Spectrum Analysis of an Ultrasonic Signal According to a Surface Status by Using a Robust Laser-Based Ultrasonic System

A laser-based ultrasonic inspection system is a non-contact scanning device with a high spatial resolution and a wide spectrum bandwidth. In this paper, we developed a laser-based ultrasonic inspection system by fabricating a pulse laser and a Confocal Fabry-Perot Interferometer (CFPI) with a dynamic stabilizer. The dynamic stabilizer generates ultrasound by adaptively obtaining the time of the maximum gain of the CFPI whose gain is varied with the time. Then, a computer adaptively corrects the measurement error by using the gain of the CFPI at the measuring time. In this paper, we describe the hardware configurations and the control algorithms to build the stable laser-based ultrasonic inspection system. We have investigated an ultrasonic signal in the time and frequency domain to detect micro cracks through experiments. We experimentally confirmed that the proposed error correction method is effective for improving the performance of the system and the configured ultrasonic inspection system is stable