聚焦探头水浸检测下的频域合成孔径聚焦技术

Frequency-domain synthetic aperture focusing technique for immersion testing using focused transducer

为了满足自动化在线定量超声无损检测(UNDT)的应用需求,解决传统相移频域合成孔径聚焦技术(SAFT)以平面探头为基础而难以适用于聚焦探头所存在的问题,开展应用于聚焦探头水浸检测的频域SAFT成像技术研究.在分析传统相移频域SAFT成像原理及建立其与时域SAFT方法等效关系的基础上,通过分析聚焦探头在焦平面前后的声程与平面探头的异同,利用上述等效关系将2种探头波达时间的差异转换为频域上的相位补偿,推导聚焦探头水浸检测信号的相移逐层递推公式,发展出一种适用于聚焦探头水浸检测的频域SAFT成像技术.仿真与实验研究表明,采用该技术解决了传统相移方法直接应用于聚焦探头水浸检测所存在的过矫正问题,在聚焦探头水浸检测中应用,具有高横向分辨率和高实时性的成像能力.

A ultrasonic SAFT imaging method in frequency domain for immersion testing using a focused transducer was proposed in order to meet the requirements of automatic online quantitative ultrasonic nondestructive testing（UNDT）and solve the problem that the phase shift synthetic aperture focusing technique（SAFT）developed on the basis of planar transducer＇s propagation feature is hard used for the focused transducer.An equivalent relationship between the conventional phase shift SAFT imaging method and the time-domain SAFT imaging method was established based on analyzing the principle of the conventional phase shift SAFT imaging method.According to this equivalent relationship,the sound path differences between planar transducers and focused transducers can be converted into the frequency-domain phase compensation.Then a formulation was derived to extrapolate the signals measured by an immersion focused transducer.A frequency-domain ultrasonic imaging technique was developed for immersion testing with a focused transducer.Simulation and experimental results indicate that the proposed method is adapted for immersion testing with a focused transducer,in which the conventional phase shift SFAT imaging method is always suffering the overcorrection.The proposed method can generate the image with high lateral resolution and high efficiency.