Ursu M.

In this paper the KLM (Krimholtz-Leedom-Matthaei) model is analyzed for the electrical circuit of piezoelectric transducers. An important issue for the accelerometer design phase is the accurate determination of the cladding layers for the crystal resonator. The shear-type effect is considered for piezoelectric materials like PZ23 and PZ27, and the resonance spectra are compared for several acoustic loads. The KLM model uses the transmission line model which describes both the piezoelectric transformation between electrical and mechanical vibration, and the propagation of acoustic waves in analogy to electrical waves. The transmission line has two ports where acoustical loads are applied, for an accelerometer these being the seismic mass at one side and the center base at the other side. The acoustical side represented by the transmission line is coupled to the electrical side through a transformer. Thus, the influence of acoustical load variations on the transducer’s electrical impedance can be modeled. By the use of this model, the piezoelectric material parameters can be varied together with the geometry of the crystal in order to obtain a desired mounted resonance. The geometry of the electrodes can also be adapted for optimizing overall transducer parameters, when sensitivity, mechanical dimensions and frequency range are seen as input data for the design. The materials chosen for the transducer base and seismic masses are stainless steel and titanium, respectively. Their geometry shapes, rectangular or prismatic for the base, and semicircular or trapezoidal for the seismic masses, are analyzed through a transfer-matrix algorithm and numerically implemented by a modified SPICE simulator. The main target is the design of low-frequency and high-sensitivity accelerometers, for seismic applications, using as electrodes a succession of thin layers that approximate the real shape of the transducer base and seismic mass.