Qu Shaobo

Broadband perfect polarization conversion metasurfaces

We propose a broadband perfect polarization conversion metasurface composed of copper sheet-backed asymmetric double spilt ring resonator (DSRR). The broadband perfect polarization convertibility results from metallic ground and multiple plasmon resonances of the DSRR. Physics of plasmon resonances are governed by the electric and magnetic resonances. Both the simulation and measured results show that the polarization conversion ratio (PCR) is higher than 99% for both x- and y-polarized normally incident EM waves and the fractional bandwidth is about 34.5%. The metasurface possesses the merits of high PCR and broad bandwidth, and thus has great application values in novel polarization-control devices.

Wide-band circular polarization-keeping reflection mediated by metasurface

In this paper, we show that circular polarization-keeping reflection can be achieved using reflective metasurfaces. The underlying physical mechanism of the polarization-keeping reflection is analyzed using a reflection matrix. A wideband circular polarization-keeping reflector is demonstrated using N-shaped resonators. Both the simulation and experiment results show that the polarization-keeping reflection can be achieved with a high efficiency larger than 98% over the frequency range from 9.2 GHz to 17.7 GHz for both incident left- and right-handed circularly polarized waves. Under oblique incidence, the bandwidth increases as the incident angle varies from 0° to 80°. Moreover, the co-polarization reflection is independent of the incident azimuth angles.

Effects of (LiCe) co-substitution on the structural and electrical properties of CaBi2Nb2O9 ceramics

The piezoelectric, dielectric, and ferroelectric properties of the (LiCe) co-substituted calcium bismuth niobate (CaBi2Nb2O9, CBNO) are investigated. The piezoelectric properties of CBNO ceramics are significantly enhanced and the dielectric loss tan δ decreased. This makes poling using (LiCe) co-substitution easier. The ceramics (where represents A-site Ca2+ vacancies, possess a pure layered structure phase and no other phases can be found. The Ca0.88(LiCe)0.040.04Bi2Nb2O9 ceramics possess optimal piezoelectric properties, with piezoelectric coefficient (d33) and Curie temperature (TC) found to be 13.3 pC/N and 960 °C, respectively. The dielectric and piezoelectric properties of the (LiCe) co-substituted CBNO ceramics exhibit very stable temperature behaviours. This demonstrates that the CBNO ceramics are a promising candidate for ultrahigh temperature applications.

Dual-band frequency selective surface with large band separation and stable performance

A new technique of designing a dual-band frequency selective surface with large band separation is presented. This technique is based on a delicately designed topology of L- and Ku-band microwave filters. The two band-pass responses are generated by a capacitively-loaded square-loop frequency selective surface and an aperture-coupled frequency selective surface, respectively. A Faraday cage is located between the two frequency selective surface structures to eliminate undesired couplings. Based on this technique, a dual-band frequency selective surface with large band separation is designed, which possesses large band separation, high selectivity, and stable performance under various incident angles and different polarizations.

In-Plane Feed Antennas Based on Phase Gradient Metasurface

We propose the design of in-plane feed antennas (IPFA) based on phase gradient metasurface (PGM). The in-plane feed is realized using PGM with large in-plane phase gradient, which can couple normally incident waves efficiently into surface waves along the surface. This is different from conventional reflector antennas and reflectarray antennas, where the focus lies above the reflector. As an example, an IPFA is demonstrated, which is composed of a superthin PGM and a waveguide feeding structure. Due to the large phase gradient of the PGM toward the feeding waveguide, incident waves can be coupled as surface waves into the waveguide; whereas transmitted waves can be radiated out along the normal of the PGM. Both the simulated and experimental results verify the high gain and high efficiency of the IPFA with in a broad band in 3.0-3.2 GHz.

Achieving a multi-band metamaterial perfect absorber via a hexagonal ring dielectric resonator*

A multi-band absorber composed of high-permittivity hexagonal ring dielectric resonators and a metallic ground plate is designed in the microwave band. Near-unity absorptions around 9.785 GHz, 11.525 GHz, and 12.37 GHz are observed for this metamaterial absorber. The dielectric hexagonal ring resonator is made of microwave ceramics with high permittivity and low loss. The mechanism for the near-unity absorption is investigated via the dielectric resonator theory. It is found that the absorption results from electric and magnetic resonances where enhanced electromagnetic fields are excited inside the dielectric resonator. In addition, the resonance modes of the hexagonal resonator are similar to those of standard rectangle resonators and can be used for analyzing hexagonal absorbers. Our work provides a new research method as well as a solid foundation for designing and analyzing dielectric metamaterial absorbers with complex shapes.

The design of metamaterial cloaks embedded in anisotropic medium

By using coordinate transformation method, this paper obtains an useful equation of designing meta-material cloaks embedded in anisotropic medium. This equation is the generalization of what was introduced early by Pendry et al (2006 Science 312 1780) and can be more widely used. As an example of its applications, this paper deduces the material parameter equation for cylinder cloaks embedded in anisotropic medium, and then offers the numerical simulation. The results show that such a cylinder cloak has perfect cloaking performance and therefore verifies the method proposed in this paper.

Varactor-tunable frequency selective surface with an embedded bias network

A new technique for designing a varactor-tunable frequency selective surface (FSS) with an embedded bias network is proposed and experimentally verified. The proposed FSS is based on a square-ring slot FSS. The frequency tuning is achieved by inserting varactor diodes between the square mesh and each unattached square patch. The square mesh is divided into two parts for biasing the varactor diodes. Full-wave numerical simulations show that a wide tuning range can be achieved by changing the capacitances of these loaded varactors. Two homo-type samples using fixed lumped capacitors are fabricated and measured using a standard waveguide measurement setup. Excellent agreement between the measured and simulated results is demonstrated.

Dual-band frequency selective surface with quasi-elliptic bandpass response

Based on the substrate integrated waveguide technology, we present a dual-band frequency selective surface (FSS) with a quasi-elliptic bandpass response. The characteristics of the quasi-elliptic bandpass response are realized by shunting two substrate integrated waveguide cavities of different sizes, with the same slots on both sides of the metal surfaces. Four cavities of different sizes and two slots of different sizes are used to design the novel FSS. Every bandpass response with sharp sidebands is induced by two transmission nulls that are generated by the coupling between the slot aperture resonance and the cavity resonance. The simulation results show that such dual-band FSS has the advantages of high selectivity and stable performance at different oblique incident angles. Moreover, it is easy to fabricate.

A Method of Analyzing Transmission Losses in Left-Handed Metamaterials

A method of analyzing transmission loss in left-handed metamaterials (LHMs) is proposed. As a demonstration of this method, transmission loss of LHMs composed of split-ring resonators (SRR) and conducting wires is studied. By means of retrieving and analyzing the effective constitutive parameters, different transmission losses as well as their origins are studied. The results show that the left-handed bandwidth is narrowed because of high loss caused by the non-zero high imaginary parts of the effective permeability and permittivity. In the effective left-handed band, the radiation loss is very low and can be neglected, and the transmission losses are the sum of the substrate loss and the ohmic loss. Moreover, when the dielectric loss tangent of the substrate is greater than 0.003, the substrate loss is higher than the ohmic loss.