A comparative study of frequency-shifting strategies for uniform and energy-efficient microwave heating in solid-state microwave systems

Inhomogeneity of microwave heating is an inherent drawback for gentle and uniform microwave processing. Innovative solid-state microwave generators have the potential to address this limitation by different multifrequency shifting strategies. Thus, we investigated different optimisation approaches derived from literature regarding uniformity and energy efficiency. We compared them to a newly-developed experimentally-derived optimisation strategy using the newly found relationship that at resonant frequencies a change of the heating pattern in the sample occurs. This was exploited by selectively exciting at neighbouring frequencies to the resonant frequencies (& PLUSMN; 2 MHz) to result in maximum uniformity achievable by frequency variation and, at the same time, high energy efficiency (i.e. 95.0%). High uniformity and high energy efficiency are, thus, not a tradeoff. This study proposes a promising optimisation strategy that relies on the individual sample feedback for frequency selection, thus it could have the potential to account for differing process and product conditions in future studies.