A procedure to extend the performance of optimization methods in ultrasonic transducer matching layer design

Matching layer is a principal part of ultrasonic transducer. The theory of selecting matching layer material and defining its thickness especially in multilayer matching are not compatible with real situation. Therefore Genetic Algorithm (GA) is a key to solve the gap between theory and reality. A theory that recently has been used for optimization of ultrasonic design by GA is Sound-Pressure Transmission Coefficient (PTC). In this theory the amount of reflected and transmitted wave when crosses over boundary of each layer is calculated. However, in PTC approach the relationship between resonance frequency of transducer and variation of matching layers thicknesses is not fully considered which smears the result. The thickness of matching layers can change the desired frequency of the transducer, but in PTC formula the resonance frequency is constant for any combination of layers with different thicknesses. This paper wants to manifest this problem and provide a procedure for better optimization process by combination of Finite Element Method (FEM) and GA without any variation in desired frequency.