Application Cases

Experiment Name: Comparative Analysis of Imaging Quality of Dense Rectangular Arrays Using Laser and Piezoelectric Sensors

Research Direction: Lamb waves, nondestructive testing, defect imaging and localization

Test Objective:
To combine dense rectangular arrays with piezoelectric sensor detection technology and laser detection technology, respectively, and to use amplitude imaging and sign coherence factor imaging methods to accurately locate simulated defects in aluminum plate structures. Additionally, to compare and analyze the imaging quality of piezoelectric sensor detection technology and laser ultrasonic detection technology.

Testing Equipment: ATA-2041 high-voltage amplifier, function generator, digital oscilloscope, piezoelectric sensor array

Figure: Experimental system of the dense rectangular piezoelectric sensor array

Experimental Procedure:

Figure 2: Imaging using the dense rectangular piezoelectric sensor array

A dense rectangular piezoelectric sensor array experimental system was built. Based on the acquisition method, 240 sets of data could be collected. To reduce interference from other frequencies, continuous wavelet transform was applied to the collected array signals to extract signals at a frequency of 40 kHz. To eliminate the influence of external environmental factors (e.g., surface inconsistencies of the aluminum plate), the signals after continuous wavelet transform were normalized. The preprocessed data were then imaged using amplitude imaging and sign coherence factor imaging methods. The results are shown in Figure 2, where the white circles indicate the defect locations and the white dots represent the array element points.

From the defect localization imaging results obtained with the piezoelectric sensor array, it can be seen that combining the dense rectangular piezoelectric sensor array with amplitude imaging and sign coherence factor imaging algorithms enables the localization of simulated defects in the aluminum plate. Compared with amplitude imaging results, the sign coherence factor imaging method improves resolution and signal-to-noise ratio while suppressing side lobes and grating lobes, resulting in imaging results with almost no artifacts.

Figure 3: Imaging using the dense rectangular laser ultrasonic sensor array

A laser ultrasonic sensor array experimental setup was built, consisting of a laser ultrasonic detection system and the aluminum plate under inspection. With the same amount of data collected as the piezoelectric sensor array, continuous wavelet transform was applied to the acquired array signals to extract signals at a frequency of 40 kHz, followed by normalization. The preprocessed data were then imaged using amplitude imaging and sign coherence factor imaging methods. The results are shown in Figure 3, where the white circles indicate the defect locations and the white dots represent the array element points.

From the defect localization imaging results obtained with the laser ultrasonic sensor array, it can be seen that laser ultrasonic sensor array technology can effectively achieve accurate localization of simulated defects in the aluminum plate. Laser ultrasonic sensor array technology offers advantages such as non-contact operation and point focusing. Therefore, compared with the imaging results of the piezoelectric sensor array, the imaging results of the laser ultrasonic sensor array show a significant reduction in artifacts, and the contrast of both imaging methods is greatly improved, thereby enhancing imaging quality.

Experimental Results:
Comparing the two imaging results in Figures 2 and 3, under the same threshold setting, amplitude imaging exhibits relatively higher contrast but lower accuracy. The sign coherence factor imaging method makes the imaging results more precise, not only accurately identifying the defect location but also greatly reducing the generation of artifacts.

1. A sign coherence factor imaging method based on the phase difference of array data was proposed. This method improves resolution and signal-to-noise ratio while suppressing side lobes and grating lobes.

2. By combining the piezoelectric sensor array and the laser ultrasonic sensor array with amplitude imaging and sign coherence factor imaging, effective localization of defects in the aluminum plate was achieved.

3. Comparing the imaging results of the piezoelectric sensor array with those of the laser ultrasonic array, it was found that due to factors such as uneven coupling and large contact area, the piezoelectric sensor array imaging results exhibited numerous artifacts. In contrast, the laser ultrasonic array, with its advantages of non-contact operation and point focusing, produced imaging results with only a few artifacts, enabling more accurate defect localization.

   

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