Extended Frequency Bandwidth and Electrical Resonance Tuning in Hybrid Terfenol-D/PMN-PT Transducers in Mechanical Series Configuration

Abstract

This article addresses the modeling and characterization of hybrid transducers incorporating both ferroelectric and ferromagnetic elements. The complementary electrical and mechanical properties of the two classes of materials can yield transducers with higher performance or enhanced functionality relative to single-element devices. As a template for studying the properties of hybrid architectures, a transducer is considered which consists of a mechanical series arrangement of a PMN-PT stack and a Terfenol-D rod. This configuration exhibits a double resonant frequency response that can be tuned for a variety of applications. We are specifically interested in the development of models and design criteria for achieving broadband electromechanical transduction over the range from 500 Hz to over 6 kHz. To that end, a model is presented which is constructed from three classical, widely available theories: (i) linear mechanical vibrations, (ii) classical electroacoustics, and (iii) linear piezoelectricity and piezomagnetism. Despite the general limitations of linear models when applied to nonlinear materials, the linear formulation is justified in this article by the consideration of biased, low signal regimes in which transducer behavior is quasilinear. The model is applicable to the design and control of high-performance devices, while being mathematically tractable and accurate over the regimes considered. The model also provides a framework which permits extraction of material property information from dynamic impedance measurements – as opposed to quasistatic measurements – that is under conditions similar to those found in transducer operation. The study also shows that it is possible to tune the electrical resonance frequency without fundamentally altering the transducer bandwidth. This result has practical implications in that it allows matching of the transducer response to individual drivers. This could allow for retrofit of an existing hybrid device with a newer, more advanced ferroelectric stack without compromising the device bandwidth.