Before we know the difference between ultrasonic bath frequencies we should know what the corresponding frequencies mean.

28KHz refers to the number of vibration per minute, which is 28,000
40KHz is the number of vibration per minute, which is 40,000

In the field of ultrasonic cleaning, the greater the number, the number of vibrations there are,the most common frequency one is 40 KHz, one is 28 KHz. Generally, the larger the bubble generated by the low-frequency acoustic wave, the stronger the cleaning force will be. And the more suitable for cleaning the surface of the product, the high frequency sound waves generated by the bubbles are relatively smaller, but there are a lot more bubbles, will be more suitable for the cleaning of high precision products.

Ultrasonic cleaner with 28KHz is often used to clean large, heavy parts or high density material workpiece.

Ultrasonic cleaner with 40KHz is usually used to clean smaller, more sophisticated parts, or to remove tiny particles.
At presen, the household ultrasonic cleaner, as well as the commercial ultrasonic cleaner used more than 40KHz or 42KHz frequency, because the machine is relatively small, and considering a cleaning range, 40KHz has much larger cleaning range han 28KHz.