Showing papers by "Qun Wu published in 2015"

Ultrathin pancharatnam-berry metasurface with maximal cross-polarization efficiency.

Abstract: Novel ultrathin dual-functional metalenses are proposed, fabricated, tested, and verified in the microwave regime for the first time. The significance is that their anomalous transmission efficiency almost reaches the theoretical limit of 25%, showing a remarkable improvement compared with earlier ultrathin metasurface designs with less than 5% coupling efficiency. The planar metalens proposed empowers significant reduction in thickness, versatile focusing behavior, and high transmission efficiency simultaneously.

A Method of Using Nonidentical Resonant Coils for Frequency Splitting Elimination in Wireless Power Transfer

Abstract: In this paper, an efficient method is proposed to eliminate frequency splitting in nonradiative wireless power transfer via magnetic resonance coupling. In this method, two nonidentical resonant coils (NIRCs) are used as wireless power transmitter and receiver, respectively. According to the elliptic integral term in the analytical expression, the pole of the mutual inductance function with respect to transfer distance can be eliminated by using the two NIRCs, and hence overcoupling between transmitter and receiver with close transfer distance is avoided. Therefore, frequency splitting caused by overcoupling can be suppressed and stable output power can be achieved. The NIRCs are analytically calculated, numerically simulated and finally, fabricated and tested to verify the theory. All the calculated and experimental results show that frequency splitting is completely eliminated and uniform voltage across the load is achieved. Furthermore, lateral misalignment between the NIRCs barely introduces frequency splitting, and the suppression level of frequency splitting can also be controlled freely.

Iterative phase-amplitude retrieval with multiple intensity images at output plane of gyrator transforms

Abstract: For the iterative phase retrieval, multiple measured intensity images in output plane are only considered for accelerating the convergence. The amplitude and phase at the observed object plane of measurement system are unknown in this research. The observing system is composed of gyrator transform, in which several images are recorded by using several transform angles for the same input image. An amplitude-phase retrieval scheme is designed and tested. The numerical simulations have demonstrated that the amplitude and phase pattern within a very small error (less than 0.04 and 0.0005 for an 8-bit two-dimensional data) can be recovered after 1000 iterations.

Magnetic metamaterial analog of electromagnetically induced transparency and absorption

Abstract: In this paper, it is theoretically demonstrated that the electromagnetically induced transparency (EIT) and absorption (EIA) can be achieved in a magnetic metamaterial. Unit cell of metamaterial consists of a split ring resonator and an “I” shaped cut-wire pair, which serves as a bright resonator and a dark resonator, respectively. It is found that the EIT effect in metamaterial results from the magnetic interaction between bright and dark resonators. A classical model is also introduced to describe the EIT behavior in magnetic metamaterial, and its analytical results are in good agreement with numerical results. Significantly, by controlling the space separation between resonators, we can obtain the destructive and constructive interferences, and thus observe the transition between EIT and EIA. These results may achieve potential applications on enhancing the nonlinear interaction.

Ultrathin planar metasurface for controlling electromagnetic wave with broad bandwidth

Abstract: In this paper, ultrathin metasurface based on phase discontinuities is proposed to manipulate electromagnetic waves in the microwave region. The gradual phase changes accumulated along the transmission path in the conventional lens are substituted with abrupt phase changes at the interface of the metasurface, which are realized by the Pancharatnam–Berry phase element. An ultrathin metasurface with a linear phase gradient is designed, fabricated, and measured. The phenomenon of anomalous refraction can be observed in a broad bandwidth, in which the cross-polarization conversion efficiency keeps approaching the theoretical limit. The measured result shows that the anomalous refraction angle can be well predicted by the generalized Snell’s laws, and the efficiency keeps >20% in a broad bandwidth of 24%. Our design makes a remarkable progress in the cross-polarization conversion efficiency of the transmission-type metasurface, which is beneficial to put metasurface into practical application.

Omnidirectional wireless power transfer system supporting mobile devices

Abstract: The growth in the use of implanted medical devices, mobile devices and electric vehicles is exciting interest in wireless power transfer system. Wireless power transfer system (WPT) via magnetic resonant coupling was firstly proposed in 2007, and the system can transfer power to the receiving device over a distance of several times of the radius of the coils [1]. The WPT is not sensitive to the biological and other environmental objects for the E/H ratio is strongly suppressed in the near field of magnetic dipole and has been shown to be a promising technology for mobile wireless charging. The issue that the transmission efficiency drops rapidly as the transmission distance is increasing has been studied. Nevertheless, the efficiency is sensitive to not only transmission distance but also the relative position between the transmitting coil and receiving coil, and this limit the mobility of device. Although several techniques such as array of resonators, transponder-based system, and spatially structured resonant coil have been studied to obtain mobile WPT [2-4], mobile WPT has still been a problem when the relative angle between the receiving coil and transmitting coil (receiving angle) is increasing. In this paper, an efficient method for the design of omnidirectional wireless power transfer (OWPT) will be proposed.

Analytical Reflection Coefficient Expressions Utilizing Load-Dependent $X$ -Parameters

Abstract: In this paper, analytical expressions of the input reflection coefficient at the source and the load ports of a two-port active microwave component are proposed. It utilizes the load-dependent $X$ -parameters in the development of these expressions. In contrast to the classical small-signal $S$ -parameters based approach, the cross frequency conversions and harmonic mismatch effects are taken into consideration in this method. In the derivation, the incident and the scattered waves of the amplifier are all represented in a matrix structure. Since the coefficient determinants of the input and output vectors are equals to zero, it is hard to obtain the analytical solutions. Therefore, the order reduction of the matrix under certain principles is introduced to solve this problem. Throughout the derivation process, the matrix transformation and the calculations are performed using only simple complex operations. Therefore, the function analyticity is transmitted from the load-dependent $X$ -parameter mathematical model to the proposed expressions. Finally, the proposed method is experimentally validated on two microwave amplifier circuits.

Electrically steerable leaky-wave antenna capable of both forward and backward radiation based on liquid crystal

Abstract: In this paper, a electrically beam scanning leaky-wave antenna (LWA) based on composite right/left-handed (CRLH) rectangular waveguide (RWG) is presented. In the proposed LWA, liquid crystal (LC) is chosen as tunable material, which could be controlled by applied electric and magnetic field. The beam of LWA proposed can be steered at a fixed frequency as the electromagnetic parameters of LC change under different bias voltages. The designed antenna supports the backward-to-forward beam scanning. It is found from simulations that the antenna has a beam scanning angle from −19° to 12° at 9.7 GHz.

Electromagnetic scattering properties of cylindrical frequency selective surface

Abstract: In this paper, the electromagnetic scattering properties of Curved Frequency Selective Surface conformal to a cylinder surface is investigated. Four unit models are used to realize required reflection and transfer characteristics in a wide band range. Simulation shows far field radiation directivity pattern and RCS diagram of cylindrical FSS. The feature influence factors by the structure unit, the curvature of the cylindrical FSS and the dielectric-slab parameters (the thickness of the plate and the dielectric constant)are discussed.

Frequency splitting elimination in wireless power transfer using nonidentical resonant coils

Abstract: We propose an approach to eliminate frequency splitting in wireless power transfer (WPT). Two nonidentical resonant coils (NIRCs) are used in this method as power transmitter and receiver, respectively. According to the elliptic integral term in the analytical expression, the pole of the mutual inductance function with respect to transfer distance can be eliminated by using NIRCs. Therefore, frequency splitting caused by over-coupling can be eliminated. Experimental measurement of the NIRCs shows that frequency splitting is completely eliminated and uniform voltage across the load is achieved.

Super-resolution imaging based on virtual Airy spot

Abstract: Based on the theoretical model of Airy spot, a method is proposed for improving the imaging speed from confocal microscopy. The virtual Airy spot is designed for obtaining the pattern on CCD at detecting plane. Here the size of the spot is determined by the parameters of imaging system and intensity data from point detector, which can receive data quicker than CCD. The treatment can improve the speed of imaging comparing with CCD at receiving end. The virtual structured detection is also utilized for generating high-resolution image. Some numerical simulation results are provided for demonstrating the validity of the proposed method.

A new compact three-way Wilkinson power divider based on LTCC technology

Abstract: A new compact three-way Wilkinson power divider with low-temperature cofired ceramics (LTCC) technology is presented in this paper. This power divider was proposed by a simple structure based on lumped-element equivalent network and achieved a good performance. Within band of 1.27GHz-1.58GHz, all output ports insertion loss is less than 0.5dB, the input port return loss is less than −15dB and the isolation among three output ports is better than 15dB. By taking advantages of high integration and vertical stacking capabilities of multilayered LTCC technology, the size of the three-way Wilkinson power divider is 0.074λg ×0.070λg ×0.0λg or 5.3mm × 5mm × 1.3 mm.

Broadband graphene absorber in THz based on superposition of bands

Abstract: A broadband graphene absorber with simple structure is proposed in this paper. The substrate used in this paper is 1.3 mm in thickness and constructed with 0.6 mm depth grooves periodically, which can be treated as substrates with a thickness of 1.3 mm and 0.7 mm arranging periodically. The combination of quartz substrate with different heights can realize the superposition of two adjacent frequency bands which leads to broad band characteristic of the absorber. The absorption rate of the absorber is obtained by software High Frequency Structure Simulator (HFSS) 14.0. The relative bandwidth for the absorption rate above 90% is 27.1%, from 134 GHz to 176 GHz. The graphene absorber proposed has potential in the development of stealth technology.

Ultrathin metasurface based on phase discontinuity with maximal cross-polarization efficiency

Abstract: An ultrathin flat metasurface experimentally realizing bi-functional microwave manipulation has been demonstrated to be able to approach the theoretical limit of cross-polarization (cross-pol) conversion efficiency of the transmission. With the excitation of a localized waveguide mode, an abrupt helicity-dependent phase change is introduced to the transmission and can be engineered by assembling the spatial orientation of each Pancharatnam-Berry phase element. By realizing a constant phase gradient, an anomalous refraction is unanimously demonstrated under circular polarized incident wave. Besides, due to the helicity-dependent phase modification, we also demonstrate an ultra-thin metalens with bi-functionality. By controlling the handedness of the incident wave, converging and diverging functions are interchangeable with the same flat lens. The proposed metalens has only one single layer as thin as 0.001λ, which massively reduces the thickness of the microwave lens along the wave propagation direction. With the great improvements in efficiency and thickness reduction, our design provides a promising approach to miniaturize, planarize and integrate multiple microwave components.

Metamaterials with broadband double negative characteristics based on mie resonance

Abstract: A broadband double negative media (DNG) is proposed and investigated theoretically in this paper. The top view of structure proposed in this paper is a combination of ellipses with minor axis at 6 mm and major axis at 16 mm, rotating 45 degrees each time. The combination of ellipses is a gradient structure at the boundary, so that there are strong superposition of coupling between each two ellipses which leads to broad the bandwidth of DNG. With the full wave simulation software CST, S11 and S21 are obtained. Afterwards, by using Nicolson-Ross-Weir (NRW) inverse method, permittivity and permeability are derived and the bandwidth for DNG is 52.17%, from 3.4 to 5.8 GHz. The structure is easy to manufacture as a result of its plane structure. It is believed that this result will accelerate the use of DNG.

Broadband planar Luneburg lens composed of artificial impedance surfaces

Abstract: A two-dimensional Luneburg lens is presented based on artificial impendence surfaces (AIS). The desired refractive index profile is controlled by the variable surface impendence, which obtained by using an array of complementary unipolar compact photonic band gap (UC-PBG) structure inside a parallel plate waveguide. Simulation results have shown that proposed Luneburg lens, which operating in TM mode during X-band, has an excellent focusing ability. The proposed Luneburg lens can be used in direction of arrival (DOA) estimation. The estimation error is smaller than 5°.

The position sampling affect on error in planar near-field radiation measurement

Abstract: In order to predict the far-field leakage level of the electromagnetic field radiated from the electronic equipment inner aeroplane cabin, the near-field to far-field transformation by near field radiation measurement data of the electric field is introduced in this paper. By modeling different planar near-field electric field measurement, the far field radiation pattern and the electric field based on the near field measurement is deduced. The half wave dipole antenna array as a radiator is used for the simulation of the uncertainty of measurement coming from all kinds of error sources. Compared with the theoretical calculation value, the simulation result shows the effect of the truncation error and the position error in a planar sampling measurement,and provides a helpful analysis for the error compensation in planar near-field measurement.

Time-domain characteristics for human tissue in THz band based on double Debye model

Abstract: Time domain characteristic for human tissue in THz band is derivate based on double Debye model. Owing to the characteristic properties of THz, there has been an increasing interest in the biological applications of THz technologies, especially in the cancer spectroscopic studies and potential therapies. The time domain characteristic properties for human tissues play an important role in the theory of cancer tissue detection. Through the comparison on electromagnetic parameters of normal and cancer tissues' (at 0.1T: cancer: σ=105.0453, er=4.1648, normal tissue: σ=92.9609, er=4.0825), it can be concluded that electromagnetic energy absorption of cancer tissue is more significant than normal tissue which is consistent with experimental result. It is believed that the result can promote the understanding and research of THz imaging technology.

A compact Ku-band Luneburg Lens reflector based on metamaterial structures

Abstract: Compared to other conventional reflectors, better Radar Cross-Section (RCS) can be efficiently produced by the Luneburg Lens reflector. In this paper, a compact Ku-band Luneburg Lens reflector composed of metamaterial-based unit cells has been designed, simulated and characterized. By adjusting the dimension of the unit cell, almost continuously varying gradient index can be achieved. The effective permittivity of the unit cell is calculated by the simulation software CST and evaluated by the effective medium theory. The simulation results show that the proposed Luneburg Lens reflector is capable of providing a RCS of −1.49 dBm2 with a diameter of 75 mm (4A0 at 16 GHz), and a sound wide angle response as well.

N-sided Irregular Polygonal Cavity Camouflage Coating with Homogeneous Parameters

Abstract: Based on transformation optics theory, a kind of N-sided irregular polygonal cavity camouflage coating is proposed in this paper. The constitutive tensors of the camouflage coating are derived, and the functionality of the proposed coating is validated by full wave simulations. Simulation results show that the designed camouflage coating all has the same near and far field distributions with that of the bare PEC cavity in different incident angles and directions. In addition, this approach can be further to design N-sided irregular polygonal ground plane cloak with homogeneously anisotropic parameters. In order to apply at optical wavelength, the performance of the nonmagnetic camouflage coating is also verified. The simulations show that the reflective fields of nonmagnetic camouflage coating well agree with that of ideal coating except for incident direction because of the boundary impedance mismatching. Since the parameters of the designed camouflage coating are homogeneously anisotropic, it is expecte...

Novel polarization independent and angle consistency absorber based on metal-dielectric metamaterial

Abstract: In this paper, a novel absorber based on metal-dielectric rod is presented. This absorber is consisted of a metal slab and a high permittivity dielectric cross which is composed by two rods vertically. The absorber is polarization independent that the electromagnetic responses always keep the same absorption both for whether the incident wave is horizontally polarized wave (TE wave) or vertically polarized wave (TM wave). The mechanism of the absorption is illustrated by the field distribution. While the incident angle changes from 0 to 65 deg, the absorber shows an excellent performance to keep the absorbance above 90%. We also show the possibility of combing different functions in the same object by using high permittivity dielectric metamaterial.

Accurate design of high-performance diplexers for mobile communication base stations applications

Abstract: This work describes a modified approach for extracting the equivalent circuit parameters, as there are the resonant frequency of each resonator, the coupling bandwidths and the external Qs from multi-port Y-matrix and group delay of the input reflection coefficients. The extractions of equivalent circuit parameters and the fine tuning for three-dimensional simulating models are achieved by utilizing the EM simulating software HFSS. Then, a novel method for designing microwave diplexers is proposed. Compared to the methods existed, all interacting effects are allowed taking into account. One circuit parameter can be related to one dominate geometrical variation in the three-dimensional model. The detailed design steps illustrating the design of a diplexer for mobile communication base stations applications are presented. The designed device with a novel tunable electrical coupling structure is then fabricated. The comparison between measurements and simulations has validated the new design method with high efficiency.

Planar metamaterial realization: From 3D metamaterial to 2D metasurface

Abstract: As a paradigm for engineering electromagnetic space and controlling propagation of waves, metamaterials has inspired many novel physical mechanism and applications for the past decades. But bulky volume and non-negligible loss indeed restrict the applications in meta-devices, especially in microwave region. In this paper, our recent efforts in planar metasurface are reviewed with emphasis on (1) ultra-thin metasurface based on phase discontinuities and (2) low-loss electromagnetic induced transparency (EIT) metasurface. Our designs provide a promising approach to miniaturize, planarize and integrate multiple microwave components.

An electronic tunable CRLH LWA with horizontal scanning properties based on liquid crystal

Abstract: An electronic tunable composite right/left-handed (CRLH) transmission line (TL) leaky-wave antenna (LWA) with horizontal scanning properties based on liquid crystal is presented. The advantages of the proposed antenna are: 1) Convenient to fabricate; 2) Scanning range from negative angle to positive angle; 3) Scanning in a horizontal plane; 4) Convenient to constitute an array. The transmission and radiation characteristics of the CRLH LWA are theoretically analyzed and simulated.