Application Cases

Experiment Name: Application of Power Amplifier in Nonlinear Vibration Acoustic Modulation Detection Test for Material Damage

Research Direction: Material Flaw Detection, Nonlinear Vibration Acoustic Modulation

Testing Equipment: Signal Generator, ATA-2041 High-Voltage Amplifier, Multifunction Tester, PZT Piezoelectric Patches, etc.

Experimental Content:
Vibration acoustic modulation technology is a nonlinear ultrasonic nondestructive testing technique with high sensitivity to  micro  defects. It works by simultaneously inputting a large-amplitude low-frequency signal (typically from an impact hammer, vibration exciter, stacked piezoelectric ceramics, etc.) and a high-frequency ultrasonic signal (typically from piezoelectric wafers) into the inspected structure. A piezoelectric wafer or laser vibrometer is used to acquire the signals. If defects exist in the specimen, the low-frequency vibration alters the contact conditions at the defect sites and modulates the high-frequency ultrasonic signal. By analyzing the ratio of modulation sidebands to the fundamental frequency, the presence of defects in the structure can be determined.

This method is not limited by the shape of the structure under test and offers advantages such as low equipment requirements, fast detection speed, and higher sensitivity compared to conventional ultrasonic testing. It provides a new approach for  remote  detection of complex and large-scale structures. Based on these characteristics, applying nonlinear vibration acoustic modulation technology to detect low-velocity impact damage in composite materials holds significant research value. Nonlinear vibration acoustic modulation technology requires low-frequency excitation at the modal frequency of the specimen to generate a strong modulation effect, so frequency selection significantly impacts the detection results.

Experimental Results:
This paper uses nonlinear vibration acoustic modulation technology to detect composite laminates with impact damage and conducts  corresponding  research on the  reasonable  selection of excitation signals. The main conclusions are as follows:

(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 assessed using the modulation index MI to determine the presence of defects 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 observed in ultrasonic C-scanning.

Figure: Modulation Coefficient of the Specimen When Selecting an Arbitrary Waveform

(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 allowed for easier identification of defective specimens.

Figure: Judgment Coefficients for Various Specimens

(3) Nonlinearities introduced by the material itself and the experimental system can affect the test results. How to minimize these effects and how to detect and quantitatively analyze the extent of damage between laminates warrants further investigation and research.

Role of the Power Amplifier in This Experiment: Successfully drove the piezoelectric ceramics and perfectly amplified the voltage signal.

Figure: ATA-2041 High-Voltage Amplifier Specifications and Parameters