Application Cases

Experiment Name: Application of Voltage Amplifiers in Detecting Concrete Using Non-Collinear Mixing Method

Research Direction: Nondestructive Testing

Test Objective:
Nondestructive testing (NDT) is a method for detecting internal damage in objects without damaging or interfering with the structural material of the test object. Traditional NDT methods have many shortcomings and limitations in terms of instrument portability, operational procedures, detection accuracy, and damage localization. Based on these circumstances, the nonlinear ultrasonic mixing detection method has been proposed. When two incident fundamental frequency ultrasonic waves meet specific conditions and interact within a medium containing nonlinear sources, a resonant effect occurs, generating a third ultrasonic wave—the mixed frequency wave. This wave contains relevant parameter information about the damage within the propagation medium. The discovery of this phenomenon has significantly advanced research in nonlinear ultrasonic non-collinear mixing methods.

Based on whether the directions of the two incident fundamental frequency ultrasonic waves are collinear and parallel, nonlinear ultrasonic mixing detection methods can be divided into two categories: non-collinear mixing detection and collinear mixing detection. Among these, non-collinear mixing detection technology offers distinct advantages such as selectable frequencies, spatial selectivity, and controllable directionality. In addition to high sensitivity to micro-damage, it can effectively eliminate the influence of nonlinear sources by separately exciting the two incident acoustic waves and employing phase reversal methods, thus holding significant research potential.

Testing Equipment: ATA-2042 high-voltage amplifier, signal generator, oscilloscope, transmitting transducers, plexiglass wedge assemblies, etc.

Figure: Physical Diagram of the Non-Collinear Mixing Test Setup

Experimental Procedure:
In the non-collinear mixing test on intact concrete, a concrete specimen was first prepared. A non-collinear mixing test setup for intact concrete was then constructed using a signal generator, a high-voltage amplifier (ATA-2042), and an oscilloscope. Subsequently, after calculating a set of plexiglass wedge angles of 52 degrees and 71 degrees, the plexiglass wedge assemblies were custom-ordered from a relevant manufacturer. The wedge assemblies were bonded to the concrete specimen and the ultrasonic transducers using ultrasonic coupling agent (Vaseline) between each pair of interfaces.

Figure: Schematic Diagram of the Non-Collinear Mixing Test Setup

The fundamental frequency ratio d was set to 0.83. The PXR04 transducer was set to near-optimal excitation parameters at 40 kHz, and the PXR07 transducer was set to excitation parameters at 48 kHz. The excitation amplitude for both was 150 V, and the oscilloscope sampling rate was set to 5 MSa/s. Due to limitations of the test instruments, the excitation waveform from the signal generator used dual-channel sine waves.

Under normal operating detection conditions, the frequency and amplitude of the fundamental waves were varied during the test process to study the variation patterns of various parameters, including the nonlinear coefficient. Both the non-collinear mixing method and the higher harmonic method were employed for detection. The higher harmonic method was primarily used for comparison with the non-collinear mixing method to demonstrate the superior detection effectiveness of the latter.

Experimental Results:

1. Influence of Fundamental Frequency Variation

Figure 3: Trends of Parameters with Fundamental Frequency Variation

Figure 4: Trend of A3 with Fundamental Frequency Variation

From Figures 3 and 4, it can be seen that while maintaining the frequency ratio d constant, as the frequency w₂ continuously increases, the amplitudes A₁, A₂, and A₃ generally show an increasing trend. Some individual points deviate from the overall trend, possibly due to poor coupling between the instrument and the specimen during the test. Additionally, concrete is a multi-component composite material with significant randomness and variability. Analysis indicates that changes in the fundamental frequency lead to changes in the mixing nonlinear coefficient; the two are correlated.

2. Influence of Fundamental Amplitude Variation

Figure 5: Relationship between A₃ and A₁

Figure 6: Relationship between A₃ and A₂

Similarly, the trends of A₃ with A₁ and A₃ with A₂ can be approximated, as shown in Figures 5 and 6. Both A₃ vs. A₁ and A₃ vs. A₂ show generally increasing trends. The sum frequency of the mixed wave is the sum of the two fundamental frequencies, meaning the energy of the mixed sum frequency wave is close to the sum of the energies of the two fundamental waves. This is basically consistent with the gradually increasing trend observed in the figures.

3. Comparison with Higher Harmonic Method Test Results

Figure 7: Comparison of Test Results with Higher Harmonic Method

As can be seen from the figure above, whether in terms of sensitivity coefficient, standard deviation, or coefficient of variation, the non-collinear mixing method shows a clear advantage over the higher harmonic method. Its nonlinear coefficient exhibits a greater magnitude of change and higher sensitivity in response to changes in the frequency and amplitude of the fundamental waves.

Under the same test conditions, comparative tests were conducted using the higher harmonic method. By evaluating characteristic parameters such as sensitivity coefficient, standard deviation, and coefficient of variation, it was found that compared to the higher harmonic method, the nonlinear coefficient of the non-collinear mixing method is more sensitive to changes in the frequency and amplitude of the fundamental waves.

Aigtek ATA-2042 High-Voltage Amplifier:

Figure: ATA-2042 High-Voltage Amplifier Specifications and Parameters