Specifically, it exploits a phenomenon called resonant coupling, in which metal coils that resonate at the same electrical frequency can exchange energy particularly efficiently.

In addition to controlling mechanical shaft and bearing loads, the coupling further protects the encoder by providing a high degree of electrical and thermal isolation between coupled shafts.

Therefore, the calculation of critical speed of anisotropic supporting rotor-bearing system of the PMSM is a typical mechanical and electrical coupling problem.