Special Feature

Human Area Networking Technology:
RedTacton
Mitsuru Shinagawa†, Katsuyuki Ochiai, Hideki Sakamoto,and Toshiaki Asahi
Abstract
Ubiquitous services that are genuinely user-friendly to everyone will require technologies that enablecommunication between people and objects in close proximity. Focusing on the naturalness, inevitability, and sense of security conveyed by touching in everyday life, this article describes human area networking technology that enables communication by touching, which we call RedTacton. Here, thehuman body acts as a transmission medium supporting IEEE 802.3 half-duplex communication at 10
Mbit/s. The key component of the transceiver is an electric-field sensor implemented with an electrooptic crystal and laser light.

1. Introduction
Today people can communicate anytime, anywhere, and with anyone over a cellular phone network. Moreover, the Internet lets people download
immense quantities of data from remotely locatedservers to their home computers. Essentially, these
two technologies enable communications between
terminals located at a distance from each other.
Meanwhile, all kinds of electronic devices including
personal digital assistants (PDAs), pocket video
games, and digital cameras are becoming smaller, so
people can carry around or even wear various personal information and communication appliances during
their everyday activities. However, user-friendly
ubiquitous services involve more than just networking between remotely located terminals. Communication between electronic devices on the human body(wearable computers) and ones embedded in our
everyday environments such as illustrated in Fig. 1 isalso critical, so this has driven extensive research anddevelopment on human area networks.
Wired connections between electronic devices inhuman area networks are cumbersome and can easily† NTT Microsystem Integration Laboratories
Atsugi-shi, 243-0198 Japan
E-mail: shina@aecl.ntt.co.jp

Vol. 3 No. 5 May 2005

become entangled. Short-range wireless communication systems such as Bluetooth and wireless local
area networks (IEEE 802.11b, etc.) have some problems. Throughput is reduced by packet collisions incrowded spaces such as meeting rooms and auditoriums filled with people and communication is notsecure because signals can be intercepted. The principle drawback of infrared communications (IrDA) isthe tight directionality of beams between terminals
needed for the system to be effective.
The ultimate human area network solution to allthese constraints of conventional technologies is“intrabody” communication, in which the humanbody serves as the transmission medium. In ubiquitous services (which imply communication between
electronic devices embedded in the environment inclose proximity to people), if we could use the humanbody itself as a transmission medium, then this would
be an ideal way of implementing human area networks because it would solve at a stroke all the problems including throughput reduction, low security,and high network setup costs.
The concept of intrabody communication, whichuses the minute electric field propagated by thehuman body to transmit information, was first proposed by IBM [1]. The communication mechanism
has subsequently been evaluated and reported by several research groups around the world. However, all41

Special Feature

Human area
network

Human area
network
Human area
network

Human area
network

LAN

Peripheral computers
Wearable computers

Fig. 1. Human area networking technology.

those reported technologies had two limitations: 1) the operating range through the bodywas limited to a few tens of centimeters and2) the top communication speed was only 40
kbit/s. These limitations arise from the use ofan electrical sensor for the receiver. An electrical sensor requires two lines (a signal line
and a ground line), whereas in intrabodycommunication there is essentially only one
signal line, i.e., the body itself, which leads toan unbalanced transmission line, so the signal
is not transmitted correctly.

Eb
Transmitter

Laser light

Ea
Es

Electric fields

Electro-optic
sensorHumanbody
Detector
circuitEbEc

2. Human area networking
Ec

NTT has had excellent success with an
Groundelectro-optic sensor combining an electrooptic crystal with laser light and recently
Fig. 2. Principle of RedTacton.
reported an application of this sensor for measuring high-frequency electronic devices [2],by the transmitter’s signal electrode is represented by[3]. The electro-optic sensor has three key features:
Ea. The system requires a ground close to the trans(1) it can measure electric fields from a device under
mitter signal electrode, so electric field Eb induced
test (DUT) without contacting it, which minimizes
from the body can follow a return path to the transmeasurement disturbance, (2) ultrawide-band meamitter ground. Moreover, since people are usuallysurement is possible, and (3) it supports one-point
standing on a floor or the ground, electric field Ec
contact measurement that is independent of theescapes from the body to ground, mainly from theground, which is the most significant feature in thepresent context. NTT utilized this third feature to fabricate an intrabody communication receiver for its* RedTacton: The name we chose for this technology is derived
human area networking technology, which is calledfrom “touch-act-on” meaning “action triggered by touching” comRedTacton*.
bined with red, which in Japanese culture is an auspicious color
The operating principle of RedTacton is illustrated
with connotations of warmth and love, to convey the cordiality
and warmth of interpersonal communications [4].
in Fig. 2. The electric field induced toward the body
42

NTT Technical Review

Special Feature

Insulation film

RedTactontransceiver

Data sense
circuit

Detector
circuit

PDA

Transmittercircuit
Human body

Interface

Transmitter

Control signal

Electro-optic
sensorReceiverTransmitting/receiving
electrodeFig. 3. RedTacton transceiver.

feet. The electric field Es that reaches
the receiver is Es = Ea – (Eb + Ec). It
couples to the electro-optic crystal andchanges the crystal’s optical properties. This change is detected by laser
light and transformed into digital databy a detector circuit.

RedTacton transceiver

3. RedTacton transceiver
Figure 3 shows a photograph of the
RedTacton transceiver connected to a
PDA and a block diagram of the RedTransmitting/receiving
electrodeTacton transceiver [5] developed by
PDANTT. The transmitter consists of atransmitter circuit that induces electricfields toward the body and a data sense
circuit, which distinguishes transmitFig. 4. Experimental setup for intrabody communication.
ting and receiving modes by detecting
both transmission and reception dataand outputs control signals corresponding to the two
ceivers. The experimental setup for intrabody commodes to enable two-way communication. We implemunication assuming communication between two
mented a receive-first half-duplex communicationelectronic devices (PDAs) is shown in Fig. 4. We prescheme that sends only after checking to make surepared two sets of RedTacton transceivers, each conthat there is no data to receive in order to avoid packnected to a PDA. The subject held one transmitting/et collisions between terminals in compliance withreceiving electrode in each hand. We quantitatively
the IEEE 802.3 protocol. The receiver consists of an
measured the bit error rates of signals sent throughelectro-optic sensor and a detector circuit that amplithe body. The results showed that the system had nofies the minute incoming signal from the electrosignificant practical problems at a transmission speed
optic sensor and converts it to electrical signal.
of 10 Mbit/s. Besides communication between two
We conducted a series of trials in which data washands, we also demonstrated reliable communication
sent through human bodies using RedTacton transbetween a foot and finger and between other locaVol. 3 No. 5 May 2005

43

Special Featuretions on the person’s body. We also verified that goodcommunication was achieved not only when the electrodes were in direct contact with the person’s skin,
but also when the signals passed through clothing andshoes.
4. Human safety
We investigated the effects of RedTacton technology on human health, which is obviously an important
issue. First, as shown in Fig. 3, the transmitting andreceiving electrodes of the RedTacton transceiver arecompletely covered with insulating film, so the bodyof the person acting as the transmission medium iscompletely insulated. This makes it impossible forcurrent to flow into a person’s body from the transceiver.
When communication occurs, displacement current
is generated by the electrons in the body because thebody is subjected to minute electrical fields. However, such displacement currents are very common
everyday occurrences to which we are all subjected.
RedTacton conforms to the “Radio Frequency-Exposure Protection Standard (RCR STD-38)” [6] issued
by the Association of Radio Industries and Businesses (ARIB). The levels produced by RedTacton are
well below the safety limit specified by this standard.
5. Applications
In this section we highlight three distinctive features of RedTacton. First, a transmission path isformed automatically by body contact and this initiates communication between electronic devices. A
device can be started, information can be obtained, orvarious services can be triggered by a wide range ofnatural human actions such as grasping, sitting down,
walking, or standing in a particular place. Second, thecommunication is interactive and broadband. In contrast to RFID (radio frequency identification), which
is only capable of one-way transmission of short ID
messages, RedTacton supports two-way exchange oflarge amounts of data between portable electronic
devices. In contrast to conventional wireless systems,
RedTacton provides an independent transmission
path for each individual person (that is, for each conductor) even in congested places, so it provides very
secure, fast communication without any interference.
Third, almost anything that acts as a conductor—ahuman or animal body, water, metal, etc.—can serve
as a RedTacton transmission path. This means that
there is no need for a dedicated cable or antenna.
44

Some representative applications of RedTacton are
shown in Fig. 5. Figure 5(a) illustrates communication between mobile electronic devices on one person. In this case, the person is listening to music froma portable audio device through earphones. Instead ofa physical cord tethering the two devices, the data ispassed through the person’s body. Similarly, one
could envision a worker wearing a head-mounted display performing a complex task based on instructionsdelivered through his body from a pocket-sized computer. Figure 5(b) shows communication between
devices on different people, enabling them toexchange electronic business cards by shaking hands.
Figure 5(c) illustrates communication between an
electronic device on a person and one embedded in
the environment. One can easily think of a wide variety of applications of this type. For example, a person
might carry a PDA that transmits an ID or a simple
script (computer program) to a device embedded in
the environment. Then, when the person briefly
touches the system or simply walks through a gate,
the transmission could trigger various kinds of action
such as opening the gate or assessing the toll or
charge. A natural gesture such as turning a knob toopen a door could enable identification and authentication of the person seeking admission. Figure 5(d)shows a museum setting where a visitor can hear adetailed description of an object from an audio device
embedded nearby by touching the object or simply bystanding in front of the object. And finally, Fig. 5(e)illustrates a system where a metal surface acts as the
conductor of electric fields instead of a human body.
A conductive metal sheet is placed on top of a table,
and a conferencing system is created simply by placing devices on it. Laptop computers could be connected to the Internet by simply placing them on sucha table. Even different networks could be supported,
such as an enterprise LAN (local area network) andInternet access, by providing separate metal sheetsfor each network.
6. Conclusion
RedTacton is an exciting new technology for humanarea networking. We have developed a transceiverthat uses the human body as a data transmission
medium based on an electric-field sensor that uses anelectro-optic crystal and laser light. Using this transceiver, we succeeded in achieving 10BASE communication in accordance with IEEE 802.3 through ahuman body from one hand to the other hand.
While our immediate objective is to implement a
NTT Technical Review

Special Feature

Exchange electronicbusiness cards
by shaking hands.

Authentication is
performed byreading ID.

No cord between
the earphones and device

Simplywalk through.
(a) Communication between
devices on the same person(portable audio)(b) Communication between devices
on different people (exchange ofbusiness card data)

Transmission
mediumPDA(c) Communication from a device on a
person to a device embedded in
the environment (gateway system)
Connect a device bysetting it on the table.

LAN
Internet

Hear music or a description
by standing
in front of an exhibit.

Links are divided into
intranet and Internet access.

(d) Communication from a device embeddedin the environment to a device on a
person (explanatory tour in a museum)(e) Communication between devices
mediated by conductor(conferencing system)

Fig. 5. Applications of RedTacton.

RedTacton system supporting two-way intrabodycommunication at a rate of 10 Mbit/s between any
two points on the body, our longer-term plans include
developing a mass-market transceiver interface supporting PDAs and notebook computers while continuing efforts to reduce the size and power consumption of the transceiver to enhance its portability. NTT
is committed to using its comprehensive commercialization functions to push this research out to the marketplace as quickly as possible while moving ahead
with tests and trials in collaboration with commercial
partners as necessary [7].

References
[1]

[2]

[3]

[4]
[5]

[6]
[7]

Vol. 3 No. 5 May 2005

T. G. Zimmerman, “Personal Area Networks: Near-field intrabodycommunication,” IBM Systems Journal, Vol. 35, Nos. 3&4, pp. 609617, 1996.
T. Nagatsuma and M. Shinagawa, “Photonic measurement technologies for high-frequency electronics,” NTT REVIEW, Vol. 14, No. 6,
pp. 12-24, 2002.
M. Shinagawa, “Development of Electro-optic Sensors for Intra-bodyCommunication,” NTT Technical Review, Vol. 2, No. 2, pp. 6-11,
2004.
http://www.redtacton.com/
M. Shinagawa, M. Fukumoto, K. Ochiai, and H. Kyuragi, “A nearfield-sensing transceiver for intra-body communication based on theelectro-optic effect,” IEEE Trans. IM, Vol. 53, No. 6, pp. 1533-1538,
2004.
http://www.arib.or.jp/english/html/overview/st_j.html
M. Mizoguchi, T. Okimura, and A. Matsuda, “Comprehensive Commercialization Functions,” NTT Technical Review, Vol. 3, No. 5, pp.
12-16, 2005.

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Special Feature

Mitsuru Shinagawa

Hideki Sakamoto

Distinguished technical member, NTT
Microsystem Integration Laboratories.
He received the B.S., M.S. and Ph.D. degrees
in electronic engineering from Tohoku University, Sendai, Miyagi in 1983, 1985, and 2005,
respectively. In 1985, he joined NTT ElectricalCommunication Laboratories, Tokyo, Japan. His
technical areas of interest include timing jitter
analysis of high-speed sampling systems, electro-optic sensors, high-precision waveform measurement for ultrafast electronics, electric fieldmeasurement of printed circuit boards, and communication technology for human area networks.
He has received the Andrew R. Chi Prize Paper
Award from IEEE Transactions on Instrumentation and Measurement in 1992 and the Okochi
Memorial Award of Japan in 1997. He is a member of IEEE and the Institute of Electronics,
Information and Communication Engineers ofJapan.

Senior Manager & Producer, Strategic Business Creation Team, NTT Department III (R&D
Strategy Department).
He received the B.S., M.S., and Ph.D. degrees
in communication engineering from Osaka University, Suita, Osaka in 1984, 1986, and 1999,
respectively. He also received the M.S. degree inManagement of Technology from MIT. Sincejoining NTT in 1986, he has mainly been
engaged in developing multimedia systems. He
served as Project Editor of ISO MPEG-21 Standardization Activity from 2000 to 2002. He is theauthor of “Textbook of MPEG (ASCII, 2002)”,“Textbook of RFID (ASCII, 2005)”, “Textbook
of Digital Broadcast (IDG, 2002)”, “Textbook of
Digital Content Distribution (ASCII, 2003)”, and“Useful English Expressions 400 for MBA(ALC, 2000)”.

Toshiaki Asahi
Katsuyuki Ochiai
Senior Research Engineer, NTT Microsystem
Integration Laboratories.
He received the B.E. and M.E. degrees in information engineering from Utsunomiya University, Utsunomiya, Tochigi, in 1988 and 1990,
respectively. He joined NTT LSI Laboratories,
Kanagawa, Japan in 1990, where he engaged inresearch on a concurrent design environment forsystem LSIs. Since 2002, he has been with NTT
Microsystem Integration Laboratories, where hehas been involved in R&D of broadband intrabody communication systems.

46

Associate Manager & Producer, Strategic
Business Creation Team, NTT Department III(R&D Strategy Department).
He received the B.S. degree in electronic engineering from Osaka Electro-Communication
University in 1992. He joined NTT’s Equipment
Engineering Department, Kobe, Japan, in 1992,
where he was engaged in access network engineering. After that, he moved to the Equipment
Planning Department, NTT Headquarters, where
he was engaged in equipment planning andinvestment. Currently he is engaged in creating
new business using technology produced by
NTT Laboratories.

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