Analysis and Optimization of Surface Acoustic Wave Floating Electrode Unidirectional Transducers Using Coupling-of-Mode Theory and Finite-Element Method

The performance of a floating-electrode unidirectional transducer (FEUDT) with acoustic wavelength of 30 μ m is analyzed by coupling-of-mode (COM) theory. In order to extract the COM parameters, a finite element model is developed. The obtained dispersion curve shows frequencies of four stopband edges different from one another which meets the necessary condition for FEUDT. The phase shift of reflection and transduction centers is derived from the standing wave distributions of electric potential in the whole substrate. When a/p = 0.92 (electrode width/period) and h/p = 0.015 (electrode height/period), the value of ϕ – ψ = 44.8° ( ϕ and ψ are phase angle of reflection and transduction centers, respectively) can be obtained fairly close to the 45°. By analyzing SAW energy transportation characteristics, FEUDT is found that the more periods it has, the better directivity it exhibits.