Multiparameter Analysis of the Ultrasonic Transducer Transfer Function Using a Genetic Algorithm

The transfer function is an important parameter describing ultrasonic transducers which are designed to operate in various media. The typically high impedance of piezoelectric transducers is matched to a particular loading medium (gas, liquid, biological medium) by using multicomponent matching layers, which have specific impedances and thicknesses in accordance with the generally known matching criteria: Chebyshev, DeSilets or Souquet. When properly selected, the materials used for the matching layers allow the most optimal parameters to be obtained for both transmitting and the receiving ultrasonic energy. However, studies rarely focus on the possibility of shaping the obtained transfer function, which is also a parameter that is important in some applications of transducers intended for pulse operation, especially in liquid media (e.g., in hydroacoustics) or in biological media (e.g., in ultrasound imaging). The values and shapes of such a function are influenced by factors which are identical to the parameters describing the matching layers. This article presents the possibilities and advantages of using a genetic algorithm to shape the characteristics of the transfer functions that have a particular importance in the search for an optimal (typically the greatest) bandwidth of a transducer intended for operation in a particular medium.