Error Sources Affecting Thermocouple Thermometry in RF Electromagnetic Fields

Publisher Website
Google Scholar
Abstract
Thermocouple thermometry errors in radiofrequency [rf] (typically 13.56 MHz) electromagnetic fields such as are encountered in hyperthermia are described. RF currents capacitatively or inductively coupled into the thermocouple-detector circuit produce errors which are a combination of interference, i.e., pick-up error, and genuine rf induced temperature changes at the junction of the thermocouple. The former can be eliminated by adequate filtering and shielding; the latter is due to junction current heating in which the generally unequal resistances of the thermocouple wires cause a net current flow from the higher to the lower resistance wire across the junction, heating in the surrounding resistive material (tissue in hyperthermia) and eddy current heating of the thermocouple wires in the oscillating magnetic field. Low frequency theories are used to estimate these errors under given operating conditions and relevant experiments demonstrating these effects and precautions necessary to minimize the errors are described. At 13.56 MHz and voltage levels below 100 V rms these errors do not exceed 0.1.degree. C if the precautions are observed and thermocouples with adequate insulation are used. Results of this study are being currently used in clinical work with good success.

This publication has 8 references indexed in Scilit: