A micromachined electret-based transponder for in situ radiation measurement

This letter reports on the development of a micromachined passive transponder for in situ measurement of ionizing radiation. gamma-ray exposure is remotely measured by monitoring the resonance frequency change correlated with a change in the surface charge of an electret. This is achieved through a micromachined capacitor with a movable plate that is partially filled with a Teflon electret and connected in parallel with an inductor, forming a passive LC tank (a microionization chamber, 1.5 cm in diameter and 3 mm in thickness). Test results show that an exposure of 60 000 R from Cs-137 produces a 687-kHz resonance frequency shift (sensitivity of 11.45 kHz/kR).