Photoacoustic measurement of thermal properties and thickness of buried layers at multilayer film

The photoacoustic model of multilayer with a strong-absorbing surface layer is developed. The phase of photoacoustic signal has been measured as a function of modulated frequency using apparatuses that are all controlled by a computer system. The thermal diffusivity, effusivity as well as thickness of several buried layers are obtained independently through best fit of experimental data according to the theoretical model. The multilayers of thin metal and alloy film are investigated and the results show agreement with literature values. This method is proved to be particularly valuable in nondestructive examinations of subsurface physical properties.