Application Cases

Experiment Name: Development and Application of Line-Focused Air-Coupled Ultrasonic Sensors Based on Gas-Based Piezoelectric Composites

Research Direction: Ultrasonic Sensors, Ultrasonic Testing

Test Objective: To conduct excitation and reception performance tests on the sensor, and to perform non-contact detection of monocrystalline silicon solar cells with crack defects using air-coupled ultrasonic Lamb wave testing technology. By analyzing the amplitude information of the received signals and utilizing the correlation coefficient method, the detection and localization of crack defects were achieved, demonstrating the application of the gas-based line-focused air-coupled sensor in defect detection.

Testing Equipment: ATA-2041 High-Voltage Amplifier, Function Generator, Digital Oscilloscope

Figure: Schematic Diagram of the Air-Coupled Ultrasonic Testing Experimental System

Experimental Procedure:
First, a gas-based line-focused air-coupled sensor was developed, followed by the fabrication of gas-based line-focused piezoelectric composite materials. The excitation performance of the fabricated gas-based line-focused air-coupled sensor was then tested.

In the experiment, a monocrystalline silicon solar cell with a centrally processed crack defect was selected as the detection target. The crack direction was parallel to the main electrode, with a crack length of 20 mm, a width of 0.1 mm, and a depth equal to the full thickness of the cell. To excite a specific AO mode Lamb wave in the cell, according to the theory of Lamb wave propagation in monocrystalline silicon, it is necessary to ensure that the excitation sensor and the receiving sensor are tilted at the same angle on opposite sides when using air-coupled excitation. Based on the structural composition of the monocrystalline silicon solar cell, the effective thickness of the monocrystalline silicon material within the cell is approximately 130–140 μm.

Figure 2: Defective Monocrystalline Silicon Solar Cell Specimen

Air-coupled detection was performed on the defective cell using the air-coupled ultrasonic testing system shown in the figure. The sensors were positioned on either side of the defect, with the excitation sensor being the gas-based line-focused air-coupled sensor and the receiving sensor being the gas-based planar air-coupled sensor. The distance between the two sensors was 70 mm. The rotating platform was adjusted so that the Lamb wave propagation path was perpendicular to the length direction of the defect. The  lateral  scanning range of the sensors was set to 40 mm, with the initial position of the experiment being 10 mm from the near end of the crack along the line connecting the two sensors. The excitation and receiving sensors were moved parallel in 1 mm steps, and the received signals at each position were collected, as shown in Figure 2, where T represents the excitation sensor and R represents the receiving sensor. The excitation signal in the experiment was a 5-cycle sinusoidal signal with a center frequency of 150 kHz and a peak-to-peak voltage of 3 V.

Figure 3: Received Signals from Defect Detection Experiment

The received signals when Lamb waves passed through the defect-free area and the defect center area were extracted separately, and the direct wave  amplitudes in the defect-free area and those transmitted through the defect were compared. The results are shown in Figure 3. It can be observed that when the sensors were positioned in the defect-free area and the defect center area of the cell, the  direct wave  amplitudes received by the receiving sensor changed significantly. This is due to the presence of the crack defect, which causes significant reflection of the acoustic waves at the interface between the cell and air when the Lamb waves propagate to the crack boundary.

Experimental Results:

1. Through simulation analysis and structural modeling, the fabrication of gas-based line-focused piezoelectric composite materials was achieved using processes such as piezoelectric pillar cutting, 3D printing, precision grinding, and sputter coating. The fabricated sensor exhibited low acoustic impedance characteristics, making it more suitable for air-coupled testing environments.

2. Using air-coupled Lamb wave testing technology, the gas-based line-focused air-coupled sensor was successfully applied to the non-contact detection of crack defects in monocrystalline silicon solar cells, achieving localization of the crack defects within the cells.

   
   

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