Application Cases

Experiment Name: Application of Power Amplifiers in Damage Identification Research of Pressure-Resistant Structures Using Lamb Waves

Research Direction: Pressure-Resistant Structures and Lamb Waves

Experimental Equipment: ATA-2022B Power Amplifier, Arbitrary Function Generator, Data Acquisition Card, Oscilloscope

Experimental Content:
Based on the structural characteristics of pressure-resistant structures, a damage identification system was designed. Without considering environmental noise, piezoelectric sensors were used to excite Lamb waves in real time and monitor the structural response. Through data collection and processing, damage parameters were determined. When damage occurs, the structure exhibits discontinuities, causing scattering and refraction of waves during propagation, leading to waveform changes. By analyzing these changes, the damage information contained within can be identified.

Figure: Instruments Used in the Lamb Wave Experiment on Pressure-Resistant Structures

Experimental Procedure:
First, a five-cycle Lamb wave with a center frequency of 200 kHz was edited using software and imported into an arbitrary waveform generator for dual-channel output. The maximum output voltage of the arbitrary function generator was 10 V. Channel one was connected to an oscilloscope for comparison and positioning of the received waveform. Channel two was amplified tenfold by an Aigtek ATA-2022H high-voltage amplifier and then connected to an excitation piezoelectric ceramic sheet. The piezoelectric ceramic sheet was attached to a polished aluminum plate using quick-drying adhesive, with positive and negative leads soldered for connection.

During attachment, care was taken to apply the adhesive evenly and press the sheet for 30 seconds, allowing several hours for the bond to achieve optimal effect. The piezoelectric ceramic sheet had a diameter of 10 mm, a thickness of 1 mm, and a maximum driving voltage of 200 V/mm. Channel one of the oscilloscope was used to display the excitation signal generated by the arbitrary function generator, while channels two, three, and four were connected to receiving sensors on the test structure to capture the received signals.

Figure: Lamb Waves at 50–300 kHz

The dispersion curve indicated the modal characteristics of the aluminum plate at different frequencies. From the dispersion curve, it was observed that lower frequencies resulted in fewer modes within the plate. To select the optimal center frequency, the experiment set the center frequency range from 50 kHz to 300 kHz in 50 kHz intervals. The center frequency of the Lamb wave was adjusted by modifying the settings on the arbitrary function generator.

Figure: Hilbert Transform

Through experimentation, the optimal excitation center frequency was determined to be 200 kHz. After applying a 250 kHz low-pass filter and noise reduction to the obtained signals, the Hilbert transform was used for envelope processing of the displacement curves to extract effective information. The application of Lamb waves in identifying damage in plate structures was investigated. Numerical simulations were conducted on aluminum plates with defects, and damage localization was studied based on the elliptical positioning method. Echo signals were acquired, and the arrival time of echo peaks caused by damage was read to determine the damage location.

Experimental Results:
The influence of the excitation center frequency on the received signals was studied experimentally, and Lamb wave response signals at center frequencies ranging from 50 kHz to 300 kHz were plotted. The optimal excitation center frequency for the experiment was determined. To effectively extract the signals collected during the experiment, 250 kHz low-pass, 150–250 kHz band-pass, and 150 kHz high-pass filters were applied for noise reduction. To eliminate the influence of individual differences among piezoelectric ceramic sheets and environmental factors, the experimental results were normalized.

The damage localization method based on the elliptical trajectory approach was validated. Echo signals were acquired, and the arrival time of echo peaks caused by damage was read to determine the damage location.

Specifications of the ATA-2022B High-Voltage Amplifier Used in the Experiment: