Ultrasonic flaw detection principle and sensor test and design

Ultrasonic transducers, horns and sound jackets are devices that convert electrical energy into vibration. To understand the principle of operation, you can compare between an ultrasonic welding machine and a car.

The sensor performs energy conversion (as), the transformer adjusts the ratio between force and speed (such as a gearbox), and the ultrasonic/ultrasonic horn guides and applies this energy to complete the required work (as a wheel).

In automobiles, all mechanical system components must be designed well and harmonically, in order to improve the energy transmission efficiency as much as possible. The same is true for ultrasonic systems, but in this case, the key parameter of efficiency is the frequency of the component that should be as close as possible (for example, 20 kHz +/- 50 Hz).

Ultrasonic probe ultrasonic flaw detection principle and sensor test and design

An analogy between acoustic ultrasonic welding and the mechanical system of a car.

operating

The sensor has two operating frequencies, which can be easily identified in its electrical impedance curve. The impedance value corresponds to the anti-resonance frequency (speed). The ultrasonic welding system works at an anti-resonant frequency. The impedance value corresponds to the resonance frequency (force). The ultrasonic cleaning system works at resonance frequency.

Ultrasonic probe ultrasonic flaw detection principle and sensor test and design

The impedance curve of the sensor vs. frequency.

Increase ultrasonic/horn frequency:

Ultrasonic probe ultrasonic flaw detection principle and sensor test and design

Reduce the length of the ultrasonic electrode/horn to increase the frequency.

Ultrasonic welding machine/mold (factory):

Reduce ultrasonic/horn frequency:

Ultrasonic probe ultrasonic flaw detection principle and sensor test and design

Steps to reduce the ultrasonic/horn frequency.

Sensor test

To work properly, the frequency and impedance of the sensor must be within tolerance. For example, for a welding system, the frequency should be 2.5% higher than the nominal acoustic setting frequency with a tolerance of +/- 0.25%.

The decisive factors for frequency and impedance are the dimensional accuracy of the part, the tightness of the application, the quality of the ceramic and the tuning (similar to the case of ultrasonic propagation).

Ultrasonic probe ultrasonic flaw detection principle and sensor test and design

Use the TRZ analyzer to determine the frequency and impedance of the transducer.

Acoustic test

The frequency and impedance of the acoustic group must be within an acceptable range. In the welding system, the frequency tolerance is ±0.25%, such as 20khz ±50Hz.

Performance depends on frequency tuning and consistency between components. When combining sensors and converters (one low frequency and the other high frequency), this can happen even when working at the correct frequency. Detect this type of problem by measuring impedance.

Ultrasonic probe ultrasonic flaw detection principle and sensor test and design

Acoustic vibration amplitude of ultrasonic welding.

Piezoelectric ceramic test

Piezoelectric ceramics are the sensor core and key components. For power applications, PZT-8 and PZT-4 types are usually used.

Before reassembly, the ceramic microcracks must be proved. Using TRZ software, cracks can be easily detected by the appearance of abnormal peaks in the electrical impedance curve.

Ultrasonic probe ultrasonic flaw detection principle and sensor test and design

Testing piezoelectric ceramics with TRZ software

Predictive maintenance

Through predictive maintenance, problems in ultrasonic systems can be easily avoided. Generally speaking, frequency deviation indicates wear, and in impedance, it indicates coupling problems. These problems are solved by re-tightening and polishing the interface

Ultrasonic probe ultrasonic flaw detection principle and sensor test and design

Predictive maintenance of systems that use TRZ for cutting and welding