PMUT-Based Non-Contact Ultrasonic Characterization of Li-ion Battery Separators

The rapid evolution of Industry 5.0 is driving the need for advanced sensing technologies capable of supporting new production paradigms, including the Internet of Things, big data, and AI training. In this context, the lithium-ion battery sector is experiencing significant growth, accompanied by increasing demands from industry and regulators for improved safety and performance. Separator membranes are critical to battery function, influencing both safety and efficiency through properties such as porosity and thickness. This work explores the use of piezoelectric micromachined ultrasonic transducers (PMUTs) for the non-contact, non-destructive inspection of battery separators. A novel air-coupled PMUT array operating at 200 kHz was designed, fabricated, and tested for high-precision through-transmission measurements of commercial separator membranes. A PMUT cell design based on the cantilever operation mode is proposed to achieve high enough sensitivity to cope with the relatively large insertion loss of separator membranes. Results demonstrate the feasibility of using the transmission coefficient to infer key membrane properties such as porosity and thickness.