超聲波是頻率高于20000赫茲的聲波，它方向性好，穿透能力強，易于獲得較集中的聲能，在水中傳播距離遠，可用于測距，測速，超聲波清洗機，焊接，碎石、殺菌消毒等。在醫學、軍事、工業、農業上有很多的應用。超聲波因其頻率下限大約等于人的聽覺上限而得名。

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.

超聲波頻率是怎么計算的固體中的聲速也各不相同，經過反復測定發現，聲波在固體中用縱波和橫波兩種形式傳播，這兩種波的波速也不相同。例如，不銹鋼中，縱波速度是5790米/秒，橫波速度是3100米/秒。把不銹鋼做成棒狀，棒內的縱波速度是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.

在超聲波清洗機清洗中，首先要正確選用超聲波清洗機的頻率。超聲波清洗機頻率是起決定性作用的工藝參數，因為它對空化作用有直接的影響。超聲波清洗機頻率越低，超聲空化作用越強，清洗效果也比較理想，但噪音較大。故一般采用的超聲波清洗機頻率為20千赫左右，此時的空化作用強，清洗效果也比較好。

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.

對于表面光潔度較高的零件以及具有較小直徑的孔類零件，宜采用波長較短、能量較集中的高頻超聲波清洗機清洗。但高頻的超聲振動在清洗液中衰減較大、作用距離較短、空化強度較弱，因而清洗效率也較低。此外，還由于高頻超聲波清洗機的方向性所產生的陰影，會造成被清洗件的某些部位清洗不到的現象。

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.

使用無頻率跟蹤的超聲波清洗機清洗機時，需經常調節超聲波清洗機發生器的頻率調節旋鈕，以便使其輸出信號的頻率與換能器的固有頻率始終保持一致，從而達到空化作用強、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.

金屬中，鈹是傳聲的能手，用鈹做的棒內，聲波的縱波速度達到12890米/秒，大氣聲遞的38倍。聚乙烯塑料傳聲本領較差，聚乙烯棒中的縱波速度只有920米/秒，不及水中聲速快。軟橡膠富有彈性，聲波在里邊走不動，速度只有30-50米／秒，還不及空氣中的聲速呢！波速除以頻率就等于波長。

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.

超聲波作用于液體中時，液體中每個氣泡的破裂會產生能量極大的沖擊波，相當于瞬間產生幾百度的高溫和高達上千個大氣壓，這種現象被稱之為“空化作用”，超聲波清洗正是用液體中氣泡破裂所產生的沖擊波來達到清洗和沖刷工件內外表面的作用。超聲波在液體中傳播，使液體與清洗槽在超聲波頻率下一起振動，液體與清洗槽振動時有自己固有頻率，這種振動頻率是聲波頻率，所以人們就聽到嗡嗡聲。

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.