R&D Spirits
Development of Electro-optic Sensors
for Intra-body Communications
Mitsuru Shinagawa
Distinguished Technical Member
Smart Devices Laboratory
NTT Microsystem Integration Laboratories

Researchers at NTT Microsystem Integration Laboratories have recently demonstrated intrabody communications at practical levels. Such communication within a person’s body, which
has up to now been difficult to achieve, brings the ubiquitous computing world one step closer
to becoming a reality. What kinds of things are possible with intra-body communications?
Where are research and development in this field headed? We put these questions to MitsuruShinagawa, a Distinguished Technical Member of the Smart Devices Laboratory and developer of electro-optic sensors, a key technology in this field.

Demonstration of intra-body communicationsat practical levels using electro-optic sensors—Mr. Shinagawa, could you describe your current
research for us?
Well, it concerns the research and development ofintra-body-communications technology in which thehuman body is used as a line for conveying a weakelectrical signal. Consider the jolt of static electricity
that most of us have felt when touching something
metallic like a doorknob. The human body is made upof material that can conduct electricity. And if electricity can flow, why shouldn’t we consider the possibility of using the body as a local area network toenable communications? This basic premise of intrabody communications, which is neither wireless nor
wired, is an entirely new concept for communications
systems.
As computers continue to decrease in size, more
and more of them are becoming a part of our daily
life. If this process of miniaturization continues andwearable computers become commonplace, we will
be able to carry information around with us in a more
evolved form of the cellular terminal. At that time, I
think it would be natural to expect computers6

attached to the body to be able to interconnect freely
with peripheral computers at high communication
speeds. I think intra-body communications will behighly effective here.
—What are some important technical features of thisresearch?
In a typical electronic circuit, a signal travels
through a signal line and returns by a ground line
forming a path that makes it possible to detect thatsignal. When attempting to form a circuit in a human
body, however, we must remember that there is only
one body, which means that there is no return patheven if a signal line can be achieved. In other words,
the electric field leaks here and there within the body.
At the same time, electricity that travels through thehuman body is intrinsically weak. Conventional technology has not been able to detect signals in such animperfect state. In response to this problem, I came touse highly sensitive electric-field sensors using electro-optic crystals and a laser beam. An electric-fieldsensor is a tool for detecting electrical signals as theypass through an electro-optic crystal. It can operate
even with imperfect circuits such as those formed in
the human body.
NTT Technical Review

R&D Spirits

Polarization
changeNon-contact probing system

Micro-probe system
E

Laser
beam

Refractive
indexchangeEO crystal

Principle of EO probing

Sampling oscilloscope

Realtime hand-held probe

Fig. 1. Electro-optic (EO) probing systems.

This electric-field sensor, by the way, is based on
the results of earlier R&D work on integrated-circuitprobing equipment (Fig. 1). An integrated circuit
consists of many signal lines on a very small chip,and a ground line does not necessarily run right next
to each signal line. This, and the fact that the directionof electric-field leakage is unknown, led me to develop a sensor that could make measurements underthese conditions. Then, I wondered whether a sensor
of this type might be able to detect signals in thehuman body.
However, this was not as simple as it seemed. To
begin with, in an experiment applying an unmodified
sensor for integrated circuits to the human body, nosignals at all could be detected. After investigating
this problem from a number of angles, I finally realized that the sensor used for integrated circuits wassimply not suitable for measuring electric fields in thehuman body. It took more than a year, however, tocome to this realization. This research was going sobadly for a while that, at one time, I even wondered
whether the human body could transmit signals!

occur when I decide to enter a room: I approach thedoor, stand in front of it, touch the doorknob, andopen the door. At this time, my hands and feet comeinto contact with the doorknob and floor in front of
the door, which suggests that this technology could
allow the processes of identifying me and unlocking
the door to be performed automatically. This is agood example of how unconscious actions can act asa key for conveying human intent. I’d like to point out
here that NTT researchers have made a career ofdetermining how to communicate freely at a distance.
Of course, this is also an important endeavor, but as
we enter the ubiquitous computing age, shouldn’t wealso pay attention to natural communication at closeproximity to ourselves? Intra-body communications
would no doubt be extremely useful here. Technologically speaking, such short-range communications
could also be accomplished by wireless means, but incongested conditions, the speed of wireless connections can drop dramatically and making a connection
itself can be difficult. In contrast, the closed environment of the human body can maintain stable communications.

—How can this technology be used in the future?
Consider, for example, the sequence of actions thatVol. 2 No. 2 Feb. 2004

—How do you think this technology will evolve inthree or five years time?
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R&D Spirits

In addition to the door-unlocking example I justgave, other ideas at this stage include exchanging
business-card data and inputting it to a PDA (personal digital assistant) simply by shaking hands andautomatically downloading information just by
touching some object (Fig. 2). We can also envisionusing this technology to display information stored ina pocket computer on a head-mounted display. I can’t
really say what might be possible in three years time,
but in about five years, I would hope to see this technology used for offering some forms of services andgaining a foothold in society.
—How is your research going at present and what aresome current issues?
We are currently able to demonstrate intra-bodycommunication speeds of 10 Mbit/s. But to bring thetechnology to a level that can support services, wemust first solve a number of issues. One is device
size. While we have been able to develop a device thatcan be carried around on one hand, it is still too large
to be considered “wearable.” Another issue is charging a device attached to the body. A battery that supplies power for only one or two hours is hardly sufficient here—power consumption must be reduced. We

need to integrate the electronics and improve the sensitivity of the electric-field sensor, the key component
here. And in addition to solving these technicalissues, it is vital to disseminate information about
applying this technology. Since intra-body communications is an entirely new concept, there will probably be some initial difficulty in applying it to businesssituations even if all technical issues have been ironedout. In this regard, some stern comments were recently expressed at the NTT R&D Forum in the form of“That’s very interesting in terms of technology, butwhat can it do for industry?” To put intra-body communications on the right path toward practical use
and enable it to contribute to society, we must give
people some idea of its usefulness.

Encountering the “perfect theme” just beforechanging fields—What research themes have you been occupied withup to now?
When I was at Tohoku University, I was involved inresearch for radio astronomy and worked on experiments and numerical analysis dealing with submillimeter-wave frequency response in superconducting

PDA

Data

PDA

Data

PDA

Unlock door

Fig. 2. Application of intra-body communications.

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R&D Spirits

Josephson junctions. Then, upon entering NTT, I
became involved with R&D in the field of circuitdesign. As the need became apparent for accurate
measurement and evaluation technologies for developing high-speed integrated circuits, I changed myfocus to this research theme. Here, as well, electrical
technologies were used at first, but I came to noticethat using the same electrical devices for the measurement and evaluation of advanced LSIs and ICs
had limits. That is how I came to develop the electrooptic sensor. Because light travels much faster thanelectricity, I thought that perhaps light could be put touse in measuring all the advanced integrated circuits
developed by NTT. I have been involved in theresearch and development of such technology eversince.
—How did your current research into intra-bodycommunications begin?
When the first phase of R&D for electro-optic sensors was completed and it came time to move on tothe next phase, a researcher at NTT DoCoMo happened to ask me whether the electric field of thehuman body could be detected. I immediately
thought of the possibility of intra-body communications. This could not have happened at a better time.
Perhaps it was insufficient dissemination of myresearch results, or maybe that the times were changing too fast, but the usefulness of my electro-optic
sensor was not well understood despite the fact that it
was a complete working system. I had therefore
decided to talk to my superiors about learning newskills. It was exactly at that point that I encountered
this somewhat crazy but extremely fascinating idea ofusing an electro-optic sensor for measuring signals in
the human body. Considering that I could apply technology that I had been cultivating for over ten years
and might make some contribution to the creation ofan entirely new form of communication services, thiswas the perfect theme. If my conversation with that
DoCoMo researcher had taken place several months
later, I might now be immersed in a completely different research topic. It feels as if this “chance”
encounter was actually fate at work and that I wasmeant to take on this research. Above all, I was quite
overwhelmed by the enthusiasm expressed by that
researcher, and it didn’t take me long to make intrabody communications my next research theme. To
this day, I still have discussions with him as myVol. 2 No. 2 Feb. 2004

research proceeds.
—What is happening in Japan and overseas in thisresearch field?
The world’s first demonstration of intra-body communications took place at MIT in 1996. This was followed, in Japan, by successive announcements fromNTT Human Interface Laboratories, Sony Computer
Science Laboratories, Matsushita Electric Works, andothers. More recently, reports have come out of
Washington University and The University of Tokyo.
All of those demonstrations, however, used electrical
technologies, and in all cases, the communication
distances in the human body were only a few tens ofcentimeters and the communication speeds were only
on the order of 10 kbit/s. We feel that our demonstration of intra-body communications using light andachieving speeds of 10 Mbit/s puts us one step aheadin this field. At the same time, the number of patentapplications related to intra-body communications isincreasing year by year, indicating that various
research institutions are beginning to devote true
R&D efforts in this direction.

Progress in intra-body communications
needs the participation of many researchers—Are you active in any international organizations
and committees?
In May of last year, I presented a paper on this topic
at an international conference for the first time, and inJuly, I presented a dynamic exhibit in collaboration
with the DoCoMo researcher. In Japan, I also prepared a dynamic exhibit for the NTT R&D Forum
held in October. Until recently, laboratory policy forbade presentations related to this research, and as aresult I am still not involved in any international
activities. From here on, I think we need to give morepresentations in various formats.
—What kind of response did you receive from lastyear’s presentations?
At the dynamic exhibits, everyone was surprised atseeing the same signal as flowing through a LAN
cable also flowing through a human body. Some people were so astonished that they wondered whether
the whole thing had been contrived like a magic trick.
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R&D Spirits

Many people were also concerned about the possibility of getting an electric shock, but once they realizedthat the signal was very weak and that they would feelnothing, they connected and disconnected the signal
many times to experience this “magic.”
I received several inquiries by mail after these presentations. For example, some people asked whether
their components could be used in our electro-optic
sensors, which was really a business inquiry, whileothers were so impressed with the exhibit that they
asked about purchasing the equipment regardless ofthe price. From our side as well, business strategies
play a role in our research, and dealing with suchinquiries is not a simple matter. We were certainly
surprised, though, on hearing such questions.
—Are any joint activities being pursued with businessenterprises or research institutions in Japan or overseas?
At present, there are none, but I think partnering isvery important. I cannot imagine excluding NTT
DoCoMo from such activities, and as long as they arewilling, I think DoCoMo will be the first partner. At
such time, we will probably select applications thatcan contribute in some way to the NTT Group. However, that is still years away.
—On the other hand, is there any competition?
As I mentioned earlier, there are research institutions and researchers in both Japan and overseas
working on intra-body communications, and I imagine that some of them would be considered competitors. There is some talk, however, that everyone iscoming up against walls and even changing research
themes. If that is the case, I think that hearing about
our progress might convince some of thoseresearchers to try again. I have even heard that someresearchers, though continuing in their research, havebegun to doubt the feasibility of realizing practicalintra-body communications and are becoming dispirited. I hope that our reports give them encouragement. While we are proud to be the leader in thiscompetitive environment at this time, we cannot
bring about a major movement in this field on ourown. As more people participate, progress in intrabody communications technology will accelerate.

10Promoting the use of electro-optic sensors inthe world as life work
—Based on your experiences, how do you think NTT
is viewed overseas?
During the time that I was researching measurement systems and giving presentations at academic
societies, it was often said that “Research at NTTLaboratories targets themes that are feasible andunderstood.” Similarly, some people would say “Wewant NTT Laboratories to make unbelievable things
possible, and to establish fundamental technologythat creates new industries.” While I could not saythat NTT at present only takes on high-risk research,
I do think that the research that my colleagues and I
are working on matches those expectations, at least inpart.
—Where do you think your research is headed in theyears to come?
As I mentioned earlier, I believe the field of intrabody communications will encompass two majoraspects: R&D of platform technology and the development of usage scenarios. I would like to continue
my R&D work in this area with the hope that intrabody communications technology will one day beinstalled in all kinds of computers including digital
home appliances and cellular phones. My dream isthat it becomes a standard technology closely connected to everyday life and can contribute to thedevelopment of easy-to-use ubiquitous computing
services.
At the same time, the origin of my current research
activities is, in the end, electro-optic sensors.
Encountering the application theme of intra-bodycommunications by chance just when I was thinkingof breaking completely from electro-optic sensors
tells me that these devices are my chosen field. If I
should depart from my current line of R&D, I would
like to take on the challenges of electro-optic sensor
technology once again. Its application is not limited
to the human body. It can be extended to animals andplants and even to buildings and the earth. I would
like to analyze the weak fields generated in suchmaterials to see what kinds of information can beconveyed and develop sensor systems that can extract
information beneficial for the human race.

NTT Technical Review

R&D Spirits—Mr. Shinagawa, what has it been like working atNTT Laboratories?
I cannot say enough about the benefits of working
at NTT Laboratories in just a few words. But something of great importance that I have recently come torealize is the great amount of freedom given toresearchers. As long as I clearly explained what I
wanted to accomplish, I was allowed to take on a newtheme within a reasonable range and I was granted
suitable resources. Furthermore, when there wassomething I wanted to know about some technology,
there was usually someone in the laboratories working on that research. That made it very easy to conduct research. NTT Laboratories also provides anenvironment where you can take on a new challenge
without the fear of failing. I was allowed to begin mywork on intra-body communications with no guarantee of success. Finally, another important benefit ofNTT Laboratories is the ability to gather information
quickly from around the world as well as to disseminate information quickly and extensively to the outside. I don’t think there is another research institution
like NTT Laboratories. It’s a wonderful working
environment that I am grateful for.

Vol. 2 No. 2 Feb. 2004

Interviewee profile
Mitsuru Shinagawa received the B.S. and M.S.
degrees in electronic engineering from Tohoku University, Sendai, Japan, in 1983 and 1985, respectively.
In 1985 he joined the Electrical Communication Laboratories, NTT, Tokyo, Japan. He is currently a Distinguished Technical Member in the Smart Devices
Laboratory, NTT Microsystem Integration Laboratories, Kanagawa, Japan. His technical areas of interest
include timing jitter analysis of high-speed samplingsystems, electro-optic sensors, high-precision waveform measurement for ultra-fast electronics, electricfield measurement of printed circuit boards, and communication technology for personal area networks.
Mr. Shinagawa is a member of IEEE and the Instituteof Electronics, Information and Communication Engineers of Japan. He received the Andrew R. Chi Prize
Paper Award from the IEEE Transactions on Instrumentation and Measurement in 1992 and the Okochi
Memorial Award of Japan in 1997.

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