University of Tokyo researchers have developed a plastic pad that allows electronic devices placed on it to communicate with each other. This communications sheet could provide a more secure and lower-energy alternative to short-range wireless communications, such as Bluetooth.

"The first application might be an 'intelligent table' " that would allow a few devices to communicate with each other without the need to wire them together, says Takao Someya, professor of engineering at the University of Tokyo. Someya says that the team's long-term goal is to develop a system that connects thousands of devices, as might one day be required. The amount of energy needed to wirelessly connect such an array of devices "would be huge," he says, and wiring them all together would be cumbersome. Someya's approach uses a combination of extremely short-range wireless communications and wires to provide a low-energy alternative.

The sheet, which is one millimeter thick, is made by inkjet-printing various insulating and semiconducting polymers, as well as metal nanoparticles, to make transistors, plastic microelectromechanical (MEMs) switches, communications coils, and memory cells. It's designed to be used in combination with another sheet developed by the Tokyo researchers last year that can sense the location of an electronic device placed on it and deliver power to it. (See "Plastic Sheet of Power.") The new technology was presented this week at the International Electron Devices meeting in Washington, DC.

Each communications sheet, which is not quite as wide as a sheet of paper, is made of an eight-by-eight-inch grid of cells. Each cell contains a coil for transmitting and receiving signals, and plastic MEMs switches for turning the coils on and off and for connecting to adjacent cells. Once someone places two electronic devices on the sheet, sensors register their location. A control chip (made using conventional silicon processes) at the edge of the sheet decides on the best way to route signals between them through the sheet.

Communication involves two processes. First, information is transmitted wirelessly between the device and the sheet using extremely short-range radio signals (on the order of millimeters). Then a series of MEMs switches are closed to form a wired connection between adjacent cells forming a path between the two devices. This forms a wired connection between a receiving coil under the first device and a transmitting coil under the second. When the devices are moved or removed, or when new devices are added, new communications links can be formed on the fly.