Initial Design and Quick Analysis of SAW Ultra–Wideband HFM Transducers

This paper presents techniques for initial design and quick fundamental and harmonic operation analysis of surface acoustic waves ultra-wideband hyperbolically frequency modulated (HFM) interdigital transducer (IDT). The primary analysis is based on the quasi–static method. Quasi–electrostatic charge's density distribution was approximated by Chebyshev polynomials and the method of Green’s function. It assesses the non uniform charge distribution of electrodes, electric field interaction and the end effects of a whole transducer. It was found that numerical integration (e.g. Romberg, Gauss–Chebyshev) requires a lot of machine time for calculation of the Chebyshev polynomial and the Green’s function convolution when integration includes coordinates of a large number of neighboring electrodes. In order to accelerate the charge density calculation, the analytic expressions are derived. Evaluation of HFM transducer fundamental and harmonics' operation amplitude response with simulation single– dispersive interdigital chirp filter structure is presented. Elapsed time of 2000 frequency response point simulations of HFM IDT with 589 electrodes is only 54 seconds (0.027 s/point) on PC with CPU Intel Core I7–4770S. Amplitude response is compared with linear frequency modulated (LFM) IDT response. It was determined that the HFM transducer characteristic is less distorted in comparison with LFM transducer.