Abstract
A novel terahertz metamaterial absorber design with broadband and polarization insensitive absorption characteristics is presented in this paper. This proposed unit cell structure consists of a single layer dielectric with a petal-shaped metallic patch on the top plane. It is found that the absorber offers a broadband absorption of more than 90% over a frequency ranging from 2.6 to 3.5 THz. The absorption mechanism, electric field distribution and parametric analysis for the observed broadband response are also investigated in this paper. The strong coupling effect in the petal-shaped structure contributes to the broadening of the absorption spectrum. Thus, the proposed single-layer absorber can have effective application in terahertz broadband applications.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Introduction
The recent growth of terahertz (THz) technology has opened up new opportunities in applications such as sensing, imaging and spectroscopy. The combination of metamaterials (MMs) with THz gained more popularity mainly due to their exotic properties [1] and effects such as negative refractive index [2], invisibility cloaking [3], inverse Doppler effect [4] and perfect lensing [5]. These properties help in creating materials having negative permittivity and permeability which is unseen in conventional materials. MMs can be employed to design perfect electromagnetic absorbers displaying near unity absorbance for a small or broad frequency band [6,7,8,9,10]. The first metamaterial perfect absorber was demonstrated by Landy et al. [11] yielding near unity absorption due to simultaneous excitation of electric and magnetic resonances. Since the first demonstration, extensive research and alternate designs have been spawned with applications in terahertz imaging, filtering, biological sensing, etc. [12,13,14,15,16,17,18,19,20,21]. Different types of THz MMAs were proposed which can be classified based on the number of absorption bands and on the absorption bandwidth. Some of the researchers focussed on developing multi-band absorbers while the others on improving the bandwidth. At present, THz MMAs with eight absorption bands have been developed [22]. However, these MMAs suffer from a drawback of narrow bandwidth [19] and so researchers attempted to design broadband absorbers [23,24,25,26,27,28,29,30,31,32].
In order to broaden the bandwidth, the most common methods used are stacking the absorbers and to use multiple metallic patch structures. These two most common methods are also known as planar arrangement and vertical arrangement. The planar arrangement is composed of multiple metallic patterns on the top of a dielectric substrate. Due to the multiple resonances, these MMAs are able to achieve perfect absorptivity over a broad spectrum. Then comes the vertical arrangement in which multiple top layers are stacked in vertical direction yielding broadband absorption. If simple fabrication and low cost are taken into consideration, then single-layer unit cell structure with single metallic pattern on top is more attractive than the above-mentioned methods. Some of the broadband absorbers that have been demonstrated in the literature are shown in Table 1.
It can be observed from Table 1 that the existing works on broadband THz MMAs use either the vertical arrangement or the horizontal arrangement for achieving broadband absorption. From fabrication perspective, such designs are complicated and so single-layer structures with a single metallic pattern are the current requirement.
In this paper, a novel broadband metamaterial absorber in terahertz frequency is proposed using a petal-shaped structure on a single-layer absorber design. In order to study the absorption properties of the MMA, numerical simulations have been performed. From the simulated results, it is seen that the metamaterial absorber exhibited a broadband spectrum along with polarization-insensitive characteristics displaying perfect absorption above 90% and the bandwidth of about ~ 1 THz ranging from 2.56 to 3.5 THz. In addition, parametric study has been performed in order to justify the parameters of the design. This broadband metamaterial absorber can find potential applications in THz spectrum [33,34,35,36,37].
Unit Cell Structure
The proposed terahertz metamaterial absorber is composed of a petal-shaped structure. The top and side view of the novel MMA is given in Fig. 1. The unit cell structure consists of three layers in which top layer is a metallic gold patch in the shape of a petal, where radius of the circle r = 3 μm, major radius of the ellipse c = 30 μm and thickness is set to t = 0.4 μm. Then, the bottom layer named as metallic ground plane also consisted of gold having conductivity given by σ = 4.07 × 107 S/m and thickness b = 0.5 μm. Next, the middle layer is the dielectric layer or dielectric spacer with a permittivity of 2.8 + 0.09i [38, 39] and thickness h = 42 μm. The thicknesses of the top and bottom metallic layer are set to such values that it is more than the gold layer coating depth in order to negligibly reduce the transmission coefficient (T). Thus, the absorptivity (A) depends only on the reflectance (R) shown by the equation (1).
So, by using the commercially available High Frequency Electromagnetic Field Simulator (HFSS) software, this metamaterial absorber is designed for terahertz frequency regime. While designing the MMA, periodic boundary conditions along the z-plane are assigned to the four side walls of the unit cell. Then for the excitation, ports are assigned in the z-direction [40].
Results and Analysis
The novel metamaterial absorber is simulated using finite element method to obtain the absorption spectrum. In Fig. 2, the absorption plot (TE polarization) is shown.
From Fig. 2, it can be observed that the metamaterial absorber structure is displaying broadband response over a frequency range of 2.6 to 3.5 THz with an absorption greater than 90%. This broad absorption is due to the coupling between the four symmetrical petals. These are designed so close to each other that the strong coupling between them results in widening of the bandwidth. There are five absorption peaks within 2.6 to 3.5 THz broadband width given by different mode of frequencies f1, f2, f3, f4 and f5. The absorptivity tends to be 99.16%, 91.42%, 95.44%, 92.17% and 97.49% for frequencies 2.66, 2.9, 3.1, 3.3 and 3.5 THz, respectively. Furthermore, the physical origin of the broadband mechanism is interpreted by electric field distributions corresponding to five absorption frequencies 2.66 THz, 2.90 THz, 3.10 THz, 3.3 THz and 3.5 THz for TE polarization and normal incidence is depicted in Fig. 3. The images indicate the electric field strength in the petal-shaped structure. The excitation of strong electric fields in the four petals gives rise to strong coupling leading to broadband performance.
In order to investigate the influence of different parameters on the design, a parametric analysis is done which is shown in Figs. 4 and 5. The first parametric analysis is done by varying the radius (r) of the circle. From the simulated result, it can be observed that at 3 μm, the MMA is yielding a broadband absorption of about 1 THz bandwidth with an absorption greater than 90%. Similarly, when radius is reduced to 2 μm, the absorption bandwidth as well as absorptivity is getting decreased. With the increase in radius to 4 μm, the bandwidth is further diminishing.
The next parametric study is shown in Fig. 5 with respect to major radius of the ellipse forming the petals. So, from the obtained absorption spectra, it can be seen that a proper broadband response is seen for c = 30 μm, and by increasing and decreasing the values, there is a fluctuation in the absorptivity and bandwidth giving undesirable output.
From the results of the parametric investigation, it is precisely indicated that the radiuses of the design were optimally selected to obtain large broadband absorption with a bandwidth greater than 90%. Increasing or decreasing the radius of the circle and ellipse results in degradation of absorption characteristics.
As the absorption spectra for TE is already shown in Fig. 2, so it is important to carry out further simulation to verify the influence of various incident and polarization angles on the proposed MMA structure. The simulated output plots are shown in Fig. 6 in which (a) gives the absorption for different polarization angle and (b) shows the plot for different angle of incidence.
Figure 6 a shows the absorption spectra for different polarization angles in which angle is changed from 0° to 90° with the step size of 15°. For various polarization angles, the absorption remains almost similar. It means the proposed absorber is insensitive to the polarization angle of the incident waves. The structure is a symmetrical design, and thus, it displays characteristics that are insensitive to polarization.
The dependence of absorption on the incident angle is specifically studied for TE polarization as shown in Fig. 6 b. The angle of incidence is varied from 0° to 60° with the step size of 15°. The broad band absorption characteristics were observed even for large incident angles. When the incident angle is increased from 0° to 30°, the absorption characteristics do not change significantly. The absorptivity decreases with the increase in angle of incidence from 45° to 60°. This result demonstrates that the broadband with highly effective absorption is sustained over a wide range of incident angle (up to 45°).
Conclusion
The broadband characteristics of a novel petal-designed MMA in terahertz frequency regime has been presented in this paper. The structure offered a broadband response of nearly 1 THz with an absorption greater than 90%. The absorption mechanism of the structure is investigated by electric field strength plots for frequencies at 2.66 THz, 2.90 THz, 3.1 THz, 3.3 THz and 3.5 THz. Parametric analysis by varying the radius of the circle and ellipse has been performed to validate the selection of design parameters. Then, the absorber was also analysed for its broadband response at different polarization and incidence angles. From the analysis, it is observed that the broadband MMA is polarization insensitive due to its symmetric pattern on top. Thus, the proposed broadband metamaterial absorber can find potential application in terahertz technology.
References
Shamonina E, Solymar L (2007) Metamaterials: how the subject started. Metamaterials 1(1):12–18. https://doi.org/10.1016/j.metmat.2007.02.001
Padilla WJ, Basov DN, Smith DR (2006) Negative refractive index metamaterials. Mater Today 9:28–35. https://doi.org/10.1016/S1369-7021(06)71573-5
Rahm M, Schurig D, Roberts DA, Cummer SA, Smith DR, Pendry JB (2008) Design of electromagnetic cloaks and concentrators using form-invariant coordinate transformations of Maxwell ’ s equations. Photonics Nanostruct Fundam Appl 6:87–95. https://doi.org/10.1016/j.photonics.2007.07.013
Seddon N, Bearpark T (2003) Observation of the inverse Doppler effect. Science 302:1537–1540. https://doi.org/10.1126/science.1089342
Pendry JB (2000) Negative refraction makes a perfect lens. Phys Rev Lett 85:3966–3969. https://doi.org/10.1103/PhysRevLett.85.3966
Watts CM, Liu X, Padilla WJ (2012) Metamaterial electromagnetic wave absorbers. Adv Mater 24:OP98–OP120. https://doi.org/10.1002/adma.201200674
Pham VT, Park JW, Vu DL, Zheng HY, Rhee JY, Kim KW, Lee YP (2013) THz-metamaterial absorbers. Adv Nat Sci Nanosci Nanotechnol 4:015001. https://doi.org/10.1088/2043-6262/4/1/015001
Mohanty A, Acharya OP, Appasani B, Mohapatra SK (2018) A multi-band terahertz metamaterial absorber based on a $Π$ and U-shaped structure. Photonics Nanostruct Fundam Appl 32:74–80. https://doi.org/10.1016/j.photonics.2018.10.008
Zou H, Cheng Y (2019) Design of a six-band terahertz metamaterial absorber for temperature sensing application. Opt Mater (Amst) 88:674–679. https://doi.org/10.1016/j.optmat.2019.01.002
Panwar R, Agarwala V, Singh D (2015) A cost effective solution for development of broadband radar absorbing material using electronic waste. Ceram Int 41:2923–2930. https://doi.org/10.1016/j.ceramint.2014.10.118
Landy NI, Sajuyigbe S, Mock JJ et al (2008) Perfect metamaterial absorber. Phys Rev Lett 100:207402. https://doi.org/10.1103/PhysRevLett.100.207402 1–4
Blanchard F, Nkeck JE, Matte D, Nechache R, Cooke DG (2019) Applied sciences a low-cost terahertz camera. Appl Sci 9:1–8. https://doi.org/10.3390/app9122531
Gupta M, Srivastava YK, Singh R (2018) A toroidal metamaterial switch. Adv Mater 30:1–8. https://doi.org/10.1002/adma.201704845
Ling X, Xiao Z, Zheng X (2018) Tunable terahertz metamaterial absorber and the sensing application. J Mater Sci Mater Electron 29:1497–1503. https://doi.org/10.1007/s10854-017-8058-0
Wang B-X, Xie Q, Dong G, Zhu H (2017) Broadband terahertz metamaterial absorber based on coplanar multi-strip resonators. J Mater Sci Mater Electron 28:17215–17220. https://doi.org/10.1007/s10854-017-7651-6
Zheng X, Xiao Z, Ling X (2017) Broadband visible perfect absorber for sensor based on ultra-thin metamaterial. J Mater Sci Mater Electron 28:7739–7744. https://doi.org/10.1007/s10854-017-6468-7
Bakir M, Karaaslan M, Dincer F et al (2016) Tunable perfect metamaterial absorber and sensor applications. J Mater Sci Mater Electron 27:12091–12099. https://doi.org/10.1007/s10854-016-5359-7
Dao R, Kong X, Zhang H, Tian X (2020) A tunable ultra-broadband metamaterial absorber with multilayered structure. Plasmonics 15:169–175. https://doi.org/10.1007/s11468-019-01013-9
Yu P, Besteiro LV, Huang Y, Wu J, Fu L, Tan HH, Jagadish C, Wiederrecht GP, Govorov AO, Wang Z (2019) Broadband metamaterial absorbers. Adv Opt Mater 7:1–32. https://doi.org/10.1002/adom.201800995
Dash S, Patnaik A (2018) Material selection for THz antennas. Microw Opt Technol Lett 60:1183–1187. https://doi.org/10.1002/mop.31127
Sharma A, Panwar R, Khanna R (2019) Experimental validation of a frequency-selective surface-loaded hybrid metamaterial absorber with wide bandwidth. IEEE Magn Lett 10:10–14. https://doi.org/10.1109/LMAG.2019.2898612
Verma VK, Mishra SK, Kaushal KK et al (2020) An Octaband polarization insensitive terahertz metamaterial absorber using orthogonal elliptical ring resonators. Plasmonics 15:75–81. https://doi.org/10.1016/j.aeue.2016.05.002
Huang L, Chowdhury DR, Ramani S, Reiten MT, Luo SN, Taylor AJ, Chen HT (2012) Experimental demonstration of terahertz metamaterial absorbers with a broad and flat high absorption band. Opt Lett 37:154. https://doi.org/10.1364/ol.37.000154
Grant J, Ma Y, Saha S, Khalid A, Cumming DRS (2011) Polarization insensitive, broadband terahertz metamaterial absorber. Opt Lett 36:3476–3478. https://doi.org/10.1364/ol.36.003476
Lu Y, Li J, Zhang S, Sun J, Yao JQ (2018) Polarization-insensitive broadband terahertz metamaterial absorber based on hybrid structures. Appl Opt 57:6269–6275. https://doi.org/10.1364/ao.57.006269
Pan W, Yu X, Zhang J, Zeng W (2017) A broadband terahertz metamaterial absorber based on two circular split rings. IEEE J Quantum Electron 53:2–7. https://doi.org/10.1109/JQE.2016.2643279
Heng YOC, Ou HAZ, Ang JIY et al (2018) Dual and broadband terahertz metamaterial absorber based on a compact resonator structure. Opt Mater Express 8:498–504. https://doi.org/10.1364/OME.8.003104
Tan S, Yan F, Xu N, Zheng J, Wang W, Zhang W (2018) Broadband terahertz metamaterial absorber with two interlaced fishnet layers. AIP Adv:8. https://doi.org/10.1063/1.5017099
Zhu J, Sun W, Ding F et al (2014) Ultra-broadband terahertz metamaterial absorber. Appl Phys Lett 105:1–4. https://doi.org/10.1063/1.4890521
Shen G, Zhang M, Ji Y, Huang W, Yu H, Shi J (2018) Broadband terahertz metamaterial absorber based on simple multi-ring structures. AIP Adv 8:8. https://doi.org/10.1063/1.5024606
Li X, Liu H, Sun Q, Huang N (2015) Ultra-broadband and polarization-insensitive wide-angle terahertz metamaterial absorber. Photonics Nanostruct Fundam Appl 15:81–88. https://doi.org/10.1016/j.photonics.2015.04.002
Wang B-X, Tang C, Niu Q, He Y, Chen R (2019) A broadband terahertz metamaterial absorber enabled by the simple design of a rectangular-shaped resonator with an elongated slot. Nanoscale Adv 1:3621–3625. https://doi.org/10.1039/C9NA00385A
Ye YQ, Jin Y, He S (2010) Omnidirectional, polarization-insensitive and broadband thin absorber in the terahertz regime. J Opt Soc Am B 27:498–504. https://doi.org/10.1364/JOSAB.27.000498
Pan W, Yu X, Zhang J, Zeng W (2016) A novel design of broadband terahertz metamaterial absorber based on nested circle rings. IEEE Photon Technol Lett 28:2335–2338. https://doi.org/10.1109/LPT.2016.2593699
Appasani B, Prince P, Ranjan RK, Gupta N, Verma VK (2019) A simple multi-band metamaterial absorber with combined polarization sensitive and polarization insensitive characteristics for terahertz applications. Plasmonics 14:737–742. https://doi.org/10.1007/s11468-018-0852-x
Panwar R, Lee JR (2019) Recent advances in thin and broadband layered microwave absorbing and shielding structures for commercial and defense applications. Funct Compos Struct 1:32001. https://doi.org/10.1088/2631-6331/ab2863
Mishra R, Sahu A, Panwar R (2019) Cascaded graphene frequency selective surface integrated tunable broadband terahertz metamaterial absorber. IEEE Photonics J 11:1–10. https://doi.org/10.1109/JPHOT.2019.2900402
Ekmekci E, Strikwerda AC, Fan K, Keiser G, Zhang X, Turhan-Sayan G, Averitt RD (2011) Frequency tunable terahertz metamaterials using broadside coupled split-ring resonators. Phys Rev B 83:193103. https://doi.org/10.1103/PhysRevB.83.193103
Tao H, Bingham CM, Strikwerda AC, Pilon D, Shrekenhamer D, Landy NI, Fan K, Zhang X, Padilla WJ, Averitt RD (2008) Highly flexible wide angle of incidence terahertz metamaterial absorber: design , fabrication , and characterization. Phys Rev B 78:1–4. https://doi.org/10.1103/PhysRevB.78.241103
Padooru YR, Yakovlev AB, Kaipa CSR, Hanson GW, Medina F, Mesa F, Glisson AW (2012) New absorbing boundary conditions and analytical model for multilayered mushroom-type metamaterials: applications to wideband absorbers. IEEE Trans Antennas Propag 60:5727–5742. https://doi.org/10.1109/TAP.2012.2209196
Author information
Authors and Affiliations
Corresponding author
Additional information
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Mohanty, A., Acharya, O.P., Appasani, B. et al. A Broadband Polarization Insensitive Metamaterial Absorber Using Petal-Shaped Structure. Plasmonics 15, 2147–2152 (2020). https://doi.org/10.1007/s11468-020-01241-4
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11468-020-01241-4