Application Cases

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

Experimental Content:
The piezoelectric composite material used in the specific fabrication process of the gas-based line-focused piezoelectric composite is obtained by embedding piezoelectric ceramic pillars coated with epoxy adhesive into a resin-based framework and curing at room temperature. A precision grinding process is employed to remove excess portions of the piezoelectric pillars, achieving mirror-like surfaces on both the upper and lower sides. A sputtering coating process is then applied to attach metal electrodes to both surfaces, resulting in the final gas-based line-focused piezoelectric composite material. The fabricated gas-based line-focused piezoelectric composite is cleaned, wired, and finally assembled into a gas-based line-focused air-coupled sensor. Its minimum resonant frequency $f_m$ is 150 kHz, and its maximum resonant frequency $f_n$ is 173 kHz, which aligns closely with simulation results. The sensor's center frequency is approximately 150 kHz. Based on this, the focused acoustic field parameters $d_L$ and $d_F$ at the sensor's center frequency are calculated as 1.88 mm and 10.45 mm, respectively, closely matching the simulation results. Additionally, the acoustic impedance of the gas-based line-focused piezoelectric composite material is measured.

Testing System:
A Lamb wave detection technology based on air-coupled ultrasonic sensors is employed to conduct non-contact detection of single-crystal silicon solar cells with crack defects. The basic structure of the solar cell is shown in Figure 11, with dimensions of 125 mm × 125 mm × 220 μm. The upper surface of the cell is coated with an anti-reflection film, on which the negative electrode is located. Two thicker parallel electrodes serve as the main electrodes, while several finer parallel electrodes perpendicular to them function as grid electrodes. The grid electrodes are all connected to the main electrodes, forming the negative electrode. The upper part of the single-crystal silicon in the cell is the N-type region, and the lower part is the P-type region. An aluminum film is coated below the P-type region as the positive electrode.

An air-coupled ultrasonic detection system is selected as the experimental setup. The system includes a motion platform to control the movement and scanning of the sensor, a function generator (AFG3021B) to generate excitation signals, an ATA-2021B high-voltage amplifier to amplify the excitation signals, and a DPO4054 digital oscilloscope to display the excitation signals and capture the received signals. The data is then sent to a computer for processing and analysis.

Conclusion:

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 sputtering coating. The resulting sensor exhibits low acoustic impedance characteristics, making it more suitable for air-coupled detection environments.

2. Utilizing air-coupled Lamb wave detection technology, the gas-based line-focused air-coupled sensor was successfully applied to non-contact detection of crack defects in single-crystal silicon solar cells, enabling the localization of crack defects within the cells.

Figure:Defect Detection Measured Signals

Figure:Correlation Coefficient Between Received and Reference Signals

Figure: ATA-2021B High-Voltage Amplifier Specifications and Parameters