Nondestructive Measurement of Microcoating Thickness Using Sweep Frequency Photoacoustic Sensing Technique

Nondestructive and rapid measurement of microcoating thickness is a challenge for most of the paint coating industries. This letter proposes a novel sweep frequency photoacoustic sensing technique for the nondestructive estimation of a coating layer thickness. The continuous wave (CW) laser diode used for the sample excitation makes the overall system compact and portable. In addition, the usage of frequency sweep enables the technique to be applied to different substrates and different coating layers. The Rosencwaig–Gersho (RG) model is employed to estimate the thickness of the coating layer by measuring the resonance frequency of the photoacoustic wave. Regression analysis is performed to obtain the microthickness through photoacoustic measurements. The photoacoustic measurements are compared with the standard (cross-sectional microscopy) thickness measurement technique and the error is found to be less than 5%. The simple computational method and instrumentation used in this technique enable it to be deployed in industries for rapid estimation of the microthickness.