中文摘要：

发展一种用于缺陷定位的非线性超声阵列成像方法。研究聚焦声场的时间-空间传播特点以及形成扩散声场的条件,分析并行聚焦和顺序聚焦的扩散声场声动能与非线性效应的关系,提出利用超声阵列在两种聚焦模式下激励带宽内（基波）声动能差值表征的非线性超声成像方法。进一步研究时延及时间窗宽对两种检测模式的扩散声动能及非线性成像的影响,优化出有效的非线性成像参数。结果表明：时延的选择对成像结果影响较大,时间窗宽的选择对成像结果影响较小;在一定时延范围内,均可以形成稳定的扩散声场,在该时延范围内可以较好实现微裂纹检测。利用提出的非线性超声阵列成像方法很好地实现了结构中微裂纹检测及成像。

英文摘要：

A nonlinear ultrasonic array imaging method used for the defect loacation is developed. The propagation characteristics of the focusing acoustic field in time-space domain and the conditions to generate the diffusion acoustic field are investigated, then the relationship between the diffused acoustic energy in two different phased mode, parallel and sequential focusing, and the nonlinear effects is analyzed, and a nonlinear ultrasonic imaging method is proposed, in which the difference of acoustic energy of two phased modes within the excitation bandwidth（fundamental wave）is considered as characteristic parameter for imaging. The influence of time delay and time window for diffuse field sound energy and nonlinear imaging are studied, and the optimal parameters for nonlinear imaging are obtained. The time delay has great influence on the nonlinear imaging, however the width of window has little effect on the nonlinear imaging. Over a range of time delay, the diffusion acoustic field is stable, therefore the micro-crack can be detected effectively. It is demonstrated that the proposed nonlinear imaging technique is an effective method for micro-crack detection.