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In this paper, a meta-surface inspired flexible antenna prototype is proposed for bio-medical applications. A 1.5 mm Rogers high frequency laminate with permittivity of 3.3 and loss tangent of 0.002 is used as substrate owing to its flexible nature. The proposed antenna is suitable for on-body applications and as such the performance of the prototype was verified on a multilayer phantom model using HFSS tool. Unique properties of meta-surface make miniaturization of the antenna possible with optimum antenna dimensions of 0.24 λ 0 × 0.15 λ 0 × 0.013 λ 0 . The designed antenna is investigated for on-body applications and thereof it is observed that the radiator radiates in the range of 2.14 GHz − 3.4 GHz resulting in resonance at 2.67 GHz.

Graphene as an organic material has attracted special attention due to its electronic and conductive properties. Moreover, its highly conjugated chemical structures and relatively easy modification have allowed varied design and control of targeted properties and applications. In addition, this nanomaterial with pseudo-electromagnetic fields has led to the emergence of photonics, electronics and quantum interactions with their surroundings, generating new properties of materials. This short review aims at discussing many of these studies of new materials based on graphene for light and electronic interactions, conductions and new modes of nonclassical light generation. These new materials and metamaterials are being developed. For this reason, some representative examples from research with potential applications have been shown and discussed, in addition to their incorporation in real advanced devices and miniaturized instrumentation. Accordingly, this special issue entitled “Design and Synthesis of Hybrid Graphene-based Metamaterials” is intended to review the state-of-the-art in this multidisciplinary field.

Metamaterials refer to a class of artificial composite structures with supernormal physical properties that natural materials do not have. The emergence of metamaterials has opened up new research directions for classical electromagnetic theory and made it possible to manipulate electromagnetic waves effectively. One of most important applications of metamaterials is metamaterial absorbers (MMAs). The properties of MMAs depend on the material composition, cell size and structure, which could often achieve "perfect" absorption through reasonable design. This review starts with the development of MMAs and describes the status of this absorber, then mainly focuses on bionic design and new artificial design. Specifically, it is to draw inspiration from natural plants and animals, design novel structures to get better absorbing properties. Furthermore, the artificial design can achieve the optimize absorption capacity as well as absorption bandwidth. What's more, this review summarizes the 3D printing technology to prepare MMAs that are different from traditional printed circuit board technology. The MMAs produced by 3D printing technology can prepare more complex shapes, and has light weight and better absorbing properties.

Graphene with tunable thermo-mechanical property is of great importance for next-generation thermal management devices. Distinct from previously reported porous graphene materials that tune the thermal conductivity at the cost of degrading their mechanical properties, non-porous hydrogenated graphene origami metamaterial exhibits a unique combination of tunable thermal conductivity, high strength, and enhanced stretchability. Through molecular dynamics simulation, an extremely broad range of thermal conductivity can be obtained by tuning the geometrical parameters of the Miura-ori nanoarchitecture of graphene origami, altering the adatom types and density, designing new origami patterns, and applying mechanical strains. By analyzing and comparing the results from atomistic and continuum-based simulations, the effect of length scale on the thermal property of graphene origami metamaterials is explored. The temperature distribution and the phonon density of states of the proposed graphene origami are examined to illustrate the heat conduction mechanism. Finally, 3D graphene origami metamaterials are constructed based on the coupling and assembling of graphene origami strips, and their thermo-mechanical performance is elucidated. Negative coefficients of thermal expansion are obtained in graphene origami nanotubes. The introduced strategy for controlling the thermo-mechanical properties of graphene metamaterials can open up new avenues for developing thermoelectric devices, heat management systems, and flexible nanoelectronics.

High-performance electromagnetic (EM) absorbers are necessary for military and industry application in view of the extensive utilization of EM devices. Carbon fibers (CFs) have been considered as promising candidates in electromagnetic wave (EMW) absorption materials, while the single carbon fiber material cannot achieve satisfactory EMW absorption performance because of its limited impedance matching. Herein, electrodeposition and hydrothermal methods were used to fabricate vertical hollow ZnS nanoarrays on carbon cloth (CC) substrate, and then one kind of novel flexible EM composite absorbers with excellent performance was obtained through adjusting morphology of hollow ZnS nanoarrays by easily changing the synthesis parameters of the precursor. Noteworthy, the miniaturized cone-shaped hollow ZnS nanoarray composite absorber shows excellent EMW absorption performance of strong absorption and wide absorption band. The maximum reflection loss value is −52.5 dB and the effective absorption bandwidth reaches 5.1 GHz when the thickness is only 1.9 mm. At the same time, the composite possesses the characteristics of light weight and thin thickness. The excellent properties of the composite absorbers are mainly attributed to their morphological structure. The unique hollow ZnS nanoarray structure enhances the interface polarization and multiple reflections, meanwhile also giving it the properties of metamaterials with resonant absorption. Furthermore, the adjustment of the ZnS nanoarray morphology can not only change the transmission behavior of EMW but also affect the resonance frequency and intensity of the ZnS nanoarray unit. This study obtains high-performance absorbing materials with flexible characteristics as well as highlights the importance of the adjustment of the morphological structure to improve the EMW absorption performance.

In this paper, a novel metamaterial absorber is designed within the visible light regime. The structure comprises nickel resonator disks placed over a silicon dioxide substrate in a uniform pattern, with the operating frequency between 350 and 800 THz. Additionally, the infrared and ultra-violet regions are also investigated. Numerical studies are carried out using a computational electromagnetic solver. The obtained results show nearly perfect absorption, with an average absorption of 99% between 100 and 1000 THz. The physical dimensions are optimized allowing for maximum absorption results. Due to the ultra-wideband characteristic in the visible regime, the proposed design can be used as a highly efficient absorber in several applications, including solar energy harvesting, IR-detector, cloaking, sensing, and EMC projects.

Pyrotechnic releasing devices have been widely used in aerospace missions to separate subsystems from spacecraft. High-frequency transient pyroshock induced by pyrotechnic release devices may cause...

Terahertz (THz) technology has made promising progress and attracted wide interests in the fields of communications, security, agriculture, and biological sciences. However, the lack of modulation materials and the great challenge of the miniaturized system have become the huge restriction of this technology. Although artificial metamaterials have shown impressive electromagnetic performances in this band, they suffer complicated and high-cost fabrication processes. In this work, we find that due to the high conductivity, laser-induced graphene (LIG) can be applied in THz wave modulation. A LIG metasurface fabrication system is developed based on a nanosecond laser, a telecentric scan lens, and scanning mirrors. Owing to the ultra-small focal spot (≤5μm) realized by the telecentric scan lens and the fast-scanning speed of the mirrors, a LIG-based THz metasurface with the size of 15 mm × 15 mm, and the resolution of 30 μm can be fabricated in 34 seconds. In addition, THz optical parameters of LIG are measured. It is anticipated that this fast-fabricating, large-area, and low-cost method may open up a brand-new way to develop THz devices.

The satisfactory realization of metamaterial (MM) absorber simultaneously occupying low profile, wide bandwidth, particularly and fully angular stability characteristics is a long-term challenge. In this paper, we propose a new design method to accomplish above realization based on radiation pattern synthesis. In the design, a mushroom-type MM absorber is simply covered with different resistive sheets, which empower it with the admirable low profile, wide bandwidth, and near-omnidirectional absorption for TM polarized wave. In order to guide our design, the characteristic mode theory is first employed to synthesize omni-directional radiation pattern and the dissipation tailoring is then utilized to achieve the impedance matching and near-omnidirectional absorption conversion. A proof-of-concept sample is fabricated and measured for verification. At quasi-normal incidence, the measured bandwidth characterized by absorption more than 90% covers 1.5-4.5 GHz with fractional bandwidth (FBW) 100% and the thickness about 0.11λ0 at 1.5 GHz. In the frequency band of 1.9–4.2 GHz, the simulation results indicate that the absorption for TM and TE polarizations of approximately 90% can respectively up to incident angles of 82° and 45°, and its effectiveness within 100-700 is verified with measurements.

A simple and multi-layer metamaterial made of graphene to realize excellent manipulation of EIT-like effect is proposed. The unit cell consists of four layers: Substrate 1, Cross 1, Substrate 2 and Cross 2, which can obtain tunable EIT-like effect by adjusting the Fermi level of graphene. The surface current distributions of four different views clearly explain the underlying physical mechanism. A three-level Λ-type system is employed to describe the coupling process between Cross 1 and 2. The calculated transmission spectra based on two-particle model have great agreement with the simulated transmission spectra. In addition, the effects of geometrical parameters on EIT-like effect are discussed and wideband EIT-like effect with high transmission can be obtained by adjusting the lengths of Cross 1 and 2. Also, the polarization-insensitive character of EIT-like metamaterial is confirmed by the transmission spectra under different polarization angles. The maximum of group delay (25.48 ps) is far greater than the group delay of previously reported EIT-like metamaterials. Our study provides a novel way for the development of slow-light devices and modulators.

This review paper examines ten current ceramic radome materials under research and development and provides a comprehensive overview of available high temperature and high frequency data from literature. An examination of metamaterials for radio-frequency transparent radomes is given and our preliminary experimental results of a high-temperature metamaterial design are presented. The next-generation hypersonic vehicles’ radome temperatures will exceed 1000℃ and speeds will exceed Mach 5. An ideal radome material will have a high flexural strength, low dielectric constant and loss tangent, and high resistance to thermal shock and corrosion. The microstructural effect on the dielectric and mechanical properties and the effects of environmental factors such as rain are discussed. The impact of metamaterial structure on key radome factors such as boresight error, gain, and polarization is examined. After examining the associated benefits with the use of metamaterials, our preliminary results for a potential high-temperature metamaterial design are presented.

This paper proposed a metamaterial design method that uses soft matter for constructing a unique soft acoustic boundary to effectively improve broadband sound absorption performance. Specifically, attaching a flexible polyvinyl chloride (PVC) gel layer with an elastic modulus as low as a few kilopascals and a thickness of a few millimeters to the inner wall of a cavity-type sound-absorbing metamaterial structure significantly improved the absorption performance of the composite structure in low-frequency broadband ranges. The sound absorption enhancement mechanism differed from those proposed in previous research. On the one hand, the soft PVC gel layer acted as a soft acoustic boundary, substantially reducing the sound speed and reflection and producing considerable elastic strain energy at the interface between two different media to improve the sound absorption performance. On the other hand, this PVC gel layer displayed extremely low stiffness and high damping, producing an abundance of plasmon-like resonance modes in low-frequency broadband ranges, achieving a resonance absorption effect. Since this sound absorption enhancement method did not require an increase in the external dimensions or a change in the structural parameters of the original absorber and achieved robust enhancement in a wide frequency band, it displayed potential application value in various engineering fields.

In this letter, a broadband, wide-scanning phased array with radar cross section (RCS) reduction performance is presented. The proposed phased array is composed of two types of antenna elements: Ant-0 and Ant-1. Ant-0 and Ant-1 are y-polarized dipole antennas that have almost the same radiation performance over the frequency range of 6.5-12 GHz. Ant-1 is obtained by co-designing Ant-0 with a polarization selective metamaterial surface (PSMS), and the PSMS has little effect on the y-polarized radiation performance. As of x-polarized incident waves, the phase difference of the reflected waves on Ant-0 and Ant-1 is around 180 over the frequency range of 3.74-15.1 GHz, thus, a broadband scattering cancellation is achieved. A 516 finite array is fabricated and measured, and the measured results show great agreement with the simulated results. The fabricated phased array antenna has the ability to scan to 60 with active VSWR < 3 over the frequency range of 6.5-12 GHz, and over the frequency range of 3.9-15.1 GHz, ultrabroadband monostatic RCS reduction is achieved.

Thermal metamaterials are a class of artificial composite structures with special thermal conduction properties. Due to the existence of complex multi-phase materials arrangement and interfaces in the thermal metamaterials, an efficient and accurate numerical method is on-demand to predict their temperature distribution and performances. In this paper, we studied the edge-based smoothed finite element method (ES-FEM) for simulating the heat conduction of thermal metamaterials in both steady-state and transient circumstances. Benefit from the adopted smoothing technique, the numerical errors caused by the complex interface are further eliminated. The most significant advantage of the proposed method is that one can directly use the automatically generated coarse triangle mesh to reduce the computational costs while ensuring accuracy. Two numerical examples are presented, in which two typical thermal metamaterials, the thermal cloak and thermal concentration device, are considered respectively in both steady-state and transient cases. The results illustrate that the ES-FEM based approach has good efficiency and accuracy in the heat conduction simulation of the thermal metamaterials.

A high gain low-frequency bow-tie antenna with artificial magnetic conductor and metamaterial lens for ground penetrating radar (GPR) is proposed. Firstly, a bow-tie antenna working in 348-772 MHz frequency band is designed. The substrate is a square with side length of 420 mm. A periodic artificial magnetic conductor reflector is designed. The in-phase reflection region of the unit is 481 MHz-1.44 GHz. The results show that the gain of antenna loaded with reflector is increased by 5 dB. A metamaterial lens based on the zero-index metamaterial element is also proposed to improve the gain. The zero refractive index frequency point is 810 MHz, the unit size of the metamaterial is 60 mm, and the lens size is consistent with the antenna substrate size. The gain of the antenna loaded with artificial magnetic conductor (AMC) reflector and the metamaterial lens is increased by 6.5 dB and the front-to-back ratio is 23 dB. The directivity of the antenna is further optimized. The measured results are in good agreement with the simulations.

Detecting circularly polarized light (CPL) signals is the key technique in many advanced sensing technologies. Over recent decades, many efforts have been devoted to both the material design and the device engineering of CPL photodetectors. CPL detectors with different sensing wavelengths have distinct applications in bio-imaging, drug discovery, and information encryption. In this review, we first introduce the working principle of state-of-the-art CPL photodetectors followed by a general material design strategy. We then systematically summarize the recent progress on the chiral materials developed for CPL detection, including inorganic metamaterials, organics, hybridized materials, etc. We compare and analyse the photocurrent dissymmetry factors of these systems and provide perspectives on strategies to improve the dissymmetry factors and extend the detection wavelength. We believe that the information we include in this review would attract broader interest from researchers working on different aspects of organic and hybridized semiconductor materials and devices.

A terahertz metamaterial refractive index/thickness sensor with flexible substrate, exhibiting low-frequency Fano resonance and high-frequency electromagnetically induced transparent (EIT) resonance, is proposed. The physical formation mechanisms of Fano and EIT resonances are investigated by calculating the electromagnetic field. Simulated results demonstrate that the refractive index sensing sensitivity based these two resonances are up to 60 and 100 GHz/RIU, and the thickness sensing sensitivity are up to 1 and 1.7 GHz/μm, respectively. Furthermore, the proposed sensor was fabricated using femtosecond laser etching technology, and its sensing performance was verified by the experimental results that it can distinguish different liquids and detect the polyimide film with different thicknesses less than 180 μm. The remarkable performances make the proposed metamaterial sensor has feasible capability for biological and chemical sensing in terahertz range.

The unique engineered material termed Metamaterials is not seen naturally and were made artificially by repeating unit cell geometry in multiple directions to form a structural composite metamaterial. The present research is to investigate the three types of uniform architecture metamaterials i.e square, auxetic and honeycomb along with three of its hybrids i.e square-auxetic, auxetic-honeycomb and square-honeycomb. All the modelled metamaterials samples were imported to Ansys modal analysis section and free vibration analysis is performed under the workbench graphic user interface via the finite element method. The materials for the simulation test is PLA (polylactic acid) adopted. The results like natural frequency and mode shapes are extracted from the simulation. It was observed that among hybrids the highest natural frequency was seen for auxetic-square hybrid geometry i.e 858 Hz at 3rd natural frequency, which decreased to 35 and 44% when compared to square-honeycomb, auxetic-honeycomb respectively. The emerging area potential application of hybrid PLA auxetic metamaterial includes robotics, aerospace, nautical, sports and bio-medical industries.

Hyperbolic metamaterial (HMM) based absorber comprising metasurface having periodically arranged hafnium nitride nanodisks was investigated. The constitutive and absorption properties of the structure were evaluated considering different parametric and operational conditions. Both the TE- and TM-incidence waves were studied along with different incidence and polarization angles. Using the finite integration technique, the absorber was found to exhibit high (polarization insensitive) ultrawideband absorption. With such features, the proposed HMM has prospects in developing plasmonic devices to enhance solar cell efficiency and other optical applications.

The paper investigates the mechanical response of a 3D auxetic structure created on the basis of a unit cell with pre-buckled structural elements to dynamic loading. The aim of the work is to study deformations of the auxetic structure made of an alpha titanium alloy during uniaxial compression at 100 m/s, to evaluate dissipative properties of the structure during high-speed deformation, and to estimate the characteristic time of the metamaterial’s compaction with a relative density of 0.0115. The numerical simulation of the metamaterial at effective strain rate of 2000 1/s has been performed using LS DYNA solver. To describe the mechanical behavior of the titanium alloy in frame elements, we use a model of an elastic-plastic damaged medium, which takes into account the strain rate sensitivity of the plastic flow, temperature changes due to dissipative effects, and the effect of the stress state triaxiality parameter on nucleation and growth of structural damages. The numerical studies have shown that the auxetic effect in the studied metamaterial is retained under high-rate elastoplastic deformation. At a speed of the uniaxial compression of 100 m/s, deformation in the volume of the metamaterial proceeds nonuniformly. Under dynamic loading of the considered auxetic metamaterial, the deformation and fracture modes depend not only on the parameters of the cell geometry, but also on the mechanical behavior of the framework material, as well as on the relative density. This makes it possible to control the deformations of the cells under mechanical stress. Layers of compacted cells are formed near the dynamic loading surface. The instability of the cells of the auxetic metamaterials increases the absorbed energy. The calculated value of the specific absorbed energy under dynamic uniaxial compression reaches 3.4 kJ/kg, and is comparable with the values for frame structures made of Ti-6Al-4V with an equivalent specific mass density. The results indicate the possibility of creating protective structures using auxetic cellular structures on the base of the pre-buckled elements of the rolled metal.

Two-dimensional (2D) crystals have renewed opportunities in design and assembly of artificial lattices without the constraints of epitaxy. However, the lack of thickness control in exfoliated van der Waals (vdW) layers prevents realization of repeat units with high fidelity. Recent availability of uniform, wafer-scale samples permits engineering of both electronic and optical dispersions in stacks of disparate 2D layers with multiple repeating units. Here we present optical dispersion engineering in a superlattice structure comprising alternating layers of 2D excitonic chalcogenides and dielectric insulators. By carefully designing the unit cell parameters, we demonstrate greater than 90% narrow band absorption in less than 4 nm of active layer excitonic absorber medium at room temperature, concurrently with enhanced photoluminescence in square-centimetre samples. These superlattices show evidence of strong light–matter coupling and exciton–polariton formation with geometry-tuneable coupling constants. Our results demonstrate proof of concept structures with engineered optical properties and pave the way for a broad class of scalable, designer optical metamaterials from atomically thin layers. Square-centimetre scale, multilayer superlattice structures based on atomically thin two-dimensional chalcogenide monolayers enable the realization of excitonic metamaterials.

Combining plasmonic and magnetic properties, namely magneto-plasmonic coupling, inspires great research interest and the search for magneto-plasmonic nanostructure becomes considerably critical. Here we designed a nanopillar-in-matrix structure with core–shell alloyed nanopillars for both BaTiO3 (BTO)-Au0.5Co0.5 (AuCo) and BTO-Au0.25Cu0.25Co0.25Ni0.25 (AuCuCoNi) hybrid systems, i.e., ferromagnetic alloy cores (e.g., Co or CoNi) with plasmonic shells (e.g., Au or Au/Cu). These core–shell alloy nanopillars are uniformly embedded into a dielectric BTO matrix to form a vertically aligned nanocomposite (VAN) structure. Both hybrid systems present excellent epitaxial quality and interesting multi-functionality, e.g., high magnetic anisotropy, magneto-optical coupling response, tailorable plasmonic resonance wavelength, tunable hyperbolic properties and strong optical anisotropy. These alloyed nanopillars-in-matrix designs provide enormous potential for complex hybrid material designs with multi-functionality and demonstrate strong interface enabled magneto-plasmonic coupling along with plasmonic and magnetic performance.

Carbon/ceramic composites with adjustable electrical properties can be promising candidates for electromagnetic metamaterials with negative permittivity. Herein, silicon nitride (Si3N4) ceramic composites incorporated with carbon fibres (CFs) were prepared via spark plasma sintering. The fibres were randomly distributed in the ceramic matrixes, and their amounts had a great influence on the microstructure, electrical conductivity, dielectric behaviour, and impedance response of the CF/Si3N4 composites. As the CF content was low, the ceramics with isolated CFs showed a dielectric type of conductivity, along with a capacitive character and positive permittivity. When the CFs were more sufficient to contact or overlap each other in the ceramics, the formation of CF networks endowed the ceramics with a metallic type of conductivity and inductive character. A plasma-type negative permittivity behaviour was observed in these ceramics and was imputed to the low-frequency plasmonic state of free electrons in the formed CF networks. The Drude model was applied to make a precise description of the negative permittivity behaviour. As the CF content increased, the plasma frequency (negative-positive transformation frequency of permittivity) of the ceramics shifted to a higher frequency, and their absolute magnitudes of negative permittivity also increased. Furthermore, equivalent circuit models were utilized to interpret the impedance response of the ceramics, which demonstrated that the negative permittivity was linked to the inductive character. This work provides support for developing ceramic-based metamaterials with tunable negative permittivity that is desirable for many applications.

How can researchers geometrically tune the extent to which a material embodies a stiff or flexible structure?

Fill factor in the negative permittivity materials are tailored within the physically permissible limits to characterize the Brillouin zone for two-dimensional crystal under the propagation of both s and p-polarized waves. Two lowermost band-gaps are computed along with corresponding mid-band frequencies, where the plane wave expansion method is invoked for computational purposes. The rectangular geometrical shape is considered for the simulation, and all the results are calculated inside the ‘Γ’ point and ‘X’ point of the first Brillouin zone. Simulated findings depict monotonous variations of both band-gap width as well as mid-band frequency for higher negative permittivity materials, when the magnitude of fill factor is comparatively low, for both TE (Transverse Electric) and TM (Transverse Magnetic) mode of propagations. Lower negative permittivity leads to random fluctuations, which makes it unsuitable for photonic component design. Multiple forbidden regions may be observed for some specific artificial materials which can be utilized in the antenna or multi-channel filter design in higher THz region. Aims: The present paper aims to compute the shape of the first Brillouin zone from the fill factor for a two-dimensional photonic crystal structure. Background: EBG (Electromagnetic Bandgap) of a photonic crystal plays a major role in determining its candidature for optical applications, which is critically controlled by the fill factor. Therefore, it is significant to investigate the effect of F.F on the wave propagation characteristics of 2D PhC(Twodimensional photonic crystal). Objective: Investigation of metamaterial-based photonic crystal structure for electromagnetic band-gap analysis in the desired spectrum of interest as a function of fill factor inside the first Brillouin zone. Methods: Maxwell’s equations are solved using the plane wave propagation method to solve the problem, and simulation is carried out in MATLAB® software. Result: Both the first and second photonic band-gaps are simultaneously computed with a variation of refractive index differences of the constituent materials as well as with the fill factors. Results are extremely significant about the formation of narrowband and wideband filters on certain material combinations and structural designs. Conclusion: Better tenability is observed for metamaterial structure compared to conventional positive index materials, and fill factor has a great role in shaping the Brillouin zone and corresponding bandgap width.

Structural metamaterials presenting negative values of one or more mechanical and thermomechanical indices – namely the Poisson's ratio, the linear compressibility, and the coefficient of thermal expansion – are the promising candidates to the applications in many fields, ranging from precision mechanics to biomedical devices or energy absorption. Although scattered mentions may be found in the literature since the late eighties of 20th century, the systematic research efforts concerning these materials became effective much later. The present work is to review the main scientific contributions to the topic in the last five years. This paper first deals with those metamaterials showing a single negative index, and then proceeds to analyze the much less frequent instances of coupled negative indices, with emphasis on the so-called anepectic case, which exhibits an unusual thermomechanical response.

The use of mechanical metamaterials in engineering applications is often limited because of uncertainty regarding their deformation behavior. This uncertainty necessitates large safety factors and assumptions about their behavior to be included in mechanical designs including metamaterials, which detracts from their greatest benefit, viz. their ultralight weight. In this study, a yield envelope was created for both a bending-dominated and a stretching-dominated cellular material topology to improve the understanding of the response of cellular materials under various load types and orientations. Experimental studies revealed that the shear strength of a cellular material is significantly lower than that predicted by Mohr’s criterion, necessitating a modification of the Mohr’s yield criterion for cellular materials. All topologies experienced tension–compression anisotropy and topology orientation anisotropy during loading, with the stretching-dominated topology experiencing the largest anisotropies.

Organic acids are important components in determining fruit taste, and it is necessary to develop rapid analysis methods for them. A simple and effective method based on laser-engraved free-standing terahertz (THz) metamaterials has been developed for rapid analysis of fruit acids. Compared with traditional fabrication methods for THz metamaterials, laser direct writing technology was employed for fabricating the Cu-foil-based THz devices in this research, which is time-saving, cost-effective, and high-throughput. To realize effective fabrication of metamaterials, proper fabrication parameters were selected according to morphology and spectral characterization. Numerical analysis was performed to reveal the fundamental mechanism of THz sensing based on metamaterials. Furthermore, experimental results indicate that fruit acid with a concentration of 0.1 mg L−1 can be successfully distinguished, which is quick and simple compared with traditional acid–base titration. The proposed strategy demonstrates great potential for rapid in situ analysis of flavor components in food products.

This article deals with the data-driven prediction of the band structures of thermoelastic waves in the nano-scale phononic crystal beams considering nano-size effects. The computational intelligen...

As an acoustic metamaterial, Metal–organic frameworks (MOFs) can absorb sound energy abnormally. In this research, a thin and flexible acoustic material was prepared by growing MOF on the fabric. The successful growth of MIL-53(Fe) on the fiber surface was confirmed by SEM, FTIR, XRD and XPS. From the sound absorption and sound insulation test results of MIL-53(Fe)@fabric, the in-situ growth of MIL-53(Fe) greatly improves the sound absorption and sound insulation performance of the fabric, and gives the fabric an abnormal acoustic effect. From the calculation results of the theoretical model, the growth of the sub-wavelength scale MIL-53(Fe) significantly increases the flow resistance of the fabric, which is the root cause of the abnormal sound absorption of the material. It is worth noting that the sound transmission loss of the prepared flexible material doesn’t follow the mass law and exhibits excellent sound insulation performance. This is not only related to the increase in the sound energy reflected by the fabric, but also to the abnormal sound absorption of MIL-53(Fe). Here, the sound insulation performance of MOFs@fabric is reported for the first time. This work promotes the research and application of MOFs in the field of acoustics, and provides a method and theoretical basis for the design and preparation of acoustic protection textiles.

High-performance gas sensors with low operating temperatures are of emerging research interest. They do not require heaters, thus guaranteeing cost-effectiveness and low power consumption. This is ...

Thermal stress has a negative effect on structural safety in many engineering fields, so it is particularly important to eliminate this negative effect as much as possible. This problem can be solved by designing the microstructure of the materials to make the coefficient of thermal expansion (CTE) close to 0, while negative thermal expansion (NTE) materials can become an important part of zero thermal expansion materials. Negative Poisson's ratio (NPR) materials have been favored by researchers because of their bright application prospects in many fields such as medical treatment and engineering. The research of lightweight mechanical metamaterials with both NTE and NPR effects is of great significance for the development of smart sensors with mechanical and temperature sensitivities, and the realization of multi-functional integration of structure. Inspired by the structure of natrolite, a material which can adjust the CTE and Poisson's ratio (PR) in a large range at the same time is designed in this paper. The analytical formulas of the equivalent CTE, PR and Young's modulus are derived and verified by finite element simulation. Meanwhile, the concept of stiffness index is introduced and analyzed by theoretical and finite element methods. Furthermore, the shear modulus of the material is analyzed by finite element method. The results show that the analytical formulas are valid for the material and the material can not only realize NTE and NPR effects at the same time, but also exhibits high stiffness in the principal axis and other directions. In addition, 3D material extended by the proposed 2D material is proposed and verified by finite element method whose parameter analysis have also been carried out, which can achieve NTE and NPR effects in three directions.

We theoreticallydemonstrate the realization of the ultranarrow dual-band perfect absorption at visible range in 3D metamaterials comprising Au vertical split-ring resonators (VSRRs) array above a thick Au film for high-sensitivity sensing. By placing the 3D metamaterial of Au VSRRs directly onto the Au substrate to remove the dielectric substrates effect, the simulated results reveal that ultranarrow dual-band perfect absorption with the two narrow absorption bandwidth of 7.3 nm and 1.1 nm in the visible regime can be excited from pure magnetic plasmon (MP) resonance and via the strong coupling between the MP resonance of the VSRRs and the surface plasmons polaritons (SPPs) propagating on the Au film, respectively. Moreover, coupling effects in the VSRRs with different structural parameters also are studied in detail. Because of the ultranarrow dual-band perfect absorption of the VSRRs being extremely sensitive to the changes of the material surrounding, our proposed 3D metamaterial exhibits ultrahigh sensitivity ( S = 918 nm/RIU, S * = 680/RIU) and figure of merit ( FoM = 835, FoM * = 4.5×106) in near-infrared regime, which hold potential applications in label-free biosensing.

Precise control of value and dispersion characteristics of negative permittivity is still an unsolved problem in the practical application of random metamaterials. In this work, the ternary percolation nanocomposites (CNTs-GR-CCTO) were prepared via a low-temperature sintering process by using graphene (GR), carbon nanotubes (CNTs), and copper calcium titanate (CCTO). As the total carbon contents increased, the three-dimensional carbon network was formed, and negative permittivity is realized, which exhibits the Lorentz-type and Drude-type dispersion behaviors. The synergistic effect between GR and CNTs was studied in detail. While the GR sheets separate the CNTs, the CNTs also act as wires to connect the GR sheets. Controlled conductive paths were created by changing the ratio of CNTs to GR, achieving precise regulation of the negative permittivity, which is further certified by the equivalent circuit analysis. We provide a novel strategy for the precise regulation of negative permittivity of carbon-matrix metamaterials, which will greatly facilitate applications of metamaterials with negative permittivity. Precise regulation of weakly negative permittivity is achieved in CaCu3Ti4O12 metacomposites by synergistic effects of carbon nanotubes and graphene.

This study describes the design and characterization of a highly sensitive THz refractive index-based metamaterial sensor for the detection of biological samples. The proposed ultra-miniaturized THz sensor is constructed using a fan-shaped resonator enclosed within a square loop. The proposed sensor has a footprint of 0.353 $\lambda$ eff × 0.353 $\lambda$ eff where $\lambda$ eff is the wavelength calculated at the operating frequency of 4.87 THz. The sensitivity of the THz sensor is estimated using the absorption characteristics of the metamaterial. The estimated free space absorptivity is 99.9%. The proposed sensor is polarization insensitive due to the rotational symmetry and it is angularly stable up to 60°. The performance of the sensor is evaluated for different materials and biomedical samples. The results indicate that the proposed sensor has an average sensitivity of 1936 GHz/ Refractive Index Unit (RIU). Furthermore, the influence of the sample thickness is analysed, and the results are presented. From the results, it is inferred that the proposed THz sensor has a good Figure of Merit (FoM) and is suitable for chemical sensing, including the nucleic acids and other components present in the biological samples.

This work presents a novel symmetrical circular-shaped metamaterial design with dual resonance frequencies for the X-and Ku-band applications. The fast-growing technology in communication systems has encouraged researchers to conduct various studies in the related bands. Therefore, this research emphasis is to design a compact 8 × 8 mm2 sized metamaterial design that can be applied to the communications system. A total of five distinct circular-shaped metamaterial (CM) structures were constructed on 1.524 mm thick Rogers RT6002 material to gain the objective of this investigation. Meanwhile, investigation of the metamaterial electromagnetic properties and effective medium parameters were carried out by utilising Computer Simulation Technology Microwave Studio (CST) software. Several design constraints and parameters were nominated, and each parameter variation was analysed in the present paper. Based on the numerical simulation data, the proposed CM unit cell manifested dual-resonance frequencies precisely at 8.667 GHz (at X-band) and 13.835 GHz (at Ku-band). Furthermore, the validation procedure was carried out by comparing the measured and simulated results and the outcome clearly shows that the second resonance frequency was increased by 0.336 GHz while the first frequency was reduced by 0.071. In the meantime, the CM design was simulated in High-frequency Structure Simulator (HFSS) to validate the numerical result. There were slight differences occurred among the simulation results of both software and the comparison was largely in agreement. The introduced CM design manifests left-handed characteristics for all peak values. Proving the CM design reaches the goal of this scientific study and can be used in communication system applications.