overview of intra-body communication research · 100 khz, and it was revealed that noise sources in...

Overview of Intra-body Communication Research

1 Wu Chen, *1,2 Shuang Zhang, 3 Yu-ping Qin, 4 Pailla Tejaswy 1, The Engineering & Technical College of Chengdu University of Techology, Leshan, 614000,

China, [email protected] 2, Biomedicine Department of Electrical and Electronics Engineering, Faculty of Science and Technology, University of Macau, Macau SAR 999078, China, [email protected]

3, School of Electrical Sciences, Indian Institute of Technology, Bhubaneswar, 751013, India, [email protected]

4, The Engineering & Technical College of Chengdu University of Techology, Leshan, 614000, China, [email protected]

Abstract

As an important component in the wireless communication and the wireless sensor network, the intra-body communication can be used to improve the people’s healthcare level through applications of intelligent information processing and wireless signal transmission technology etc., and increasing attention is being paid to the communication technology by relevant researchers and enterprises. At present a great many research results on the intra-body communication have been achieved. In this paper, the existing research results are summarized; then they are classified and summed up based on coupling modes of the intra-body communication, with sufficient discussion. Due to less environmental impact and steady signal transmission in the current coupling intra-body communication only, a selective analysis is made for advantage and shortcoming of existing achievements on the field in this paper. Meanwhile, the property that the quasi-static condition in the current coupling intra-body communication within the high frequency area is not valid is proposed, to point out the direction for further research.

Keywords: Intra Body Communication (IBC), Capacitive Coupling, Current Coupling,

Communication Frequency 1. Introduction

Human life span has been augmenting continuously owing to the rapid advancement in

science and technology and sophistication of the medical technology. In addition to that, the birth rates in many nations across the globe have been decreasing over the years and problems of the global senior population are exacerbated. Aging population and poor-health of people increase the demand for constant monitoring. Limited existing medical resources and expensive conventional medical attention are unable to meet these requirements. Hence, it has become necessary to replace the conventional health care system with a novel, efficient and economic one.

The wearable medical care system [1,2], which serves this purpose, is a novel portable pathological care system with real-time monitoring. The system has multiple basic modules for detecting and processing a physiological signal, signal feature extraction and data transmission. Through this system, not only non-invasive and continuous monitoring, diagnosis and treatment on the human body can be achieved, but also the user’s health status and physiological information can be displayed in a real-time manner. The wearable medical care system can be seamlessly connected with the wide area network (WAN)[3], and this is helpful to implementation of regular monitoring and remote consultation.

Because all physiological parameters in the human body can be monitored by means of various sensors, required physiological signal monitoring sensors are firstly mounted on corresponding parts in the human body in pathological monitoring[4]. The human body is used as the communication connection medium, through which detected physiological signals are transmitted to the human body base station for signal analysis and summarizing[5-7]. Finally, the information is delivered to the community base-station through wireless network, to realize information interconnection. The theory is illustrated in Figure 1.

Overview of Intra-body Communication Research Wu Chen, Shuang Zhang, Yu-ping Qin, Pailla Tejaswy

Journal of Convergence Information Technology(JCIT) Volume 7, Number 20, Nov 2012 doi : 10.4156/jcit.vol7.issue20.27

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Figure 1. Real-time guarding network

In Figure 1, sensor arrangement and signal transmission channels in the human body real-time

guarding network are analyzed systematically and reasonably. Real time monitoring and transmission of physiological signals via various sensors are implemented so as to achieve real-time monitoring for health indicators of the human body, which plays an important role in the modern medical healthcare. In general, connection modes employed between these sensors and base stations include wired mode, wireless mode and Intra-Body Communication (IBC) mode.

In IBC, excellent conductive property of the human body is utilized to transmit signals. Therefore IBC [3], which is a short-distance wireless communication technology with the human body as the data transmission medium, plays an important role in the advancement of the wearable medical care system due to low power consumption, insusceptibility to external electromagnetic noise and small radiation energy [1,2] as well as reduced complexity in connecting lines.

2. Coupling techniques in IBC

Currently, based on coupling modes between the electrical signal and the human body, IBC is classified into two categories [4]; namely: the electric field coupling IBC and the current coupling IBC. At present, many international research institutions are carrying out relevant research in these two domains [4-11].

2.1. Electric field coupling Technique.

The electric field coupling IBC, is also known as the Capacitive Coupling IBC [4], in which the human body is regarded as a capacitor. Oscillation of the transmitter is employed to generate electric field in the body, and variation of the field is detected by means of the receiver and thus communication is achieved. In this technique, dielectric polarization is generated in the human body because neighboring electric field demonstrates a status that the whole body is enveloped in the electric field. The transmitter or the receiver need not be in direct contact with the human body. Furthermore, communication is available even in the presence of insulator in the signal path. This method is widely used because of fewer restrictions on the application method and relatively less requirements for the device.

Zimmerman of Massachusetts Institute of Technology (MIT) [3] achieved 2.4kbit/s transmission rate with 330 KHz carrier frequency and 30V voltage amplitude, with a power consumption of only 1.5mW, which opened a new chapter in the study of Intra-Body Communication. Later, M. Gray [12] designed a device, in which bandwidth was raised to 2000kbps in principle under the modulation frequency of 100 KHz, and it was revealed that noise sources in the IBC device were mainly electromagnetic interferences of the amplifier in the circuit and the external environment. Later, E. R. Post etc. [5] achieved FSK (Frequency Shift Keying) half-duplex communication with a transmission rate of 9600


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baud rate, developing IBC to the level of practical application for data and energy transmission. Later on K. Partridge [10] of University of Washington designed an improved device with the transmission rate of 38.4kbps. In this device, 180 KHz and 140 KHz carrier frequencies with the FSK modulation mode were used, with an adjustable maximum voltage of magnitude 22V. On the basis of the above results, a large number of experiments for signal intensity and transmission rate are carried out. Those experiments showed that appearance of the ground electrode of the transmitter / the receiver had no obvious effect on the signal. Instead, the distance between signal electrodes produced a remarkable effect upon the signal, and the attenuation of signal was rapid with the decrease of grounding area.

In 2004 Japan’s NTT (Nippon Telegraph & Telephone) [7] released RedTacton, which marked beginning of IBC application. In addition, they achieved half-duplex transmission of 10Mbps (maximum rate). Later, an IBC device named Wearable ID Key was developed by Sony corporation and Chiba University [8,13,14] of Japan. The device was used to achieve the transmission rate of 9600bps in 10MHz and 14MHz FSK modulation modes; more importantly, the first FDTD (Finite Difference Time Domain) simulation model in IBC study was proposed. It revealed the effect of position the transmitting electrode on receipt signal. J.A. Ruiz [15,16] from Waseda University analyzed the IBC mechanism in the near zone field and channel features of the communication with Body Are Network (BAN) as the background. On the basis of Zimmerman's achievement, the distributed RC model of the whole human body was proposed in Korea Advanced Manufacturing Research Institute [17] from the circuit’s point of view which made a significant contribution to the research on the Capacitive Coupling IBC and developing it for practical applications.

In the RedTacton system, the weak electric field on the surface of the human body is utilized as the transmission medium. As soon as the user touches it gently, data transmission between PDAs can be achieved (see Figure 2).

Figure 2. NTT electric field sensor unit

In the RedTacton system, the electric field sensor with electro-optic probes and the laser technology

is applied. The electro-optic sensors have extremely high input impedance and ultra-wide detection range, which is quite helpful to precise detection of the weak and high-speed electric field signal. The transmitter produces a very weak electric field on the surface of the human body, and the electric field is transmitted to the receiver of the RedTacton through the skin of the human body. The weak electric field can make the photo transistor of the receiver in the RedTacton system generate optical changes, then these optical changes are transformed into electric signals by means of laser beam, as shown in Figure 2. In the device, half-duplex transmission of 10Mb/s (maximum) can be achieved.

However, signal detection has become difficult because it is impossible to achieve direct coupling with the ground. The signal became unstable due to the effect of common-mode noise. In addition, the communication mode is quite sensitive to the external electromagnetic interference, making it unsuitable for use near the device with great electromagnetic interference and this demands a better communication technique.


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2.2. Current coupling technique

The Current Coupling IBC [4], refers to the communication achieved by a weak current signal through the body which acts as a communication wire to transmit the signal. The Current Coupling IBC has the same communication theory as the wire communication, with the relatively simpler circuit structure. Due to the Capacitive Coupling between the human body and the ground plane, the Current Coupling communication is affected by the common-mode noise as well as the electric field coupling Intra-Body Communication (IBC). As the current flows through the human body, Current Coupling has a very strong ability to resist electromagnetic interference and is more stable than the Electric field coupling, so this facilitates the achievement of high speed communication.

A simplified two-electrode intra-body communication mode based on [4] is presented in Tokyo University, together with equivalent circuit models in two-electrode and four-electrode modes (see Figure 3).

(a) Four-electrode model

(b) Two-electrode model

Figure 3. University of Tokyo IBC model

In fact, comparison between the two-electrode mode and the four-electrode mode may be considered to be comparison between the current coupling and capacitive coupling intra-body communication modes. In the two-electrode mode, because the impending electrodes at the transmitting terminal / the receiving terminal are coupled via air, the signal circuit is formed. Therefore, potential difference between the signal electrode and the impending electrode is sure to be larger than that between two electrodes mounted on the human body.

T. Handa [9] of Japan’s Chiba University studied Current Coupling technique of IBC. According to his article published in 1997, about 20uA (effective value) alternating current was injected in the human body to realize electro-cardio signal transmission in the body and a simplest equivalent circuit model of the human body, electrodes and detection amplifier have been presented. D. P. Lindsdey etc. [10] of University of California used a novel biomedical telemetry method to measure the tension of the fore cruciate ligament after surgery with the human body as the transmission medium of current signal. After comparing effects on the signal attenuation produced by different carrier frequencies and


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currents, he finally proposed the best communication scheme, in which 3mA current and 37 KHz carrier frequency are introduced. On the basis of this, K. Hachisuka and his team at University of Tokyo proposed the waveguide mode IBC, in which human body is considered as a waveguide pipe to transmit the high-frequency electromagnetic waves generated in the transmitting terminal. Meanwhile, he presented a simplified two-electrode IBC technique based on [11,18,19], together with equivalent circuit models in two-electrode and four-electrode modes(see Figure 3). On the basis of the model of University of Tokyo, Y. Song [20] of Beijing Institute of Technology simplified the circuit model in the four-electrode mode and provided the transfer function of the circuit model, finally derived the transfer function of the equivalent circuit by means of the relationship between input and output. A modified value K was given to correct the difference between the individual simulated result and the measured result.

In the electroencephalogram, the human brain is always thought to be equivalent to a multi-layer sphere. PUN adopted a concentric cylinder model with the finite length which consists of three layers (skin, fat and muscle) to analyze the transmission law of the electromyographic signal in the human body. He even considered the anisotropic feature of the muscle layer. In the transcutaneous electrical stimulation, the human arm is equivalent to a five-layer (skin, fat, muscle, periosteum and marrow) concentric cylinder with the infinite length. However, the experiment demonstrates that the periosteum and the marrow have a little impact on electrical stimulation effect, so the human arm is abstracted as a multi-layer cylinder as shown in Figure 4.

Figure 4. Human arm equivalent multilayer cylinder model

In the model in Figure 4, based on actual tissue thickness, the tissue which will produces a

significant impact on the research result is taken into account, especially the skin; this reduces complexity level of the model. In combination with the knowledge on the anatomy and in consideration of modeling rationality, the human fore arm is abstracted as a four-layer concentric cylinder with a finite length, which includes skin, fat, muscle and skeleton from the outside to the inside. For this reason, abstract and modeling of the human body are implemented.

M. Oberle etc. [3] of Eidgenoessische Technische Hochschule Zurich (ETH) designed and completed a device to couple mA-level alternating current by means of dielectric properties of human tissue. Furthermore, he proposed a simpler engineering channel model as well. By combining electromagnetic features of human tissue, M. S. Wegmuller etc. [3] followed him to construct preliminary finite element model and the layered tissue model of the human forearm and quantitatively compare effects of electrode size and position on signal attenuation. It is noteworthy that 1 mA orthogonal current with the M. S. Wegmuller of 10 KHz-1 MHz, which was used by M. S. Wegmuller in the experiment, was transmitted at the maximum transmission rate of 4.8 kbps. On the basis of the layered tissue model proposed by M. S. Wegmuller, Y. M. Gao of Fuzhou University and S. H. Pun [21] from University of Macau took the human arm as a standard cylinder (see Figure 4), derived the voltage control equation of the Current Coupling IBC employing Maxwell’s equations and according


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to the fact that the biological tissue meets the quasi-static conditions within the frequency range below 1MHz, the voltage equation is expressed as follows:

( ) 0V , i .

As the capacity effect within the frequency range below 1MHz is negligible, the complex permeability is approximated to the conductivity and the control equation is simplified as follows:

( ) 0V

Different IBC models can be obtained from the different boundary conditions; the three-dimensional equation and the separating variable method in cylindrical-coordinate system are applied to solve the control equation. The solution is expressed as follows:

(1) (2)

0

( , , ) [ ( ) ( )][ cos( ) sin( )][ cos( ) sin( )]n n n n n n k kn

V r z A Z kr B Z kr C n D n E kz F kz

where An, Bn, Cn, Dn, Ek and Fk are the undetermined constants; (1) ( )nZ kr and (2) ( )nZ kr indicate the

Bessel functions Jn(kr) and Yn(kr) or modified Bessel functions In(kr) and Kn(kr) respectively. Finally the solution of the model with N layers of concentric cylinder is derived through different boundary conditions. Establishment of the model firstly provides theoretical support for the study of the IBC.

In our experiment, in combination with the electromagnetic field of the IBC, 12 volunteers are chosen to analyze parameters involved in the model with 0.5mA current and within the frequency range of 10 KHz to 1MHz. The experiment shows that, computed result of the electromagnetic field analytical model for the IBC approximates to experimental results, so it can be used for rational explanation of all experimental phenomena.

3. Scope of Research

Channel capacity of the IBC is limited, so the focus of IBC study is how to improve the signal

transfer rate in the limited channel and to enhance the stability. Two ways are commonly used to resolve the problems: one way is to improve SNR of the channel through channel optimization. The other is to increase the signal transmission rate, which is easy to be achieved and verified as well. When the communication frequency is raised to 10MHz, although some of the quasi-static conditions are still valid, the penetration depth of the electromagnetic wave becomes smaller and smaller, capacity effect and skin effect becomes more and more obvious, and impedance of the electrode and the contact area gets increasingly strong with the increase of signal frequency. These factors play a key role in affecting the communication and will be thoroughly taken into account in the further research.

4. Conclusion

Currently, Capacitive Coupling communication prototypes with the transmission rate of up to 10M

bit/s have been developed, but signal transmission in this mode needs the circuit generated through the ground electrode, which increases difficulty in designing transceiver due to uncertainty of the circuit. The field signal is distributed in the form of surface wave [22-25], so most energy of the electrical signal flows through the surface of the human body and good conductor feature of the human body is not utilized well. In the communication process, working mode of the ground coupling electrode is similar to that of the stray field with outward radiation and subject to external electromagnetic interference because of great uncertainty. As the frequency rises, the electrical signal energy radiated through the human body increases and the safety problem needs further verification.

At present, the study on the Current Coupling IBC is still in its infancy, and signal transmission in the Current Coupling mode is completed directly through the transmitter, the receiver and the human body, furthermore, the communication mode requires no signal circuit produced through ground coupling and is insusceptible to external electromagnetic noise. Signal in the current form is transmitted in the human body with less external radiation [16], which makes full use of the good conductive characteristics of the human body and eliminates hidden dangers of information leakage. The transmitting terminal / receiving terminal achieve differential coupling and receive the electrical signal to suppress common mode noise effectively, so the transmission signal is stable; however, the transfer rate is low, mostly at tens of kbit/s. For this reason, it is expected to promote the transmission rate by increasing the communication frequency. Up to now, Y. M. Gao of Fuzhou University in China


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and S. H. Pun of University of Macao have studied distribution of the electrical signal in various layers within the frequency range of 10KHz to 1MHz. Besides, they firstly proposed the mathematical model with the layered structure to analyze the transmission mechanism of the alternating current in the complicated volume conductor such as the human body and to guide the study of the Current Coupling IBC model.

5. Acknowledgements

The work presented in this paper is supported by The Key Fund Project of Sichuan Provincial

Department of Education under grant 12ZB192.

6. References [1] S. D. Bao, Y. T. Zhang, “Telemedicine: Wearable Biomedical Devices”, China Medical Device

Information”, vol. 10, no. 3, pp. 1-3, 2004. [2] Q. K. Deng. “A Novel Model of the Medical Instrumentation----An Overview of Wearable

Sensors and Systems”, Chinese Journal of Medical Instrumentation, vol. 30, no. 5, pp. 327-329, 2006.

[3] T. G. Zimmerman. “Personal Area Networks: Near-field intra Body Communication”, IBM Systems Journals, vol. 35, pp. 609-617, 1996.

[4] M. S. Wegmueller, “A. Kuhn, J. Froehlich, et al., “An Attempt to Model the Human Body as A Communication Channel”, IEEE Transactions on Biomedical Engineering, vol. 54, no. 10, pp. 1851-1857, 2007.

[5] E. R. Post, M. Reynolds, M. Gray, et al., “Intra body Buses for Data and Power”, In Proceedings of First International Symposium on Wearable Computers, pp. 52-55, 1997.

[6] K. Partridge, B. Dahlquist, A. Veiseh, et al., “Empirical Measurements of Intra Body Communication Performance under Varied Physical ConFigure Urations”, In Proceedings of the 14th Annual ACM Symposium on User Interface Software and Technology Table of Contents, pp. 183-190, 2001.

[7] M. Shinagawa, M. Fukumoto, K. Ochiai, et al., “A Near-Field-Sensing Transceiver for Intrabody Communication Based on the Electro-Optic Effect”, IEEE Transactions on Instrumentation and Measurement, vol. 53, no. 6, pp. 1533-1538, 2004.

[8] K. Fujii, M. Takahashi, K. Ito, “Electric Field Distributions of Wearable Devices Using the Human Body as A Transmission Channel”, IEEE Transactions on Antennas and Propagation, vol. 55, no. 7, pp. 2080-2087, 2007.

[9] T. Handa, S. Shoji, S. Ike, et al., “A Very Low-power Consumption Wireless ECG Monitoring System Using Body as A Signal Transmission Medium”, In Proceedings of 1997 International Conference on Solid State Sensors and Actuators, pp. 1003-1006, 1997．

[10] D. P. Lindsey, E. L. McKee, M. L. Hull, et al., “A New Technique for Transmission of Signals from Implantable Transducers”, IEEE Transactions on Biomedical Engineering, vol. 45, no. 5, pp. 614-619, 1998．

[11] K. Hachisuka, Y. Terauchi, Y. Kishi, et al., “Simplified Circuit Modeling and Fabrication of Intrabody Communication Devices”, Sensors and Actuators, pp. 322-330, 2006．

[12] M. Gray, “Physical Limits of Intrabody Signalling”, Massachusetts Institute of Technology, pp. 1-49, 1997．

[13] N. Matsushita, S. Tajima, Y. Ayatsuka, et al., “Wearable Key Device for Personalizing Nearby Environment”, In Proceedings of the Fourth International Symposium on Wearable Computers, pp. 119-126, 2000.

[14] K. Fujii, K. Ito, S. Tajima, “A Study on the Receiving Signal Level in Relation with the Location of Electrodes for Wearable Devices Using Human Body as A Transmission Channel”, In Proceedings of IEEE Antennas and Propagation Society International Symposium, pp. 1071-1075, 2003．


232

[15] J. A. Ruiz, S. Shimamoto, “Experimental Evaluation of Body Channel Response and Digital Modulation Schemes for Intra-Body Communication (IBC)s”, In Proceedings of IEEE International Conference on Communications, pp. 349-354, 2006.

[16] J. A. Ruiz, J. Xu, S. Shimamoto, “Propagation Characteristics of Intra-Body Communication (IBC)s for Body Area Networks”, In Proceedings of Consumer Communications and Networking Conference, pp. 509-513, 2006．

[17] N. Cho, J. Yoo, S. J. Song, et al., “The Human Body Characteristics as A Signal Transmission Medium for Intrabody Communication”, IEEE Transactions on Microwave Theory and Techniques, vol. 55, no. 5, pp. 1080-1086, 2007.

[18] K. Hachisuka, A. Nakata, T. Takeda, et al., “Development and Performance Analysis of An Intra-Body Communication (IBC) Device”, In Proceedings of the 12th International Conference on Solid Slate Sensors, Actuators and Microsystem, pp. 1722-1725, 2003.

[19] K. Hachisuka, T. Takeda, Y. Terauchi, et al., “Intra-body Data Transmission for the Personal Area Network”, Microsystem Technologies, pp. 1020-1027, 2005．

[20] Yong Song, Qun Hao, Kai Zhang, Ming Wang, Yifang Chu, Bangzhi Kang, “The Simulation Method of the Galvanic Coupling Intrabody Communication with Different Signal Transmission Paths”, IEEE Transactions on Instrumentation and Measurement, vol. 60, no. 4, pp. 1257-1266, 2011.

[21] S. H. Pun, Y. M. Gao, P. U. Mak, M. I. Vai, M. Du, “Quasi-Static Modeling of Human Limb for Intra-Body Communication (IBC)s with Experiments”, IEEE Transactions on Information Technology in Biomedicine, vol. 15, no. 6, pp. 870-876, 2011.

[22] K. Fujii, K. Ito, “Evaluation of the Received Signal Level in Relation to the Size and Carrier Frequencies of the Wearable Device Using Human Body as A Transmission Channel”, In Proceedings of IEEE Antennas and Propagation Society International Symposium, pp. 105-108, 2004．

[23] Hemanta Kumar Bhuyan, Sanjit Kumar Dash, Subrata Roy, Dillip Swain, “Privacy Preservation with Penalty in Decentralized Network Using Multiparty Computation”, IJACT: International Journal of Advancements in Computing Technology, vol. 4, no. 1, pp. 297-303, 2012.

[24] Hamid Mohammed Farhan, “A New Parallel Concatenated Coding Transceiver System Using Three Convolutional-Interleaver Sections”, IJIPM: International Journal of Information Processing and Management, vol. 3, no. 1, pp. 79-83, 2012.

[25] Tao Ma, Chunhong Zhang, Zhimin Zeng, “Selecting Relays for Faster Paths in Embedded Internet Delay Space1”, IJACT: International Journal of Advancements in Computing Technology, vol. 4, no. 2, pp. 176-184, 2012.


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