Chang-Yin Ji

Locally resonant seismic metasurfaces can suppress surface waves at sub-wavelength scales, but their fixed configurations are difficult to adapt to site-specific dominant frequency spectra. Seismic surface waves carry large seismic energy and decay slowly with distance, threatening low-rise buildings, lifeline engineering and above-ground infrastructure; site-adaptive surface-wave mitigation is therefore of clear engineering necessity. This paper proposes a mass-tunable spring-resonator seismic metasurface that reconfigures band-gaps in situ by adjusting resonator counterweight mass. Three-dimensional Bloch eigenmode simulations over 2–6 kg show that increasing mass shifts all band-gaps toward lower frequencies, and that at 3 kg or above higher-order modes decouple, generating a fourth band-gap (BG4). Full-scale frequency-sweep tests on a 7 × 6 array on an 8.0 m × 2.0 m × 1.0 m sand bed validate this trend: the measured second band-gap (BG2) shifts from 48–74 Hz at 2 kg to 35–68 Hz at 6 kg. Wavefield decomposition reveals clear modal selectivity: BG2 and the third band-gap (BG3) respond to both Love and Rayleigh waves, whereas BG4 is excited only by Rayleigh waves. Resonator mass is thus a reversible, low-cost, engineering-feasible degree of freedom for in situ band-gap tuning, and wave polarization must be considered in site-adaptive seismic metasurface deployment.

Locally resonant seismic metasurfaces can attenuate surface waves at sub-wavelength scales; however, fixed configurations are unable to adapt to varying site-specific frequency spectra. This paper proposes a mass-tunable spring-mass metasurface that achieves in-situ bandgap reconfiguration by altering the resonator mass. Combining three-dimensional Bloch simulations with full-scale sand-site experiments (7 × 6 array), the bandgap evolution within the 2–6 kg mass range is systematically investigated. Simulations demonstrate that increasing mass shifts all bandgaps toward lower frequencies, and when the mass reaches ≥3 kg, the decoupling of higher-order modes gives rise to a fourth bandgap, BG4. Experiments confirm this trend and further reveal the modal selectivity of bandgaps: BG2 and BG3 are effective for both Love and Rayleigh waves, whereas BG4 can only be excited by Rayleigh waves. Due to finite periodicity and damping effects, the low-frequency BG1 is difficult to observe experimentally. Overall, the resonator mass serves as a reversible and low-cost tuning degree of freedom, providing an engineering-feasible pathway for adaptive metasurface design.

Despite recent numerical simulations and limited laboratory studies highlighting the potential of semi-embedded seismic metamaterials (SEM) in attenuating Rayleigh waves, their real-world effectiveness remains unverified, particularly for Love waves. Love waves pose significant destructive risks to slender structures but have rarely been the focus of research. To address this gap, we present the first full-scale 2D field experiment on an SEM composed of an array of semi-embedded rubber column resonators. The experimental results reveal a global bandgap spanning 25–37 Hz and a localized bandgap at 37–42 Hz. At the central frequency of the global bandgap (f₀ = 31 Hz), the attenuation reaches −9.3 dB for Love waves and −5.3 dB for Rayleigh waves, with the mitigation of Love waves being notably pronounced. Furthermore, our theoretical and experimental analyses provide novel mechanistic insights: the primary energy dissipation in flexible rubber resonators arises from the resonance of their exposed above-ground sections, while the underground buried parts introduce damping that moderately reduces the efficiency of surface wave attenuation. This pioneering full-scale on-site validation bridges the critical gap between simulation-based predictions and practical seismic protection systems, providing valuable reference for the engineering application of SEM, especially for mitigating destructive waves.

Despite recent numerical and laboratory studies highlighting the potential of semi-embedded seismic metamaterials (SEM) with concrete oscillators in attenuating Rayleigh waves, their real-world effectiveness—particularly in mitigating Love waves—remains unvalidated. In this study, we present the first field experimental validation of an SEM comprising an array of rubber column resonators. Experimental results show that the SEM exhibits a global bandgap spanning 25–37 Hz and a localized bandgap in the 37–42 Hz range. Within the central frequency (ƒ₀ = 31 Hz) of the global bandgap, the attenuation reaches − 9.3 dB for Love waves and − 5.3 dB for Rayleigh waves. Theoretical and experimental analyses reveal that the energy dissipation in flexible rubber resonators is mainly attributed to the resonance of their exposed above-ground sections, while the damping introduced by the parts buried underground somewhat diminishes the effectiveness of surface wave energy attenuation. This work bridges the critical gap between simulation-based predictions and deployable seismic protection systems, providing valuable insights for designing novel seismic metamaterials.

Surface lattice resonances (SLRs) are the coherent collective interactions between periodically arranged nanoparticles, which are generally considered to be formed by the resonant electric dipole, magnetic dipole, or electric quadrupole moments of a single nanoparticle coupled with the Rayleigh anomaly (RA). Here we reveal the first observation of the chiral SLRs that are formed by the coupling of the chiral toroidal electric dipole (TED) moment and RA mode through the theoretical design and experimental fabrication of a nano-kirigami based propeller metasurface. By engineering the rotational symmetry of the propeller, e.g., from C2 (C3) symmetry to C4 symmetry, we find that the electric dipole (electric quadrupolar) chiral SLRs have evolved into the TED associated chiral SLRs. Furthermore, it is found that the excitation amplitude of the TED moment can be tailored by controlling the stereo twisted height of the propeller and the spin of the incident light. Finally, the chiral TED moment enhanced circular dichroism is verified in the near-infrared wavelength region. Our study provides an effective yet simple scheme to manipulate the TED-dependent chiral SLRs, paving the way toward exploring the unconventional physical properties of TED and advanced chiroptical physics.

Nano-kirigami metasurfaces have attracted increasing attention due to their ease of three-dimension (3D) nanofabrication, versatile shape transformations, appealing manipulation capabilities and rich potential applications in nanophotonic devices. Through adding an out-of-plane degree of freedom to the double split-ring resonators (DSRR) by using nano-kirigami method, in this work we demonstrate the broadband and high-efficiency linear polarization conversion in the near-infrared wavelength band. Specifically, when the two-dimensional DSRR precursors are transformed into 3D counterparts, a polarization conversion ratio (PCR) of more than 90% is realized in wide spectral range from 1160 to 2030 nm. Furthermore, we demonstrate that the high-performance and broadband PCR can be readily tailored by deliberately deforming the vertical displacement or adjusting the structural parameters. Finally, as a proof-of-concept demonstration, the proposal is successfully verified by adopting the nano-kirigami fabrication method. The studied nano-kirigami based polymorphic DSRR mimic a sequence of discrete bulk optical components with multifunction, thereby eliminating the need for their mutual alignment and opening new possibilities.

Nano‐kirigami method enables rich diversity of structural geometries that significantly broaden the functionalities of optical micro/nano‐devices. However, the methodologies of various nano‐kirigami are still limited and as a result, the chiral nano‐kirigami structure has yet been pushed to the limit for operation at visible wavelength region. Here, the merits of the various nano‐kirigami strategies are comprehensively explored and bio‐inspired nano‐cilia metasurface with enhanced circular dichroism at visible wavelengths is demonstrated. The stereo chiral nano‐cilia metasurface is designed with three‐fold rotational symmetry, which exhibits tuneable chiroptical responses when the nano‐cilia are deformed to form strong chiral light–matter interactions. By employing electron‐beam lithography (EBL) and focused ion beam (FIB) lithography, on‐chip nano‐cilia metasurfaces are experimentally realized in near‐infrared wavelengths region and at visible wavelengths, respectively, successfully validating the giant circular dichroism revealed in simulations. Our work is useful to broaden the existing platform of micro/nano‐scale manufacturing and could provide an effective method for the realization of versatile bioinspired nanostructures with profound chiroptical responses.