Elastic complementary meta-layer for ultrasonic penetration through multi-layered battery pouch cells

초록

Ultrasonic inspection is a promising non-destructive approach for evaluating the internal state of lithium-ion batteries, but its application to pouch cells is strongly limited by wave reflection and scattering caused by densely stacked multi-layer structures. In this work, we propose an elastic complementary meta-layer (CML) that enables ultrasonic penetration through battery pouch cells by compensating the wave response of the battery. The penetration condition is formulated within a transfer matrix framework in terms of impedance matching and phase compensation. To satisfy these conditions, a novel meta-atom with independently tunable effective mass and stiffness is employed, enabling precise control of dynamic properties through geometric design. Theoretical analysis and numerical simulations show that the proposed CML restores near-complete ultrasonic transmission through both single and multiple stacked pouch cells, despite severe impedance mismatch and accumulated phase delay in the bare battery structures. This study presents a general wave-based strategy for penetrating complex multi-layer barriers and provides a new route for ultrasonic inspection of battery systems that are difficult to access using conventional methods.

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