Ultrasound is not a source of radiation and is generally harmless to humans. We know that when something vibrates it makes a sound, and the number of vibrations per second is called the frequency of sound, which is in Hertz. The frequency of sound waves that we can hear ranges from 20 to 20,000 Hertz. If the frequency of a sound wave is greater than 20,000 Hertz or less than 20 Hertz, we cannot hear it. Sound waves with frequencies higher than 20,000 Hertz are called ultrasonic. The frequency of ultrasound usually used in medical diagnosis is 1 ~ 5 MHZ. Ultrasonic wave has the characteristics of good directivity, strong penetrability, easy to obtain concentrated sound energy, and long propagation distance in water. Can be used for ranging, speed measurement, cleaning, welding, gravel and so on. In the medical, military, industrial, agriculture has obvious effect, high power focused ultrasound can be used in the treatment of tumors, in 0.5 seconds can quickly organize target area temperatures soared to 70 ℃ above, make rapid emergence intracellular protein coagulation necrosis (tumor cell death the critical point of temperature in 42.5 ~ 43.0 ℃, while normal cells to 45 ℃, for the liver tissue, local temperature more than 58 ℃ can cause tissue coagulation necrosis).
Local sound intensity as high as > 10,000 watts /cm2 above, of course, may have damage to local normal tissue, need accurate positioning. In terms of ultrasonic protection, it should be noted that people with hearing diseases and neurological disorders should not work around such devices. High-intensity ultrasonic devices should be shielded to block the ultrasound. At present, there is no accurate data to prove that ultrasonic welding machine has too much harm to human body, but the only disadvantage is, welding must take earplugs, to prevent a long time to work, have an impact on hearing! If it is high frequency, it will not work. (girls should pay special attention to it)