Nondestructive Evaluation of Coating Thickness by Ultrasonic Technique

Abstract

Nondestructive measurement of the thickness of thin coatings was investigated. After examining some ultrasonic methods to measure coating thickness, we considered that arrival time difference method was a most simple and effective method to measure coating thickness. It was found that the incident ray from the coating surface reflects at the bottom surface, while the incident ray from the bottom reflects at the interface between coating film and substrate. The arrival time difference is therefore appeared between the ultrasonic waves emitted from the surface and the bottom of the specimen. By use of this time difference, we can estimate the thickness of thin foils and coating films.