Composite circular split ring resonator (CSRR)-based left-handed metamaterial for C- and Ku-band application

Results in Physics 14 (2019) 102435

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Composite circular split ring resonator (CSRR)-based left-handed metamaterial for C- and Ku-band application

T

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Tayaallen Ramachandran, Mohammad Rashed Iqbal Faruque , Eistiak Ahamed Space Science Center (ANGKASA), Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia

A R T I C LE I N FO

A B S T R A C T

Keywords: Circular ring CSRR C- and Ku-band Dual-band Electromagnetic properties

The aim of this study is to introduce a compact metamaterial structure for dual-band (C- and Ku-band) applications. Due to their unique electromagnetic properties, metamaterials find wide use in satellite applications to improve performance, and have therefore received great attention from researchers all over the world. In this article, a left-handed circular split ring resonator metamaterial structure is designed for satellite application. The inner circular split rings are split with thickness of 0.20 mm and a 0.25 mm thickness rectangular bar tilted at angles of 0°, 90°, 180° and 270° to connect all the main resonator rings. The metamaterial design proposed here is developed on a square Epoxy Resin Fiber (FR-4), which serves as the dielectric substrate layer. The metamaterial structure was successfully designed and simulated using numerical analytical methods such as Finite Integration Technique (FIT)-based electromagnetic simulator, and Computer Simulation Technology Microwave Studio (CST). Several designs were used to perform parametric studies while varying the subtract strip line thicknesses and subtraction angles. A frequency range of 0–18 GHz was used in simulation, where the design manifested resonance frequencies at 6.46 GHz and 16.92 GHz. In addition, the fabricated metamaterial showed resonance frequencies at 6.54 GHz and 17.06 GHz, making this design applicable for both C- and Ku-bands. Comparison between experimental and numerical results showed that transmission coefficient graphs obtained from the two methods were largely in agreement with each other and showed only small differences. The resonance frequency at Ku-band exhibited left-handed metamaterial behavior that makes the designed metamaterial suitable for satellite communication system.

Introduction Over the past decade, the quality of human life has changed drastically due to the connectivity via satellite. Satellite applications help to create a new world of possibilities such as the GPS system in a car, live football match broadcasting, current weather updates and help us to communicate with people all over the world. Essentially satellite applications today fall in and primarily use three frequency bands which are C-, Ku-, and Ka-bands. These frequencies cover the research area of small spot coverage broadband, small antennas, and wide area coverage, which is extremely resilient to severe weather conditions. A large number of research works have been devoted for the development of miniaturize, lightweight and low-cost metamaterials to achieve improved performance and functionality in satellite applications. Many different types of materials have been explored in the past to develop a new concept or invention with the aim to achieve improved technology. Most conventional materials are limited under circumstances while unusual or exotic materials are demanded for many applications.

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The composite material that consists of unusual effects broadly known as a metamaterial, has inspired many researchers to create a new pathway, that is applicable to almost all fields. From a more practical perspective, a metamaterial is an artificial composite material where light and sound waves interact in unusual manner as compared to conventional natural materials. For instance, light propagation in waveguides and free space can be controlled in a metamaterial and thus, the manipulation of electromagnetic wave fronts is highly interesting for various applications such as data processing, focusing, holography and signal multiplexing. Indeed, the development of a metamaterial can allow to control light by applying external electric and magnetic signals, so as to improve the efficiency of signal absorption and harvesting. Furthermore, a metamaterial also has other less-visible but unique characteristics such as chirality, perfect absorption, artificial magnetism and hyperbolic dispersion [1–3]. In view of these superior performances, metamaterials can be applied in diverse interdisciplinary fields such as invisibility cloaking, small electric and magnetic dipole antennas, super-lenses, microstrip patch antenna, SAR reduction, and

Corresponding author. E-mail address: [email protected] (M.R.I. Faruque).

https://doi.org/10.1016/j.rinp.2019.102435 Received 4 April 2019; Received in revised form 7 June 2019; Accepted 7 June 2019 Available online 13 June 2019 2211-3797/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).

Results in Physics 14 (2019) 102435

T. Ramachandran, et al.

14 GHz. Within this framework, the metamaterial had resonance frequencies at 7.53 and 12.02 GHz. A highly flexible elastomer liquid metamaterial-based 5 × 5 mm2 split-ring resonator was proposed by Liu et al. in 2015 [20], but the flexible metamaterial design proposed in this work propagated along the y-axis, exhibited a single negative characteristic with a narrow bandwidth, and operated only in X-band. In 2017, Hasan and Faruque designed a Z-shaped split ring resonator with resonance frequencies in the S-, C-, X-, and Ku-bands [21]; the proposed metamaterial design was analyzed in the azimuthal angles from 0° to 90° at 15° intervals. Despite the fact that the metamaterial could operate at multi-band frequencies, the proposed design exhibited left-handed characteristics in the X-band only. Thus, the major drawback in all the previous results described above include a bigger substrate dimension or the designed metamaterial applicable for single negative metamaterial. Recently, the metamaterial Epsilon Near Zero (ENZ) has emerged as an important new discovery due to its unique characteristics that allows its potential implementation in electromagnetic invisible and transparency cloaking [22–24]. In this context, our study describes a left-handed and dual-band metamaterial with resonance frequencies in both C- and Ku-bands. The metamaterial is a compact circular split ring resonator designed on a FR-4 substrate with z-axis wave propagation. The rest of this article is organized as follows. Section “Metamaterial design structure” describes the structure and dimension of the proposed metamaterial design. In Section “Methods and techniques”, the methodology of simulation and experimental study with respect to single unit cell as well as periodic array cell, are discussed in detail. Scattering parameters (or also known as S-parameter) such as transmission and reflection coefficients, and electromagnetic properties such as permeability, permittivity and refractive index of the proposed metamaterial design are analyzed in Section “Results and discussion”. In Section “Parametric study”, parametric studies with various metamaterial designs and the electromagnetic properties of the designs are reviewed; Section “Conclusion” contains a brief conclusion on the experimental study.

bio-sensors [4–8]. Furthermore, metamaterial inspired polarized and monopole antennas with working resonance bands of GPS, Bluetooth, WiMAX or satellite communication applications are also possible [9,10]. The motivation behind pursuing these research fields is to construct components and devices using complex material for lower frequency applications. The theory of left-handed metamaterials was first investigated in the 1960s by the Russian physicist, Victor Veselago, who reported a theoretical study on the electromagnetic properties of an artificial material in which, both the magnetic permeability and electric permittivity have negative real values at certain frequencies. In addition, Veselago demonstrated the occurrence of negative refractive index, where the flow of energy is in a direction opposite to that of the phase velocity. This theory gives an enormous inference nearly for all electromagnetic phenomena. A left-handed metamaterial with a negative refractive index would reverse both Snell and Doppler effects at a certain frequency [11]. In the reverse Snell effect, light travelling from a conventional material to the left-handed material will experience a unique refractive effect causing it to bend in a direction opposite to what normally occurs. However, at the time of Veslago’s report, left-handed metamaterials were not commonly known to exist and therefore, this concept remained a curiosity for several decades. Since the discovery of unique properties in metamaterial, the negative-index characteristic also becomes popular among researchers besides left-handed metamaterial. For instance at 2012 [12] and 2014 [13], Cheng et al. and Fang et al. demonstrated a numerical study of three-dimensional isotropic metamaterial at microwave frequency ranges. A double periodic array metallic fishnet structure and metallic closed rings etched on six sides of a cubic dielectric substrate were respectively proposed in these journals. Fishnet structure metamaterial exhibits negative-index characteristic, while metallic closed rings metamaterial produces left-handed characteristic. Furthermore, in 2011 [14], Zhi et al. proposed and investigated the negative index characteristic for split-ring resonator pairs metamaterial. The proposed design manifest left-handed transmission passband clearly and demonstrated low loss at the broadband frequency range. A combined ring and cross pairs metamaterial design which manifest multi-band resonant frequencies, was proposed by Liu et al. at 2013 [15]. The proposed design was numerically simulated using FDTD method and focused on terahertz regime only. These combined composite structure exhibit left-handed characteristic at 0.43 and 1.32 THz and righthanded characteristic at 0.84 THz. After 2010, several important experiments related to the application of metamaterials in satellites were carried out in many parts of the world. In 2015, Islam et al. investigated the electromagnetic cloaking effect by introducing a left-handed metamaterial in the microwave frequency regime [16]. The proposed metamaterial design manifested left-handed properties in all the three wave propagation directions x, y, and z; the x-axis and y-axis had almost similar resonance frequencies. These wave directions produced effective parameters in the S- and Cbands for the y-axis, and in S-, C- and X-bands for the x-axis, whereas in the z-axis, resonance frequencies were observed only in X- and Kubands. Moreover, in 2014, Islam et al. [17] introduced a 30 × 30 mm2 multi-band H-shaped metamaterial which exhibited resonance frequencies in S-, C- X- and Ku-bands. Although this metamaterial structure operates at multi-band frequencies, it showed double negative metamaterial (DNG) behavior only at these frequency bands. A double Z-shaped metamaterial design with dimension of 8.5 × 8.5 mm2 was proposed by Zhou et al. in 2015 [18]. This left-handed metamaterial designed using coplanar electric and magnetic resonators had resonance frequencies of 7.1 GHz, 8.9 GHz and 11.8 GHz, which were applicable in the C- and X-bands only. Hasan et al. suggested in 2016, a 10 × 10 mm2 dual band metamaterial with a double negative characteristic, that enabled its application in C- and X-bands [19]. z-axis wave propagation was used in this experiment and the operating frequency was in the range from 2 to

Metamaterial design structure Initially, the proposed structure consists of a single outer and six inner circular lossy metal rings with thicknesses of 0.5 and 0.25 mm, respectively. Annealed copper with conductivity, σ = 5.8 × 107 S/m was used to construct both outer and inner circular rings. Two copper strip lines of 0.25 mm thickness and 7.7 mm long at angles of 0-degree and 90-degree were used to connect all the circular split ring resonators (CSRR). Then, four copper bars of 0.35 mm thickness and 7.6 mm long at 30°, 60°, 120° and 150° from the x-axis were used to subtract the inner circular rings. Hence, the final proposed design is constructed as shown in Fig. 1(a). FR-4 lossy material with the thickness, S = 1.6 mm (as shown in Fig. 1(b)), a dielectric constant of 4.3, and tangent loss of 0.025 was used as the substrate in this design. The dimension of the square-shaped unit cell structure was 8 × 8 mm2. Table 1 lists the dimensions of the proposed metamaterial design of the single unit cell structure. Methods and techniques The proposed unit cell metamaterial design structure was numerically simulated using commercially available Finite Integration Technique (FIT)-based Computer Simulation Technology Microwave Studio (CST) program. The CST Microwave Studio is a quick, precise and user-friendly three-dimensional high frequency software for solving electromagnetic problems. For any electrically small devices or structures, the Frequency Domain Solver (FDS) is the better choice. Hence, the FDS was used for this journal. The proposed metamaterial unit cell design was placed in the middle of two waveguide ports on the negative and positive z-axis, and was excited by a transverse electromagnetic (TEM) wave, as shown in Fig. 2(a). The x-axis and y-axis were defined 2

Results in Physics 14 (2019) 102435

T. Ramachandran, et al.

parameters of the proposed metamaterial design were analyzed. Data on the reflection coefficient, S11 and transmission coefficient, S21 were used to express the various metamaterial properties such as permeability ( μr ), permittivity (εr ), and refractive index (nr ) using the wellknown MATLAB software, based on the Nicolson–Ross–Weir (NRW) method. The extracted electromagnetic properties by using NRW method [19,25,26] can be expressed as follows:

V1 = S21 + S11

(1)

V2 = S21 − S11

(2)

The S11 and S21 can be written as,

S11 =

S21 =

(1 − Γ 2) z 1 − Γ 2z 2

(3)

z 2)Γ

(1 − 1 − Γ 2z 2

(4)

The effective permeability ( μr ) can be calculated by,

μr =

2 (1 − V2) × jkd (1 + V2)

μr =

2 (1 − S21 + S11) × jπfd (1 + S21 − S11)

(5)

The effective permittivity (εr ) can be expressed as follows,

εr =

2 (1 − V1) × jkd (1 + V1)

εr =

2 (1 − S21 − S11) × jπfd (1 + S21 + S11)

Fig. 1. Schematic metamaterial prototype: (a) Top view; (b) Side view. Table 1 Design specifications of unit cell. Parameter

Hence, the refractive index (nr ) can be obtained as follows, Dimensions

Thickness of 1st Ring, d1 Thickness of 2nd–7th Ring, d2 Gap between the rings, g Strip line thickness, t1 Strip line thickness, t2 Length of substrate, a Length of substrate, b Thickness of substrate, c Thickness of copper, e Strip line angle, f1 and f3 Strip line angle, f2 and f4

(6)

0.500 mm 0.250 mm 0.200 mm 0.250 mm 0.350 mm 8.000 mm 8.000 mm 1.600 mm 0.035 mm 30° 60°

nr =

2 × jkd

nr =

2 × jπfd

2 2 ⎧ (S21 − 1) − S11 ⎫ 2 2 ⎨ ⎩ (S21 + 1) − S11 ⎬ ⎭ 2 2 ⎧ (S21 − 1) − S11 ⎫ 2 − S2 ⎬ ⎨ ( S + 1) 11 ⎭ ⎩ 21

(7)

The Equations from (1) to (6) were used to write code in MATLAB software to obtain metamaterial properties. The same steps were employed also to simulate the proposed 9 × 9-unit cells (72 × 72 mm2) periodic array metamaterial design as shown in Fig. 2(b). Measurements were made to verify the experimental performance. The unit cell and array CSRR metamaterial structures were fabricated on a printed circuit board (PCB), and vector network analyser (VNA) model number Agilent N5227A was used to obtain the S-parameters of the metamaterial. This PNA Series network analyser has frequency range from 10 MHz to 67 GHz and has high stability of < 0.03 dB/°C.

as the perfect electric conductor (PEC) and the perfect magnetic conductor (PMC) boundaries, respectively. A tetrahedral mesh from 0 to 18 GHz frequency was used in this simulation. At the end of this simulation, S-parameters were obtained, and the effective medium

Fig. 2. Simulation geometry for z-axis wave propagation: (a) Single unit cell; (b) 9 × 9-unit cells. 3

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(a)

(b) L2 L4 L1

C1

C2

L3 C3

L2 R1

L5 L6

C5

C4

(c)

(d)

Fig. 3. Fabricated metamaterial: (a) Single unit cell, (b) 9 × 9-unit cells, (c) Agilent N5227A vector network analyser, and (d) Equivalent circuit model of the proposed unit cell metamaterial.

The metamaterial unit cell and 9 × 9-unit cells (72 × 72 mm2) were placed between two waveguide ports which are A-INFOMW WG to adapter P/N: 137WCAS for C-band and A-INFOMW WG to adapter P/N: 51WCAS-CU for Ku-band. Since the perfect hardware is not possible, hence error can happen during the measurement. An Agilent N469460001 was used to calibrate the VNA for better measurement performance. Fig. 3(a) to (c) show the fabricated metamaterial for unit cell, array cell, and for the experimental setup used for measurement. Once the transmission coefficient, S21 and reflection coefficient, S11 were obtained from this measurement, the methodology and equations as mentioned above, were adopted, to obtain the electromagnetic properties of the metamaterial design. A circuit model for the unit cell of proposed circular split ring resonator metamaterial structure is presented simply in Fig. 3(d). The split gaps in this circuit diagram are retained as capacitive effect which symbolised by C1, C2, C3, C4 and C5. Meanwhile the inductive effect designated as L1, L2, L3, L4, L5 and L6 and the effect conversely depends on the strip lines. Since, the CSRR excited by an electric field intensity, the equivalent circuit diagram designed with series capacitance in each split gap. The inductance and capacitance can be calculated through the equations as expressed in (8), (9) and (10). The Eq. (8) has been applied to calculate the inductance in strip shaped metamaterial, but it does not quite represent the full metamaterial structure. A totally different equation as expressed in (9) is used to calculate the inductance in circular shaped metamaterial. While, the capacitance calculated using Eq. (10) for whole metamaterial structure. Furthermore, from these equations, the resonance frequencies manifest at 6.43 and 16.90 GHz, whereas the simulated and measured resonance exhibit 6.46, 16.92, 6.54 and 17.06 GHz respectively (as shown in Fig. 4(a)). The inductance for strip line structure can be expressed as,

l ⎞ W+t ⎤ ⎞ Kg L (nH ) = 2 × 10−4l ⎡In ⎛ + 1.193 + 0.2235 ⎛ ⎢ W t + ⎝ l ⎠⎥ ⎠ ⎦ ⎣ ⎝

(8)

While circular structure inductance can be measured as follow,

a=

Do + Di ; 4

c=

Do − Di ; 2

L (nH ) = 0.03937

a2n2 Kg 8a + 11c

(9)

The capacitance can be calculated from equation,

C (pF ) =

10−3 ∊rd Wl 36πd

(10)

where W is width of microstrip line, l is length of microstrip line, t is thickness of microstrip line, Do is outer diameter of CSRR, Di is inner diameter of CSRR and the ∊rd is the dielectric constant of dielectric film. Results and discussion The S-parameter and amplitude of the effective medium parameters for the numerical and experimental studies on z-axis wave propagation, including the magnitudes of transmission coefficient (S21), reflection coefficient (S11), permeability (μ), permittivity (ε) and refractive index (n) are depicted in Fig. 4(a)–(d). In Fig. 4 (a), S21 displays two clear resonance frequencies at 6.46 GHz (in C-band) and 16.92 GHz (in Kuband), while experimentally measured resonance frequencies are 6.54 GHz (C-band) and 17.06 GHz (Ku-band). The magnitudes of transmission coefficient determined from simulation and from experimental measurement were in good agreement almost were nearly 4

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the negative refractive index from 4.01 GHz with amplitude of −9.30 dB to 6.17 GHz with amplitude of −0.002 dB, and from 7.70 GHz with an amplitude of −16.39 dB to 7.99 GHz with an amplitude of −27.91 dB (highest peak value in C-band) as shown in Fig. 4(d). In conclusion, combining two or more distinct materials in a certain way will improve the electromagnetic patterns as shown in measurement and numerical results for proposed metamaterial design. Generally, the effective medium parameters can modify by the structures in metamaterial design as known as metallic wire arrays or splitring resonators (SRRs). Moreover, the adjustment of the spacing and size of the elements in split-ring resonators, produces a desire effective parameter values at a certain wavelength [4]. Thus, in general the implementation of the metamaterial periodic unit cells builds upon on few essential parameters such as metallic strip lines, split gaps, thickness and size of the metamaterial structure. The passive elements, multilayer metamaterial structure and multi resonance frequencies are the key variables in obtaining wide operational bandwidth. Furthermore, miniaturization of unit cell is possible through the design techniques and current density distribution. Although this approach will increase the current path, but it causes a rise in unwanted coupling effects and decreases operational bandwidth. Aside from that, the resonances are producing in the strip lines and split gaps of metamaterial structure and act as inductive-capacitive lumped circuit.

equal. The slight difference between the experimental and numerical results is probably due to minor errors in fabrication and in measurement. Although a negative effective permeability curve is observed starting from 8.33 GHz with an amplitude of −2.76 dB (as shown in Fig. 4 (b)), the negative permeability at resonance frequency of the proposed metamaterial begins from 12.01 GHz with an amplitude of −6.20 dB up to 17.75 GHz with an amplitude of −0.004 dB. In Fig. 4(c), it is seen that negative permittivity behavior is observed from 4.01 GHz to 7.06 GHz with a change in amplitude from −277.73 dB to −0.14 dB, and at 17.60 to 17.68 GHz, where the with amplitude changes from −1.05 dB to −4.23 dB. In the Ku-band, the permittivity exhibits a unique characteristic, also known as the ENZ metamaterial behavior. Besides, at this frequency, the left-handed behavior of the metamaterial where the refractive index becomes negative, is also revealed. Here, in the frequency range 17.60–17.68 GHz, the proposed metamaterial design has amplitudes of permeability and refractive index of −0.11 dB to −0.06 dB and −2.45 dB to −2.35 dB, respectively. These results show that the design satisfies the conditions for a left-handed material where the permeability, permittivity and refractive index have negative values. Due to effect of polarization, the difference between the permeability and permittivity is controlled by the internal structure of the material. Besides the frequency range where left-handed behavior is observed, the metamaterial also shows 5

Results in Physics 14 (2019) 102435

T. Ramachandran, et al.

Fig. 5. Surface current distribution on the metamaterial at: (a) 6.462 GHz, (b) 16.92 GHz; Electric field distribution at: (c) 6.46 GHz, (d) 16.92 GHz.

Parametric study

The excited surface current distribution on the proposed single unit cell metamaterial (xy-plane) at 6.46 GHz and 16.92 GHz are displayed in Fig. 5(a) and (b), while Fig. 5(c) and (d) show the electric field distribution of the design at the same frequencies. The current intensity is expressed by the color and the direction of current is indicated by arrows in the figures. In Fig. 5(a), it is seen that the current distribution appears to be mainly concentrated around and near the inner surface of the outer circular ring. Indeed, the figure shows that the current is lower in the middle portion or in the gaps between circular rings. At 16.92 GHz frequency, as shown in Fig. 5(b), the metamaterial design has a higher current intensity (indicated by the yellow color) in the inner part of the design structure, as compared to the current intensity at 6.46 GHz. Moreover, it is observed that the current flow in each of the split ring resonators are in opposite directions. This because, the skin effect on the copper strip causes a sustainable electrostatic condition and the opposing current flows are unequal to each other. When the current flowing in the two directions are equal, the fields will internally cancel each other, and a stop band will occur. In addition, a powerful electric field is generated in the gaps between the rings and this effect extends to the center of the design at C-band frequencies. On the other hand, at Ku-band frequencies, the design also has a powerful electric field in gaps between the rings, but the electric field is reduced before reaching the fifth inner circular ring. Usually, sole dielectric substrate which also known as electrical insulator, do not have free electrons like metal materials. Since the proposed design has metal circular rings arrangement on dielectric substrate, the exist electron oscillations at interface between metal and dielectric materials are delocalized. In other word, across the interface the real part of dielectric function changes sign. Hence the visual effect can see in the Fig. 5(c) and (d) where the electric field occur not only in circular rings but also on the surface of dielectric substrate.

Design optimization done in this journal through several constrains. All the restrictions placed on the designs were set as constraints such as: The number of frequency bands ( x1) can be expressed as follows:

x1 ≥ 2

(11)

The effective permeability, μr ( x2),effective permittivity, εr ( x3) and refractive index, nr ( x 4 ) constraints can be expressed as follows:

x2 < 0; x3 < 0; x 4 < 0

(12)

The subsection below showed the analysis of various design options. This concept called iterative process where several trial designs one after another were analysed until suitable design was obtained. During this process the above constraints were used to find the acceptable design. In every parametric study, one best design was selected based on the maximum value of x1, x2 , x3 and x 4 . Finally, the selected designs in each parametric study were compared to choose optimized design. Strip line thickness of 0.15 mm In this work, we carried out a few parametric studies to compare the electromagnetic properties of different designs. These studies help to evaluate the proposed parameters and in the analyses of the results while varying each of these parameters. In the first parametric study, a thickness of 0.15 mm for the copper strip line was used to subtract the inner circular rings. The different angles of subtraction used in the metamaterial designs are shown in Fig. 6(a)–(c). The dimensions of outer and inner circular rings are homogeneous to the proposed metamaterial design. The magnitudes of transmission coefficient (S21) and reflection coefficient (S11) for the unit cell operating at single- and multi-band frequencies are shown in Fig. 7(a), and Fig. 7(b)–(d), depict the amplitude of magnetic permeability (μ), electrical permittivity (ε) and 6

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T. Ramachandran, et al.

Fig. 6. Circular metamaterial design subtract strip line (thickness 0.15 mm) angle: (a) ± 45°; (b) ± 25°, ± 50°, and ± 75°; (c) ± 15°, ± 30°, ± 45°, ± 60°, and ± 75°.

at the frequency of 6.95 GHz. The main conclusion from these results is that when the number of subtract copper strip lines in the design are increased, the inductive effect is also increased, which causes the resonance frequency to be shifted towards higher frequencies; this proves that the inductive reactance is proportional to the frequency. Furthermore, the negative permeability for all these designs occurs in the Ku-band frequency, as shown in Fig. 7(b). At the frequency of 12.01 GHz, the three designs show amplitudes of −7.36 dB, −6.37 dB and −5.73 dB. The negative permeability of these designs is maintained almost up to the end of the Ku-band. However, the negative

refractive index (n) for strip line thickness of 0.15 mm. The design in Fig. 6(a) exhibits multi-band applications with resonance frequencies at 5.00 GHz (under C-band), 15.01 GHz and 16.99 GHz (under Ku-band) with magnitudes of −23.50 dB, −28.42 dB and −15.00 dB, respectively. The design in Fig. 6(b) also produces multi-band frequencies similar to the previous design, and resonance frequencies at 6.35 GHz (under C-band) and 16.74 GHz (under Ku-band) with acceptable magnitudes of −29.75 dB and −28.44 dB, respectively, are observed. Moreover, the design in Fig. 6 (c) leads to a single-band frequency with the highest magnitude for transmission coefficient, namely, −31.23 dB

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negative permeability at 8.66 GHz to 17.96 GHz (under X- and Kuband) with amplitudes in the range −1.91 dB to −0.01 dB, and at 8.80–17.53 GHz (under X- and Ku-band) with amplitude in the range −2.44 dB to −1.23 dB, respectively; for design (c), the negative permeability occurs in the frequency range 8.86 GHz to 16.76 GHz. Although this design has a shorter negative permeability range as compared to the other two designs, it exhibits a higher permeability value of −92.00 dB at X-band frequency. In addition to results in Fig. 8(b) and (c), which show operation at similar frequencies, permittivity results also exhibited nearly similar values, as shown in Fig. 9(c). The negative permittivity value for design (b) in Fig. 8 produced at the resonance frequency of 8.01 GHz with amplitude of −4.23 dB to 9.97 GHz with amplitude of −0.03 dB, and from 11.59 GHz with an amplitude of −0.45 dB to 11.99 GHz with amplitude of −0.29 dB, under X-band frequency. For Ku-band frequencies, this design shows negative values at 12.01 GHz with amplitude of −0.21 dB up to 12.04 GHz with amplitude of −0.06, and at 17.37 GHz with amplitude of −0.13 up to 17.84 GHz with an amplitude of −0.03 dB. Moreover, design (c) has a negative permittivity value that starts with a slight difference in amplitude of −0.36 dB (at frequency of 8.01 GHz) and ends with the same amplitude (at frequency of 9.76 GHz), as compared to design (b). In addition, design (a) has negative permittivity values at frequencies in the range between 8.01 GHz and 11.09 GHz, as well as in the range 14.38 GHz to 14.85 GHz with an amplitude near to zero, a behavior that is almost similar to those of designs (b) and (c). Moreover, designs (a) and (c) exhibit a left-handed metamaterial behavior at frequencies from 8.66 GHz to 11.09 GHz, and from 14.38 GHz to 14.85 GHz, respectively. Besides permeability and permittivity, at these frequencies, the refractive index also shows a negative value (as shown in Fig. 9(d)) which satisfies the conditions for a left-handed metamaterial. However, for design (b), the left-handed characteristic occurs only at X-band frequencies, which is from 8.80 GHz to 9.68 GHz, and from 11.59 GHz to 11.99 GHz. Although these designs have interesting electromagnetic properties, they do not satisfy the purpose of this article, since the aim of the work is to produce multi-band frequency operation for satellite applications.

permittivity of these three designs is observed at the same frequency (as shown in Fig. 7(c)), 4.01 GHz, with different amplitudes of −113.33 dB, −226.97 dB and −391.95 dB. The negative permittivity for the design shown in Fig. 6(a) occurs at a single-band only, from 4.01 to 5.35 GHz, and from 6.19 to 7.99 GHz (which are both C-band frequencies) with amplitudes of −113.33 to −0.21 dB and −42.51 to −7.45 dB. However, in addition to C-band frequency, the design in Fig. 6(b) and (c) show negative permittivity values also at Ku-band resonance frequency. These designs produce negative permittivity values at frequency ranges 17.55 GHz–18.00 GHz and 12.00–12.46 GHz with amplitudes of −0.57 dB to −6.76 dB and −0.71 to −0.02, respectively. Both these designs fall in the ENZ metamaterial regime, since the permittivity values are near-zero. In addition, as referred to in Fig. 7(d) the design Fig. 6(b) also exhibits a left-handed metamaterial behavior at the resonance frequency. At Ku-band frequencies of 17.55 GHz to 17.68 GHz, the designed metamaterial reveals amplitudes of permeability, permittivity and refractive index from −0.16 dB to −0.07 dB, −0.57 dB to −5.76 dB and −2.61 dB to −2.41 dB, respectively. However, even though the design in Fig. 6(b) shows ENZ and left-handed metamaterial behavior, the dual-band metamaterial proposed provides a better performance than the single-band metamaterial. Strip line thickness of 0.25 mm In another experiment, as a part of the parametric study, a subtract copper strip line with thickness of 0.25 mm and 6.2 mm long was placed at different angles, as presented in Fig. 8(a)–(c). The subtraction action that takes place is in this case, is slightly different from that of the proposed metamaterial design, where the rectangular bar (thickness of 0.25 mm) connected with circular rings are not subtracted together during the process. Fig. 9(a–d) show, respectively, the magnitude of the transmission coefficient (S21) and reflection coefficient (S11), and the amplitudes of permeability, permittivity, and refraction index. Both the designs shown in Fig. 8(b) and (c) can operate at multiband frequencies and can be utilized for X- and Ku-band applications as shown in Fig. 9(a). While the resonance frequency for the design in Fig. 8(a) falls at 13.68 GHz, this metamaterial design is applicable only for Ku-band. For design (b), resonance frequencies at 10.84 GHz (under X-band), 14.56 GHz, 15.79 GHz, 16.63 GHz (under Ku-band) are observed and those at 10.69 GHz (under X-band), and 16.09 GHz are found for design (c) in Fig. 8. From the transmission coefficient results, it is also inferred that when the subtract copper strip line is placed at 30 and 210°, it exhibits a higher magnitude of −39.90 dB at the resonance frequency and −31.86 dB at 10.69 GHz (under X-band) for designs in Fig. 8(a) and (c), respectively. This proves that the unorthodox electromagnetic properties of a metamaterial depend on its design geometry. Furthermore, Fig. 9(b) clearly indicates that all the three designs produce almost similar magnetic permeability plots. There are however, slight differences in value, for example, the design (a) and (b) in Fig. 8 manifest

Strip line thickness of 0.35 mm In a third parametric study, a copper strip line with thickness of 0.35 mm was used to subtract inner circular rings of the metamaterial design, as shown in Fig. 10(a) and (c). The design (b) in Fig. 10 is the proposed metamaterial design in this study and the other designs in this parametric study have dimensions that are partially similar to the proposed design. Furthermore, various angles have been used to construct different designs. The transmission coefficient, reflection coefficient, permeability, permittivity and refractive index plots of this parametric study are shown in Fig. 11(a) to (d). From Fig. 11(a), we infer that designs (a) and (b) have similar resonance frequencies, and can operate in dual-band (C- and Ku-band). At the resonance frequency, the design (a) exhibits

Fig. 8. Circular metamaterial design subtract strip line (thickness of 0.25 mm) angle: (a) 30°, 210°; (b) 160°, 330°; (c) 30°, 210° and 160°, 330°. 8

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17.28 GHz with amplitudes of refractive index of −2.32 dB to −1.76 dB, as shown in Fig. 11(d). For a metamaterial to be left-handed, besides the refractive index, the permeability (as shown in Fig. 11(b)) and permittivity should also show negative values, which in this case, are −0.41 dB to −0.05 dB and −0.10 dB to −0.58 dB, respectively. Thus, increasing the number of subtract copper strip line in the metamaterial structure results in boosting the performance, where the magnitude of transmission coefficient increases by 13.69%, as compared to design (a).

negative permittivity starting from 4.01 GHz with an amplitude of −155.78 dB as shown in Fig. 11(c). When the frequency increases in the C-band, the metamaterial has the lowest negative permittivity value, which is at 5.99 GHz with an amplitude of −0.29 dB. This design also shows ENZ and left-handed metamaterial behavior at Ku-band frequencies, which is similar to design (b). The ENZ metamaterial behavior is seen in the frequency range from 16.92 GHz to 17.48 GHz with amplitudes from −0.10 dB to −0.02 dB. Left-handed metamaterial behavior is observed in the frequency range from 16.92 GHz to

Fig. 10. Circular Metamaterial Design Strip line (0.35 mm) angle: (a) ± 45°; (b) ± 30° and ± 60°; (c) ± 20°, ± 40°, ± 60° and ± 80°. 9

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as shown in Fig. 12(a)–(c). Subtract copper strip lines of 0.25 mm thickness with various angles have been used in the three designs. In addition, the 0° and 90° copper strip lines have been used to connect the outer and the only first inner circular rings. The permittivity, permeability and transmission coefficient (S21) exhibits more or less similar values for all the three designs. Furthermore, the designs also show resonance frequencies only in X-band. From these results, it can be inferred that without the copper strip lines that connect all the outer and inner circular rings, there is no increase in inductive effect. Moreover, although the number of subtract copper strip lines in the designs are increased, the resonance frequency of the designs do not shift to higher frequencies. These designs show resonance at singleband frequencies only, which makes it very difficult to achieve

For the design in Fig. 10(c), the single-band metamaterial exhibits resonance frequency at 7.04 GHz (under X-band) with a magnitude of −32.03 dB. Moreover, this design also shows ENZ and left-handed metamaterial behavior at frequencies in the range from 9.50 GHz to 11.99 GHz with amplitude of permeability, permittivity and refractive index ranging from −0.94 dB to −1.20 dB (as shown in Fig. 11(b)), −24.74 dB to −5.62 dB (as shown in Fig. 11(c)), and −22.84 dB to −2.60 dB (as shown in Fig. 11(d)) respectively. Despite the fact that designs (a) and (c) can operate at satellite frequencies, with respect to performance, design (b) is more acceptable when considering the goals of this study. The final comparative parametric study shows that the subtraction takes place in a different way if the first inner circular ring is excluded,

Fig. 12. Circular metamaterial design subtract strip line (thickness of 0.25 mm) angle: (a) 45° and 90°; (b) ± 30°, ± 60°, and ± 90°; (c) 0°, ± 20°, ± 40°, ± 60°, and ± 80°. 10

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Table 2 Comparison of the designed structure with the previously published research results. References

Operating Frequency

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Left-handed Metamaterial Negative Index Left-handed Metamaterial Negative Index Chiral Metamaterial Left-handed Metamaterial

6×6 9×9 10 × 10 10 × 10 12 × 12 8×8

Roger RT 5880 Roger RT 5880 FR-4 FR-4 ARLON-AD350 FR-4

performance improvement. Generally, the designs in this final comparative parametric study are unsuitable with respect to the objectives of this study. Table 2 shows a comparison of resonance frequency band, substrate type and dimension of introduced design with previously reported structures. Although the previous research works have strong effective parameters, they show certain drawbacks. The designs in references [27] and [11] exhibit left-handed metamaterial behavior, but the designed metamaterials either operate in a single band or have a larger substrate dimension. Recently, industrial applications in many fields have increased utility for left-handed metamaterials. The metamaterial designs reported in Refs. [28,19,29] show resonance frequency that either has a negative index or a chiral metamaterial characteristic. Over the course of time, new technology requires miniaturization which has been progressed exponentially over the past couple of decades. Therefore, the metamaterial design introduced in this work with its compact in size and left-handed metamaterial behavior, is more suitable for satellite application.

References [1] Zheludev NI. Metamaterials at the University of Southampton and beyond. J Opt 2017;19(8):1–18. [2] Shekhar P, Atkinson J, Jacob Z. Hyperbolic metamaterials : fundamentals and applications. Nano Converg 2014;1(1):14. [3] Liu Y, Zhang X. Metamaterials: a new frontier of science and technology. Chem Soc Rev 2011;40:2494–507. [4] Liu Y, Zhang X. Physical sciences. Britannica Book of the Year 2014. Encyclopaedia Britannica, Inc; 2014. p. 311–7. [5] Faruque MRI, Hossain MI. Effects of hand on EM absorption and antenna performances for internal handset PIFA. Teh Vjesn 2017;24:459–67. [6] Lashab M, Zebiri C, Benabdelaziz F, Jan NA, Abd-Alhameed RA. Horn antennas loaded with metamaterial for Ku band application. 2014 International Conference on Multimedia Computing and Systems (ICMCS), Marrakech. 2014. p. 1372–5. [7] Schurig D, et al. Metamaterial electromagnetic cloak at microwave frequencies. Science (80-) 2006;314(5801):977–80. [8] Lahiri Basudev. Split Ring Resonator (SRR) based metamaterials. University of Glasgow; 2010. [9] Pokkunuri P, Taraka B, Madhav P. Metamaterial inspired reconfigurable fractal monopole antenna for multiband applications. Int J Intell Eng Syst 2019;12(2):53–61. [10] Rao MV, Madhav BTP, Anilkumar T, Nadh BP. Metamaterial inspired quad band circularly polarized antenna for WLAN/ISM/Bluetooth/WiMAX and satellite communication applications. AEUE – Int J Electron Commun 2018;97:229–41. [11] Hasan MM, Faruque MRI, Islam MT. Composite left-handed meta-atom for tri-band operation. Mater Res Express 2017;4(9):1–9. [12] Cheng YZ, Nie Y, Gong RZ. Broadband 3D isotropic negative-index metamaterial based on fishnet structure. Eur Phys J B 2012;85(2):1–6. [13] Fang F, Cheng Y, Liao H. Numerical study on a three-dimensional broadband isotropic left-handed metamaterial based on closed rings. Phys Scr 2014;89(2):1–6. [14] Zhi Y, He C, Yang L, Nie Y. Investigation of negative index properties of planar metamaterials based on split-ring pairs. Appl Phys A Mater Sci Process 2011;103:989–94. [15] Liu Y, Cheng Y, Gao Y, Li S, Fang C. Multi-band terahertz two-handed metamaterial based on the combined ring and cross pairs. Opt – Int J Light Electron Opt 2014;125(9):2129–33. [16] Islam SS, Faruque MRI, Islam MT. A novel biaxial double-negative metamaterial for electromagnetic rectangular cloaking operation. Sci Eng Compos Mater 2015;24(3):335–43. [17] Islam SS, Faruque MRI, Islam MT. The design and analysis of a novel split-H-shaped metamaterial for multi-band microwave applications. Materials (Basel) 2014;7:4994–5011. [18] Zhou H, Wang C, Peng H. A novel double-incidence and multi-band left-handed metamaterials composed of double Z-shaped structure. J Mater Sci Mater Electron 2015;27(3):2534–44. [19] Hasan MM, Faruque MRI, Islam SS, Islam MT. A new compact double-negative miniaturized metamaterial for wideband operation. Materials (Basel) 2016;9:1–12. [20] Liu P, Yang S, Jain A, Wang Q, Jiang H, Song J. Tunable meta-atom using liquid metal embedded in stretchable polymer. J Appl Phys 2015;118. [21] Hasan MM, Faruque MRI. Left-handed metamaterial using Z-shaped SRR for multiband application by azimuthal angular rotations. Mater Res express 2017;4(4):1–8. [22] Silveirinha MG, Alù A, Edwards B, Engheta N. Overview of theory and applications of epsilon-near-zero materials. URSI Gen Assem 2008:44–7. [23] Gao J, Sun L, Deng H, Mathai CJ, Gangopadhyay S, Yang X. Experimental realization of epsilon-near-zero metamaterial slabs with metal- dielectric multilayers. Appl Phys Lett 2013;103(5):1–9. [24] Maas R, Parsons J, Engheta N, Polman A. Experimental realization of an epsilonnear-zero metamaterial at visible wavelengths. Nat Photon 2013;7(November):907–12. [25] Hasan MM, Faruque MRI, Islam MT. Compact Left-Handed Meta-Atom for S-, C- and Ku-band Application. Appl Sci 2017;7:1–20. [26] Rothwell EJ, Frasch JL, Ellison SM, Chahal P, Ouedraogo RO. Analysis of the Nicolson-Ross-Weir method for characterizing the electromagnetic properties of engineered materials. Prog Electromagn Res 2016;157:31–47. [27] Hasan MM, Faruque MRI, Islam MT. A mirror shape chiral meta atom for C – band communication. Access IEEE 2017;5:21217–22. [28] Hasan MM, Faruque MRI, Islam MT. A single layer negative index meta atom at microwave frequencies. Microw Opt Technol Lett 2017;59(6):1450–4. [29] Cao H, Chen H, Liu J, Wu X, Pi Y. A Design of Dual Band 90° polarization using chiral metamaterial based on four ‘ V ’ resonators. IEEE Int Symp Antenna Propag 2016:377–8.

Conclusion In this article, we report experimental and numerical studies on a novel modified compact circular split ring resonator and left-handed metamaterial unit cell and periodic array structure. The CSRR metamaterial design was printed on a dispersive material (FR-4), and MATLAB software was used to obtain the effective parameters of the unit cell and array structure, based on the Nicolson Ross Weir (NRW) method. The design exhibits resonance frequencies in C- and Ku-bands, which are mostly dedicated to satellite applications. Our multi-band metamaterial shows ENZ and left-handed characteristic at the resonance frequency of 6.46 GHz (in C-band) and 16.92 GHz (in Kuband), respectively. The C-band is commonly used for satellite TV networks, satellite communication systems, radio communications, etc., and the Ku-band is also mostly used in satellite communications and satellite TV networks. Therefore, the metamaterial design reported in this work can be efficiently utilized in satellite applications. Acknowledgement This work was supported by UKM Research Universiti Grant, Geran Univesiti Penyelidikan, Code: GUP-2018-134. Author contributions Tayaallen Ramachandran made substantial contributions to design, analysis, characterization and application. Mohammad Rashed Iqbal Faruque participated in the conception and critical revision of the article for important intellectual content. Eistiak Ahmed provided necessary instructions for experimental purposes. Conflicts of interest The authors declare no conflict of interest.

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