Study on the Transmission Mechanism for …takahashi/pdf/A31.pdfStudy on the Transmission Mechanism...

IEICE TRANS. COMMUN., VOL.E88–B, NO.6 JUNE 20052401

PAPER Special Section on 2004 International Symposium on Antennas and Propagation

Study on the Transmission Mechanism for Wearable Device Usingthe Human Body as a Transmission Channel

Katsuyuki FUJII†a), Student Member, Masaharu TAKAHASHI††, Koichi ITO††, Members,Keisuke HACHISUKA†††, Yusuke TERAUCHI†††, Yoshinori KISHI†††, Ken SASAKI†††,

and Kiyoshi ITAO††††, Nonmembers

SUMMARY Recently, wearable devices which use the human body asa transmission channel have been developed. However, there has been alack of information related the transmission mechanism of such devicesin the physical layer. Electro-magnetic communication trials using humanbody as transmission media have more than a decade’s history. However,most of the researches have been conducted by researchers who just wantto utilize the fact and practically no physical mechanisms have been re-searched until recently. Hence, in previous study, the authors proposedcalculation models of the wearable transmitter and the receiver attachedto the arm using the FDTD method. Moreover, the authors compared thecalculated received signal levels to the measured ones by using a biologi-cal tissue-equivalent phantom. However, there was little analysis on eachcomponent of the propagated signal. In this paper, the authors clarifiedthe transmission mechanism of the wearable device using the human bodyas a transmission channel from the view point of the interaction betweenelectromagnetic wave and the human body. First, the authors focused theirattention on measuring the each component of the propagated signal us-ing a shielded loop antenna. From these results, the favorable direction ofelectrodes of the transmitter was proposed to use the human body as a trans-mission channel. As a result, longitudinal direction is effective for sendingthe signal to the receiver, compared to the transversal direction. Next, theauthors investigated the dominant signal transmission channel, because thequestion of whether the dominant signal channel is in or around the armhad remained unsettled. To clear this question, the authors proposed thecalculation model of an arm wearing the transmitter and receiver placedinto a hole of a conductor plate. The electric field distribution and receivedsignal voltage was investigated as a function of the gap between the hole ofthe conductor plate and the surface of the arm. The result indicated that thedominant signal transmission channel is not inside but the surface of thearm because signal seems to be distributed as a surface wave.key words: personal area network, intra-body communication, humanbody, phantom, FDTD

1. Introduction

As cellular phones, personal digital assistants (PDAs), dig-ital video cameras, pocket video games, and other informa-tion and communication devices become smaller and morewidespread, we have begun to adorn our bodies with these

Manuscript received October 1, 2004.Manuscript revised January 13, 2005.†The author is with the Graduate School of Science and Tech-

nology, Chiba University, Chiba-shi, 263-8522 Japan.††The authors are with Research Center for Frontier Medical

Engineering, Chiba University, Chiba-shi, 263-8522 Japan.†††The authors are with the Department of Environmental Stud-

ies, Graduate School of Frontier Sciences, The University of To-kyo, Tokyo, 113-8656 Japan.††††The author is with Management Of Science and Technology

(MOT), Tokyo University of Science, Tokyo, 162-8601 Japan.a) E-mail: [email protected]

DOI: 10.1093/ietcom/e88–b.6.2401

Fig. 1 Transmission system using the human body as a transmissionchannel.

appliances and the opportunities to use these small comput-ers have been increased in our everyday lives. We can saywith fair certainty that miniaturization of these devices willevolve, and we will meet the ubiquitous computing society[1]. However, currently there is no method for these per-sonal devices to exchange data directly. If these devices arewire-connected, it is clearly impractical because they eas-ily become tangled, so some sort of short-range wirelesstechnology is required. The concept for networking thesepersonal devices has been proposed as Personal Area Net-works (PANs) which uses the human body as a transmissionchannel [2]. Although many studies have been made on thedevelopment of wearable devices using the human body as atransmission channel, little is known about the transmissionmechanism of such devices in the physical layer [2]–[9].

Figure 1 shows an example of communication sys-tem of the PANs. When a user wearing the transmittertouches the electrode of the receiver, a transmission channelis formed using the human body. In this case, the receiverrecognizes the user’s ID and it can be personalized. Themerit of this system is that the data is exchanged throughdaily natural actions, such as simply touching the receiver.This communication system uses the near field region ofthe electromagnetic wave generated by the device which iseventually coupled to the human body by electrodes. Hence,the structure of electrodes is one of the key issues for thetransmission using human body.

In previous study, the authors proposed some calcula-tion models of the transmitter and the receiver attached tothe arm using the FDTD method to clarify the transmission

Copyright c© 2005 The Institute of Electronics, Information and Communication Engineers

2402IEICE TRANS. COMMUN., VOL.E88–B, NO.6 JUNE 2005

mechanism [10], [11]. From them, the authors estimatedthe difference in the received signal level due to the elec-trode structures of the transmitter under various conditions.Moreover, in order to verify the validity of these calculationmodels, the calculated received signal levels were comparedto the measured ones by using a biological tissue-equivalentphantom. The result showed a good agreement between cal-culated and measured received signal levels. In addition, itwas found that the GND electrode of the transmitter attachedto the arm strengthens the generated electric field around thearm. However, there was little analysis on each componentof the propagated signal.

In this paper, the authors clarified the transmissionmechanism of the wearable device using human body asa transmission channel from the view point of the interac-tion between electromagnetic wave and the human body.First, the authors focused their attention on measuring theeach component of the propagated signal using a shieldedloop antenna. Moreover, in order to clarify the validity ofthe measurement, the authors compared the measured datato the calculated ones. Then the authors considerated thecurrent distribution inside the arm from each component ofthe distributed signal. From these results, the favorable di-rection of electrodes of the transmitter for using the humanbody as a transmission channel was proposed.

After the validity of this calculation model was demon-strated, the authors clarified the dominant signal transmis-sion channel, because the question of whether the dominantsignal channel was in or around the arm still remained unset-tled. To clear this question, the authors proposed the calcu-lation model of an arm wearing the transmitter and receiverplaced into a hole of a conductor plate. The electric fielddistribution and received signal voltage was investigated asa function of the gap between the hole of the conductor plateand the surface of the arm when signal passed through thehole made in the conductor plate. If the dominant signalchannel is around the arm, the received signal is not gener-ated when the gap between the conductor plate and surfaceof the arm does not exist. On the other hand, if the domi-nant signal channel is inside the arm, the received signal isgenerated in the same condition.

2. Investigation of the Signal Propagation in Relationwith the Direction of the Electrodes of the Transmit-ter

2.1 Measurement of the Magnetic Field Distributions

In this part, the authors investigate each component of mag-netic field around the arm in relation with the direction ofelectrodes of the transmitter. The reason of measuring themagnetic field is that it is difficult to measure the each com-ponent of the electric field around the arm precisely. Forthe measurement, a shielded loop antenna with a diameterof 1 cm is used. Figure 2 shows the condition of the mea-surement for the various components of the magnetic fielddistribution. The transmitter has two electrodes. One is the

(a) Longitudinal direction.

(b) Transversal direction.

Fig. 2 Direction of the transmitter attached to the arm.

Fig. 3 Setup for measurement.

signal electrode to feed an excitation signal (3 Vp−p, Sinewave of 10 MHz), and the other is GND electrode which isconnected to the ground level of the electrical circuit [11].The direction of the transmitter is changed according to twopatterns to compare the magnetic field distributions. One isthe longitudinal direction shown in Fig. 2(a), the other one isthe transversal direction shown in Fig. 2(b). In addition, theconventional distance between signal electrode and GNDelectrode was 4 cm [11]. However, the distance between sig-nal electrode and GND electrode is closed up to 1 cm not tostick out of the width of the arm. The experimental muscle-equivalent phantom used for the arm, which is modeled bya rectangular parallelepiped (5 cm × 5 cm × 45 cm) has therelative permittivity εr set to 81 and the conductivity σ set to0.62 S/m. Although, the relative permittivity of the muscleat 10 MHz equals 170.73 [12], the authors have verified thatthey can use this phantom from the reference [11]. Becausethe received signal voltage is almost same. The reason of us-ing the phantom whose relative permittivity εr equals 81 as asubstitute for the εr equals 170.73 comes from the difficultyof making a phantom with such a high relative permittivity.Moreover, in the same reference, the authors investigatedthe electric field distribution around the whole body modelwearing the transmitter and found electric field concentratesaround the arm. Hence, only arm model can be evaluated inthis paper.

Figure 3 shows the experimental setup for measure-

FUJII et al.: STUDY ON THE TRANSMISSION MECHANISM FOR WEARABLE DEVICE2403

ment to enhance the accuracy of the measurement position.For the shielded loop antenna, a coaxial cable and copperwire with a diameter of 1.6 mm are used. At the tip of the an-tenna, a 0.5 mm gap is constructed to generate the receivedsignal voltage. A spectrum analyzer and a power amplifierare also used. The shielded loop antenna is set 3 cm abovethe surface of the arm and the magnetic field distributionsare measured along the x axis at y=0 and z=3 cm.

Figure 4 shows the various components of the mag-netic field distribution around the arm with the transmit-ter. The level of each point is normalized by the value ofHz at x=26 cm in Fig. 4(b), which is the maximum value ofall measured data in Fig. 4. In the case of the transmitterset to the longitudinal direction in Fig. 4(a), from Ampere’slaw, the dominant current distribution inside the arm is thex component because Hy component is stronger comparedto the Hx and Hz components near the tip of the arm (x=30to 45 cm). On the other hand, in the case of the transmitterattached to the transversal direction in Fig. 4(b), the domi-nant current distribution inside the arm is the y componentbecause the Hx and Hz components are stronger than the Hycomponents near the tip of the arm (x=30 to 45 cm). Fromwhat has been discussed above, it can be concluded that thedirection of the dominant current distribution inside the armis the same as the direction of the electrodes of the transmit-ter, because the current is formed between signal electrodeand GND electrode.



Fig. 4 Measured magnetic field distributions around the arm with thetransmitter.

2.2 Comparison between Measured and Simulated Mag-netic Field

Figures 5 and 6 indicate the comparison between mea-sured and simulated magnetic field by the use of the FDTDmethod to show the validity for the measurement. Thesefigures show the transmitter set to the longitudinal directionand transversal direction, respectively. In the FDTD calcu-lation, two electrodes and circuit board of the transmitter aremodeled as perfect conductor sheets [11]. The sizes of theelectrodes are 2 cm × 3 cm and the size of the circuit boardis 8 cm × 3 cm. The numerical muscle-equivalent phantomused for the arm has the relative permittivity εr set to 81 andthe conductivity σ set to 0.62 S/m. The size of the cells is∆x = ∆y = ∆z = 1 mm. The absorbing boundary condi-tion is the Liao, and the time step is 1.92 ps to satisfy the

(a) Hx component.

(b) Hy component.

(c) Hz component.

Fig. 5 Longitudinal direction.


(a) Hx component.

(b) Hy component.

(c) Hz component.

Fig. 6 Transversal direction.

Courant stability condition. In Fig. 5 and 6, all the simu-lated data are normalized by the value of Hx at x=24.5 cm inFig. 6(a), which is the maximum value of all the simulateddata in Fig. 5 and Fig. 6.

To discuss the difference between measured and calcu-lated magnetic field, Eq. (1) is defined

Difference

=

√1

x2 − x1

∫ x2

x1

{HMeas.(x) − HFDT D(x)}2dx (1)

where the HMeas.(x) and HFDT D(x) indicate the measuredand calculated magnetic field, respectively. x2 and x1 equal45 cm and 0 cm, respectively. Table 1 shows the differencebetween HMeas.(x) and HFDT D(x) by using Eq. (1).

From Table 1, all the differences of Fig. 5 and Fig. 6 arealmost less than 7 dB. As the dynamic range for the mea-

Table 1 Difference between measured and calculated magnetic fielddistributions.



Fig. 7 Electric field distributions in and around the arm with thetransmitter and receiver.

surement is about −55 dB, these differences is arisen. How-ever, the rate of decrease and the null point as a functionof the distance x is generally fit. From this view point, theauthors can relatively compare the each component of themagnetic field distribution that indicates validity in both theFDTD and measurement.

2.3 Electric Field Distributions in and around the Arm

Figure 7 illustrates the electric field distributions (root-sum-square) of both directions of the electrodes of the transmit-ter. The reason of discussing the electric field distribution isthat the received signal voltage of the receiver is calculatedfrom the electric field. Thus, the argument from the viewpoint of the electric field is essential.

The structure of the receiver is illustrated in Fig. 8. Thereceiver has a receiving electrode and LCD that can indi-cate the received signal voltage directly [11]. The reason ofno GND electrode is that the existence of the GND elec-trode for the receiver reduces the received signal voltage[10]. Hence, there is no optimal direction of the receiverbecause the receiver has only one electrode. Figure 8(b) isthe FDTD calculation model of the receiver. The receiv-ing electrode and the circuit board are modeled as perfectconductor sheets. The received signal voltage is calculatedfrom the electric field at the receiving point. Therefore, thisreceiver does not detect the magnetic field but the electricfield.

The distance between the transmitter and receiver is


(a) Exterior of the receiver.

(b) FDTD calculation model.

Fig. 8 Structure of the receiver.

fixed to 17 cm because the transmitter is located at the cen-ter of the arm and the receiver is also located at the tip of thearm. The observation plane is the x-z plane including the re-ceiving point of the receiver. The electric field is normalizedto the value at the feeding gap. In the case of the longitudi-nal direction of the transmitter in Fig. 7(a), the electric fieldis propagated along the surface of the arm (−50 to −60 dB).However, in Fig. 7(b), the level of the electric field on thesurface of the arm seems low (−60 to −70 dB) and the elec-tric field is not propagated along the surface of the arm and itis radiated on the upper side of the arm. So, this result meansdisadvantage for practical use compared to the Fig. 7(a) interms of the higher signal reception. In addition, Fig. 9 indi-cates the electric field distribution without the arm to showthe validation of using human body as a transmission chan-nel. The loss of the electric field at the receiving point isquite large (less than −80 dB) compared to the Fig. 7. Theauthors can conclude that this transmission system uses thehuman body as a transmission channel.



Fig. 9 Electric field distributions without arm.



Fig. 10 Measurement condition of the received signal voltage.

Fig. 11 Received signal voltage.


Below is a physical meaning of the difference betweenFig. 7(a) and Fig. 7(b). As shown in Fig. 4(a), dominant cur-rent distribution is the x component when the transmitter isset to the longitudinal direction. Hence, electric field is dis-tributed along the length of the arm (x direction). On theother hand, as shown in Fig. 4(b), dominant current distri-bution is the y component when the transmitter is set to thetransversal direction. Hence, electric field is not distributedalong the x direction. Consequently, the difference of thecurrent distribution causes the difference of the electric fielddistribution.

2.4 Received Signal Voltage of the Receiver

The pictures shown in Fig. 10 are the measurement condi-tions of the received signal voltage according to the direc-tion of the electrodes of the transmitter. In order to verify thevalidity of the calculation models, we compared the receivedsignal voltages by the calculation to the measured ones byusing a biological tissue-equivalent phantom. In Fig. 10(a),the transmitter is attached in the longitudinal direction. Onthe other hand, Fig. 10(b) indicates the transversal direction.

Figure 11 shows the comparison between the measuredreceived signal voltages and the calculated ones. The re-sult shows a good agreement of the calculated and measuredreceived signal levels that indicates a considerable validityin both the FDTD and measurement. When compared tothe received signal voltage of the longitudinal direction, theone of the transversal direction drops of nearly 10 percents.Moreover, the received signal voltages without arm is al-most zero. So, the transmission system using the humanbody as a transmission channel has advantage over those

Fig. 12 Calculation model.

using airborne radio waves. Regarding the difference of therelative permittivity, the received signal voltages are almostsame. Hence, it is appropriate to use the phantom with εr

set to 81 as a substitute for the εr set to 170.73.As a conclusion, longitudinal direction is effective for

sending the signal to the receiver, compared to the transver-sal direction. These investigations have made it clear thatwe can use the human body as a transmission channel effec-tively by flushing the current along the length of the arm.

3. Investigation of Dominant Signal TransmissionChannel

3.1 Calculation Model

In this section, the authors investigate the dominant signaltransmission channel, because the question of whether thedominant signal channel is in or around the arm still remainsunsettled. To clear that question, the authors proposed a cal-culation model of an arm wearing the transmitter and re-ceiver placed into a hole of a conductor plate. Figure 12shows the calculation model of the arm with the transmit-ter and receiver using the FDTD method. The size of theconductor plate d is infinity because it is attached to theabsorbing boundary of the FDTD. The size of the cells is∆x = ∆y = ∆z = 1mm. The absorbing boundary conditionis the Liao, and the time step is 1.92 ps to satisfy the Courantstability condition. The distance between signal electrodeand GND electrode was set to the conventional size (4 cm)[11]. By using this model, the electric field distribution andthe received signal voltage is investigated as a function ofthe gap g between the hole of the conductor plate and the


surface of the arm. The reason of discussing the electricfield distribution in this section is that the received signalvoltage of the receiver is calculated from the electric field.Thus, the argument from the view point of the electric fieldis essential.

3.2 Electric Field Distributions and Received Signal Volt-age

Figure 13 illustrates the electric field distributions (root-sum-square) in and around the arm. The observation planeis the x-z plane and y plane includes the receiving point. Theelectric field is normalized to the value at the feeding gap.Figs. 13(a), (b) shows the distributions when the gap g is−1 mm and 0 mm, respectively. It can be seen that the elec-tric field is not propagated toward the receiver but reflectedat the point of the conductor plate. However, in Figs. 13(c)–(f), as the gap g between conductor plate and the surface ofthe arm becomes wider, the electric field is more propagatedtoward the receiver.

Figure 14 shows the comparison between the measuredreceived signal voltages and the calculated values as a func-tion of the gap g. To measure the received signal voltages,the conductor plate with a size of 200 cm × 200 cm is used(d = 200 cm). When the size of the gap g is −1 mm and

(a) Gap g = −1 mm. (b) Gap g = 0 mm.

(c) Gap g = 1 mm. (d) Gap g = 5 mm.

(e) Gap g = 10 mm. (f) Without conductor plate.

Fig. 13 Electric field distributions in and around the arm with the transmitter and receiver.

0 mm, the received signal voltage is almost zero. How-ever, as the gap g between conductor plate and surface ofthe arm becomes wider, the received signal voltage risessharply. Moreover, the result shows a good agreement ofthe calculated and measured received signal levels that in-dicates a considerable validity in both the FDTD and mea-surement. The reason of the difference of the received signalvoltage between longitudinal direction in Fig. 11 and w/oconductor in Fig. 14 is come from the difference of the dis-tance between the signal electrode and GND electrode. In

Fig. 14 Received signal voltage as a function of the gap betweenconductor plate and surface of the arm.


Fig. 11, the distance between the signal electrode and GNDelectrode is 1 cm. The circuit of the transmitter is almostshorted. Hence, electric field generated from the transmitteris lower than the conventional size.

On the basis of these results, dominant signal transmis-sion channel using the human body as a transmission chan-nel is not inside but the surface of the arm, because signalseems to be distributed as a surface wave.

4. Conclusions

In this paper, the authors clarified the transmission mech-anism of the wearable device using the human body as atransmission channel from the view point of the interactionbetween electromagnetic wave and the human body. First,in order to investigate desirable direction of the electrodes ofa transmitter using the human body as a transmission chan-nel, the magnetic field distributions around the arm with thetransmitter was measured by the use of the shielded loopantenna and biological tissue-equivalent phantom. Then, inorder to verify the validity of these measured data, the au-thors compared the calculated magnetic field distribution tothe measured ones by using the FDTD method. The resultshowed a good agreement of both the calculated and mea-sured magnetic field distribution. As a conclusion, longi-tudinal direction is effective for sending the signal to thereceiver, compared to the transversal one. These investiga-tions have made it clear that we can use the human bodyas a transmission channel effectively by flushing the currentalong the length of the arm.

Next, the dominant signal transmission channel was in-vestigated, because the question of whether the dominantsignal channel was in or around the arm remained unset-tled. To clear the question, the authors proposed the cal-culation model of running the arm wearing the transmitterand receiver into the hole of the conductor plate. Then, theelectric field distribution and received signal voltage was in-vestigated as a function of the gap between the hole of theconductor plate and the surface of the arm. The results leadus to the conclusion that the dominant signal transmissionchannel of a wearable device using human body as a trans-mission channel is near the surface of the arm because thesignal seems to be propagated as a surface wave. However,there has been still room for theoretical argument about sur-face propagation of this result, for further study. In the fu-ture, real human model will be applied to this study.

Acknowledgments

The authors would like to thank Mr. Shigeru Tajima, SonyComputer Science Laboratories, for his cooperation. It hasbeen a great experience to study with him. The authorswould also like to express their appreciation to Mr. AtsushiYamamoto and Mr. Shoichi Kajiwara, Matsushita ElectricIndustrial, for providing the setup for measurement of themagnetic field distribution.

References

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[5] N. Matsushita, S. Tajima, Y. Ayatsuka, and J. Rekimoto, “Wear-able key: Device for personalizing nearby environment,” Proc. 4thInternational Symposium on Wearable Computers (ISWC 2000),pp.119–126, Oct. 2000.

[6] K. Doi, M. Koyama, Y. Suzuki, and T. Nishimura, “Developmentof the communication module used human body as the transmissionline,” Proc. Human Interface Symposium 2001, pp.389–392, 2001.

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Katsuyuki Fujii was born in Chiba, Japan,in October 1978. He received the B.E. and M.E.degrees all in electronic engineering from ChibaUniversity, Chiba, Japan, in 2001 and 2003, re-spectively. He is currently a Ph.D. candidate atChiba University. His main interest is evalua-tion of the interaction between electromagneticfields and the human body by use of numeri-cal and experimental phantoms. He received theTechnical Achievement Award from the Insti-tute of Image Information and Television Engi-

neers of Japan (ITE) in 2002, the Suzuki Memorial Achievement Awardfrom the ITE in 2004, the 2004 International Symposium on Antennas andPropagation Poster Presentation Award from the IEICE, 2005 IEEE To-kyo Student Workshop IEICE Best English Prize from the IEICE StudentBranch Doctoral Student Forum and 2005 Young Researcher’s Award fromthe IEICE. Mr. Fujii is a member of the IEEE, and the Institute of ImageInformation and Television Engineers of Japan (ITE).


Masaharu Takahashi received the B.E. de-gree in electrical engineering in 1989 from To-hoku University, Miyagi, Japan, and the M.E.and D.E. degree in electrical engineering fromTokyo Institute of Technology, Tokyo, Japan, in1991 and 1994, respectively. He was a ResearchAssociate from 1994 to 1996, an Assistant Pro-fessor from 1996 to 2000 at Musashi Instituteof Technology, Tokyo, Japan, and an AssociateProfessor from 2000 to 2004 at Tokyo Univer-sity of Agriculture & Technology, Tokyo, Japan.

He is currently an Associate Professor at Chiba University, Chiba, Japan.His main interests have been electrically small antennas, planar array an-tennas (RLSA) and EMC. He received the IEEE AP-S Tokyo chapter youngengineer award in 1994. He is a senior member of the IEEE.

Koichi Ito was born in Nagoya, Japan, inJune 1950. He received the B.S. and M.S. de-grees from Chiba University, Chiba, Japan, in1974 and 1976, respectively, and the D.E. de-gree from Tokyo Institute of Technology, To-kyo, Japan, in 1985, all in electrical engineer-ing. From 1976 to 1979, he was a Research As-sociate at Tokyo Institute of Technology. From1979 to 1989, he was a Research Associate atChiba University. From 1989 to 1997, he was anAssociate Professor at the Department of Elec-

trical and Electronics Engineering, Chiba University, and is currently a Pro-fessor at the Research Center for Frontier Medical Engineering as well as atthe Faculty of Engineering, Chiba University. In 1989, 1994, and 1998, hestayed at the University of Rennes I, France, as an Invited Professor. Hismain interests include analysis and design of printed antennas and smallantennas for mobile communications, research on evaluation of the inter-action between electromagnetic fields and the human body by use of nu-merical and experimental phantoms, and microwave antennas for medicalapplications such as cancer treatment. Professor Ito is a Fellow member ofthe IEEE, and a member of URSI Commission K in Japan, AAAS, the In-stitute of Image Information and Television Engineers of Japan (ITE) andthe Japanese Society of Hyperthermic Oncology. He served as Chair ofTechnical Group on Radio and Optical Transmissions of ITE from 1997 to2001. He also served as Chair of the IEEE AP-S Japan Chapter from 2001to 2002. He is now Chair of Technical Group on Human Phantoms for Elec-tromagnetics, IEICE and Vice-Chair of the 2004 International Symposiumon Antennas and Propagation (ISAP’04).

Keisuke Hachisuka was born in Tokyo,Japan, in July 1978. He received the B.S. de-gree in precision engineering and the M.S. de-gree in environmental studies from the Univer-sity of Tokyo, Tokyo, Japan, in 2001 and 2003,respectively. Since 2004, he has been a researchfellow with the Japan Society for the Promotionof Science, and he is currently a Ph.D. candidateat the Institute of Environmental Studies, Grad-uate School of Frontier Sciences, the Universityof Tokyo. His main interests include mechatron-

ics, sensor networks and wireless communication among wearable devices.He received the Hatakeyama Award of the Japan Society of Mechanical En-gineers for outstanding graduates in 2001, the Aoki Award of the Horolog-ical Institute of Japan for the best paper in 2003 and the Technical Achieve-ment Award of Japan Institute of Electronics Packaging in 2005. He is amember of the Japan Society of Mechanical Engineers, Japan Institute ofElectronics Packaging and the Horological Institute of Japan.

Yusuke Terauchi was born in Tochigi,Japan, in August 1979. He received the B.S.degree in System Innovations from the Univer-sity of Tokyo, Japan, in 2003. He is currently aM.S. candidate at the Institute of EnvironmentalStudies, Graduate School of Frontier Sciences,the University of Tokyo. His main interest is inintra-body communication. He is a member ofJapan Society of Precision Engineering.

Yoshinori Kishi was born in Nagoya, inApril 1981. He received the B.S. degree inphysics from the University of Tokyo, TokyoJapan in 2004. In 2004, he entered departmentof Environmental Studies, Faculty of FrontierSciences, the University of Tokyo. His main in-terest includes intra-body communication.

Ken Sasaki was born in Fujisawa, in Jan-uary 1957. He received the B.S., M.S. and D.E.degrees from the University of Tokyo, Tokyo,Japan, in 1980, 1982 and 1987 respectively, allin Precision Engineering. From 1982 to 1985,he worked at NEC Corporation. From 1985 to1986, he was a research associate at departmentof Precision Engineering. From 1986 to 1987,he was a lecturer at International Liaison Office.From 1987 to 1999, he was an associate profes-sor at department of Precision Engineering. In

1996, he was a visiting researcher at Stanford University. In 1999, he wastransferred to department of Environmental Studies, Faculty of FrontierSciences, and from 2004, he is a professor at the department. His maininterests include mechatronics, signal processing, and sensors for wearabledevices. Dr. Sasaki is a member of Japan Society of Precision Engineering,Robotics Society of Japan, The Horological Institute of Japan, Japan Soci-ety of Computer Aided Surgery, Japan Institute of Electronics Packaging,and The Society of Naval Architects of Japan.


Kiyoshi Itao received the B.E., M.E. andPh.D. degrees in precision engineering from theUniversity of Tokyo in 1966, 1968 and 1976, re-spectively. He joined NTT (Nippon Telegraph &Telephone) in 1968 and researched on the high-speed positioning of printer mechanisms and de-veloped advanced teleprinters during the first tenyears. In his experience at the Massachusetts In-stitute of Technology as a Research Associate,he researched on the wide-band random vibra-tions. During the last ten years in NTT, he was

a laboratory manager, and developed magnetic tape cartridge-type terabytestorage systems and magnetooptical disk memory systems, and conductedthe development policy of NTT Storage Systems as the Director of the Stor-age Systems Laboratories. He contributed to the international standardiza-tion of 130 mm/90 mm optical disks. In 1992, he became professor at ChuoUniversity in the Department of Science and Engineering, and started re-search on microsystem and dynamics for information & communicationequipment. In 1996, he moved to professor at the University of Tokyo inthe Department of Precision Machinery Engineering. In 1999, he becameprofessor at the University of Tokyo in the Department of EnvironmentalStudies. In 2004, he became professor and dean in the School of Man-agement of Science & Technology at Tokyo University of Science. Hismain interests include wearable computer equipment design, microtech-nologies for watchtype information & communications devices based onmicrovibration & microphotonics technologies, integrated information de-vice synthesis and management of technology. Prof. Itao is President ofthe Horological Institute of Japan, Chairman of the Optical Disk Standard-ization Committee of Japan, Director of Advanced Technology Institute,President of non-profitable organization of Wearable Environmental Infor-mation Network (WIN) and President of Japan Society of Precision Engi-neering.

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