPC over inductively coupled circuits. We consider three problems, namely, wireless power transfer (WPT), simultaneous wireless information and power transfer (SWIPT), and wireless powered communication network (WPCN) using multiple coupled coils. Each configuration is modeled by an abstract circuit model in which various effects, including mutual coupling and parasitic elements, are captured by a small number of measurable parameters. This technique allows us to not only eliminate the need for solving the circuit but also apply well-known signal processing techniques such as beamforming and channel estimation to inductively coupled models. For each of the three models, we derive the properties of the optimal source signal. In addition, we propose methods to design the load impedance of WPCN by taking into account the nonlinear effects due to impedance mismatches in the circuits.

This thesis purposes and develops inductively coupled LC (inductive-capacitive) pH sensors based on pH-sensitive electrode pair. The LC resonator circuit is based on a varactor and measures the low frequency potential difference. For wireless pH monitoring, the resonator circuit is integrated with a pH-sensitive electrode pair. This sensor demonstrates a linear response over 2 to 12 pH dynamic range, 0.1 pH accuracy and long-term stability. Accurate measurement of pH using electrode-based sensors is affected by temperature variation. A technique of simultaneously measuring two parameters, pH and temperature, with a single RLC resonator based sensor is presented. An algorithm is developed, which applies both pH and temperature measurement to incorporate temperature compensation in pH measurement. For in-fluid applications, an encapsulation method is applied to the LC resonator based sensor to reduce the influence of medium permittivity and conductivity on the sensor measurement. Non-invasive way to obtain reliable pH information from bacterial culture bioprocesses is demonstrated with the fluid embeddable sensor. The pH sensor is remodeled to an acidic and basic volatile sensor by embedding the electrodes in a hydrogel host electrolyte. Tests demonstrate that the volatile sensor has a detection limit of 1.5 ppm and 2 ppm for ammonia and acetic acid vapor, respectively. Application of the volatile sensor to fish spoilage monitoring shows that the sensor is capable of detecting the product rejection level with good sensitivity in real-time. It is important to develop low cost wireless passive pH sensor technologies for embedded applications such as bioprocess and food spoilage monitoring. The electrode-based passive LC sensor approach employed in this thesis overcomes drawbacks of some of the early developed passive pH sensors and can lead to an inexpensive implementation using printed electronics technology.

After nearly a decade of development, human-implantable sensors for detection of muscle activity have recently been demonstrated in the literature. The implantable sensors are powered and communicate wirelessly through the skin using coupled inductor coils. The focus of the present work has been the development of a new approach to modeling the inductively coupled link by using the finite element method (FEM) to simulate a three-dimensional representation of the coils and surrounding magnetic field. The validity of the simulation is tested by comparison to analytically-developed formulas for self-inductance, ac resistance and mutual inductance of the coils. Determination of these parameters is necessary for calculation of the coupling coefficient between the coils, and to fully define the lumped circuit model of the link. This 3D FEM approach is novel and attractive because it is able to encompass physical geometric parameters and material properties that have been traditionally been a challenge to determine. In particular the contribution of a ferrite-core, and the case of non-symmetrical relative coil positioning can be evaluated. / Graduate

In 1865 Maxwell outlined the theoretical framework for electromagnetic field propagation. Since then many important developments have been made in the field, with an emphasis on systems using high frequencies for long-range interactions. It was not until recent years that applications based on short-range inductive coupling demonstrated the advantages of using low frequency transmissions with magnetic fields to transfer power and information. This thesis investigates magnetic transmissions in the near-field and the possibility of producing induced voltages in printed circuit boards. A near-field magnetic induction system is designed to generate a magnetic flux in the very low frequency region, and used experimentally to evaluate circuit board induction in several interesting environments. The resulting voltages are measured with digital signal processing techniques, using Welch’s method to estimate the spectrum of the received voltage signal. The results show that the amount of induced voltage is proportional to the inverse cube of the transmission distance, and that the system is able to achieve a maximum induced voltage of 65 \micro V at a distance of 2.5 m and under line-of-sight conditions. It is also concluded that conductive obstructions, electromagnetic shielding and background noise all have a large impact on the obtained voltage, either cancelling the signal or causing it to fluctuate.

Made available in DSpace on 2015-03-26T13:35:22Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1377074 bytes, checksum: 9d0bcaa0daae6ad97072fe3a335f2cad (MD5) Previous issue date: 2007-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The quantum Hall effect (QHE) remains the target of an immense research effort twenty six years after its discovery. In fact this phenomenon has been a source of fundamental questions. Among the open problems in the field is the spatial distribution of the electric current in the quantum Hall effect. This question has been in debate since its discovery. Some experimental and theoretical results indicate the Hall current is distributed uniformly across the width of a Hall bar. Contradictorily, other results suggest the current flows mostly in a narrow region along the device s edges. Prominent works by Yahel et al. [PRL 76, 2149 (1996) and PRL 81, 5201 (1998)] shed new lights on the subject by using an experimental technique that came to known as inductive coupling . This method is based on the measurement of the nanovoltage signal induced by an alternating Hall current in a compact coil, carefully positioned above one edge of a Hall bar. It is perhaps the least invasive method available to study the current distribution in the QHE. It remained nonetheless a challenging experiment, as regards the positioning and making of the coil and the measurement of the minute induced voltage. We showed with calculations that it is possible to greatly simplify the aforementioned technique and make it more sensitive and useful by fabricating the coil on the chip containing the Hall bar. The concept was tested experimentally replacing the semiconductor Hall bar with a metal strip whose current distribution is known to be uniform from the electrodynamics. The voltage induced by the current in the metal strip in a nearby coil fits was measured. It fits in precisely, in magnitude and phase, with the values calculated. As our most important contribution, we found out that the presence of a two dimensional electron gas (2DEG), located 200 nm underneath the coil, increases the induced signal by thirty times. The magnitude and phase of the signal indicate it comes mostly from the current induced in the 2DEG by the alternating Hall current. This amplification effect renders a stronger signal with a sample containing a milimetric size Hall bar and a coil with ten turns, conveniently fabricated by simple optical lithography, than the signal measured by Yahel, using a ten times larger Hall bar and a handcrafted coil with 3,000 turns. We speculate that the effect of the 2DEG shall allow the use of our technique to map the current distribution in the QHE and also to study nanoscopic magnetic systems. / O efeito Hall quântico (EHQ) permanece como foco de um imenso esforço de pesquisa vinte e seis anos após sua descoberta. De fato este fenômeno tem levantado uma série de questões fundamentais. Entre os problemas em aberto nesse campo está a distribuição espacial de corrente elétrica durante o efeito Hall quântico. Esta questão tem sido continuamente debatida desde a sua descoberta. Alguns experimentos e modelos teóricos indicam que a corrente se distribui uniformemente pela largura da ponte Hall. Contraditoriamente, outros resultados sugerem que a corrente flui predominantemente nas bordas do dispositivo. Trabalhos importantes de Yahel et al. [PRL 76, 2149 (1996) e PRL 81, 5201 (1998)] trouxeram novas pistas sobre o assunto usando a técnica experimental que ficou conhecida como "acoplamento indutivo . O método é baseado na medida da tensão induzida (da ordem de dezenas de nanovolts) por uma corrente Hall alternada em uma bobina compacta, cuidadosamente posicionada acima de uma das bordas da ponte Hall. Ele é talvez o método menos invasivo disponível para estudar a distribuição de corrente no EHQ. Entretanto, trata-se de uma técnica experimentalmente desafiadora no que se refere ao posicionamento e a fabricação da bobina e a medida tênue da tensão induzida. Mostramos com cálculos que é possível simplificar grandemente a técnica mencionada e fazê-la mais sensível e útil fabricando a bobina no mesmo chip da ponte Hall. O conceito foi testado experimentalmente substituindo a ponte Hall semicondutora por uma tira metálica cuja distribuição de corrente é conhecida a priori da eletrodinâmica. Medimos a tensão induzida pela corrente na tira metálica na bobina vizinha. O resultado ajusta-se perfeitamente, em magnitude e fase, aos valores calculados. Como nossa contribuição mais importante, descobrimos que a presença de uma gás bidimensional de elétrons (2DEG), localizado a 200 nm abaixo da bobina, aumenta o sinal induzido por um fator de trinta. A magnitude e a fase do sinal indicam que ele tem origem na corrente induzida no 2DEG pela corrente Hall alternada. O efeito de amplificação fornece um sinal mais forte em uma amostra contendo uma ponte Hall com dimensão milimétrica e com uma bobina com dez voltas, convenientemente fabricada por litografia óptica, do que o sinal medido por Yahel, usando uma ponte Hall dez vezes maior e uma bobina manufaturada com 3000 voltas. Especulamos que o efeito do 2DEG poderá permitir que a nossa técnica seja usada para mapear a distribuição de corrente no EHQ e também no estudo de sistemas magnéticos com dimensões nanométricas.

The wireless charging market has seen exponential growth in recent years and wireless charging is quickly becoming the standard in consumer electronic devices to eliminate inconveniences of wired chargers. The adoption of wireless charging technology is most visible in the smartphone industry. This thesis report elicits the process involved in designing a Wireless charger that complies with the Qi- Wireless Standards set by the Wireless Power Consortium. The drawbacks of current product offerings and user needs are identified, and conceptual solutions that could strengthen the wireless charging experience are explored. The most promising solution is developed upon which results in a full-scale functional prototype.

Wireless power transfer (WPT) systems are important in many areas, such as medical, communication, transportation, and consumer electronics. The underlying WPT system is comprised of a transmitter (TX) and receiver (RX). For biomedical applications, such systems can be implemented on rigid or flexible substrates and can be implanted or wearable. The efficiency of a WPT system is based on power transfer efficiency (PTE). Many WPT system optimization techniques have been explored to achieve the highest PTE possible. These are based on either a figure-of-merit (FOM) approach, quality factor (Q-factor) maximization, or by sweeping values for coil geometries. Four WPT systems for biomedical applications are implemented with inductive coupling. The thesis later presents an optimization technique for finding the maximum PTE of a range of frequencies and coil shapes through frequency, geometry and shape sweeping. Five optimized TX coil designs for different operating frequencies are fabricated for three shapes: square, hexagonal, and octagonal planar-spirals. The corresponding RX is implemented on polyimide tape with ink-jet-print (IJP) silver. At 80 MHz, the maximum measured PTE achieved is 2.781% at a 10 mm distance in the air for square planar-spiral coils.