Showing papers on "Metamaterial absorber published in 2015"

Experimental demonstration of ultrasensitive sensing with terahertz metamaterial absorbers: A comparison with the metasurfaces

Abstract: Planar metasurfaces and plasmonic resonators have shown great promise for sensing applications across the electromagnetic domain ranging from the microwaves to the optical frequencies. However, these sensors suffer from lower figure of merit and sensitivity due to the radiative and the non-radiative loss channels in the plasmonic metamaterial systems. We demonstrate a metamaterial absorber based ultrasensitive sensing scheme at the terahertz frequencies with significantly enhanced sensitivity and an order of magnitude higher figure of merit compared to planar metasurfaces. Magnetic and electric resonant field enhancement in the impedance matched absorber cavity enables stronger interaction with the dielectric analyte. This finding opens up opportunities for perfect metamaterial absorbers to be applied as efficient sensors in the finger print region of the electromagnetic spectrum with several organic, explosive, and bio-molecules that have unique spectral signature at the terahertz frequencies.

A broadband terahertz absorber using multi-layer stacked bars

Abstract: We present the simulation, implementation, and measurement of a broadband terahertz (THz) metamaterial absorber. By stacking 12 metallic bars of varying lengths on three polyimide layers with equal spacing, a broadband absorption spectrum is formed through merging multiple successive resonance peaks. The measured total absorption exceeds 95% from 0.81 to 1.32 THz at the normal incidence and the full width at half maximum is 64% (from 0.76 to 1.48 THz). The absorption decreases with fluctuations as the incident angle increases but remains above 62% even at the incident angle of 40°. The physical explanation to the absorption mechanism is presented and verified by a 9-bar example, which exhibits narrower absorption bandwidth. It is also experimentally demonstrated that the proposed structure is robust against misalignment of each metallic layer.

Flexible metasurfaces and metamaterials: A review of materials and fabrication processes at micro- and nano-scales

Abstract: The ability to bend, stretch, and roll metamaterial devices on flexible substrates adds a new dimension to aspects of manipulating electromagnetic waves and promises a new wave of device designs and functionalities. This work reviews terahertz and optical metamaterials realized on flexible and elastomeric substrates, along with techniques and approaches to lend tunability to the devices. Substrate electromagnetic and mechanical characteristics suitable for flexible metamaterials are summarized for readers, followed by fabrication and processing techniques, and finally novel approaches used to-date to attain tunability. Future directions and emerging areas of interests are identified with these promising to transform metamaterial design and translate metamaterials into practical devices.

Large-Scale All-Dielectric Metamaterial Perfect Reflectors

Abstract: All-dielectric metamaterials offer a potential low-loss alternative to plasmonic metamaterials at optical frequencies. Here, we take advantage of the low absorption loss as well as the simple unit cell geometry to demonstrate large-scale (centimeter-sized) all-dielectric metamaterial perfect reflectors made from silicon cylinder resonators. These perfect reflectors, operating in the telecommunications band, were fabricated using self-assembly based nanosphere lithography. In spite of the disorder originating from the self-assembly process, the average reflectance of the metamaterial perfect reflectors is 99.7% at 1530 nm, surpassing the reflectance of metallic mirrors. Moreover, the spectral separation of the electric and magnetic resonances can be chosen to achieve the required reflection bandwidth while maintaining a high tolerance to disorder. The scalability of this design could lead to new avenues of manipulating light for low-loss and large-area photonic applications.

A novel dual-band terahertz metamaterial absorber for a sensor application

Abstract: We present a new type of dual-band terahertz metamaterial absorber formed by a patterned metallic strip and a dielectric layer on top of a metallic ground plane. It is found that besides a strong absorption in the fundamental resonance, a prominent high-order resonance with near-unity absorption is also unveiled. The origin of the induced dual-band absorption was elucidated. Importantly, the quality factor (Q) and the figure of merit (FOM) of the high-order resonance are 8.4 and 22.7 times larger than that of the fundamental resonance, respectively, which makes the proposed absorber to have significant potential in biological monitoring and sensing. Moreover, we demonstrate a dual-band and insensitive for two orthogonal polarizations terahertz absorber based on a metallic cross and a metallic ground plane separated by a dielectric layer. The Q and FOM of the high-order resonance are still larger than that of the fundamental resonance. The proposed absorbers appear to be very promising for solar cells, detection, and imaging applications.

Metamaterial electromagnetic energy harvester with near unity efficiency

Abstract: We present the design of a metamaterial medium for electromagnetic energy harvesting based on the full absorption concept. A metamaterial slab was designed comprising 13 × 13 electrically small cells, each loaded with an 82 Ω resistor which mimics the input impedance of a rectification circuitry. Unlike earlier designs of metamaterial absorbers, here the power absorption is mostly dissipated across a resistive load instead of the dielectric substrate. This implies that effective electromagnetic energy harvesting can be achieved. The power is channeled through a via connected to each cell. For a design optimized at 3 GHz, simulation and experimental results show power absorption efficiency of 97% and 93%, respectively.

Multispectral terahertz sensing with highly flexible ultrathin metamaterial absorber

Abstract: We report the simulation, fabrication, and experimental characterization of a multichannel metamaterial absorber with the aim to be used as a label-free sensing platform in the terahertz regime. The topology of the investigated resonators deposited on a thin flexible polymer by means of optical lithography is capable of supporting multiple resonances over a broad frequency range due to the individual contribution of each sub-element of the unit cell. In order to explore the performance of the chosen structure in terms of sensing phenomenon, the reflection feature is monitored upon variation of the refractive index and the thickness of the analyte. We achieve numerically maximum frequency sensitivity of about 139.2 GHz/refractive index unit. Measurements carried out using terahertz time-domain spectroscopy show good agreement with the numerical predictions. The results are very promising, suggesting a potential use of the metamaterial absorber in wide variety of multispectral terahertz sensing applications.

Water: Promising Opportunities For Tunable All-dielectric Electromagnetic Metamaterials.

Abstract: We reveal an outstanding potential of water as an inexpensive, abundant and bio-friendly high-refractive-index material for creating tunable all-dielectric photonic structures and metamaterials. Specifically, we demonstrate thermal, mechanical and gravitational tunability of magnetic and electric resonances in a metamaterial consisting of periodically positioned water-filled reservoirs. The proposed water-based metamaterials can find applications not only as cheap and ecological microwave devices, but also in optical and terahertz metamaterials prototyping and educational lab equipment.

Terahertz dual-band metamaterial absorber based on graphene/MgF(2) multilayer structures.

Abstract: We design an ultra-thin terahertz metamaterial absorber based on graphene/MgF2 multilayer stacking unit cells arrayed on an Au film plane and theoretically demonstrate a dual-band total absorption effect. Due to strong anisotropic permittivity, the graphene/MgF2 multilayer unit cells possess a hyperbolic dispersion. The strong electric and magnetic dipole resonances between unit cells make the impedance of the absorber match to that of the free space, which induces two total absorption peaks in terahertz range. These absorption peaks are insensitive to the polarization and nearly omnidirectional for the incident angle. But the absorption intensity and frequency depend on material and geometric parameters of the multilayer structure. The absorbed electromagnetic waves are finally converted into heat and, as a result, the absorber shows a good nanosecond photothermal effect.

Metamaterial Absorber for Electromagnetic Waves in Periodic Water Droplets.

Abstract: Perfect metamaterial absorber (PMA) can intercept electromagnetic wave harmful for body in Wi-Fi, cell phones and home appliances that we are daily using and provide stealth function that military fighter, tank and warship can avoid radar detection. We reported new concept of water droplet-based PMA absorbing perfectly electromagnetic wave with water, an eco-friendly material which is very plentiful on the earth. If arranging water droplets with particular height and diameter on material surface through the wettability of material surface, meta-properties absorbing electromagnetic wave perfectly in GHz wide-band were shown. It was possible to control absorption ratio and absorption wavelength band of electromagnetic wave according to the shape of water droplet–height and diameter– and apply to various flexible and/or transparent substrates such as plastic, glass and paper. In addition, this research examined how electromagnetic wave can be well absorbed in water droplets with low electrical conductivity unlike metal-based metamaterials inquiring highly electrical conductivity. Those results are judged to lead broad applications to variously civilian and military products in the future by providing perfect absorber of broadband in all products including transparent and bendable materials.

Micro- and Nanostructured Surfaces for Selective Solar Absorption

Abstract: Efficient absorption of solar radiation is desired for the renewable energy sector, such as solar thermophotovoltaics and solar thermal applications. In order to minimize thermal re-radiation, wavelength-selective devices are required. Absorbers with structured surfaces are attractive because they derive their electromagnetic properties to a greater extent from their geometry and to a lesser extent from the intrinsic properties of the constituent materials. Thus, they offer greater flexibility in the design and control of absorber features and can be tailored to suit requirements. This article reviews various classes of patterned structures: photonic crystals, metal-dielectric-metal slab arrays, metamaterials, and nanostructures operating in the visible and infrared wavelength ranges. Operation requirements, design principles and underlying physical phenomena, material and temperature considerations, as well as fabrication methods are discussed. Recent progress in achieving various desirable absorber features, such as broadband and multiband operation, polarization and angle independence, flexibility, and tunability is presented. Suggestions are also given regarding future research directions.

Reconfigurable Electromagnetics Through Metamaterials—A Review

Abstract: The introduction of electromagnetic (EM) media with unique field manipulation properties, collectively labelled as metamaterials, has boosted the interest toward the design, the fabrication, and the testing of artificial materials whose features can be engineered according to the applicative requirements and user objectives. In this framework, the long-term promise of reconfigurable metamaterial theory (i.e., the possibility to change the EM response of a 2-D/3-D material arbitrarily and in real time) has given the designers an extremely wide number of new degrees of freedom for the synthesis of innovative adaptive systems. Moreover, successful experimental validations of reconfigurable metamaterials in the entire EM spectrum from microwaves to optical frequencies have further stimulated academic and industrial interests in developing devices with enhanced performances, efficiency, and robustness. Nevertheless, the exploitation of reconfigurable metamaterials in commercial devices is still an open problem with several challenges from both the theoretical and technological viewpoints. This paper is then aimed at reviewing the latest advances on reconfigurable metamaterial engineering from the methodological perspective also providing a comprehensive and balanced survey on latest concepts, current trends, and envisaged future developments on this active field of research.

An Ultrawideband Ultrathin Metamaterial Absorber Based on Circular Split Rings

Abstract: A simple design model for making ultrawideband ultrathin metamaterial absorber has been presented in microwave frequency regime. The proposed structure is composed of two concentric circular split rings imprinted on a metal-backed dielectric substrate. A 10-dB absorption bandwidth from 7.85 to 12.25 GHz covering the entire X-band has been observed in numerical simulation under normal incidence. The absorptivities of the proposed structure have been investigated under different polarization angles as well as oblique incidence. The electromagnetic field distributions and surface current plots have been illustrated to analyze the absorption mechanism of the proposed structure. The proposed absorber has been fabricated and its performance is experimentally verified at different angles of incidence and polarizations of incident electromagnetic wave. The designed absorber is compact, ultrathin (only ${\lambda _0}/15$ thick corresponding to center frequency) and provides an alternative to construct broadband absorber for many potential applications.

An Equivalent Circuit Model of FSS-Based Metamaterial Absorber Using Coupled Line Theory

Abstract: An equivalent circuit model of an ultra-thin metamaterial absorber comprising a square-ring-shaped frequency selective surface (FSS) is presented. The model can be considered as series $RLC$ resonators connected in parallel with coupling capacitance and short-circuited transmission line. The even- and odd-mode couplings have been incorporated to accurately determine the lumped parameters as well as the absorption frequency of the absorber structure. The effects of substrate thickness and dielectric permittivity variation on the lumped parameters and full width at half-maximum (FWHM) bandwidth are investigated based on the proposed model. The absorber has been fabricated, and close matching among the calculated, simulated, and measured results has been observed.

Exchanging Ohmic Losses in Metamaterial Absorbers With Useful Optical Absorption for Photovoltaics

Abstract: Using metamaterial absorbers, we have shown that metallic layers in the absorbers do not necessarily constitute undesired resistive heating problem for photovoltaics. Tailoring the geometric skin depth of metals and employing the natural bulk absorbance characteristics of the semiconductors in those absorbers can enable the exchange of undesired resistive losses with the useful optical absorbance in the active semiconductors. Thus, Ohmic loss dominated metamaterial absorbers can be converted into photovoltaic near-perfect absorbers with the advantage of harvesting the full potential of light management offered by the metamaterial absorbers. Based on experimental permittivity data for indium gallium nitride, we have shown that between 75%–95% absorbance can be achieved in the semiconductor layers of the converted metamaterial absorbers. Besides other metamaterial and plasmonic devices, our results may also apply to photodectors and other metal or semiconductor based optical devices where resistive losses and power consumption are important pertaining to the device performance.

Design of a Four-Band and Polarization-Insensitive Terahertz Metamaterial Absorber

Abstract: We present a four-band and polarization-insensitive terahertz metamaterial absorber formed by four square metallic rings and a metallic ground plane separated by a dielectric layer. It is found that the structure has four distinctive absorption bands whose peaks are over 97% on average. The mechanism of the four-band absorber is attributed to the overlapping of four resonance frequencies, and the mechanism of the absorption is investigated by the distributions of the electric field. In particular, the frequency of each absorption peak can be flexibly controlled by varying the size of the corresponding metallic ring. The proposed concept is applicable to other types of absorber structures and can be readily scaled up to the structures that are working in the microwave frequency range. Moreover, the characteristic of the design can be used to design a five-band metamaterial absorber by adding one more metallic ring. The proposed absorber has potential applications in detection, imaging, and stealth technology.

Infrared Aluminum Metamaterial Perfect Absorbers for Plasmon‐Enhanced Infrared Spectroscopy

Abstract: Matured surface chemistry and excellent chemical stability have enabled gold to become the material-of-choice for plasmonic sensing in both visible and infrared wavelength range. Here, successful surface functionalization of metamaterials made from a low-cost abundant plasmonic material, aluminum, with phosphonic acid and subsequent detection of the CO vibration mode via surface-enhanced infrared absorption spectroscopy is demonstrated. The metamaterial consists of infrared perfect absorbers fabricated by colloidal lithography. Near perfect absorption is achieved at resonance wavelengths, which can be readily tuned by changing the diameters of the Al disk resonators, enabling excellent overlapping with the molecular vibration. Separately, the detection of a physically adsorbed protein layer on the Al metamaterial is also demonstrated. Surface functionalization with phosphonic acid provides various functional groups to the Al surfaces. Combined with tunable metamaterials, the work herein opens up great opportunities for Al-based plasmonic nanostructures for biochemical sensing applications.

Dual broadband metamaterial absorber

Abstract: We propose polarization-independent and dual-broadband metamaterial absorbers at microwave frequencies. This is a periodic meta-atom array consisting of metal-dielectric-multilayer truncated cones. We demonstrate not only one broadband absorption from the fundamental magnetic resonances but additional broadband absorption in high-frequency range using the third-harmonic resonance, by both simulation and experiment. In simulation, the absorption was over 90% in 3.93–6.05 GHz, and 11.64–14.55 GHz. The corresponding experimental absorption bands over 90% were 3.88–6.08 GHz, 9.95–10.46 GHz and 11.86–13.84 GHz, respectively. The origin of absorption bands was elucidated. Furthermore, it is independent of polarization angle owing to the multilayered circular structures. The design is scalable to smaller size for the infrared and the visible ranges.

A Triple-Band Ultrathin Metamaterial Absorber With Wide-Angle and Polarization Stability

Abstract: This letter presents a triple-band compact and efficient ultrathin metamaterial absorber with wide-angle and polarization stability. The compact single unit cell includes a metallic background plane, four groups of dipoles lying around a metallic ring connected by four groups of pins, and only 1-mm low-cost dielectric layer. In addition, the main parameters of the designed absorber are investigated and optimized to show that each of three absorption frequency points can be effectively separately adapted, respectively. The simulation results demonstrate that this absorber has good absorption rates and polarization-insensitive characteristic over wide angles of incident waves for both transverse electric (TE) and transverse magnetic (TM) in three frequency bands. The waveguide measurement method is utilized to test the simulated results of three good absorption peaks.

Bandwidth-enhanced dual-band dual-layer polarization-independent ultra-thin metamaterial absorber

Abstract: In this paper, a polarization-independent metamaterial absorber with enhanced bandwidth at two separate frequency bands is proposed over wide angle of incidence. The proposed structure consists of two layers of dielectric substrate. The unit cell is designed on the top surfaces of both the layers of the dielectric by parametric optimization in such a way that bandwidth-enhanced absorptions occur in C and X bands. The proposed structure is fabricated, and experimental results are in good agreement with the simulated responses. This bandwidth-enhanced dual-band absorption nature is maintained for any angle of polarization under normal incidence, thus making the absorber polarization independent in nature. The structure also shows bandwidth-enhanced dual-band absorptions over wide angle of incidence up to 45° under TE polarization and 30° under TM polarization. Moreover, the proposed structure is ultra-thin, having total thickness of 3.2 mm, ~λ/14 and λ/10 with respect to the center frequencies of two absorption bands.

High-performance terahertz wave absorbers made of silicon-based metamaterials

Abstract: Electromagnetic (EM) wave absorbers with high efficiency in different frequency bands have been extensively investigated for various applications. In this paper, we propose an ultra-broadband and polarization-insensitive terahertz metamaterial absorber based on a patterned lossy silicon substrate. Experimentally, a large absorption efficiency more than 95% in a frequency range of 0.9–2.5 THz was obtained up to a wave incident angle as large as 70°. Much broader absorption bandwidth and excellent oblique incidence absorption performance are numerically demonstrated. The underlying mechanisms due to the combination of a waveguide cavity mode and impedance-matched diffraction are analyzed in terms of the field patterns and the scattering features. The monolithic THz absorber proposed here may find important applications in EM energy harvesting systems such as THz barometer or biosensor.

Electrically Tunable Critically Coupled Terahertz Metamaterial Absorber Based on Nematic Liquid Crystals

Abstract: Technology to efficiently handle light in the terahertz range is sought for a wide range of applications, including nondestructive testing, medical diagnostics, and weapons detection. Liquid-crystal devices are cheap and promising, but currently suffer from high operating voltage and long response times. The authors exploit coupling between periodically arranged patch resonators and external fields to propose a low-voltage absorber whose reflectance can be modulated from nearly 0 to 90%, with switching times around 50 ms--a dramatic improvement over existing technology that stands to enable new, low-cost, highly tunable terahertz devices.

High-Impedance Surface-Based Broadband Absorbers With Interference Theory

Abstract: A broadband and polarization-insensitive high-impedance surface (HIS) metamaterial absorber (MA) based on octagonal ring-shaped resistive patches is presented. The absorber is investigated theoretically, experimentally, and by simulation. The simulated results indicate that this structure obtains 10.28 GHz wide absorption from 3.65 to 13.93 GHz with absorptivity larger than 90% at the normal incidence. Experimental results are in accordance with those of the simulation results. The electromagnetic (EM) field distributions and the plots of surface power loss density have been illustrated to analyze the absorption mechanism of the structure. Further simulations of the absorptivity of the proposed absorber with different surface resistances and substrate thicknesses indicate that there exist optimal values for the design. The polarization-insensitive feature and the properties under oblique incidence are also investigated. Finally, the interference theory is introduced to analyze and interpret the broadband absorption mechanism at both normal and oblique incidences. The calculated absorption rates of the proposed absorber coincide well with the simulated results. Therefore, the simulated and experimental results verify the validity of the theoretically analytical method for this type of broadband absorber.

Design and Development of Software Defined Metamaterials for Nanonetworks

Abstract: This paper introduces a class of programmable metamaterials, whose electromagnetic properties can be controlled via software. These software defined metamaterials (SDMs) stem from utilizing metamaterials in combination with nanonetworks. Metamaterials are artificial structures with properties that may not be found in nature. Since their initial advent, they have inspired ground-breaking applications to a range of research topics, such as electromagnetic invisibility of objects (cloaking), radiation absorption, filtering of light and sound as well as efficient antennas for sensors and implantable communication devices in recent years. However, existing metamaterial structures are ?rigid?, i.e. they cannot be restructured once constructed. This trait limits their fabrication to some well-equipped laboratories worldwide, slows down innovation, and, most importantly, restricts their applicability to static structures only. The proposed SDMs act as ?plastic? (reconfigurable) metamaterials, whose attributes can be changed programmatically via a computer interface. This control is achieved by a network of nanomachines, incorporated into the structure of the metamaterial. The nanomachines may receive commands from the user and perform simple, yet geometrically-altering, actions on the metamaterial profile and tuning of its electromagnetic behavior. Architectural aspects, expected features and implementation issues are covered in this paper, while a suitable nanonetworking model is presented along with simulation results on its anticipated performance. The paper concludes by outlining the research challenges pertaining to the analysis, design, prototyping, manufacturing, and initial application scenarios of the proposed SDMs.

Wide-angle, polarization-independent and dual-band infrared perfect absorber based on L-shaped metamaterial

Abstract: We propose a wide-angle, polarization-independent and dual-band infrared perfect metamaterial absorber made of double L-shaped gold patches on a dielectric spacer and opaque gold ground layer. Numerical and experimental results demonstrate that the absorber has two near-unity absorption peaks, which are result from magnetic polariton modes generated at two different resonant wavelengths. In addition, the proposed structure also shows good absorption stability in a wide range of incident anglesθfor both TE and TM incidences at azimuthal angle φ = 0°. Moreover, we demonstrate that such structure has good absorption stability for a wide range of azimuthal angles due to the excitation of perpendicular magnetic polariton modes within the asymmetric double L-shaped structure. Such structure will assist in designing magnetic polaritons absorbing element for infrared spectroscopy and imaging.

A frequency and bandwidth tunable metamaterial absorber in x-band

Abstract: Smart control is an attracting and important function for modern electromagnetic wave absorber. This paper presents the design, fabrication, and measurement of a frequency and bandwidth tunable metamaterial absorber (MA) in X-band. The unit cell of the MA consists of a microstrip resonator loaded with the varactors. Simulation and measurement results show that by tuning the bias voltage on the varactors, the peak absorption frequency can be tuned by 0.44 GHz with the peak absorption greater than 95%. Field and circuit model analysis is conducted to reveal the working mode and predict the absorbing frequency. After that, by specially designing the bias circuit so as to adjust the bias voltage on neighboring unit cells separately, dual resonance and absorption peaks occur, and the overall absorption bandwidth can thus be tuned conveniently by controlling the difference of the two resonance frequencies. The center absorbing frequency can also be tuned. Simulation and experiment results show that the 75% absorption (−6 dB reflection) bandwidth can be tuned from 0.40 GHz to 0.74 GHz, which is a two-fold tuning range. This work is believed to improve the state-of-the-art smart metamaterial absorber.