An improved model for chirped slanted SAW devices

Abstract

Three improvements for modeling chirped slanted array compressor (SAC) transducer devices are presented. First, the generalized impulse response model for an in-line chirped IDT (interdigital transducer) is applied to individual longitudinal segments of a SAC transducer to obtain transversely distributed source profiles. The inherent simplicity of the coupling-of-mode formalism conveniently encompasses effects of both the chirped transduction and the transducer internal reflections. Second, these source profiles are the driving terms for an accurate propagation model, which calculates the total propagation loss between the transducers by successive applications of Snell's-law refraction and angular-spectrum diffraction, together with an experimentally characterized substrate attenuation. Third, in addition to the static capacitance and subsurface acoustic wave (SAW) conductance, the basic transducer equivalent circuit also includes the SAW susceptance, bulk radiation conductance and susceptance, and a revised parasitic resistive element. The SAW conductance is calculated by integrating the power in the source profiles. This in turn is used to calculate the SAW susceptance and the bulk conductance and susceptance. The combined model and its various elements have been verified by electrical and laser probe measurements. Good agreement with device data, amounting to better than 1 dB in device insertion loss and 0.3 dB in transducer mismatch loss, is reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>