Non-invasive Measurement of Water Temperature by a Combined Method of Ultrasound and Laser

In this study, we have developed a combined method of ultrasound and laser to make non-invasive measurements of water temperature. In the proposed method, a laser Doppler vibrometer (LDV) is used to detect ultrasonic pulse waves propagating through a certain distance of water so that the ultrasonic velocity can be determined from the detected ultrasonic waves. Water temperature can then be determined from the ultrasonic velocity of the water as long as the temperature dependence of the velocity is known. In order to verify the validity of the proposed method, experiments have been performed in temperatures ranging from 3 .C to 70 .C. The results show that the water temperatures measured by the proposed method agree well with those measured using thermocouples immersed in water. In addition, an attempt to measure the temperature distribution in a water tank has been made. It is expected that the proposed method will be a promising tool to make noninvasive measurements of liquid temperature.