Narrow-band Metamaterial Absorber Research Articles

Design of metamaterial perfect absorbers in the long-wave infrared region.

We designed a narrow-band metamaterial absorber (NMA) and an ultra-broadband metamaterial perfect absorber (UMPA) based on the impedance matching theory. The narrow-band metamaterial absorber mainly consists of Si3N4 cylinders with Si3N4 and Ti substrates. Numerical analysis shows that the absorption peak of the NMA is about 99.9% and the absorption bandwidth with more than 90% absorption is about 4.8 μm (9.5-14.3 μm). To further extend the absorption bandwidth, an ultra-broadband absorber was designed by integrating a Ti hyperbolic rectangle into the Si3N4 cylinder of the NMA. Numerical analysis shows that the absorption bandwidth of the UMPA is up to 10 μm (7-17 μm) with an average absorption rate of 96.6%. The designed UMPA has polarization insensitive properties with wide-angle absorption characteristics, and the average absorption can reach 85% and 76% in transverse magnetic (TM) and transverse electric (TE) modes, respectively, at 60° oblique incidence. The high absorption and wide band are mainly dominated by localized surface plasmon resonance, Fabry-Perot resonance and inter-resonance interactions. The designed absorber achieves excellent absorption in the long infrared wavelength band, which has potential applications in energy absorption, infrared sensing and other fields.

Multi-peak narrow-band metamaterial absorber for visible to near-infrared wavelengths

This study developed a multiband metamaterial-absorbing device based on an array of gold nano-crosses for visible to near-infrared wavelengths. The proposed absorbing device is deposited on a silicon substrate and uses a metal–insulator–metal (MIM) classical structure. Numerical analyses were performed using the finite difference time domain (FDTD) method. The underlying physical mechanisms were analyzed on the basis of the structural parameters affecting the surface plasmon resonance field in the nanoarray structure. The calculations show that the proposed absorber achieves a five-band absorption in the visible to near-infrared region (700–3000 nm). After parameter adjustment and optimization, there were three absorption peaks with absorption of 99% or more and an average absorption value of 96.4% for the five peaks. Moreover, the array can be used as a biosensor to identify certain viruses, demonstrating its utility in label-free clinical sensing. In addition, the absorber is polarization- and incident-angle-insensitive. Therefore, this device exhibits considerable potential for designing ideal absorbers and nanosensors.

Narrowband metamaterial absorbers based on interlaced T-shaped all-dielectric resonators for sensing application

In this paper, a narrowband metamaterial absorber and its complementary structure absorber are proposed, which can be used for refractive index sensing in the terahertz (THz) band. The proposed two absorbers are composed of complementary rotating interlaced T-shaped all-dielectric resonators located on gold plates. It is demonstrated that the interlaced T-shaped absorber has a narrow single absorption peak with absorptivity of 99.4% at 2.987 THz; its full width at half maximum (FWHM) is 0.0219 THz, and the relative bandwidth is 0.73%. The complementary absorber has two narrow absorption peaks at 3.171 THz and 3.409 THz with absorptivity of 99.3% and 99.8%, corresponding FWHMs of 0.0133 THz and 0.0074 THz, and relative bandwidths of 0.42% and 0.22%, respectively. Based on the narrowband absorption characteristics of the absorbers, the sensing applications for different refractive indices of analyte layers are studied. The sensing sensitivity of the two absorbers can reach 1030 GHz/RIU and 3190 GHz/RIU, respectively. The proposed absorbers are promising in the fields of electromagnetic detection, imaging, and sensing.

Narrowband Plasmonic Absorber Using Gold Nanoparticle Arrays for Refractive Index Sensing

Here, a design of localized surface plasmon resonance (LSPR)-based sensor using narrowband metamaterial absorber based on a gold nanoparticle array is studied. The LSPR based sensor has found comprehensive applications in clinical analysis and environmental monitoring. The simulation outcomes demonstrate that the proposed structure has an absorption bandwidth (FWHM) of 5.7nm. Sensors with narrow bandwidth can develop efficiency and correctness detection. Furthermore, as a refractive index sensor, the sensitivity is obtained as high as S = 964nm/RIU with large value of figure of merit (FOM = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.653\times 10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ). The proposed design displays polarization independence, which will remove the polarization requirement of equipment. We further demonstrate the array as a biosensor for detecting some viruses, suggesting the applicability for label-free clinical sensing. The device has an extensive performance, such as perfect absorption, polarization insensitivity, high sensitivity, and FOM, appropriate for applied applications.

Thermally-stable graphene metamaterial absorber with excellent tunability for high-performance refractive index sensing in the terahertz band

Graphene plasmons have attracted great interest for constructing high-performance functional metamaterial devices, among which graphene-based narrowband metamaterial absorbers are valuable in numerous applications. In this paper, a graphene-dielectric-metal hybrid structure is proposed to achieve dual-band excellent absorption and high-performance refractive index sensing. Numerical simulations show that the designed structure exhibits a high Q factor of 277.8 at 1.945 THz, which is higher than most previously-reported results. The sensitivity of the proposed structure can be up to 1.84 THz/RIU when the analyte thickness is 80 μm, and it exhibits promise for sensing thin-film biomolecule and thick biologic tissues. The electromagnetic field distributions show that the electromagnetic energy is highly confined in the structure at the higher order plasmon resonance, which plays an important role in achieving the excellent characteristics of the proposed structure. The tunability of the proposed structure is realized via changing the gate voltage applied to the graphene and the angles of the incident THz wave. In addition, we reveal that the proposed structure can be switched between single-band, dual-band, and 3-band absorption by tuning the incident angle under TM and TE polarization. Further results demonstrate that the proposed device possesses good thermal stability, polarization insensitivity, and outstanding fabrication tolerance. We believe that the proposed dual-band narrowband absorber can serve as a good example for other devices based on plasmons, such as selective sensors, modulators, and optical detectors.

Design and measurement of a narrow band metamaterial absorber in terahertz range

In this paper, we proposed and measured a metamaterial absorber with cross metal array in 12–28 THz range. A narrow absorption band (the absorption amplitude is 96%) is obtained at resonance frequency 19.24 THz, which is excited by the bright-bright modes coupling effect. Impedance matching is achieved at this resonance frequency between samples and free space. This absorption peak is enhanced and its resonance frequency is shifted with lattice constant reducing or structural parameter w1 increasing. The absorption peak is highly sensitive to the variation of structural parameters due to the bright-bright modes coupling effect on the cross strips. An equivalent LC circuit mode is proposed to understand the physical mechanism of the resonance frequency shifting. The effect of three gases on this absorption peak is measured. Moreover, high absorption performance is revealed when the incident angle reaches 480.

Polarization-maintaining reflection-mode THz time-domain spectroscopy of a polyimide based ultra-thin narrow-band metamaterial absorber

This paper reports the design, the microfabrication and the experimental characterization of an ultra-thin narrow-band metamaterial absorber at terahertz frequencies. The metamaterial device is composed of a highly flexible polyimide spacer included between a top electric ring resonator with a four-fold rotational symmetry and a bottom ground plane that avoids misalignment problems. Its performance has been experimentally demonstrated by a custom polarization-maintaining reflection-mode terahertz time-domain spectroscopy system properly designed in order to reach a collimated configuration of the terahertz beam. The dependence of the spectral characteristics of this metamaterial absorber has been evaluated on the azimuthal angle under oblique incidence. The obtained absorbance levels are comprised between 67% and 74% at 1.092 THz and the polarization insensitivity has been verified in transverse electric polarization. This offers potential prospects in terahertz imaging, in terahertz stealth technology, in substance identification, and in non-planar applications. The proposed compact experimental set-up can be applied to investigate arbitrary polarization-sensitive terahertz devices under oblique incidence, allowing for a wide reproducibility of the measurements.

Broadband and ultra-thin terahertz metamaterial absorber based on multi-circular patches

An ultra-thin narrow-band metamaterial absorber (MA) based on a periodic array of circular metal patch is numerically proposed at terahertz frequencies. The MA could exhibit an absorption peak at 5.91 THz with the absorptivity of 99.9%. The surface current distributions and distributions of the z-component electric field indicate that high absorption is due to the strong magnetic resonance between the two metallic layers and prefect impedance-matched to the free space at the resonance frequency. By simply assembling a diagonal arrangement of several circular patches with slightly different geometric parameters into a unit cell, the bandwidth of strong absorption (more than 90%) can be effectively improved. Finally, the bandwidth of strong absorption for the four-patch MA achieves 0.98 THz and the corresponding full width at half maximum (FWHM) increases to 1.49 THz. Moreover, the thickness of the four-patch MA is only about 22 times smaller than the central wavelength and it could operate well at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.

Design of a tunable terahertz narrowband metamaterial absorber based on an electrostatically actuated MEMS cantilever and split ring resonator array

A dynamically tunable terahertz (THz) narrowband metamaterial absorber is presented. The absorber is based on an electrostatically actuated micro-electro-mechanical systems (MEMS) cantilever and split ring resonator (SRR) array. An equivalent LC circuit model for a transverse electric (TE) polarization wave is introduced to analyze the mechanism of frequency tuning. A finite element method is applied to simulate the mechanical characteristics of the cantilever, and a finite integration technique is used to study the frequency tuning properties of the absorber. The results show that, for a TE polarization wave, there is only one absorption peak in the frequency range from 0.6 to 1.6 THz. The absorption peak frequency can be continuously tuned from 1.32 to 1.28 THz, and then abruptly to 1.12 THz. The maximum tunable frequency is 0.20 THz, which is about 15% of the initial resonance frequency. For a transverse magnetic (TM) polarization wave, there are two tunable absorption peaks in this frequency range. Moreover, for a TE wave, some geometric dimensions affecting the initial resonance frequency are investigated.

Interference theory of metamaterial perfect absorbers

The impedance matching to free space in metamaterial perfect absorbers has been believed to involve and rely on magnetic resonant response, with direct evidence provided by the anti-parallel surface currents in the metal structures. Here I present a different theoretical interpretation based on interference, which shows that the two layers of metal structures in metamaterial absorbers are linked only by multiple reflections with negligible near-field interactions or magnetic resonances. This is further supported by the out-of-phase surface currents derived at the interfaces of resonator array and ground plane through multiple reflections and superpositions. The theory developed here explains all features observed in narrowband metamaterial absorbers and therefore provides a profound understanding of the underlying physics.