Application Cases

Experiment Name: U-Shaped Steel Bar Corrosion Monitoring Experiment Using Ultrasonic Guided Wave Technology

Research Direction: To address the challenge of monitoring corrosion in U-shaped steel bars within concrete structures, leveraging the long-distance monitoring advantages of ultrasonic guided wave technology, a surface-bonded monitoring structure and waterproof packaging technique were designed. The response patterns of corrosion degree in U-shaped steel bars to parameters such as ultrasonic guided wave velocity, signal amplitude, and time delay were investigated. A precise judgment system for U-shaped steel bar corrosion driven by ultrasonic guided wave technology was established, providing technical support for long-term health monitoring.

Experiment Objective: To overcome the difficulties of rapid, comprehensive, and accurate monitoring of steel bar corrosion inside concrete structures using traditional methods, and to mitigate the susceptibility of ultrasonic guided wave monitoring to environmental interference in structural testing, this experiment utilizes ultrasonic guided wave technology. By designing a surface-bonded ultrasonic monitoring structure and waterproof packaging for U-shaped steel bars, accurate assessment of the corrosion degree of U-shaped steel bars is achieved.

Testing Equipment: Signal generator, high-voltage amplifier, transducer, DC power supply, excitation-end PZT-4 transducer, receiving-end PZT-5 transducer, digital oscilloscope.

Experimental Procedure: In the U-shaped steel bar corrosion monitoring experiment using ultrasonic guided wave technology, the power amplifier serves as the critical device connecting the signal generator and the excitation-end PZT-4 transducer. Its core function is to amplify the low-power electrical signal (50 kHz–500 kHz) output by the signal generator by a factor of 50–100 times to over 100 V, enhancing the driving capability. This ensures that the transducer efficiently excites stable ultrasonic guided waves through the inverse piezoelectric effect, preventing guided wave attenuation or excitation failure due to insufficient signal power, and guaranteeing accurate signal capture by the receiving-end PZT-5 transducer.

During the experiment, the power-amplified guided waves propagate along the U-shaped steel bar. The digital oscilloscope collects the raw time-domain waveform containing noise. After FFT band-pass filtering (retaining signals within ±20 kHz of the excitation frequency) using ORIGIN software, the signal-to-noise ratio increases from 9.54 dB to 23.52 dB. For a bare U-shaped steel bar with a diameter of 12 mm and a length of 35 cm, electrochemical accelerated corrosion was applied (the bar was fixed in a foam ring and immersed in a 5% NaCl solution, with the bar connected to the positive terminal of the power supply and the solution to the negative terminal). Filtered signals at different corrosion stages were simultaneously acquired, and parameters were extracted to establish the corrosion response relationship. The power amplifier, through energy enhancement, signal stabilization, and mode matching, ensures the reliability of the monitoring system.

Figure 2: Relationship Curve Between Received Signal Amplitude of Bare Steel Bar and Theoretical Corrosion Rate

Figure 3: Appearance Record Diagram During the Corrosion Test Process

Experimental Results:
From the time-domain diagram before corrosion, three signal wave packets can be clearly observed. The time difference between the arrival of the first wave packet and the transmitted signal is 84.27 μs. The calculated propagation velocity of the first wave packet is 4153 m/s, consistent with the theoretical velocity of the L(0,1) mode [4101 m/s] in the dispersion curve for a 12 mm diameter steel bar, confirming that the experiment successfully excited the L(0,1) mode. The travel time of the second wave packet from transmission to reception aligns with the theoretical velocity of the F(1,1) mode. The travel time of the third wave packet is approximately three times that of the first, corresponding to the reflection of the first wave packet at the end of the steel bar.

From the time-domain diagram after corrosion, two wave packets are observed. The travel time of the first wave packet is 64.81 μs, corresponding to a calculated guided wave propagation velocity of 5400 m/s, slightly higher than the theoretical propagation velocity for steel bars within a 6 mm diameter range. The waveform of the second wave packet has changed, forming a superposition of the F(1,1) mode wave packet and the reflected wave of the first wave packet from the bar end. After the corrosion test, the minimum diameter of the steel bar was reduced from 12 mm to 5 mm, with the maximum diameter in the middle section being 9 mm. The theoretical guided wave propagation velocity at 180 kHz ranges from 3809 to 5026 m/s. The calculated propagation velocity after corrosion generally conforms to the dispersion curve.

Figure 4: Time-Domain Signal Diagram of U-Shaped Steel Bar Before Corrosion

Figure 5: Time-Domain Signal Diagram of U-Shaped Steel Bar After Corrosion

Product Recommendation: ATA-2000 Series High-Voltage Amplifier

Figure: ATA-2000 Series High-Voltage Amplifier Specifications and Parameters

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