MILLIMETER WAVE RADIO RESPONDER FOR REMOTE SENSING OF SURFACE CONDUCTIVITY AND LASER LIGHT INTENSITY

Abstract

A millimeter wave radio responder was evaluated as a remote sensor of surface conductivity and laser light intensity. A 10 mm CdSe photocell was illuminated by a 1/4 mW, 632.8 nm He-Ne laser light. The photocell was not connected to anywhere. The terminals were left open. The photocell was interrogated by a remotely placed millimeter wave radio responder operated with the frequency of 69.6 GHz and the transmitter power of 3 mW. The millimeter wave radio responder was able to sense the radio echo from the surface of the photocell. The laser illuminated area on the photocell was only 2.86% of the entire active area, yet the radio responder output showed up to 15 dB difference between the laser spot on and off from the target. The minimum reflected signal change observed was 0.002 dB by tilting the target 20 degrees from the normal incidence of the millimeterwave beam. This was translated to be 0.025% of surface conductance change on the target. This remote sensing was done using an instrumentation of the sensitivity of !40 dBm. Thus, the usefulness and advantage of employing a millimeter wave radio responder for remote sensing of minute change in the surface conductivity and/or the laser light intensity have been demonstrated in this research.