Abnormal absorption of subcritical water posts in microwave heating

Abstract

Subcritical water has been widely used as the solvent in microwave‐assisted extractions, but the interaction between microwaves and subcritical water has been not yet fully understood. In this article, we find that there exists abnormal absorption of subcritical water posts in microwave heating at some temperatures with low loss factors. By calculating the absorbed power of a subcritical water post under exposure plane waves, the water post can still absorb microwave energies well at some temperatures even with low loss factors. It is different from the traditional view that materials can absorb little microwave power with low loss factors. By analyzing the characteristic equation, we show that the abnormal absorption is caused by dielectric resonance. This abnormal phenomenon can also be observed in applications with microwave cavities. It indicates that even with low loss factors, materials can be possibly heated by microwaves with good efficiency.