Compensation for decay of signal strength in damage detection by ultrasonic imaging: Application to migration technique

A compensating procedure for decay with distance of an ultrasonic wave propagating in a structure is presented. In structural health monitoring, many damage identification techniques involve ultrasonic wave propagation from actuators and reflection from defects. Some of them use imaging techniques to approximate damage configuration, such as location, size, and shape. However, the accuracy of detection result is not good enough to be used for prognostic. We found that the inaccuracy is often caused by decay of wave strength as function of distance when a wave propagates through the structure. Thus, we propose to compensate for geometric decay by multiplying the obtained image intensity with the distances to the actuator and to the sensor. We applied the compensation idea to a migration technique, which is a recently developed damage imaging technique. By adjusting image intensity to compensate for distance between actuator and defect, we were able to achieve a better accuracy for identifying the location of cracks. In addition, an experimental study on the possible errors related to experiment is attached. This idea can be extended to any damage detection techniques which produce images as their final detection result.