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This paper investigates a theoretical analysis of electrical transient responses of a bolt-clamped Langevin ultrasonic transducer (BLT) and its verifications based on simulations and experiments during ON/OFF transient states immediately after turning on/off. The simulations are determined by a power electronic simulator originally designed for power converters and motor drives. The responses include the open-circuit voltage, the terminal current, the motional current and the mechanical power loss. A linear equivalent circuit model with the initial conditions is stated first. This model is used to derive the responses characterized by simple closed-form equations. The off transient state as specified by the initial conditions regarding switching-off time of an ac sine source for the drive of the BLT is related to cyclic behavior. The derived responses are further checked by simulations and experiments. To obtain the experiments, a test system which contains an ac power supply, a digital oscilloscope and a control switch is needed. Finally, characteristics of the responses and effects of switching-on/off times of the ac sine source on the characteristics are discussed. The characteristics comprise the dc/ac time constants and the maximum/minimum wave amplitudes for the BLT during ON/OFF transient states. Index Terms--Equivalent circuit model, initial condition, power electronic simulator (PSIM), transient state, ultrasonic transducer.

A high-sensitivity magnetic transducer able to sense magnetic fields from dc up to tens of kilohertz is analyzed in this paper. The system is based on a nulling field coil fed by a current on the basis of the residual field, sensed by a magnetic sensor (Hall or magnetoresistive) placed in the coil center. In this way, the coil current proportionally represents the external field component along the coil axis, and it can be easily converted in a voltage signal by a series resistor. Then, a one-axis Gauss meter can be readily obtained. The sensitivity and the bandwidth of the overall system are discussed by a transfer function analysis. A hardware prototype has been realized, and significant test results are shown by means of a reference magnetic-field-generation setup. Useful guidelines for the overall system design are given. Index Terms--Hall devices, magnetic measurements, magnetic transducers, magnetoresistive devices.