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Ultrasonic TOFD detection technology

News by ninechip | On 2019-01-09 09:22
TOFD technology, fully called Time of Flight Diffraction, was invented by British Harwell laboratory in the late 1970s. It is a kind of ultrasonic detection technology that can accurately measure the size of defects, and can accurately measure the height of plane defects in the direction of wall thickness, so as to provide test data for the usability evaluation of equipment. The technology will be widely used for its rapidity of detection and reliability of dimension measurement.
The conventional ultrasonic detection technique is a kind of pulse reflectance, and it measures the defects by using the wave to reflect the defect on the surface. The TOFD technique is based on the effects of the ultrasound at the edge of the defect, using the echo and diffraction of the ultrasound to test the metal parts. When the ultrasonic wave encounters a plane defect, it produces normal reflection wave and diffraction wave at the edge and tip of the defect. The diffracted wave spread in wide angle, and the strength is very weak. Using the principle of reflection and diffraction, TOFD uses two probes to detect, one as the transmitting probe and the other as the receiving probe. The distance between the probes is called the probe spacing.
When a plane defect is present in a specimen, the diffraction signal at the upper end of the defect reaches the receiving probe before the diffraction signal at the lower end, and the two longitudinal wave signals are located between the transverse and bottom waves. Therefore, TOFD system can measure not only the height of defects in the direction of wall thickness, but also the depth of defects.
Compared with conventional pulse-reflection ultrasonic detection technology, TOFD has the advantages of high detection sensitivity while detection accuracy is not affected by the amplitude, and it can detect defects that cannot be detected by conventional detection methods. At present, the detection field is mainly used for the research and development of ultrasonic pest repeller, mouse repellent, animal repellent and so on.