A kirigami-based reconfigurable metasurface for selective electromagnetic transmission modulation

Electromagnetic (EM) metasurfaces, characterized by subwavelength unit cells, offer powerful control over EM waves, enabling applications in diverse areas such as negative refractive index materials, antennas, cloaking, and superlenses. However, conventional 2D metasurfaces have a fixed structure and EM response, limiting their functionality. Tunable metasurfaces, capable of dynamic EM response manipulation, address this limitation. Various tuning methods have been explored, including magnetic fields, temperature changes, barometric pressure, optical control, and voltage adjustments. While some approaches like rapid thermal annealing offer rapid tuning, they lack continuous adjustability. Others, such as 3D flexible frequency selective surfaces and origami-based designs, provide dynamic control through strain or folding, but often necessitate complex designs and specialized materials. Kirigami-based designs offer a simpler alternative for creating reconfigurable metasurfaces, allowing intricate deformations with simpler manufacturing. This research presents a kirigami-based metasurface designed for selective transmission modulation of polarized waves using mechanical strain. The innovative design allows for the transition between a 2D planar state and a 3D configuration through simple stretching, enabling selective modulation of linearly and circularly polarized waves.

The existing literature extensively covers the development and applications of electromagnetic metasurfaces. Early research focused on demonstrating fundamental concepts such as negative refractive index and perfect lensing. Subsequently, studies explored various applications, including cloaking devices, advanced antennas, and absorbers. The limitations of fixed-structure metasurfaces led to the pursuit of tunable metasurfaces, employing diverse tuning mechanisms including magnetic fields, temperature, optical control, and voltage. While these approaches demonstrate tunability, many suffer from complexities in design, fabrication, or integration. The use of flexible and stretchable substrates combined with origami or kirigami techniques has emerged as a promising approach for creating reconfigurable metasurfaces. Previous work has shown the potential of these methods, although challenges remain in terms of achieving precise control and minimizing unwanted effects, such as significant resonant frequency shifts due to deformation.

The kirigami-based metasurface comprises a thin-film polyimide (PI) substrate with periodically arranged copper (Cu) split-ring resonators (SRRs). The kirigami cuts enable out-of-plane deformation under uniaxial stretch. The metasurface geometry is defined by parameters such as unit cell length (l), width (w), and SRR dimensions (a, b, c). A thicker PI layer behind the SRRs minimizes bending deformation. The relationship between the rotation angle (θ) of the SRRs and the applied strain (εapp) is derived analytically. Finite element analysis (FEA) using ABAQUS software simulated the deformation behavior, modeling the PI substrate and Cu SRRs using C3D8R elements. The metasurface was fabricated using flexible printed circuit board (FPCB) technology. Uniaxial tensile experiments, using a custom-built stretcher, validated the FEA simulations. Electromagnetic (EM) transmission properties were measured using a vector network analyzer (VNA) in an anechoic chamber with broadband horn antennas. The deformed 3D configurations from FEA were imported into CST Microwave Studio for EM simulations, providing a direct comparison with experimental results. Equivalent circuit analysis, using inductance (L) and capacitance (C) models for the SRRs, complemented the experimental and numerical analysis to elucidate the tuning mechanism. The influence of geometric parameters (x and y spacing of the SRRs) on transmission characteristics was investigated both experimentally and numerically, examining the resonant frequency shift and transmission changes for both TE and TM waves under various strain levels. The response of the metasurface to bending and twisting was also characterized. Finally, the chiral behavior of the metasurface under applied strain was investigated through simulations of transmission for left circular polarization (LCP) and right circular polarization (RCP) waves. Circular dichroism (CD) was calculated to quantify the chiral response.

The study demonstrated that the kirigami-based metasurface effectively and selectively modulates the transmission properties of both linearly and circularly polarized waves. Applying a 30% stretch significantly altered the transmission of transverse electric (TE) and transverse magnetic (TM) waves, while the resonant frequency remained nearly constant. FEA and experimental results showed good agreement, confirming the predicted deformation behavior and transmission characteristics. The analytical model accurately predicted the rotation angle of the SRRs as a function of applied strain. Surface current analysis indicated that the transmission modulation originates from changes in the impedance of the SRRs due to their rotation during deformation. The equivalent circuit analysis supported this finding, demonstrating that changes in surface current density directly correlate with transmission changes. The investigation into the effect of geometric parameters revealed that variations in x-direction spacing influenced the resonant frequency at 0% strain for TE waves, while y-direction spacing had no effect. Under strain (20%), both x and y spacing changes affected resonant frequencies and transmission for both TE and TM waves, demonstrating the sensitivity of the metasurface to geometric parameters. The metasurface also exhibited insensitivity to bending and twisting deformations within certain ranges, suggesting robustness in practical applications. Notably, the metasurface showed a chiral response under strain, exhibiting significantly different transmission for LCP and RCP waves, with the capability to switch between chiral and achiral states.

The findings of this study address the need for reconfigurable metasurfaces with simple design and fabrication. The kirigami-based approach presented here successfully achieved selective transmission modulation for both linear and circularly polarized waves with minimal resonant frequency shift under applied strain. This contrasts with previous designs which frequently suffer significant resonant frequency shifts. The mechanism underlying this tunability was elucidated through surface current analysis and equivalent circuit modeling. The insensitivity to bending and twisting deformations adds to the practical applicability of this design. The demonstrated chiral response under strain opens avenues for polarization-selective applications. The results highlight the versatility and potential of kirigami structures for developing advanced tunable electromagnetic devices. This work has implications for various applications, including satellite communications, where a deployable, lightweight, and dynamically tunable metasurface can offer significant advantages.

This research successfully demonstrated a kirigami-based reconfigurable metasurface for selective electromagnetic transmission modulation. The simple stretch-based tuning mechanism, combined with the ease of fabrication using standard FPCB techniques, makes this design highly promising for various applications. Future research could explore more complex kirigami designs to enhance tunability and functionality. Integrating this metasurface with other technologies, such as shape-memory materials or advanced actuators, could lead to even more sophisticated reconfigurable electromagnetic devices.

While the study demonstrates the effectiveness of the kirigami-based metasurface, some limitations exist. The current design focuses on a specific frequency range (8-12 GHz). Extending the operational bandwidth would enhance its versatility. The fabrication process may require further optimization to improve uniformity across the metasurface, leading to a better match between experimental and simulation results. A more comprehensive study of the metasurface's long-term stability under repeated strain cycles would also enhance its practical applicability.