基于虚拟聚焦的板结构兰姆波换能器阵列检测方法研究

Virtual Focusing Based Lamb Wave Transducer Array Method for Plate Structure Inspection

针对板结构大范围无损检测问题,发展一种基于软件虚拟聚焦的兰姆波换能器阵列检测方法,即基于相控阵中等相位叠加原理,在无需相位控制硬件系统条件下,通过对换能器阵列接收数据进行软件处理,实现换能器阵列声束的指向聚焦。利用仿真数据,研究阵列直径、阵元数量、声束数量等对虚拟聚焦成像周向分辨率和旁瓣噪声的影响,得出检测结果无明显旁瓣噪声所需要满足的条件为阵元间距应小于检测兰姆波的半波长。基于数值仿真处理结果,进行电磁声换能器阵列兰姆波检测试验研究。结果表明,在选择合适的阵列直径、阵元数量、声束数量的条件下,通过对换能器阵列检测信号进行虚拟聚焦处理,可以实现板结构任意方向特征体(如边界)的识别和缺陷检测。

Aiming at wide range nondestructive testing of plate structure,the technique of Lamb wave transducer array based on software virtual focusing is developed,i.e.based on the principle of equiphase superposition in the phased array,through the software processing of the data received by the array,the directional focusing of beam of array is implemented without needing for hardware system of phase control.By using the simulation data,the influences of diameter of array,number of array elements and number of beams on the circumferential resolution and side lobe noise of virtual focusing image are studied.It is found that the spacing of array elements should be smaller than half-wavelength of Lamb waves in order to avoid the obvious side lobe noise.Lamb wave experiments are conducted for detecting the plate structure by using array of electromagnetic acoustic transducer（EMAT）.The results show that by selecting appropriate diameter of array,number of array elements and number of beams,and through virtual focusing processing of the signals detected by the transducer array,defect detection and identification of structural features of plate in any direction（such as boundary） can be realized.