Even the microprocessor will be in an off mode as needed, he notes. Only a small unit will stay alive to awaken the rest of the system when necessary. After the devices are activated, they will operate from very low voltage power supplies, currently running between 0.3 volt and 1 volt. At its present stage of development, smart dust requires a battery the size of one used in a hearing aid, which composes 70 percent of the mote's total size, Hollar says. In later versions, the dust will use solar power, allowing the mote's size to shrink dramatically.
Communications is another consideration in the device's design.
The Smart Dust team chose to use free-space optical communication rather than radio frequency communication because this method requires significantly less energy per bit, university researchers say. The CCR is made of three gold-coated polysilicon mirrors positioned at right angles. When a laser shines on the mirrors, the light is reflected back to the source, Hollar explains. This method, which consumes little power, is an effective way to send information. A base station receiver that collects the information from each mote is an important aspect of the communication system, Brian Leibowitz, graduate student, says.