超声探头的响应特性及暂态回波模型

建立检测系统的数学模型,可以更好地理解超声检测的物理本质。分析了超声波从产生、介质中传播、缺陷耦合以及接收的全过程,将缺陷回波表示为探头响应函数与缺陷响应的时域卷积。利用空间脉冲响应和基尔霍夫近似建立了超声波与平面型缺陷的耦合模型,用大平面试块底面回波和大平面响应进行反卷积求得了探头的响应函数,并详细分析了探头在不同偏置位置时不同大小缺陷响应的特点,发现缺陷回波由直达回波和边缘回波组成,直达回波和边缘回波极性相反,且直达回波的幅值远远大于边缘回波。 

A model for determining electromechanical response profile of ultrasonic transducers and ultrasonic transient echo

Models for calculating the radiation, scattering and reception of ultrasound are developed to provide a good understanding of the physical essence of ultrasonic testing. The process of ultrasonic wave generating by pulse, propagation in the medium and received by the transducer is analyzed, and the received ultrasonic signal can be found by convolving of the electromechanical response of transducer with the flaw impulse response. A model is proposed to predict the echo response from a defect of complex geometry based on the Huygens' principle of superposition. Spatial impulse response and Kirchhoff approximation are applied to model the interaction of the ultrasonic wave with flaws. The electromechanical response profile of transducer is calculated by deconvolution the echo of plane test block with impulse response of the test block. Characteristics of flaw impulse response of targets on and off-axis are analyzed in detail, the received ultrasonic echo is explained in terms of the plane and edge echoes, however, polarity is opposite. The amplitude of the direct echo is far greater than the edge echo. The theoretically predicted results are in good agreement with the experimentally results.