Application Cases

Experiment Name: Application of High-Voltage Power Amplifier in Impact Damage Detection Technology for Composite Materials

Research Direction: Ultrasonic Nondestructive Testing, Composite Materials

Experimental Principle:
Nonlinear vibration acoustic modulation technology involves inputting two continuous sinusoidal signals of different frequencies into the structure: a low-frequency vibration signal and a high-frequency ultrasonic signal. When the structure is intact, the frequency spectrum of the received signal contains only the two input signal components. When defects exist in the structure, the applied low-frequency vibration causes the contact interfaces of the defects to repeatedly open and close, creating a modulation effect between the low-frequency vibration and the high-frequency ultrasound. Consequently, the received signal create other components such as modulation sidebands and higher-order harmonics. By observing the frequency spectrum components of the received signal, the presence of defects in the structure can be determined. The principle of nonlinear vibration acoustic modulation detection is illustrated in the figure below.

Figure: Principle of Nonlinear Vibration Acoustic Modulation Detection

According to the principle of vibration acoustic modulation, when defects exist in the structure, the low-frequency vibration and high-frequency ultrasonic  signal  interact to produce modulation sidebands. The order and amplitude of the modulation sidebands depend on the modulation intensity and the degree of damage to the structure.

Testing Equipment: ATA-2041 High-Voltage Power Amplifier, PZT Piezoelectric Wafer, Stacked Piezoelectric Ceramics, Vibration Exciter, Signal Generator, Multifunction Tester

Experimental Procedure:
In nonlinear vibration acoustic modulation testing, it is necessary to excite high-frequency ultrasonic signals and low-frequency vibration signals in the specimen. PZT piezoelectric wafers, with a diameter of 15 mm and a thickness of 4 mm, were used as high-frequency ultrasonic excitation and  receiving  transducers. Vibration exciter are commonly used as low-frequency excitation devices in vibration acoustic modulation specimens, but they require fixing the specimen and have limited excitation positions. Using stacked piezoelectric ceramics for low-frequency excitation offers advantages such as flexible position selection and simple installation. Low-frequency vibration was excited by stacked piezoelectric ceramics, all of which were bonded to the specimen using two-component epoxy resin to ensure coupling quality. A signal generator was used to excite a continuous sinusoidal signal, which was then  applied  to the stacked piezoelectric ceramics through the ATA-2041 high-voltage power amplifier to generate low-frequency vibration. The vibration frequency was selected as the modal frequency of each composite laminate, with the amplitude starting at 10 V and increasing in 10 V increments up to 100 V. After establishing a stable vibration field, a multifunction tester was used to emit a continuous high-frequency ultrasonic  signal  with an amplitude of 10 Vpp, and the modulated  signal  was received by the PZT piezoelectric wafer. To compare the influence of different high-frequency ultrasonic frequencies on the test results, a specific ultrasonic frequency was used, and 91 kHz, close to the specific frequency, was arbitrarily selected as the ultrasonic excitation frequency for the three composite laminates, while the low-frequency vibration frequencies for each specimen remained unchanged. To ensure high frequency resolution, the sampling frequency was set to 1 MHz, and the sampling length was 100 kpts. Nonlinear vibration acoustic modulation detection tests were performed on the three specimens respectively, and the data were transmitted to a computer for analysis after acquisition. To minimize the influence of boundaries on the specimen results, nylon ropes were used to hang the specimens during the test to simulate free boundary conditions. To improve test accuracy and reduce the influence of factors, measurements were taken three times for each low-frequency voltage excitation, and the average value of the modulation coefficient was taken as the test result. To facilitate comparison of the influence of ultrasonic frequency on the modulation coefficient, the vertical axis ranges of the modulation coefficients for each mode of the three specimens were set to the same range. A schematic diagram of the test platform is shown in the figure below.

Figure: Nonlinear Vibration Acoustic Modulation Test Platform

Experimental Results:

1. Nonlinear vibration acoustic modulation technology generates modulation sidebands through the interaction of high-frequency ultrasound and low-frequency vibration within the structure. The magnitude of the modulation effect is judged by the modulation index MI to determine whether defects exist in the specimen. By appropriately selecting the excitation frequency and amplitude, this technology can effectively distinguish whether impact damage defects exist in composite materials, and the results are consistent with the trends of ultrasonic C-scan results.

2. The modulation coefficient of the specimen exhibits an approximately linear increasing trend with voltage. The modulation effects produced under different vibration modes vary. Reasonable selection of ultrasonic frequency and vibration mode is beneficial for distinguishing defects. In this paper, selecting a specific ultrasonic frequency, the fifth vibration mode, and a relatively small low-frequency excitation amplitude (greater than 20 Vpp) allowed for easier identification of defective specimens.

   
   

Figure: Judgment Coefficients for Various Specimens

Figure: Specifications of the ATA-2041 High-Voltage Amplifier