Sound waves are mechanical waves that can propagate in gases, liquids, and solids. Sound waves can be divided into infrasound waves, sonic waves and ultrasonic horns by frequency
The sound wave frequency is between 16Hz-20kHz, which is a mechanical wave that can be heard by the human ear; the infrasound wave is a mechanical wave with a frequency lower than 16Hz; and the ultrasonic wave is a mechanical wave with a frequency higher than 20kHz.
Ultrasonic sensors emit a set of high-frequency sound waves, and when the sound waves hit an object, they bounce back and are picked up. By calculating the time from the launch to the return of the sound wave, and multiplying the speed of the sound wave in the medium, the distance value of the object relative to the sensor can be obtained. The characteristics are high frequency, short wavelength and small diffraction phenomenon. Its remarkable characteristics are good directionality, small attenuation in liquids and solids, large penetration ability, and obvious reflection and refraction when it encounters the interface of the medium, so it is widely used in industrial testing.
Auto parts plastic welding machine uses piezoelectric ceramics to expand and contract according to the direction of voltage, convert electrical signals into ceramic vibrations, make air vibrate through repeated expansion and contraction of ceramics, and emit ultrasonic waves.
In actual use, an ultrasonic sensor applies an electrical signal to an ultrasonic transducer (transmitter), transmits ultrasonic waves by expanding and contracting piezoelectric ceramics, and then a receiver converts the ultrasonic waves into electrical signals for analysis, and adds various This application is mainly used to measure distances. The main performance of ultrasonic sensor:
(1) Working frequency:
The operating frequency is the resonant frequency of the piezoelectric sheet. When the frequency of the AC voltage applied to it is equal to the resonance frequency of the piezoelectric sheet, the output energy is greater and the sensitivity is higher.
(2) Sensitivity:
Refers to the ratio of sensor output increment to input increment. In practical applications, the sensitivity can express the degree of amplification of the input signal by the sensor.
(3) Direction angle:
The sensor has a conical directivity from the top surface, which is defined as the sound pressure from the front to -6dB. Compared with the optical sensor, the directivity is wider, but the directivity becomes sharper as the frequency increases.
(4) Working temperature:
Because the Curie point of piezoelectric materials is generally relatively high, especially when the ultrasonic probe for diagnosis uses less power, the working temperature is relatively low, and it can work for a long time without failure. Ultrasound probes for medical use have relatively high temperatures and require separate refrigeration equipment.