Advantages and disadvantages of ultrasonic sensors

A pulse (emission wave) generated by the high-frequency pulse generator is applied to the ultrasonic sensor probe to excite the piezoelectric crystal to oscillate to generate ultrasonic waves. Ultrasonic waves propagate to the inside of the workpiece at a certain speed. A part of the ultrasonic wave is reflected back when it encounters the defect F; the other part of the ultrasonic distance sensor continues to be transmitted to the bottom surface B of the workpiece, and is also reflected back. When the ultrasonic wave reflected by the defect and the bottom surface is received by the probe, it becomes an electric pulse again. The transmitted wave f, the defective wave F, and the bottom wave are amplified and displayed on the display screen. 

The horizontal line on the screen is the scan line (time base), and its length is proportional to time. The position of the defect can be found from the position of the emission ultrasonic transducer circuit, the defect wave, and the bottom wave on the scanning line. From the amplitude of the defect wave, the defect size can be judged; from the shape of the defect wave, the nature of the defect can be analyzed. When the defect area is larger than the cross section of the sound beam, the sound waves are all reflected back from the defect. There are only T and F waves on the screen, and there is no B wave. When the workpiece is free of defects, there are only T and B waves on the screen, and there is no F wave. The advantages of ultrasonic flaw detection are large thickness detection, high sensitivity, high speed, low cost, harmless to the human body, and the ability to locate and quantify defects. However, the detection of ultrasonic sensor circuit by ultrasonic flaw detection is not intuitive, the flaw detection technique is difficult, it is easy to be affected by the main and objective factors, and the flaw detection results are inconvenient to save, so that the ultrasonic flaw detection also has its limitations.

1. The applicable frequency range is small. The frequency of ultrasonic sensor is relatively fixed. For example, the 40KHz sensor can only be used at 38-42KHz. At present, almost no sensors in a wide frequency range are available, such as products ranging from 40 kHz to 500 kHz.
   

2. High driving voltage
   Drive voltage of distance measuring transducer is generally between 100Vp-p and 1500Vp-p. Pulse transformer boost is required on many low-voltage devices, which will bring unnecessary trouble. Reducing the range of application of ultrasonic sensors.

3. Sensitivity is too small
   Mainly due to the use of piezoelectric ceramic materials for ultrasonic sensors, the limitations of their materials have led to the inability to achieve the sensitivity of other sensors.

4. Applicable distance range is small
   Due to the high ultrasonic frequency, the attenuation is fast when propagating in the medium, so the propagation depth measurement equipment of the ultrasonic sensor is short and cannot be reached.