Application Cases

Experiment Name: Air-Coupled Ultrasonic Testing System

Research Direction: Ultrasonics

Testing Equipment: ATA-8202 radio frequency power amplifier, probes, ATA-5620 preamplifier, ultrasonic receiver, data acquisition card, computer.

Experimental Procedure:

Figure: Air-Coupled Ultrasonic Testing System for Lithium Batteries

The specific process of air-coupled ultrasonic testing for lithium batteries is as follows:
First, the required excitation signal is output via the ATA-8202 radio frequency power amplifier to drive the highly sensitive 0.4K20N-TXR40 air-coupled transmitting probe, converting the electrical signal into an ultrasonic signal and transmitting it into the air. The ultrasonic signal propagates through the lithium battery and into the air, where it is received by the 0.4K20N-RXR40 air-coupled receiving probe. The receiving probe converts the acoustic signal back into an electrical signal, which is then input into the ATA-5620 preamplifier. After filtering and amplification by the preamplifier, the signal is received by the JPR-10CN ultrasonic receiver. The receiver converts the electrical signal into a digital signal and transmits it to the NI5114 data acquisition card, which then inputs it into the computer. The computer controls the motor motion controller and scanning stage to execute scanning tasks with specific parameters. Finally, relevant waveform signals and scanning images are displayed to achieve detection of the lithium battery.
The hardware setup of the experimental system includes:

1. High-power signal generator

2. Preamplifier

3. Specialized air-coupled probe

4. Motion control stage

5. Motor controller

The experiment utilizes the designed air-coupled ultrasonic testing system, conducted at room temperature (25°C). Air-coupled ultrasonic non-destructive testing of lithium batteries is performed using the through-transmission method. The transmitting and receiving probes are vertically positioned on opposite sides of the lithium battery, with their central axes aligned. The probes are adjusted to maximize the amplitude of the received ultrasonic signal, and their relative positions are fixed. The specific setup is illustrated below.

Figure: Air-Coupled Ultrasonic Through-Transmission Testing of Lithium Battery

After setting the positions of the air-coupled probes and the lithium battery, specific experimental parameters are configured in the testing software. These parameters include sampling frequency, sampling length, gain, and various motion parameters, adjusted according to different battery specifications. For the custom defect battery shown in Figure 3-4, the experiment involves programming the motion controller to perform air-coupled ultrasonic through-transmission C-scans over an area of 268 mm × 368 mm, with step increments of 0.3 mm in the X and Y directions. Air-coupled ultrasonic signals are sampled at a frequency of 10 MHz, with the gain set to 33 dB. Each acquisition collects 3,584 data points, and multiple sets of data are collected for scanning and imaging.

During the propagation of ultrasonic waves emitted by the air-coupled ultrasonic probe inside the lithium battery, when encountering areas without air layers, the waves transmit through the battery and are received by the air-coupled receiving probe. However, when encountering air bubbles (air layers), the acoustic transmittance decreases, leading to a reduction in the ultrasonic signal received by the air-coupled receiving probe. Therefore, by analyzing the amplitude variations in the ultrasonic A-scan signals, the presence of air bubbles (air layer defects) in the lithium battery can be determined. The ultrasonic waveforms of lithium batteries with and without air bubble defects obtained from the experiment are shown below.

Figure: Ultrasonic Waveforms of Lithium Batteries With and Without Air Bubble Defects

Experimental Results:

Based on the average maximum amplitudes of the different waveforms obtained, a graph illustrating the relationship between the maximum amplitude of the air-coupled ultrasonic transmission wave signal and the diameter of the air bubble defect is plotted, as shown below.

Figure: Relationship Between Maximum Amplitude of Ultrasonic Transmission Wave Signal and Diameter of Air Bubble Defect

Using air-coupled ultrasonic technology to detect air bubble defects in lithium batteries, when the depth of the air bubble defect in the lithium battery is constant and the ultrasonic waves propagate vertically through it, the maximum amplitude of the transmitted wave signal generally exhibits a decaying trend as the diameter of the air bubble defect increases. This decay is not linear; rather, it decays gently at first, then more sharply, and finally returns to a gentle decay after reaching a certain value. Specifically, the data shows that when the defect diameter is 1 mm or 2 mm, the decay rate is relatively gentle. Subsequently, the decay rate becomes faster. When the defect diameter reaches 8 mm, the amplitude of the transmitted ultrasonic waves in the lithium battery returns to a slow decay state.

Aigtek ATA-8000 Series Radio Frequency Power Amplifier:

Figure: ATA-8000 Series Radio Frequency Power Amplifier Specifications and Parameters