Session: P2I

This paper presents an accurate method to calculate the P-matrix of an arbitrary transducer on an arbitrary substrate material. The approach is based on the COM model, and COM-parameters (transduction, reflectivity, capacitance and velocity) are calculated for each individual cell of the transducer in a manner such that the influence of the neighboring cells is taken into account. This method is particularly well suited for the analysis of the RSPUDT. Since in RSPUDT both reflectivity and transduction are weighted, there are transducer areas with different types of basic cells (reverse or forward SPUDT, non-SPUDT) as well as areas transitional from one cell type to another. The common approach to calculate the COM parameters for the cells is to use the same set of COM parameters (usually evaluated for the case of an infinite periodic SPUDT structure) throughout the transducer with transduction and reflectivity multiplied by corresponding weighting coefficients. As a result, the mutual influence of the cells is ignored. In this paper a model is developed which provides a more accurate analysis approach. An IDT is subdivided into a sequence of cells starting and ending in the middle of electrodes gaps; each cell containing only one electrode for which the COM parameters are evaluated. The transduction coefficient and capacitance are calculated based on the charge distribution on all electrodes of the transducer. The reflectivity of a cell is calculated as a sum of piezoelectric and mechanical terms [1]. The velocity perturbation within a cell is also presented as a sum of piezoelectric and mechanical terms. The piezoelectric term for both velocity perturbation and reflectivity, is calculated based on charge distribution induced on the transducer electrodes by an incident wave. As in [1], basic material parameters are extracted from FEM/BEM analysis for a single electrode structure. In the paper the theoretical approach and model will be discussed. Experimental results for several RSPUDT filters on quartz and langasite are presented. Excellent agreement between modeled and measured data is shown which verifies the approach. [1] S. Malocha, B.P. Abbott, Ultrasonics Symposium, pp.258-261, 2002