Non-Contact Detection Of Pulsed Acoustic Displacements For The Evaluation Of Sub-Surface Defects

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Abstract
The development of optical methods for detection of ultrasound is important for the technology of non-contact Non-Destructive Evaluation of materials. Several optical methods are limited in their application by their sensitivity for ambient vibrations or their complexity. In this paper a Fiber Time Delay Interferometer is proposed which can be applied to the detection of pulsed ultrasonic vibrations. A practical instrument has been built with a detection limit of 2.10-11m, determined with a detection bandwidth of 10 MHz. Results of experiments show that the method can be used for the detection of (artificial) sub-surface fatigue cracks, using pulsed ultrasonic excitation.

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