塑料焊接机的产生
Production of plastic welding machine
超声波是指振动频率大于20KHz以上的，其每秒的振动次数（频率）甚高，超出了人耳听觉的上限（20000Hz），人们将这种听不见的声波叫做超声波。超声和可闻声本质上是一致的，它们的共同点都是一种机械振动，通常以纵波的方式在弹性介质内会传播，是一种能量的传播形式，其不同点是超声频率高，波长短，在一定距离内沿直线传播具有良好的束射性和方向性，腹部超声成象所用的频率范围在 2∽5MHz之间，常用为3∽3.5MHz（每秒振动1次为1Hz，1MHz=10^6Hz，即每秒振动100万次，可闻波的频率在16－20，000HZ 之间）。
Ultrasonic refers to the vibration frequency more than 20kHz, the vibration frequency per second (frequency) is very high, beyond the upper limit of human hearing (20000hz), people call this kind of invisible sound wave ultrasonic. Ultrasound and audible sound are essentially the same. Their common ground is a kind of mechanical vibration, which usually propagates in the elastic medium in the form of longitudinal wave, which is a form of energy transmission. The difference is that the ultrasonic frequency is high, the wavelength is short, and the propagation along a straight line within a certain distance has good beam emission and directivity. The frequency range used for abdominal ultrasound imaging is within 2 ∽ 5MHz, usually 3 ∽ 3.5MHz (vibration once per second is 1Hz, 1MHz = 10 ^ 6Hz, i.e., vibration 1 million times per second, audible wave frequency is between 16-20000 Hz).