Application of power amplifier in the study of elliptical ultrasonic assisted mechanical polishing

Experiment name: Fabrication and vibration characteristics test application of power amplifier based on two-dimensional elliptical ultrasonic vibrator

Experimental purpose: To test and verify whether the actual resonant frequency of the piezoelectric ceramic vibrator is the same as the design.

Experimental content:

By dividing the electrodes on a large piece of piezoelectric ceramic, it actually achieves the effect of arranging four pieces of piezoelectric ceramics in parallel. The material of the electrode is Ag. The power amplifier drives the piezoelectric ceramic to be plated on the surface of the piezoelectric ceramic by a coating method. The piezoelectric ceramic and the 304 stainless steel substrate are bonded by epoxy resin glue to achieve vibration transmission.

Experimental process:

The circuit diagram used for resonance characteristic analysis is shown in the figure. The frequency characteristic analyzer provides a swept frequency output signal and can measure the voltage across the piezoelectric ceramic vibrator and the current passing through the piezoelectric ceramic vibrator. The power amplifier (ATA-4052) amplifies the input signal and adds it to the vibrator circuit. The piezoelectric ceramic vibrator is connected in series with an ohm standard resistor. The sweep frequency range is 20k-30kHz. When only the two electrodes separated are energized, the B4 mode of the vibrator is excited. When the four electrodes are energized at the same time, the L1 mode of the vibrator is excited.

Circuit diagram for analyzing resonance characteristics of elliptical ultrasonic vibrator

Experimental results:

As can be seen from the figure, the resonant frequency of the vibrator B4 mode is 24.10kHz, the anti-resonant frequency is 24.22kHz, the resonant frequency of the L1 mode is 24.01kHz, and the anti-resonant frequency is 24.24kHz. The difference between the resonant frequencies of the two vibration modes is about 0.09kHz, and this degree of error is within the allowable range when using the ultrasonic vibrator. In addition, since the difference in resonant frequency between the two oscillation modes is small, the maximum amplitude can be obtained at the same frequency for both longitudinal and bending vibrations, and the amplitude of the synthesized elliptical vibration will be the largest.

On the other hand, the difference between the anti-resonance points in the two vibration modes is about 0.02kHz, which is very small. Because when the ultrasonic vibrator is excited at the resonance point, although the impedance is small and the amplitude is maximum. However, if a frequency close to the resonance point is used, a relatively large load will be applied to the piezoelectric ceramic, which may cause cracking or rupture of the piezoelectric ceramic material. When excited at the anti-resonance point, the impedance increases and the power consumption is minimized. Therefore, the frequency of the excitation signal is usually located at the anti-resonance point, and the difference of 0.02kHz meets the requirements. Therefore, it can be seen that the vibrator shown in the figure will produce the optimal ultrasonic elliptical trajectory when excited at a frequency of 24.22kHz.

Impedance characteristic curve of L1 mode

Impedance characteristic curve of B4 mode

The difference between the anti-resonance points in the two vibration modes is about 0.02kHz, which is a small difference. Because when the ultrasonic vibrator is excited at the resonance point, although the impedance is small and the amplitude is maximum. However, if a frequency close to the resonance point is used, a relatively large load will be applied to the piezoelectric ceramic, which may cause cracking or rupture of the piezoelectric ceramic material. When excited at the anti-resonance point, the impedance increases and the power consumption is minimized. Therefore, the frequency of the excitation signal is usually located at the anti-resonance point, and the difference of 0.02kHz meets the requirements. Therefore, it can be seen that the vibrator shown in the figure will produce the optimal ultrasonic elliptical trajectory when excited at a frequency of 24.22kHz.

Comparison of impedance characteristics between L1 mode and B4 mode