Noise-limited thermal/infrared nondestructive testing

In thermal/infrared nondestructive testing (T/I NDT), the presence of noise in the infrared signal is an inconvenience in the method. It is convenient to introduce two extreme types of T/I NDT noise: (1) this type is purely additive and is defined by background reflections and the IR detector and (2) this is purely multiplicative and is defined by the material's absorptivity/emissivity variations. Multiple T/I NDT tests performed on various materials have shown that none of materials reveal a 'pure′ additive or multiplicative type of noise. However, in the case of optical heating, many composite and black-painted materials exhibit multiplicative noise with a noise contrast of C _n=2-5%, and this determines the defect detection limits. The C _n concept has been applied to a graphite epoxy composite to demonstrate that the maximum depth of detected defects in a one-sided procedure is about 4 mm. Also, in 1-10 mm-thick black-painted steel, the minimum detectable material loss is from 3% to 9%.