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Reprogrammable metasurfaces, which establish a fascinating bridge between physical and information domains, can dynamically control electromagnetic (EM) waves in real time and thus have attracted great attentions from researchers around the world. To control EM waves with an arbitrary polarization state, it is desirable that a complete set of basis states be controlled independently since incident EM waves with an arbitrary polarization state can be decomposed as a linear sum of these basis states. In this work, we present the concept of complete-basis-reprogrammable coding metasurface (CBR-CM) in reflective manners, which can achieve independently dynamic controls over the reflection phases while maintaining the same amplitude for left-handed circularly polarized (LCP) waves and right-handed circularly polarized (RCP) waves. Since LCP and RCP waves together constitute a complete basis set of planar EM waves, dynamically-controlled holograms can be generated under arbitrarily polarized wave incidence. The dynamically reconfigurable meta-particle is implemented to demonstrate the CBR-CM’s robust capability of controlling the longitudinal and transverse positions of holograms under LCP and RCP waves independently. It’s expected that the proposed CBR-CM opens up ways of realizing more sophisticated and advanced devices with multiple independent information channels, which may provide technical assistance for digital EM environment reproduction.

Reconfigurable metasurface enriches the functional integrated design into the originally limited space. Electrical control, through the external power supply to control the electromagnetic response control, is a common and simple control method. However, current methods of electrical control require external biasing circuits and even metallized through-holes to power the metasurface, thus leading the design and machining of the metasurface more complicated. In order to address this problem, we propose a coplanar self-biasing structure with feeder-structure multiplexing. Metasurface design is generated under connectivity control, and the electromagnetic responses under different voltage states are searched. The designed metasurface is fabricated and verified by measurement, which can prove that the metasurface can control one-dimensional far-field scattering beams. Moreover, the deicing function of the metasurface with integrated biasing line is verified by infrared measurement. All the measured results are consistent well with the expected targets, which shows the effectiveness of our ideas. Importantly, our design opens up a new way to simplify the reconfigurable metasurfaces design, which has a wide application value in the dynamic control of metasurfaces.

Microwave absorbing materials (MAMs) are used to prevent electromagnetic pollution and enhance equipment stealth. However, their limited absorption intensity and narrow effective bandwidth restrict their applicability. MAMs with a single absorption mechanism, whether dielectric or magnetic, often exhibit poor impedance matching. This paper introduces a new multiscale approach—encompassing microstructures, mesostructures and macrostructures—for designing high-performance MAMs. At the microscopic–mesoscopic level, Pomb materials derived from pomegranate peel are combined with magnetic nanoparticles (Co3O4) using a hydrothermal method. The microwave absorption properties of these composite materials were examined by varying the proportion of Pomb materials in the absorber. The effective absorption bandwidth (EAB) reached 5.5 GHz for a thickness of 2.3 mm. At the macroscopic level, a metastructure based on Pomb@Co3O4 (0.1 g) was designed to achieve ultrabroadband absorption with an EAB of 15.56 GHz, a range of 2.24–18 GHz and a total thickness of 15 mm. Additionally, the radar cross-section value of Pomb@Co3O4 (0.1 g) is below − 10 dB m2 across the angle range of − 60° to 60°, with a maximum scattering intensity of only − 7.6 dB m2. This multiscale structure design offers a promising direction for future research and development in MAMs.

Abstract Metasurfaces have exhibited unprecedented degree of freedom in manipulating electromagnetic (EM) waves and thus provide fantastic front-end interfaces for smart systems. Here we show a framework for perception enhancement based on vision-driven metasurface. Human’s eye movements are matched with microwave radiations to extend the humans’ perception spectrum. By this means, our eyes can “sense” visual information and invisible microwave information. Several experimental demonstrations are given for specific implementations, including a physiological-signal-monitoring system, an “X-ray-glasses” system, a “glimpse-and-forget” tracking system and a speech reception system for deaf people. Both the simulation and experiment results verify evident advantages in perception enhancement effects and improving information acquisition efficiency. This framework can be readily integrated into healthcare systems to monitor physiological signals and to offer assistance for people with disabilities. This work provides an alternative framework for perception enhancement and may find wide applications in healthcare, wearable devices, search-and-rescue and others.

Miura origami's reconfigurable characteristic and structural asymmetry, combined with electromagnetic (EM) wave manipulation, crashed a unique spark. However, the complexity of the three‐dimensional (3D) origami structure after folding makes it challenging to study the phase regulation mechanism. Here, we propose a reconfigurable phase gradient metasurface based on Miura origami and derive the underlying mechanism of phase modulation in detail under linearly and circularly polarized (LP and CP) incidence. We adopt the one‐dimensional (1D) gradient design along the x direction to verify the idea. The phase calculation formulas are given under LP and CP incidence through the Jones matrix's derivation. The beam deflector angles corresponding to LP and CP waves are identical in the planar state. As the folding angle increases, the phase evolution rules corresponding to the LP and CP waves are discrepant, leading to differential beam steering. Finally, the origami sample is processed for verification, and the experimental data are consistent with the simulation and theoretically calculated values. We believe this work can help analyze the EM behavior of complex 3D origami structures and lay a foundation for designing a multifunctional EM origami metasurface.

Complex-amplitude holographic metasurfaces (CAHMs) with the flexibility in modulating phase and amplitude profiles have been used to manipulate the propagation of wavefront with an unprecedented level, leading to higher image-reconstruction quality compared with their natural counterparts. However, prevailing design methods of CAHMs are based on Huygens-Fresnel theory, meta-atom optimization, numerical simulation and experimental verification, which results in a consumption of computing resources. Here, we applied residual encoder-decoder convolutional neural network to directly map the electric field distributions and input images for monolithic metasurface design. A pretrained network is firstly trained by the electric field distributions calculated by diffraction theory, which is subsequently migrated as transfer learning framework to map the simulated electric field distributions and input images. The training results show that the normalized mean pixel error is about 3% on dataset. As verification, the metasurface prototypes are fabricated, simulated and measured. The reconstructed electric field of reverse-engineered metasurface exhibits high similarity to the target electric field, which demonstrates the effectiveness of our design. Encouragingly, this work provides a monolithic field-to-pattern design method for CAHMs, which paves a new route for the direct reconstruction of metasurfaces.

In this letter, we propose the design and manufacture of an all-dielectric metasurface using high-permittivity ceramics. The unit structure consists of a rectangular ceramic, which is asymmetric in the x and y direction. Electric and magnetic resonances are generated to form cross-polarization reflection. As an example, cross-polarization reflection is demonstrated both numerically and experimentally. This work not only gives the designing method but also discusses how to manufacture a large sample and the difference between ideal simulation and the practical sample. After a large number of simulations and experiments, the feasible design methods and problems needing attention in design are given. The experiment result is according to the adjusted simulated result. The result confirms the feasibility of the design and processing of an all-dielectric metasurface in the microwave band. If we can find a suitable material preparation process or optimize the unit structure that is easy to process, the all-dielectric polarization conversion metasurface can realize a maximum conversion efficiency of nearly 100% and form a broadband working band. Since such metasurfaces are made of low-loss high-permittivity ceramics, they are of important value especially in high temperature or high-power applications. This method can also be used to design all-dielectric metasurfaces in other frequencies by changing the geometry parameters.

Broadband and high efficiency are the two core indexes of absorption research, which usually requires a balance between them. Therefore, how to take into account both and achieve broadband and efficient absorption is a hot topic in current research. In this paper, by the compound design of multiple mechanisms, a kind of wideband hybrid metamaterial absorber (HMA) is proposed. The overall structure consists of a layer of patterned resistive film and a layer of magnetic absorbing material (MAM) separated by the air. The resistive layer is designed as square ring type to regulate the local magnetic field, which results in significant magnetic field enhancement within the MAM layer, and this mechanism provides a prerequisite for wideband and high-efficiency absorption in the low frequency band. Furthermore, due to the electrical losses of the resistive film, another absorption band is additionally excited in the high frequency band. Thanks to the multiple mechanisms, the absorption efficiency above 90% in the 3.2–22.0 GHz frequency band can be realized, and the thickness of the overall structure is 7.0 mm that is 0.07 of the wavelengths at the lowest frequency point. To demonstrate this method, a prototype is designed, fabricated and measured. Both the simulation and experiment results verify the effectiveness of the proposed method. This work provides a new method to design wideband and high-efficiency electromagnetic absorption structures and may find potential applications in multi-functional planar or conformal structures.

Humans have been long dreaming of obtaining the ability of changing electromagnetic (EM) attributes intelligently according to the environment so as to camouflage just as chameleons do. Thanks to the unprecedented high degree of freedom in manipulating EM waves, metasurfaces can mimic EM characteristics of various environments vividly and have pushed a giant step towards this long-desired dream. Nevertheless, for most metasurfaces, the EM characteristics are fixed and thus cannot be altered according to changing environments, which hinders their applications in intelligent scenarios such as moving target camouflage. With the aim to achieve intelligent camouflage, in this work we propose a chameleon-like framework for intelligent camouflage based on EM metasurface, which integrates transfer-learning-empowered perceptron into a reconfigurable metasurface. As a demonstrative example, a chameleon-like intelligent camouflage metasurface (CLICM) system with robust extendibility was developed and measured in laboratory. The system can dynamically control the reflection spectrum in 5.1–6.5 GHz according to what it sees. Both the simulation and experiment results verify this framework. This work provides a perceptron-algorithm-metasurface framework with robust extendibility for intelligent EM manipulation and may find wide applications in camouflage and wireless communication.

Abstract Diffusion‐like scattering along multiple directions based on coding metasurface (CM) is proposed for both mono‐static and bi‐static radar cross section (RCS) reduction in this work. Different from the previous CMs achieving diffusion‐like scattering only in one direction, the proposed CMs can realize diffusion‐like scattering along multiple directions via designing the phase spatial distributions of the consisted coding elements. The multiple diffusion‐like scattering CMs were designed by using the co‐polarization reflection resonators under circularly polarized wave incidence based on Pancharatnam–Berry (PB) phase. By elaborately arranging the phase spatial distribution of coding elements, two, three, and four beams of diffusion‐like scattering were realized. The bi‐static RCS reduction was improved with increasing number of the backward diffusion‐like scattering beams. The measured results agree well with the simulations, and both demonstrated the excellent performance on mono‐static and bi‐static RCS reduction. Our strategy can help realize stealth applications under bi‐static detections.

Metasurfaces, which are usually passive or non-radiating, have provided unprecedented degree of freedom especially for scattering manipulation. For the manipulating radiation, metasurfaces often serve as auxiliaries to radiators since they cannot radiate themselves. Thus, it is unfavorable for integration and miniaturization. In this work, we propose the concept of active–passive compound metasurface (APCM) and explore the possibility of utilizing meta-atoms as active radiators, so as to simultaneously achieve flexible radiation and scattering manipulations at the same time. To this end, a meta-atom structure with large reflection phase-span is delicately designed. In this way, the meta-atom can serve both as wideband radiator fed by a probe and reflection-phase modulator. Flexible scattering-pattern manipulation for one polarization state and high-efficiency radiation-pattern manipulation for the orthogonal polarization state can be simultaneously achieved within the same band from 8.0 to 12.0 GHz. As a proof of concept, two prototypes, one for scattering-cancellation and high-directive radiation while the other for deflected reflection and vortex-beam radiation, were designed, fabricated, and measured, respectively. Both the simulated and measured results verify the active–passive compound design. This work paves an alternative route to integrated multi-functional materials or interfaces and may find wide applications in next-generation communication, radar, smart skin, and others.

Abstract In this paper, a novel dual‐stopband frequency selective surface (FSS) based on the knitted and strong‐coupled structures is proposed. The proposed FSS works stably at frequencies of 2.51 and 5.06 GHz for both TE and TM mode, even when the incident angles vary from 0° to 75°. The element size and thickness of the proposed structure are λ0/16 and λ0/170, respectively, where λ0 represents the free‐space wavelength. To clarify the operating principle, a general equivalent circuit model (ECM) is developed. A prototype of the proposed FSS is fabricated and measured. It is demonstrated that the proposed structure has good angular stability, polarisation insensitivity, and independent operation in the dual‐stopband. Importantly, the proposed structure has good prospects for application in dual‐band electromagnetic shielding in complex environments.

Reconfigurable metasurfaces have enriched metasurface design with a wide range of application prospects. However, traditional reconfigurable phase-modulated metasurfaces primarily rely on active devices such as diodes to change the resonant response, which means that many feeders and external circuitry are additionally loaded on the metasurface, thus leading the increasing complexity for metasurfaces design. In this paper, a reconfigurable phase-modulated metasurface based on adjustable chip resistor is proposed to control the reflected phase by rotating the knob of the rheostat. The designed metasurface can realize the functional reconstruction without external circuitry. As an example, a reconfigurable digital coding metasurface is fabricated, which is verified through both the simulation and experimentation. All the results show that the designed sample can customize the far-field scattering mode. This work provides a new idea for reconfigurable metasurfaces, which will lay the foundation for the intelligent control of metasurfaces.

The Airy beam has intrigued long-held research interests and developed various striking applications attributed to the unprecedented diffraction-free, self-bending and self-healing properties. Metasurfaces with superior design freedom and small structure size open a fire-new avenue for generating efficient and broadband Airy beam. Nevertheless, most existing Airy beam generators can only respond to one polarization state of electromagnetic waves and produce the single Airy beam, which immensely limit the serviceability and utilization of the Airy beam generators. Herein, an inspiring strategy of multichannel Airy beam generator based on the multichannel amplitude and phase controlled metasurface is proposed to independently generate the Airy beams for linear polarized waves in 20–24 GHz and orthogonal circular polarized waves in 12–14 GHz and 15–17 GHz. Notably, an appealing paradigm of multichannel beam focusing can be realized by the integrated multichannel Airy beam generator, which possesses strong ability to circumvent the obstacle owing to the self-healing feature of the Airy beam. A proof-of-concept prototype is constructed to verify the feasibility of our methodology, and multitudinous simulations and experiments are in excellent accordance with our theoretical predictions. This novel design of multichannel Airy beam generator will have tremendous application potential in sensing, communication and other multifunctional metadevices.

Abstract Spin light manipulation based on chiral metasurfaces is a striking hotspot that has intrigued huge attention. Circular dichroism, a unique phenomenon of chiral atoms/molecules, has been regarded as another auxiliary dimension for guiding electromagnetic waves, which has been explored in the field of artificial material sciences yet a challenging issue. Here, a generic strategy based on dynamic chiral meta-atom for revealing strong circular dichroism as well as applicable electromagnetic functionality is proposed in microwave regime. We demonstrate a dynamic metasurface that enables the fully independent holograms reconstruction for one circular polarization or the other at the active operating state. On the other hand, the electromagnetic scattering is realized for lowering observable backward reflection at the passive state. Numerical simulation and experimental verification are conducted to manifest the feasibility. It is expected that the proposed strategy can be applied to broaden the horizon for dynamic chiral meta-devices and may find applications in information encryption, anti-counterfeiting, and other dynamic systems.

In order to achieve compatibility stealth for the radar stealth and infrared stealth, a multifunctional coating for achieving both radar stealth through the polarization conversion and infrared emission reduction at high temperature was skillfully designed in this paper. The multifunctional coating consists of three layers, from outside to inside, followed by the metasurface, the high-temperature resistant dielectric and the metal background. The radar stealth at microwave frequency was mainly generated from polarization conversion excitation through the unsymmetrical metasurface structure. Infrared emission reduction is attributed to the reflection of the metasurface with a high filling ration. By the simulation, radar stealth with an efficiency of 90% could be achieved in the low-frequency band of 5.2-7.8 GHz, and the infrared emission of the multifunctional coating could be as low as 0.22. Furthermore, the experimental results at different temperatures demonstrate that the theoretical design is effective. The measured co-polarization reflection in the 5–9 GHz frequency band is below −8 dB and lower as the frequency increases, indicating more than 84% polarization conversion is achieved. A low emission performance is also validated, with the mean emissivity as low as 0.25. Because of the excellent multispectral compatibility, the multifunctional coating may find applications in multispectral stealth technology.

A novel array antenna with reconfigurable polarizations and radiation pattern agility is presented in this paper. The digital-controllable array antenna has the functional capabilities of reconfigurable polarization and switching beam, which consists of cavity-backed antenna element based on substrate integrated waveguide (SIW) technique, parasitic patch array, power dividers and phase shifters. Polarization modes and radiation patterns can be dynamically controlled by means of Microcontroller Unit (MCU) with the different feeding ports and phase difference. To validate this proposal, the performance of the fabricated device was measured at the operating frequency of 5.4 GHz. Measured results indicate that the 10 dB impedance bandwidths and 3 dB axial ratio (AR) bandwidths cover from 5.25 to 5.6 GHz, and the measured gains range from 7.9 to 10.1 dBic. The experimentation and simulation verify that the proposed antenna can achieve two polarization states and five radiation beams of each polarization state, which indicate a good performance of the polarization reconfigurable and beam switching antenna array.

Chromatic dispersion in phase gradient metasurface and its impact on the scattered electromagnetic signals are studied in this paper. Due to its intrinsic material dispersion and special spatial arrangement of unit cells, phase gradient metasurfaces produce large chromatic dispersion for the scattering waves, resulting in anomalous reflection and refraction phenomena. Moreover, from the perspective of signal domain, the scattered waves no longer carry the whole information of the incident wave, especially for the wideband ones, because different frequencies are scattered into different directions due to the large chromatic dispersion. This progress is equivalent to a signal modulation in each scattering direction. Here we utilized a simple calculation method to achieve the direction-related spectral response characteristic for a given metasurface using 2D Fourier transform of the 2D phase pattern. Furthermore, a typical wideband radar signal was adopted to give a visualized display of the modulation effect. The simulated results showed that the scattered signals were greatly distorted, causing the correlation reduction and range deviation in radar detection. This work opens a new possibility for metasurface to manipulate the signal characteristic of electromagnetic waves and may prompt new applications in antennas, communication and radar systems

Self-adaptable materials with autonomous morphological transformation by sensing environmental changes have emerged as one of the most promising but challenging approaches for various chiral devices. Unlike previous work on reconfigurable chirality through human intervention, we proposed a temperature-adaptive chiral meta-device. It can autonomously sense the environment and manipulate the optical chirality through 3D-to-3D morphological transformation. As a proof of concept, a 3D morphable chiral meta-device was designed with shape memory alloy (SMA), resulting in reconfigurable circular dichroism (CD). The curving direction of SMA enables the meta-device to switch between left-handed, right-handed, and non-chirality by sensing environmental temperature. The analysis of surface currents and CD spectra reveals that the underlying physical mechanism behind the chirality originates from the surge of toroidal and electric quadrupole dipole moments. Simultaneously, the spin-to-orbital angular momentum conversion is realized based on the Pancharatnam-Berry phase, where the topological charge is modulated by the environmental temperature. Encouragingly, this work paves the way for the self-adaptive chiral meta-devices with 3D morphological transformation and can be applied to a series of novel photon-spin-selective devices for optical communication and biosensing.

Holography has been continuously spurring tremendous interest of researchers attributed to its unparalleled capability of photographically reconstructing the desired images. Based on the metasurfaces with multiple degrees of freedom, multiplexing meta-holograms are experiencing the research upsurge because of enormous application potential. However, existing multiplexing meta-holograms cannot tailor the amplitude information, and possess limited imaging channels and high channel crosstalk, which hinder the improvement of information capacity and imaging quality of multiplexing meta-holograms. Herein, an innovative multiplexing meta-hologram based on the helicity-assisted meta-atoms is proposed, which can perfectly reconstruct four independent images by altering the working frequency, polarization state and propagation direction of incident waves, and theoretically realize the holography in sixteen different channels by easily rotating, mirroring, and arranging the structures of meta-atoms. Numerous simulations and experiments collectively corroborate the feasibility of our methodology, and the quantitative analyses verify the high fidelity of the reconstructed images, which results from the low crosstalk between the amplitude modulation and phase modulation in different imaging channels. This inspiring strategy of multiplexing meta-hologram with large channel capacity and high imaging quality will have promising application prospects in information display, storage and encryption, and provide an alternative path for the design of multifunctional microwave devices.

Metasurfaces can provide unprecedented degree of freedom in manipulating electromagnetic waves and have been introduced to holography. Aiming to explore the full capability for information presentation, vectorial metasurface holography is sprung up, which exhibits mesmerizing capability in carrying information compared with scalar counterpart. However, the more flexible modulation means the more complex design dimension, which hinders the development of vectorial metasurface holography. In this work, we propose an orthogonal I-shaped structure embedded with resistors to synthesize arbitrary polarization with less crosstalk. Benefiting from the independent control of phase and amplitude on orthogonal base, the orthogonality-simplified machine learning framework is employed to assist vectorial metasurface holography design. As a proof-of-concept, a vectorial metasurface holography carrying multi-polarization information was designed, simulated and measured. All the results exhibit a high degree of consistency, which fully demonstrates the effectiveness of our design. Encouragingly, our method paves a new route to simplify machine learning framework based on physical significance, which can be handily extended to more functional structures.

In this study, we present a high temperature-resistant linear-to-linear polarization conversion metasurface for wideband RCS reduction in the microwave regime. The linear-to-linear polarization conversion metasurface is composed of a single layer high-temperature-resistant metallic pattern array. When linearly polarized waves impinge on the metasurface, the polarization conversion rate is greater than 90% from 9 GHz to 16.8 GHz at 800°C. The polarization conversion unit arrangement forms a checkerboard configuration metasurface, which can effectively reduce RCS reflection. The wideband RCS reduction mechanism is scattering cancellation rather than absorption. The metasurfaces were designed, fabricated, and measured, which can realize linear-to-linear polarization conversion and wideband RCS reduction. The simulation results and measurement results are all in good agreement. Meanwhile, the measurement provides a solid verification for our design. The results provide an alternative method to reduce the RCS at high temperatures.

The design and optimization of a metasurface is a computationally- and time-consuming effort. Here, the authors propose a neural network-based algorithm for functional metasurface design, and demonstrate it for some functional metasurfaces.

At present, research on metamaterials is continuously advancing to engineering applications, and great progress is being achieved in the areas of physical mechanisms and effects, design theory and methods, and fabrication and measurement. However, traditional metamaterials design mainly relies on artificial design and optimization. In the face of large-scale engineering applications, it is impossible to realize the rapid overall design of a large number of metamaterial structural units. In recent years, the proportion of intelligent algorithms covering traditional heuristic algorithms and neural network algorithms in metamaterials design has increased gradually. Metamaterials design based on intelligent algorithms can surpass the limitation of traditional methods in different substrate systems, frequency variation, and different performance indicators, offering the unique advantages of rapid design and architectural innovation. This paper summarizes the application of several typical intelligent algorithms, including the genetic algorithm, Hopfield network algorithm, and deep learning algorithm in metamaterials design, which include forward designs and an inverse design. The use of intelligent algorithms can achieve the rapid design of frequency selective surfaces under different performance indexes, multi-mechanisms composite absorber metamaterials, flat focusing, and abnormal reflection metasurfaces, providing the necessary support for design methods while promoting the engineering applications of metamaterials.

The low RCS level out of operating band is urgent for radome while keeping its communication window. To solve this problem, we propose a frequency selective rasorber (FSR) that exhibits a pass-band between two absorption bands in this paper. The surface currents on a finite metallic wire media is analyzed firstly to elaborate transverse standing waves mechanism. High-efficiency and broadband absorption can be achieved by loading lumped resistors at high amplitude of standing waves. By delicately engineering the transverse standing waves versus frequency, a transparent window can be opened within an absorption wideband and it can be modulated by adjusting structural parameters. The transparent window centered around 10.0 GHz in the absorption band from 5.8 GHz to 18.0 GHz. Prototypes were fabricated and measured. Both the simulated and measured results show that for both x- and y-polarized waves, insertion loss of the transparent window at 9.85 GHz is below 0.2 dB while the absorption is above 90% in the two sidebands of 5.8-7.8 GHz and 11.8-18.0 GHz. Furthermore, the rasorber can also work well under oblique incidence angles up to 45 degrees. This work may find wide applications in electromagnetic compatibility, stealthy radomes, etc.

Abstract In this paper, we propose a method of designing ultra-wideband single-layer metasurfaces for cross-polarization conversion, via the introduction of Fano resonances. By adding sub-branches onto the unit cell structure, the induced surface currents are disturbed, leading to coexistence of both bright and dark modes at higher frequencies. Due to the strong interaction between the two modes, Fano resonance can be produced. In this way, five resonances in all are produced by the single-layer metasurface. The first four are conventional and are generated by electric and magnetic resonances, whereas the fifth one is caused by Fano resonance, which further extends the bandwidth. A prototype was designed, fabricated and measured to verify this method. Both the simulated and measured results show that a 1:4.4 bandwidth can be achieved for both x- and y-polarized waves, with almost all polarization conversion ratio (PCR) above 90%. This method provides an effective alternative to metasurface bandwidth extension and can also be extended to higher bands such as THz and infrared frequencies.

Based on polarization conversion metamaterial, a novel method to counter single-polarization radar is proposed and discussed in this paper. Due to the resonance feature in the polarization conversion, energy attenuation and waveform distortion dual functions can be achieved. For radar, that will strongly reduce the SNR (Signal-to-Noise Ratio) of the matched filter and the probability of detection. A broadband polarization conversion metamaterial structure was designed with multi resonance frequencies. To evaluate the effectiveness, a typical pulse compression radar model was established, the waveform property, correlation loss in the matched filter and probability of radar detection were simulated and calculated. It was found that the metamaterial achieved the function of passive signal modulation, the echo energy was reduced markedly and great distortion was generated near the resonance frequencies, also the correlation loss in the matched filter was significantly increased especially near the resonance frequencies. Finally the calculated probability of radar detection gave furthermore proof of the effectiveness of the method.

The integration of the metasurface and antenna has brought new vitality to function integration and performance improvement for metasurfaces. In this study, we propose a radiation-scattering–integrated (RSI) design method of functional metasurfaces by incorporating antenna radiators into the substrates. The antenna radiators can also be considered as a band-stop frequency selective surface (FSS) embedded within the dielectric substrate, which adds up to the degree of freedom (DOF) in tailoring electromagnetic (EM) properties of the substrate. In this way, not only radiation function is added to the metasurfaces but also the original scattering-manipulation function is augmented. As an example, we apply this method to the design of a metasurface that can achieve a high radiation gain in-band and low-RCS out-of-band simultaneously. An antenna array was first designed, which uses circular patches as the radiators. Then, the antenna array was used as the substrate of a typical polarization conversion (PC) metasurface. The circular patch lies between the ground plane and the PC meta-atom, providing optimal electrical substrate thickness for PC at two separate bands. By adjusting structural parameters, the operating band of the antenna array can be made to lie in between the two PC bands. In this way, the metasurface can simultaneously possess high-gain radiation function in-band and high-efficiency PC function for RCS reduction out-of-band. A prototype was fabricated and measured. Both the simulated and measured results show that the metasurface can achieve satisfactory radiation gain in-band and significant RCS reduction out of band. This work provides an alternative method of designing multi-functional metasurfaces, which may find applications in smart skins and others.

A reliable numerical simulation method and large-scale in-situ test method for super-thick coal seams are very important to determine the failure range of mining floors, which is often the basis to protect Ordovician limestone water, an important drinking water source for people in North China. This paper takes Yushupo Coal Mine as an example; the explicit–implicit coupling simulation method and the corresponding double scalar elastic–plastic constitutive model were established to predict the failure depth of the floor numerically, and verified by the full section borehole stress–strain in-situ testing method. The results show that the explicit–implicit coupling numerical program and the double scalar elastoplastic constitutive model are suitable for predicting the floor failure depth under the condition of extra-thick coal seams. In this condition, the overburden moves violently, resulting in a loading–unloading–reloading process with large stress variation amplitude in the mining floor, which leads to serious rock failure compared with that of medium-thick coal seam conditions. In Yushupo 5105 working face, the floor failure starts to develop from 9.3–24.2 m ahead of the coal wall of working face, and the failure depth no longer increases after 35 m behind the coal wall, with the maximum failure depth of 28 m; the envelope line of the floor failure depth presents an inverted saddle distribution. The above research results lay a foundation for further protecting the Ordovician limestone water, and realizing green coal mining.

Improving the microwave absorption performance of Co-MOF-derived Co@N-C composite by constructing the morphology and spatial structure is a known challenge. In this work, under the action of the binder polyvinylpyrrolidone, 3D-graphene particles can be well decorated on the surface of the Co@N-C composite after high-temperature pyrolysis. In addition, due to the structural characteristics of MOFs, Co particles can be well covered by a carbon layer, which effectively solves the problem that magnetic metal particles are prone to corrosion and oxidation. The microwave absorption performances of the composite can be well adjusted by changing the average dotted density of the 3D-graphene on the Co@N-C composite. It is worth noting that the maximum reflection loss can reach −58.72 dB at the thickness of 1.64 mm, and the maximum effective absorption bandwidth can achieve 5.74 GHz at the 1.79 mm thickness, which almost covers the whole Ku band. Importantly, these results demonstrate that 3D-graphene@C/Co@N-C composites have great potential as high-efficiency microwave absorption materials.

According to the principle of Babinet, this paper designs a novel frequency selective surface (FSS) with high performance. Using the Babinet principle, an asymmetric Jerusalem cross patch structure and its complementary aperture structure are mixed on one side of the dielectric substrate, namely, self-complementary FSS (SCFSS). The theoretical analysis and experimental results show that SCFSS has excellent multi-bands polarization separation characteristics in different frequency ranges. In each passband, the insertion loss is less than 0.5 dB, and the out-of-band suppression level is relatively high. By individually adjusting the size of a certain structural parameter of SCFSS, the position of polarization separation frequency band can be adjusted in a specific frequency band range, thus meeting the requirements of the practical application. By rotating the surface, its filtering characteristics for polarized waves of a certain mode can be mechanically tuned from bandpass to bandstop. Furthermore, the SCFSS has an excellent incident angle stability in a wide range from 0° to 60°. Therefore, when designing polarization separation structure and polarization wave generator for the wireless communication system (such as the satellite communication system), the novel SCFSS structure proposed in this paper can provide an excellent reference.

In this paper, a novel frequency selective surface (FSS) is designed; it has the characteristics of the low profile, second-order, multi-band, and the remarkable polarization selection properties. In the following, such an FSS having polarization selection characteristics will be referred to simply as a polarization selection surface (PSS). In a specific frequency band, the proposed PSS has a second-order selective transmission characteristic for TE and TM waves. Based on the coupling resonance filtering mechanism, the proposed PSS is composed of three metallic layers separated by two layers of dielectric substrates, which serves as the spatial form of the second-order microwave filter. The proposed PSS uses a sub-wavelength periodic structure array consisting of a non-resonant unit, and the unit size and the period within the range of 0.08λ1-0.15λ1, where the λ1 = 40.76 mm is the first passband wavelength of free space, so the PSS miniaturization characteristic is remarkable. The theoretical analysis and measure results show that the proposed bandpass PSS has good second-order polarization selection characteristics, out-of-band suppression level, and the flat transmission band, compared with the first-order bandpass PSS. In the range of incident angle of 0°-60°, it has a stable frequency response. It provides a reference for the design of a polarization wave generator and a polarization separation structure in a multipath communication system.

In this paper, we propose to enhance the transmission of EM waves through fiber-reinforced polymers (FRPs) by modifying the local field distributions using the metamaterial inclusions. Due to the higher permittivity of FRPs relative to the air, the transmission of the s-polarized waves decreases drastically with the incidence angle θi. By doping metallic strips into an FRP plate, the magnetic vectors in the plate are tilted vertically under large incidence angles, and hence, the refracted angle in the plate is increased. This is equivalent to reduce the effective permittivity of the FRP, which enables significant transmission enhancement, especially under large incidence angles. A Ku-band prototype was designed, fabricated, and measured. Both simulated and measured results verify that the metamaterial doping can achieve transmission enhancement in an ultra-wide incidence angle range θi ∈ [0, 80°]. This paper provides an effective route to the design of transparent radomes for base stations, aircraft, and so on.

A broadband tunable metematerial absorber is proposed and demonstrated. As demonstrated in waveguide, the absorber consists of eight U-shaped ferrite particles and a metallic ground plane. These U-shaped ferrites directly act as resonators, and when the incident electromagnetic wave and applied magnetic field are simultaneously acting on the U-shaped ferrite particles, U-shaped ferrites can produce ferromagnetic resonance (FMR). Absorption frequency of the all-ferrite absorber can be tuned by the applied magnetic field and the saturation magnetization. Simulation results show absorption above 70% in the frequency range from 8.55 GHz to 10 GHz under applied magnetic field with H0 = 2700 Oe. By analysis, we find that the magnetic loss and dielectric loss lead to broadband absorption. The experiment test agrees well with the simulation results under different applied magnetic fields. This work provides an alternative route to realize tunable perfect absorbers with all-ferrite structures. With the artificial design of ferrite materials, the broadband tunable absorber can be designed and well serve in high power environment.

The compatible stealth functionality in the infrared (IR) and radar wave bands is the most important research topic in the field of stealth material technology. Here, a new hybrid metasurface (HMS) for infrared-multiband radar stealth-compatible materials was proposed and studied. Two specifically designed metasurface layers that can control the infrared emission and microwave absorption were combined to realize radar and IR bi-stealth. The simulated and experimental results show that the HMS has five strong absorption peaks at f1 = 6.35, f2 = 8.38, f3 = 12.10, f4 = 15.37 and f5 = 18.05 GHz. In addition, the emissivity of the proposed HMS is less than 0.32 from 3 to 14 μm and shows low emissivity characteristics in the infrared band. These results demonstrate that the proposal has practical application to multispectral stealth technology.

In this paper, we propose a strategy to achieve a single-feed multi-beam metasurface antenna by combining phase gradient and coding sequence. Theoretically, the multi-beam antennas with various far-field patterns can be realized via superimposing different kinds of phase coding sequences. As three proof-of-concepts, the 0101.../0101...coding sequence, chessboard coding sequence, and 1-bit sector coding sequence are selected to design double-beam, four-beam, and eight-beam circular-polarized reflector antennas, respectively. Furthermore, the four-beam reflector antenna is fabricated and measured to demonstrate the feasibility of our strategy. The fabricated antenna can produce four perfect pencil-shaped beams in a wide frequency range from 11 to 13 GHz. At central frequency, the realized gain is about 19.9 dB and the axial ratio is lower than 3 dB. Moreover, the circular polarization state of the reflective beams is consistent with the polarization state of spot source, which differs from the reflector antennas based on the polarization-insensitive unit cells. This paper connects the multi-beam patterns with binary digits, which provide the potential for reconfiguring the multi-beam patterns by computer programs.

In this paper, a novel design of a co-polarized transmission window within the cross-polarized reflection band of a polarization converted meta-surface (PCM) is presented. First, a dual-band reflective polarization converted meta-surface is designed. In each band, the incoming linearly-polarized electromagnetic wave will be efficiently reflected with its cross-polarized state. The two bands are separated by a co-polarized reflective band. Second, a pass-band frequency selective surface (FSS) with the high-selective response is constructed. Its operating pass-band is positioned in the same range as the co-polarized reflective band of the PCM. Third, the reflected PCM without metal backing is integrated with the pass-band FSS, namely, a novel dual-band reflected PCM with a transmission window is realized. The -0.5dB-bandwidths of the two cross-polarized reflective bands are about 3.8 GHz (5.66~9.46GHz) and 2.0 GHz (16.9~18.9GHz), respectively. The -3-dB bandwidth of the transmission window is approximately 1.35 GHz (12.2~13.55 GHz). Lastly, the proposed structure prototype is fabricated and tested. The measured results are in good agreement with the simulated ones. In addition, the principle of operation and detailed design is also presented and discussed.

In this paper, the design of a synthetical absorber with topology optimization resistance frequency selective surface and metal wires array structure is proposed. This design attempts to provide a broadband strong absorption over wide-angle incidence at microwave band, especially for TE-polarization wave. Commonly, thickness is positively correlated with the absorption performance, and the thin thickness with high absorption of the absorber is taken into adequate consideration in our work. As a result, the optimal structure designed by genetic algorithm achieves absorption over a wide frequency range of 8.2 to 19.5GHZ with reflection below -10dB and the broadband absorption is tolerant for the incident angle under 70 degrees (high absorption less than 60 degrees). The results of experiment and simulation are highly consistent. What's more, the thickness of the resistive frequency selective surface and metal wires' dielectric substrate are 2mm and 0.4mm respectively, enabling a wide range of applications in stealth technology, electromagnetic radiation protection, electromagnetic control and so on.

Tailoring electromagnetic properties by meta-devices has aroused great interest with respect to manipulating light. However, the uncertainty of angular dispersion introduced by the incident waves prevents their further applications. Here, we propose a general paradigm for achieving dual-transmission windows while simultaneously eliminating the corresponding angular dispersions by a dynamic manner. The strategy of loading varactor diodes into a plasmonic meta-atom is used. In this way, the blue shifts of angular dispersion can be dynamically compensated by the red shifts introduced by the varactor diodes when driven by bias voltage. As a proof-of-principle, an active meta-atom with varactor diodes is presented. The varactor diodes embedded can independently regulate dual-transmission windows. The test results are consistent with the simulation ones. The presented meta-device is used for intelligent radome, angle-multiplexed communications, and incident-angle-insensitive equipment while providing tunable angular dispersion properties.

Foam sandwich structures reinforced with the fiber column arrays are proposed to achieve broadband absorption at microwave frequencies as well as good mechanical properties. To achieve the microwave absorption, two layers of resistive films are embedded into the sandwich structures. The results show that the proposed sandwich structure with the whole thickness of 9.73 mm can achieve broadband absorption with the reflection less than −10 dB in the frequency range of 2.6–21 GHz. The absorption mechanism has been discussed by using the equivalent circuit model. It is further indicated that introduction of the fiber column array in the sandwich structure has little influence on the absorption performance, but can remarkably enhance the mechanical properties. This has been well demonstrated experimentally by three-point bending experiment. Compared with the ordinary sandwich absorbing structures, enhanced mechanical properties make the designed structure suitable in some loading applications. It is expected that the proposed multifunctional structure may find great potentials in the applications of stealth technology, electromagnetic interferences and so on. Keywords: Sandwich structure, Broadband absorption, Mechanical properties, Equivalent circuit model

In this paper, the magnetic squeezing effect in metamaterials is explored and applied to achieve wideband absorption in low-frequency microwave bands. To this end, a metamaterial absorber (MA) is proposed, which consists of a square lattice of a split ring resonator (SRR) placed on top of a magnetic absorbing material (MAM) layer backed by a conducting ground. In the positive resonance region of SRRs, a strong magnetic squeezing effect occurs and more concentrated magnetic field lines are confined within SRRs. This results in significant magnetic field enhancement within the MAM layer, which provides a prerequisite for high-efficiency absorption enhancement at low frequencies. To verify this method, we fabricated a prototype using a 3.0 mm thick silicone MAM sheet. Both the simulation and experiment results show that with the assistance of magnetic squeezing in the SRR array, the absorption at lower frequencies is significantly enhanced and is above 90% in 1.25–2.31 GHz under normal incidence. Furthermore, the MA exhibits satisfactory stability for different polarization states and incident angles due to the square lattice of the SRR array. This design method may find potential applications in fields such as electromagnetic compatibility, wireless communication, and others.

Edge scattering is one of the main scattering sources for metal objects, especially for those with thin front edges. In this paper, based on the principle of scattering cancelation, a coding metasurface purfle is proposed and employed to suppress the edge back-scattering of electromagnetic (EM) waves. To this end, two split-ring resonators with a π phase difference between them are designed to act as the 0- and 1-element of the coding metasurface. The coding metasurface fixed on the front edge of a thin metal plate can reduce the edge back-scattering significant for EM waves polarized along the edge direction due to the anti-phase scattering of the two coding elements. Both the simulation and experiment results verify the reduced back-scattering of the flat edge. A maximal reduction of 24 dB is attained within the central frequency of about 11 GHz. This work provides a novel alternative to suppressing edge scattering and may find applications in EM compatibility, radar stealth technologies, etc.

In this paper, the idea of spoof surface plasmon polaritons (SSPPs) realized by unidirectional carbon fibers (CFs) arrays are proposed and investigated. A structure/function integrated sandwich structure (SISS) with excellent microwave absorption and mechanical properties was designed. It is composed of two corrugation layers with gradient CFs arrays between them. According to our research, the absorption performance can be modulated by adjusting structure parameters. As the corrugation angle increases, the absorption performance becomes better whether in normal or oblique incidence. In addition, compression tests were also performed and the results indicate that this proposal can realize a higher compressive strength at a lower sandwich core density. The compressive strength is more than 3 times comparing with 304 stainless steel (SS) corrugation when the core density is 0.25 g/cm3. This structure/function integrated design is more competitive in practical applications comparing with other metamaterials topologies.

Plasmonic structures that support the spoof surface plasmon polariton (SSPP) mode can be tailored to achieve strong absorption of electromagnetic (EM) waves. In particular, the profile of an absorbing plasmonic structure (APS) plays an important role in realizing its wideband absorption performance. In this paper, we propose a method of optimizing the longitudinal profile of APS based on Genetic Algorithm (GA), with the aim of obtaining high-efficiency wideband absorption of EM waves. The APS unit cell is composed of a longitudinal array of metallic strips, the length profile of which can be optimized to improve k-matching between free-space waves and SSPPs and meanwhile to customize absorption at each frequency within a wide band. Our investigation shows that non-linear variation of the strip lengths will make better k-matching and wideband absorption. As an example, a wideband APS is demonstrated using this method. The simulated and measured results show that the absorbance is higher than 90% in 10–30 GHz, which convincingly verifies the effectiveness of this method. This method provides an efficient approach to the design of radar absorbing structures and can also be extended to optimized design of other metamaterials.

Abstract Metasurfaces provide unprecedented routes to manipulations on electromagnetic waves, which can realize many exotic functionalities. Despite the rapid development of metasurfaces in recent years, the design process of metasurface is still time‐consuming and computational resource‐consuming. Moreover, it is quite complicated for layman users to design metasurfaces as plenty of specialized knowledge is required. In this work, a metasurface design method named REACTIVE is proposed on the basis of deep learning, as deep learning method has shown its natural advantages and superiorities in mining undefined rules automatically in many fields. REACTIVE is capable of calculating metasurface structure directly through a given design target; meanwhile, it also shows the advantage in making the design process automatic, more efficient, less time‐consuming, and less computational resource‐consuming. Besides, it asks for less professional knowledge, so that engineers are required only to pay attention to the design target. Herein, a triple‐band absorber is designed using the REACTIVE method, where a deep learning model computes the metasurface structure automatically through inputting the desired absorption rate. The whole design process is achieved 200 times faster than the conventional one, which convincingly demonstrates the superiority of this design method. REACTIVE is an effective design tool for designers, especially for laymen users and engineers.

Polarization-correlation customizable metasurface absorbers based on circular dichroism (CD) meta-atoms were proposed in this paper, of which the polarization-correlation can be altered by controlling the coupling effect between the CD meta-atoms with the same chirality. CD meta-atoms implemented via introducing resistance film into chiral resonators were firstly proposed. Wideband, high-efficiency left-handed/right-handed CD meta-atoms were demonstrated, respectively, for which the left-handed/right-handed circularly polarized (LCP/RCP) incident wave was strongly absorbed but the RCP/LCP incident wave was reflected into LCP/RCP wave with high efficiency. The metasurface absorber consisting of CD-meta-atom pairs were put forward for polarization-correlation customizable absorption. The coupling between two CD meta-atoms was investigated by theoretical and simulation analysis, which can be manipulated by controlling the orientation angles of the CD meta-atoms. As a proof-of-concept, a polarization-insensitive absorber utilizing a C _4 2 × 2 CD-meta-atom pair was designed, simulated and measured. Attributed to the strong coupling between the four CD meta-atoms, both LCP and RCP wave were strongly absorbed in a wide frequency range from 8 GHz to 20 GHz. This paves a new way for designing wideband metasurfaces with polarization-correlation customizable performance.

Ultra-sensitive inertial sensors are one of the key components in satellite Earth’s gravity field recovery missions and space gravitational wave detection missions. Low-noise capacitive position transducers are crucial to these missions to achieve the scientific goal. However, in actual engineering applications, the sensor head and electronics unit usually place separately in the satellite platform where a connecting cable is needed. In this paper, we focus on the stray-capacitance influences of coaxial cables which are used to connect the mechanical core and the electronics. Specially, for the capacitive transducer with a differential transformer bridge structure usually used in high-precision space inertial sensors, a connecting method of a coaxial cable between the transformer’s secondary winding and front-end circuit’s preamplifier is proposed to transmit the AC modulated analog voltage signal. The measurement and noise models including the stray-capacitance of the coaxial cable under this configuration is analyzed. A prototype system is set up to investigate the influences of the cables experimentally. Three different types and lengths of coaxial cables are chosen in our experiments to compare their performances. The analysis shows that the stray-capacitance will alter the circuit’s resonant frequency which could be adjusted by additional tuning capacitance, then under the optimal resonant condition, the output voltage noises of the preamplifier are measured and the sensitivity coefficients are also calibrated. Meanwhile, the stray-capacitance of the cables is estimated. Finally, the experimental results show that the noise level of this circuit with the selected cables could all achieve 1–2 × 10−7 pF/Hz1/2 at 0.1 Hz.

In this paper, a triple-band-pass frequency selective structure is designed by combining traditional frequency selective surfaces (FSSs) with the spoof surface plasmon polariton (SSPP) guiding structure array. The FSSs consist of Jerusalem cross unit cell array with dual-band-pass property. And the SSPP guiding structure array is composed of vertical metallic blade structure array with high-efficiency transmission by engineering the dispersion of SSPP. By arranging the FSSs above the SSPP guiding structure array, a null located between the two passbands is introduced, resulting in a triple-band-pass characteristic. Furthermore, the triple-band-pass frequency selective structure is simulated, fabricated and measured. Both the simulated and measured results agree well, and verify that the transmissivities are all higher than -0.5dB in three frequency ranges: 2.42-2.90GHz, 5.57-5.85GHz and 9.48-9.85GHz. And the transmissivities of stopbands are lower than -10dB in three frequency ranges: 3.12-5.46GHz, 6.65-7.89GHz and 10.32-15.20GHz.

A hybrid frequency selective surface (FSS) with low-frequency absorption and high-frequency transmission is designed and demonstrated experimentally. The waveguide array with the spatial filtering characteristics of low-frequency reflection and high-frequency transmission is firstly proposed and the resistor-loaded loop array is then introduced on the top layer. Since the metal-like behavior of the waveguide array at low frequencies, the hybrid FSS can achieve strong absorption, while the transmission at high frequencies can be kept all the same. Simulated results show that the proposed hybrid structure can achieve broadband absorption with the efficiency more than 90% in the frequency range of 7.7-12.4 GHz and effective transmittance more than 80% from 16.5 to 18.0 GHz. The maximum transmittance of 89% can be gained at 17.4 GHz. Finally, the experimental measurement has also been performed to provide a good demonstration.

In this work, a quadruple-band dielectric metamaterial absorber (MMA) was proposed and studied, which is composed of eight cuboid dielectric particles and a metallic ground plate. When electromagnetic wave is incident on the dielectric particles, dielectric particles act as resonators and produce abundant resonant modes, which can result in perfect absorption. In simulation, four absorption peaks are observed at 9.13, 9.62, 10.0 and 10.46GHz with 88%, 89%, 100% and 96%, respectively. By adjusting geometry parameters of the dielectric particles, dielectric MMAs with different bands can be obtained. Further investigation shows that the absorption peaks can be changed by increasing the permittivity of the dielectric. Based on the designing technique of using simple cuboid dielectric particles directly acting as resonator, this work provides a simple method to construct multiband all-dielectric MMA.