Passive electromagnetic buzzer works are:

AC signal through the coil wrapped around the bracket in the stent produced a core of the alternating flux, alternating magnetic flux and ring constant magnetic flux superimposed, the molybdenum film at a given frequency of alternating signal vibration and With the resonant cavity sound. The response curve and the gap values of the entire frequency and the sound pressure of the product, the natural vibration frequency of the molybdenum sheet (which can be roughly refracted as the thickness of the molybdenum sheet), the frequency of the shell (Helmholtz resonance cavity) The diameter is directly related.