(1) When the ultrasonic wave propagates in the medium, it has the characteristic of reflection at different quality interfaces. If the defect is encountered and the size of the defect is equal to or greater than the ultrasonic wavelength, the ultrasonic wave is reflected back on the defect, and the flaw detector can display the reflected wave. Come out; if the size of the defect is even smaller than the wavelength, the sound wave will bypass the ray and cannot reflect it;

(2) The directionality of the wave sound is good. The higher the frequency, the better the directionality. The beam is radiated into the medium with a narrow beam, and the position of the defect is easily determined.

(3) The propagation energy of the ultrasonic wave is large, such as the energy propagated by the super-wave with a frequency of 1 MHZ (100 Hz), which is equivalent to 1 million times the sound wave with the same amplitude and a frequency of 1000 Hz (Hertz).