Polarization is an important characteristic of electromagnetic wave. Due to novel optical properties, graphene-based anisotropic structure is widely used to control polarization state of electromagnetic wave. In this work, four graphene-based meta-atoms are designed to regulate polarization state of terahertz wave by changing Fermi energy level of graphene. When Fermi energy level is 0.01 eV, cross-polarized wave is emitted by four meta-atoms with phase difference of 90° at 1.18 THz, and the corresponding polarization conversion ratio reaches ∼90%. When Fermi energy level is adjusted to 0.70 eV, linear phase gradient will disappear, and cross-polarized wave almost disappears. Using four selected elements, three dynamic metasurfaces are designed for controlling wavefront of reflected beam, and they are gradient metasurface, metalens, and vortex beam generator. The designed metasurfaces successfully combine wavefront control and polarization manipulation, and greatly improve the ability to control electromagnetic wave. Our designs may have many potential applications, such as terahertz switching, imaging, and polarization beam splitter.

Terahertz graphene metasurfaces for cross-polarized deflection, focusing, and orbital angular momentum.

|In this work, a high-gain and wideband microstrip-fed slot antenna is proposed and investigated, which is composed of an anisotropic metasurface (AMS) and an aperture coupled structure. The proposed microstrip antenna with four resonances can be obtained by merging the AMS with an anomalous inverted (cid:25) -slot feed structure in a low pro(cid:12)le (1 : 07 (cid:21) (cid:2) 1 : 07 (cid:21) (cid:2) 0 : 06 (cid:21) ). The simulated results indicate that the proposed microstrip antenna can achieve a wide impedance bandwidth of 56.1% from 3.32 to 5.91 GHz, which is veri(cid:12)ed by experiment. In addition, the measured results show that the peak gain of the proposed microstrip-fed slot antenna is 10.7 dBi at 5.3 GHz, and the relative bandwidth of 3-dBi gain is 42.2% from 3.85 to 5.91 GHz. Compared with previous works, the proposed design has a lower pro(cid:12)le while achieving a much wider operating bandwidth, where the four controllable resonance modes oﬀer more possibilities for band expansion. This work shows potential application in integration with high data rate systems.

http://www.jpier.org/PIER/pier175/06.22062201.pdf

Low-profile high-gain wideband multi-resonance microstrip-fed slot antenna with anisotropic metasurface

Efficiency tunable broadband terahertz graphene metasurface for circular polarization anomalous reflection and plane focusing effect

A high-gain bidirectional radiative circular polarization (CP) antenna loaded with a dual-mode focusing metasurface (MS) is proposed. The original microstrip patch antenna consists of two coaxially fed tangential patches with different sizes, enabling CP radiation at 8.15 GHz and 14.8 GHz with the gain of 5.4 dBic and 6.2 dBic, respectively. The unit-cell of the focusing MS is composed of two metallic layers separated by a dielectric substrate based on geometric phase principle, which can independently tailor the focusing effect of transmitted and reflected CP waves at 8.15 GHz and 14.8 GHz, respectively. Then, the high-gain bidirectional radiation antenna can be formed by combining the original CP microstrip antenna and focusing MS. The final designed antenna can achieve a CP radiation converge characteristic in transmission at 8.15 GHz with a peak gain of 15.9 dBic, and at 14.8 GHz with a peak gain of 19.4 dBic in refection, respectively. In order to verify the feasibility of the proposed design, the bidirectional radiative CP antenna with/without focusing MS were fabricated and measured, and the results are consistent basically with the simulated ones. The proposed bidirectional focusing MS antenna could provide an effective solution for dual-mode radiation and high-rate information transmission of the communication system. 

High-gain bidirectional radiative circularly polarized antenna based on focusing metasurface

In this letter, a wideband circular polarization (CP) metasurface (MS) antenna is proposed, which is composed of a centrosymmetric structure with a mode suppressor and an asymmetric aperture-coupled feed structure separated by dielectric substrates. Based on the characteristic mode theory, the aperture-coupled feed structure consisted of an L-shaped slot and a microstrip line is employed to excite two orthogonal modes, which have a 90° phase difference to obtain CP radiation. Meanwhile, two methods have been proposed to expand CP bandwidth: one is the direct suppression of characteristic mode by decreasing the overlap frequency of operating and nonoperating mode. The other one is indirect suppression using a mode suppressor. Finally, the MS antenna with a low profile of λ 0 × λ 0 × 0.075 λ 0 at 5 GHz is fabricated and measured. The measured results show that the proposed antenna has a 3 dB axial ratio bandwidth of 45.2% from 4.1 to 6.5 GHz and an impedance bandwidth of 41.8% from 4.1 to 6.31 GHz, and a peak gain of 7.94 dBic at 5.9 GHz.

Low-Profile Wideband Circular Polarization Metasurface Antenna With Characteristic Mode Analysis and Mode Suppression

Metasurfaces (MSs) have received great attention due to their wide application potentials in terahertz (THz) wavefront manipulation. Although great achievements have been obtained in MSs so far, the functionalities are almost static. The active adjustable MS-based devices are far less explored. In this paper, an efficiency adjustable MS composed of a dielectric substrate sandwiched with bi-layered complementary Z-shaped (CZS) structure graphene is proposed and investigated theoretically, which can control the THz circular polarization (CP) wavefront in transmission mode. The simulation results show that the MS structure under a Fermi energy level of 1.0 eV can realize CP conversion with efficiency of about 0.9, and the full range of a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>2</mml:mn> </mml:mrow> </mml:mrow> <mml:mi>π</mml:mi> </mml:math> phase shift also can be achieved by changing the rotation angle of the CZS structure graphene along the wave propagation direction. More importantly, the transmission CP conversion efficiency is positively correlated with the Fermi energy levels of graphene. The anomalous refraction and planar focusing effect can be realized by the specific design of a spatial phase profile of the graphene MS, and the corresponding efficiencies can be adjusted by changing the Fermi energy level of the graphene. Adjustable graphene MSs have wide application prospects in the fields of communication, imaging, and other THz wavefront manipulation devices.

Efficiency adjustable terahertz circular polarization anomalous refraction and planar focusing based on bi-layered complementary Z-shaped graphene metasurface

This paper presents a HI-bright LED driver based on quasi-resonant flyback converter. With the DC/DC converters operating in valley switching mode, the converter approaches low EMI and high efficiency. The paper results in a control-to-output transfer function of the system close to that of a quasi-resonant flyback converter for ease of feedback loop design. By designing the parameters of the control loop, the driver achieves a output mode of constant current and constant voltage. Design considerations and experimental results are presented for 40W LED driver, demonstrating high power factor and high efficiency.

The control-loop design of quasi-resonant flyback converter for HI-bright LED driver

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Efficiency adjustable terahertz circular polarization anomalous refraction and planar focusing based on bi-layered complementary Z-shaped graphene metasurface

High-gain bidirectional radiative circularly polarized antenna based on focusing metasurface

The control-loop design of quasi-resonant flyback converter for HI-bright LED driver