Ultrasound is a kind of sound wave with frequency higher than 20,000 Hz, it has good directionality, strong penetrating ability, easy to obtain more concentrated sound energy, and propagates far in water, which can be used for distance measurement, speed measurement, cleaning, welding, stone crushing, sterilization and so on. There are many applications in medicine, military, industry and agriculture. Ultrasound is named because its lower frequency limit is greater than the upper limit of human hearing. Scientists call the number of vibrations per second the frequency of sound, which is measured in Hertz (Hz). The frequency of sound waves that can be heard by our human ears is 20 Hz to 20,000 Hz. Therefore, we call sound waves with a frequency higher than 20,000 Hz "ultrasound". The frequency of ultrasound that is usually used for medical diagnosis is 1 megahertz - 30 megahertz. Theoretical research shows that, under the same conditions of amplitude, the energy of an object vibration is proportional to the frequency of vibration, ultrasound propagation in the medium, the frequency of vibration of the media mass is very high, and thus the energy is very large. In the dry winter in northern China, if the ultrasonic wave into the water tank, the violent vibration will make the tank of water broken into many small droplets, and then a small fan to blow the droplets into the room, you can increase the indoor air humidity, which is the principle of ultrasonic humidifier. Such as laryngitis, bronchitis and other diseases, it is difficult to use the blood flow to make the drug reach the diseased parts, the use of the principle of humidifier, the drug solution atomized, so that the patient inhaled, can improve the effectiveness of treatment. The use of ultrasound huge energy can also make the human body of the stone to do violent forced vibration and broken, so as to slow down the pain and achieve the purpose of healing. Ultrasound is widely used in medicine, and can sterilize and disinfect objects.