Acoustic waves are a type of mechanical waves that can propagate in gases, liquids, and solids. According to frequency, acoustic waves can be divided into infrasound waves, acoustic waves, and ultrasonic waves.
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 machine with a frequency lower than 16 Hz, and the ultrasonic wave is a mechanical wave with a frequency higher than 20kHz.
Ultrasound is characterized by high frequency, short wavelength and low diffraction. Its most notable feature is good directivity, small attenuation in liquids and solids, large penetration ability, and obvious occurrence when encountering the interface of the medium Reflection and refraction, so it has been widely used in industry. Detection.
Ultrasonic wave propagation speed: Ultrasonic wave usually has longitudinal wave, transverse wave and surface wave, and its propagation speed depends on the elastic constant and density of the medium. Only the longitudinal wave can propagate in gas and liquid. The speed of sound in gas is 344m/s, the speed of sound in liquid It is 900-1900m/s. In solids, the sound velocity of longitudinal waves, transverse waves and surface waves has a certain relationship. Generally speaking, the shear wave velocity is half of the longitudinal wave velocity, and the surface wave velocity is about the shear wave velocity. 90%.
When ultrasonic waves propagate in the medium, as the propagation distance increases, the energy gradually attenuates. The attenuation of energy depends on the diffusion, scattering, and absorption of ultrasound.
Using ultrasound as a detection method, it can generate ultrasound and receive ultrasound. The device that performs this function is an ultrasound sensor.
The main properties of ultrasonic sensors include;
(1) Working frequency.
The operating frequency is the resonance frequency of the piezoelectric chip. When the frequency of the AC voltage applied to it is equal to the resonance frequency of the chip, the output energy is the largest and the sensitivity is also the highest.
(2) Working temperature.
Because the Curie point of piezoelectric materials is generally high, especially when the ultrasonic probe for diagnosis uses less power, the operating temperature is relatively low, and it can work for a long time without failure. The temperature of the ultrasonic probe for medical use is relatively high and requires Separate refrigeration equipment.
Mainly depends on the manufacturing wafer itself. The electromechanical coupling coefficient is large and the sensitivity is high; otherwise, the sensitivity is low.
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