Displacement Measurement of Air-coupled Ultrasonic

For non-contact measuring the distance or displacement in the air a few millimeters apart from the test surface, the laser is the main means of detection. However, the easy-to-absorb black rubber, the transparent material with weak surface reflection, and the translucent material with superficial reflection and bottom reflection being overlapped, the laser detection method cannot do anything. Air-coupled ultrasonic nondestructive testing technology can make up for the lack of laser detection technology. The use of air-coupled ultrasonic surface emission method, simply measuring the surface reflection of the specimen can measure the distance or displacement of any material specimen. In this paper, the real-time measurement of the air-to-specimen displacement was performed by the surface emission method through using 2 MHz air coupling point focus probe, and the experimental results show that when the temperature changes in the range of 0.1℃, the detection accuracy is of 0.01 mm.