The method involves evaluating a misalignment of an HF resonator caused by the presence of the material. The HF resonator is supplied with microwaves of two frequencies, which are each associated with a falling flank of a resonance curve. A high-frequency signal is recorded, whose resonance frequency displacement and attenuation is compared with a signal unaffected by the material. The resonance frequency displacement is recorded by comparing resonance curves of the resonator as it is affected and unaffected by the material, and the attenuation is recorded by comparing the amplitude of the resonance curves at the frequencies of the microwaves.
