We have presented our preliminary results on studying the effect of two different coupling materials in Sonic Infrared (IR) Imaging, which is a hybrid ultrasonic/infrared NDE technology and can detect defects in materials and structures by detecting the changes of IR radiation of defective objects through sensors during an ultrasound excitation pulse (can be a fraction of a second), in the Smart Structures and NDE in San Diego in March 2007. Those two coupling materials produced different results in the sense of producing different IR signal levels. We have been further investigating the non-linear phenomena of different coupling materials in Sonic IR Imaging because this non-linear effect appears to play a very important role in Sonic IR Imaging technology. We focus our study on the effect of the level of coupling mechanical energy from the ultrasound transducer to the target, and the level of infrared signals produced around the defects. We present our results from those aspects in this paper.