Thickness measurement research using transmission step-heating thermography

Pulsed thermography techniques are used most widely in quantitative evaluation applications but are limited by the specimen thickness. A thickness prediction method that uses transmission step-heating thermography is presented. A halogen lamp is used as a simple and inexpensive step-heating source. Because the halogen lamp undergoes a temperature rise process before reaching maximum output, its output differs from an ideal step function and this is the main cause of the measurement accuracy limitations. Therefore, an expression for the halogen lamp heating process is proposed. On this basis, under the halogen step-heating excitation condition, an equation for the specimen temperature rise over time is obtained. The specimen thickness is then calculated after nonlinear fitting of experimental data to the theoretical function. To evaluate the measurement accuracy of this thickness prediction method, specimens composed of different materials and with differing thicknesses were designed. All measurement errors were below 2%, demonstrating the method's high accuracy and wide applicability.