What is ultrasound? What is the application principle of ultrasonic equipment? Please everyone, thank you!

People can hear the sound is due to object vibration, its frequency in the range of 20HZ-20KHZ, more than 20KHZ known as ultrasound, less than 20HZ known as infrasound. Commonly used ultrasonic frequency of tens of KHZ - tens of MHZ. Ultrasound is a kind of mechanical oscillation in an elastic medium, there are two forms: transverse oscillation (transverse) and longitudinal and oscillation (longitudinal). Applications in industry mainly use longitudinal oscillation. Ultrasonic waves can propagate in gases, liquids and solids at different speeds. In addition, it also has refraction and reflection phenomena, and there is attenuation in the propagation process. In the air propagation of ultrasound, its frequency is low, generally tens of KHZ, while in the solid, liquid is available in higher frequency. In the air faster attenuation, while in the liquid and solid propagation, attenuation is smaller, spread farther. The use of ultrasound characteristics, can be made into a variety of ultrasonic sensors, with different circuits, made of a variety of ultrasonic measuring instruments and devices, and in communication, medical home appliances and other aspects of a wide range of applications.