Microwave dielectric properties of agricultural biomass at high temperature and in inert environment

Abstract

Abstract. The fundamental understanding of dielectric properties is very important to know the heating characteristics of material and the changes in microwave absorption characteristics during processing to design, model and simulate the microwave system for high temperature applications. The aim of this research work was to investigate the microwave dielectric properties of agricultural biomass (oat and barley straw) in the temperature range of 30 to 700 °C at 915 and 2450 MHz frequencies and under nitrogen (N 2 ) environment. Cavity perturbation technique was used to measure the dielectric properties. The heating process was divided into three distinct stages, namely drying (from room temperature to ~200EsC), pyrolysis (from ~200EsC to ~450EsC), and char region (from ~450EsC to ~700EsC). Overall, the dielectric properties of the selected agricultural biomass decreased during drying and pyrolysis stages. A dramatic change in dielectric properties was observed in the char region. Selected agricultural biomass can be considered as a low loss material since they are poor absorber of microwave at temperature below 400 °C. However, their microwave absorption capability improved significantly when the temperature went beyond 450 °C. This was because of conversion of agricultural biomass into carbonaceous char material. Lastly, numerical modeling of microwave dielectric properties of agricultural biomass is also presented in the paper.