A comparison of and the compensation for magnetostrictive core inductances in magnetic transducer systems

Abstract

Magnetostrictive materials have been utilized for the production of ultrasonic frequency vibrations for a number of years. This has particularly been the case in laminated nickel-based ultrasonic dental-scaler cleaning systems. In this study, a comparison has been made between the impedances of a number of magnetostrictive stacks of 50 mm×4 mm×∼0.3 mm strips at frequencies in the range of 10–50 kHz in a coil used for the excitation of a stack in a dental-scaler system. The magnetostrictive stacks tested comprised of potential replacement materials for standard nickel ones. The study showed that it was possible to compensate for the inductive ‘imaginary’ components of the impedance through the use of a tuned, series capacitance so that only the ‘real’ resistive component of the impedance remained. This reduced the electrical losses associated with the excitation of the magnetostrictive stacks as a result of the frequency-dependent inductance of the coil system. Consequently, the maximum power transfer from an amplifier to the transducer was increased. Also, the investigation showed how the ‘real’ component of impedance of the different stacks varied with frequency. In a tuned resonant electrical circuit, the resistive component of the impedance, if considered as a loss, would be the lowest that could be achieved with such a magnetic circuit. Consequently, the losses associated with resonant magnetostrictive devices, like dental scalers, can be reduced.