Noncontacting detection in ultrasonic nondestructive evaluation of materials: Simple optical sensor and fiber-optic interferometric application

Abstract

An optical displacement sensor based on the two-beam interferometry of coherent light using two principal diffracted orders of a fine reflection blazed grating is constructed. The inherent capability of the interferometer for absolute calibration, its maximum sensitivity adjustment, and the simplicity of the configuration of its components are explained. Utilization of a single-mode optical fiber in the test arm of the interferometer to enhance the geometric flexibility of the optical system is demonstrated. The sensor's application in the noncontacting detection of stimulated ultrasonic stress waves for nondestructive evaluation of advanced composite materials is emphasized. The detected signal is digitized and recorded using an IBM PC with a plug-in data-acquisition board. The combination of high sampling rate capability of the device and optical detection has facilitated the signal processing of ultrasonic waves in order to achieve interpretation and quantification of the physical parameter of interest (i.e., displacement).