An induction heating device having an adjustable heating power output includes at least one resonant circuit, which includes an induction heating coil, and a heating power adjusting device, which is designed to vary a resonant frequency of the resonant circuit in order to adjust the heating power output. Therefore, the thickness of the medium is detected with high accuracy without using a dedicated sensor. In this way, delayed engine starts using gaseous fuel may be mitigated. The operating frequency of the first ring oscillator module, during a second mode, is a function of a gate leakage current of the stressed dielectric layer. When they are assembled, the present invention is used as a swim fin. The coupling element can be inserted into the hole in a chosen orientation as desired in one of four equidistant angular positions and then rotated through about 22.