球形腔聚焦换能器的非线性声场建模

球形腔聚焦换能器是一种特殊形式的聚焦换能器。为理论证实球形腔聚焦换能器能突破传统超声聚焦在聚焦精度和聚焦增益上的限制,采用Westervelt非线性方程并结合时域有限差分法,建立了球形腔聚焦换能器的非线性声场的数值模型。数值计算了直径为120 mm的0.6 MHz球形腔聚焦换能器的非线性声场,并与传统球壳形聚焦换能器进行了对比。当激励声压为100 kPa时,球形腔聚焦换能器与同尺寸壳形聚焦换能器相比,焦点正声压增益提高约8.5倍,且焦域精度更高,-6 dB聚焦区域在z方向减小约20倍,达到次波长尺度。研究表明球形腔聚焦换能器在高强度聚焦超声精细治疗上具有潜在的应用前景。 

Modeling of the acoustic nonlinear field generated from a spherical cavity transducer

Spherical cavity transducer is a special focused ultrasound transducer. In order to theoretically prove that it could break through the limit of the dimension of focal region and focal gain in conventional focusing ultrasound, a numerical model is developed for describing the nonlinear acoustic field generated from the spherical cavity transducer using the finite difference time domain (FDTD) method to solve the nonlinear Westervelt equation. Numerical simulation is performed using a spherical cavity transducer with diameter 120ram working at 0.6 MHz, and results are compared with those obtained from the conventional curved transducer with the same configuration. Results indicate that as the exciting acoustic pressure is 100 kPa, the spherical cavity transducer could increase focusing gain by about 8.5 times and reduce -6 dB focal region by 20 times in z direction. This study suggests that the spherical cavity transducer will be promising in the application of High intensity focused ultrasound (HIFU) for precise treatment.