Methods for Selecting Multicomponent Layers Which Match the Acoustic Impedance of Ultrasound Transducers to Various Media

The problem of optimal selection of materials for matching layers e.g. of piezoceramic transducers for ultrasonic emission and reception is closely related to the type of medium into which ultrasonic energy is radiated. Due to the unfavoruable ratio of acoustic impedance between piezoelectric ceramics and gaseous, liquid and biological media, the conversion of electrical to acoustic energy introduces significant losses. The paper presents, among other methods of impedance-matching layer selection, a method based on genetic algorithms. The method enables the search of state-space of possible solutions - in this case, of combinations matching layers' materials. The optimal choice of computation method depends closely on ultrasonic impulse parameters such as: impulse shape, impulse energy, transmission band shape and width. When using a single matching layer, its impedance can be calculated based on upon Chebyshev's, DeSilets' or Souquet's criterion. The choice of criterion depends on, among other factors, the expected shape of the transfer function; the calculated values of matching layer's impedance exhibit large variability, so the choice of suitable material is a complex task. The solution might be to use multiple matching layers. The use of a genetic algorithm allows for finding the optimal matching layers combination, fulfilling the chosen matching criterion.