Abstract: Motor control of a variable reluctance motor is obtained by providing a periodic voltage waveform to a coil of a motor. No coil current control or current or flux feedback is needed to obtain flux waveforms that allow for low-distortion or distortion-free operation of the motor. The periodic voltage waveform may be a sinusoidal or sawtooth signal, for example, and has a substantially zero mean for each cycle of the signal. The periodic voltage waveform may be offset to compensate for the resistance of the coil, and the coil current may be monitored in order to determine the amount of offset required. By providing a zero-mean or substantially zero-mean periodic voltage waveform, the coil current and flux in the gap between the core and the moving part are guaranteed to reach a zero value at some point during each period (or cycle) of the periodic voltage waveform.

Abstract: A vibrational acoustic unit comprises a dynamic force motor, a power take-off spring having one end attached to the dynamic force motor and the other end attached to a fluid filled acoustic resonator. The motor oscillates the entire acoustic resonator so as to excite a resonant mode of the acoustic resonator.A method of delivering power to an acoustic resonator comprises resiliently connecting a motor to the resonator, and driving the motor to oscillate the entire acoustic resonator so as to excite a resonant mode of the acoustic resonator.

Abstract: Provision of a digital controller in which the controller controls the bearing coil current by means of a switching bridge that periodically reverses the applied voltage to the coil. The controller selects an applied voltage from a plurality of discrete voltage sources. When a rapid change in the load current is required, a relatively large magnitude of applied voltage is used. When a relatively constant magnitude of average load current is required, a relatively smaller value of voltage is applied.

Abstract: A minimum pulse width switching power amplifier utilizes digital logic for generating a control pulse having a pulse width at least as large as a fixed minimum period of time when a base control pulse generated by a comparator has a pulse width at least as large as a given value. A high power switching output stage is switched between different voltage levels under control of the control signal generated by the digital logic so that an average actual output of the amplifier is equal to the desired output.