Index of content:
Volume 106, Issue 6, December 1999
- TRANSDUCTION 
106(1999); http://dx.doi.org/10.1121/1.428185View Description Hide Description
A one-dimensional phenomenological model of hysteresis is presented. The model is suitable for application both to electrostrictive materials, such as leadmagnesiumniobate (PMN), and to magnetostrictive materials, such as Terfenol D. The concepts of “inflation,” “field space,” and the “reference ellipse” are introduced as suitable mechanisms for transforming measured hysteretic data into corresponding anhysteretic versions. An anhysteretic model is then fitted (in the least-squares sense) to the transformed data. By applying the inverse transforms to the fitted anhysteretic model, a hysteretic model is deduced. Good agreement with the original (hysteretic) data is seen. It is shown that, when a sample is driven by a monofrequency electric field, the area of the polarization vs electric-field hysteresis loop is independent of all harmonics in the polarization but the first. A principle useful for understanding the shapes assumed by and hysteresis loops in general is described.
106(1999); http://dx.doi.org/10.1121/1.428186View Description Hide Description
A model of hysteresis is applied to determine material response to multifrequency drives, and to the output control problem. Although as presented in Paper I the model is based on a monofrequency sinusoidal drive, it can readily be generalized. The generalization is based upon the fact, at least for quasistatic drives, that the shape of the hysteresis loop is independent of the shape of the drive waveform used to produce it provided that the drive is characterized by only one wave amplitude. The material response to a given arbitrarily shaped drive can be determined if the drive is first subdivided into single-amplitude regimes or epochs. Each such regime then has associated with it a unique hysteresis loop, which can be determined from the model. Each theoretical loop is generated using a monofrequency sinusoidal drive whose amplitude is equal to the single amplitude contained within the corresponding drive epoch. The material response is then determined by correlating the level of the given drive field (and the sign of its time derivative) with that of the sinusoidal drive used to generate the associated theoretical loop. The response to the arbitrary drive is taken to be equal to the response to the sinusoidal drive at the corresponding drive level and correspondingly signed time derivative. This process is capable of inversion. Thus, not only can the material response be determined for a drive of arbitrary waveshape, but also the drive waveshape required to produce a desired output trajectory can be determined. The procedure is illustrated by determining the drive necessary to produce a monofrequency sinusoidal magnetization response from a biased, prestressed sample of Terfenol D driven at high-amplitude magnetic field.
106(1999); http://dx.doi.org/10.1121/1.428187View Description Hide Description
An electroacoustic system which directly converts analog acoustic signals to digital electric signals is described. The system consists of a subtractor, a sampling and holding circuit, a sigma–delta modulator as a comparator, an accumulator, and a local direct digital-to-analog converting transducer similar to a typical electronic analog-to-digital converter. The subtractor is an electrostatic device which has a diaphragm, driving electrodes, and a detectingelectrode. The surface area of the driving electrodes corresponds to the significant bits in the digital signal, as an electroacoustic digital-to-analog converter. The detectingelectrode produces an electrical signal proportional to the displacement of the diaphragm driven by subtracting the received acoustic signal from the electrostatically driven force. This is regarded as a subtractor. The detected signal is amplified and sampled-held and modulated by the sigma–delta procedure and generates a signal of ±1 bit, which is added to the accumulator memory by a high clock frequency. The output of the accumulator is the digital signal output and is also fed to the driving electrodes. A 4-bit conceptual system was developed to affirm this concept.