Why Ultrasonic Cleaning Frequency Cannot Be Adjusted

Many people ask: “Can we adjust the frequency of one ultrasonic cleaning machine? Wouldn’t that make the cleaning performance better?”

In theory, using 28 kHz first to remove larger particles and oil contamination, then switching to 40 kHz for finer cleaning, can indeed achieve cleaner results.

However, in practice, most ultrasonic cleaning equipment is designed with a fixed frequency, commonly 28 kHz or 40 kHz.

This is not because manufacturers are cutting corners, but because both the transducer and the generator circuit must operate at a fixed resonant frequency.

To achieve adjustable frequency cleaning, a more advanced and complex multi-frequency ultrasonic system is required. This type of equipment is usually used in high-end industries, and the cost is also higher than standard industrial models.

Difference 1
Limitation of the Transducer: One Transducer Cannot Be Shared Across Different Frequencies

Each ultrasonic transducer has a fixed resonant frequency, also known as its mechanical resonance point.

This frequency is determined by factors such as the thickness of the piezoelectric ceramic, the length of the metal structure, and the electrical impedance.

The design differences between transducers of different frequencies are as follows:

If a 28 kHz transducer is connected to a 40 kHz generator, the following problems may occur:
• Unable to resonate, resulting in extremely weak or almost no ultrasonic output
• Abnormal current and temperature, causing the transducer to overheat and shortening its service life
• Power efficiency may drop by 50% to 80%

Therefore, transducers with different frequencies cannot be shared.
Each frequency must be matched with the corresponding generator and transducer to maintain stable resonance and optimal cleaning performance.

Item: Piezoelectric Ceramic Thickness

• 28 kHz Transducer: Thick, approximately 1.5 mm

• 40 kHz Transducer: Thin, approximately 1.0 mm
  
  Item: Mechanical Length

• 28 kHz Transducer: Longer and heavier

• 40 kHz Transducer: Shorter and lighter
  
  Item: Impedance

• 28 kHz Transducer: Approximately 11–13 Ω

• 40 kHz Transducer: Approximately 15–18 Ω
  
  Item: Resonance Peak

• 28 kHz Transducer: Single resonance peak near 28 kHz

• 40 kHz Transducer: Single resonance peak near 40 kHz

The circuit design inside the ultrasonic generator is built to produce an AC signal at a specific frequency in order to drive the transducer into resonance.

This frequency is preset and cannot be freely “adjusted” like turning an audio knob.

If the generator frequency deviates from the resonant point of the transducer, the following problems may occur:

• The transducer cannot resonate properly
• Ultrasonic output energy becomes lower
• Long-term operation may damage the components

Difference 2

Design of the Ultrasonic Generator: The Frequency Is Fixed

Therefore, ultrasonic cleaning equipment is already designed with a specific frequency when it is manufactured.

For example, 28 kHz is suitable for heavy oil contamination cleaning, while 40 kHz is suitable for general precision parts cleaning.

Some high-end models or custom-designed systems may include a sweep function.
Sweep frequency does not mean freely changing the cleaning frequency. Instead, it creates a small variation of about ±2 kHz within the same frequency range.

The purpose is to:

• Avoid standing waves inside the tank
• Improve the uniformity of cleaning energy distribution
• Reduce local over-cleaning or dead zones

The Generator Can Use Sweep Technology, but It Is Not Frequency Adjustment

For example:

When a 40 kHz generator uses sweep frequency, the actual output range is approximately 39–41 kHz.
The transducer still operates within its own resonance range.
This is completely different from “adjusting from 28 kHz to 40 kHz.”

• The key to ultrasonic cleaning is the resonance matching between the transducer and the generator.
• Transducers of different frequencies cannot be shared or directly switched.
• If multiple cleaning requirements are needed, the system should be designed with multiple tanks and different frequencies, such as using 28 kHz in the first tank for oil removal and 40 kHz in the second tank for precision cleaning.
• Sweep frequency is an auxiliary technology used to improve cleaning uniformity, not a function for freely adjusting frequency.

Conclusion: Choose the Right Frequency

YONG JI Enterprise can configure different frequencies, sweep control, and automated cleaning processes according to customer requirements, ensuring stable output, optimal cleaning efficiency, and long equipment service life.
We also provide customized design and manufacturing services, including frequency, power, tank size, and process configuration, to create the most suitable high-efficiency cleaning system for your application.