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Abstract
In this paper, a triple-band polarization converting metasurface for X and Ku band applications is investigated. The unit cell consists of an asymmetric circular ring, terminated with a T-shaped stub, printed on FR-4 substrate, and backed by copper cladding. The triple-band polarization convertibility of the metasurface results from the proper engineering and anisotropy along the x- and y-axis. The metasurface has three plasmonic resonances with a polarization conversion ratio (PCR) of almost 100% in the lower two frequencies bands and 95% in the higher frequency band. The plasmonic resonances at 8.2 and 13.6 GHz are due to magnetic dipole moment while response at 19 GHz is due to electric dipole moment. Cross linear polarization conversion, linear to circular polarization conversion, and circular to circular polarization conversion are observed, both for normal and oblique wave incidences. Measured and simulation results are in good agreement with an excellent polarization conversion in three frequency bands, i.e., 7.7 to 9.2 GHz, 10.8 to 15.5 GHz, and 17.5 to 19.2 GHz. The polarization conversion response of the metasurface is same for both x- and y-polarized waves and is quite stable under oblique incidence of the impinging wave. The metasurface dominates the merits of multi-band resonances, angle sensitivity, and higher PCR, and thus has eminent values for application in polarization-control appliances.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Metamaterials (MM) have recently captured the imagination of researchers to convert traditional bulky size material into nanoscale devices in the microwave to terahertz frequencies range. It is used in many fields, including mimicking the black holes [1], terahertz invisibility [2], metamaterials-based superconductors [3], super lenses [4], beam scanning manipulation [5], and tunable Fano resonance [6]. The working process of metamaterials is much innovative that cannot be proved by traditional natural materials. These innovative characteristics of metamaterials purely depends on the structural geometry of the surface. Which further allow fascinating properties of metamaterial like polarization conversion [7], electromagnetic wave absorption [8], RCS reduction [9], and biosensing applications [10]. The extraordinary properties of metamaterials are obtained by properly designing and engineering the unit cell in a unique way to produce negative index materials [11]. Negative index materials can be sorted as single or double negative materials. Materials having single negativity have negative dielectric permittivity or magnetic permeability, while double negative materials have both negative permittivity and permeability. Metamaterial is a composite material, intentionally engineered to issue material properties that are not attainable with ordinary materials [12,13]. The metamaterial field has become a multi-department initiative, surrounded by material science, engineering, applied physics, and nanotechnology [14]. In the recent year intensive research on metasurfaces (MS), which is a two-dimensional counterpart of the metamaterials, has drawn increasing attention due to its planar subwavelength thickness, fabrication easiness, and small insertion losses [15]. Metasurfaces can be grouped in an aperiodic manner, strictly or in a quasi-periodic fashion. Metasurface can be fabricated easily by methods of lithography and nano-printing [16]. Metasurfaces are employed to manipulate and control the polarization of the electromagnetic (EM) waves and hence used in a diverse range of applications, i.e., planar optics [17] recent, angular momentum of light [18] purity, optical vortex generation [19], polarization conversion [7], and anomalous refraction [20]. Metasurface offers great suitability for attainment and has exceptional abilities for light molding offering new ways of relief to manage the phase, amplitude, and polarization response [16,21]. Mainly research involving metasurface is interested in surfaces, manipulating, and controlling the polarization of the electromagnetic wave. Polarization is an important phenomenon of the EM wave devolving valuable information in signal properties and sensitive measurements.
Different designs had been recommended in the literature [21,22] for manipulating and controlling the state of polarization for broad bandwidth purposes. In [21], an anisotropic double symmetrical C- shaped metasurface with a cross in its center is presented for conversion of a linear polarized wave into an orthogonally polarized wave. Metasurface operating in the microwave to visible wavelengths range is presented in [16] which demonstrates the concept of anomalous refraction and reflection. A resonator with asymmetric double spilt ring design backed by copper sheet is used for perfect broad-band polarization in the reflection mode [23] and a converter is proposed for polarization conversion of circularly polarized wave [24]. In [25] an experimental demonstration on high impedance structure that resonate at three neighboring frequencies work as a broadband polarization rotator is studied. In [26] a flexible disk-shaped polarization conversion metasurface is proposed for high-efficiency and broad bandwidth. In the microwave range, different structures have been proposed for polarization conversion [23,24,27,28], such as circular split ring [23], rectangular ring [25], [29], flexible disk [26], and arrow-shaped structure [28]. A thin, efficient, and wideband polarization converting oval shaped metasurface is presented for transforming linear to orthogonal polarization [30].
Manipulation of polarization can also be obtained through conventional methods like Faraday Effect and optical activity of the crystals; however, these methods have the limitations of narrow bandwidth and bulky volume. Metasurface designed for polarization conversion is generally comprised of an anisotropic periodic array of elements made up of metal fixed on a dielectric material. The bandwidth of a MS can be increased by proper designing of the unit cell structure or multilayer metallic-dielectric configuration [31,32] to resonate at multi/wide plasmonic resonance. In Refs. [23,28,33–35] different polarization conversion metasurfaces designs have been proposed only for the normal incidence, reducing its application for the devices used in oblique incidence in the practical world.
This paper presents a compact electrically thin, triple-band, efficient linear and circular polarization converter. The proposed design is capable to resonate at three peak frequencies working in the three-adjacent band from 7.7 to 9.24 GHz, 10.8-15.5 GHz, and 17.5 to 19.2 GHz. The MS transform linear to linear and circular to circular state of polarization in the aforementioned frequencies. Also, the linear to circular polarization state has been obtained at the frequencies of 7.6, 9-11.5 (band), and 19.4 GHz. The response of the reflection coefficient of the metasurface is independent of the incident wave polarization. Also, the engineered MS has quite balanced response for the variation in incident angle up to 40 degrees.
2. Design and analysis
2.1 Unit cell configuration
The generalized view of the triple-band cross converter is shown in Fig. 1(a). It comprises of a 2-dimensional periodic array of T-shaped made up of metal microstrip attach to a circular ring placed on FR-4 dielectric substrate, which is supported by a metallic plane. Figure 1 (b) illustrates the metasurface unit cell. The geometrical dimensions are $B$ = 7, $I$ = 2, $L$ = 1, $a$ = 1, $w$ = 1.5, $H$ = 1.6, and $k$ = 3.6 (all in mm). The dielectric used is FR-4 (4.4 (permittivity) and 0.02 (loss tangent)). The upper patch and ground plane have been composed from 0.018 mm thick copper ($5.8\times 10^{7}$ S/m (conductivity)). The upper layer (patch) of the unit cell is placed at a degree of 45 inclined to the $x$-axis. This arrangement of the T-shaped circular ring makes the structure efficient for co- and cross-polarization of the EM wave. The boundary conditions used in the simulations are depicted in Fig. 1(c). The incident and reflected fields of electric components are decomposed along $u$- and $v$- coordinates as shown in Fig. 1(d) to show the concept of polarization conversion. Photograph of the fabricated sample is shown in Fig. 1(e).
Fig. 1. Structural Details (a) Layout of surface (b) Unit cell. (c) Boundary conditions (d) Decomposition of incident and reflected electric fields along $u$- and $v$-coordinates (e) Snapshot of fabricated prototype.
2.2 Operating principle
The metasurface is made up of repetitive sub-wavelength unit cell structures with polarized magnetic and electric densities that can be charged electrically or magnetically when they interact with the incident EM wave [36]. The field of electromagnetic wave is also integrated with continual magnetic and electric polarization perpendicular to the metasurface [36] as follow:
where, Ps and Ms denotes the electric polarization and magnetization density for the surface, respectively. Here $z$ is the direction of the metasurface perpendicularly, accommodating the subwavelength unit cells at $z$ = 0, and subscript “t” denote the two tangential ($x$ or $y$) components.Each particle on the metasurface could be identified by its electric ($\alpha$, $e$) and magnetic polarizability ($m$). The magnetization density and electric polarizability of the particles are established from the dipole moment on the surface of the magnetic and electric densities of their respective field. These dipole moments also rely on the acted field of each unit cell, together with the unit cell polarizabilities [28].
The surface of the metasurface is to be used for integration, Where $R$ denotes the distance between the integration point and observation point. To enhance knowledge about the cross exchange of the polarization, consider a y-polarized wave which is excited normally as displayed in Fig. 1(d).
The metasurface projected in the figure has a unit cell that is anisotropic along the $u$- and $v$-axis, which possesses mirror symmetry in the direction along the $u$-axis. The electric field of the incident wave is split to two orthogonal, $u$- and $v$- components, such as $\overrightarrow {E_{\mathrm {i}}} = {{\overrightarrow {u}} {E_{\mathrm {i}u}} {e^{i\varphi }} +{\overrightarrow {v}} {E_{\mathrm {i}v}} }{e^{i\varphi }}$, and the reflected field is written as $\overrightarrow {E_\mathrm {r}} = {{\overrightarrow {u}} {\stackrel {\sim }{R_u}}{E_{\mathrm {i}u}}}{e^{i\varphi }} + {{\overrightarrow {v}} {\stackrel {\sim }{R_v}}{E_{\mathrm {i}v}} } {e^{i\varphi }}$. Here $R_u= |R_u |e^{(i\varphi _{u} )} = E_{ru}/E_{iu}$ and $R_v= |R_u |e^{(i\varphi _{v} )} = E_{rv}/{E_iv }$ , and both are complex numbers. If, in any frequency band, the magnitude of $R_u$ and $R_v$ is unity $(|R_u |{\approx } |R_v |{\approx }1)$ and one component has in-phase reflection (phase difference, $\triangle \varphi$=0° ) and the other has out-of-phase reflection ( $\triangle \varphi$=180°), then the reflected wave electric field is 90 degrees inverted regarding the incident wave [38]. To be specific, the asymmetric nature of the unit cell of the MS down the $u$- and $v$-axis, causes cross- conversion (i.e., $x$-to-$y$ and $y$-to-$x$). To verify this concept, the proposed surface was exposed to $u$- and v-polarized waves, and the reflection coefficients and their respective phases were analyzed as shown in Fig. 2(a) and 2(b), respectively. It is evident from the graphs that the aforementioned conditions are satisfied which confirms that the surface possesses the ability of cross-polarization conversion.
2.3 Design process and optimization
The geometrical analysis for the proposed metasurface is explained here to demonstrate the effects of structural evolution on the polarization conversion of the impinging electromagnetic waves. The final design i.e., an efficient polarization converter has been obtained through proper evolutionary stages. In all those stages the structure has been changed, examined, and evaluated as shown in Fig. 3. In stage-1 a circular ring with an offset of 1.4 mm from the center of the front layer along the u-axis is demonstrated in Fig. 3(b), which shows no sign of polarization conversion. In stage-2 a small vertical stub of length 2 mm from the center of the front layer is attached with the ring as shown in Fig. 3(c). The stub attached with the circle originate a single resonance of 3 GHz bandwidth at the frequency of 13.5 GHz, however efficient and multiband polarization conversion is still not achieved. In stage-3 a T-shaped microstrip is attached with the ring which is symmetrical along the $x$- and $y$-axis as outlined in Fig. 3(d), it does not show any sign of polarization. The structure is stage-3 shows symmetry to our proposed design, but it does not show any sign of polarization conversion. In stage-4 as depicted in Fig. 3(e), the structure is rotated down the $u$-axis with an angle of 45 degrees making it anisotropic and asymmetrical down the $x$- or $y$-axis. Due to the asymmetrical and anisotropic geometry, the surface generates three plasmonic resonances imposing multiband and well potent polarization converter. Consequently, when the circular ring, T-shaped stub were combined and then rotated by 45 degrees, the required multiband polarization conversion response is achieved.
Fig. 3. Stages involved in structure design. Coefficients of the co- and cross-polarized reflection for (a) Circular ring resonator (b) Circle with a strip attach and (c) Circle with a T shaped stud without rotation (d) Circle with a T shaped stud with rotation (e) T shape, All the dimensions for above design are same as the proposed unit cell as in Fig. 1 (b).
3. Simulation results
The EM waves incident on the recommended metasurface has only one polarization component while the reflected wave from the metasurface have both components of $x$- and $y$-polarization. The co-polarization reflection coefficients for the wave of $x$- and $y$- polarization are expressed as $R_{xx}=R_{rx}/R_{ix}$ , and $R_{yy}=R_{ry}/R_{iy}$ . While the cross-polarization conversion coefficients for $x$- and $y$- polarized waves are given as, $R_{yx}=R_{ry}/R_{ix} ,R_{xy}=R_{rx}/R_{iy}$.
The simulated reflection graphs of co- and cross-polarization in conventional incidence for $x$ and $y$-polarized waves are shown in Fig. 4. The metasurface response for the wave in x-polarization is a triple band response that resonates at the frequencies of 8.2, 13.6, and 19 GHz. The peak value of co- and cross-polarization graph at all the three resonant frequencies (8.2, 13.6, and 19 GHz) is -20.4, -27.2, and -15.1 dB and -0.7, -0.3 and -2.0 dB respectively. The cross-polarization coefficient is very high ($\geq$ -3 dB) at the three plasmonic resonances of 8.2, 13.6, and 19 GHz, while the co-polarization coefficient is weaker in these frequency bands ($\leq$-5 dB). The reflection response of the surface for $y$-polarization is identical to that of $x$-polarized incidence due to the symmetrical geometry of the metasurface along the $u$-axis. The response to the wave in $y$-polarization is revealed in Fig. 4 (b).
Fig. 4. Reflection response for the field of incidence in (a) $x$-polarization and (b) $y$-polarization.
To gain more physical observation in the performance of the MS, the distribution of surface current on the upper layer (ring with T shaped microstrip) and lower layer (the ground plane) of the MS is studied for conventionally polarized incident waves at resonance frequencies (8.2, 13.6 and 19 GHz) as shown in Fig. 5. The resonance causes in our proposed design is the sum of electric and magnetic responses. The distribution of current in parallel direction on the upper (patch) and lower layer (ground) indicate an electric dipole response while current on both layers in an anti-parallel direction constitutes the magnetic dipole response. As stated by Faraday’s principle, a time-varying field of magnet linking two metals will induce surface currents in the opposite direction on both (upper and lower) metallic layers. This representation of the net surface current is shown by a red-colored arrow with a J symbol (Fig. 5). At lower resonance frequencies (8.2 and 13.6 GHz), the distribution of current is pointed in opposite (anti-parallel) directions which ensure that these resonances (8.2 and 13.6 GHz) are magnetic resonances. The anisotropic behavior of the surface along the $x$- and $y$-axis plays an essential role in providing a different response to an electromagnetic wave for normal incidence in a particular frequency band.
Fig. 5. The Distribution of surface current at 8.2 GHz [(a) and (b)], 13.6 GHz [(c) and (d)], and 19 GHz [(e) and (f)] upper patch layer [(a), (c), and (e)] and the lower metallic ground [(b), (d), and (f).
The large value of magnetization is observed on both (upper and lower) layers of the unit cell by oppositely directed surface currents, producing a large value for asymmetric permeabilities and impedance of the surface [39]. The direction of net surface current distribution at 19 GHz is in parallel which shows that it is an electric resonance.
4. Angular stability
The cross-polarization conversion feedback of the metasurface should be solid against variation in the incident angle of the electromagnetic wave, to make the metasurface suitable for many practical applications. The substrate dielectric constant and thickness are the two factors that depict a vital part in the angular stability of the metasurface [40]. By using a thin dielectric substrate, the angular stability for the metasurface could be increased however the bandwidth for conversion of polarization will be decreased. Thicker is the metasurface less stable will be the response to the incident angle. To obtain a stable response to the variation in the angle of incidence thinner surfaces should be taken into consideration. If a substrate with a larger value of the dielectric constant is used in the design, the stability in angular sensitivity is achieved at the cost of a reduction in the polarization conversion bandwidth [40]. In terms of stability, the sensitivity in a case for variation in the angle of incidence the permittivity of the dielectric substrate also plays a role for some metamaterials.
The proposed metasurface shows angular stability due to its specialized structural geometry. For different angles of incidence, the reflection of co- and cross-polarized coefficients are revealed in Fig. 6. The surface shows different responses for $x$- and $y$- polarized wave. Figure 6(a), 6(b) shows the response for the wave in $x$- polarization. Figure 6(a) show co-polarized reflection coefficients, and Fig. 6(b) reveal the reflection of the cross-polarized coefficient for distant incident angles in incident of $x$-polarized wave. In all figures, the suggested structure is fairly steady against distinction in angle up to 40 degrees. The co-polarization response for the $x$-polarized wave is almost the same with an increase in resonances depth at the two higher frequencies for 20-degrees. While for 40 degree the increase in depth of the resonance is recorded at higher and lower frequencies with a decrease at the middle resonance depth. Also, at a 40-degree angle total of four resonances are recorded. In Fig. 6(b) angular stability of the reflection for the cross-polarized coefficient is obtained for $x$-polarized waves. The reaction of the surface for $x$-polarization to variation in angle is much stable with un-notable change. The response for the increase in angle degree is shifted toward a lower frequency range. Stability in angle for the metasurface is obtained due to its small unit cell size and structural symmetry of the patch along $u$- axis
Fig. 6. $x$-polarized wave incident for reflection in (a) Co and (b) Cross-polarization coefficients.
5. Experimental verification
The suggested metasurface was manufactured on a $308\times 308$ mm FR4 dielectric including $44\times 44$ unit cells as indicated in Fig. 1(e). On the backside of the FR-4, a sheet of metallic copper is used. The experimental validation of the co- and cross-polarization coefficients conversion was performed in an anechoic chamber by utilizing an N5232A Agilent vector network analyzer (VNA). The measurement is conducted using the same setup as in [34]. Two broadband (2-20 GHz) ridged horn antennas, were used to transmit and receive EM waves in the experimental setup. For co-polarization, we placed both antennas in the horizontal direction. While for cross-polarization we placed the receiving antenna in the vertical direction. The comparison of the simulated and measured co- and cross-polarized reflections are shown in Fig. 7.
Figure 7(a) shows the comparison of simulated and measured co and cross-polarization reflection responses for the $x$-polarized incident wave. These results indicate that the surface has retained its triple-band response. In all three measured resonances, an efficient and stable polarization conversion is obtained for both $x$-polarized wave. The only deviation in the measured results is that the resonances have shifted toward higher frequencies due to fabrication tolerances. Besides that, the experimental and measured results are in good agreement.
The polarization conversion ratio (PCR) is another metric that explains the polarization conversion efficiency of the metasurface and is given by
The PCR for normal incidence of electromagnetic waves is revealed in Fig. 7(b). For the resonance at 8.2 GHz, 13.6 GHz, and 19.0 GHz frequencies, almost a ratio of perfect polarization conversion is realized. The value of PCR at 8.2 and 13.6 GHz is $100\%$ where all the incident wave is converted into orthogonal polarization, while for 19 GHz the value is more than $95\%$. In all three resonant frequencies, a normal incidence $x$- polarized wave on the surface is observed which is totally converted into an $y$-polarized wave as on its reflection from the surface and vice versa for an electromagnetic wave of $y$-polarization.
6. LP to CP conversion
The condition for linear to circular polarization is that the co- and cross reflection coefficients have the same magnitude and the phase difference of the reflected co- and cross-polarized is
As shown in Fig. 4(a) the co- and cross-polarization coefficients have the same magnitude at three frequencies of 7.6 GHz, 9-11.5 GHz (band), and 19.4 GHz. Whereas the phase difference at 7.6 GHz and 19.4 GHz is almost equal to $\triangle$ $\varphi$ = $+{90}^{\circ}$ while the phase difference at frequency band of 9-11.5 GHz is $\triangle \varphi$ = -${90}^{\circ}$ as shown in Fig. 8(a) and 8(b). Hence linear to circular polarization is achieved at these frequencies. A reflected wave is RHCP when the phase difference between the component is either ${90}^{\circ}$, ${270}^{\circ}$. At 7.6 GHz, the $\triangle \varphi$= $+{90}^{\circ}$ so the reflected wave is RHCP. A reflected wave is LHCP when the phase difference is either $-{90}^{\circ}$, $-{270}^{\circ}$. At the band frequency of 9.6-10.6 GHz, the $\triangle \varphi$= -${90}^{\circ}$ so the reflected wave is LHCP. Axial ratio (AR) is used to characterize the circular polarization and is calculated as
The axial ratio plot is shown in Fig. 8(b), it is less than 3dB at frequencies of 7.6, 9-11.5, and 19.4 GHz. Hence linear to circular polarization is achieved at these frequencies.
7. Response to CP wave
The response of the proposed metasurface is investigated for circularly polarized incident waves, hence the linear and circular polarized reflection amplitudes are related by
The $+$ and $-$ denotes right- and left-handed circular polarizations (RHCP and LHCP). Interestingly, it can be deduced from Eq. (9) and the results shown in Fig. 4(a), 4(b) respectively, that the proposed design is able to reflect an RHCP wave as RHCP, and LHCP as LHCP and act as meta-mirror, which unlike traditional mirrors retains handedness for the whole CPC frequency band. The polarization sustaining capability of the MS for circular polarized wave is calculated by the polarization maintaining ratio (PMR). For RHCP, it is described as:
It is noted that in the frequency band of interest (7-20 GHz) PMR = PCR, also $|R_{++}|$ = $|R_{--} |$ = $|R_{yx} |$ = $|R_{xy} |$ and $|R_{-+} |$ = $|R_{+-} |$ = $|R_{xx} |$. Also, from Eq. (9) we can conclude that for the circular polarization case the proposed surface converts a circularly polarized wave into the circularly polarized wave. It can be deducted that our proposed metasurface not only converts an LP-to-LP and CP-to-CP wave but also has the ability to transform a linear polarization to circular polarization. The comparison between our proposed and other multi-band polarization converting metasurface is given in Table 1 Improvement is noted in terms of size, thickness, polarization conversion, and the number of frequency bands.
Table 1. Proposed PCM performance comparison with recent studies
8. Conclusion
In conclusion, a compact thin, triple-band $90\%$ polarization conversion MS is recommended and presented by both simulation and experiment. The triple-band broadband polarization conversion MS is composed of anisotropic T-shaped CRR unit cells. Due to properly engineered anisotropy, the surface is able to resonate at three plasmon resonances in the microwave range and independent to the angle and polarization of the incident wave and perform linear to linear , linear to circular, and circular to circular polarization conversion. Both the simulated and measured results are in good accordance with high-efficiency cross-polarization reflection and low co-polarization reflection. Because of its triple broadband polarization conversion bandwidth, multi-functionality, and angular stability, such polarization conversion MS are the potential candidates for modern polarization-controlled devices, stealth surfaces, and antennas.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are available from the corresponding author.
References
1. S. Hendi, Z. Taghadomi, and A. G. Ardakani, “Metamaterials mimic the black holes: the effects of charge and rotation on the optical properties,” Prog. Theor. Exp. Phys. 2020(7), 073E01 (2020). [CrossRef]
2. D. Liu, Y.-L. Hong, R.-H. Fan, H. Jing, R.-W. Peng, Y. Lai, X.-R. Huang, C. Sun, and M. Wang, “Bendable disordered metamaterials for broadband terahertz invisibility,” Opt. Express 28(3), 3552–3560 (2020). [CrossRef]
3. V. N. Smolyaninova, J. W. Lynn, N. P. Butch, H. Chen-Mayer, J. C. Prestigiacomo, M. Osofsky, and I. I. Smolyaninov, “Observation of plasmon-phonons in a metamaterial superconductor using inelastic neutron scattering (conference presentation),” in Metamaterials XII, vol. 11344 (SPIE, 2020), p. 1134419.
4. S. Datta, X. Shi, S. Mukherjee, Y. Deng, and L. Udpa, “Model-based study of a metamaterial lens for nondestructive evaluation of composites,” J. Nondestruct. Eval. Diagn. Progn. Eng. Syst. 3(4), 041001 (2020). [CrossRef]
5. Y. Luo, K. Qin, H. Ke, B. Xu, S. Xu, and G. Yang, “Active metamaterial antenna with beam scanning manipulation based on a digitally modulated array factor method,” IEEE Trans. Antennas Propag. 69(2), 1198–1203 (2020). [CrossRef]
6. A. Bhardwaj, V. Sridurai, N. M. Puthoor, A. B. Nair, T. Ahuja, and G. G. Nair, “Evidence of tunable fano resonance in a liquid crystal-based colloidal metamaterial,” Adv. Opt. Mater. 8(11), 1901842 (2020). [CrossRef]
7. T. Yang, X. Liu, C. Wang, F. Wang, and J. Zhou, “High-efficiency cross-polarization conversion metamaterial using spiral split-ring resonators,” AIP Adv. 10(9), 095210 (2020). [CrossRef]
8. H. Zhang, F. Ling, H. Wang, Y. Zhang, and B. Zhang, “A water hybrid graphene metamaterial absorber with broadband absorption,” Opt. Commun. 463, 125394 (2020). [CrossRef]
9. X. Kong, S. Jiang, L. Kong, Q. Wang, H. Hu, X. Zhang, and X. Zhao, “Transparent metamaterial absorber with broadband radar cross-section (rcs) reduction for solar arrays,” IET Microwaves, Antennas & Propag. 14(13), 1580–1586 (2020). [CrossRef]
10. H. Ou, F. Lu, Y. Liao, F. Zhu, and Y.-S. Lin, “Terahertz metamaterial with multiple resonances for biosensor application,” in 2020 Opto-Electronics and Communications Conference (OECC), (IEEE, 2020), pp. 1–3.
11. L. Chandiea and K. Anusudha, “pentagon shaped microstrip patch antenna with metamaterial for uwb application,” in i2016 International Conference on Control, Instrumentation, Communication and Computational Technologies (ICCICCT), (IEEE, 2016), pp. 377–381.
12. W. Xin, Z. Binzhen, W. Wanjun, W. Junlin, and D. Junping, “Design, fabrication, and characterization of a flexible dual-band metamaterial absorber,” IEEE Photonics J. 9(4), 1–12 (2017). [CrossRef]
13. W. Cao, X. Yang, and J. Gao, “Broadband polarization conversion with anisotropic plasmonic metasurfaces,” Sci. Rep. 7, 1–9 (2017). [CrossRef]
14. F. Monticone and A. Alu, “Metamaterials and plasmonics: From nanoparticles to nanoantenna arrays, metasurfaces, and metamaterials,” Chin. Phys. B 23(4), 047809 (2014). [CrossRef]
15. F. Ding, A. Pors, and S. I. Bozhevolnyi, “Gradient metasurfaces: a review of fundamentals and applications,” Rep. Prog. Phys. 81(2), 026401 (2017). [CrossRef]
16. H.-T. Chen, A. J. Taylor, and N. Yu, “A review of metasurfaces: physics and applications,” Rep. Prog. Phys. 79(7), 076401 (2016). [CrossRef]
17. P. Genevet, F. Capasso, F. Aieta, M. Khorasaninejad, and R. Devlin, “Recent advances in planar optics: from plasmonic to dielectric metasurfaces,” Optica 4(1), 139–152 (2017). [CrossRef]
18. B. Sephton, Y.-W. Huang, A. Ambrosio, C.-W. Qiu, A. Vallés, T. Omatsu, F. Capasso, and A. Forbes, “Purity and efficiency of hybrid orbital angular momentum-generating metasurfaces,” J. Nanophotonics 14(01), 1 (2020). [CrossRef]
19. H. Ahmed, A. A. Rahim, H. Maab, M. M. Ali, N. Mahmood, and S. Naureen, “Phase engineering with all-dielectric metasurfaces for focused-optical-vortex (fov) beams with high cross-polarization efficiency,” Opt. Mater. Express 10(2), 434–448 (2020). [CrossRef]
20. S. W. Lee and J. H. Oh, “Single-layer elastic metasurface with double negativity for anomalous refraction,” J. Phys. D: Appl. Phys. 53(26), 265301 (2020). [CrossRef]
21. C. Fu, Z. Sun, L. Han, C. Liu, T. Sun, and P. K. Chu, “High-efficiency dual-frequency reflective linear polarization converter based on metasurface for microwave bands,” Appl. Sci. 9(9), 1910 (2019). [CrossRef]
22. Z. Wei, J. Huang, J. Li, G. Xu, and Z. Ju, “Dual-broadband and near-perfect polarization converter based on anisotropic metasurface,” Opt. Quantum Electron. 49(9), 298 (2017). [CrossRef]
23. H.-Y. Chen, J.-F. Wang, H. Ma, S.-B. Qu, J.-Q. Zhang, Z. Xu, and A.-X. Zhang, “Broadband perfect polarization conversion metasurfaces,” Chin. Phys. B 24(1), 014201 (2015). [CrossRef]
24. B. Kamal, S. Ullah, B. Khan, T. Rahim, and J. Ren, “Ultrathin and high efficient wideband polarization converting metasurface,” Int. J. RF Microw. Comput. Eng. 31, e22673 (2021). [CrossRef]
25. Y. Qi, B. Zhang, C. Liu, and X. Deng, “Ultra-broadband polarization conversion meta-surface and its application in polarization converter and rcs reduction,” IEE Access 8, 116675 (2020). [CrossRef]
26. Q. Wang, X. Kong, X. Yan, Y. Xu, S. Liu, J. Mo, and X. Liu, “Flexible broadband polarization converter based on metasurface at microwave band,” Chin. Phys. B 28(7), 074205 (2019). [CrossRef]
27. N. Pouyanfar, J. Nourinia, and C. Ghobadi, “Multiband and multifunctional polarization converter using an asymmetric metasurface,” Sci. Rep. 11(1), 9306 (2021). [CrossRef]
28. H. Chen, J. Wang, H. Ma, S. Qu, Z. Xu, A. Zhang, M. Yan, and Y. Li, “Ultra-wideband polarization conversion metasurfaces based on multiple plasmon resonances,” J. Appl. Phys. 115(15), 154504 (2014). [CrossRef]
29. S. Zahertar, A. Yalcinkaya, and H. Torun, “Rectangular split-ring resonators with single-split and two-splits under different excitations at microwave frequencies,” AIP Adv. 5(11), 117220 (2015). [CrossRef]
30. M. Karamirad, C. Ghobadi, and J. Nourinia, “Metasurfaces for wideband and efficient polarization rotation,” IEEE Trans. Antennas Propag. 69(3), 1799–1804 (2020). [CrossRef]
31. P. E. Sieber and D. H. Werner, “Reconfigurable broadband infrared circularly polarizing reflectors based on phase changing birefringent metasurfaces,” Opt. Express 21(1), 1087–1100 (2013). [CrossRef]
32. J. Cheng, S. Inampudi, F. Fan, X. Wang, S. Chang, and H. Mosallaei, “Dielectric metasurfaces in transmission and reflection modes approaching and beyond bandwidth of conventional blazed grating,” Opt. Express 26(10), 12547–12557 (2018). [CrossRef]
33. L. Wu, M. Zhang, B. Zhu, J. Zhao, T. Jiang, and Y. Feng, “Dual-band asymmetric electromagnetic wave transmission for dual polarizations in chiral metamaterial structure,” Appl. Phys. B 117(2), 527–531 (2014). [CrossRef]
34. B. Khan, B. Kamal, S. Ullah, I. Khan, J. A. Shah, and J. Chen, “Design and experimental analysis of dual-band polarization converting metasurface for microwave applications,” Sci. Rep. 10(1), 15393 (2020). [CrossRef]
35. B. Khan, S. Ullah, B. Kamal, and Abdullah, “An extended split ring resonator type metasurface for microwave applications,” in 2019 16th International Bhurban Conference on Applied Sciences and Technology (IBCAST), (IEEE, 2019), pp. 1046–1049.
36. E. F. Kuester, M. A. Mohamed, M. Piket-May, and C. L. Holloway, “Averaged transition conditions for electromagnetic fields at a metafilm,” IEEE Trans. Antennas Propag. 51(10), 2641–2651 (2003). [CrossRef]
37. H. Cao, J. Liang, X. Wu, Y. Pi, H. Xu, J. Liu, Z. Meng, and Y. Zhang, “Dual-band polarization conversion based on non-twisted q-shaped metasurface,” Opt. Commun. 370, 311–318 (2016). [CrossRef]
38. B. Kamal, J. Chen, Y. Yin, J. Ren, and S. Ullah, “A broad band polarization converting metasurface for c and x-band applications,” in 2020 IEEE International Conference on Signal Processing, Communications and Computing (ICSPCC), (IEEE, 2020), pp. 1–4.
39. B. Kamal, J. Chen, Y. Yin, J. Ren, and S. Ullah, “Wide band cross polarization converting metasurface based on circular split rings resonators,” in 2020 IEEE International Conference on Computational Electromagnetics (ICCEM), (IEEE, 2020), pp. 223–225.
40. O. Luukkonen, F. Costa, C. R. Simovski, A. Monorchio, and S. A. Tretyakov, “A thin electromagnetic absorber for wide incidence angles and both polarizations,” IEEE Trans. Antennas Propag. 57(10), 3119–3125 (2009). [CrossRef]
41. C. Fu, Z. Sun, L. Han, and C. Liu, “Dual-bandwidth linear polarization converter based on anisotropic metasurface,” IEEE Photonics J. 12(2), 1–11 (2020). [CrossRef]
42. X. Huang, H. Yang, D. Zhang, and Y. Luo, “Ultrathin dual-band metasurface polarization converter,” IEEE Trans. Antennas Propag. 67(7), 4636–4641 (2019). [CrossRef]
43. B. Kamal, J. Chen, Y. Yin, J. Ren, S. Ullah, and U. Ali, “Design and experimental analysis of dual-band polarization converting metasurface,” Antennas Wirel. Propag. Lett. 20(8), 1409–1413 (2021). [CrossRef]
44. B. Kamal, S. Ullah, B. Khan, H. Ali, and T. Rahim, “Cross polarization conversion metasurface for fixed wireless and ku-band applications,” Int. J. Commun. Syst. 35, e5033 (2022). [CrossRef]
