Fundamental understanding of the dielectric properties of a material is essential for studying the heating characteristics and changes in microwave absorption characteristics of the material during processing. Moreover, this understanding can help in the design, modeling, and simulation of microwave systems for high-temperature applications. The aim of this research was to investigate the microwave dielectric properties of two types of agricultural biomass (oat straw and barley straw) in the temperature range of 30°C to 700°C at 915 and 2450 MHz in a nitrogen (N2) environment. The cavity perturbation technique was used to measure the dielectric properties. The heating process was divided into three distinct stages: drying (from room temperature to ∼200°C), pyrolysis (from ∼200°C to ∼450°C), and char (from ∼450°C to ∼700°C). Overall, the dielectric properties of the selected agricultural biomass decreased during the drying and pyrolysis stages. A dramatic increase in dielectric properties was observed in the char stage. The selected agricultural biomass can be considered as low-loss materials since they are poor absorbers of microwave energy at temperatures below 400°C. However, their microwave absorption capability improved significantly when the temperature increased beyond 450°C. This was because of conversion of the biomass into carbonaceous char material. Lastly, the experimental data were fitted using regression, and a sigmoidal function of the dielectric properties was developed. The modeled dielectric values were in close agreement with the measured values. The developed model can be useful in the modeling and simulation of microwave pyrolysis processes.
- Dielectric properties