Parallel Vector Lock-In Thermal Wave IR Video Imaging of Microcracks in Cu Foils Deposited on Polyimide

摘要

Recently, the concept of area-wide lock-in detection in infrared video imaging and its application to thermal wave imaging was demonstrated.[1] This technique combines the lock-in detection method with an IR video camera and almost real-time digital image processing to form a parallel vector lock-in thermal wave IR video imaging system. In this method each pixel of an image is processed in the manner similar to the lock-in detection method while the sample is excited (heated) synchronously with a square-wave modulated joule heating. The synchronous detection allows the non-synchronous background radiation to be subtracted from the signal resulting in an enhanced signal-to-noise ratio, thus allowing the signal of interest to be measured even in situations where it is completely masked by noise. The advantage of IR detection (8–12 µm) and high speed data acquisition combined with the area-wide lock-in detection makes this a unique thermal wave imaging technique for non-destructive evaluation. In this paper we report the application of this lock-in thermal wave IR video imaging technique using ac Joule heating to the imaging of microcracks in Cu foils deposited on polyimide substrates. Comparison of the lock-in video images of good and faulty samples are presented.