Due to the loose coupling nature and separated primary/secondary side, achieving tight load regulation or implementing closed-loop control of output voltage/current is nontrivial in a wireless power transfer (WPT) system. Previously presented methods for regulating or controlling the output of a WPT system include incorporating either post-regulator stage, wireless communication from secondary to primary side, primary side sensing and modulation scheme, or dual active bridge type of topology. However, all existing methods have limitations and disadvantages in terms of increased size/cost, control complexity, or reliability in electrically noisy environments. This dissertation proposes a single switch control and regulation mechanism based on the secondary side of the WPT system. Specifically, the duty cycle of the secondary side synchronous rectifier (SR) switch is modulated to control the output voltage or current. By modulating the SR duty cycle, output of the WPT system can be controlled without requiring additional regulator stages/power devices, a primary side sensing mechanism, or secondary to primary communication. The proposed control method lowers cost and simplifies the design of WPT systems while improving reliability in noisy environments. The proposed control and modulation mechanism maintains zero voltage switching of all power semiconductor switches so efficiency of the WPT system would not be compromised by implementing the proposed control scheme. The proposed secondary side SR based control method can be applied to dc-dc WPT systems to control output voltage or current, or it could be used in a dc-ac WPT system to generate and regulate ac output if combined with an unfolding stage. When used in dc-ac WPT systems, the bulky output filter stage usually required in conventional dc-ac inverters is eliminated. The proposed control scheme is evaluated with computer simulation as well as hardware implementation and testing. / Doctor of Philosophy / Wireless power transfer (WPT) is an emerging technology that supplies electric power to loads without using wires or electrical contacts. WPT technology has many promising uses in consumer, industrial, transportation, biomedical, and other applications. However, unlike controlling the output voltage of a conventional power supply or power converter, controlling the output of a WPT system is not a simple task due to the physical separation between the transmitting and receiving sides. State-of-the-art methods for controlling the output of a WPT system include adding another power regulator stage to regulate output, incorporating secondary side (power receiver) to primary side (power transmitter) communication so that output information can be passed back to the primary side where that information is used to monitor and regulate output. In some systems, output information may also be estimated indirectly from primary side voltage/current information. However, all these methods have significant disadvantages. Adding another power converter stage increases cost and efficiency loss of the WPT system. Incorporating secondary to primary communication for output control is detrimental to the reliability of the PWT system because communication may be impacted by external noise. The reliability of primary side sensing and regulation is also severely impacted by component parameter variations in the WPT system. This dissertation proposes a new mechanism that controls output of a WPT system at the receiver or secondary side without needing another power conversion stage, communication or any cooperation from primary side. The proposed control mechanism controls the turn on duration of the synchronous rectifier (SR) switch at the receiver side to modulate output voltage or current. Since SR technology is already prevalently used in power electronics systems, including WPT systems, to efficiently convert high frequency ac to dc before delivering power to the load, implementing the proposed control mechanism does not increase complexity or cost of the WPT system. The proposed control mechanism is useful in both dc-dc and dc-ac WPT systems. In a dc-dc WPT system, the proposed mechanism can control or regulate output voltage or current independently from the primary side, while in a dc-ac WPT system the proposed mechanism can generate and regulate ac output. If used in a dc-ac WPT system an unfolding stage needs to be added, but the bulky output filter stage required in conventional pulse width modulation (PWM) dc-ac inverters for suppressing switching ripple is not needed. The proposed mechanism is verified with computer simulation as well as hardware prototyping in this dissertation.

A transferência de energia sem fio (WPT) rege um importante papel no carregamento de aparelhos remotos. Em um acoplamento indutivo ressonante há várias topologias de sistemas WPT que podem ser implementados para realizar a transferência de energia. Neste trabalho é utilizado uma topologia que utiliza quatro capacitores de compensação para realizar o ajuste da potência entregue a carga, onde estes capacitores são calculados através das fixações dos demais parâmetros do circuito elétrico. Quando o sistema WPT é projetado, uma distância fixa entre as bobinas é almejada, todavia há incertezas e movimentos que podem provocar a alteração desta distância. Há várias técnicas na literatura que buscam realizar a sintonia do acoplamento indutivo para compensar estes desalinhamentos gerado entre as bobinas. Este trabalho apresenta um método multivariável para maximização da potência entregue a carga em um sistema de transferência sem fio. O método proposto utiliza os conceitos de um capacitor variável e a variação de frequência a fim de variar a potência entregue a carga. Os resultados experimentais obtidos para os fatores de acoplamento magnético k > 0;3 mostraram que controlando a frequência e uma capacitância da rede de compensação o desempenho do sistema é melhor que os casos onde apenas uma dessas variáveis é controlada. / Wireless power transfer (WPT) plays an important rule in charging remote devices. In a resonant inductive coupling there are several topologies of WPT systems that can be implemented to perform the energy transfer. In this work, a topology is used that uses four capacitors of compensation to realize the adjustment of the power delivered to load, where these capacitors are calculated through the xations of the other parameters of the electric circuit. When the WPT system is designed, a xed distance between coils is desired, however there are uncertainties and movements that may cause this distance to change. There are several techniques in the literature that seek to realize the tuning of the inductive coupling to compensate for these misalignments generated between the coils. This work presents a multivariable method to maximize the power delivered to the load in a wireless transfer system. The proposed method uses the concepts of a variable capacitor and the frequency variation in order to vary the power delivered to the load. The experimental results obtained for the magnetic coupling factors k > 0:3 showed that controlling the frequency and capacitance of the compensation network system performance is better than the cases where only one of these variables is controlled.

A transferência de energia sem fio (WPT) rege um importante papel no carregamento de aparelhos remotos. Em um acoplamento indutivo ressonante há várias topologias de sistemas WPT que podem ser implementados para realizar a transferência de energia. Neste trabalho é utilizado uma topologia que utiliza quatro capacitores de compensação para realizar o ajuste da potência entregue a carga, onde estes capacitores são calculados através das fixações dos demais parâmetros do circuito elétrico. Quando o sistema WPT é projetado, uma distância fixa entre as bobinas é almejada, todavia há incertezas e movimentos que podem provocar a alteração desta distância. Há várias técnicas na literatura que buscam realizar a sintonia do acoplamento indutivo para compensar estes desalinhamentos gerado entre as bobinas. Este trabalho apresenta um método multivariável para maximização da potência entregue a carga em um sistema de transferência sem fio. O método proposto utiliza os conceitos de um capacitor variável e a variação de frequência a fim de variar a potência entregue a carga. Os resultados experimentais obtidos para os fatores de acoplamento magnético k > 0;3 mostraram que controlando a frequência e uma capacitância da rede de compensação o desempenho do sistema é melhor que os casos onde apenas uma dessas variáveis é controlada. / Wireless power transfer (WPT) plays an important rule in charging remote devices. In a resonant inductive coupling there are several topologies of WPT systems that can be implemented to perform the energy transfer. In this work, a topology is used that uses four capacitors of compensation to realize the adjustment of the power delivered to load, where these capacitors are calculated through the xations of the other parameters of the electric circuit. When the WPT system is designed, a xed distance between coils is desired, however there are uncertainties and movements that may cause this distance to change. There are several techniques in the literature that seek to realize the tuning of the inductive coupling to compensate for these misalignments generated between the coils. This work presents a multivariable method to maximize the power delivered to the load in a wireless transfer system. The proposed method uses the concepts of a variable capacitor and the frequency variation in order to vary the power delivered to the load. The experimental results obtained for the magnetic coupling factors k > 0:3 showed that controlling the frequency and capacitance of the compensation network system performance is better than the cases where only one of these variables is controlled.

A transferência de energia sem fio (WPT) rege um importante papel no carregamento de aparelhos remotos. Em um acoplamento indutivo ressonante há várias topologias de sistemas WPT que podem ser implementados para realizar a transferência de energia. Neste trabalho é utilizado uma topologia que utiliza quatro capacitores de compensação para realizar o ajuste da potência entregue a carga, onde estes capacitores são calculados através das fixações dos demais parâmetros do circuito elétrico. Quando o sistema WPT é projetado, uma distância fixa entre as bobinas é almejada, todavia há incertezas e movimentos que podem provocar a alteração desta distância. Há várias técnicas na literatura que buscam realizar a sintonia do acoplamento indutivo para compensar estes desalinhamentos gerado entre as bobinas. Este trabalho apresenta um método multivariável para maximização da potência entregue a carga em um sistema de transferência sem fio. O método proposto utiliza os conceitos de um capacitor variável e a variação de frequência a fim de variar a potência entregue a carga. Os resultados experimentais obtidos para os fatores de acoplamento magnético k > 0;3 mostraram que controlando a frequência e uma capacitância da rede de compensação o desempenho do sistema é melhor que os casos onde apenas uma dessas variáveis é controlada. / Wireless power transfer (WPT) plays an important rule in charging remote devices. In a resonant inductive coupling there are several topologies of WPT systems that can be implemented to perform the energy transfer. In this work, a topology is used that uses four capacitors of compensation to realize the adjustment of the power delivered to load, where these capacitors are calculated through the xations of the other parameters of the electric circuit. When the WPT system is designed, a xed distance between coils is desired, however there are uncertainties and movements that may cause this distance to change. There are several techniques in the literature that seek to realize the tuning of the inductive coupling to compensate for these misalignments generated between the coils. This work presents a multivariable method to maximize the power delivered to the load in a wireless transfer system. The proposed method uses the concepts of a variable capacitor and the frequency variation in order to vary the power delivered to the load. The experimental results obtained for the magnetic coupling factors k > 0:3 showed that controlling the frequency and capacitance of the compensation network system performance is better than the cases where only one of these variables is controlled.

No description available.

Near-field wireless power transfer (WPT) technology facilitates the energy autonomy of heterogeneous systems, significantly augmenting complementary metal-oxide-semiconductor field-effect-transistor (CMOS) technology. In low-power wearable devices, existing power conditioning integrated circuits do not maximize the power factor (PF) for rectification and power conversion efficiency (PCE) due to multiple conversion. Additionally, there is no core power management for the entire power flow. The majority of the research focuses on active rectifiers, which reduce the turn-on voltage for rectification. Certain studies target the output voltage regulation via feedback to the transmitter or direct battery charging without power maximization. Firstly, this study investigates a high-power factor WPT front-end circuit that is namely the mono-periodic switching rectifier (MPSR) and implemented in a 0.18µm 1.8V/5V CMOS process. Integrated phase synchronizers are used to align the waveshape of a wirelessly-coupled sinusoidal voltage source in a receiving coil to the corresponding conducting current. Using this approach, the PF can be increased from roughly 0.6 to unity without requiring any wireless or wired feedback to the transmitter. The proposed MPSR can also provide AC-DC rectification, and step up and down the sinusoidal voltage source's peak amplitude using a pulse-width modulator. Measured voltage conversion ratios range between 0.73X and 2X, and the PF can be boosted up to unity. Secondly, the wireless power system-on-chip (WPower-SoC) is proposed and implemented in a 0.18µm 1.8V/3.3V CMOS process. The WPower-SoC integrating power management can provide rectification, output voltage regulation, and battery charging. Additionally, the implementation of feedforward envelope detection (FED) can reduce the variation in a wireless power link and improve load transient responses. Simulated results demonstrate that 5% of the output voltage regulation is improved when an output load changes. Moreover, the FED reduces approximately 40% of the transient response time. Overshoot and undershoot voltages are decreased by 23% and 26.5%, respectively. The measured output voltage regulates at 3.42V and can supply output power up to 342mW. A temperature sensor as part of the power management core remains active when the WPT receivers enter sleep mode to prolong the battery usage time. In the final part of this study, a nano-watt high-accuracy temperature sensing core is implemented in a 0.18µm 1.8V/3.3V CMOS process that can self-compensate the temperature shift without the need for additional compensating techniques that consume extra power.

This thesis is an examination of one of the main technologies to be developed on the path to Space Solar Power (SSP): Wireless Power Transfer (WPT), specifically power beaming. While SSP has been the main motivation for this body of work, other applications of power beaming include ground-to-ground energy transfer, ground to low-flying satellite wireless power transfer, mother-daughter satellite configurations, and even ground-to-car or ground-to-flying-car power transfer. More broadly, Wireless Power Transfer falls under the category of radio and microwave signals; with that in mind, some of the topics contained within can even be applied to 5G or other RF applications. The main components of WPT are signal transmission, propagation, and reception. This thesis focuses on the transmission and propagation of wireless power signals, including beamforming with Phased Array Antennas (PAAs) and evaluations of transmission and propagation efficiency. Signals used to transmit power long distances must be extremely directive in order to deliver the power at an acceptable efficiency and to prevent excess power from interfering with other RF technology. Phased array antennas offer one method of increasing the directivity of a transmitted beam through off-axis cancellation from the multi-antenna source. Besides beamforming, another focus of this work is on the equations used to describe the efficiency and far field distance of transmitting antennas. Most previously used equations, including the Friis equation and the Goubau equation, are formed by examining singleton antennas, and do not account for the unique properties of antenna arrays. Updated equations and evaluation methods are presented both for the far field and the efficiency of phased array antennas. Experimental results corroborate the far field model and efficiency equation presented, and the implications of these results regarding space solar power and other applications are discussed. The results of this thesis are important to the applications of WPT previously mentioned, and can also be used as a starting point for further WPT and SSP research, especially when looking at the foundations of PAA technology.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis proposes a reconfigurable phased array of antennas for wireless power transfer. The array finds use in many applications, from drone destruction (for defense) to wireless charging of robots and mobile devices. It utilizes a novel feeding architecture to greatly reduce the number of high cost elements (such as amplifiers and phase shifters) as well as the quantity of unused resources in the system. Upon the instruction of the CPU, the array can separate into any number of subarrays, each of which transmits power to a single receiver, steering its beam as the receiver changes location. Currently dormant elements in the array can be used to provide position information about the receivers, either via Radar, or by listening for beacons pulses from the receiver. All of this is made possible, with only 4 amplifiers and 3 phase shifters, by the proposed 4-Bus Method. The source signal is divided into four buses, which are respectively phase shifted by 270 degrees, 180 degrees, 90 degrees, and 0 degrees (no shifter required) and then amplified. The CPU calculates, based on the number and positions of the receivers / targets, what the amplitude and phase excitation must be at each element. Any phase and amplitude which could be required can be achieved by simply adding together appropriate quantities of the correct two buses. In order to achieve this, the key piece is the variable power divider. These differ from Wilkinson dividers in that the dividing ratio can be changed via an applied DC voltage. Therefore, at each junction, by properly diverting the power levels on each phase bus to their proper location, complete delocalization of both amplifiers and phase shifters can be achieved. A method has also been developed which helps overcome the limitations of each variable power divider. That is, in certain instances, it may be desirable to pass all the power to a single output port or the other, which is not a possibility inherently possible with the device. With the use of a unique combination of RF switches, the nodes achieve much enhanced flexibility. Finally, an intensive study is carried out, in an attempt to yield greater understanding, as well as quick, useful approximations, of the behaviors of both rectangular and hexagonal arrays of various sizes and beam steering angles for wireless power.

<p>The advent of resonant metamaterials with strongly dispersive behavior allowed scientists to design new electromagnetic devices -- including (but not limited to) absorbers, antennas, lenses, holograms, and arguably the most well-known of them all, invisibility cloaks -- exhibiting properties that would otherwise be difficult to obtain. At the heart of these breakthrough designs is our ability to model the behavior of individual metamaterial elements as Lorentzian dipoles, and -- in applications that call for it -- collectively model an entire array of such elements as a homogenous medium with effective electromagnetic properties retrieved from measurements or simulations. </p><p>Of particular interest in the context of this dissertation is a certain type of metamaterials elements which -- while composed entirely of essentially non-magnetic materials -- respond to a magnetic field, can be modeled as magnetic dipoles, and are able to form a material with effective magnetic response. This thesis describes how such ``magnetic metamaterials'' have been utilized by the author when designing devices for applications in wireless power transfer (WPT) and computational imaging. For the former, I discuss in the thesis a metamaterial implementation of a magnetic `superlens' for wireless power transfer enhancements, and a magnetic reflector for near field shielding. For the latter I detail how we model the imaging capabilities of a recently-introduced class of dispersive metamaterial-based leaky apertures that produce pseudo-random measurement modes, and demonstration of novel Lorentzian-constrained holograms able to tailor their radiation patterns. </p><p>To design a magnetic superlens for WPT enhancements, we first demonstrate how an array comprising resonant metamaterial elements can act as an effective medium with negative permeability ($\mu$) and enhance near-field transmission of quasi-static non-resonant coil antennas. We implement a new technique to retrieve all diagonal components of our superlens' permeability, including its normal component, which standard techniques cannot retrieve. We study the effect of different components of the $\mu$ tensor on field enhancements using analytical solutions as well as 2D rotationally-symmetric full-wave simulations which approximate the lens as a disc of equal diameter, enabling highly efficient axisymmetric description of the problem. Our studies indicate enhancements are strongest when all three diagonal components of Re$(\mu)$ are negative, which we attribute to the excitation of surface waves.</p><p>The ability to retrieve permeability's normal component, awarded to us with the implementation of the aforementioned retrieval technique, directly enabled the design of a near field magnetic shield, which -- in contrast to the tripple-negative superlens -- relies on the normal component of $\mu$ assuming values near zero. The thesis discusses the theory behind this phenomenon and explains why such an anisotropic slab is capable of reflecting magnetic fields with component of their wave vector parallel to the slab's surface (fields which contain significant portions of the energy transferred in WPT systems with dipole-like coils). Furthermore, the dispersive nature of the resonant metamaterials used to realize the shield grants us the ability to block certain frequencies while allowing the transmission of other, which can be particularly useful in certain applications; conventional materials used for shielding or electromagnetic interference (EMI) suppression, on the other hand, block frequencies indiscriminately. </p><p>The thesis also discusses a single-pixel, metamaterial-based aperture we designed for computational imaging purposes. This aperture, termed \textit{metaimager}, forms pseudo-random radiation patterns that vary with frequency by leaking energy from a guided mode via a collection of randomly distributed resonant metamaterial elements. The metaimager, then, is able to interrogate a scene without any moving parts or expensive auxiliary hardware (both are common problems which plague synthetic aperture and phased array systems, respectively). While such a structure cannot be homogenized, when modeling its imaging capabilities we still rely on the fact each of its irises can be modeled analytically as a magnetic dipole using a relatively simple Lorentzian expression. Accurate qualitative modeling of such apertures is of paramount importance in the design and optimization stages, since it allows us to save time and money by avoiding prohibitively slow full-wave simulations of such complex structures and unnecessary fabrication processes. </p><p>Lastly, the thesis discusses how such an aperture can be viewed as a hologram in which pixels are realized by the metamaterial elements and the reference wave is realized by the fields that excite them. While the current metaimager implementation produces pseudo-random modes, the last section of the thesis discusses how, by accounting for the Lorentzian constraints of each pixel, a novel metamaterial hologram can be designed to yield tailored radiation patterns. An experiment utilizing a Fraunhofer hologram excited in a free-space illumination configuration indicates tailored modes can indeed be formed by carefully choosing the resonance frequency and location of each metamaterial. While this proof-of-concept example is relatively simple, more sophisticated realizations of such holograms can be explored in future works.</p> / Dissertation

Rodents are essential models for research on fundamental neurological processing and for testing of therapeutic manipulations including drug efficacy studies. Telemetry acquisition from rodents is important in biomedical research and requires a long-term powering method. A wireless power transfer (WPT) scheme is desirable to power the telemetric devices for rodents. This dissertation investigates a WPT system to deliver power from a stationary source (primary coil) to a moving telemetric device (secondary coil) via magnetic resonant coupling. The continuously changing orientation of the rodent leads to coupling loss/problems between the primary and secondary coils, presenting a major challenge. We designed a novel secondary circuit employing ferrite rods placed at specific locations and orientations within the coil. The simulation and experimental results show a significant increase of power transfer using our ferrite arrangement, with improved coupling at most orientations. The use of a medium-ferrite-angled (4MFA) configuration further improved power transfer. Initially, we designed a piezoelectric-based device to harvest the kinetic energy available from the natural movement of the rodent; however, the harvested power was insufficient to power the telemetric devices for the rodents. After designing our 4MFA device, we designed a novel wireless measurement system (WMS) to collect real-time performance data from the secondary circuit while testing WPT systems. This prevents the measurement errors associated with voltage/current probes or coaxial cables placed directly into the primary magnetic field. The maximum total efficiency of our novel WPT is 14.1% when the orientation of the 4MFA is parallel to the primary electromagnetic field, and a current of 2.0 A (peak-to-peak) is applied to the primary coil. We design a novel controllable WPT system to facilitate the use of multiple secondary circuits (telemetric devices) to operate within a single primary coil. Each telemetric device can tune or detune its resonant frequency independently of the others using its internal control algorithm. / Graduate / 2018-04-26