I think we are looking at this definition (after looking at the possible patent):
https://www.duden.de/rechtschreibung/einstellen(als Folge von etwas) eintreten
https://en.wikipedia.org/wiki/Cavity_Perturbation_TheoryWhen a resonant cavity is perturbed, e.g. by introducing a foreign object with distinct material properties into the cavity or when the shape of the cavity is changed slightly, electromagnetic fields inside the cavity change accordingly. The underlying assumption of cavity perturbation theory is that electromagnetic fields inside the cavity after the change differ by a very small amount from the fields before the change. Then Maxwell's equations for original and perturbed cavities can be used to derive expressions for the resulting resonant frequency shift.
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If you want a plug-in: a harmonic (of the fundamental frequency of the microwave resonator) is resulted.
More English: a frequency shift to a harmonic is induced
https://www.sciencedirect.com/science/article/abs/pii/S00304...https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-3040...