Effects of Cores on the Characteristics of an Induction VCM

An induction voice coil motor (VCM) is composed of a moving metal ring, permanent magnets, cores and exciting coils. The moving ring current induced by an exciting coil current, and the magnetic flux of the permanent magnets, generate a driving force acting on the moving ring. The induction VCM is not able to generate forces below the lower cutoff frequency or above the higher cutoff frequency. The lower cutoff frequency is lowered by raising the permeability and lowering the hysteresis loss of the core; the higher cutoff frequency is raised by reducing core eddy current losses and lowering the leakage inductance of the moving ring. There is an electromechanical parallel resonance near the lower cutoff frequency, and the higher permeability and lower loss make the resonance stronger and lowers the resonance frequency.