Detecting Defects in Polymer Plates by using an Infrared 2-D Lock-in Amplifier System

Abstract

We have developed a two-dimensional lock-in amplifier system which can detect very small changes in images and can be used to detect subsurface defects in polymer plates nondestructively. This system uses modulated lights to heat and to cool the polymer surfaces. If there is a defect in the subsurface, heat conduction is disturbed at the edges of the defect. The subsurface defect should be identified by the observation of the localized variant temperature variation region on the surface. The temperature distribution can be observed by using an infrared thermography, and the variation can be detected by using a two-dimensional lock-in amplifier system. This inexpensive measurement system should therefore be very useful in detecting small defects in various polymers, rapidly, nondestructively, and without any contact.