Development and Testing of a Method for Continuous Mass Measurement of Dielectric Material Samples During Microwave Heat Treatment

The paper considers methods for continuous mass measurement of dielectric material samples during microwave heat treatment at a frequency of 2.45 GHz. It is shown that the direct measurement of the sample mass by electronic scales during microwave treatment is complicated, since it is not possible to use conductive materials inside the process chamber due to induction of currents, which distort the measurement results. The paper proposes a technique for continuously measuring the mass of dielectric material samples during microwave heat treatment. The technique is based on thermogravimetric analysis methods. A unique measurement system has been developed, which utilizes this technique and consists of the following individual modules: a sample hanger located inside the process chamber, and a strain gauge, spectrometer and signal processing and conversion systems located outside the chamber. The use of a modular configuration makes it possible to distance the measurement system as far as possible from the source of electromagnetic radiation, avoid signal distortion, and isolate the measuring equipment from microwave exposure. The developed technique for continuously measuring sample mass during microwave heat treatment was tested, and the resulting dependences of mass changes revealed two characteristic stages of material carbonization, which differ based on the sample mass variation rate. The total error of the technique is less than 1%, with the quantization error during analog-to-digital conversion being the main contributor. The proposed technique can be used in automated control systems associated with microwave treatment of materials.