1. Generation of ultrasonic waves

Piezoelectric effect: Piezoelectric chips are usually used as the emission source of ultrasonic waves. When high-frequency electrical pulse signals are applied to piezoelectric chips, the chips will generate mechanical vibrations, thereby emitting ultrasonic waves. The vibration frequency of piezoelectric chips is consistent with the frequency of the applied electrical pulses, typically in the range of several megahertz (MHz).

High frequency oscillation circuit: The high-frequency oscillation circuit inside the instrument generates high-frequency electrical signals, driving the piezoelectric chip to vibrate. The frequency of this high-frequency electrical signal can be adjusted according to the material and thickness of the detected object.

2. Propagation of Ultrasonic Waves

Propagation characteristics in media: Ultrasonic waves are mechanical waves that need to propagate in media. It can propagate in solids, liquids, and gases, but its propagation characteristics are most stable in solids. When ultrasound propagates in a medium, its energy gradually decays with increasing distance, and the degree of attenuation depends on the properties of the medium, the frequency of the ultrasound, and the length of the propagation path.

Reflection and Refraction: When ultrasound encounters interfaces between different media (such as solid and air, solid and liquid), reflection and refraction occur. If there are defects on the interface (such as cracks, pores, inclusions, etc.), ultrasonic waves will reflect at the defect site. The intensity and direction of the reflected wave depend on the nature, size, and location of the defect.

3. Reception of ultrasonic waves

The receiving function of piezoelectric chips: Piezoelectric chips in ultrasonic testing instruments are not only used to emit ultrasonic waves, but also to receive reflected ultrasonic signals. When the reflected wave acts on a piezoelectric chip, the chip generates an electric charge, forming an electrical signal.

Signal amplification and processing: The received ultrasonic signals are usually very weak and need to be amplified through the internal amplification circuit of the instrument. The amplified signal is processed through filtering, shaping, etc., and finally converted into a waveform or data that can be displayed.

4. Signal analysis and defect judgment

Waveform analysis: Determine the presence or absence of defects by analyzing the received reflected waveform. The main parameters include the amplitude, time delay, and waveform characteristics of the reflected wave. For example, the higher the amplitude of the reflected wave, the more severe the defect; The shorter the time delay of the reflected wave, the closer the defect is to the surface.

Threshold judgment: Instruments usually set a threshold, and when the amplitude of the reflected wave exceeds this threshold, the instrument will issue an alarm signal, indicating that there is a defect in the detection personnel.

Imaging technology: It also has imaging functions, such as phased array ultrasonic testing technology. Through the collaborative work of multiple piezoelectric chips, two-dimensional or three-dimensional images of defects can be generated, which more intuitively display the location and shape of defects.

5. Application scope of ultrasonic testing

Material testing: used to detect internal defects such as cracks, pores, inclusions, etc. in metals, plastics, composite materials, etc.

Weld seam inspection: Check the quality of the welded joint and discover defects such as incomplete fusion, incomplete penetration, and porosity in the weld seam.

Pipeline inspection: Detecting defects such as wall thickness reduction, corrosion, and cracks in pipelines to ensure their safe operation.

Casting inspection: Check for defects such as shrinkage, porosity, and sand inclusions inside the casting to improve its quality.

Ultrasonic testing instruments have been widely used in the industrial field due to their advantages of non-destructive, high efficiency, and high sensitivity.