Projects (Selected)


Multimode Quasistatic Cavity Resonators

Wireless power transfer (WPT) using quasistatic cavity resonators (QSCR) proposed a route towards truly ubiquitous WPT, which allows devices to be safely charged as they enter a WPT enabled space. However, there are still several drawbacks to this approach such as the need for a conductive pole in the middle of the cavity and the non-uniform magnetic field intensity. To address these issues, this study proposes multimode QSCR, which enables pole-less operation and control of magnetic field distribution.


(a) and (b) show the current of the two resonant modes of the multimode-QSCR. (c) shows the "efficiency vs position" plot in single mode operation (conventional method), whereas (d) shows the "efficiency vs position" plot in dual mode operation (proposed method).

  1. T. Sasatani, M. J. Chabalko, Y. Kawahara, and A. P. Sample, “Multimode Quasistatic Cavity Resonators for Wireless Power Transfer,” IEEE Antennas and Wireless Propagation Letters, vol. 16, pp. 2746-2749, 2017. [PDF]
  2. T. Sasatani, A. P. Sample, and Y. Kawahara, “Demo: 3-D Wireless Charging for Indoor Electronics Using Multimode Quasistatic Cavity Resonators,” Adjunct Proc. of ACM Ubicomp 2018, Singapore, Oct. 2018. (To Appear)
  3. T. Sasatani, and Y. Kawahara, “Multimode Quasistatic Cavity Resonators for Wireless Power Transfer: Towards Empowering Freely Moving Animal Experiments in 3-D Environments,” International Symposium on Systems Science of Bio-Navigation 2018, To Appear, Kyoto, Japan, Sept. 2018.
  4. 笹谷拓也,川原圭博,“三次元無線電力伝送のためのMultimode Quasistatic Cavity Resonatorの実装,” 電子情報通信学会 ソサイエティ大会,Sept. 2018.(発表予定)

Alvus: A Reconfigurable 2-D Wireless Charging System

Under Construction
Wireless charging pads such as Qi are rapidly gaining ground, but its limited power supply range still requires precise placement on a specific point.2-D wireless power transfer (WPT) sheets consisting of coil arrays are one well-known solution for this issue. However, these approaches require custom-made designs by experts; what we need is a WPT system that can be reconfigured by simply placing ready-made modules on the intended surface (i.e., table, floor, shelf board, etc). In this paper, we present "Alvus", a reconfigurable 2-D WPT system which enables such simple construction of WPT surfaces.
Our system is based on multihop WPT, which constructs "virtual power codes" and consists of three types of ready-made resonator modules: (i) transmitter, which outputs energy, (ii) relays, which passes down energy to the next module, and (iii) receivers, which receives energy and charges the load; we show that power can be transferred efficiently (over 25%) within a range of 19.6 square meters using a single transmitter. We implemented an end-to-end WPT system and demonstrated that Alvus is capable of intuitive construction/reconfiguration of WPT surfaces, as well as automatically deciding the power routes based on the sensed information (e.g., receiver location, module placement, obstructive objects).

  1. K. Sumiya, T. Sasatani, Y. Nishizawa, Y. Narusue, K. Tsushio, Y. Kawahara, “Demo: A Reconfigurable 2-D WirelessCharging System,” Adjunct Proc. of ACM Ubicomp 2018, Singapore, Oct. 2018. (To Appear)
  2. Y. Narusue, A. Hashizume, T. Sasatani, X. Shi, Y. Mizutani, Y. Kawahara, and T. Asami, “Indoor Wireless Power Transfer,” TECO Green Tech Contest 2016, Taipei, Taiwan, Aug. 2016.
  3. 角谷和宣,西澤勇輝,笹谷拓也,橋詰新,成末義哲,川原圭博,“二次元共振器アレイを用いた給電領域を自由に変更可能な無線給電システムの構成,” 電子情報通信学会 総合大会,B-18-15,March 2018.

Cuttable Wireless Power Transfer Sheet

Under Construction
We propose a cuttable wireless power transfer sheet which allows users to modify its size and shape. This intuitive manipulation allows the users to easily add wireless power transmission capabilities to everyday objects. The properties of the sheet such as thinness, flexibility, and lightness make our sheet highly compatible with various configurations. The sheet includes H-tree wiring that allows the sheet to remain functional even when cut from the outside of the sheet. To show its feasibility, we present three applications in the combinations of our sheet and daily objects: wireless charging furniture, bag, and jacket.

  1. R. Takahashi, T. Sasatani, F. Okuya, Y. Narusue, Y. Kawahara, “Demo: Design of Cuttable Wireless Power Transfer Sheet,” Adjunct Proc. of ACM Ubicomp 2018, Singapore, Oct. 2018. (To Appear)
  2. 高橋亮,笹谷拓也,奥谷文徳,成末義哲,川原圭博,“切断により形状の変更が可能な無線電力伝送シートの設計の一検討,” 電子情報通信学会 総合大会,B-21-19,March 2018.

Genetic Algorithm-Based Design of Receiving Resonator Arrays

Resonator design methods play an important role in realizing efficient wireless power transfer via magnetic resonant coupling (WPT-MRC) systems. In WPT-MRC systems, transmitting (Tx) resonator arrays are often used to extend the range of the power supply. However, it is difficult to design a receiving (Rx) resonator that prevents significant drops in transfer efficiency across the Tx resonator array owing to the complexity that stems from fluctuating coupling coefficients. In order to resolve this difficulty, this paper proposes a genetic algorithm-based Rx resonator array design method. Using the proposed design method, the computed minimum transfer efficiency of a power supply system using a Tx resonator array increased from 3.8% to 42.6%, and the computed results were verified by simulations and measurements.


(a) An receiver resonator array designed by the proposed method. (b) The transmitter array to mobile device wireless power system premised in the study. (c) The circuit model used in our proposed method.

  1. T. Sasatani, Y. Narusue, Y. Kawahara, and T. Asami, “Genetic Algorithm-Based Design of Receiving Resonator Arrays for Wireless Power Transfer via Magnetic Resonant Coupling,” Proceedings of IEEE Wireless Power Transfer Conference (WPTC) 2016, pp. 1-4, Aveiro, Portugal, May 2016.
  2. 笹谷拓也,成末義哲,川原圭博,浅見徹,”磁界共振結合型無線電力伝送における遺伝的アルゴリズムを用いた受電共振器アレイの設計,” 電子情報通信学会 総合大会,B-21-22,March 2016.
  3. 笹谷拓也,成末義哲,川原圭博,浅見徹,”送電共振器アレイを用いた無線電力伝送における給電効率向上のための受電共振器アレイ形状の検討,” 電子情報通信学会 ソサイエティ大会,B-21-6,Sept. 2015.

Dynamic Complex Impedance Conversion Using Multiple-Input DC/DC Converters

The performance of a wireless power transfer (WPT) system is highly dependent on the complex impedance of the receiver (RX). Therefore, dynamic complex impedance tuning methods are critical pieces for gaining sufficient control over WPT systems. However, prior methods cannot achieve the following three requirements simultaneously: high-frequency (i.e., MHz, GHz) operation, continuous complex impedance tuning, and few additional components. To overcome these challenges, we present a dynamic complex impedance tuning method based on multiple-input DC/DC converters and LC filters. The active operations used in our method are closed in the low-frequency (i.e., after-rectification) region of the circuit; it has the promise of achieving the three above-mentioned requirements.

(a) shows the circuit topology of the proposed impedance conversion mechanism. (b) and (c) are the converted impedance plotted on a complex plane ((b) conventional method, (c) proposed method). It can be seen that the proposed method can convert the impedance freely on a "plane" within complex plane, whereas the conventional method can only move within a single "line".

  1. T. Sasatani, Y. Narusue, and Y. Kawahara, “Dynamic Complex Impedance Tuning Method Using a Multiple-Input DC/DC Converter for Wireless Power Transfer,” Proceedings of IEEE Wireless Power Transfer Conference (WPTC) 2018, To Appear.
  2. 笹谷拓也,成末義哲,川原圭博,“無線電力伝送のための DC/DC コンバータを用いた複素インピーダンス変換手法についての一検討,” 電子情報通信学会 総合大会,B-21-2,March 2018.


Passive and Contactless Epidermal Pressure Sensor Printed with Silver Nano-particle Ink

In this project, we propose a passive and contactless epidermal pressure sensor patch printed on a paper substrate with silver nano-particle ink. This disposable patch can be used to measure the pressure between the clothes and the human body. Different from the conventional pressure sensors, the pressure can be measured wirelessly without disturbing the motion of the users. The sensor circuit pattern is printed by a conductive inkjet printer and the sensor’s pressure value is detected by a reader coil through the change of the capacitance of an LC resonant circuit. We propose a sensor design method that minimizes the effect of the human body. We demonstrate our sensor patch by measuring the pressure exerted by compression garments whose pressure distribution is important for the wearer’s health.

衣服や靴などの適切なフィット感の提示や筋肉疲労の軽減の効果があるとされるcompression garmentsの研究用途を目的とし,衣服を着た時に体表面に加わる圧力である着圧を,無電源・非接触で服の上から読み取ることのできる圧力センサの提案・設計・実装を行った.センサは導電性インクを用いて印刷により形成され,共振回路のキャパシタンス成分の変化として圧力の変化を非接触コイルで読み取る.人体に貼り付けても圧力計測を行えるセンサ設計手法を提案し,衣服において最も着圧が重要となるcompression garmentsの着圧を計測することで実用性を確認した.

(a) The implemented printed pressure sensor. (b) Measurement of the pressure of compression garments using our proposed sensor. (c) Resonant frequency shift induced by the change in pressure.

    1. T. Hashizume, T. Sasatani, K. Narumi, Y. Narusue, Y. Kawahara, and T. Asami, “Passive and Contactless Epidermal Pressure Sensor Printed with Silver Nano-particle Ink,” Proceedings of ACM International Joint Conference on Pervasive and Ubiquitous Computing (UbiComp) 2016, pp. 190-195, Heidelberg, Germany, Sept. 2016.
    2. 橋爪崇弘,笹谷拓也,成末義哲,川原圭博,浅見徹,”銀ナノインクを用いた非接触読み取り可能なパッシブ型静電容量式圧力センサと着圧測定への応用,” マルチメディア,分散,協調とモバイル (DICOMO2017) シンポジウム,4G-1,pp.840-845, July 2016.
    3. 橋爪崇弘,笹谷拓也,成末義哲,川原圭博,浅見徹,”銀ナノインクを用いたパッシブ型圧力センサの人体貼付用途における設計手法,” 電子情報通信学会 総合大会,B-18-17,March 2016.