Design of a Deployable Strain-invariant Electromagnetic Wave Absorber Enabled by Magnetic Auxetic Metamaterial

Abstract

The rapid expansion of high-capacity wireless communication has accelerated the use of millimeter- wave (mmWave) electromagnetic radiation, intensifying concerns over electromagnetic interference (EMI) in emerging electronic systems. In particular, the growing demand for wearable, conformable, and stretchable electronics necessitates broadband EMI absorbers capable of maintaining stable performance under mechanical deformation. However, conventional absorbers exhibit strain-induced degradation of impedance matching and resonant characteristics, posing a significant challenge for mechanically reconfigurable platforms. This dissertation presents a strain-invariant and deployable electromagnetic absorber enabled by a synergistic integration of magnetic materials, auxetic mechanical metamaterials, and electromagnetic metapatterns. The core novelty of this work lies in a co-design strategy in which the auxetic deformation pathway and the meta-pattern geometry are engineered together to suppress absorption degradation during mechanical stretching. The proposed absorber comprises three key design components: (1) a magnetic composite layer providing effective mmWave absorption through controlled complex permeability; (2) a laser-cut auxetic topology that enables large, reversible deployment while regulating in-plane strain distribution; and (3) circular screen-printed silver meta-patterns whose rotational symmetry minimizes strain-dependent variations in effective impedance. To establish the design framework, theoretical analyses based on electromagnetic wave propagation was conducted to identify optimal material parameters, geometric structures, and pattern motifs for strain-invariant absorption. The absorber was fabricated as a 0.45-mm-thick magnetic composite film using a thermoplastic polyurethane matrix, followed by precision laser cutting to introduce the deployable auxetic structure. Circular conductive meta-patterns were subsequently deposited via screen printing to achieve robust electromagnetic behavior under mechanical deformation. The strain-invariant EMI absorption performance was experimentally validated using a millimeter- wave vector network analyzer. The fabricated absorber exhibits a broad absorption bandwidth of 25 GHz (more than 90% absorption), which is preserved up to 20% linear strain (44% areal strain) without noticeable decrease of the absorption bandwidth. Comparative analysis with state-of-the-art absorbers confirms that the proposed design not only achieves superior bandwidth stability under strain but also uniquely provides deployability, enabling compact storage and on-demand expansion—a capability rarely demonstrated in existing mmWave absorption technologies.