The nonmetallic thermocouple: A differential-temperature probe for use in microwave fields


  • Richard G. Olsen,

  • Efrain A. Molina


A simple temperature probe is described that is suitable for use in microwave dosimetry. The sensor's tip is a thermocouple junction in which dissimilar nonmetallic conductors form the sensing element. The conductors themselves, although not entirely lossless, are readily available, carbon-loaded materials such as conductive silicone or conductive fluorocarbon. Secondary thermocouple junctions are formed where metallic leads attach to the nonmetallic conductors and the voltage output from the device is, for certain temperature ranges, proportional to the temperature difference between the primary and secondary junctions. An instrumentation amplifier is described that boosts the output of the probe and eliminates much 60-Hz interference. Tracking accuracy of the nonmetallic thermocouple (NMT) with the secondary junctions thermally insulated is within 0.1°C, and comparative dosimetric data are given to show that the NMT produces results that compare favorably with those obtained by other, much more expensive, probes. Use of the NMT in the laboratory environment requires the probe to be stationary to avoid noise pickup, a common problem associated with devices using high resistance leads.