Adventures in the Skin Trade

This month, NTT Labs, the research and development wing of Nippon Telegraph and Telephone Corporation, plans to start conducting field trials for a radical new “human area networking” technology called RedTacton that uses the naturally-occurring electrical fields of human skin to transmit data.

The slim, PCMCIA-based RedTacton transceiver combines an optical receiver circuit equipped with a super-sensitive photonic electrical field sensor and a crystal to transmit data over the surface of human body at up to 10 megabits per second between wearable devices.

Linked only by touch, the transceivers can also connect to similar transceivers worn by other users or embedded in any objects in real space, such as turnstiles or consumer electronics. Promising better security and far less interference than short-range wireless technologies such as Bluetooth, ZigBee and Near-Field Communications, RedTacton will likely be targeted for use in applications such as wireless headphones, wearable medical devices, security applications, and point-of-sale interactions.

RedTacton may be new, but the guiding principles behind it have been around for almost a decade. In 1996, MIT Media Lab researchers Thomas Zimmerman and Neil Gershenfeld published a paper that quickly engaged the mainstream media. The team developed a prototype of an intra-body communication network that exploited minute electrical fluctuations along the surface of the human skin to transmit data between devices. Penn and Teller used the technology for a magic trick in which a musical instrument was played without it being touched. IBM Almaden Research Center, which had backed the project, quickly snapped up Zimmerman and the technology for wearable-computer networks.

To date, though, no applications have seen the light of day. In fact, since then, there are has been little more heard on the subject. Further research was done at MIT, The University of Washington, The University of Tokyo, Microsoft, Sony, and Matsushita, but nobody seemed to be able to overcome the basic barriers of distance (measured in centimeters) and limited bandwidth (low double-digit kilobits per second). The dream of having two people shake hands and exchange anything more than the contents of a business card between wrist-mounted computers seemed nowhere in sight.

Enter Mitsuru Shinagawa, a Distinguished Technical Member of NTT’s Smart Devices Laboratory. Several years ago, Shinagawa had been working with the latest electro-optical sensors for a project on integrated circuit probes when he decided to apply the gizmos to the old intra-body problem. Replacing the electrical sensors of a Media Lab-style system with faster lasers and electro-optic sensors showed dramatic results.

“The first breakthrough was the idea to apply EO sensors,” says Hideki Sakamoto, senior manager for NTT’s R&D Strategy Department. “We accidentally realized that highly sensitive integrated circuit probes could be used for communication over the human body.”

The phenomenon that Shinagawa first detected was that the optical properties of an electro-optic crystal vary when there are changes in a weak electric field. When the body’s natural electric field interacts with that of the nearest transceiver, for example, distinctive oscillations are transmitted between the fields. Polarized by the oscillations, a tiny laser beam shoots through the RedTacton crystal, and the sensor measures the reflection and converts it to an electrical signal.

First demonstrated at Siggraph by NTT in 2003 under the name ElectAura-Net, the technology has been significantly upgraded in the latest RedTacton prototype.

“We had various problems, including noise and energy consumption, but we have solved one after another,” says Sakamoto.

According to Kurt Partridge, who was the principal designer of a recent intra-body networking system at The University of Washington, RedTacton far exceeds the capabilities of any of the existing electrical-sensor-based projects.

“The speed they’re getting is very impressive,” says Partridge, who is now a researcher at PARC. “It makes the technology competitive with other short-range communications technologies like Bluetooth, Zigbee, and UWB.” 

Partridge is looking forward to seeing how well NTT has solved the power-consumption issue.

“Their early prototypes consumed a lot of power;” he says. “Hopefully they’ve addressed this problem.”

Although some potential customers might balk at the idea of their bodies being lit up like a Christmas tree, Sakamoto claims the system is completely safe because no current flows into the body. He also says that the signal integrity is invulnerable to rain, cold, heat, static electricity, or electrical storms.

He does admit, however, despite its infrequence, “data exchanges are sometimes disrupted by electromagnetic waves–radio waves of a particular frequency.”

The big breakthough for RedTacton, says Sakamoto, is that it frees the technology from the more severe problems of interference among wireless devices. RedTacton apparently maintains its bandwidth even during simultaneous communications with multiple users. (If true, the group hug could turn into a productivity tool as well as a motivational technique.)

The small transceiver fits comfortably in a shirt pocket and unlike previous systems does not require a direct connection to the skin. The prototype can communicate at 10Mbps with other transceivers on the body, for example, mediating transmission between an MP3 player and a headset, and Sakamoto says it will soon shrink to the size where it can be built-into cell phones and other devices. When connecting beyond the body, the electric field can travel through conductors and dialectrics at a distance ranging from centimeters to meters, depending on the level of conductivity.

NTT is particularly enthusiastic about touch-based personalization applications. For example, the act of sitting in your car seat could instruct seats and mirrors to adjust accordingly or picking up a shared cell phone would instantly make it yours. NTT also envisions touch-based interactive advertising that customizes itself to an individual’s profile or smart medicine bottles that would sound an alarm if you try to take the wrong pill.

Before the technology goes commercial, Sakamoto says, it will probably first be integrated into security applications. Because RedTacton avoids wireless snooping, touch-based purchases would be private and provide authentication to vendors, allowing people to do things such unlocking a door simply by touching the knob.

Edging toward the Big-Brother scenarios that all such pervasive technologies seem to enable, RedTacton could be built into objects such as filing cabinets so companies could keep track of who used what.

Assuming NTT Labs has solved its power problems and can regularly achieve even a quarter of its top, 10Mbps rate, it should find a place in the market. The biggest challenge is the glut of competing short-range wireless formats that use more proven technology.

While NTT positions RedTacton against the leading short-range contender, Bluetooth, perhaps the more apt comparison is with the up and coming Near Field Communications technology. NFC’s RFID-like technology only transmits at a few hundred kilobits per second, but it’s likely to be much cheaper than RedTacton (or any other competing technology), and like RedTacton, it boasts greater security due to its short, 10-centimeter range. Sony and Philips hope to get NFC embedded in everything from cell phones to smart cards over the next few years.

Aside from offering greater bandwidth, RedTacton’s biggest advantage over NFC and other wireless technologies is convenience.

“You do not have to take your ID card from your pocket,” says Sakamoto. “Just touching or walking with your PDA in your pocket is enough for authentication.”

Some people will be highly attracted to the idea of using their bodies as networks, and new applications could flourish. Yet psychological barriers could prove a problem with many users. Even if convinced of the device’s safety, some might worry about privacy or theft from accidental physical contact. With proper security, these are not serious problems, yet some users might also feel a vague sense of violation of their personal space.

Sakamoto argues that we have overcome such psychological barriers many times in the past.

“If the user benefit is much larger than their concerns, people will start to use it,” he says. “This is exactly what happened to cell phones.”