Feature: Batteries


cross-sections. Multi-layer scans can include up to 50 independent layers. Depth-specific information can be extracted and applied to create two- and three-dimensional images without the need for time-consuming tomographic scan procedures and more costly X-rays. Te images are then analysed to detect and characterise flaws. Scanning Acoustic Microscopy,


acknowledged for its capability to identify defects as minuscule as 50-microns, is extensively embraced in the semiconductor industry as a metrology technology for failure analysis and reliability detection. Now the same high-speed technology is being applied to testing and failure analysis of Li-ion battery cells. Manufacturers are increasingly


integrating SAM inspection tools into their processes to catch defects at an early stage. For high volume operations, automated systems are also available that enable 100 per cent inspection of battery cells, ensuring safety and performance. According to Polu, effective testing for


Li-ion battery flaws across the diverse form factors utilised requires both expertise in SAM technology as well as customisation to the specific application. Li-ion battery cells can be packaged in various sizes and shapes such as square, round and pouch to optimise how energy is stored and delivered. Te different packaging requires adjustments in the manufacturing process along with reliable quality assurance to detect defects. For some types of inspection, such as


electric vehicle (EV) Li-ion batteries, an immersive type of SAM is proving effective. With this method, battery components are submerged in a fluid (typically water) to facilitate the transmission of ultrasonic waves during scanning. For this application, custom, low-


frequency transducers are utilised, serving as both a transmitter and receiver of ultrasonic sound waves. For thick materials, high-frequency ultrasound (which provides high resolution) cannot penetrate deeply enough. Te lower-frequency ultrasound can penetrate deeper into thick packages but has lower spatial resolution. A transducer is an energy conversion device that generates ultrasonic waves


when a voltage is applied to them and can turn ultrasonic waves back into voltage. Combined with the shape of the lens on the transducer, frequency and focal length can be controlled to provide the best results when inspecting the internal characteristics of samples, explains Polu. “For thick battery packages like EV


vehicles, we use relatively low-frequency, highly customised transducers to penetrate through the parts. Te special transducers need to have very high surface penetration to a depth of approximately five millimetres while still maintaining resolution." says Polu. OKOS designs and manufactures a large


variety of transducers up to 300 MHz for different applications. Some transducers require direct contact with a material in order to operate, others use an air gap or are immersed in a fluid, usually water, in order to better transmit the sound through a material. Transducers come in a variety of sizes and shapes for different applications. Among the specialised transducers


for custom applications are phased array transducers, which contain multiple elements unlike the single element in other transducers. Te transducer can also be curved in shape, which allows for faster scans as the elements simultaneously brush over samples and faster scans of curved surfaces. Using constructive interference between the elements, focal lengths can be changed at any time to achieve the best results. Phased array transducers are


typically 20 MHz or below. According to Polu, the utilisation of


special transducers and soſtware enables efficient detection of Li-ion battery defects across a wide range of form factors. “It’s a combination of using the


transducers to measure signals along with soſtware to extract features out of a very noisy environment. It’s like the Hubble Space Telescope; you need to detect one small feature (the potential defect) amidst a hell of a lot of noise,” explains Polu. He anticipates that SAM technology will


become increasingly automated to ensure Li-ion battery safety and performance as production volumes continue to rise. As an example, he comments on the trajectory of EV battery inspection. itially, they're trying to ascertain the


failure modes of Li-ion batteries. Once that’s achieved, implementing quality assurance is the focus, ideally at an automated level because no one wants to drive an EV if battery safety is in question,” says Polu. As technology progresses, new variations


and form factors of Li-ion batteries are emerging. Manufacturers across a wide range of industries that work with an expert provider of SAM, which can customise the technology to their specific application, will have an advantage in ensuring the safety, quality and reliability of their products. For more information, contact OKOS at info@okos.com or visit www.okos.com. OKOS is a wholly owned subsidiary of PVA TePla AG, Germany.


SAM uses ultrasonic waves to scan and create detailed images, detecting structural flaws in batteries, even at the micron level.


www.electronicsworld.co.uk April 2025 31


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