Double element ultrasonic piezoceramic transducer modeling with VHDL-AMS: application to b/a nonlinear ultrasonic parameter measurement in pulse-echo mode

This paper presents an ultrasonic transducer modeling with VHDL-AMS standard (Very High speed integrated circuits Hardware Description Language - Analog and Mixed Signal) referenced IEEE 1076.1, integrated in a global measurement cell modeling dedicated to biological tissues ultrasound characterization. Usual modeling of ultrasonic transducer are based on electrical analogy and are not simulated in the global measurement environment which must include non linear medium behavior and electronic coupling. The ultrasonic transducer modeling proposed is simulated with the nonlinear acoustic load and electronic excitation. It was composed by a first element with a piezoceramic ring structure vibrating at a frequency of 2,25 MHz in thickness mode. The second element is stuck into the center of the first. This geometrical form is a disc vibrating at 4,5 MHz in thickness mode too. Nonlinear B/A parameter is used to characterize medium with a comparative method. The measurement cell is composed by a piezoceramic transducer which is implemented with the Redwood's electric scheme and a metallic reflector into a Plexiglas structure. The analyzed medium is placed between the transducer and a metallic reflector. Medium is modeled with take into account the nonlinear propagation with B/A parameter. The usual transmission line model has been modified to take into account the nonlinear propagation for a one dimensional wave. Simulations of the transducer pulse response and impedance show a VHDL-AMS model in good agreement with measurement. Results simulation of the measurement cell modeling are in agreement with well known B/A values of biological mediums.