Analytical modeling of harmonically driven focused acoustic sources with experimental verification. 

Applied Acoustics, 2024;221,1-19:

T. Zawada, T. Bove.


Recently, a high intensity focused ultrasound (HIFU) is drawing a lot of attention from medical and non-medical fields due to its potential for extreme high pressure levels as well as ultra high spatial resolution. At the heart of every HIFU system is a focused ultrasound transducer, and its electrical and acoustic properties play a key role. During the transducer design phase, it is important to quickly obtain the electrical and acoustic parameters corresponding to the transducer structure. Currently, researchers mainly use finite element methods for simulation, but by doing so they lose the deeper insight into the key aspects of the complex electro-acoustic interaction between the transducer, the electric matching network and the front and back acoustic load. A theoretical model based on the Krimholtz-Leedom-Matthaei (KLM) approach of a focused acoustic source is presented. The model includes the impact of the dielectric and mechanical losses and allows for evaluation of the performance of the transducer in terms of electro-acoustic efficiency. The theoretical performance and the impact of the included loss mechanisms on it is calculated up to 9th harmonic resonance frequency. The model is verified using test transducers operating at 4 MHz (fundamental), 12 MHz (3rd harmonic) and 20 MHz (5th harmonic) resonance frequencies. Both the predicted input impedance and predicted electro-acoustic efficiency exhibit very good agreement with the experimental data. An effective material and device parameter identification method based on multi-dimensional minimization algorithm is presented, as well. The results can be directly applied to optimization and development of high-frequency focused acoustic sources taking advantage of the high focusing gain and very high spatial resolution.