Correlation of electric field and acoustic output on a prismatic biaxial transducer: A finite element study

Abstract

In single multiaxial transducers, the ultrasound beam can be steered by shifting the phases of the signals of two or more orthogonal electric fields applied to the piezoelectric. These capabilities can improve focusing on therapy applications such as transcranial focused ultrasound. A biaxial piezoelectric transducer (DL47, DelPiezo, FL) was modelled using the finite element software COMSOL Multiphysics®. The upper face was in contact with a volume of water, while the rest were free. The steering angle was controlled by varying the difference between the electrodes’ phases at the crystal’s resonant frequency. To reduce bias, the acoustic particle velocity was recorded at various lengths above the upper transducer's face while the average electric field was calculated for different areas on the surface. Linear regression fits of the steering angle with respect to the average electric field and particle velocity were calculated. A correlation can be observed between the average electric field at the center of the piezoelectric and the steering angle. Furthermore, by reducing the recorded length of the particle velocity by 30%–40% there is a high correlation with the steering angle. A model can be derived using these correlations in which the ultrasound beam direction can be known by obtaining the electric field at the center of the crystal. [The authors want to acknowledge the support of the Government of Canada by the scholarship provided by Global Affairs Canada through the Emerging Leaders in the Americas Program.]