Linear-to-circular Polarization Converter Research Articles

Bidirectional triple-band truly incident angle insensitive polarization converter using graphene-based transmissive metasurface for terahertz frequency

Abstract The design and response of a triple-band linear-to-circular polarization converter (LTCPC) in the terahertz frequency regime using a graphene-based transmission-type metasurface have been studied numerically and analytically. The unit cell of the converter is constructed using lossy silicon dioxide (SiO2) with a relative permittivity of 3.9 as the substrate. And two similar layers of graphene-based sub-wavelength structures are used at the top and bottom of it. Multiband linear to circular polarization conversion is achieved from 0.74 THz to 0.98 THz, 1.70 THz to 2.33 THz, and 4.06 THz to 5.19 THz, i.e., about 28 %, 31 %, and 24 % fractional bandwidths, respectively. As the same metasurface configuration is used at the top and bottom layers of the transmission-type unit cell, it can be used as a bidirectional polarization converter with identical responses from both sides. The geometrical optimization of the unit cell is done, and an equivalent lumped parameter circuit model is also proposed for the same, considering analogous responses. Tunability over the operating frequency is achieved by varying the chemical potential and relaxation time of graphene. Moreover, due to the ultrathin width and special types of identical configuration of the metasurfaces, the response of the system remains excellent over a wide range of incident angle variations up to 80° angle of incidence.

Metasurface-based conformal linear-to-circular polarization converter for emerging wireless applications

This paper proposes the analysis and design aspects of a metasurface-based reflective type linear-to-circular polarization (LCP) converter in both planar and conformal profiles. The metasurface unit cell consists of a diagonally placed split circular metallic ring on top of a metal backed dielectric substrate. The structure provides LCP conversion with axial ratio (AR) < 3 dB at two frequency bands, which are 27.38–28.61GHz and 33.1–52GHz corresponding to fractional bandwidths of 4.4% and 44.5%, respectively. It exhibits two different handedness at the aforementioned two bands for a TE (or TM) linearly polarized incident wave. Moreover, it shows dual polarized and angularly stable (up to 25°) characteristics. It is observed from the far-field characteristics that the LCP converter with an array of 29 × 29 unit cells (12λ×12λ) produces peak gain of 26dBi, cross polarization level 20 dB below the maximum main lobe level when illuminated by a linearly polarized source at far-field. Subsequently, the same unit cell is used to design a cylindrical conformal metasurface with different radius of curvatures (r). It provides quite stable AR, gain and radiation patterns till r=100mm. The array has been fabricated to experimentally validate the numerical results of both the planar and conformal geometries.

Multifunctional metamaterial for realizing absorption and polarization conversion on the basis of vanadium dioxide

In this paper, the phase change material vanadium dioxide (VO2) is introduced to propose a tunable multifunctional metamaterial device, which treats the phase change property of VO2 to realize the switching of absorption, linear to linear (LTL) polarization conversion, and linear to circular (LTC) polarization conversion functions. When VO2 is in metal state, the structure can be applied as an absorber to achieve the wide-band and narrow-band absorption. In the broad frequency area of 2.007–2.803 THz, the absorption is above 90%. And the narrow-band absorption near the center frequency 1.0126 THz reaches 95.04%. When VO2 is in the insulator state, the studied device can be treated as a polarization conversion device to achieve LTL and LTC polarization conversion. In the low frequency range, the device achieves LTL with polarization conversion efficiency (PCR) above 90% when the frequency is between 0.439 and 0.907 THz. In the high frequency range, the structure can be treated as the LTC polarization converter to achieve right-hand circular polarization, left-hand circular polarization (LHCP), and LHCP in the ranges of 2.317–2.329 THz, 2.356–2.531 THz and 2.582–2.633 THz, respectively. In addition, the ellipticity is above 0.9. Finally, the effects of geometric parameters, angle of incidence and polarization angle on the absorption and PCR are also discussed. The proposed structure has great potential for advanced technologies such as imaging, sensing, communication, and stealth.

Terahertz linear to circular polarization converter based on reflective metasurface

Metasurfaces are two-dimensional artificial structures which have extraordinary electromagnetic properties. They have been used in myriad of devices such as nano-antennas, cloaking coatings, imaging devices, flat lenses, and polarization converters over a wide range of frequency. Due to high dependency of many devices on incident wave polarization, manipulating the polarization of electromagnetic waves would be useful, especially in the THz regime. In this study, we propose a linear to circular polarization converter (LTC-PC) based on a THz reflective metasurface. For a TE linear polarization incident wave, this structure has two distinct bands; the first one lays in a wideband frequency range of 0.5-1.41 THz, in which the reflected wave would be a left-handed circular polarization (LHCP) with minimum efficiency of 89% and maximum efficiency of more than 95% in 80% of the bandwidth. The second band lays in the narrowband frequency range of 1.45-1.55 THz, resulting a right-handed circular polarization (RHCP) wave with a minimum efficiency of 82%. The proposed polarization converter can be used in optical communication and electronic devices.

Linear-to-Circular Polarization Converter with Adjustable Bandwidth Realized by the Graphene Transmissive Metasurface

A tunable linear-to-circular polarization converter (LTCPC) for the terahertz (THz) regime which consists of two conductive layers and a graphene transmissive metasurface layer separated by two dielectric layers is reported in this work. The equivalent surface resistance modeling method is adopted to investigate the peculiar electronic properties of graphene. The simulation results show that when the Fermi energy (Ef) is 1.1 eV, the linearly-polarized wave can be transformed into the circularly-polarized wave in the working band ranging from 0.9498 to 1.3827 THz (the relative bandwidth is 37.1%) with axial ratio (AR) less than 3 dB. Moreover, the bandwidth can be regulated to the desired one by varying the Fermi level of graphene metasurface via a bias voltage rather than manually modifying the structure. We have analyzed the mechanism of the polarization conversion, especially, the magnitudes and the phase difference of cross- and co-polarization transmission coefficients, AR curves, and surface current diagrams at y-polarized incidence. Our findings open up promising possibilities towards the realization of graphene controllable devices for polarization modulation, which has advantages of adjustability over traditional devices.

Switchable terahertz broadband absorption and linear-to-circular polarization conversion

We proposed a switchable bifunctional metasurface for broadband absorber and linear-to-circular polarization converter (LTCPC) in terahertz regime. When vanadium dioxide (VO2) is in the metallic state, the designed metasurface acts as a broadband terahertz absorber. The results demonstrate that the absorptance is above 90% and the bandwidth ratio is 68.6% from 0.981 to 2.011 THz. When VO2 is in the insulated state, the proposed structure behaves as an LTCPC with ellipticities 1 and −1 in frequency bands of 0.391∼0.517 and 0.673∼2.363 THz, respectively. The axis ratio is lower than 3 dB. The designed metasurface provides a new method for designing multifunctional terahertz devices.

Tunable terahertz all-dielectric linear-to-circular polarization conversion metasurface

Terahertz (THz) linear-to-circular (LTC) polarization conversion plays a crucial role in imaging and 6G wireless communication. This paper will give an account of a thermally tunable THz LTC polarization converter by using the active all-dielectric metasurface. It consists of zirconium oxide (ZrO2) microsphere resonators, active strontium titanate (STO) cladding, and flexible polyimide substrate. Through numerical simulation, the amplitude of the ellipticity of the proposed polarization converter at 0.265 THz is –1, indicating that perfect right-hand circular polarization (RHCP) wave is achieved. Meanwhile, the amplitude of the ellipticity is less than –0.8 between 0.247 and 0.278 THz (relative bandwidth is 12%). In addition, with the temperature changes of 180 K (from 200 to 380 K), the operating frequency of the converter can be tuned from 0.220 to 0.291 THz, a sensitivity about 39 GHz/100 K is achieved. Besides, the modulation depth of the ellipticity amplitude can achieve 92% at 0.220 THz, which demonstrates that the converter can output terahertz wave with different polarization states, and the device can be fabricated on a large scale. These perfect conversion performances show that the converter has potential applications in high-speed communication and imaging.

Dual-Band Miniaturized Linear-to-Circular Metasurface Polarization Converter With Wideband and Wide-Angle Axial Ratio

A dual-band miniaturized linear-to-circular polarization converter (LCPC) metasurface with wideband and wide-angle axial ratio (AR) is proposed and demonstrated. The metasurface is formed with periodic arrays of unit cells. The unit cells consist of three metallic layers separated by two substrates. The top and bottom metallic layers contain the identical cells with two metal strips and an “I”-type strip with four stubs for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula> -polarization each. The middle metallic layer comprises an infinitely long metal strip and two “I”-type strips for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -polarization. The LCPC performs a wideband response in both operating bands with the wide passbands generated by the orthogonal “I”-type strips. Prototyped <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -band design shows that the simulated/measured AR remains below 3 dB over the lower bandwidth of 15–21.2 GHz (34.3%)/16.3–21.1 GHz (25.7%) and higher bandwidth of 27–30.3 GHz (11.5%)/27–29.8 GHz (9.9%) under normal incidence in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y-{z}$ </tex-math></inline-formula> plane, respectively. For a 45° incidence, the measured AR still achieved the 3 dB bandwidth of 33.7%/9.4% in both the bands. The study shows that by virtue of orthogonal structures placed at different layers, the element size and the cross-polarization level are suppressed by 65% and 10 dB, respectively, compared to the previous work. Furthermore, the LCPC with the miniaturized elements shows wide-angle response in both the bands.

Broadband of linear-to-linear and double-band of linear-to-circular polarization converter based on a graphene sheet with a π-shaped hollow array

In this manuscript, we propose a tunable multifunctional reflection polarization converter based on a graphene sheet, which is decorated by a π-shaped carved-hollow array. Our design can achieve the linear-to-linear (LTL) polarization conversion with 3.58 THz bandwidth and two linear-to-circular (LTC) polarization conversion bands with opposite handedness, which originates from the excitation of the three graphene surface plasmons (GSPs) modes. The LTL polarization converter can be switched to the LTC polarization converter by only changing the medium height. The performances of this multifunctional reflection polarization converter under different geometric parameters, incident angles, and electron scattering time of graphene are investigated. Besides, it is found that the broadband of LTL and double bands of LTC have the blue shift with increasing the Fermi energy (Ef) of graphene. Especially, the conversion between line-to-left-circular and line-to-right-circular polarization converter can be achieved by changing Ef. All the simulation results are conducted by finite element method, and our design has potential applications in integrated terahertz systems.

Multi-functional high-efficiency reflective polarization converter based on an ultra-thin graphene metasurface in the THz band

In this study, an ultra-thin reflective metasurface is proposed for polarization conversion in the terahertz band. Each unit cell of metasurface is composed of graphene ribbons lying diagonally on silicon substrate. A reflective metal is also placed at the bottom of the structure. Our polarization converter works as a linear polarization converter (LPC) and linear to circular polarization converter (LTC-PC) by variation of the chemical potential of graphene, which can actively be changed by chemical doping or electrical bias of the graphene. The working bandwidth of LPC changes by adjusting the chemical potential of the graphene. The LPC structure has more than 99% polarization conversion ratio in the frequency range of 0.83-0.92 THz, even by changing the angle of incident wave up to 45°, the results are still acceptable. The LTC-PC has less than 3dB axial ratio (AR) in the frequency range of 0.6-0.67 THz for left-handed circularly polarized (LHCP) waves and 0.72-0.97 THz for right-handed circularly polarized (RHCP) waves. To verify the simulation results, an equivalent circuit model based on the structure performance is proposed. Equivalent circuit model results agree very well with the simulation results. Due to the fabrication feasibility, ultra-thin thickness, incident angle insensitive, and high efficiency, our structure has great potential in state-of-the-art technologies such as imaging, sensing, communication, and other optical applications.

Design and Analysis of Broadband Ultrathin Reflective Linear-to-Circular Polarization Converter Using Polygon-Based Anisotropic-Impedance Surface

A broadband reflective linear-to-circular polarization converter (LCPC) is designed using a polygon-based single-layer anisotropic-impedance surface on an ultrathin (thickness is 0.053λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>0</b></sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>0</b></sub> is the wavelength corresponding to the mid operating frequency) ground-backed substrate. Using the admittance analysis of the equivalent circuit model (ECM) and extraction of the admittance through the area moment of inertia equations, simple and generalized design guidelines are presented. The proposed polarization converter produces left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) reflected waves, respectively, for the linearly polarized (LP) TE and TM incident waves. It offers 46% (7.62-12.16 GHz) 3 dB axial ratio bandwidth (ARBW) for normal incidences of both the TE- and TM-polarized waves. Moreover, for oblique incidences (up to 30°) of both the LP waves, the ARBW response remains quite stable. The far-field radiation characteristics, which are often not studied, are provided to show its usability as a dual-LP to dual-CP converting reflector for X-band communications. The measurement results show good agreement with the numerically simulated results.

Graphene-Based High-Efficiency Broadband Tunable Linear-to-Circular Polarization Converter for Terahertz Waves

Broadband tunable terahertz (THz) polarization converter is a vivid necessity due to its great significance in functional utilization. Graphene is a promising material for the evolution of tunable terahertz devices, thanks to its tunable surface conductivity and extraordinary electrical properties. In this paper, we present a high-efficiency graphene-based ultra-thin metasurface manifesting linear-to-circular (LTC) polarization conversion for THz wave. A broadband LTC conversion with ellipticity over 0.95 can be achieved for the entire operating bandwidth of 14 THz to 40 THz for any graphene chemical potential from 0.4 eV to 0.6 eV. It is also shown that tuning the graphene chemical potential may provide much improved ellipticity and efficiency for different frequencies. The proposed LTC converter also provides over 90% efficiency for the complete operating bandwidth for graphene chemical potential from 0 eV to 0.7 eV. Simulation results also reveal that a perfect LTC converter (ellipticity = 1) with more than 90% efficiency can be realized from 16 THz to 37 THz by tuning the graphene chemical potential between 0 eV to 0.7 eV. Altogether, the proposed LTC polarization converter provides the advantage of dynamic regulation, simpler structure, higher efficiency, enhanced ellipticity and greater relative bandwidth.

Linear-to-Circular Polarization Converters With Both E-Field and H-Field Hybrid Responses

This article presents a novel method to design a linear-to-circular polarization converter (LCPC) by using a hybrid array structure, which is composed of meander lines and the split ring resonators (SRRs). The LCPC can respond to both the $E$ -Field and $H$ -Field for the incident wave. When the meander line and the SRR are placed along two orthogonal directions, the composed unit cell would have different electromagnetic response characteristics in the two orthogonal directions. Using this method, two LCPCs working in frequency bands of 6–18 and 2–6 GHz are designed, respectively. The simulated results show that for the LCPC working in 6–18 GHz, the axial ratio (AR) is lower than 3 dB in 6.8–17.32 GHz with a maximum insertion loss (IL) of 1.25 dB. When the angle of incident wave is less than 45°, the 3 dB AR bandwidth is 7.87 GHz. For the LCPC working in 2–6 GHz, the AR of entire frequency band is all lower than 3 dB and the maximum IL is 0.82 dB when the incident angle increases to 15°. Even at incident angle of 45°, the bandwidth with the function of polarization conversion is 3.5 GHz. Experiments on the LCPC (6-18 GHz) are carried out, and the measured results are in agreement with the simulated ones, which proves that the LCPCs design method proposed in this paper is effective and reliable.

Frequency-Selective Surface-Based Compact Single Substrate Layer Dual-Band Transmission-Type Linear-to-Circular Polarization Converter

In this article, a compact dual-band linear-tocircular polarization converter designed on a single-layer substrate is proposed. The unit cell of the converter has a size of 3.72 × 3.90 × 1.52 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (0.0072λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , λo is calculated with respect to 20.67 GHz). The converter consists of split rings and a pair of metallic strips printed on both sides of a single-layer substrate for dual-band operation. The proposed converter has a measured 3-dB axial ratio bandwidth of 5.56% (20.10-21.25 GHz) in the lower band and 3.97% (29.12-30.30 GHz) at the upper band. The converter transmits a right-hand circularly polarized (RHCP) wave at the lower band and left-hand circularly polarized (LHCP) wave at the upper band for a linearly polarized (LP) incident wave. The characteristics of the polarization converter are validated by integrating an array of 7 × 7 elements of its unit cell in the endfire direction of a dual-band LP dipole antenna operating in the same frequency bands such as that of the polarization converter. The antenna integrated with the polarization converter exhibits measured circularly polarized (CP) bandwidths of 7.80% and 6.57% in the lower frequency band: 20.10-21.75 GHz and the upper frequency band: 29.4-31.4 GHz, respectively. The integrated antenna can act as a feed source of a high-gain dualband transmit array for uplink (30.0-31.0 GHz) and downlink (20.2-21.2 GHz) of Ka-band military satellite communication.

Wideband and Wide-Angle Single-Layered-Substrate Linear-to-Circular Polarization Metasurface Converter

A wideband and wide-angle linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed. The converter element consists of a metal strip cross backed by a strip horizontally and centrically located on the other metallic layer. The vertical arm of the strip across the whole surface performs as a high- pass filter with a wide passband above a low cutoff frequency. Meanwhile, the horizontal strip resonates at a high out-of-band frequency and also offers a wideband response below the resonant frequency. Another two short strips vertically and horizontally placed around the crosses increase the phase shift caused by the crosses and improve both the passbands. Using equivalent circuit models and ANSOFT HFSS, an example of LCPC is designed with the overall element size of only $0.11\lambda _{0}\times 0.21\lambda _{0}$ for a 90° phase difference and wide-angle stability over the wide operation band. The prototype shows the simulated / measured axial ratios (ARs) below 3 dB over the bandwidth of 69%/74% for a normal incidence wave and 54% for the oblique incident angle of 55° in yz plane, respectively. With the insertion loss of less than 3 and 2 dB, the measured 3 dB AR bandwidth keeps 70% and 55%, respectively.

Ultra-wideband linear-to-circular polarization converter with ellipse-shaped metasurfaces

Generally, a traditional method to generate circularly polarized waves faces limitations like the narrow band, bulky volume and low efficiency. In this paper, a linear-to-circular (LTC) polarization converter based on metasurface with high efficiency and maneuverable ultra-wideband is proposed. By utilizing the ellipse-shaped structure on reflective metasurface, the LTC polarization converting condition can be achieved at four closer frequencies, leading to a quite wide frequency band. The simulated results show that the axial ratio of the reflective circularly polarized wave is lower than 3 dB within the frequency band of 10.21–24.97 GHz, and a relative band reaches above 83.91%. Furthermore, the bandwidth of the polarization conversion can be sustained from 10.21 to 22.71 GHz at incident an angle of 48°. The electrical field and current flows are given to analyze the circular polarization performance. For validation, a sample is fabricated and measured; measured results and simulated results coincide with each other. The proposed LTC polarization converter is easy in terms of design and fabrication complexity, showing promising potentials in real-world circularly polarized wave generator applications.

Single-Layer Dual-Band Linear-to-Circular Polarization Converter With Wide Axial Ratio Bandwidth and Different Polarization Modes

A dual-band linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed. The element of the converter consists of two identical metallic layers with a combination of a connected Jerusalem cross (JC) and an “I”-type dipole for each layer. The proposed converter is designed by using an equivalent circuit model (ECM). Left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) beams can be, respectively, generated at ${K}$ -band and Ka -band excited by a linearly polarized (LP) wave tilted 45° relative to the ${x}$ - and ${y}$ -directions of the converter. In addition, the converter covers two operation bands for ${K}$ -/ Ka -band satellite communications with high conversion efficiency and low polarization extinction ratio (PER). After full-wave optimization, the proposed converter is fabricated and measured. The measured results show a good agreement with the simulated ones. Even though there exists a tradeoff between the angular stability and the bandwidth of the dual-band LCPCs, the measured axial ratio (AR) remains stable in the lower operation band and a slight fluctuation in the higher band with the incident angle of 20°.

A Three-Dimensional Linear-to-Circular Polarization Converter Tailored by the Gravity Field

In this paper, a three-dimensional (3D) linear-to-circular polarization converter (LCPC), innovatively tailored by the gravity field through the fluidity of liquid metal mercury (Hg), is designed and studied. The proposed LCPC is composed of a 3D glass cavity filled with Hg, a copper reflector, a trenched dielectric layer, and a copper patch. Due to the specially designed 3D glass cavity, Hg will flow in different parts of the glass cavity to form different resonant structures by means of rotation under the action of the gravity field. When the proposed LCPC is not rotated (is placed parallel to the xoy plane), the axial ratio band which is less than 3 dB (3-dB AR band) is obtained in the band of 32.42–42.82 GHz (the relative bandwidth is 27.64%). And when such a LCPC is rotated (is placed perpendicular to the xoy plane), the 3-dB AR band shifts to 18.88–32.86 GHz (the relative bandwidth is 54.04%). Besides, the surface current diagrams are investigated to explain the physics mechanism of the proposed LCPC, and relevant parameters are also discussed. In our design, the proposed LCPC has the advantages of wideband, tunable characteristics, and easy adjustment. In addition, it provides an innovative design idea of LCPC to promote potential applications of tunable devices.

An ultrawideband linear-to-circular polarization converter based on multiphysics regulation

In order to design a tunable linear-to-circular polarization converter in microwave band, an ultra-broadband linear-to-circular polarization converter (LCPC) based on multiphysics regulation is proposed and studied by combining solid state plasma and vanadium dioxide (VO&lt;sub&gt;2&lt;/sub&gt;) in this article. By using the electric control way to control the states of the solid plasma resonator, the solid state plasma can generate excitation and non-excitation state. By using the temperature (&lt;i&gt;T&lt;/i&gt;) control way to regulate the phase transition state of the VO&lt;sub&gt;2&lt;/sub&gt; resonator, the VO&lt;sub&gt;2&lt;/sub&gt; can generate insulating and metallic state. The purpose of dynamic shift of the proposed LCPC′s operating band can be realized. The polarization conversion rate curve, reflection phase curve, the axial ratio curve and the surface current diagram of the proposed LCPC are analyzed and simulated by the full-wave simulation software HFSS and the effects of parameters &lt;i&gt;r&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt; and&lt;i&gt; r&lt;/i&gt;&lt;sub&gt;3&lt;/sub&gt; on the axial ratio are also discussed. When none of all the solid plasma regions are excited and &lt;i&gt;T&lt;/i&gt; &lt; 68 ℃ , the presented LCPC is in No. 1 state. On the basis of No. 1 state, if all the solid state plasma are excited, the presented LCPC is in No. 2 state. Similarly, on the basis of No. 1 state, the presented LCPC will be transformed to No. 3 state when &lt;i&gt;T&lt;/i&gt; ≥ 68 ℃. The axial ratio band which is less than 3 dB (3 dB AR band) is 14.3−29.7 GHz (the relative bandwidth is 70%) in No. 2 state. The 3 dB AR bands which are 14.4−23.4 GHz and 28.6−35.9 GHz (the relative bandwidths are 47.61% and 22.64%) show that the proposed LCPC has the ability to shift the working band to high frequency range. When switching the LCPC to No. 3 state, the 3 dB AR bands which are 8.4−11.2 GHz and 18.7−29.5 GHz (the relative bandwidths are 28.57% and 44.81%) are shifted to low frequency region. Compared with traditional LCPC, our design has the advantages of diverse control means, wide bandwidth, flexible design and strong functionality. At the same time, this LCPC presents a new design method and idea for multiphysical field regulated devices.

Tunable Linear-to-Circular Polarization Converter Using the Graphene Transmissive Metasurface

In this article, a tunable linear-to-circular polarization converter (LTCPC) in terahertz (THz) regime using the graphene transmissive metasurface is proposed, which is composed of two resonant layers containing the metal and graphene resonators separated by a dielectric spacer. The linearly-polarized wave with normal incidence can be transformed to the circularly-polarized wave. The operating band can be dynamically regulated in THz band by electrically controlling the Fermi energy ( $E_{\mathrm {f}}$ ) of the graphene sheets rather than reforming the structures. The optimized result of axial ratio (AR) band which is less than 3 dB is located at 2.64-3.29 THz (the relative bandwidth is 21.92%) in the case of $E_{\mathrm {f}}=0.1$ eV. The physical characteristics of graphene are explored and the relevant operational results of the presented LTCPC are elucidated in this article. Compared with the conventional LTCPC, our design provides a more effective implementation method for wide applications, and it offers a further step in graphene controllable devices.