Microwave absorbing properties and structural design of a double-layer microwave absorber based on auxiliary absorbing of SiC for microwave drying

Compared with conventional drying technology, microwave assisted drying technology has some remarkable properties, such as material-selective, instantaneous and volumetric heating, which leads to extremely broad applications in materials drying. The efficiency of microwave drying is found to be dependent on various factors, such as temperature, moisture content, the dimension of material and so on. But it is not heavy enough only to optimize the parameters mentioned above to improve the efficiency of microwave drying material, especially drying those with relatively low microwave absorbing ability (low-loss absorbers). In this paper, a double-layer absorber consisting of high-loss silicon carbide ceramic layer and low-loss silica sand layer has been devised to enhance the microwave absorption capabilities of relatively poor microwave absorbing materials at first. Then the optimal thickness of SiC ceramic auxiliary absorbing layer is presented by calculating reflection loss for individual layer SiC. Moreover, the microwave absorbing properties of an individual absorber of silica sand and the double-layer absorber are investigated by simultaneously considering the effects of various factors (temperature, humidity and absorber dimension) at 2.45 GHz, respectively. The result indicates that a 0.0075-m-thick SiC layer has strong microwave absorption and can be considered as optimal auxiliary absorbing ceramic substrate. Moreover, the reflection loss remarkably decreases based SiC ceramic auxiliary absorbing, that is to effectively increase the microwave absorbing ability. Moreover, the double-layer absorber substantially broadens the range of optimal thicknesses within absorption bandwidth with reflection loss less than −20 dB and a smaller thickness region of silica sand layer is particularly essential to achieve the maximum absorption throughout the microwave drying. The current work provides a new method on designing microwave absorber, which could provide insight on improving microwave absorption capabilities of relatively poor microwave absorbing materials throughout the microwave drying.