Abstract. We present the calculation results of a full-sized ultra broadband absorber
metamaterial structure at THz region from 19-26 THz. After being integrating the metal viawall and controlling unit cells, this structure provides a broadband absorption and becomes
independent on the polarization of the incident wave. This structure can be applied to
improve the performance of telecommunications systems such as micro antenna systems,
micro-electromagnetic transmitter system. This structure is particularly feasible to integrate
into the antenna system due to its size and that it possesses superior electromagnetic
properties and is easy to handle. Simulations and calculations show that for the structure after
appropriately applied an electromagnetically shielded wall, the absorption bandwidth is
increased sharply to 5 THz with the absorptivity is over 95%. This structure can easily
integrate with a micro-antenna system and other terahertz imaging or sensor technology.
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HNUE JOURNAL OF SCIENCE DOI: 10.18173/2354-1059.2018-0071
Natural Sciences 2018, Volume 63, Issue 11, pp. 65-70
This paper is available online at
SIMULATION OF METAL VIA-WALL BASED ULTRA BROADBAND TERAHERTZ
FULL-SIZED METAMATERIAL ABSORBER
Tran Manh Cuong
1
, Nguyen Thi Thuy
1
, Do Hoang Tung
2
, Pham Van Hai
1
and Vu Dinh Lam
3
1
Faculty of Physics, Hanoi National University of Education
2
Institute of Physics, Vietnam Academy of Science and Technology
3
Graduate University of Science and Technology, Vietnam Academy of Science and Technology
Abstract. We present the calculation results of a full-sized ultra broadband absorber
metamaterial structure at THz region from 19-26 THz. After being integrating the metal via-
wall and controlling unit cells, this structure provides a broadband absorption and becomes
independent on the polarization of the incident wave. This structure can be applied to
improve the performance of telecommunications systems such as micro antenna systems,
micro-electromagnetic transmitter system. This structure is particularly feasible to integrate
into the antenna system due to its size and that it possesses superior electromagnetic
properties and is easy to handle. Simulations and calculations show that for the structure after
appropriately applied an electromagnetically shielded wall, the absorption bandwidth is
increased sharply to 5 THz with the absorptivity is over 95%. This structure can easily
integrate with a micro-antenna system and other terahertz imaging or sensor technology.
Keywords: Absorber, defect, metamaterial, THz.
1. Introduction
Metamaterial is artificially periodic structure which attracted immense research attentions in
the recent decade for their exotic dynamic features that are cannot be found in the natural
materials. Their properties were first predicted by Veselago [1] and demonstrated experimentally
by Smith et al. [2]. Due to the extraordinary properties, metamaterials are promised to provide a
numerous outstanding applications such as super-lens, invisible cloaking, and bio sensor,
especially in the antenna and the telecommunication fields as well as the perfect absorber [3-5].
Since the first proposal of Landy et al. in 2008 [4], the metamaterial perfect absorber (MPA)
which simultaneously excite electric and magnetic resonances to satisfy the impedance matching
with the surrounding air has remarkably become one of the most crucial research trends.
With the development of science and technology nowadays, especially in the field of
electromagnetic telecommunications, great demands on the integration of electronic materials into
the system are increasing. Besides, Terahertz is a spectrum that possesses many important
technological applications, such as imaging, sensor, recycle energy or micro antenna
communication, which all require a perfect absorber to efficiently collect wave energy [3].
Received October 29, 2018. Revised November 15, 2018. Accepted November 22, 2018.
Contact Tran Manh Cuong, e-mail address: tmcuong0279@gmail.com
Tran Manh Cuong, Nguyen Thi Thuy, Do Hoang Tung, Pham Van Hai and Vu Dinh Lam
66
Therefore, metamaterial terahertz absorber (MTA) has various potential applications and attracts
many researchers in the world. The MPA working in THz frequency was first proposed by Tao et al.
in 2008 [5]. Since then many structures have been investigated and put forward, nevertheless, the
simple designed structure create a narrow perfect absorption band, the ultra- even super-
broadband MPA was engineered by complex configuration of structure [6-14].
This paper proposes a full-sized metamaterial configuration which can generate a super broadband
absorbance in THz frequency region. Originally, the full-sized structure metamaterial was
investigated by varying the number of cell. Interestingly, the absorptivity of this full structure is
much better when it is integrated the defects and a metal via wall. In order to obtain the super
broadband absorption, two layers via wall were integrated into a full-sized 10 10 unit cell
structure. It is found that, the absorptivity of this structure is not only strengthened but also be
expanded to 5 THz ultra-broadband absorption. It is worth mentioning that the thickness of
substrate is 0.11 λ0 with respect to the center frequency of the operating bandwidth. The presence
of the gold via wall plays the principle role in increasing the absorptivity of the full structure.
2. Content
2.1. Numerical design, results and discussions
Figure 1. A unit cell with its dimensions
A single unit cell of the original structure with the geometric parameters is presented in
Figure 1. In the simulation, the incident wave was normal to the structure, the electric and
magnetic fields are parallel to the y-axis and the x-axis and corresponding to the electric field E
and magnetic field H directions, respectively. The original structure could be designed by
applying the laser lithography process with a 1.5 m-thick (td) polyimide dielectric substrate
which has 3.5 dielectric constant sandwiched between 0.026 m-thick (ts) gold film in both sides.
In the top layer, the 1.25 m-width (t) square ring surround the dish which has the diameter d =
3.5 m. The bottom layer is covered with a full gold film with an electric conductivity σ = 4.56 ×
10
7
S/m. The lattice constant of a single unit cell is a = 9 m (Figure 1).
Figure 2 exhibits the full structure metamaterial with 10 × 10 unit cells and the total size is 8100
m2. In this work, the absorbance of various full structure metamaterial such as 8 × 8, 10 × 10 are
also discussed (the results are in Figure 3), in there, the size and the geometrical parameters of a
single unit cell are unchanged. One can see that, without via wall, the structure shows only one
principle absorption peak and enduring at 25.5 THz. Figure 2 is also the schematic representing of
the 100 unit cells structure with 2 via walls. In fabrication process, the via wall could be realized
by filling gold into the holes between two metal layer. The via wall has the depth h = 1.5 m, the
same with the thickness of the dielectric layer, and the via radius is rv = 0.6 m. It is noted that at
Simulation of metal via-wall based ultra broadband terahertz full-sized metamaterial absorber
67
the position of the via-wall, the defects on the structure are performed by removing unit cells at
the same place.
For the numerical simulation, we use the commercial CST Microwave Studio [15] based on
Finite Integration Technique (FIT) technique. In simulation, a waveport, which is used to
simultaneously transmit microwave beam and receive the reflected beam from the sample, is
placed upon the structure. The absorption is calculated through the formula A(ω) = 1 − R(ω) = 1 −
|S11(ω)|2, where S11(ω) is scattering parameter and R(ω) = |S11(ω)|2 is reflection (transmission is
not applied due to the gold layer at the backplate).
Figure 2. Optimal full structure with 100 unit cells size
Figure 3. Absorption of full metamaterial absorber with different configurations
The full structure of 100 unit cells then is integrated 1 and 2 gold via wall. The results show
that, for the full structure without via, the principle absorption frequency is centered at 25.5 THz.
For the structure with 1 via wall, the absorber broadband has formed and has a relative width of 5
THz with a weak absorption range around 24 THz. To optimize the broadband absorption, the
second via wall was introduced to the structure at the position of the third cell layer. The
calculated results were shown in the Figure 3. This indicates that the structure with two via wall
layers has a super absorbance band of up to 5 THz and the absorption is over 95%.
Tran Manh Cuong, Nguyen Thi Thuy, Do Hoang Tung, Pham Van Hai and Vu Dinh Lam
68
Figure 4. Simulation result: Absorptivity curve of the full-sized absorber structure with 2 via
wall; comparison with different via radius r1 = 0.6 µm, r2 = 1.0 µm
The formation of the ultra-broad absorption band can be explained as: When forming the via
wall layer in the structure, this configuration is considered as an electromagnetic blackbody - a
type of an electromagnetic resonance cavity, the electromagnetic waves of the absorption
frequency range entered and are confined in the structure. This occurs in the form of standing
wave electromagnetic resonance in the absorption frequency range. This is related to the
Helmholtz effect of the electromagnetic resonance occurring in the cavity structure with a
broadband frequency range, and this is related to the size of the resonance cavity in the blackbody,
which concerns directly the optimized distance between two layers of via wall of full sized
structure [8].
In Figure 4, we show the results of the optimized structure with different radius of the via.
One can see that the radius of the gold via is not strongly affect on the absorption band. When the
radius varies from 0.6 to 1.0 µm, the absorption is stable.
Figure 5. Absorption spectrum at different polarization angle of the incident wave for the
structure with 100 UCs and 2 via walls
To confirm the polarization insensitivity of the structure, we present the absorbance of the
structure with 100 unit cells integrating 2 via walls for different polarization angles in Figure 5. As
Simulation of metal via-wall based ultra broadband terahertz full-sized metamaterial absorber
69
predicted, due to the symmetric configuration of the structure, these results show that the
absorption is independent of polarization angle of the incoming wave.
To understand more the underlying mechanism of energy concentration in the absorption
regime, we analyze and observe the electric field and power loss at 19, 23, and 25 THz, which are
three main position peaks on the absorption curve (Figure 6), they are chosen for investigating the
field in the range of absorption band. One can see that, the electromagnetic energy concentrated
mostly on the surface and at the metal via-wall cavity region of the structure. It is noted that the
cavity region formed by via-wall acts like an electromagnetic resonance cavity and confines the
incoming energy inside.
Figure 6. Electric field distribution patterns in the structure at frequencies
of (a) 19 THz, (b) 23 THz and (c) 25 THz
The distribution of power loss density for the structure at 19, 23, 25 THz are also
respectively observed (Figure 7). The power loss is observed in the structure and at the cross
section shows that the loss energy concentrates mainly in the dielectric layer and at the wall cavity
region at absorption frequency.
Figure 7. The distributions of power loss density for the structure
at of (a) 19 THz, (b) 23 THz and (c) 25 THz
3. Conclusions
We presented a new full-sized metamaterial structure which possessed a unit cells system
integrated with the metal via wall working at the THz frequency range. Simulations show that for
the optimized structure applying 2 gold via walls, the working bandwidth is increased up to 5 THz
with the absorptivity is over 95 %. The electromagnetic energy and power loss in the structure,
which are observed at the resonance range, show that the cavity metal wall is the origin of the
perfect absorption. This structure can be used to improve the performances of the micro-antennas,
high rate telecommunication systems or other terahertz imaging or sensing technology.
Acknowledgement. This research is funded by the Vietnam National Foundation for Science and
Technology Development (Grant No. 103.99-2017.26).
Tran Manh Cuong, Nguyen Thi Thuy, Do Hoang Tung, Pham Van Hai and Vu Dinh Lam
70
REFERENCES
[1]. V.G. Veselago, 1968. The electrodynamics of substances with simultaneously negative
values of ε and μ. Sov. Phys., Uspeki 10, 509.
[2]. D.R. Smith, J.B. Pendry, and M.C.K. Wiltshire, 2004. Metamaterials and negative
refractive index. Science 305, 788.
[3]. C.M. Watts, X. Liu, and W.J. Padilla, 2012. Metamaterial Electromagnetic Wave Absorbers,
Adv. Mater. 24, OP98.
[4]. N.I. Landy, S. Sajuyigbe, J.J. Mock, D.R. Smith, and W.J. Padilla, 2008. Perfect
metamaterial absorber. Phys. Rev. Lett. 100, 207402.
[5]. Tao, H. et al, 2008. A metamaterial absorber for the terahertz regime: Design, fabrication
and characterization. Opt. Express 16, 7181-7188.
[6]. Lin-Lin Zhong, Chao-Ming Luo, and Jing-Song Hong, 2015. Dual-band polarization-
/angle-insensitive metamaterial absorber. AIP Advances 5, 067162; doi: 10.1063/1.4923319.
[7]. Dan Hu, Hongyan wang, Zhenjie tang, and Xiwei zhang, 2016. Investigation of a
broadband refractory metal metamaterial absorber at terahertz frequencies. Applied Optics,
Vol. 55, No. 19.
[8]. Changlei Zhang, Cheng Huang, Mingbo Pu, Jiakun Song, Zeyu Zhao, Xiaoyu Wu &
Xiangang Luo, 2017. Dual-band wide-angle metamaterial perfect absorber based on the
combination of localized surface plasmon resonance and Helmholtz resonance. Scientific
Reports, 7: 5652, doi: 10.1038/s41598-017-06087-1.
[9]. Daecheon Lim, Dongju Lee & Sungjoon Lim, Angle-and Polarization-Insensitive
Metamaterial Absorber using Via Array, 2016. Scientific Reports, 6:39686, DOI:
10.1038/srep39686.
[10]. Jianfei Zhu, Zhaofeng Ma, Wujiong Sun, Fei Ding, Qiong He, Lei Zhou, and Yungui Ma,
2014. Ultra-broadband terahertz metamaterial absorber. Applied Physics Letters 105,
021102; doi: 10.1063/1.4890521.
[11]. Yongzheng Wen, Wei Ma, Joe Bailey, Guy Matmon, Xiaomei Yu, and Gabriel Aeppli, 2014.
Planar broadband and high absorption metamaterial using single nested resonator at
terahertz frequencies, Vol. 39, No. 6, Optics letters.
[12]. Cheng Gong, Mingzhou Zhan, Jing Yang, Zhigang Wang, Haitao Liu, Yuejin Zhao &
Weiwei Liu, 2016. Broadband terahertz metamaterial absorber based on sectional
asymmetric structures. Scientific Reports, 6:32466, doi: 10.1038/srep32466.
[13]. Manh Cuong Tran, Dinh Hai Le, Van Hai Pham, Hoang Tung Do, Dac Tuyen Le, Hong Luu
Dang, Dinh Lam Vu, 2018. Controlled Defect Based Ultra Broadband Full-sized
Metamaterial Absorber, Scientific Reports, 8:9523, Doi:10.1038/s41598-018-27920-1.
[14]. Beeharry T, Yahiaoui R, Selemani K, Ouslimani H.H. A Co-Polarization Broadband Radar
Absorber for RCS Reduction. Materials, 2018, 11(9). Doi: 10.3390/ma11091668.
[15] https://www.cst.com/.