超声散斑相移法测量技术

Ultrasonic speckle phase-stepping measurement technique

超声散斑相移法能满足工程建设中对水下物内层界面关键点位移进行测量的特殊要求。测量时,引入数字参考信号与物面测点上的散斑信号进行数字干涉,获得叠加信号强度。界面位移前后,应用软件逐步改变参考信号相位,可逐步改变叠加信号强度,根据这些信号强度值可计算出测点的位移量。应用此技术对水下试件内层表面的法线和切线方向上的位移进行了实测,测量结果与理论值有较好的吻合;研究表明打磨后的粗糙外层界面不影响应用相移法进行测量。在应用相移法测量时,不需声像转换,不需全场扫描,测量精度不受散斑尺寸限制。

The ultrasonic speckle phase-stepping technique can be used to measure the displacement of some key point on inner surface of an underwater object. In performing this technique, a digital reference signal is introduced to intervene with the speckle signal picked up on a scattering surface. Then, the intensity of the added signal is obtained. Before and after object displacement, the intensity of the added signal is changed as the phase of the reference signal is shifted several times by the software. According to the intensities of these added signals, as a result, the displacement of the testing point can be measured. The out-of-plane and in-plane displacement of the inner surface of an underwater specimen were measured. The measuring data was in good agreement with the real ones. Besides, the experiment showed that a rough outer surface after being ground had no influence to the measurement. In performing this technique, complicated conversion between ultrasound and image is not needed, a whole field recording of ultrasonic speckles is not necessary, and the accuracy is no longer limited by speckle size.