高斯叠代法研究相控阵栅瓣的优化

Optimization of side-lobes generated from a phased array using Gaussian superposition technique

高强度聚焦超声(High intensity focused ultrasound,HIFU)是一种新兴的治疗肿瘤的技术,将声波能量聚焦到人体组织内的靶区,产生热效应消融肿瘤组织,而不损伤正常组织.HIFU中的相控阵技术可以根据病灶区域的深度以及大小通过控制多阵元发射声束的相位与幅度,实现焦点的精确控制,并可实现多焦点聚焦及电子扫描.相控阵在聚焦超声治疗应用中不可避免地受到栅瓣的影响,本文结合高斯声束叠加与相控阵技术中的伪逆矩阵算法研究相控阵的声场,并对栅瓣进行优化研究.该方法利用预设焦点参数并应用伪逆矩阵算法得到阵元的激励参数;然后将阵元近似拟合成一组高斯声束的叠加,通过高斯声束叠代计算声场.数值计算中以9×9二维相控阵列为研究对象;线性条件下,高斯叠代法结果与菲涅耳积分结果的误差低于1%,验证了该方法的可行性;二维相控阵在单焦点模式下减小阵元间距可以有效抑制旁瓣,但不能完全抑制.进一步的实验研究将进一步优化理论模型.本文的结果将有效促进相控阵聚焦换能器在HIFU中的应用.

High intensity focused ultrasound（HIFU）has attracted much attention as a new non-invasive cancer therapy technique. It focuses the ultrasonic energy into the target tissues inside the body, and the temperature of the target tissues rapidly increases in a short time, leading to the tumor cells coagulation necrosis with minimal impact on the normal tissues outside the focusing area. The phased array technology has some advantages of electronic beam focusing and multi-focuses, it is required to control the exciting vector and the phase of the elements based on the depth and size of the lesion area. Phased array is inevitably influenced by grating lobes in focused ultrasound therapy. Based on the superposition technique of Gaussian beams combined with the inverse matrix algorithm,the sound fieldgenerated from a phased array is calculated, and the optimization study of grating lobes is developed. The parameters of the phased array elements are first estimated from the focal parameters using the inverse matrix algorithm^Then the elements are expressed as a set of Gaussian functions~ Finally, the sound field can be calculated using the superposition technique of Gaussian beams. A 9 ;K 9 two dimensional phased array is performed in the numerical sim ~ - ulation. In the linear case,the difference between the results of the Gaussian superposition technique and the Fresnel integral is less than 1%, which verifies the feasibility of the approach. The side-lobes generated from a 2-D phased array can be effectively suppressed through the decrease of element spacing in a single focus mode, but cannot be fully suppressed. The theoretical approach will be improved by further experimental works. This study will promote the application of the phased array in HIFU.