Finite‐element and experimental study of ultrasonic beam pattern characterization

In this paper a study on the characterization of the acoustic beam pattern for two PZT‐5H, 3.5‐MHz transducers using both experimental and FEA methods is reported. To obtain actual pressure‐field measurements, a three‐axis positioning system was constructed. The transducers were submerged in an acoustic test tank and the positioning system was used to maneuver a 200‐micron PVDF hydrophone within the pressure field. At each location the output voltage of the hydrophone was measured along with the corresponding location. Using SPYGLASS^■, these data were plotted to yield a two‐dimensional ‘‘slice’’ of the actual pressure field. A finite‐element model of the water‐loaded ultrasonic transducer was created using ANSYS^■. Material properties that were needed to model the piezoceramic and polymers properly in the transducer were measured via pulse–echo technique. To validate the FEM results the electrical impedance of the transducers was calculated and compared to the actual measured values. The frequency‐dependence of the impedance curves match closely. Using harmonic analysis, the pressure field in the water generated by the transducer was calculated and compared to the measured pressure‐field data. Excellent agreement was obtained.