General analysis on the use of tesla's resonators in domino forms for wireless power transfer

In this paper, we present a brief overview of historical developments of wireless power and an analysis on the use of Tesla's resonators in domino forms for wireless power transfer. Relay resonators are spaced between the transmitter and receiver coils with the objectives of maximizing energy efficiency and increasing the overall transmission distance between the power source and the load. Analytical expressions for the optimal load and maximum efficiency at resonance frequency are derived. These equations are verified with practical measurements obtained from both coaxial and noncoaxial domino resonator systems. To avoid the use of high operating frequency for wireless power transfer in previous related research, the technique presented here can be used at submegahertz operation so as to minimize the power loss in both the power supply and the output stage. We demonstrated both theoretically and practically that unequal spacing for the coaxial straight domino systems has better efficiency performance than the equal-spacing method. Also, the flexibility of using resonators in various domino forms is demonstrated. © 2012 IEEE.published_or_final_versio

Parameter identification of wireless power transfer systems using input voltage and current

Wireless power transfer (WPT) systems based on the use of resonators with high quality factors are highly sensitive to the parameters of the resonant tanks. While the inductance terms can be theoretically calculated, the mutual inductance terms require very accurate measurements of the coil dimensions, locations and orientations. Slight deviations of these measurements could therefore lead to significant errors. In addition, capacitors have fairly large tolerance in terms of their capacitance, making it difficult to assume their rated values in the determination of the optimal operating frequency of the WPT systems. In this paper, a parameter identification method for WPT systems based on the measurements of the input voltage and current is presented. Using an evolutionary algorithm, accurate parameter values required for modeling the WPT system can be determined. This method has been successfully illustrated in a 3-coil WPT system. Good agreements between calculated and measured parameters have been achieved. © 2014 IEEE.published_or_final_versio

Load monitoring and output power control of a wireless power transfer system without any wireless communication feedback

For mid-range wireless power applications, the load is normally far away from the power source. In this project, a new method is proposed to determine the load impedance and load power without using any direct output feedback. Based only on the information of the input voltage and current, the load impedance and load power can be monitored and controlled without using any wired or wireless feedback from the load. This new method can therefore eliminate the need for any directly measured output feedback, which was previously thought to be essential. It also makes the power control of a wireless power transfer very simple. The concept is verified by the comparison between the computed results and practical results of an 8-ring domino wireless power transfer system. A good degree of accuracy has been achieved in the verification. 2013 IEEE.published_or_final_versio

Recent progress in mid-range wireless power transfer

This is a review paper describing recent progress of mid-range applications of wireless power transfer. Starting from Tesla's principles of wireless power transfer a century ago, it outlines magneto-inductive research activities in the last decade on wireless power transfer with the transmission distance in the order of or greater than the coil dimension. It covers the basic characteristics of 2-coil systems, 4-coil systems, systems with relay resonators and the wireless domino-resonator systems. © 2012 IEEE.published_or_final_versio

A Novel Electric Insulation String Structure With High-Voltage Insulation and Wireless Power Transfer Capabilities

High-voltage insulation (HVI) strings are commonly used to hold high-voltage electric cables and electrically isolate them from the grounded transmission tower. In this paper, a novel concept of an electric insulation string with HVI and wireless power transfer (WPT) capabilities is presented. Based on the concept of the domino-resonator WPT system, this new structure consists of coil resonators embedded inside totally sealed insulation discs, which are then connected in series to form the new insulation string structure with the simultaneous HVI and WPT functions. This structure allows energy harvested from the ac magnetic field around the high-voltage cable to be transmitted wirelessly to power an online monitoring system in high-voltage transmission tower continuously, thereby reducing the storage requirements of the battery. The design and analysis of this new WPT structure based on the dimensions of commercially available HVI rod are included. Practical measurements obtained from a hardware prototype of about 25 W have been obtained to confirm the WPT capability of the proposal. An energy efficiency of more than 60% has been achieved for a transmission distance of 1.1 m over a wide range of load

A critical review of recent progress in mid-range wireless power transfer

Starting from Tesla’s principles of wireless power transfer a century ago, this critical review outlines recent magneto-inductive research activities on wireless power transfer with the transmission distance greater than the transmitter coil dimension. It summarizes the operating principles of a range of wireless power research into (i) the maximum power transfer and (ii) the maximum energy efficiency principles. The differences and the implications of these two approaches are explained in terms of their energy efficiency and transmission distance capabilities. The differences between the system energy efficiency and the transmission efficiency are also highlighted. The review covers the 2-coil systems, the 4-coil systems, the systems with relay resonators and the wireless domino-resonator systems. Related issues including human exposure issues and reduction of winding resistance are also addressed. The review suggests that the use of the maximum energy efficiency principle in the 2-coil systems is suitable for short-range rather than mid-range applications, the use of the maximum power transfer principle in the 4-coil systems is good for maximizing the transmission distance, but is under a restricted system energy efficiency (< 50%); the use of the maximum energy efficiency principle in relay or domino systems may offer a good compromise for good system energy efficiency and transmission distance on the condition that relay resonators can be placed between the power source and the load.published_or_final_versio

Novel Conformal Strongly Coupled Magnetic Resonance Systems

Wireless Power Transfer (WPT) is an emerging technology in today’s society. Recently, many advancements to WPT systems have been implemented, such as, the introduction of the Strongly Coupled Magnetic Resonance (SCMR) and Conformal SCMR (CSCMR) methods. These methods allow WPT systems to operate at increased distances with smaller dimensional footprints. However, their range is still limited and needs to be expanded, and their footprint is sometimes large and needs to be miniaturized. Therefore, the goal of this research is to develop new designs and methodologies that can achieve the range extension and miniaturization of CSCMR systems. Furthermore, many wireless devices are used today in the proximity of the human body (e.g., wearable and implantable applications). Therefore, WPT systems should be safe to use when placed on or inside the human body. To address this need, the secondary goal of this research is to study the effects of WPT systems when placed on or inside the human body

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

無線電力伝送における同時複数給電の実現と受電器の配置自由度改善に関する研究

　送受電回路に低損失の共振器を用いることで、数10cm から数m程度の無線給電を可能にする共鳴方式の無線電力伝送技術が注目されている。これまでIC カードや電子機器の充電などで実用化されている電磁誘導方式の伝送距離が数cm 程度であるのに対し、共鳴方式は数10cm を超える伝送距離を有することから、ロボット掃除機やモバイル機器、センサネットワークへの給電といったアプリケーションが期待されている。しかしながら、ロボット掃除機やモバイル機器の位置は常に一定ではないし、センサネットワークでは1対多の給電が必要となる。また共鳴方式の無線電力伝送は送受電端を整合させて使用するため、共振器間の結合度や負荷の個数が伝送効率に顕著に影響を与える。したがって、無線給電技術の実用化にあたっては、これらの制約を緩和し、複数機器への同時給電及び高い配置自由度の実現が必要不可欠である。　複数機器への同時給電という課題に対し、これまで送電部の共振器に対して並列に複数の受電側共振器を結合させ電力分配を実現する手法が報告されている。同手法はテーブル上に置かれた複数のモバイル端末に給電する用途などに適するが、センサネットワークへの給電といった用途では直列に並べた受電器に対して電力分配できることが望ましい。共鳴方式は送電側共振器と受電側共振器の間に中継共振器を配置することで電力をマルチホップさせることが可能であることが知られているが、各中継共振器に電力を分配する構成について検討された例はない。本論文では送受電共振器間に中継共振器を複数配置した無線電力伝送系に対して設定した電力分配比を実現する設計手法を提案する。また、提案手法を7 ノード，6 ホップの無線電力伝送系に対して適用し、実測評価において誤差± 1dB 以内で電力分配が実現されることを示す。　一方で受電器の配置自由度の改善という課題に対しては、大きく分け動作周波数の動的制御や可変整合回路の利用といった回路パラメータを制御する手法と、コイルの配置や構造を変えることで受電器の配置依存性を改善する手法の2 つのアプローチがとられてきた。後者の手法は、動作周波数を固定できることから法規制や他の無線通信との共存といった観点でメリットがある他、構造自体で課題を克服するため制御回路や大規模な整合回路を設ける必要がない。具体的な構成としては、無線給電を行う空間の上下に共振器を配置した閉空間に対して受電器の自由な配置を実現する構成や、複数の平面コイルを組み合わせることで水平面方向の配置自由度を改善する手法、直交するコイルを組み合わせることで受電器の角度依存性を改善する手法などが提案されている。しかしながら、共鳴方式の伝送条件に大きな影響を与える距離方向の配置自由度を、共振器構造により改善する方法については検討されていない。本論文では、水平方向に配置したコイル同士の結合と、垂直方向に配置したコイル同士の結合、導電板間の電界結合が、それぞれ距離に対して異なる分布をとることに着目し、これらを組み合わせることで距離に対する結合度変化を抑制する共振器構造を2 種類提案する。第1 の構造は垂直コイルと水平コイルを組み合わせた2 軸コイル構造であり、距離に対する結合度の変化をノイマンの公式により導出した結合度の計算式の1 階微分として表すことで、設定した距離で結合度変化が最小となるようなコイルの寸法を導出する手順を明らかにした。さらに、同手順を用いて導出した2軸コイル構造の寸法を基準に作製したプロトタイプが設計した距離で結合度変化を抑制する領域を有することを実験により示した。第2 の構造は垂直コイルの前面または背面に2枚の平板キャパシタを配置した構造であり、2 軸コイルと比較して構造の薄型化が可能である。同構造の等価回路モデルについてDifferential モードにおける結合度を表す式を導出し、2 軸コイルと同様に特定の距離において結合度変化が最小となる特性を有することを示した。さらに、作製したプロトタイプについて結合度の測定を行い、結合度変化を抑制する領域を有することを実験により示した。電気通信大学201