Electrification of thermal processes is key for the transformation of industry towards carbon-neutral production. Depending on the technology, process intensification can be advanced in parallel to the defossilization. Microwave heating is very well known for its theoretically high energy efficiency. The fast internal heating additionally improves product yield and quality. But until now, an experimental gap hinders the advancement of microwave heating in high-temperature processes with phase change. So far, accurate models for high temperature microwave processes are not available. Operation of such processes is therefore hardly controllable. The overall conversion degree or inner material temperatures are not accessible inside of high-power electromagnetic fields. B5N has therefore the goal to develop a new measurement method that allows for the first time to monitor, both, material conversion due to phase changes and temperature inside of the products. This will be enabled by utilizing electromagnetic waves themselves for measurements, because their transmission, absorption and reflection is material composition and temperature dependent. Correlations of detected signals with material composition and temperature will be based on characteristic dielectric changes. 3D spatial resolution will be achieved by rotation of the sample during measurement. The experimental data sets will be combined with heat and mass transfer simulations, coupled with simulation of electromagnetic wave propagation, in order to gain a detailed insight into the thermal conversion processes.