Qualitative experimental study of the electromagnetic field distribution in microwave multimode cavities

The most common applicator for the microwave treatment of materials is a multimode cavity. Because of its own experimental geometry, the electromagnetic field inside this kind of oven is usually extremely unhomogeneous, in this work, the energy distribution has been qualitatively studied investigating the thermal effect caused by the coupling of the field with a dielectric and detected by a white thermal paper, which gradually blackens when reaching temperature around 100-150 °C. We proved that the spatial behaviour of the microwave filed inside the cavity depends strongly on the kind of load, i.e. the sample to be treated, its size and position (x, y, z) in the applicator and the presence or absence of metallic devices, such as a mode stirrer or a thermocouple to measure the sample temperature.