The principle and application of ultrasound
The propagation laws of reflection, refraction, diffraction, and scattering of ultrasonic waves in the medium are not essentially different from the laws of audible sound waves. But the wavelength of ultrasound is very short, only a few centimeters, even a few thousandths of a millimeter.
The propagation laws of reflection, refraction, diffraction, and scattering of ultrasonic waves in the medium are not essentially different from the laws of audible sound waves. But the wavelength of ultrasound is very short, only a few centimeters, even a few thousandths of a millimeter.
The technical application of ultrasound, in summary, mainly includes two aspects:
(1) Ultrasonic treatment. Ultrasonic treatment mainly uses its power characteristics and cavitation to change or accelerate the change of certain physical, chemical, biological properties or states of substances. The use of strong ultrasonic waves for processing, ultrasonic cleaning, ultrasonic welding, ultrasonic emulsification, ultrasonic crushing, ultrasonic degassing, ultrasonic medical treatment, ultrasonic seed treatment, etc., has been widely used in various sectors such as industry, agriculture, medical and health. In industry, strong ultrasonic waves are used to drill and cut hard objects such as steel, ceramics, gems, and diamonds. Usually, we can use hammers and steel drills to make holes in hard rocks one by one. Ultrasonic processing is also the reason.
(2) Ultrasonic flaw detection, thickness measurement, distance measurement, medical diagnosis and imaging. In industrial production, the ultrasonic transmission method is often used for non-destructive detection of products. The ultrasonic wave emitted by the ultrasonic generator can penetrate the sample to be tested and be received by the receiver on the opposite side. If there is a defect inside the sample, the ultrasonic wave will be reflected at the defect. At this time, the receiver on the opposite side cannot receive or cannot receive all the ultrasonic signals emitted by the generator. In this way, it is possible to detect whether there are defects in the sample without damaging the sample to be tested. In medical diagnosis, the echo method is often used: weak ultrasound is penetrated into the human body. When the ultrasound encounters the interface of the organ, it will reflect and transmit. Ultrasonic waves transmitted into the organs will be reflected and transmitted again when they encounter the interface. The ultrasonic receiver specifically receives the reflected waves each time. Medical staff can understand the size and location of organs and their internal lesions based on the time interval and wave strength of each reflected wave received. Compared with audible sound waves, ultrasonic waves have many strange characteristics:
1. Cavitation-when ultrasonic waves propagate in liquid, small cavities will be created in the liquid due to the violent vibration of liquid particles. These small cavities expand and close rapidly, causing violent collisions between the liquid particles, resulting in pressures of thousands to tens of thousands of atmospheres. This violent interaction between the particles will cause the temperature of the liquid to rise suddenly, and play a good stirring effect, so that the two immiscible liquids (such as water and oil) emulsify, and accelerate the dissolution of solutes. chemical reaction. The various effects caused by the action of ultrasonic waves in the liquid are called ultrasonic cavitation.
2. Power characteristics-when sound propagates in the air, it pushes the particles in the air to vibrate back and forth and do work on the particles. The sound wave power is a physical quantity that expresses the speed of the sound wave's work. Under the same intensity, the higher the frequency of the sound wave, the greater the power it has. Due to the high frequency of ultrasonic waves, the power of ultrasonic waves is very large compared with ordinary sound waves.
3. Propagation characteristics-the wavelength of ultrasonic waves is very short, and the size of ordinary obstacles is many times larger than the wavelength of ultrasonic waves. Therefore, the diffraction power of ultrasonic waves is very poor. It can propagate in a straight line in a uniform medium. The shorter the wavelength of ultrasonic waves , This feature is more remarkable.
