Ultrasonic Systems for Determining Quality and Service Life of Batteries, Solar Cells and Supercapacitors
Ultrasonic pulse shadow equipment allows detection of interior defects including flaws, voids, or separations (de-laminations) in layered or composite structures such as those found in batteries, super-capacitors and solar cells.
Patterns of acoustic energy attenuation can be used to detect defects in multi-layered structures such as battery electrodes, finished batteries, or other layered or laminated structures. Unlike the more familiar pulse-echo ultrasonic probes, which use co-located transducers, pulse shadow uses transducer pairs positioned on opposite sides of the test article.
Mechanical defects such as de-laminations or voids affect the acoustic transmission properties of solid or layered structures. These defects give rise to acoustic discontinuity between the components of electrode structure. Propagation of the mechanical oscillations inserted on one side of the test article is disrupted at the boundary between the normal structural material and the defect. Ultrasonic energy will be largely reflected from this interface and is therefore attenuated before it reaches receiving transducer on the other side of the test article. This attenuation forms a “shadow” of the mechanical defect in the structure.
Attenuation of the ultrasonic signal at the boundary of a de-lamination normal to the surface of the test article is an indication of a flaw. Unlike many ultrasonic methods, no liquid coupling between the transducer and the test article is required.
Pulse shadow ultrasonic testing is an easily deployed and reliable solution for quality assurance of batteries, supercapacitors, organic solar cells and their components. The method is capable of determining the charge state of energy generation devices and of providing information about the charge-discharge process.
Theoretical work underpinning this method includes mathematical descriptions of the propagation of elastic ultrasonic oscillations in multi-layer systems. This work has resulted in determination of the important boundary conditions including the particle continuity and acoustic overpressure at such interfaces.
The test conditions and results shown below are typical for the pulse shadow method developed by Enerize as applied to flaw detection:
Frequency range: 50 kHz to 10 MHz
Sensor size: 6-20 mm diameter
Measurement time: dependent on defect size, for example:
Defect surface size: 16 mm2
Sensor size: 6 mm diameter
Manual test time: 20 sec
Min size of defect detected, example:
Defect surface size 1 mm2
Material thickness: 6 mm
Accuracy is +/- 1-2 mm
dependent upon size of defects