| Popis: |
This paper describes micromachined gas-based radiation sensors that are capable of radio frequency wireless signaling, and their possible utility in networks. The devices include a gas-filled region with a high electric field, in which incident beta-particles initiate avalanche breakdown. Under the proper circumstances, the resulting current pulses can inherently produce wireless transmissions. Two types of lithographically-manufactured devices are presented: (1) a silicon/glass stack with etched detection cavities and (2) a planar, 3-electrode metal-on- glass structure that uses a high-impedance electrode for increased control of discharge energy. Both are capable of producing ultra-wideband signals spanning >2.9 GHz. Permanent magnets (integrated with both structures) can enhance the RF performance by ap15-20 dBmuV. The impact of operating pressure, fill-gases (which are typically a mixture of Ne and N2) and electrode materials (Ni, Cu) on device performance is described. Tests performed in the proximity of weak (0.1-1.0 muCi) beta sources (90Sr, 204Tl), show that a 25% decrease in pressure permits a 55% decrease in operating voltage. Increasing Ne content in the fill-gas (e.g. Ne-to-N2 ratio from 1:5 to 3:5) decreases the minimum operating voltage by 200 V without loss in RF performance. Ni electrodes, which have a higher secondary electron emission coefficient than Cu, provide 30% more overall signal power. |
