A Simple Method for Profiling Surface Temperature Distributions by Laser-Ultrasound

Abstract

In the fields of materials science and engineering, it is often required to measure surface temperatures of heated materials. Although infrared radiations are used for measuring surface temperature, they are not always acceptable for some applications because of the limitation in their ability. Therefore, it is required to develop an alternative technique for surface temperature measurements. In this work, a simple ultrasound method for measuring surface temperature distributions of a heated material is presented. A laser ultrasound scanning technique has been employed for non-contact measurements of surface temperature distributions. The principle of the methods is based on the temperature dependence of a surface acoustic wave (SAW). SAWs are generated at different positions on a material surface consecutively by pulsed laser irradiation scanning (Nd:YAG, wavelength=1064 nm, energy 200 mJ/pulse, pulse width 3 ns) using a one-dimensional galvanometer scanner, and each SAW is detected at a certain position using a laser interferometer based on photorefractive two-wave mixing (Nd:YAG, wavelength=532 nm, energy 200 mW). Based on the laser ultrasound scanning, a number of surfaced temperatures at different positions in series are obtained and are combined together to construct the overall temperature distribution. The proposed ultrasonic method has been applied to the surface temperature measurement of an aluminum plate whose single side is being heated. The surface temperature distributions determined by the present method almost agree with those measured using an infrared camera.