Ultrasonic noncontact inspection system with optical fiber methods

In inspection of materials, noncontact generation and detection of ultrasound using laser techniques has a growing interest. Before using these techniques in practical inspection tasks, some problems have to be overcome. To obtain maximum sensitivity for the detection of defects, control of beam direction and focusing of the generated ultrasound is of major importance. For this purpose a fiber-optic phase array technique was developed. Some optical techniques for ultrasound detection are compared, especially for detection at diffusely reflecting surfaces. A system based on the use of a confocal Fabry-Perot interferometer is best suited for this detection task. With the addition of a multimode fiber to this system as a flexible sensing lead, inspection can be carried out from a remote location and scanned detection is facilitated.