Comparison of the Optical Lock-in Thermography using the Reflection Mode and the Transmission Mode

Abstract

Optical lock-in thermography is a non-destructive testing method. The surface of the sample is excited using the thermal waves and the response is recorded by the thermal camera. This image thermal sequence is processed using the image processing method named lock-in method. Optical lock-in thermography can be used to detect cracks and damages in metal or composite material. Two position modes are used: the reflection and the transmission mode. In this paper, are compared these two modes. An experiment is carried out on a printed composite plane with the square blinded holes placed in the different depths below the surface. The phase images are created using the lock-in method for both position modes. The results are compared and the advantages and the disadvantage of these position modes find out.