Index of content:
Volume 103, Issue 6, June 1998
- TRANSDUCTION 
103(1998); http://dx.doi.org/10.1121/1.423047View Description Hide Description
New leadmagnesiumniobate (PMN) ceramics, which can generate large strains at moderate electric fields, are good candidates for future actuators or sonar projectors. In this paper, two finite element models are proposed to describe static analysis of electrostrictive materials. Both models include quadratic dependence of strain with electrical displacement, assume constant temperature, and exclude hysteresis. One of the models includes the saturation of the polarization. The theoretical formulation is justified by the method of the weighted residuals. The numerical implementation is presented. The validation is performed by comparing numerical results with measurements for a PMN bar subjected to mechanical prestress and dc electric field.
103(1998); http://dx.doi.org/10.1121/1.423048View Description Hide Description
Temporal resolution in an ultrasonic system may be enhanced by the application of mechanical damping to the transducer rear face, thereby reducing internal reverberation and increasing effective bandwidth. However, for thickness drive transducers, this is accompanied inevitably by a reduction in sensitivity and, moreover, manufacture of suitable damping blocks can be difficult, particularly for lower frequency, small signal applications such as the detection of gas coupled ultrasound. This work describes an interesting alternative approach that utilizes the relatively strong coupling between the fundamental thickness mode and first lateral mode in 1-3 connectivity piezocomposite transducers.Finite elementmodeling is used to evaluate the influence of mode interaction on electromechanical coupling efficiency, surface displacement, sensitivity, and bandwidth as functions of the ceramic pillar dimensions for operation into both water and air load media. A range of composite devices was constructed and close agreement between theory and experiment is demonstrated, with a measured device bandwidth of 130% centered at 1.15 MHz. An example of using such a device within a gas-coupled ultrasonic system is presented and the response is shown to compare favorably with alternative transducer configurations.
103(1998); http://dx.doi.org/10.1121/1.423049View Description Hide Description
Tonpilz transducer head piston diameters are usually about one-half wavelength in diameter, so that “ρ- ” radiation loading will be approximately achieved. However, for this underwater tracking application, the transducer is required to fit inside the throat of a 360-degree horn. The piston diameter is limited to 1 in. (25 mm), or about 0.22 wavelength at the resonance frequency, 13 kHz. The design is based on a lumped-element model. The lead zironate-titanate (PZT-8) ring stack is 2.1 in. (53 mm) long with an outer diameter of 0.49 in. (12.5 mm) and an inner diameter of 0.24 in. (6.0 mm). The head mass is 0.25-in. (0.635-mm)-thick aluminum, and the tail mass is wolfram (tungsten), with a mass of 93 g. The transducer is isolated from its cylindrical housing with a syntactic foam spring. An O-ring piston seal is used, and a similar O-ring provides support for the tail mass. The results of free-field measurements are used to determine the parameters of a lumped-parameter equivalent circuit model, which is then used to predict the performance after installation in the horn.