
==== Front
Proc Natl Acad Sci U S A
Proc Natl Acad Sci U S A
PNAS
Proceedings of the National Academy of Sciences of the United States of America
0027-8424
1091-6490
National Academy of Sciences

38285934
202309096
10.1073/pnas.2309096120
research-articleResearch Articleapp-physApplied Physical Sciences405
Physical Sciences
Applied Physical Sciences
Chimera metasurface for multiterrain invisibility
Xu Zhao-Hua a 1
Xu Su xusu@jlu.edu.cn
a 1 2
Qian Chao b c d 1
Xu Wenya e
Ren Hang a
Su Wenming wmsu2008@sinano.ac.cn
e 2 https://orcid.org/0000-0003-1721-1923

Chen Qi-Dai a
Chen Hongsheng hansomchen@zju.edu.cn
b c d 2
Sun Hong-Bo hbsun@tsinghua.edu.cn
a f 2 https://orcid.org/0000-0003-2127-8610

aState Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
bZhejiang University-University of Ilinois Urbana-Champaign Institute, Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, Zhejiang University, Hangzhou 310027, China
cZhejiang University-Hangzhou Global Science and Technology Innovation Center, Key Laboratory of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang, Zhejiang University, Hangzhou 310027, China
dJinhua Institute of Zhejiang University, Zhejiang University, Jinhua 321099, China
ePrintable Electronics Research Centre, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China
fState Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Haidian, Beijing 100084, China
2To whom correspondence may be addressed. Email: xusu@jlu.edu.cn, wmsu2008@sinano.ac.cn, hansomchen@zju.edu.cn, or hbsun@tsinghua.edu.cn.
Edited by Guoliang Huang, University of Missouri, Columbia, MO; received May 31, 2023; accepted November 17, 2023 by Editorial Board Member Yonggang Huang

1Z.-H.X., S.X., and C.Q. contributed equally to this work.

29 1 2024
6 2 2024
29 7 2024
121 6 e230909612031 5 2023
17 11 2023
Copyright © 2024 the Author(s). Published by PNAS.
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).

Significance

Although camouflage technology has been a long-standing topic, the enthusiasm towards a practical-oriented invisibility has never weakened. Past decades have witnessed a proliferation of metasurface-based invisibility owning to the advent of metasurfaces that can freely customize the electromagnetic waves. However, state-of-the-art works only achieve broadband invisibility in an individual terrain with its specific electromagnetic background. In this study, we introduce a multiterrain invisibility metasurface that integrates biomimetic camouflage strategies, enabling dynamic invisibility across diverse terrains characterized by varying electromagnetic properties. This innovation is designed to effectively counter advanced synthesized detection methods encompassing microwaves, infrared, and visible light. In addition, our work has brought the multiband independent control capability of electromagnetic devices to a new level.

Invisibility, a fascinating ability of hiding objects within environments, has attracted broad interest for a long time. However, current invisibility technologies are still restricted to stationary environments and narrow band. Here, we experimentally demonstrate a Chimera metasurface for multiterrain invisibility by synthesizing the natural camouflage traits of various poikilotherms. The metasurface achieves chameleon-like broadband in situ tunable microwave reflection mimicry of realistic water surface, shoal, beach/desert, grassland, and frozen ground from 8 to 12 GHz freely via the circuit-topology-transited mode evolution, while remaining optically transparent as an invisible glass frog. Additionally, the mechanic-driven Chimera metasurface without active electrothermal effect, owning a bearded dragon-like thermal acclimation, can decrease the maximum thermal imaging difference to 3.1 °C in tested realistic terrains, which cannot be recognized by human eyes. Our work transitions camouflage technologies from the constrained scenario to ever-changing terrains and constitutes a big advance toward the new-generation reconfigurable electromagnetics with circuit-topology dynamics.

chimera
adaptive
invisibility
multiterrain
poikilotherm
MOST | National Natural Science Foundation of China (NSFC) 501100001809 62175083 Su XuHongsheng Chen MOST | National Natural Science Foundation of China (NSFC) 501100001809 61935015 Su XuHongsheng Chen 吉林省科学技术厅 | Natural Science Foundation of Jilin Province (Jilin Natural Science Foundation) 100007847 20230101359JC Su Xu MOST | National Natural Science Foundation of China (NSFC) 501100001809 11961141010 Su XuHongsheng Chen MOST | National Natural Science Foundation of China (NSFC) 501100001809 61975176 Su XuHongsheng Chen MOST | National Key Research and Development Program of China (NKPs) 501100012166 2022YFA1404704 Hongsheng Chen MOST | National Key Research and Development Program of China (NKPs) 501100012166 2022YFA1405200 Hongsheng Chen
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pmcInvisibility is a consummate survival philosophy that blends natural creatures into surroundings (Fig. 1). Different from creatures that achieve camouflage only in a constrained environment [e.g., kallima inachus in yellow leaves (1)], some more fantastic poikilotherms (cold-blooded creatures) can adapt themselves into various environments. The most canonical poikilotherms with adaptive camouflage ability are chameleons, who can dynamically alter its skin color to match the habitant (2). In addition to chameleons, glass frogs (hyalinobatrachium pellucidum) allow light to penetrate their transparent bodies and introduce a significant optical scattering reduction for self-invisibility (3), whereas bearded dragons (pogona vitticeps) can vary their body temperature based on thermal acclimation and merge themselves into surroundings in the infrared regimes (4, 5).

Fig. 1. Conceptual illustration of the Chimera metasurface with multiterrain adaptive invisibility. The proposed metasurface, just like Chimera made up of three animals in Greek mythology, incorporates the environment-adaptation traits of three poikilotherms. The photo of bearded dragon is reproduced from previous literature (5). Chameleon, glass frog and terrain photos are reproduced from Visual China Group Co., Ltd. All the photos are used with permission.

Learning from these natural creatures, artificial camouflage strategies have been extensively studied for a significant amount of time (6–12). More recently, metamaterials/metasurfaces (13–20), artificial electromagnetic media with the ability to control electromagnetic waves on demand, have been rapidly developed for their potential in camouflage technology. Conventionally, metamaterials or metasurfaces enabled broadband kallima inachus-like invisibility devices are constrained to predefined and single surrounding environment, e.g., absorbers for electromagnetically dark surroundings (21–24) and carpet invisibility cloaks for electromagnetically bright backgrounds (25–30). Notably, fully transmissive cloak (31, 32) that support multiterrains invisibility of large objects are still challenging for practical applications over a broadband frequency range. Apart from this, there have been camouflage efforts in the visible spectrum, such as the fusion of transparent and matte appearances (33), and the phase-abolished ray optics (34). To break this limit, several experimental demonstrations of reconfigurable invisibility metasurfaces have been conducted by imbedding various active components, such as using dynamic electronic elements (35–39), two-dimensional materials (40–43), phase-changing materials (44–47), and structural transformation (48–50). Yet, reconfigurable invisibility metasurfaces are still restricted within few working states, not to mention the constraints of significant dispersion, continuous power supply, active thermal dissipation, considerable switching time, or polarization sensitivity. These constraints make it naturally difficult to perfectly reconstruct the supreme environmental adaptation of poikilotherms.

Here, we experimentally demonstrate a Chimera metasurface for multiterrain invisibility over various spectral regimes. The proposed metasurface, just like the monster Chimera made up of three animals in Greek mythology, incorporates the environment-adaptation traits of three poikilotherms (Fig. 1). At microwaves, the reflection characteristics of the metasurface can be adapted to various landforms with low-dispersion properties in nature (e.g., water surfaces, shoals, beaches/deserts, grasslands, or frozen grounds) based on the mechanically controlled circuit-topology-transition-induced mode evolution, just as chameleons modify their photonic-crystal skin tissues for optical camouflage (2). In the visible regime, the proposed metasurface maintains body transparency, behaving similarly to an invisible glass frog. Furthermore, our mechanic-driven metasurface eliminates the unneeded resistance-related thermal effect by avoiding continuous power supply and has a poikilotherm-mimetic nonactive thermoregulation. This biomimetic thermal management indicates that similar to the bearded dragon in nature, the proposed metasurface can be hardly discovered by infrared thermal detection. In particular, like the Chimera, a synthetic monster with three independently thinking brains in Greek mythology, the proposed metasurface can independently respond to the environmental characteristics of terrains over microwave, infrared, and visible light. The circuit-topology-transited mode evolution, a previously unidentified paradigm for constructing terrain-dispersion-matched response and in situ electromagnetic tuning, expands the applicable range of adaptive invisibility technologies from a few constrained scenarios to multiple terrains and can serve as a powerful platform for novel reconfigurable electromagnetic devices.

Results

Geometry and Circuit Topology Transition of the Chimera Metasurface.

The Chimera metasurface and its meta-atom are schematically illustrated in Fig. 2 A and B, respectively. Each meta-atom is constructed by two parts of artificial structures separated with a varying vertical distance δ   . The upper part of the meta-atom is a Type-I indium tin oxide (ITO) pattern on the bottom surface of a 0.175-mm-thick polyethylene terephthalate (PET, ϵPET≈3   ), while the lower part consists of a Type-II ITO pattern, a 3.75-mm-thick quartz substrate ( ϵglass≈3.7   ) and a piece of 0.2-Ω/sq optically transparent metal-mesh from the top to the bottom. Both the Type-I and Type-II ITO patterns are divided into four segments with a sheet resistance of 60 Ω/sq. By calibrating the upper and lower parts of the meta-atom to the same local coordinate system (xL,yL,zL)   , the projection of Type-I and Type-II patterns could form a circular ring. Here, we define the genus of the transmission-line model as the topological invariants of the circuit, or the so-called circuit-topology number (CTN), which can reflect the electromagnetic property of metasurface to some extent. When the Type-I and Type-II patterns touch each other and construct a closed cylindrical lossy ring modeled as a series of circuity elements, i.e., resistance R   , capacity C   , and inductance L   in Fig. 2C, the CTN equals to 1. When Type-I and Type-II patterns are separated from each other, the CTN begins to transition from 1 to 2, as shown in Fig. 2D, and the original RLC series transforms into two groups of RLC series separated by an interlayer impedance Zδ . When δ increases to a relatively large value, i.e., the weak coupling status of two patterns, the CTN fully turn to 2.

Fig. 2. The geometry and circuit topology transition of the Chimera metasurface. (A) The schematic view of Chimera metasurface. (B) The geometries of meta-atom. Here, l= 13.4 mm, wI= 3.85 mm, lI= 2.37 mm, g= 3.70 mm, din= 5.56 mm and dout= 10.30 mm. The circuit topology of equivalent transmission-line model for microwave adaptation: (C) the gapless case ( δ = 0, CTN = 1) with strong absorption and (D) the hybrid-layer case ( δ ≠ 0, CTN = 2) with tunable interlayer coupling and continuously adaptive reflection. The CTN is the abbreviation of the circuit topology number.

Mode Evolution and Electromagnetic Reflection Management.

During the topological transition of the circuit model, the Chimera metasurface experiences interesting mode evolution (Fig. 3A). We verified this mode evolution process through numerical simulations. For the case of CTN = 1, the strongly absorptive Mode 1 is constructed at 10.10 GHz (Fig. 3B) and introduces broadband absorption from 8 to 12 GHz based on the well-designed impedance-matching boundary and surface current lossy loops. For the transiting cases, Mode 1 disappears. Meanwhile, two new absorptive modes occur and evolve in the low-frequency (e.g., modes 2, 4, and 6) and high-frequency regions (e.g., modes 3, 5, and 7) of the original band for any interlayer distance, respectively. The absorptive bands of two modes synthesize a relatively flat (i.e., low-dispersive) camouflage region, while the continuously tunable absorptivity of the synthesized camouflage region is decided by the strength of the modes in the evolution. In addition, the positions of high-frequency and low-frequency modes ensure broadband in situ (frequency-range-invariant) tunability. At the end of evolution, the working state of the metasurface turns to quasiperfect reflection (Mode 8). This mode-evolution-based continuous reflection management between strong absorption and quasiperfect reflection satisfies the invisibility in the surroundings with the full range of electromagnetic darkness and brightness. It is worth noting that, the observed in situ, low-dispersive, and highly reconfigurable invisibility is significantly different from all the current circuit-topology-invariant camouflage techniques (35, 36, 38–41, 43).

Fig. 3. The mode evolution reveals the microwave chameleon-like tunability. (A) The process of mode splitting and evolution during the change of layer spacing. (B) The surface current distribution corresponding to the modes shown in Fig. 3A, as well as the change trend of the low-frequency mode and high-frequency mode.

Experimental Verification of Multiterrain Microwave Camouflage.

The whole practical sample (Fig. 4C) is fabricated by using nanoimprinting (Fig. 4A) and an etching process (Fig. 4B) with 20 meta-atoms in both the x   and y   directions. The reconfigurable microwave reflection management of the sample is experimentally verified in the microwave anechoic chamber with an arc testing platform (Fig. 5A). When δ   varies from 0 to 7 mm with the use of an electrical lifting platform (Fig. 5B), the normalized reflectance of the Chimera metasurface covers a range from −18 to −1 dB (Fig. 5C) under the quasinormal incidence ( θi   = 10°) of the TE-polarized wave, which is consistent with the numerical simulation (SI Appendix, Fig. S1A). The microwave reflection properties of five typical terrains, i.e., water surfaces, shoals, beaches/deserts, frozen grounds, and grasslands, are mimicked in the lab as the reference group to explore the applicable potential of Chimera metasurfaces in the real world. During the Chimera metasurface sample experiments, it is intriguing that suitable working states of the Chimera metasurface can be found to match all the five terrains over the whole frequency range of interest, i.e., 8 to 12 GHz. As shown in Fig. 5D, a quasitotal reflection state ( δ≥ 4.90 mm) can be used to achieve invisibility in water-surface environments. For highly absorptive environments, e.g., beaches/deserts (Fig. 5F), frozen grounds (Fig. 5G), and grasslands (Fig. 5H), the Chimera metasurface can mimic the corresponding microwave characteristics by tuning δ to 1.47, 0.77, and 0 mm, respectively. Regarding terrains with semireflection scattering characteristics, e.g., shoals (Fig. 5E), the Chimera metasurface can also realize a specific transition state ( δ = 2.38 mm) to match the corresponding electromagnetic brightness. Polarization insensitivity and tolerance to oblique incidence are crucial performance factor for practical application of metasurfaces. A few pioneering works have tried to extend the angular stability at large-angle oblique incidence by using anomalous Brewster effect (51) and grazing incidence (52). In our work, the Chimera metasurface can experimentally match the electromagnetic property of multiple terrains under oblique incidences of both TE and transverse magnetic (TM) waves at the incident angles up to about 40∘ (SI Appendix, Figs. S3–S6). This is attributed to the top PET film performing as a matching layer in the meta-atom to address the undesired upward shift of the center frequency and the reflection mismatch at large incident angles (53), ensuring the metasurface’s stable operation within an approximate range of 40° (the simulation results are presented in SI Appendix, Fig. S12). This microwave adaptive reflection matching accurately imitates the optically adaptive color of chameleons and can be applied to microwave reconfigurable camouflage for various terrains.

Fig. 4. Fabrication and sample structure of the Chimera metasurface. (A) The nanoimprinting process for metal-mesh back coating. (B) The etching process for ITO patterns. (C) Sample and local structure details of the Chimera metasurface. Black background is used for photographing.

Fig. 5. Microwave experimental demonstration of the Chimera metasurface. (A) The microwave testing environment. (B) The reconfigurable setup for microwave adaptative camouflage. (C) The experimental reflectance of Chimera metasurface under quasinormal ( θi = 10∘ ) incidence of TE polarized waves with different interlayer spacings. (D–H) The invisibility matching performance for the environments of water surfaces, shoals, beaches/deserts, frozen grounds, and grasslands. The photos of terrains are reproduced from Vision China Group Co., Ltd., used with permission. The Envir. is the abbreviation of environment.

Poikilotherm-Mimetic Adaptivity at Infrared and Visible Regimes.

Matching the infrared characteristics of various background environments closely is crucial for achieving multiterrain infrared camouflage. In practice, typical infrared detectors on satellites and airborne (54, 55) conduct their duty over a long distance that is far larger than the geometries of our metasurface meta-atom, and the localized infrared inhomogeneity of the metasurface can be neglected. From a macroscopic perspective, the effective infrared emissivity of the metasurface can be derived by the ratio between the practical detected intensity of infrared waves and the reference of the detector. In this context, through the combination of high-emissivity quartz glass, low-emissivity PET, and low-emissivity ITO, it becomes possible to modulate the effective emissivity of the Chimera metasurface within little deviation from the background environments whose infrared emissivities are around 0.8 to 0.9 (56–59). To prove this concept, we deploy the Chimera metasurface in real-world scenarios, including water surfaces, shoals, beaches/deserts, frozen grounds, and grasslands, to simulate thermal detection (Fig. 6 A–E). The temperature differential between the Chimera metasurface and each of these five distinct environments consistently remains within 2.7 ∘C   , 1.6 ∘C   , 2.4 ∘C   , 3.1 ∘C   , and 1.9 ∘C   , respectively. Thermal imaging vividly illustrates the Chimera metasurface’s ability to seamlessly blend into environments with varying temperatures and thermal emissivity. Furthermore, we have implemented mechanical switches and locks to ensure that the microwave camouflage remains adjustable and maintained without a continuous power source which typically results in unavoidable infrared radiation. This feature effectively prevents the generation of infrared radiation associated with ohmic heating (60, 61), thereby breaking the correlation between microwave and infrared adaptation across diverse terrains (SI Appendix, Fig. S9). Therefore, the proposed Chimera metasurface has a bearded dragon-like inactive thermoregulation function and can match its temperature to the surrounding terrain, which may be useful for infrared self-cloaking. Therefore, the Chimera metasurface can reduce the possibility of being discovered by far-field thermal/temperature detection to some extent, similar to what bearded dragons do in natural environments.

Fig. 6. The optical characterization of the Chimera metasurface. (A) The thermal image of sample on the water surface. (B) The thermal image of sample on the shoal. (C) The thermal image of sample on the beach/deserts. (D) The thermal image of sample on the frozen ground. (E) The thermal image of sample on the grass. Trans., Refle., and Absor. are the abbreviations of transmittance, reflectance, and absorptance, respectively. (F) The transmittance, reflectance, and absorptivity of Chimera metasurface over visible and near-infrared regions. The Inset is the optical photo of the sample.

The optical property of the Chimera is investigated experimentally. Fig. 6F exhibits the Chimera placed in front of a picture with the words “Jilin University.” The photograph indicates that the sample has satisfactory optical transparency. More quantitively, the Chimera metasurface achieves an average transmittance of 75.0% over the visible (380 to 780 nm) and near-infrared (780 to 2,000 nm) regimes. Simultaneously, the Chimera metasurface exhibits low absorption and low reflectance over the same spectra. This optical transparency can be treated as an analog of the self-invisibility strategy of glass frogs.

Discussion

In summary, we experimentally demonstrate a Chimera metasurface for multiterrain invisibility by synthesizing the natural survival philosophies of poikilotherms. By exploiting switchable circuit topology and corresponding mode evolution, a chamberlain-like in situ microwave reflection manipulation is achieved continuously from −18 to −1 dB with low spectral dispersion over the frequency range from 8 to 12 GHz. The mechanic-based cold-blooded thermoregulation keeps the temperature of the Chimera metasurface approaches that of the surrounding environment and ensures a <3.1 ∘C thermal imaging recognition difference in the tested realistic terrains, which cannot be recognized by human eyes. Additionally, the Chimera metasurface has glass frog–like transparency over visible frequencies.

Compared to previous tunable invisibility strategies (31, 32, 35–38, 40) (Table 1), our demonstration artificially reconstructs the environment-adaptive behaviors of chameleons, bearded dragons, and glass frogs in an integrated manner with the outstanding camouflage properties of broad bandwidth, polarization insensitivity, and angular allowance (see SI Appendix for more details). Remarkably, the circuit-topology-transition-induced mode evolution enables the terrain-scattering-matched response and broadband in situ tunability, thereby resolving the fundamental challenge that prevents all the current circuit-topology-invariant camouflage techniques from the practical multiterrain application. Our Chimera metasurface allows independent invisibility adaptivity over microwave, infrared, and visible regions and supports long-term multistable working states, also significantly differs from electronics-based tunable strategies (35–43).

Table 1. Comparison between current dynamic invisibility strategies and our work

		Multi-terrain adaptation		
	Method	Microwave	Infrared	Visible	Long-term stability	References	
Natural	Chameleon	No	Yes	Yes	–	(2, 5)	
Glass frog	No	Yes	Yes	–	(3)	
Artificial	Heterostacked metacamouflage	No	No	No	Yes	(20)	
Ultrabroadband metamaterial absorber	No	No	No	No	(22)	
Structural transformation	Partial	Yes	No	Yes	(48)	
Diode metasurface	Partial	No	No	No	(35)	
Graphene metasurfaces	Partial	No	Yes	No	(40, 43)	
Electrochromic	No	No	Partial	No	(11)	
Phase-changing metasurfaces	No	Yes	No	No	(44, 46, 47)	
Our work	Yes	Yes	Yes	Yes	–	

Our work has potential practical applications. On one hand, the continuous low-dispersion in-situ tunability between quasiperfect reflection and strong absorption provides an abundance of states to mimic the electromagnetic characteristics of various real-world terrains, thus avoiding recognition by microwave radars from natural surroundings. On the other hand, the proposed metasurface may also reduce the long-distance detected probability of infrared detectors and optical video equipment by reappearing the thermal regulation of bearded dragons and the self-transparency of glass frogs. The Chimera metasurface also retains potential compatibility with current infrared and visible camouflage materials and equipment. Our work extends the applicable range of camouflage techniques from the constrained scenario to more terrains and advances reconfigurable electromagnetic devices to a multistable and circuit-topology-dynamic stage.

Methods

Numerical Simulation.

The frequency solver of the commercial software CST Microwave Studio is employed to investigate the electromagnetic response of the proposed metasurface. In the simulation, the meta-atom is considered with unit-cell boundaries. As shown in Fig. 2B, unit-cell boundary conditions are employed in the simulation, to construct periodic arrays in the xL and yL directions. The open add space boundary condition is applied in the zL direction to avoid multiple reflections. The mesh size meets the convergence and accuracy requirements. See Results for the material parameters of the meta-atom composition and Fig. 2B’s legend for the geometric parameters. The material type of ohmic sheet is assigned to model the ITOs and metal-meshes. The absorption curves in Figs. 2B and 5C are derived from the Gaussian fitting algorithm.

Fabrication.

The proposed metasurface is fabricated through a hybrid process of metal mesh preparation (Fig. 4B), ITO pattern etching (Fig. 4C) and manual assembly. Regarding the metal-mesh preparation, the all-dielectric grooved pattern is first imprinted on a photoresist-coated PET substrate by using a photolithography-produced mask. Then, the pattern is filled with metallic nanoparticle ink. After a series of filling, blading and drying steps, the metallic ink in the grooves forms low-resistance metal mesh. Regarding the ITO pattern preparation, a photoresist layer is first spin-coated onto a commercial PET-substrate ITO film. Then, a photolithography process is adopted for the film for exposure and photoresist removal. Next, by adopting a typical etching process and removing excess photoresist, Type-I and Type-II ITO patterns are obtained. Finally, the metasurface is manually assembled.

Microwave Experimental Setup.

The microwave measurement is carried out in a microwave anechoic chamber, as shown in Fig. 5A. A pair of standard horn antennas working from 1 to 18 GHz is used as the transmitter and receiver, both of which are placed on an arc platform and connected to a Keysight E5071C vector network analyzer. The positions of antennas can be controlled with an automatic measurement system. The minimum measurable angle of incidence θi   is 10°, which is limited by the practical size of the antennas. The sample is placed at the center of the arc platform. An electric lifting stage with a frame fixture and a stepper motor controller construct the interlayer spacing system, as shown in Fig. 5B. The distance between the upper and lower parts of the metasurface is adjusted by 56BYG250BK-SASSBL-0241 electronic step motors with a step of 0.01 mm and a response time of 50 ms/mm. The mechanical locking structure ensures that the states can be maintained without an additional power supply. Five kinds of typical natural environments, i.e., water surfaces, sand grounds, shoals, grasslands, and frozen grounds, are mimicked in the experiment, as shown in Fig. 5 D–H, respectively. A plastic container with dimensions of 81 × 60 × 48 cm3 is used to embark the typical natural elements, such as water, sand, grass, and snow. Photographs of five kinds of natural environments and their corresponding geometries can be found in SI Appendix, Fig. S2.

Optical Characterization.

The optical and near-infrared transparency from 380 to 2,000 nm is measured with the use of an ultraviolet–visible spectrophotometer UV-3600. An XthermII thermal imaging camera is used to study the poikilotherm-like thermal characteristics of the sample in realistic natural environments. In infrared tests, the interlayer distances of metasurface for each typical terrain are consistent with the microwave tests.

Supplementary Material

Appendix 01 (PDF)

Click here for additional data file.

This work at Jilin University was sponsored by National Natural Science Foundation of China (NNSFC) under Grants No. 62175083, No. 61935015 and No. 61825502, the Natural Science Foundation of Jilin Province No. 20230101359JC, and the Fundamental Research Funds for the Central Universities. This work at Zhejiang University was sponsored by the NNSFC Grants No. 11961141010, No. 61975176 and No. 62101485 and Key Research and Development Program of the Ministry of Science and Technology Grants No. 2022YFA1404704 and No. 2022YFA1405200.

Author contributions

Z.-H.X. and S.X. designed research; Z.-H.X., S.X., W.X., and W.S. performed research; Z.-H.X., S.X., H.C., and H.-B.S. contributed new reagents/analytic tools; Z.-H.X., S.X., H.R., W.S., Q.-D.C., H.C., and H.-B.S. analyzed data; and Z.-H.X., S.X., and C.Q. wrote the paper.

Competing interests

The authors declare no competing interest.

Data, Materials, and Software Availability

All study data are included in the article and/or SI Appendix.

Supporting Information

This article is a PNAS Direct Submission. G.H. is a guest editor invited by the Editorial Board.
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