A Novel 5G Wideband Metamaterial Based Absorber for Microwave Energy Harvesting Applications

Abstract

This paper proposes a novel design of compact and thin metamaterials (MMs) based wideband absorber aiming at specific microwave energy harvesting for 5G applications. The developed unit cell is obtained by combining two letters-like patches printed on a grounded dielectric substrate. The developed operating band is achieved based on the superposition of the two resonances generated by the two letters. The simulations are based on Rogers RT5880 (thickness of 1.575 mm, dielectric constant of εr=2.2, loss tangent of tanδ=0.009) and FR-4 substrates (thickness of 1.2 mm dielectric constant of εr=4.3, loss tangent of tanδ=0.02). The obtained results show a wide 10 dB absorption bandwidth in the frequency range between 18 GHz and 30 GHz with absorptivity close to 99% for normal and oblique incident up top to 30° in the case of Rogers RT5880. An absorptivity rate of 96% is obtained for the cased of FR-4 because of high dielectric losses. The obtained results are reasonable compared to other studies in the literature.

Full text

A Novel 5G Wideband Metamaterial Based Absorber
for Microwave Energy Harvesting Applications
Gökberk Akarsu
Faculty of Engineering
Izmir University of Economics
Izmir, Turkey
gokberkakarsu97@gmail.com
Mohammed Farouk Nakmouche
Faculty of Engineering
Izmir University of Economics
Izmir, Turkey
Nakmouche.MFarouk@gmail.co
m
Diaa E. Fawzy
Faculty of Engineering
Izmir University of Economics
Izmir, Turkey
diaa.fawzy@gmail.com
A.M.M.A Allam
Faculty of Information Engineering
and Technology
German University in Cairo
Cairo, Egypt
abdelmegid.allam@guc.edu.eg
Kadir Başköy
Faculty of Engineering
Izmir University of Economics
Izmir, Turkey
Kadir_kedir@hotmail.com
Mehmet Faruk Cengiz
Faculty of Engineering
Izmir University of Economics
Izmir, Turkey
mehmetfarukcengiz@gmail.com
Abstract—This paper proposes a novel design of a compact and
thin metamaterials (MMs) based wideband absorber aiming at
specific microwave energy harvesting for 5G applications. The
developed unit cell is obtained by combining two letters-like
patches printed on a grounded dielectric substrate. The developed
operating band is achieved based on the superposition of the two-
resonances generated by the two letters. The simulations are based
on Rogers RT5880 (thickness of 1.575 mm, dielectric constant of
εr=2.2, loss tangent of tanδ=0.009) and FR-4 substrates (thickness
of 1.2 mm dielectric constant of εr=4.3, loss tangent of tanδ=0.02).
The obtained results show a wide 10 dB absorption bandwidth in
the frequency range between 18 GHz and 30 GHz with
absorptivity close to 99% for normal and oblique incident up top
to 30° in the case of Rogers RT5880. An absorptivity rate of 96%
is obtained for the cased of FR-4 because of high dielectric losses.
The obtained results are reasonable compared to other studies in
the literatures.
Keywords—metamaterials, wideband metamaterials, microwave
energy harvesting, 5G, UAV
I. INTRODUCTION
Metamaterials (MMs) with their great capabilities beyond
natural materials to manipulate electromagnetic waves are
attracting increasing attention day by day [1]-[3]. MMs offer
great opportunities to control the absorption, transmission and
reflection of electromagnetic waves over narrow or wide ranges
of frequencies. Many applications include sensors [4], filters and
antenna [5], [6], photodetectors [7] and even solar cells [8]
require the development of perfect absorbers.
On the aim of achieving wideband absorptivity over a wide
bandwidth for RF energy harvesting applications, different
techniques were proposed in the literature [9], one is the
combination of many different resonances generated from
geometries [10]. Different MMs were developed at different
frequency ranges from MHz to THz for different applications
such as energy harvesting, wireless power transfer (WPT), space
solar power (SPS), polarization insensitive antennas and thermal
detectors [9], [11].
Furthermore, energy requirements are considered to be one
of the basic principles for the current and future developments.
In the ecosystem of IoT lots of autonomous devices, sensor,
vehicles, smart houses and cities will be increasingly connected
to internet [12]. To supply the required energy demands, energy
harvesting systems are becoming more popular in the fields of
aviation and IoT. The principle of 5G is a large infrastructure
with a huge amount of connected devices and this large
connected device infrastructure will also create lots of undesired
electromagnetic noises and fields [13]. In the RF energy
harvesting system, one could collect ambient undesired
electromagnetic energies and use them to charge UAVs batteries
or power up small IoT devices [14].
The aim of the current work is four folds: (1) developing a
simple, compact and low-cost wide bandwidth MMs based
absorber with perfect absorptivity rate, near 100%, (2)
enhancing the absorptivity for waves with incident angles up to
30°. (3) investigating the role of the dielectric losses on the MMs
structures. (4) integrating the proposed absorber with a rectifier
circuit. In section II, the design of the proposed MMs based
absorber is presented, the parametric study are given in section
III with a focus on the properties of the effects of different
parameters. Simulation and performance analysis are reported in
section IV. Section V gives the summary and conclusions of the
work.
II. THEORETICAL AND ABSORBER DESIGN
The aim of this paper is designing a novel MMs absorber
unit cell for 5G applications. The fundamental principle for
designing a perfect MMs absorber is reaching the perfect
impedance matching with impedance of free space.
The rate of absorption in the Metamaterial Perfect Absorbers
(MPA) is related to the transmission and reflection coefficients.
309
2021 8th International Conference on Electrical and Electronics Engineering
978-0-7381-1356-2/21/$31.00 ©2021 IEEE

The reflected waves from the MPA surface should be near
to the zero in a great matched structure. To check whether the
design is perfectly matched, or it absorbs perfectly the wave, the
reflection and transmission coefficient (S11 and S21) can be used
for the calculation of absorptivity as :
A= 1-|S11|2 - |S21|2
The design of the MPA consists of three layers, the bottom
layer or ground, the middle layer or dielectric material and the
top layer of the patch as shown in Figure 1 and the design
parameters values are given in Table I.
Fig. 1. Proposed MMs with the design parameters.
TABLE I. PARAMETER VALUES OF THE DESIGN
Parameters
W
L1
L2
L3
L4
Value (mm)
0.2585
0.943
1.2
3.438
0.629
Parameters
L5
L6
L7
L8
Value (mm)
0.427
0.629017
1.40
0.943
Parameters
L9
L10
L11
L12
Value (mm)
1.146
0.4265
1.46
1.72
The overall size of a MPA unit cell dimension is 4.540 mm
x 2.771 mm which is very compact compared to other studies
[15]-[17]. The bottom and top layers are made of copper with a
thickness of 0.035 mm and conductivity of 5.96 x 107 S/m. The
substrate height is 1.2 mm for FR-4 with a dielectric constant εr
=4.4 and loss tangent tanδ=0.02, while for a Rogers RT5880 the
thickness is 1.575 mm, dielectric constant εr=2.2 and a loss
tangent tan δ=0.009.
III. PARAMETRIC STUDIES
For the sake of achieving good absorptivity over a wideband,
a parametric study is conducted on the different parameters
depicted in Table I. The most significant affecting parameter is
W. Figure 2 illustrate the reflection coefficient for different
values of W from 0.15 mm up to 0.25 mm for the absorbers
implemented on both FR-4 and Rogers RT5880. It could be
observed that the optimal value for W is 0.2585 for both. It
should be pointed out that the absorptivity rate and bandwidth
are changed dramatically for some values of W such that for
W=0.15 in FR-4 results in drastically diminished (It is not
depicted in Figure and also the other effect of parametric are not
included due to limited space).
15 20 25 30
-50
-40
-30
-20
-10
0
Reflection Coefficient [dB]
Frequency [GHz]
W=0,15 mm
W=0,17 mm
W=0,20 mm
W=0,22 mm
W=0,25 mm
(a)
15 20 25 30 35 40
-35
-30
-25
-20
-15
-10
-5
0
Reflection Coefficient [dB]
Frequency [GHz]
W=0,15 mm
W=0,17 mm
W=0,20 mm
W=0,22 mm
W=0,25 mm
(b)
Fig. 2. The reflection coefficients for FR-4 and Rogers RT5880 based MM
with different values of the parameter “W”: (a) FR-4 (b) Rogers RT5880.
IV. SIMULATIONS AND PERFORMANCE ANALYSIS
15 20 25 30
-50
-40
-30
-20
-10
0
Reflection Coefficient [dB]
Frequency [GHz]
(a)
15 20 25 30
0,0
0,2
0,4
0,6
0,8
1,0
Normalized Absorption
Frequency [GHz]
(b)
Fig. 3. The reflection and Normalized Absorption for FR-4: (a) Reflection
Coefficient (b) Normalized Absorption.
A 5G MPA unit cell has been accomplished with CST
Microwave Studio. The parametric study is carried out in section
310

III for a periodic structure of the unit cell. The return loss values
S11 of the optimum value of W is depicted in Figure 3. It is clear
that the MPA has a wideband property in the operating
frequency range from 21.5 GHz to 30 GHz in Rogers RT5880,
however, the FR-4 shows a frequency range from 18 GHz to
26.8 GHz. Both bands cover the dedicated 5G applications.
Similarly, the absorption rate of the MPA with FR-4 is well
above 96%, meanwhile for the case of Rogers RT5880 is higher
(99%) as shown in Figure 4.
15 20 25 30 35 40
-40
-35
-30
-25
-20
-15
-10
-5
0
Reflection Coefficient [dB]
Frequency [GHz]
(a)
15 20 25 30 35 40
0,0
0,2
0,4
0,6
0,8
1,0
Normalized Absorption
Frequency [GHz]
(b)
Fig. 4. The reflection and Normalized Absorption for Rogers RT5880: (a)
Reflection Coefficient (b) Normalized Absorption.
V. EFFECTS OF INCIDENT ANGLES
It is required to have a stable absorptivity for MPAs
subjective to oblique incident at different angles. Figure 5, show
the variations in absorptivity as a function of incident angle θ
from 0° to 30° (TE/TM mode). The absorptivity of the proposed
structure remains higher than 96% in FR-4 and 99% in Rogers
RT5880 dielectric material. At higher incident angles the
absorption starts diminishing.
The absorptivity values are compared with other related
studies in terms of the unit cell size and substrate thickness as
depicted in Table II. It is clear that the proposed structure is
thinner and smaller compared to other studies conducted in this
research field. Furthermore, it must be taken into consideration
that our unit cell has more absorptivity rate compared to other
studies. With the target to obtain wide- angle-of-incidence
absorber, as summarized in Table III, the current design also
shows absorptivity value of about 94% at an incident angle θ =
30° which is higher than the values reported by similar studies.
15 20 25 30
0,0
0,2
0,4
0,6
0,8
1,0
Normalized Absorption
Frequency [GHz]
Theta=0°
Theta=15°
Theta=30°
(a)
15 20 25 30 35 40
0,0
0,2
0,4
0,6
0,8
1,0
Normalized Absorption
Frequency [GHz]
Theta=0°
Theta=15°
Theta=30°
(b)
Fig. 5. Normalized absorption rate for different angle of incident: (a) FR-4 (b)
Rogers RT5880.
TABLE II. A COMPARISON OF THE OBTAINED ABSORPTIVITY VALUES
IN TERM OF DIMENSION AND SUBSTRATE THICKNESS WITH RELATED
PREVIOUS STUDIES
Frequency
Range
Absorptivity
(%)
Absorption
Bandwidth
Unit Cell
Size
(mm2)
Substrate
Thickness
(mm)
Reference
Number
8 -18
GHz
≈ 90
10 GHz
7.5 x 7.5
2.5
[15]
10.6 -16.6
GHz
≈ 85
6 GHz
7 x 7
1.6
[16]
15.7 -23.8
GHz
≈ 90
8.1 GHz
7 x 7
1.6
[17]
21 - 30
GHz
≈ 96
9 GHz
4.5 x 2.7
1.2
Our
Proposed
Structure
TABLE III. A COMPARISON OF THE CURRENT ABSORPTIVITY VALUES AS
A FUNCTION OF INCIDENT ANGLE WITH RELATED PREVIOUS STUDIES
Incident
Angle (θ)
Frequency
Range
Absorption
Bandwidth
Absorptivity
(%)
Reference
Number
0°
15°
30°
8-18
GHz
10 GHz
> 90
Not Depicted
Not Depicted
[15]
0°
15°
30°
10.6-16.6
GHz
6 GHz
≈ 85
≈ 71
≈ 77
[16]
0°
15°
30°
15.7-23.8
GHz
8.1 GHz
≈ 90
≈ 75
≈ 30
[17]
0°
15°
30°
21 - 30
GHz
9 GHz
≈ 99
≈ 96
≈ 94
Our
Proposed
Structure
311

VI. CONCLUSION
In this study, the designed absorber is compact and thin. It
could be applied to microwave energy harvesting applications.
The work focused on a novel wideband MPA with various
incident angles in the range between 0° - 30°. The unit cell is
developed and simulated based on the superposition of two
resonances generated by two different letters (G and S).
Moreover, it offers high absorptivity rate with different
dielectric materials. The absorptivity rate is higher than 96% in
FR-4 with a substrate height of 1.2 mm and 99% for Rogers
RT5880 with a substrate height of 1.575 mm. In future work this
study could be validated by fabrication and measurements and
its application could be extended to be applied to UAV devices
with microwaves energy harvesting based systems.
REFERENCE
[1] Cui, T. J. ,”Microwave metamaterials”, Natl. Sci. Rev. 5, 134–136 (2018).
[2] Cui, T., Smith, D. & Liu, R., “Metamaterials: Theory, Design, and
Applications”, Vol. 13 (Springer, New York, 2010).
[3] Wang, B.-X., Wang, G.-Z. & Wang, L.-L., “Design of a novel dual-band
terahertz metamaterial absorber”, Plasmonics 11, 523–530 (2016).
[4] Liu, N., Mesch, M., Weiss, T., Hentschel, M. & Giessen, H. Infrared
perfect absorber and its application as plasmonic sensor. Nano Lett. 10,
2342–2348 (2010).
[5] Gao, X., Zhou, L., Liao, Z., Ma, H. F. & Cui, T. J. An ultra-wideband
surface plasmonic filter in microwave frequency. Appl. Phys. Lett. 104,
191603 (2014).
[6] Mohammed Farouk Nakmouche and Mahammedi Nassim, “Impact of
Metamaterials DGS in PIFA Antennas for IoT Terminals Design”, The
6th international conference on Image and Signal Processing and their
Applications, November 2019.
[7] Song, S., Chen, Q., Jin, L. & Sun, F. Great light absorption enhancement
in a graphene photodetector integrated with a metamaterial perfect
absorber. Nanoscale 5, 9615–9619 (2013).
[8] Rufangura, P. & Sabah, C. Dual-band perfect metamaterial absorber for
solar cell applications. Vacuum 120, 68–74 (2015).
[9] A. A. G. Amer, S. Z. Sapuan, N. Nasimuddin, A. Alphones and N. B.
Zinal, "A Comprehensive Review of Metasurface Structures Suitable for
RF Energy Harvesting," in IEEE Access, vol. 8, pp. 76433-76452, 2020.
[10] Swett, D.W. Near Zero Index Perfect Metasurface Absorber using
Inverted Conformal Mapping. Sci Rep 10, 9731 (2020).
[11] Hu Tao, Nathan I. Landy, Christopher M. Bingham, Xin Zhang, Richard
D. Averitt, and Willie J. Padilla, "A metamaterial absorber for the
terahertz regime: Design, fabrication and characterization," Opt. Express
16, 7181-7188 (2008).
[12] G. A. Akpakwu, B. J. Silva, G. P. Hancke and A. M. Abu-Mahfouz, "A
Survey on 5G Networks for the Internet of Things: Communication
Technologies and Challenges," in IEEE Access, vol. 6, pp. 3619-3647,
2018.
[13] M. Agiwal, A. Roy and N. Saxena, "Next Generation 5G Wireless
Networks: A Comprehensive Survey," in IEEE Communications Surveys
& Tutorials, vol. 18, no. 3, pp. 1617-1655, thirdquarter 2016, doi:
10.1109/COMST.2016.2532458.
[14] X. Lu, P. Wang, D. Niyato, D. I. Kim and Z. Han, "Wireless Networks
with RF Energy Harvesting: A Contemporary Survey," in IEEE
Communications Surveys & Tutorials, vol. 17, no. 2, pp. 757-789,
Secondquarter 2015.
[15] J. Feng, L. Si, L. Sun, Y. Tian and D. Li, "An ultrathin polarization-
independent wideband metamaterial absorber for EMC applications,"
2017 International Symposium on Electromagnetic Compatibility - EMC
EUROPE, Angers, 2017, pp. 1-4.
[16] Ramya, S, Srinivasa Rao, I. A compact ultra‐thin ultra‐wideband
microwave metamaterial absorber. Microw Opt Technol Lett. 2017; 59:
1837– 1845.
[17] Y. Khanna and Y. K. Awasthi, "Wideband Ultra-thin Metamaterial
Absorber for Ku & K- Band Applications," 2020 7th International
Conference on Signal Processing and Integrated Networks (SPIN), Noida,
India, 2020, pp. 367-371.
312