Smart Table Based on Metasurface for Wireless Power Transfer

Metasurfaces have been investigated and its numerous exotic functionalities and the potentials to arbitrarily control of the electromagnetic fields have been extensively explored. However, only limited types of metasurface have finally entered into real products. Here, we introduce a concept of a metasurface-based smart table for wirelessly charging portable devices and report its first prototype. The proposed metasurface can efficiently transform evanescent fields into propagating waves which significantly improves the near field coupling to charge a receiving device arbitrarily placed on its surface wirelessly through magnetic resonance coupling. In this way, power transfer efficiency of 80$\%$ is experimentally obtained when the receiver is placed at any distances from the transmitter. The proposed concept enables a variety of important applications in the fields of consumer electronics, electric automobiles, implanted medical devices, etc. The further developed metasurface-based smart table may serve as an ultimate 2-dimensional platform and support charging multiple receivers.Comment: 8 pages, 7 figure

Coupled resonator based wireless power transfer for bioelectronics

Implantable and wearable bioelectronics provide the ability to monitor and modulate physiological processes. They represent a promising set of technologies that can provide new treatment for patients or new tools for scientific discovery, such as in long-term studies involving small animals. As these technologies advance, two trends are clear, miniaturization and increased sophistication i.e. multiple channels, wireless bi-directional communication, and responsiveness (closed-loop devices). One primary challenge in realizing miniaturized and sophisticated bioelectronics is powering. Integration and development of wireless power transfer (WPT) technology, however, can overcome this challenge. In this dissertation, I propose the use of coupled resonator WPT for bioelectronics and present a new generalized analysis and optimization methodology, derived from complex microwave bandpass filter synthesis, for maximizing and controlling coupled resonator based WPT performance. This newly developed set of analysis and optimization methods enables system miniaturization while simultaneously achieving the necessary performance to safely power sophisticated bioelectronics. As an application example, a novel coil to coil based coupled resonator arrangement to wirelessly operate eight surface electromyography sensing devices wrapped circumferentially around an able-bodied arm is developed and demonstrated. In addition to standard coil to coil based systems, this dissertation also presents a new form of coupled resonator WPT system built of a large hollow metallic cavity resonator. By leveraging the analysis and optimization methods developed here, I present a new cavity resonator WPT system for long-term experiments involving small rodents for the first time. The cavity resonator based WPT arena exhibits a volume of 60.96 x 60.96 x 30.0 cm3. In comparison to prior state of the art, this cavity resonator system enables nearly continuous wireless operation of a miniature sophisticated device implanted in a freely behaving rodent within the largest space. Finally, I present preliminary work, providing the foundation for future studies, to demonstrate the feasibility of treating segments of the human body as a dielectric waveguide resonator. This creates another form of a coupled resonator system. Preliminary experiments demonstrated optimized coupled resonator wireless energy transfer into human tissue. The WPT performance achieved to an ultra-miniature sized receive coil (2 mm diameter) is presented. Indeed, optimized coupled resonator systems, broadened to include cavity resonator structures and human formed dielectric resonators, can enable the effective use of coupled resonator based WPT technology to power miniaturized and sophisticated bioelectronics

방사 무선전력전송을 위한 무지향성 안테나 및 전송 효율 한계에 대한 연구

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 남상욱.본 논문에는 방사하는 전자파를 이용한 무선 전력 전송에 대해 집중적으로 연구를 진행하였다. 보다 구체적으로는, 무지향성 안테나의 분석과 설계, 자유공간과 손실매질에서의 최적 송신 전류 분포, 전송 효율의 한계에 대한 연구를 기술하였다. 추가적으로, 전자파의 인체 영향에 대한 비교 및 이론적인 최적 전류 분포의 효과적 구현에 대한 연구를 진행하였다. 본 연구에서는 방사형 무선전력전송을 전원을 공급 유무에 따라 수동형과 능동형 무선전력전송으로 구분하고, 수동형 방사 무선전력전송부터 능동형 방사 무선전력전송까지의 연구를 순차적으로 기술하였다. 먼저, 수동형 방사 무선전력전송 연구에서는 전자파 에너지 하베스팅용 안테나에 대한 분석 및 설계에 대한 연구를 진행하였다. 수동 방사 무선전력전송의 상황을 고려하여 등방성 패턴, 전기적으로 작은 크기, 높은 효율 특성을 나타내는 안테나를 제안하였다. 전기적으로 소형이면서 등방성 패턴을 방사하는 SRR이 기본 구조로 활용되었다. SRR에 대한 이론적 분석을 진행하였고, 시뮬레이션 결과와 잘 맞는 것을 확인하였다. 분석에 기초하여 FSRR 안테나를 설계하였고, 측정을 통해 제안한 아이디어를 검증하였다. 수신 파워의 크기를 향상시키기 위해, 이중 대역 및 확장된 대역에서 동작하는 FSRR 안테나를 추가로 설계하였다. 제안된 구조는 선행연구와 비교하였을 때, 상대적으로 우수한 성능을 보여주었다. 한편 수동형 방사 무선 전력전송의 경우, 주변의 낮은 전력 밀도로 인해 수신 전력이 매우 낮은 한계점이 존재한다. 따라서, 송신 타워를 이용해 모바일 안테나로 무선 전력을 전송할 수 있는 능동형 방사 무선전력전송에 대한 후속 연구를 진행하였다. 능동형 방사 무선전력전송에서는, 송신 타워를 활용하여 모바일 기기에 효과적으로 무선전력전송을 수행하는 방법에 대한 연구를 진행하였다. 본 연구에서는 방사형 무선전력전송의 효율을 최대화 하는 송신 전류분포와 주어진 면적을 활용할 때 얻을 수 있는 최대 한계 효율을 이론적으로 도출하였다. 본 연구의 결과를 통해, 기존의 방식으로는 파악할 수 없었던 중거리 무선전력전송 효율의 최대 한계치와 송신 전류분포의 최적 형태를 파악할 수 있다. 연구의 결론에 따르면, 수신하는 안테나의 송신 방사 패턴이 효율을 결정함에 있어 중요한 역할을 하였다. 제안한 이론을 실제 안테나에 적용하여 선행연구와 비교를 하였고, 선행 연구로 파악할 수 없는 이론적 한계 효율을 도출하였다. 제안한 연구를 일반적인 상황으로 확장하기 위해 손실 매질 내부에서의 무선전력전송에 대한 추가 연구를 진행하였다. 손실 매질이 있는 경우에서도 최적 전류 분포와 효율의 최대 한계치를 도출하였다. 최적 송신 전류를 활용하여, 실제 안테나 어레이를 구현하고 인체 팬텀에 미치는 영향을 파악해보았다. 마지막으로, 앞서 도출한 이론적인 전류분포를 실제 안테나로 구현하는 방법에 대해 연구를 진행하였다. 선행 연구를 참고하여, 이상적인 전류분포를 thinned 배열로 구현하는 두가지 방법을 제안하였다. 이론적인 전류 분포에 유전 알고리즘을 활용한 방법과, density tapering을 응용한 방법을 적용하였다. 두 방법 모두 동일한 개수의 균등 어레이에 비해 성능이 개선되는 결과를 보였다. 특히 density tapering을 이용하면 같은 개수 및 같은 면적의 격자구조보다 비용, 무게, 효율 등에서 장점이 있으며, 수신기의 위치가 변할 때에도 더 높은 효율로 송신이 가능하다.In this thesis, research on the radiative-wireless power transmission (R-WPT) using radiated electromagnetic(EM) fields is presented. More specifically, the analysis and design of quasi-isotropic antennas, the analytical study on the optimal transmitting current, and the efficiency bounds are described. In addition, research on the comparison of the EM effects on the human phantom, and the effective implementation of the optimal current distribution are conducted. The research is described sequentially from the passive R-WPT to active R-WPT, which indicate the absence or presence of the power supplying base station. First, research is conducted on the analysis and design of the passive R-WPT antenna. Considering the ambient environment, an antenna with quasi-isotropic pattern, electrically small size, and high efficiency is proposed. A split-ring resonator (SRR) that radiate quasi-isotropic pattern with electrically small size is used as a basic structure. The analysis on the SRR is well matched with the simulation results. Based on the analysis, folded split-ring resonator (FSRR) is proposed and designed for the passive R-WPT antennas, and verified through the measurement. A dualband and wideband FSRR that can harvest more ambient power is designed as an extended work. The proposed antennas are compared with recent studies showing superior performances. On the other hand, the receiving power of the passive R-WPT is very low due to low power density of ambient field, a study on the active R-WPT, which can transfer wireless powers from the base station to the mobile antenna, is conducted as a next step. In the active R-WPT, a study on the way to effectively transfer wireless power to the mobile devices by using a transmitting tower is described. The optimal current distribution of the transmitting surface, and maximum power transfer efficiency (PTE) bounds when the transmitting area is limited are analytically derived. Through the results, it is possible to figure out the maximum efficiency bounds for the mid-range R-WPT and the optimal shape of transmission current distribution that could not be found by the conventional method. The results indicate that the optimum current distribution on the transmitting surface and the maximum efficiency of radiative WPT depend on the radiating field pattern of the mobile antenna. To generalize the proposed theory, an additional analysis in lossy environment is carried out. The optimal transmitting current and efficiency bound in lossy media is found for a couple of examples. The results are compared with the previous works to verify the proposed theory. Based on the results in lossy media, the EM effects on the human body is investigated. Lastly, research on the effective implementation of the theoretical current distribution as practical antenna arrays is described. Based on the previous research, two techniques that can effectively realize the ideal current are proposed in designing a thinned array. An optimization using genetic algorithm, and deterministic density tapering are applied to sample the theoretical current distribution. As a results, the proposed thinned arrays show improved performance compared to the same number of densely arranged regular arrays. In particular, the use of density tapering has advantages in cost, weight, efficiency than the same number of the regular array. In addition, it is possible to transmit wireless power with better efficiency even when the position of the receiver changes.Chapter 1. Introduction 1 1.1. Classification of Wireless Power Transmission 1 1.2. Separation of Regions 3 1.3. Passive and Active Radiative-Wireless Power Transmission 6 1.4. References 14 Chapter 2. Passive: RF Energy Harvesting Antenna 18 2.1. Motivation 18 2.2. Analytical Study on RF Energy Harvesting Antenna 19 2.2.1. Previous Research 19 2.2.2. Analysis on Split-Ring Resonator 21 2.2.3. Analysis on the Symmetric Folded Split-Ring Resonator 25 2.2.4. Analysis on the Asymmetric Folded Split-Ring Resonator 30 2.3. Design of RF Energy Harvesting Antenna 34 2.3.1. Antenna Design 37 2.3.2 Results and Discussion 44 2.4. Design of RF Energy Harvesting Antenna with Dual-band Operation 45 2.4.1. Motivation 45 2.4.2 Antenna Design 45 2.4.3. Results and Discussion 48 2.5. RF Energy Harvesting Antenna with Wide-band Operation 53 2.5.1. Motivation 53 2.5.2 Antenna Design 54 2.5.3. Results and Discussion 57 2.6. Conclusion 65 2.7. References 69 Chapter 3. Active: Radiative-WPT in Lossless Medium 73 3.1. Motivation 73 3.2. Previous Research 73 3.3. Theoretical Approach 77 3.3.1. Power Transfer Efficiency 77 3.3.2. Optimum Transmitting Current 80 3.3.3. Minimizing Transmitting Area 84 3.4. Numerical Examples 86 3.3.1. Dipole Antenna 88 3.3.2. Patch Antenna 90 3.3.3. Horn Antenna 91 3.5. Results and Discussion 93 3.5. Conclusion 98 3.6. References 99 Chapter 4. Active: Radiative-WPT in Lossy Media 103 4.1. Motivation 103 4.2. Previous Research 103 4.3. Theoretical Approach 106 4.3.1. Problem Formulation 108 4.3.2. Maximum Power Transfer Efficiency 110 4.4. Practical Examples 114 4.4.1. Planar Inverted-F Antenna 116 4.4.2. Half-Mode Cavity-Backed Antenna 120 4.5. Electromagnetic Human Exposure in Radiative WPT System 125 4.5.1. Motivation 125 4.5.2. Simulation Results 126 4.6. Conclusion 132 4.7. References 134 Chapter 5. Active: Implementation of Optimal Transmitting Current Distribution 138 5.1. Motivation 138 5.2. Theoretical Approach 139 5.2.1. Radiation Pattern Matching 139 5.2.2. Optimal Excitation Coefficient 141 5.2.3. Thinning of Transmitting Array 141 5.3. Implementation of the Optimal Current Sheet 145 5.3.1. Array Thinning using Genetic Algorithm 145 5.3.2. Results and Discussions 148 5.3.3. Array Thinning using Density Tapering 151 5.3.4. Results and Discussions 154 5.4. Conclusion 158 5.5. References 159Docto

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

Analysis and practical considerations in implementing multiple transmitters and receivers for wireless power transfer via coupled magnetic resonance

The technology to wirelessly power mobile devices has started to gain momentum especially in industry. Cables have started to become the thing of the past as both wireless power efficiency and communication speeds become viably attractive. The first part of this work gives analysis and practical considerations in implementing multiple transmitters for wireless power transfer via coupled magnetic resonance. Through the multiple transmitter scheme, there is an increase in gain and `diversity\u27 of the transmitted power according to the number of transmit coils. The effect of transmitter resonant coil coupling is also shown. Resonant frequency detuning due to nearby metallic objects is observed and the extent of how much tuning can be done is demonstrated. A practical power line synchronization technique is proposed to synchronize all transmit coils. This reduces additional dedicated synchronization wiring or the addition of an RF front end module. The second part of this study introduces a time division multiplexing (TDM) technique for tightly coupled receivers via the same method of coupled magnetic resonance. Two or more receivers can be powered simultaneously using a single transmit coil. In a tightly coupled receiver scenario, the received power is significantly reduced. Experimental and simulation results implementing TDM show vast improvements in received power in the tightly coupled case. Resonant frequency splitting is eliminated through synchronized detuning between receivers, which divide power equally between receivers at specific time slots. The last chapter gives insight on the capacity of a single-input single-output system at varying distances between receiver and transmitter. It is shown that the highest information rate is achieved at critical coupling

Wireless Power Transfer Technology for Electric Vehicle Charging

In the years 1884-1889, after Nicola Tesla invented "Tesla Coil", wireless power transfer (WPT) technology is in front of the world. WPT technologies can be categorized into three groups: inductive based WPT, magnetic resonate coupling (MRC) based WPT and electromagnetic radiation based WPT. MRC-WPT is advantageous with respect to its high safety and long transmission distance. Thus it plays an important role in the design of wireless electric vehicle (EV) charging systems. The most significant drawback of all WPT systems is the low efficiency of the energy transferred. Most losses happen during the transfer from coil to coil. This thesis proposes a novel coil design and adaptive hardware to improve power transfer efficiency (PTE) in magnetic resonant coupling WPT and mitigate coil misalignment, a crucial roadblock to the acceptance of WPT for EV. In addition, I do some analysis of multiple segmented transmitters design for dynamic wireless EVs charging and propose an adaptive renewable (wind) energy-powered dynamic wireless charging system for EV

General Analysis of Resonance Coupled Wireless Power Transfer (WPT) Using Inductive Coils

In this paper, parameter analysis of the inductive coils is evaluated for low power Wireless Power Transfer (WPT) applications. Inductive coils are the major element used in the WPT systems, in which different shaped coils are employed. The selection of coils is very critical, depends purely on the fundamental characteristics (shape and geometry) of the coils. In order to design a better system, three different shapes of coils, namely, circular, square and rectangular are designed and analysed. The vital parameters such as self-inductance, mutual inductance, quality factor, magnetic field and efficiency are evaluated for all three coils. It is observed that these parameters are maximal for circular as compared to the other two shapes. The circular coils produce higher voltage efficiency of 29% as compared to rectangular (25%) and square (23%) shaped coils. Thus, this paves a way to other researchers to suitably select circular inductive coils for wireless electricity applications

Harvesting Energy of Radio Frequency

Renewable Energy sources are the center of attraction for research and development all over the world nowadays. Oil and Gas are no more the main source of Energy, consequently the demand of a lasting cheap source of energy that is environmental friendly, is the main challenge recently. During the last decade, power consumption has decreased opening the field for energy harvesting to become a real time solution for providing different sources of electrical power. Energy Harvesting is a new technology that is going to make a revolution in the coming decade. Energy Harvesting is a technique to provide alternative sources of energy that are environmental friendly and low in cost. Radio Frequency Energy Harvesting is one of the methods to provide electrical energy from the ambient Radio Frequency Energy that already exists in the environment. For example Hand phones can be directly charged from Radio frequencies in the environment like 915 MHz. Laptops can be charged by frequencies like 2.45 GHz. RFID passive tags can be powered by these radio frequencies without the supply of any batteries increasing the range of passive RFID tags to longer distances with lower cost. Radio Frequency Energy Harvesting can provide a world with batteryless devices. With RF Energy Harvesting, the true mobility can be achieved where mobile devices do not depend on centralized power sources for charging. Instead they make use of the existing energy in the environment

Improving the mechanistic study of neuromuscular diseases through the development of a fully wireless and implantable recording device

Neuromuscular diseases manifest by a handful of known phenotypes affecting the peripheral nerves, skeletal muscle fibers, and neuromuscular junction. Common signs of these diseases include demyelination, myasthenia, atrophy, and aberrant muscle activity—all of which may be tracked over time using one or more electrophysiological markers. Mice, which are the predominant mammalian model for most human diseases, have been used to study congenital neuromuscular diseases for decades. However, our understanding of the mechanisms underlying these pathologies is still incomplete. This is in part due to the lack of instrumentation available to easily collect longitudinal, in vivo electrophysiological activity from mice. There remains a need for a fully wireless, batteryless, and implantable recording system that can be adapted for a variety of electrophysiological measurements and also enable long-term, continuous data collection in very small animals. To meet this need a miniature, chronically implantable device has been developed that is capable of wirelessly coupling energy from electromagnetic fields while implanted within a body. This device can both record and trigger bioelectric events and may be chronically implanted in rodents as small as mice. This grants investigators the ability to continuously observe electrophysiological changes corresponding to disease progression in a single, freely behaving, untethered animal. The fully wireless closed-loop system is an adaptable solution for a range of long-term mechanistic and diagnostic studies in rodent disease models. Its high level of functionality, adjustable parameters, accessible building blocks, reprogrammable firmware, and modular electrode interface offer flexibility that is distinctive among fully implantable recording or stimulating devices. The key significance of this work is that it has generated novel instrumentation in the form of a fully implantable bioelectric recording device having a much higher level of functionality than any other fully wireless system available for mouse work. This has incidentally led to contributions in the areas of wireless power transfer and neural interfaces for upper-limb prosthesis control. Herein the solution space for wireless power transfer is examined including a close inspection of far-field power transfer to implanted bioelectric sensors. Methods of design and characterization for the iterative development of the device are detailed. Furthermore, its performance and utility in remote bioelectric sensing applications is demonstrated with humans, rats, healthy mice, and mouse models for degenerative neuromuscular and motoneuron diseases