Maximizing Air Gap and Efficiency of Magnetic Resonant Coupling for Wireless Power Transfer Using Equivalent Circuit and Neumann Formula

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < Maxiizing Air Gap and Efficiency of Magnetic Resonant Coupling for Wireless Power Transfer Using Equivalent Circuit and Neuann Forula Takehiro Iura, Meber, IEEE and Yoichi Hori, Fellow, IEEE Abstract The progress in the field of wireless power transfer in the last few years is rearkable. With recent research, transferring power across large air gaps has been achieved. Both sall and large electric equipent has been proposed, e.g., wireless power transfer for sall equipent (obile phones and laptops) and for large equipent (electric vehicles). Furtherore, replacing every cord with wireless power transfer is proposed. The coupled ode theory was proposed in 6 and proven in 7. Magnetic and electric resonant coupling allows power to traverse large air gaps with high efficiency. This technology is closely related to electroagnetic induction and has been applied to antennas and resonators used for filters in counication technology. We have studied these phenoena and technologies using equivalent circuits,- which is a ore failiar forat for electrical engineers than the coupled ode theory. In this study, we analyzed the relationship between axiu efficiency air gap using equivalent circuits and the Neuann forula and propose equations for the conditions required to achieve axiu efficiency for a given air gap. The results of these equations atch well with the results of electroagnetic field analysis and experients. Index Ters wireless power transfer, resonance frequency, axiu efficiency R I. INTRODUCTION earkable progress has been ade in the field of wireless power transfer, and this technology has been attracting a lot of attention. The progress in the field of wireless power transfer in the last few years shows that traversing larger air gaps with high efficiency is ore probable than with previous technologies. Many types of electronic equipent have been proposed for wireless power transfer, e.g., obile phones [] and laptops [], which have secondary batteries, and lighting and TV sets that do not have secondary batteries and thus Manuscript received January,. Accepted for publication January,. Copyright 9 IEEE. Personal use of this aterial is peritted. However, perission to use this aterial for any other purposes ust be obtained fro the IEEE by sending a request to pubs-perissions@ieee.org T. Iura is with the Graduate School of Frontier Sciences, The University of Tokyo, 5--5 Kashiwanoha, Kashiwa, Chiba 77-856, Japan (e-ail: iura@hori.k.u-tokyo.ac.jp) Y. Hori is with the Departent of Advanced Energy, Graduate School of Frontier Sciences, The University of Tokyo, 5--5 Kashiwanoha, Kashiwa, Chiba 77-856, Japan (e-ail: hori@k.u-tokyo.ac.jp). require continuous power supply. The direct feeding ethod can be used for wireless power transfer with all electrical equipent. Thus, an on-the-go rechargeable society where the wires in the house are replaced with autoatic wireless power transfer can be realized. Of course, this technology can be used outside of the house too. It is possible to use wireless power transfer for charging electric bicycles and electric vehicles [3]-[] in the parking area. Furtherore, it is proposed that electric vehicles and electric trains in otion and robots []-[3] can be charged wirelessly [4]-[6]. This technology does not depend on the equipent size. Therefore, any equipent that uses electricity can be fed wirelessly [7]. It is iportant to achieve the transfer of power over large air gaps with a high efficiency to ake this kind of society possible. At present, there is no such technology. Microwave power transfer [9][] or laser power transfer [8] can be achieved across air gaps larger than a few kiloeters; however, it is still not possible to do so with high efficiency. In typical electroagnetic induction, which is a type of nonradiative power transfer, the air gap can be only a few centieters. Recently, the air gap has been increased to around c at 4 khz. However, a longer distance is required for an on-the-go rechargeable society [9]. For this purpose, wireless power transfer over is required. Moreover, the efficiency of electroagnetic induction drops when there is isalignent and becoes alost zero even if the isalignent is only a few centieters. To use wireless power transfer anywhere one ight want, conventional electroagnetic induction is not suitable. Therefore, an electroagnetic resonant coupling technology is proposed. In this technology, power is transitted wirelessly with high efficiency across large air gaps. The efficiencies are above approxiately 9% within and 45% 5% within. This is called WiTricity and was proposed theoretically in 6 and confired experientally in 7 [][]. It has been reported that ultiple receivers can be powered wirelessly by agnetic resonant coupling []. This ight lead us to an on-the-go society. In papers [] and [], the phenoenon of electroagnetic resonant coupling has been explained in great detail; however, the theory is based on the coupled ode theory, which ost people are not failiar with. Fro an electrical engineering perspective, electric circuits are required for the design of the antenna itself and the circuit connected to the antenna. Electroagnetic resonant coupling is closely related

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < to electroagnetic induction, which uses nonradiative power transfer, antennas, and resonators for filters used in counication technologies [3] [6]. We have studied the effect of changing the paraeters of antennas for agnetic resonant coupling [7] and designed equivalent circuits for both agnetic and electric resonant couplings [8]. In this paper, we derive equations for the relationship between axiu efficiency and air gap using equivalent circuits and the Neuann forula and present electroagnetic field analysis and experiental results. II. CHARACTERISTICS OF MAGNETIC RESONANT COUPLING Wireless power transfer can be achieved using agnetic resonant coupling when the transitting and receiving antennas are in resonance and the resonance frequency of the receiving and transitting antennas are the sae. This allows transfer of power across large air gaps with high efficiency. Wireless power transfer is achieved using agnetic field couplings that are nonradiative. Therefore, the radiation produced is negligible. A helical antenna is an open-type antenna, which is self-resonant using self-inductance and capacitance, and a short-type antenna, which has separate excitation using self-inductance and an installed capacitor [9]. In this paper, the short-type antenna, which needs a capacitor, is used. Magnetic resonant coupling uses an antenna that is in resonance and has a very high Q-value; its efficiency is easily influenced by air gaps, utual influence, and ipedance of the antenna. In this chapter, we will study the frequency and efficiency using electroagnetic field analysis for varying lengths of the air gap. Air gap The proposed short-type helical antennas, which are used as the odel used for the electroagnetic field analysis, are shown in Fig.. These antennas coprise of two eleents, and the transitting and receiving antenna are the sae. The paraeters of these antennas and the experiental setup are shown in Fig.. A vector network analyzer (VNA) is used to easure the transission and reflection ratio of the syste. The transission equation () and the relationship between transission and efficiency of transission, as given by equation (), indicates the efficiency of power transfer. The equation for power reflection is defined in (3). The relationship between frequency the efficiency of wireless power transfer is studied using electroagnetic field analysis by varying the length of the air gap. The ethod of oents is used in the electroagnetic field analysis. The distance of the air gap is varied between 49, 8, 7, and 357 in the efficiency vs. frequency plots shown in Fig.4. The characteristic ipedance is 5 Ω. The power is output fro port and flows fro the transitting antenna across the air gap to the receiving antenna and enters through port, which is the transitting power. The efficiency is represented by η. A portion of the power is reflected back to port ; the ratio of reflected power is denoted as η. When g 49 or 8 (sall gaps), efficient power transfer is possible at the two resonance frequencies [f, f e (f < f e )]. Most of the power that is not transferred is reflected back to port. Most of the power that is neither transferred nor reflected is lost in internal resistance. Thus, there is little radiation and it can be ignored. As the air gap is increased fro g 49 to g 8, the two resonance frequencies becoe alost equal. When the air gap is increased to g 7, the two resonance frequencies becoe equal and the efficiency at the resonance frequency is the sae as that for sall air gaps. The single resonance frequency is the sae as the self resonance frequency of a single antenna. As the air gap further increases to g 357, the efficiency at the resonance frequency reduces. These results are plotted in detail in Fig.5, which shows the relationship between efficiency and length of the air gap at resonance frequencies. Fig.5 also shows that, as the length of the air gap increases, the two resonance frequencies becoe equal at g 7 with high efficiency. Then, the efficiency worsens. In this paper, the conditions in which the two resonance frequencies becoe equal and the efficiency changes are analyzed and discussed. Fig.. Model of helical antennas used for electroagnetic field analysis. (g 7 ) S jl Z ω ( ω ) () L ω + ( Z + R) + j ωl ωc η S () η S 3(3) The nuber of turns in the antennas is one, and a capacitor is installed in series. The radius R is 5, and the length of the air gap is denoted as g. Fig.. Paraeters of helical antennas and experiental setup.

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 3 µ ( ) π π r cos θ θ L dθdθ 5(5) 4π r + g r cos( θ θ ) The coupling coefficient k is defined in equation (6); k is related to two resonance frequencies when the characteristic ipedance is and the internal resistance R is (Fig.6). Equation (7) shows that utual inductance L is obtained fro the division of self inductance L and the coupling coefficient k. Fig.3. Photograph of experiental setup. (g 7 ) 8 6 4 3 4 5 6 7 Frequency (a) g 49 8 6 4 3 4 5 6 7 Frequency (c) g 7 8 6 4 3 4 5 6 7 Frequency 8 6 4 (b) g 8 η η 3 4 5 6 7 Frequency (d) g 357 Fig.4. Results of electroagnetic field analysis for efficiency vs. frequency at different gap lengths. η 8 6 4 3 4 5 6 7 8 Fig.5. Results of electroagnetic field analysis for peak efficiency vs. air gap length. III. AIR GAP AND MUTUAL INDUCTANCE USING NEUMANN FORMULA The utual inductance L of coils of one turn is given by equations (4) and (5), i.e., the Neuann forula [3][7]. D is the distance between dl and dl. Mutual inductance becoes large as the radius of the coil and the nuber of turns is increased. In this paper, the nuber of turns is one and the radius is 5. L µ π 4 C C dl dl D 4(4) e e ω ω k 6(6) ω + ω L k L kl 7(7) L The theoretical result, as obtained fro the Neuann forula, and the electroagnetic result, as obtained fro the ethod of oents, are shown and copared in Fig.7. The results are the sae. The utual inductance is inversely proportional to the length of the air gap. k L [nh].8.6.4. 3 4 5 6 7 8 6 5 4 3 Fig.6. Coupling coefficient k vs. gap length. Neuann forula Electroagnetic field analysis 4 6 8 Fig.7. Optiized paraeters of utual inductance and characteristic ipedance in relation to axiu efficiency for different air gap lengths. IV. THEORY OF AIR GAP AND MAXIMUM EFFICIENCY In the previous sections, we have studied agnetic resonant couplings using electroagnetic field analysis; however,

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 4 (a-) Ω, (a-) Ω, 49 (5) (a-3) Ω, 8 (a-4) Ω, 7 (a-5) Ω, 357 (36) (b-) 5 Ω, (b-) 5 Ω, 49 (5) (b-3) 5 Ω, 8 (b-4) 5 Ω, 7 (b-5) 5 Ω, 357 (36) η 5 η 5 η 5 η 5 η 5 3 5 7 3 5 7 3 5 7 3 5 7 3 5 7 (c-) Ω, (c-) Ω, 49 (c-3) Ω, 8 (c-4) Ω, 7 (c-5) Ω, 357 Fig.9. Efficiency and frequency at characteristic ipedance and different air gap lengths using equivalent circuit and experiental results. The paraeters are characteristic ipedance [Ω] and air gap length [] of theoretical and experiental results. For the case when the paraeters of the equivalent circuit are different fro those of the experient, the experiental paraeters are added within parentheses. Bold lines denote the theoretical results, and fine lines denote results of the experients. agnetic resonant coupling can also be explained by the theory of equivalent circuits. Wireless power transfer using agnetic resonant coupling is achieved when the transitting and receiving antennas are in resonance. The resonance is twofold; one resonance is self resonance, being driven by the self inductance and parasitic- and self-capacitance of the antenna, and the other is external, separated, excited resonance, being driven by the self-inductance of the antenna with the installed capacitance. Antennas can be replaced with their equivalent circuit; the antenna and the phenoenon of electroagnetic resonant coupling can be represented by the series resonance of L and C, as shown in Fig.8. In this paper, the sae antennas are used for transitting and receiving so that the paraeters of L and C are the sae in the equivalent circuit and the electroagnetic field analysis. The self inductance L of the antennas is 5 nh, internal resistance R is. Ω, and installed capacitance C is 4 pf in both the equivalent circuit and the electroagnetic field analysis. In the experient, L of the transitting and receiving antennas is 37 nh and 5 nh, internal resistance R is.48 Ω and.46 Ω, and installed capacitance C is 39 pf and 38 pf, respectively. (a) Equivalent circuits of agnetic resonant coupling of two antennas (b) Equivalent circuit of T-type coupling. Fig.8. Equivalent circuit of two antennas in agnetic coupling.. Characteristic Ipedance and Air Gaps In the previous section, only the characteristics for varying lengths of the air gap were studied; here, we also study the characteristic ipedances (which are due to the circuits that are connected to the antennas) are exained. The results of efficiency vs. frequency easureents for varying air gap lengths and characteristic ipedances fro equivalent circuit analysis and experient are shown in Fig.9. That is, we changed other characteristics for a given, fixed air gap length. The characteristic ipedances are changed fro Ω to 5 Ω to Ω. The length of the air gap is varied between, 49, 7, and 357. The results are shown in Fig.9 (a-) (a-5), (b-) (b-5), and (c-) (c-5). At each characteristic ipedance, as the air gap length increases, the two resonance frequencies coe closer together and becoe one resonant frequency. Until the two resonance frequencies becoe equal, the efficiency of the power transfer reains constant at a high level. After they have fored one resonant peak, as the air gap length increases, the efficiency of power transfer worsens. In this situation, the efficiency of the power transfer becoes higher if the characteristic ipedance is higher; however, the air gap length is very sall. On the other hand, the efficiency is lower at the lower characteristic ipedance when the air gap length is very large. The situation in which the characteristic ipedances are changed (with a fixed air gap length) is exained in Fig.9. Results for air gap lengths of 49, 7, and 357 are shown in Fig.9 (c-), (b-), (a-); Fig.9 (c-4), (b-4), (a-4); and Fig.9 (c-5), (b-5), (a-5). Data when the air gap length is 7 (which is between g 49 and 357 ), as shown in Fig.9(c-4), (b-4), (a-4), indicate that when the characteristic ipedance is low ( Ω) the nuber of resonance frequencies is two and the efficiency is not axiized. At this

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 5 air gap length, when the characteristic ipedance is 5 Ω, the values of resonance frequency becoe equal and the efficiency for this air gap length is at its axiu. Furtherore, as the characteristic ipedance increases to Ω, the efficiency worsens at the equal resonant frequency. This indicates that, as the characteristic ipedance increases, the two resonance frequencies becoe equal and the efficiencies at resonance are iproved to their axiu for a given air gap length. After that point, as the characteristic ipedance becoes even larger, the efficiency at the equal resonance frequency worsens. When the air gap length is sall (g 49 ) it can be shown that the process of two resonance frequencies erging into one resonant frequency is possible; therefore, the efficiencies increase as the characteristic ipedance increases. On the other hand, when the air gap length is large at g 357, the two resonance frequencies have already becoe equal. After this point the efficiency worsens as the characteristic ipedance increases. The results of the experient are alost the sae as the theoretical results for the equivalent circuit. The losses at the ipedance transforation section are.8% and 5.9% at Ω and 5 Ω, respectively. Therefore, when the characteristic ipedance is 5 Ω the error is larger than that at Ω. The details of the relation of the efficiencies of the two resonance frequencies vs. air gap lengths (Fig.9) are shown in Fig.. Not only the results using equivalent circuits but also the results using electroagnetic field analysis are shown in Fig. to verify the accuracy of the results fro the equivalent circuit. The lines are the results of the equivalent circuit and the dots are the results of the electroagnetic field analysis. These data show good agreeent between the two analyses. The efficiency of the resonance frequencies is constant when the air gap length increases and when the resonance frequencies becoe equal, which is confired in Fig.9. The efficiency drop is also shown in Fig.. The efficiency is high and air gap length is sall when characteristic ipedance is high. On the other hand, the efficiency is low and air gap length is large when the characteristic ipedance is low (Fig.). η 8 6 4 3 4 5 6 7 8 Z Ω Z Ω Z Ω Z 5Ω Z Ω Z 5Ω Z Ω Z Ω Z 5Ω Z Ω Fig.. Peak efficiency for each gap length related to characteristic ipedance. Dots denote the results of electroagnetic field analysis, and lines denote the theoretical results based on equivalent circuits.. Theory of air gap and axiu efficiency The axiu efficiencies that are achieved at each air gap length and the characteristic ipedance when the two resonance frequencies becoe equal have been discussed above. Based on these results, the conditions for axiu efficiency are discussed. The resonance frequency, where the two resonance frequencies becoe equal is the sae as the resonant frequency of one eleent, is defined in (8). Equation (9) is the efficiency at resonance of ω, which is defined by equations () and (8). The axiu value in equation (8) is the axiu of one resonant frequency, which is described by the equation for the axiu efficiency. The conditions of the equation of axiu efficiency at a given resonant frequency are defined by equation (), which is derived fro equations () and (). Equation () is defined by only 4 paraeters, L, Z, R, and ω, which define the conditions for axiu efficiency. Condition equation (3) has two resonance frequencies and equation (4) is the condition equation when there is one resonance frequency with worse efficiency. The discussed equation for the axiu efficiency is defined in equation (5) or (6) fro equations (9) and (). Equations (5) and (6) are essentially the sae. Equation (5) is defined by the relation of R and Z. Equation (6) is defined by the relation of Z, R, ω and L ; L is related to the air gap length. Equation (6) expresses the relationship between air gap lengths and axiu efficiency. ω ωl 8(8) LC ωc S jl Z ω ( ω ) 9(9) L ω + ( Z + R) S ( ) Z Lω ( R + Lω Z ) Z ( Z ) + RZ + R + Lω S L L L ω ( ω ) () () Z R () ω R ω Z R > 3(3) ω Z < 4(4) Z R η ( ω ) 5(5) Z + R ( ω ) Lω L ω + ( Z R) η 6(6) ( Z R) The ain plots of efficiency vs. air gap length in the case of characteristic ipedances at Ω, 5 Ω, and Ω in Fig. are plotted again in Fig.. The dots in Fig. are the axiu air gap lengths for axiu efficiencies at each characteristic ipedance. The dots shown in Fig. are also shown in Fig.. The line is the theoretical result and the dots are the experiental result. This curve shows the axiu efficiency of each air gap length in agnetic resonant coupling. This condition is defined by equation () and the paraeters are when internal resistance R is. Ω and the resonance frequency is 3.56 MHz. Therefore, L and Z vs. air gap lengths are shown in Fig.3 fro equations () and (6). The coupling coefficient k is shown in Fig.6 and the axiu efficiency is shown in Fig.. High efficiency wireless power

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 6 transfer is possible when the utual inductance is sall and the coupling coefficient k is below. because of the large air gap lengths that are indicated in Fig.6 and Fig.. Also, the internal resistance R in (), that is the condition equation for axiu efficiency, was exained. In the case in which R doubles and triples (starting fro. Ω), the results for axiu efficiency at each air gap length are shown in Fig.4. As is expected, the efficiency and the air gap length worsen as R increases. These results show that the loss fro internal resistance should be iniized. The resonance frequency ω is exained in equation () which is the condition equation for axiu efficiency. The resonance frequency ω can be varied by changing L and C, which are connected to the antenna. The air gap lengths becoe large as the resonant frequency increases; the air gap length reduces as the resonance frequency decreases. η 8 6 4 3 4 5 6 7 8 Z Ω Z 5Ω Z Ω Fig.. Peak efficiency at each gap length related to characteristic ipedance. Dots are the boundary conditions at axiu efficiency. η 8 6 4 R. oh R.45 oh R.68 oh 3 4 5 6 7 8 Fig.4. Maxiu efficiency vs. air gap length for internal resistances. V. CONCLUSION The equations for the relationship between axiu efficiency and air gap length in agnetic resonant coupling are proposed using the Neuann forula and the equivalent circuit ethod. Using the Neuann forula, the air gap length was confired to be related to the radius and nuber of turns of the coils. Maxiu efficiencies are achieved at various air gap lengths via four paraeters: utual inductance L, characteristic ipedance Z, internal resistance R, and resonance frequency ω. The axiu efficiency at each air gap length is achieved by setting the optiized characteristic ipedances in each case. η Z 5Ω Z Ω Z 5Ω 8 6 4 3 4 5 6 7 8 Fig.. Maxiu efficiency vs. air gap length. The line is the theoretical result, and the dots are the results of experients. L [nh] 8 6 4 3 4 5 6 7 8 Fig.3. Optiized paraeters of utual inductance and characteristic ipedance with axiu efficiency at each air gap length. L Z 5 4 3 Z [Ω] REFERENCES [] J. Yungtaek and M. M. Jovanovic, A contactless electrical energy transission syste for portable-telephone battery chargers, IEEE Trans. Ind. Electron., vol. 5, no. 3, pp. 5-57, 3. [] K. Hatanaka, F. Sato, H. Matsuki, S. Kikuchi, J. Murakai, M. Kawase and T. Satoh, Power transission of a desk with a cord-free power supply, IEEE Transactions on Magnetics 38 (Septeber (5)) (), pp. 339 333. [3] J. Sallan, J. L. Villa, A. Llobart, J. F. Sanz, "Optial Design of ICPT Systes Applied to Electric Vehicle Battery Charge," IEEE Trans. on Industrial Electronics, vol. 56, no. 6, pp. 4-49, June 9. [4] C. Geng, L. Mostefai, M. Denai, Y. Hori, "Direct Yaw-Moent Control of an In-Wheel-Motored Electric Vehicle Based on Body Slip Angle Fuzzy Observer," IEEE Trans. on Industrial Electronics, vol. 56, no. 5, pp. 4-49, May 9. [5] D. Yin, S. Oh, Y. Hori, "A Novel Traction Control for EV Based on Maxiu Transissible Torque Estiation," IEEE Trans. on Industrial Electronics, vol. 56, no. 6, pp. 86-94, June 9. [6] A. Alden, T. Ohno, A POWER RECEPTION AND CONVERSION SYSTEM FOR REMOTELY-POWERED VEHICLES, ICAP 89 Antennas and Propagation, vol., pp535-538, Apr. 989. [7] Chwei-Sen Wang, Stielau O.H., Covic G.A., Design Considerations for a Contactless Electric Vehicle Battery Charger, IEEE Transactions on Industrial Electronics, vol.5, Issue5, pp38-34, 5. [8] Y. Kaiya, T. Nakaura, T. Sato, J. Kusaka, Y. Daisho, S. Takahashi, K. Narusawa, Developent and perforance evaluation of advanced electric icro bus equipped with non-contact inductive rapid-charging syste, Proceedings of the 3rd international electric vehicle syposiu (EVS), Electric/ hybrid-electric session, pp. - 4, 7. [9] SHINOHARA Naoki, MATSUMOTO Hiroshi, Wireless Charging Syste by Microwave Power Transission for Electric Motor Vehicles, IEICE. C, Vol.J87-C, No.5, pp.433-443, 4. [] N. Shinohara, J. Kojia, T. Mitani, T. Hashioto, N. Kishi, S. Fujita, T. Mitaura, H. Tonoura and S. Nishikawa, "Assessent Study of Electric Vehicle Charging Syste with Microwave Power Transission

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[9] Takehiro Iura, Hiroyuki Okabe, Toshiyuki Uchida, Yoichi Hori, Study on Open and Short End Helical Antennas with Capacitor in Series of Wireless Power Transfer using Magnetic Resonant Couplings, IEEE Industrial Electronics Society Annual Conference, pp. 3884-3889, 9. [3] H. Chan, K. Cheng, and D. Sutanto, A siplified neuann s forula for calculation of inductance of spiral coil, in Power Electronics and Variable Speed Drives,. Eighth International Conference on (IEE Conf. Publ. No. 475),, pp. 69 73. Takehiro Iura (S 9 M ) received the B.S degrees in electrical and electronics engineering fro Sophia University, Tokyo, Japan in 5. He received the M.S. degree in electronic engineering and the Ph.D. degree in electrical engineering fro The University of Tokyo, Tokyo, Japan, in 7 and, respectively. In, he joined the Departent of Advanced Energy, Graduate School of Frontier Sciences, The University of Tokyo, as a Research Associate. He is now researching in the wireless power transfer for EV using electroagnetic resonant couplings. Yoichi Hori (S 8 M 83 SM F 5) received the B.S., M.S., and Ph.D. degrees in electrical engineering fro The University of Tokyo, Tokyo, Japan, in 978, 98, and 983, respectively. In 983, he joined the Departent of Electrical Engineering, The University of Tokyo, as a Research Associate, where he later becae an Assistant Professor, an Associate Professor, and, in, a Professor. In, he oved to the Institute of Industrial Science as a Professor in the Inforation and Syste Division and, in 8, to the Departent of Advanced Energy, Graduate School of Frontier Sciences, The University of Tokyo. During 99 99, he was a Visiting Researcher with the University of California, Berkeley. His research fields include control theory and its industrial applications to otion control, echatronics, robotics, electric vehicles, etc. Prof. Hori has been the Treasurer of the IEEE Japan Council and Tokyo Section since. He was the recipient of the Best Paper Award fro the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS in 993 and and of the Best Paper Award fro the Institute of Electrical Engineers of Japan (IEEJ). He is a eber of the Society of Instruent and Control Engineers, the Robotics Society of Japan, the Japan Society of Mechanical Engineers, the Society of Autootive Engineers of Japan, etc. He is currently the President of the Capacitors Foru.