Probing multimode applicator of microwave heating system for E‐field distribution using a silicon carbide sensor and a shielded thermocouple

Abstract

AbstractMeasurement of the field distribution in a multimode applicator of a microwave heating system has been a challenging problem. We report here a simple but comprehensive scheme for its semi‐quantitative estimation under no‐load conditions. It involves the measurement of temperature (T) versus time (t) profiles in a small silicon carbide (SiC) sensor ring positioned at the junction end of a metal‐jacketed microwave‐compatible thermocouple probe arrangement. These heating profiles (T vs. t) were measured using a data acquisition system, keeping the SiC ring at different (x, y, z) positions in the applicator. Using this measurement scheme, the spatial positions with local field minimum as inferred from very high reflected power or those with local field maximum with associated thermal runaway type condition could be well identified. Given the thermal and the dielectric properties of SiC material and the physical dimensions of the sensor ring, a uniform microwave field‐based model with a thermal lumped element type approximation (with no thermal gradient across SiC) was applied for analysis of the T versus t heating profiles. Within this model, the locally effective electric field E could be inferred for low and moderate electric field ranges. While the accuracy of the field estimation is currently limited by the use of the metal‐jacketed thermocouple and other factors, this SiC sensor‐based methodology has the potential to be developed further to be useful in the area of microwave applicator design.