How to know the quality of ultrasonic transducer? What parameters affect it?

Ultrasonic transducer

1. Parameters

1) Mechanical resonance frequency (Fs)

This refers to the operating frequency of the vibration system, which should be as close to the expected value as possible in the design and must match the power supply operating point.

2) Dynamic resistance (R1)

The resistance of the series branch of the piezoelectric vibrator is as small as possible under the same support conditions! For cleaning or welding vibrator, it is generally between 5 Ω and 20 Ω. If it is too large, the vibrator or vibration system will have problems in operation, such as circuit mismatch, low conversion efficiency, short life of the vibrator, etc.

3) Mechanical quality factor (Qm)

It is determined by conductance curve method that Qm=Fs/(F2-F1), the higher Qm is, the better, because the higher Qm is, the higher the efficiency of the vibrator is. However, Qm must match the power supply. If the Qm value is too high, the power supply cannot match. For cleaning the vibrator, the higher the Qm value, the better. Generally speaking, the Qm for cleaning the vibrator should be 500-1000. If it is too low, the efficiency of the vibrator is low. If it is too high, the power supply cannot match. For ultrasonic welding or processing, the Qm value of the vibrator itself is generally 50-1000, and the overall system is 1500-3000. If it is too low, the vibration efficiency is low, but it cannot be too high, because the higher the Qm, the narrower the working bandwidth, and the power supply is difficult to match, that is, the power supply is difficult to work at the resonant frequency point, and the ultrasonic welding equipment cannot work normally.

4) Free capacitance (CT)

The capacitance value of the piezoelectric device at the frequency of 1kHz is consistent with the value measured by the digital capacitance meter. Subtract the dynamic capacitance C1 from this value to get the real static capacitance C0, C0=CT-C1. C0 should be balanced with inductance when using. In the circuit design of ultrasonic machining machine, properly balancing C0 can improve the power factor of the power supply. There are two ways to use inductance balance, parallel tuning and series tuning.

5) Anti resonant frequency (Fp)

The resonant frequency of the parallel branch of the piezoelectric vibrator. At this frequency, the impedance Zmax of the piezoelectric vibrator is large. If the anti resonant impedance Zmax is very low, the vibrator is faulty.

Ultrasonic transducer

2. Graphics

Generally speaking, the vibration performance or ultrasound piezoelectric transducer of the ultrasonic vibration system can be judged directly through the logarithmic coordinate diagram, which is simple and intuitive.

1) Normally, the admittance circle is a single circle, and the logarithmic coordinate graph has only a pair of minimum and maximum values.

2) Under abnormal conditions, there are many parasitic small circles on the admittance circle graph, and there are many pairs of minima and maxima on the logarithmic coordinate graph.

Under what circumstances will the admittance circle and conductance curve of piezoelectric ceramics or ultrasonic transducers be abnormal? There are mainly the following situations:

1) Piezoelectric ceramics have their own problems, such as internal delamination.

2) The transducer was cracked during assembly.

3) Problems occurred in the design or assembly of ultrasonic horn and ultrasonic mold.

4）The parts around the stress bar collide due to the poor concentricity of the transducer.