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Newbie

## Modeling of SAW Delay Lines

By W.C. Wilson and G.M. Atkinson

Using PTC Mathcad to Model and Solve

PLEASE NOTE: At the request of the original file creator the attachements to this document have been removed, the text provided is meant to provide an archive for members who have previously bookmarked this resource.

• Demonstrates how NASA engineers use PTC Mathcad to model SAW (Surface Acoustic Wave) sensors to be used for Integrated Vehicle Health Monitoring in aerospace vehicles
• Relevant for sensor design in aerospace and defense, electronics, hight tech, industrial applications, and automotive applications
• Allows users to implement clear, understandable mathematical models and transfer functions

This worksheet using PTC Mathcad shows how you can use Mathcad to model SAW sensors in aerospace vehicles. The lack of support for transcendentals within the Differential Algebraic Equation framework prevents the use of the frequency domain analysis in analog extended Hardware Description Languages (HDLs). Although frequency domain analysis exists in VHDL-AMS it is rudimentary and is not sufficient for some general frequency domain modeling, that is why NASA chose to use Mathcad. These functions are constructed with the help of PTC Mathcad's standard function library which includes:

• Trigonometric functions
• piece-wise continuous functions
• logarithmic functions
• user defined functions

The Impulse Response method was used to model the SAW delay line. This is a first order model and it models the piezoelectric, mechanical and electrical behaviors of the SAW device. The Impulse Response method uses the Mason equivalent circuit. For each IDT the model is comprised of the radiation conductance, the acoustic susceptance, and the total capacitance CT. 2D plots of the frequency response, radiation conductance, and the acoustic susceptance of the example design allow complete analysis of the SAW device .

2D plots are used to show the measured and calculated frequency response to verify requirements have been met. This worksheet provides you with a very in-depth example of how you can use Mathcad to model. Graphs, plots, images, notation, inputs, and solutions are all included to aid you.