超声波是频率高于20000赫兹的声波，它方向性好，穿透能力强，易于获得较集中的声能，在水中传播距离远，可用于测距，测速，超声波清洗机，焊接，碎石、杀菌消毒等。在医学、军事、工业、农业上有很多的应用。超声波因其频率下限大约等于人的听觉上限而得名。

Ultrasonic wave is a kind of sound wave whose frequency is higher than 20000 Hz. It has good directivity, strong penetrability, and easy to obtain concentrated sound energy. It can be used for distance measurement, velocity measurement, ultrasonic cleaning machine, welding, gravel, sterilization and disinfection. It has many applications in medicine, military, industry and agriculture. Ultrasound is named because its lower frequency limit is approximately equal to the upper limit of human hearing.

超声波频率是怎么计算的固体中的声速也各不相同，经过反复测定发现，声波在固体中用纵波和横波两种形式传播，这两种波的波速也不相同。例如，不锈钢中，纵波速度是5790米/秒，横波速度是3100米/秒。把不锈钢做成棒状，棒内的纵波速度是5000米/秒。

How to calculate the frequency of ultrasonic wave, the sound velocity in solid is also different. After repeated measurement, it is found that the sound wave propagates in the solid in the form of longitudinal wave and transverse wave, and the wave velocity of these two kinds of waves is also different. For example, in stainless steel, the P-wave velocity is 5790 M / s and the S-wave velocity is 3100 M / s. The stainless steel is made into a rod with a longitudinal wave velocity of 5000 m / s.

在超声波清洗机清洗中，首先要正确选用超声波清洗机的频率。超声波清洗机频率是起决定性作用的工艺参数，因为它对空化作用有直接的影响。超声波清洗机频率越低，超声空化作用越强，清洗效果也比较理想，但噪音较大。故一般采用的超声波清洗机频率为20千赫左右，此时的空化作用强，清洗效果也比较好。

In the cleaning of ultrasonic cleaning machine, the frequency of ultrasonic cleaning machine should be selected correctly. The frequency of ultrasonic cleaning machine is a decisive process parameter, because it has a direct impact on cavitation. The lower the frequency of ultrasonic cleaning machine is, the stronger the ultrasonic cavitation effect is, and the cleaning effect is ideal, but the noise is large. Therefore, the frequency of ultrasonic cleaning machine is about 20 kHz, which has strong cavitation effect and good cleaning effect.

对于表面光洁度较高的零件以及具有较小直径的孔类零件，宜采用波长较短、能量较集中的高频超声波清洗机清洗。但高频的超声振动在清洗液中衰减较大、作用距离较短、空化强度较弱，因而清洗效率也较低。此外，还由于高频超声波清洗机的方向性所产生的阴影，会造成被清洗件的某些部位清洗不到的现象。

For parts with higher surface finish and smaller diameter holes, the high frequency ultrasonic cleaner with shorter wavelength and more concentrated energy should be used. However, the high frequency ultrasonic vibration in the cleaning fluid attenuates greatly, the action distance is short, and the cavitation intensity is weak, so the cleaning efficiency is also low. In addition, due to the directionality of high frequency ultrasonic cleaning machine, some parts of the cleaned parts can not be cleaned.

使用无频率跟踪的超声波清洗机清洗机时，需经常调节超声波清洗机发生器的频率调节旋钮，以便使其输出信号的频率与换能器的固有频率始终保持一致，从而达到空化作用强、清洗效果好的目的。

When using ultrasonic cleaning machine without frequency tracking, it is necessary to adjust the frequency adjusting knob of ultrasonic cleaning machine generator frequently, so as to keep the frequency of output signal consistent with the natural frequency of transducer, so as to achieve the purpose of strongest cavitation effect and best cleaning effect.

金属中，铍是传声的能手，用铍做的棒内，声波的纵波速度达到12890米/秒，大气声递的38倍。聚乙烯塑料传声本领较差，聚乙烯棒中的纵波速度只有920米/秒，不及水中声速快。软橡胶富有弹性，声波在里边走不动，速度只有30-50米／秒，还不及空气中的声速呢！波速除以频率就等于波长。

Among metals, beryllium is a master of sound transmission. In the rod made of beryllium, the longitudinal wave velocity of sound wave reaches 12890 M / s, 38 times of atmospheric sound transmission. The longitudinal wave velocity in polyethylene rod is only 920 M / s, which is not as fast as that in water. Soft rubber is full of elasticity. The sound wave can't move in it. The speed is only 30-50 M / s, which is not as fast as the sound speed in the air! Wave speed divided by frequency equals wavelength.

超声波作用于液体中时，液体中每个气泡的破裂会产生能量极大的冲击波，相当于瞬间产生几百度的高温和高达上千个大气压，这种现象被称之为“空化作用”，超声波清洗正是用液体中气泡破裂所产生的冲击波来达到清洗和冲刷工件内外表面的作用。超声波在液体中传播，使液体与清洗槽在超声波频率下一起振动，液体与清洗槽振动时有自己固有频率，这种振动频率是声波频率，所以人们就听到嗡嗡声。

When the ultrasonic wave acts on the liquid, the rupture of each bubble in the liquid will produce a shock wave with great energy, which is equivalent to hundreds of degrees of high temperature and thousands of atmospheres in an instant. This phenomenon is called "cavitation effect". Ultrasonic cleaning is to use the shock wave generated by the bubble breaking in the liquid to clean and wash the internal and external surface of the workpiece. The ultrasonic wave propagates in the liquid, which makes the liquid and the cleaning tank vibrate together under the ultrasonic frequency. When the liquid and the cleaning tank vibrate, they have their own natural frequency. This vibration frequency is the acoustic frequency, so people hear the buzz.