Introduction to plastic welding machine

When an object vibrates, it makes a sound. Scientists call the number of vibrations per second the frequency of sound. Its unit is hertz. The frequency of sound waves that we human ears can hear is 20 ~ 20000 Hz. When the vibration frequency of sound wave is greater than 20000 Hz or less than 20 Hz, we can't hear it. Therefore, we call sound waves with frequencies higher than 20000 Hz "ultrasonic". The ultrasonic frequency commonly used in medical diagnosis is 1 ~ 5 MHz. Ultrasonic wave has the characteristics of good directivity, strong penetration ability, easy to obtain concentrated sound energy, long propagation distance in water and so on.