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The mechanism of reflective electromagnetic metasurfaces has potential applications in information transfer and electromagnetic scattering suppression. In this article, the relation between the geometric entropy of the electromagnetic metasurface pattern and the scattering entropy of the metasurface is studied by introducing the power spectrum in the coding sequence generation, considering the correlation nature in the initial random geometric coding. The geometric entropy is found to generate an impact on the scattering form and scattering entropy of the 2 bit order random coding. The 2-D wideband power spectrum with central sunken is found to form the highest entropy in the scattering pattern. A metasurface sample is designed, prepared, and measured in the experiment to validate this theory. The results indicate another possible control parameter in entropy modulation, which has potential uses in multibeamforming and information transfer techniques. [ABSTRACT FROM AUTHOR]

• A theoretical model for the dynamic and vibro-acoustic of three novel honeycomb sandwich panels is established. • The vibration and acoustic properties of three novel honeycomb sandwich panels are analyzed. • An improved constrained YDSE is proposed by introducing penalty functions, circle chaotic mapping, and levy flight. • Optimization of the vibrational and acoustic performance of three novel honeycomb sandwich panels is conducted. Utilizing the first-order shear deformation theory (FSDT) and Hamilton's principle, dynamic equations for tunable Poisson's ratio metamaterial honeycomb sandwich panels have been derived. These panels include petal-shaped, star-shaped, and butterfly-shaped designs. The acoustic response of these panels when subjected to plane harmonic sound waves has been formulated, treating them as fluid-structure interaction systems. To enhance the structural vibration and sound propagation attributes, traditional metallic aluminum has been replaced with graphene platelet-reinforced composites (GPLRC). Through computational analysis and finite element simulation data, the natural frequencies and sound transmission loss (STL) characteristics of the panels have been determined. An improved heuristic algorithm called the circle chaos mapping and levy flight enhanced Young's double-slit experiment optimizer (CLYDSE) has been introduced to optimize their vibrational and acoustic properties. This algorithm builds upon Young's double-slit experiment optimizer (YDSE) by incorporating circle chaos mapping for initializing a monochromatic light source and utilizing the levy flight principle for more accurate search results. These enhancements allow the CLYDSE algorithm to avoid local optima and improve convergence velocity. A penalty function method was employed to establish mass and equivalent elastic modulus as optimization constraints, aiming to achieve superior specific stiffness. Finally, structural optimization using the proposed CLYDSE method was conducted to enhance the vibrational and acoustic performance of the three types of honeycomb sandwich panels. The results validate the effectiveness of the theoretical model in predicting vibration and acoustic response, as well as the improved performance of the CLYDSE algorithm in terms of convergence velocity and optimization accuracy. This demonstrates the algorithm's efficacy in refining the acoustic and vibrational qualities of these advanced honeycomb structures. [ABSTRACT FROM AUTHOR]

Wideband operation ability becomes an obstacle for many metamaterial applications since they are generally based on effective material (medium) hypothesis, which is intrinsically functional on single frequency or narrowband. Effective biological camouflage strategies involve concealment under sunlight with multiple frequency (color) components, for example, a shark could fuse itself into sea water environment for better invisibility and hunting effectiveness. A wideband 3-D metasurface ground cloak in gigahertz frequency order is proposed and realized in the experiment with a hemispherical profile. A complex unit structure to broaden the operational frequency range for a phase-preserved electromagnetic metasurface based on the difference of elevation is also proposed. Comparison between the wideband and its contrast narrowband metasurface clearly indicates the scattering improvement effect that demonstrates the proposed metasurface’s significance. Both instantaneous electric field scanning and reflection cross section shrinking quantitatively give strong evidence of the wideband operational functions. Comparison between simulation and experiment validated each other. These results indicate that the proposed metasurface conceals itself into a background inside a wide frequency spectrum of 7.0–9.5 GHz. This structure has a great application value for object security under wave package illumination and in landscape fusion. This mechanism also demonstrates the possibility to change other effective material properties in a wide frequency band. [ABSTRACT FROM AUTHOR]

Piezoelectric materials with shunt circuits have aroused much research interest due to flexible parameter adjustment. However, shunted piezoelectric elements are difficult to respond to the dynamic changes in the whole system due to the absence of autonomous control ability, which constrains their practical applications. Here, we propose a digital metalayer to control the wave energy transmission across different materials in real time. This digital metalayer comprises a stack of multiple piezoelectric lead zirconate titanate (PZT) disks connected with shunt capacitance circuits (SCCs). The external digital control system adjusts the effective acoustic impedance of the PZT disks through digital potentiometers and microprogrammed control unit, thereby enabling digital manipulation of wave transmission. Utilization of optimized SCCs further enhances adjustment accuracy, supporting both negative and positive capacitance values. The experiments demonstrate that this digital metalayer exhibits remarkable performance in controlling wave transmission. Moreover, the distinct variations in transmitted amplitudes, precisely controlled by the digital metalayer, are harnessed as binary signals for information transmission. An image of letters is encoded into a series of amplitude-modulated waves by the digital metalayer and clearly transmitted. The proposed digital metalayer shows great promise for applications in intelligent impedance matching and the real-time modulation systems. [ABSTRACT FROM AUTHOR]

In wide band electromagnetic absorbers, absorption in high and low frequency domain usually influence each other. Rasorber structure with blocking gate resonator (BGR) sub‐wavelength unit surface is proposed and applied in electromagnetic wave absorber to resolve this problem. The absorber has −10 dB low‐reflectivity performance operating in bandwidth ratio 161.2% and approaches Rozanov's theory limit in low frequency. BGR unit surface also generate a 2‐step design method for multi‐layer absorber structure. Rasorber BGR unit surface helps to enhance low frequency absorption with limited thickness while maintain absorption in relative higher wide frequency range by impedance matching at low frequency. Sample fabrication and experiment measurement basically testify the numerical speculations. [ABSTRACT FROM AUTHOR]

Abstract Microwave absorbers as an effective way to reduce microwave radiation in stealth technologies and electromagnetic compatibility have attracted great attentions recently. Herein, a novel multifunctional carbon fiber (CF)/glass fiber (GF) reinforced lossy lattice metastructure for broadband microwave absorption and effective load bearing is proposed for the first time based on the structural similarity of photonic crystal and lightweight mechanical lattice. The lossy lattice is fabricated with nano lossy composite composed of multiwall carbon nanotube (MWCNT) and spherical carbonyl iron (CI) particles to manipulate complex permittivity and complex permeability. Sub-wavelength effect and structural optimization are applied for the metastructure to extend −10 dB absorption bandwidth from 3.42 GHz to 19.73 GHz with thickness of 3.5 mm. With solid attachment of CF and GF, the metastructure achieves high average equivalent strength of 167.35 MPa and fracture strain of 5.45%. A long plastic stage of the metastructure is observed after GF fracture or GF delamination in three-point flexural test. The integrated design of microwave absorbing and mechanical properties make it promising for practical applications in mass production. Graphical abstract Dielectric-magnetic lossy lattice metastructure composed of carbonyl iron and multiwall carbon nanotube is fabricated with a four-step method. Broadband absorption from 3.42 GHz to 19.73 GHz with thickness of 3.5 mm and large tensile strength of 167.35 MPa with fracture strain of 5.45% are achieved. Integrated design shed light on practical applications and mass production in stealthy technologies and lightweight armor. Image 102 [ABSTRACT FROM AUTHOR]

ABSTRACT A concise transmissive/absorbing radome principle model is presented, which realizes flat-top wide-band transmission band and two electromagnetic absorbing wide band located above and beneath the transmission band. Simulation indicates reflection signature of this radome structure could be reduced by over −10 dB out of transmission band. Frequency-selective characters are achieved by one resistive FSS layer and two metallic FSS layers with nested square element, along with two dielectric spacer layers. An experimental-demonstration sample plate fabrication and measurement testifies the model preliminarily. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2016-2019, 2016 [ABSTRACT FROM AUTHOR]

• Metamaterials became hotspot in electromagnetics, acoustics, and mechanics fields. • Since the integration of mechanical features and specific functions is still a challenge, the application of metamaterials has so far been limited. • Researches emerge in incorporating multifunctional design into a single structure. • Advances in design of multifunctional structures based on metamaterials are reviewed. Metamaterials, with unconventional properties realized through various ingenious designs of micro-architectures, have become a recent research hotspot in the fields of electromagnetics, acoustics, mechanics, and physics. Since the integration of mechanical features and specific functions is still a challenge, the application of metamaterials has so far been limited. The research in relevant areas has shown a clear trend of incorporating the multifunctional design into a single integrated structure. Here, we review the latest advances in the design and fabrication of multifunctional structures based on metamaterials, covering three main aspects, i.e., the direct design of mechanical metamaterials and their multifunctional structures, the intelligent multifunctional structures with shape-shifting capabilities, the metamaterials-based design to achieve both the load bearing capability and other specific functions. We emphasize the important roles that the mechanics-driven designs play, as well as the mechanisms and other key aspects behind the multifunctional structures. The structure-level innovations could not only improve multifunctional features, but also pave the way to function fusion structures that allow the incorporation of 'conflicting' functions into a single structure. [ABSTRACT FROM AUTHOR]

Acoustic metasurfaces show non-traditional abilities in wave manipulation and provide alternate mechanisms for information communication and invisibility technology. However, most of the mechanisms remain narrow band (relative bandwidth ∼5%), and a wideband trait is essential for engineering applications. For example, controllable effective material properties—reflection or transmission phase—has barely been realized in wideband because the intrinsic dispersion relation is not always editable. In this paper, wideband reflection phase editing is realized, and wideband invisibility of a phase preserved Huygens's metasurface on a flat background is achieved with anomalous reflection. This metasurface is built with proposed unsymmetrical twin Helmholtz resonators which reach a predefined dispersion relation target value. The total instantaneous acoustic fields show nearly identical carpeting effects in a consecutive band with relative bandwidth 52.1% (from 5400 to 9200 Hz) in simulation and experiment. [ABSTRACT FROM AUTHOR]

Camouflage skills are important for understanding the relationship between predators and prey in ecological systems. Mimicry is a common strategy used by creatures to alter their appearance in order to blend in with their surroundings and avoid detection. This paper unveils a previously unknown camouflage strategy that creates false object information and positions of an object in the visual range of radar sensor vision. A dispersion‐modulated illusionary metasurface to realize focal spot coding in a 3‐dimensional space to fit the radar imaging process is proposed. As the radar image indicates, an aircraft image is created by a flat metasurface plane with good polarization adaptation ability. Design, simulation, and experimental results validate the study. This camouflage strategy indicates the complexity of the food chain and can be used by both predators and prey, providing accessible insights for maintaining biological diversity. The metasurface‐based system can be potentially utilized in future radar markers for marine traffic control systems. [ABSTRACT FROM AUTHOR]

An effective quasi-real-time inversion algorithm based on the super-resolution generative adversarial network (SR-GAN) is proposed to quantitatively image the 2-D biaxial anisotropic scatterers. The SR-GAN was originally proposed for the purpose of super-resolution image reconstruction, which exactly fits the need for inverse problem. In addition, Visual Geometry Group (VGG) loss is introduced to extract the high-level features of the object instead of the low-level pixel-wise error measures. The angle-dependent reconstruction effect due to the dipole radiation as in the traditional inversion methods is effectively resolved by the machine learning method. Numerical results using both synthetic data and experimental data are given to validate the effectiveness of the proposed method. Both the imaging quality and resolution are greatly improved by the proposed SR-GAN algorithm, compared to the traditional iterative inversion algorithm. In addition, the computational time is reduced significantly and the quasi-real-time imaging is finally realized, which promises a potential real-time application of the inverse scattering method. [ABSTRACT FROM AUTHOR]

Since broad temperature range electromagnetic attenuation materials and structures are conventionally manufactured based on ceramic-based materials and composites, an alternative strategy is developed here to construct metal electromagnetic metastructures based on triangulated cylindrical origami design and metal 3D printing technology. The experimental and simulated results suggest that the as-manufactured 3D-printed metal origami metastructures enable to effectively scatter electromagnetic wave, resulting in effective low reflectivity stably over a broad temperature range of 20-800 °C. Implication of the discussion on mechanism, materials, processing, and performance suggests a novel platform for achieving metallic electromagnetic metastructures and metastructures for broad temperature range stealth technology. [ABSTRACT FROM AUTHOR]

Since Materials Genome Initiative has been proposed for demonstrating promising approaches in achieving high-performance materials, here we employ such concept to present a Materials Genome Initiative inspired universal permittivity-attenuation evaluation diagram (PAED) for accelerating design of highly efficient dielectric-based microwave absorption composites. Initially, parameter sweeping has been applied to screening the best microwave absorption parameters based on the absorption-permittivity mode, aiming to creating a novel PAED. For well demonstrating the validity of such diagram, experiments are applied to scalable fabricate various graphene-based composites with a simple approach, achieving strong microwave absorption (−57 dB with full-band qualified absorption in X-band) and considerably high radar cross scattering reduction (24.25 dBm 2 at 90°) with the guide of the proposed diagram. Noticeably, implication of the verification results from experiments, previous literature and simulation indicates validity of such novel PAED, and thus it highlights a new general roadmap for rationally designing high-performance microwave absorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel compact multifunctional metastructure is proposed for both low-frequency broadband sound absorption and excellent crash energy dissipation. • An optimization method, resisting degradation from impedance coupling effect, contributes to flatter and higher sound absorption coefficient curves. • The as-designed metastructure with deep-subwavelength thickness exhibits quasi-perfect broadband sound absorption performance. • The as-designed metastructure is verified to have the same superior load-bearing and crash energy dissipation performance as an intact honeycomb structure. Sound absorption structures, as an effective approach to reducing sound radiation, have always received extensive attention in the engineering of vibration and noise reduction. In this work, a novel compact multifunctional metastructure is proposed for both low-frequency broadband sound absorption and excellent crash energy dissipation. Cavity resonators with internally extended tubes (CRIET) with hexagonal honeycomb configuration were selected as unit components. An optimization method was proposed to against degradation from impedance coupling effect and contribute to flatter and higher sound absorption coefficient (SAC) curves. The as-designed metastructure has been demonstrated experimentally to have quasi-perfect broadband sound absorption in the target range of 600–1000 Hz with an average SAC above 0.9 and a deep-subwavelength thickness of 30 mm. Compression experiment showed that the CRIET metastructure with hexagonal honeycomb configuration had the same unique excellent load-bearing and crash energy dissipation performance as an intact honeycomb structure. This study provides inspirations and methods for the compact and multifunctional design of broadband sound absorption structures. [ABSTRACT FROM AUTHOR]

Multifunctional composite structure with unique mechanical and physical characteristics is essential for the lightweight design of engineering structures. Here, we develop a multifunctional sandwich structure for both effective loadbearing and customizable microwave absorption by employing glass fiber reinforced plastic, polyvinyl chloride foam, carbon fiber reinforced plastic, and frequency selective surfaces. The resultant sandwich structures are endowed with effective specific flexure stiffness (up to 130 N/mm), benefiting from the efficiency in material distribution configuration. Moreover, the proposed structures also show highly customizable microwave absorbing capacity in both bandwidth (from 2 GHz to 18 GHz) and band depth (from −10 dB to −15 dB), due to the flexible design ability of multiple interfaces, electromagnetic loss artificial film. The optimized structures highlight a tradeoff among microwave absorption, flexure stiffness, and surface density and thus are promising a smart stage on which high-performance customizable properties can be envisaged. [ABSTRACT FROM AUTHOR]