Engineers are developing a wireless device the size of a grain of rice which could be implanted in tumors within the body to track radiation exposure and tumor position during treatment. The device is intended to provide doctors with exact, real time radiation dosage information during cancer treatments. The rice sized device would be powered externally by placing the patient next to electrical coils which create localized magnetic fields. This eliminates the need for batteries, allowing unlimited use during treatment. The device would also be able to pinpoint the exact position of tumor after implantation, and provide dosage information through wireless communication from within the body. The device, which contains a miniature version of dosimeters worn by people in occupations involving radioactivity, could provide up-to-date information about the cumulative dose a tumor is receiving over time. The technology uses the same principle as electret microphones, popular products found in consumer electronics stores. The microphones contain a membrane that vibrates in response to sound waves. Between the membrane and a metal plate is an air gap that serves as a capacitor, or a device that stores electricity. As the membrane vibrates, the size of the air gap changes slightly, increasing and decreasing the capacitance and altering the flow of electric current through the circuit, creating a signal that transmits information stored in the dosimeter. "It's basically like a very small tuning circuit in your radio," Ziaie said. "This will be a radiation dosimeter plus a tracking device in the same capsule. It will be hermetically sealed so that it will not have to be removed from the body." The device is an example of a microelectromechanical system, or a tiny mechanical device fabricated using methods generally associated with microelectronics.