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We present a polarization-insensitive five-band terahertz perfect metamaterial absorber composed of two metallic circular rings and a metallic ground film separated by a dielectric layer. The calculated results show that the absorber has five distinctive absorption bands whose peaks are greater than 99% on average. The physical origin of the absorber originates from the combination of dipolar, hexapolar, and surface plasmon resonance of the patterned metallic structure, which is different from the work mechanism of previously reported absorbers. In addition, the influence of the structural parameters on the absorption spectra is analyzed to further confirm the origin of the five-band absorption peaks. The proposed absorber has potential applications in terahertz imaging, refractive index sensing, and material detecting. [ABSTRACT FROM AUTHOR]

We propose a simple structure based on monolayer graphene with two layers dielectric grating. The effect of structural parameters on the optical behavior is studied by using the rigorous couple wave analysis method. The situation of changing incident angle for TM polarization is considered without changing the geometrical parameters. The absorption of about 77% and the Q-factor value of about 3390 can be obtained. In order to enhance absorption, we further design perfect absorption based on monolayer graphene with multiple-layer dielectric grating structure. The guide-mode resonances of both the grating and the dielectric layers are excited to achieve perfect multi-peak absorption. The proposed structure uses relatively less layers to achieve the perfect absorption, which can provide a reference for the further development of high sensitive modulators. [ABSTRACT FROM AUTHOR]

A new scheme to achieve a simple design of triple-band metamaterial absorber at terahertz frequency is presented. In this scheme, we employ a traditional sandwich structure, which is consisted of a metallic resonator and an appropriate thickness of the dielectric layer backed with an opaque metallic board, as the research object. Three strong but discrete resonance peaks with the narrow bandwidths and high absorptivities are realized. The combination of the dipolar resonance, LC (inductor-capacitor circuit) resonance, and the surface resonance of the metallic resonator determines the triple-band absorption. Numerical results also show that the frequencies of the three absorption bands and the number of the resonance peaks can be effectively tuned by adjusting or changing the geometric parameters of the metallic resonator. Moreover, we present a simple design of five-band terahertz absorber by further optimizing the sizes of the metallic elements in the top layer of the metamaterial. The design of the unit structures will assist in designing innovative absorbing devices for spectroscopy imaging, detection, and sensing. [ABSTRACT FROM AUTHOR]

We present a multi-band terahertz absorber formed by periodic square metallic ribbon with T-shaped gap and a metallic ground plane separated by a dielectric layer. It is demonstrated that absorption spectra of the proposed structure consist of four absorption peaks located at 1.12, 2.49, 3.45, and 3.91 THz with high absorption coefficients of 98.0, 98.9, 98.7, and 99.6%, respectively. It is demonstrated that the proposed absorber has the tunability from single-band to broadband by changing the length of square metallic ribbon and we can also select or tune the frequencies which we want to use by changing polarization angles. Importantly, the quality factor Q at 3.91 THz is 30.1, which is 5.6 times higher than that of 1.12 THz. These results indicate that the proposed absorber has a promising potential for devices, such as detection, sensing, and imaging. [ABSTRACT FROM AUTHOR]

A perfect absorber based on plasmonic resonance for a variety of remarkable properties has motivated vivid research during the last few decades. However, most of the perfect absorbers had been focused on polarization-insensitive and narrow-band absorption, due to the existence of a theoretical limit. It is urgent to extend the optical properties of absorbers with omnidirectional and broadband performances to satisfy the requirements for practical application. Hence, we adopt a new convenient, energy-saving, and environmentally friendly silk mediated layer nanoimprint technology to obtain biomimetic moth eye structures with omnidirectional and broadband perfect absorption. Experimental and simulation results show that the absorbers can realize the absorption efficiency to a maximum of 99% over the entire visible spectrum for angles up to 70° from normal. In addition, it also exhibits excellent bidirectional absorptive characteristic of this design. We anticipate that this absorber may have greatly potential application in the photovoltaic and thermal imaging area. [ABSTRACT FROM AUTHOR]

An ultrathin metasurface-based absorber consisting of titanium nitride (TiN) nano-disk arrays-dielectric layer-TiN substrate is proposed in this paper. The absorber exhibits near-unity absorption in the whole visible range of 380-780 nm. Our results demonstrate that the proposed metasurface-based absorber is not only independent of light polarization, but also exhibits angle-independent absorption behavior for oblique incidence up to 70. The high absorption performance of the TiN nano-disk arrays-based absorber can attribute to two different loss mechanisms associated with the intrinsic loss and plasmonic resonance. [ABSTRACT FROM AUTHOR]

We theoretically investigate a metasurface perfect absorber based on indium-tin-oxide as active material. Our design scheme relies on conventional metal-oxide-semiconductor model and the Drude model. Inducing a voltage into the device causes a blue-shift of 50 nm in the reflectance spectrum in the infrared region. The total thickness of the device is only 3.5% of the working wavelength λ = 2.56 μm, and the rate of reflectance change reaches 5.16 at λ = 2.56 μm. Because the material that we use has advantages of easy fabrication and fast response, our design approach can be used for numerous applications on active plasmonic sensors and filters. [ABSTRACT FROM AUTHOR]

In this article a new design of metamaterial perfect absorber (MPA) has been proposed which comprises a periodic array of LiTaO 3 microcylinders grown over a silver substrate. The fundamental principle of the structure is the occurrence of Mie resonance in the cylinders due to high value of refractive index ( ∼ 10) of LiTaO 3 in the wavelength range 65–100 μ m. This remarkably high refractive index is a manifestation of polaritonic resonance of LiTaO 3 in the considered wavelength range. The proposed structure shows high absorption coefficient in the said wavelength range with a maximum of 99.9% around 88 μ m. [ABSTRACT FROM AUTHOR]

• Proposed ultra-narrow dual-band perfect absorber achieved ultrahigh Q -factor (greater than1200). • Novel phase-change materials In 3 SbTe 2 was introduced in metasurface. • The sensing characteristics of ultra-narrow band perfect absorber were investigated. • Continuous active tunable absorption characteristics has realized by controlling the phase state of In 3 SbTe 2. Recent progress on metasurface with high quality factors (Q -factors) based absorption of light is promising for optical filtering and sensing. However, most reported metasurface-based absorbers are suffering from limited bandwidth due to the single mode and non-reconfiguration features, which have greatly restricted their practical applications. Herein, we propose a tunable absorber with high Q -factors combined with the phase-change materials (PCM) In 3 SbTe 2 (IST), whose optical properties can change from dielectric to metallic upon crystallization in the whole infrared spectral range. Moreover, we investigate the dual-band resonant modes separately. The Q -factors of the proposed dual-band perfect absorber are both greater than 1200 when the IST is amorphous state, which can be attributed to the low radiative loss of the guide-mode resonances and low intrinsic loss of the constituent materials. Hence, the proposed high Q -factors absorber is the best candidate for a sensitive refractive index sensor since its corresponding absorption spectrum changes significantly with the slight change of the refractive index of surrounding mediums. Our dual-band sensor scheme shows extreme spectral sensitivity with respect to the refractive index change to be 185.2 nm/RIU and 57.2 nm/RIU with a figure of merit of 84.2 and 22.9, respectively. Furthermore, by controlling the phase transition in IST, we further proved that the proposed absorber can be modulated continuously due to the non-volatile property of IST. Overall, the proposed dual-band absorber provides an alternative and simple pathway for the construction of dynamic and multifunctional optical devices, such as optical modulators, tunable multiband filters and biochemical sensors. [ABSTRACT FROM AUTHOR]

Plasmonic metamaterials are artificial materials typically composed of noble metals in which the features of photonics and electronics are linked by coupling photons to conduction electrons of metal (known as surface plasmon). These rationally designed structures have spurred interest noticeably since they demonstrate some fascinating properties which are unattainable with naturally occurring materials. Complete absorption of light is one of the recent exotic properties of plasmonic metamaterials which has broadened its application area considerably. This is realized by designing a medium whose impedance matches that of free space while being opaque. If such a medium is filled with some lossy medium, the resulting structure can absorb light totally in a sharp or broad frequency range. Although several types of metamaterials perfect absorber have been demonstrated so far, in the current paper we overview (and focus on) perfect absorbers based on nanocomposites where the total thickness is a few tens of nanometer and the absorption band is broad, tunable and insensitive to the angle of incidence. The nanocomposites consist of metal nanoparticles embedded in a dielectric matrix with a high filling factor close to the percolation threshold. The filling factor can be tailored by the vapor phase co-deposition of the metallic and dielectric components. In addition, novel wet chemical approaches are discussed which are bio-inspired or involve synthesis within levitating Leidenfrost drops, for instance. Moreover, theoretical considerations, optical properties, and potential application of perfect absorbers will be presented.

Mid-infrared perfect absorbers (PAs) based on metamaterials have many applications in material analysis and spectral detection thanks to the associated strong light−matter interaction. Most of the PAs are built as ‘metal nanostructure’-insulator-metals (MIM). In this paper, we propose an ultra-narrow band absorber based on dielectric metasurface with a metal film substrate. The absorptance comes from the plasmonic absorption in the metal film, where the absorption is enhanced (while the band of that is compressed) by the super cavity effect of the dielectric metasurface. Based on our numerical calculation, the full-width at half-maximum (FWHM) can reach 67 nm at 8 μm (8‱), which is more than two orders of magnitude smaller than the resonance wavelength and much narrower than the theoretical FWHMs of MIM absorbers. Moreover, we studied their application in infrared thermal imaging, which also has more benefits than MIM absorbers. This kind of hybrid dielectric metasurface provides a new route to achieve ultra-narrow band perfect absorbers in the mid-infrared regime and can be broadly applied in detectors, thermal emitters and bio-spectroscopy.

Vanadium dioxide (VO2) is a temperature phase change material that has metallic properties at high temperatures and insulation properties at room temperature. In this article, a novel device has been designed based on the dielectric metasurface consisting of VO2 and graphene array, which can achieve multiple functions by adjusting temperature and voltage. When the temperature is high (340 K), the device is in the absorption state and its absorptivity can be dynamically controlled by changing the temperature. On the other hand, the device is in the polarization state under room temperature, and the polarization of electromagnetic waves can be dynamically controlled by adjusting the voltage of graphene. This device can achieve a broadband absorber (the maximum absorptance reaches 99.415% at wavelengths ranging from 44 THz to 52 THz) and high polarization conversion efficiency (>99.89%) in the mid-infrared range, which has great advantages over other single-function devices. Our results demonstrate that this multifunctional device may have widespread applications in emitters, sensors, spatial light modulators, IR camouflages, and can be used in thermophotovoltaics and wireless communication.

Metamaterials integrated with graphene exhibit tremendous freedom in tailoring their optical properties, particularly in the infrared region, and are desired for a wide range of applications, such as thermal imaging, cloaking, and biosensing. In this article, we numerically and experimentally demonstrate an ultrathin (total thickness < λ 0 / 15 ) and electrically tunable mid-infrared perfect absorber based on metal−insulator−metal (MIM) structured metamaterials. The Q-values of the absorber can be tuned through two rather independent parameters, with geometrical structures of metamaterials tuning radiation loss (Qr) of the system and the material loss (tanδ) to further change mainly the intrinsic loss (Qa). This concise mapping of the structural and material properties to resonant mode loss channels enables a two-stage optimization for real applications: geometrical design before fabrication and then electrical tuning as a post-fabrication and fine adjustment knob. As an example, our device demonstrates an electrical and on-site tuning of ~5 dB change in absorption near the perfect absorption region. Our work provides a general guideline for designing and realizing tunable infrared devices and may expand the applications of perfect absorbers for mid-infrared sensors, absorbers, and detectors in extreme spatial-limited circumstances.

Integration of metamaterial and nonvolatile memory devices with tunable characteristics is an enthusing area of research. Designing a unique nanoscale prototype to achieve a metasurface with reliable resistive switching properties is an elusive goal. We demonstrate a method to exploit the advantages of a phase-change material (PCM) as a metamaterial light absorber and a nanoscale data storage device. We designed and simulated a metamaterial perfect absorber (MPA) that can be reconfigured by adjusting the visible light properties of a chalcogenide-based PCM. The suggested perfect absorber is based on a Ge2Sb2Te5 (GST) film, and is tuned between two distinct states by heat treatment. Furthermore, we fabricated and characterized a resistive switching memory (ReRAM) device with the same features. The MPA/ReRAM device with a conventional metal/dielectric/metal structure (Ag/GST/Al2O3/Pt) consisted of arrays of Ag squares patterned on a GST thin film and an alumina-coated Pt mirror on a glass substrate. Based on the numerical data, amorphous GST showed perfect absorbance in the visible spectrum, whereas, crystalline GST showed broadband perfect absorbance. The fabricated ReRAM device exhibited uniform, bidirectional, and programmable memory characteristics with a high ON/OFF ratio for nonvolatile memory applications. The elucidated origin of the bipolar resistive switching behavior is assigned to the formation and rupture of conductive filaments.

The spectral range of solar radiation observed on the earth is approximately 295 to 2500 nm. How to widen the absorption band of the plasmonic absorber in this range has become a hot issue in recent years. In this paper, we propose a highly applicable refractory perfect absorber with an elliptical titanium nanodisk array based on a silica⁻titanium⁻silica⁻titanium four-layer structure. Through theoretical design and numerical demonstration, the interaction of surface plasmon resonance with the Fabry⁻Perot cavity resonance results in high absorption characteristics. Our investigations illustrate that it can achieve ultra-broadband absorption above 90% from a visible 550-nm wavelength to a near-infrared 2200-nm wavelength continuously. In particular, a continuous 712-nm broadband perfect absorption of up to 99% is achieved from wavelengths from 1013 to 1725 nm. The air mass 1.5 solar simulation from a finite-difference time domain demonstrates that this absorber can provide an average absorption rate of 93.26% from wavelengths of 295 to 2500 nm, which can absorb solar radiation efficiently on the earth. Because of the high melting point of Ti material and the symmetrical structure of this device, this perfect absorber has excellent thermal stability, polarization independence, and large incident-angle insensitivity. Hence, it can be used for solar cells, thermal emitters, and infrared detection with further investigation.

We propose a new broadband metamaterial perfect absorber (MPA) based on structure of metallic dishes in the THz region. It demonstrated that the coupling interaction between the central dish and adjacent dishes leads to absorption characteristics. By optimizing the geometrical structure, the bandwidth is gained up to 1.0THz with absorption better than 90%. The mechanism of the absorption results was explained by induced current, magnetic and electric distributions. Furthermore, LC equivalent circuit was used to elucidate resonant frequencies. The obtained results can provide a general guideline for fabricating broadband MPA. [ABSTRACT FROM AUTHOR]

A broadband perfect absorber based on loading effect–induced single-layer/trench-like thin metallic (LISTTM) structures is demonstrated. These LISTTM structures take advantage of both surface plasmon resonance and three-dimensional cavity effects to provide efficient, tunable, polarization-insensitive absorption from the ultraviolet (UV) to the infrared (IR) regime. The optimized hole-width of the LISTTM arrays was approximately one half of the designed wavelength. Therefore, even when the designed absorption band was in the visible regime, the feature sizes of the LISTTM structure could remain on the order of several hundred nanometers. Moreover, the loading effects, which were generated during the etching and deposition processes, further improved the maximum absorption to greater than 95% and widened the absorption bandwidth of the structures significantly. These LISTTM structures exhibited superior photothermal performance; they also displayed very low emissivity, thereby decreasing heat dispersion through thermal radiation. Therefore, the LISTTM arrays could efficiently absorb light of higher photon energy in the UV, visible, and near-IR regimes, effectively conduct the generated heat through the continuous metal films, and barely disperse any heat through thermal radiation. Accordingly, these attractive properties suggest that such LISTTM absorbers might have promising applications in many fields related to energy harvesting. [ABSTRACT FROM AUTHOR]

We design and numerically investigate a wide angle and broadband perfect absorber with compact multilayer structures. The proposed structure is composed of three stacks of semiconductor films and one metal layer. The absorber presents a broadband absorption between 450 nm and 700 nm with an average absorption above 99.2%. For oblique incidence, the absorber shows an average absorption about 90% for a wide range of incident angles from 0 to 60 with p polarization and s polarization. The electrical field intensity distributions are also studied to disclose the broadband absorption mechanism. This designed broadband absorber appears to have very promising applications in solar thermal energy harvesting, thermal emitters and detection. [ABSTRACT FROM AUTHOR]

Broadband absorbers are essential components of many light detection, energy harvesting, and camouflage schemes. Current designs are either bulky or use planar films that cause problems in cracking and delamination during flexing or heating. In addition, transferring planar materials to flexible, thin, or low-cost substrates poses a significant challenge. On the other hand, particle-based materials are highly flexible and can be transferred and assembled onto a more desirable substrate but have not shown high performance as an absorber in a standalone system. Here, we introduce a class of particle absorbers called transferable hyperbolic metamaterial particles (THMMP) that display selective, omnidirectional, tunable, broadband absorption when closely packed. This is demonstrated with vertically aligned hyperbolic nanotube (HNT) arrays composed of alternating layers of aluminum-doped zinc oxide and zinc oxide. The broadband absorption measures >87% from 1,200 nm to over 2,200 nm with a maximum absorption of 98.1% at 1,550 nm and remains large for high angles. Furthermore, we show the advantages of particle-based absorbers by transferring the HNTs to a polymer substrate that shows excellent mechanical flexibility and visible transparency while maintaining near-perfect absorption in the telecommunications region. In addition, other material systems and geometries are proposed for a wider range of applications. [ABSTRACT FROM AUTHOR]

Multi-band or broadband perfect metamaterial absorbers, based on coplanar super-unit structure or multiple vertically stacked layers, have received intense attention because of their potential for practical applications. The resonance mechanism of them usually only utilizes the overlapping of the fundamental resonance of the different-sized patterns, and neglects the high-order resonance of the structure, and thus making the proposed structures quite troublesome to be fabricated and the mechanism of the current demonstrated absorbers lack of novelty. In this paper, a simple design of dual-band terahertz absorber consisted of only a traditional square metallic patch and a dielectric layer on top of a continuous ground plane is presented. Simulation results show that the single resonant structure has two resonance absorption peaks, which are both average over 99.5 %. The mechanism of the dual-band absorber is due to the overlapping of the fundamental mode and three-order response of the patterned structure, which is totally different from previous reports that only combining the fundamental resonances of the different-shaped complex structures to obtain the dual-band response. Furthermore, the proposed single-patterned structure can be used to extend the number of the absorption peaks (for example, triple-band absorber) by combining one more resonance (the five-order response). The proposed absorbers with the simple structure design have potential applications in many areas, such as detection, sensing, and selective thermal emitters. [ABSTRACT FROM AUTHOR]

A new strategy for realizing ultra-narrowband plasmonic absorber has been theoretically demonstrated. Dual-band perfect light absorber with the bandwidth down to single digit level and the maximal absorption exceeding 99.2 % is achieved. Moreover, novel absorber-based sensor platform with high-quality factors ( S > 420 nm/RIU, FOM > 84, and FOM* > 5600) are obtained. These features hold the proposed absorber to be a feasible candidate for applications in the sensing detection and notch filtering. [ABSTRACT FROM AUTHOR]

• The proposed metamaterial absorber can obtain three perfect absorption peaks (98.7% (878 nm), 99.8% (1020 nm), 99.5% (1276 nm)) in the wavelength range from 600 nm to 1600 nm. • Single or multiple absorption peaks of metamaterial perfect absorber can be adjusted individually. • The absorber with a simple structure, multi-narrowband, tunability, polarization-independence and high sensitivity. In recent years, metamaterials have been widely used as a new type of optoelectronic device materials, such as optical stealth, holographic imaging, and metamaterial absorbers. In particular, the research of metamaterial absorbers with multi-narrowband, high absorption and tunability has attracted much attention. However, it is a great challenge to integrate multi-narrowband, high absorption, polarization independence, high sensitivity and tunability into a simple absorption structure. In this paper, we use FDTD to design a multi-narrow band, polarimetric independent, high sensitivity and tunability of metamaterial perfect absorber, which is a metal-dielectric-metal three-layer structure. From the bottom to the top of the structure, they are Au layer, SiO 2 layer and Au pattern layer. The simulation results show that three resonance absorption peaks are obtained under the coaction of local surface plasmon resonance, magnetic resonance and cavity resonance. The absorption peaks are located at 878 nm, 1020 nm and 1276 nm, and the absorption rates are 98.7%, 99.3% and 99.5%, respectively. In addition, it is found that the number of absorption peaks can be changed by adjusting the top pattern layer structure. Further, the position of the absorption peak and the absorption rate can be altered by adjusting the geometric parameters of the structure. Besides its simple structure, the analysis also show that the structure has high sensitivity under different refractive index environment. Finally, it can also be used for optical conversion devices, such as optical absorption switches, splitters, optical modulators. [ABSTRACT FROM AUTHOR]

A mid-infrared perfect metamaterial absorber (PMA) consisting of well-engineered unit cells, composed of metallic backed layer (Cu), dielectric layer (Al 2 O 3), matts-shaped meta cell (Cu), and an anti-oxidation layer from bottom to top, is proposed in this paper. The electromagnetic response of the designed PMA is analyzed using 3D full-wave computational model. Our analysis demonstrates that the maximum absorption is enhanced to 99.9% at the resonance wavelength of 7.35 µm, which is caused by magnetic polaritons (MPs) resonance between the incident beam and magnetic polaritons formed by three fluxing currents. Specially, a three-circulation equivalent circuit model is proposed to predict the resonant wavelength of the designed PMA, which comprehensively considers the influence of coupling capacitance not only between neighboring unit cells, but also between the metal lines inside the top metal pattern for the first time. The influence of geometrical parameters on resonant wavelength is predicted by the equivalent circuit model proposed in this paper, and the prediction error is less than 5% as compared with that of computational analysis. With well-engineered plasmonic meta-atoms, the designed PMA presents the characteristics of angle and polarization- independent with a smaller relative size (0.245λ) and a thinner relative thickness (0.053λ). Besides, an obvious red-shift of the resonance frequency of PMA is observed as the permittivity of dielectric layers is increased. The approach of establishing equivalent circuit model will provide methods for the analysis of PMA based on MPs with complex electromagnetic behavior. [ABSTRACT FROM AUTHOR]

Compared with homogeneous metamaterials, realizing unidirectional reflectionlessness (UR) is relatively challenging for heterogeneous metamaterials. Herein, we study UR based on the near field phase coupling mode in a silver/gold heterogeneous metamaterial system using the finite-difference time-domain (FDTD) and scattering matrix theory. The results show that unidirectional reflectionless propagation can be effectively controlled by appropriately adjusting the distance (the phase) between the two heterogeneous resonators. At the same time, the unidirectional perfect absorber (UPA) can be obtained near EPs. What's more, the change in the eigenvalue of the scattering matrix can clearly describe the physical mechanisms for the evolution of UR and UPA. In particular, the analytical calculation results are consistent with the numerical simulation conclusions. These results potentially have important implications for achieving nanoscale unidirectional devices. • The UR light propagation can be realized in a non-Hermitian heterogeneous metamaterial system. • The excitation intensity of induced current at two exceptional points (EPs) is completely distinct in our proposed system. • The physical mechanism of UR is confirmed by the scattering matrix theory. [ABSTRACT FROM AUTHOR]

A switchable ultra-wideband THz absorber based on vanadium dioxide was proposed, which consists of a lowermost gold layer, a PMI dielectric layer, and an insulating and surface vanadium dioxide layer. Based on the phase transition properties of vanadium dioxide, switching performance between ultra-broadband and narrowband can achieve a near-perfect absorption. The constructed model was simulated and analyzed using finite element analysis. Simulations show that the absorption frequency of vanadium dioxide above 90% is between 3.8 THz and 15.6 THz when the vanadium dioxide is in the metallic state. The broadband absorber has an absorption bandwidth of 11.8 THz, is insensitive to TE and TM polarization, and has universal incidence angle insensitivity. When vanadium dioxide is in the insulating state, the narrowband absorber has a Q value as high as 1111 at a frequency of 13.89 THz when the absorption is more excellent than 99%. The absorber proposed in this paper has favorable symmetry properties, excellent TE and TM wave insensitivity, overall incidence angle stability, and the advantages of its small size, ultra-widebands and narrowbands, and elevated Q values. The designed absorber has promising applications in multifunctional devices, electromagnetic cloaking, and optoelectronic switches.

Spatial overlap between the electromagnetic fields and the analytes is a key factor for strong light-matter interaction leading to high sensitivity for label-free refractive index sensing. Usually, the overlap and therefore the sensitivity are limited by either the localized near field of plasmonic antennas or the decayed resonant mode outside the cavity applied to monitor the refractive index variation. In this paper, by constructing a metal microstructure array-dielectric-metal (MDM) structure, a novel metamaterial absorber integrated microfluidic (MAIM) sensor is proposed and demonstrated in terahertz (THz) range, where the dielectric layer of the MDM structure is hollow and acts as the microfluidic channel. Tuning the electromagnetic parameters of metamaterial absorber, greatly confined electromagnetic fields can be obtained in the channel resulting in significantly enhanced interaction between the analytes and the THz wave. A high sensitivity of 3.5 THz/RIU is predicted. The experimental results of devices working around 1 THz agree with the simulation ones well. The proposed idea to integrate metamaterial and microfluid with a large light-matter interaction can be extended to other frequency regions and has promising applications in matter detection and biosensing. [ABSTRACT FROM AUTHOR]

Metamaterials are composed of nanostructures, called artificial atoms, which can give metamaterials extraordinary properties that cannot be found in natural materials. The nanostructures themselves and their arrangements determine the metamaterials’ properties. However, a conventional metamaterial has fixed properties in general, which limit their use. Thus, real-world applications of metamaterials require the development of tunability. This paper reviews studies that realized tunable and reconfigurable metamaterials that are categorized by the mechanisms that cause the change: inducing temperature changes, illuminating light, inducing mechanical deformation, and applying electromagnetic fields. We then provide the advantages and disadvantages of each mechanism and explain the results or effects of tuning. We also introduce studies that overcome the disadvantages or strengthen the advantages of each classified tunable metamaterial.