Showing papers by "Qun Wu published in 2012"

Polarization-Independent Metamaterial Analog of Electromagnetically Induced Transparency for a Refractive-Index-Based Sensor

Abstract: A polarization-independent metamaterial analog of electromagnetically induced transparency (EIT) at microwave frequencies for normal incidence and linearly polarized waves is experimentally and numerically demonstrated. The metamaterial consists of coupled “bright” split-ring resonators (SRRs) and “dark” spiral resonators (SRs) with virtually equal resonance frequencies. Normally incident plane waves with linear polarization strongly couple to the SRR, but are weakly interacting with the SR, regardless of the polarization state. A sharp transmission peak (i.e., the transparency window) with narrow spectral width and slow wave property is observed for the metamaterial at the resonant frequency of both, the bright SRR and the dark SR. The influence of the coupling strength between the SRR and SR on the frequency, width, magnitude, and quality factor of the metamaterial's transparency window is theoretically predicted by a two-particle model, and numerically validated using full-wave electromagnetic simulation. In addition, it is numerically demonstrated that the EIT-like metamaterial can be employed as a refractive-index-based sensor with a sensitivity of 77.25 mm/RIU, which means that the resonance wavelength of the sensor shifts 77.25 mm per unit change of refractive index of the surrounding medium.

Multi-band slow light metamaterial.

Abstract: In this paper, a multi-band slow light metamaterial is presented and investigated. The metamaterial unit cell is composed of three cut wires of different sizes and parallel to each other. Two transparency windows induced by two-two overlaps of absorption bands of three cut wires are observed. The multi-band transmission characteristics and the slow light properties of metamaterial are verified by numerical simulation, which is in a good agreement with theoretical predictions. The impacts of structure parameters on transparency windows are also investigated. Simulation results show the spectral properties can be tuned by adjusting structure parameters of metamaterial. The equivalent circuit model and the synthesis method of the multi-band slow light metamaterial are presented. It is seen from simulation results that the synthesis method accurately predicts the center frequency of the multi-band metamaterial, which opens a door to a quick and accurate construction for multi-band slow light metamaterial.

A Novel Active Frequency Selective Surface With Wideband Tuning Range for EMC Purpose

Abstract: A novel symmetric anchor-shaped active frequency selective surface (AFSS) with a wide tuning frequency range is proposed. Varactor diodes are used as the active tuning components at the center of each AFSS unit. The equivalent circuit model of the AFSS unit is extracted. SPICE-based circuit simulation and full-wave simulation are compared to predict the resonant frequency. A wide tunable frequency range from 1.76 to 2.45 GHz with a relative bandwidth of 33% is achieved. A prototype of AFSS is fabricated and tested. The measurement result is consistent with the simulation. The design has low power consumption and is potentially used for selectively shielding or reusing of GSM, TD-SCDMA, or Wi-Fi spectrums.

An electromagnetically induced transparency metamaterial with polarization insensitivity based on multi-quasi-dark modes

Abstract: To investigate the polarization and angle insensitive mechanism of an electromagnetically induced transparency (EIT) metamaterial, we designed, fabricated and measured a planar symmetry metamaterial structure. The planar symmetry metamaterial's cell consists of eight identical inner rings surrounded by a bigger outer ring, which serve as multi-quasi-dark elements and a bright element, respectively. A polarization and angle insensitive transparency window is clearly observed in the spectrum owing to the coupling between the multi-quasi-dark modes and the bright mode, which is verified by numerical simulations and experiments. A wider angle consistency is achieved because the multi-quasi-dark modes commonly participate in the destructive interference of scattering field. In addition, the excited principle and the resonance nature of EIT-like effects are investigated numerically. Simulation results show that the EIT-like effect is associated with the anti-symmetry current, which is induced by coupling fields introducing the phase delay. Finally, the slow wave property of the metamaterial is verified by numerical simulation.

A Detached Zero Index Metamaterial Lens for Antenna Gain Enhancement

Abstract: In this paper, a detached zero index metamaterial lens (ZIML) consisting of metal strips and modifled split ring resonators (MSRRs) is proposed for antenna gain enhancement. The efiective permittivity and permeability of the detached ZIML are designed to synchronously approach zero, which leads the ZIML to having an efiective wave impedance matching with air and near-zero index simultaneously. As a result, neither does the detached ZIML need to be embedded in horns aperture nor depends on auxiliary re∞ectors in enhancing antenna gain, which is quite difierent from conventional ZIMLs. Moreover, the distance between antenna and the detached ZIML slightly afiect the gain enhancement, which further conflrms that the ZIML can be detached from antennas. Simulated results show that the efiective refractive index of the detached ZIML is near zero in a broad frequency range where the efiective relative wave impedance is close to 1. The detached ZIML is fabricated and tested by placing it in front of an H-plane horn antenna. One flnds that evident gain enhancement is obtained from 8.9GHz to 10.8GHz and the greatest gain enhancement reaches up to 4.02dB. In addition, the detached ZIML can also work well at other frequencies by adjusting its geometric parameters to scale, which is demonstrated by designing and simulating two detached ZIMLs with center frequencies of 2.4GHz and 5.8GHz, respectively.

An Approach to Configure Low-Loss and Full Transmission Metamaterial Based on Electromagnetically Induced Transparency

Abstract: A low-loss and full transmission metamaterial is proposed and numerically investigated, based on analog of electromagnetically induced transparency. Its unit cell is composed of a split ring enclosed by additional two-gap ring, which is assigned as quasidark and bright modes, respectively. From numerical results, we mimic the EIT phenomenon and suppress radiation loss by exploiting the coupling between quasidark and bright modes. Moreover, the influences of structure parameters and dielectric environment on the transparency windows are also investigated in detail. In addition, the active medium is added to compensate for the intrinsic loss in the metal in EIT metamaterial, resulting in the transmission coefficient enhanced from 0.8 to 0.98, almost achieving the full transmission. These results provide new possibilities for achieving low-loss metamaterial and new EIT-like metamaterial with high gain.

Influence of symmetry breaking in a planar metamaterial on transparency effect and sensing application

Abstract: The influence of symmetry breaking in a planar metamaterial on transparency effect is numerically investigated. The planar metamaterial's cell is formed by three parallel metal wires. From numerical simulation results, we can see that the transparency effect results from the asymmetric coupling between the cut wires. The excited mechanism of the transparency effect is further analyzed by using the hybridization concept. It is found that the coupling fields between the cut wires play key roles and lead to the spectral splitting of the resonance, i.e., the classical electromagnetically induced transparency effect. The metamaterial sensor based on the refractive index variation of the surrounding material is also numerically demonstrated and yields a sensitivity of 9.47 mm/RIU and a figure of merit of 13.5. In addition, the spectral response of the metamaterial is quantitatively described via the "three-particle" model. The analytically calculated results of the model show a good agreement with the simulation results.

Novel Frequency Selective Surfaces with compact structure and ultra-wideband response

Abstract: A novel bandstop Frequency Selective Surface (FSS) is presented, in which a unit cell consists of two metallic of spiral strips of different lengths and a dielectric substrate in the middle. Both simulation and measurement are presented to show that the FSS can realize size reduction and ultra-wideband response. By changing the lengths of some outer strips the miniaturization amount and bandwidth can be adjusted. Moreover, all these responses are stable with respect to different incident angles, which make the proposed structure more valuable for practical application.

A Magnetic Coupling Dipole for UHF Near-Field RFID Reader

Abstract: In this paper, a novel printed-folded dipole for ultra-high frequency (UHF) near-field (NF) radio-frequency identification (RFID) reader using magnetic coupling is proposed. The strong and uniform magnetic field is excited by two opposite-directed currents (ODCs). The folded dipole is printed on an FR-4 substrate with the scale 32 cm × 20 cm. The bandwidth of the antenna ranges from 826 to 853 MHz. When the transmit power of the proposed antenna is 17 dBm, the reading area can be managed to 35.3 × 24 cm2 on the surface for Impinj F43 tag, and the reading distance is around 5 mm. For the case of ceramics ISO1800-6-C tag, and at the same time, the reading area increases to 58 × 42 cm2, and the reading distance is around 77 mm at the center of the antenna. Both simulations and measurements show that the proposed antenna can provide a broad reading area with a very low transmit power of 17 dBm.

Metamaterials With Tunable Negative Permeability Based on Mie Resonance

Abstract: Metamaterials with tunable negative permeability are proposed and investigated theoretically in this paper. First, the model of the dielectric bilayer sphere embedded in the dielectric substrate is put forward. Second, expressions of the electromagnetic fields in the model are derived based on the Mie scattering theory, and the general formula for the effective permeability of the model is deduced via the Maxwell-Garnett theory, which is further verified through the simulation results. Finally, the tunable bandwidth of the negative permeability of the metamaterials changing with the geometrical parameters is investigated based on the full-wave simulations, and the relative mechanisms are also discussed. It is believed that the results would be helpful for the practical applications of the metamaterials, and the metamaterials with tunable negative permeability proposed in the paper would facilitate the constructions of the left-handed materials in some degree.

Waveguide connector constructed by normal layered dielectric materials based on embedded optical transformation

Abstract: Based on embedded optical transformation, a connector for waveguides of the same size and different positions is proposed, fabricated and tested. Compared with previous work on reflectionless waveguide bends or tapers with minimized distortions, the connector proposed in this paper can be constructed with normal homogeneous and isotropic dielectric materials with layered structure, and the results of both the full-wave simulations and the experiments validate the design. It is believed that this study provides a feasible way to fulfill the proper transmission of electromagnetic waves between waveguides of different positions.

Metamaterial Based Electronically-Scanned Circularly-Polarized LWA

Abstract: An electronically-scanned circularly-polarized leaky-wave antenna (LWA) designed for ETC system is proposed in this paper. Based on the theory of composite right/left-handed (CRLH) transmission line (TL), the proposed antenna can fulfill the beam-scan from -6° to -21° in the half plane continuously at the fixed frequency of 5.8 GHz by tuning the bias voltage of varactors loaded on the CRLH TL. By loading corner-cut square patches, a circularly-polarized radiation is obtained at the main beam, and the maximum gain in the main beam direction keeps above 11 dB.

Analogue of Electromagnetically Induced Transparency in a Magnetic Metamaterial

Abstract: In this paper, the analogue of electromagnetically induced transparency is achieved in a magnetic metamaterial consisting of coupled “radiative” square closed loop (SCL) and “dark” square spiral resonator (SSR). Full-wave numerical simulations are carried out to validate the EIT-like effect of the magnetic metamaterial. Transmission spectrums and surface current distributions for the metamaterial are presented. It is shown that placing the SSR close to the SCL causes the electromagnetic field energy to be coupled back and forth between them. This leads to destructive interference and the transparency window in the transmission stop-band of the metamaterial. In addition, it is numerically demonstrated that the magnetic metamaterial can be employed as a refractive-index based sensor with a sensitivity of 41.3 mm/RIU, which means that the resonance wavelength of the sensor shifts 41.3 mm per unit change of refractive-index of the surrounding medium.

Multifunctional complementary cloak with homogeneous anisotropic material parameters

Abstract: Based on the concept of complementary media and optical transformation, a multifunctional complementary cloak composed of homogeneous anisotropic materials with no singularities is proposed in this paper. The full-wave simulations based on the finite element method are performed to demonstrate the multifunctional characteristics of the proposed multifunctional cloak. The simulation results show that the proposed multifunctional cloak can be used as a complementary cloak, a transparency device, and an illusion cloak. In addition, the effect of loss on the performance of the multifunctional cloak is analyzed for future practical application.

Complementary cloak based on conventional cloak with axial symmetrical cloaked region

Abstract: Based on the concept of complementary medium, a method which can make the conventional cylindrical cloak with axial symmetrical cloaked region to be not blind by filling the isotropic complementary in inner cloaked region is proposed. Firstly, the perfect electric conductor cylindrical shell was removed. Secondly, the symmetrical cloaked region was separated into two symmetrical regions along the symmetry axis and filled with isotropic complementary medium according to folding transformation. Full wave simulations are performed to confirm the effectiveness of the proposed method. The simulation results show that the converted cloak not only can exchange information with the outside, but also its presence cannot be detected.

A broadband fractal AMC ground plane for low-profile antennas

Abstract: Through introducing Koch fractal theory, an ordinary AMC structure and broadband Koch fractal AMC ground planes are designed and compared. The bandwidth and performance improvement of the fractal AMC ground plane are taken into consideration to acquire the low-profile antenna system at the frequency band from 40MHz to 70MHz. This research establishes the theoretical foundation for further experimental study.

A novel miniaturized band-pass frequency selective surface

Abstract: In this paper, a novel band-pass miniaturized FSS is proposed, in which a unit cell consists of four spiral etched slot lines arranged central-symmetrically on a dielectric substrate, and the spiral elements are placed interlaced so that each element is connected to an adjacent one in another unit cell. Simulation results show the FSS has the dimension of a unit cell only 0.060λ×0.060λ, where λ represents the wavelength corresponding to the resonant frequency. And the miniaturization is stable with respect to different polarizations and incident angles. Prototype of the FSS is fabricated and tested. The measured results show very good agreement with simulated ones.

Surface Plasmon Resonant THz Wave Transmission on Carbon Nanotube Film

Abstract: The properties of the terahertz resonant surface plasmons wave on the carbon nanotube film and dielectric interface have been investigated. As a first step towards engineering terahertz SPPs-like surface modes, we present a computer experiment to demonstrate that the carbon nanotube film surface can also be employed to concentrate and guide the terahertz SPPs wave. The carbon nanotube film is modeled in an experimentally realizable geometry. It is shown that a unique electromagnetic surface mode in terahertz region can be supported along the carbon nanotube film/dielectric interface when the free-space broadband terahertz pulse is incident on the carbon nanotube film with subwavelength gratings. Comparing with noble metals, plasmonic nano-structure materials based on carbon nanotube film offer a potentially more versatile approach to engineering tightly confined surface modes in the THz regime.

A design of Rotman lens for phase antenna array

Abstract: In this work, a wide banded planar multi-input/output port Rotman lens for phase array antennas is investigated by simulation. The Rotman lens consists of lens and delay lines. With essential parameters, the outline of the lens is calculated by Matlab, in this way we can design a Rotman lens with certain functions, also the model is constructed by simulation software with the data imported from Matlab. The lens consists of the lens and the delay line. A useful segmented design of the delay line is applied to improve the transmission efficiency. A principle for dumpy port design is raised to improve the output characteristics. By this way, the magnitude error of different frequency is limited within 3 dB and below 5 dB when the port is changed. The lens offers a phase shift from −70 degree to +70 degree with a changeable step.

High gain patch antenna with broadband metamaterial lens

Abstract: Antenna lens can obviously eincrease the gain of the antenna by method of gathering. Also, metamaterial lens can achieve the gathering effect with aspheric surface. In this paper, a new type of metamaterial lens is designed. It is easy to identify as Left-hand material with double negative electromagnetic constant, realizing a negative permittivity and a negative permeability simultaneously. The new structure can perform at a lower frequency and the band of the structure can get a good result in broad band. In addition, the new proposed metamaterial lens do not change the S-parameter of the original antenna. The gain can be increased by 2 dB with the new structure of the metamaterial lens.

A wide-band phased array antennas with unequal space

Abstract: In this paper, a wide-band phased array antennas with unequal space presented, antenna consists 18 ridge horn radiating elements. which the array elements arranged by the unequal space, so that the performance that the patterns in the visible range has a peak value in the radiation direction and do not have grating lobes in wide band. The design of phased array antenna for a wide-band application is discussed. The rule of arrays with unequal space for several elements is derived using this synthetical method. Sinulation results show that the array antennas can scan in a range of ±45°in wide band.

Metamaterial analogue of electromagnetically induced transparency

Abstract: In this paper, three types of EIT metamaterials are presented and numerically investigated. The type I metamaterial consists of the SR and the SRR, which are coupled with each other and assigned as the dark resonator and the radiative resonator, respectively. The metamaterial can exhibit EIT effect to both normally and laterally incident electromagnetic waves because of its electric and magnetic response, respectively. The type II magnetic metamaterial consists of the split ring resonator (SRR) and the spiral resonator (SR) along two orthogonal axes. For the excitation with the magnetic field perpendicular to the SRR plane, the SRR and the SR are designated as the radiative element and the dark element, respectively. A transparency window is observed in the overlapped absorption band of the independent resonator because of the destructive interference between the radiative and dark resonators of the metamaterial. The type III metamaterial is consisted of three cut wires of different sizes and parallel to each other. The resonance frequencies are different because the lengths of three metal wires are different. Under the polarization of electrical field, because three cut wires experience strong resonance, two-two overlaps of absorption bands of three cut wires will induce two transparency windows. Numerical simulations are carried out to validate the three types of EIT metamaterials, and the results have proven to be quite effective.

Miniaturized microstrip-based metamaterials quasi-standard transmission lines unit

Abstract: A compact distributed metamaterials quasi-standard transmission lines unit cell is proposed in this paper. It consists of interdigital capacitor and single or double spiral inductor based on microstrip transmission lines. The area of the unit cell is much reduced when compared with the conventional microstrip metamaterials transmission lines. The performance and the fundamental properties of the conventional and the proposed unit cells are verified by 3D planar electromagnetic (EM) simulation, and the electric size is calculated and compared. The designed transmission lines including 10 proposed unit cells and the traditional transmission lines are simulated by full 3D simulator. The forward and backward waves in the left-handed band from the simulation demonstrate the effective of the proposed metamaterials transmission lines unit cell.

Electromagnetic scattering of the carbon nanotubes excited by an electric line source

Abstract: An analytical solution is presented for the electromagnetic scattering from an infinite-length metallic carbon nanotube and a carbon nanotube bundle. The scattering field and scattering cross section are predicted using a modal technique based on a Bessel and Hankel function for the electric line source and a quantum conductance function for the carbon nanotube. For the particular case of an isolated armchair (10, 10) carbon nanotube, the scattered field predicted from this technique is in excellent agreement with the measured result. Furthermore, the analysis indicates that the scattering pattern of an isolated carbon nanotube differs from that of the carbon nanotube bundle of identical index (m, n) metallic carbon nanotubes.

Novel multifunctional optical device with only axial material parameter spatially variant

Abstract: Based on the concept of complementary media and theory of coordinate transformation, a novel kind of optical device, exhibiting the multiple performances of a complementary cloak and a transparent device, is proposed. Only the axial material parameter of the proposed device is spatially variant, and the transverse material parameters are constant. The multiple functions of the proposed device are validated by full wave simulations. In addition, the effects of loss and parameter perturbations on the performances of the device are also investigated. These results can be used in field of antenna protection and other electromagnetic field engineering.

The nonlinear dynamic response of microbeam of MEMS capacitive switch under mechanical shock

Abstract: The microelectromechanical system (MEMS) capacitive switch based on clamped---clamped microbeam has garnered significant attention due to their geometric simplicity and broad applicability, and the accurate model which describes the multiphysical effects of MEMS capacitive switch should be developed to predict the nonlinear dynamic response of clamped---clamped microbeam. A improved macromodel of the clamped---clamped microbeam-based MEMS capacitive switch is presented to investigate the nonlinear dynamic response of clamped---clamped microbeam of MEMS capacitive switch under different mechanical shock in this article, the macromodel provides an effective and accurate design tool for this class of MEMS devices because of taking account into some effects simultaneously including midplane stretching effect, residual stress and different mechanical shock loads. A numerical analytical method based on multimode Galerkin discretization is presented to investigate the nonlinear response of clamped---clamped microbeam of MEMS capacitive switch under the different mechanical shock loads. The results show that using five or more modes can be sufficient to capture the nonlinear dynamic response of clamped---clamped microbeam, and the microbeam experiences a mechanical shock load as a quasi-static load or a dynamic load depending on the ration between the natural periods of the structure and the period or frequency of mechanical shock load. The proposed method gives the identical results to other numerical methods in the literature. Moreover, this method is straightforward to implement and could save computation efforts while not losing accuracy.

Electromagnetic radiation from carbon nanotube at terahertz frequency

Abstract: The feasibility of terahertz wave radiation emitted form carbon nanotube has been studied based on the simple tight-binding theory. The properties of terahertz wave and the current distribution on carbon nanotube have been characterized. The radiation efficiency of carbon nanotube bundles has been compared with that of single walled carbon nanotube. The result shows the efficiency of single walled carbon nanobue bundle dipole antennas is much higher than that of a single walled carbon nanotue dipole antenna.

Transmission-line modeling characterization for multi-wall carbon nanotube antenna radiation

Abstract: This paper presents an equivalent single conductor (ESC) model for multi-wall carbon nanotubes (MWCNTs) using transmission line theory. Based on the model, for the first time, it gives the radiation properties of the symmetrical dipole antenna of MWCNTs. The results show that, for 1V excitation and 100 nm length, the resonant frequency of the antenna is in the terahertz band, and with the number of MWCNT shells increasing, the radiation resistance, the resonant frequency and the radiation efficiency increase accordingly at the same time. We can also find unique feature of that return loss of the antenna is fairly high and the radiation efficiency is fairly low compared with traditional antennas.

Influence of mixed finite conductivity on lightning electromagnetic fields under the ground

Abstract: In this paper, the lightning electromagnetic fields under the mixed finite conductivity ground were calculated using a modified 2-D finite-difference time-domain (FDTD) method. The data of each grid in the entire area were obtained and expressed into groups of pictures efficiently. The spatial characteristic of the peak value of lightning electromagnetic field and its time derivatives under the complex ground is investigated, which are very important for lightening electromagnetic field shielding. And the influence of mixed finite conductivity on peak value of electromagnetic field and its time derivatives were also analyzed. Furthermore, the method employed has been test and compared with the issued experiment data and results from theoretical approach firstly.

A novel reconfigurable antenna based on active band reflective frequency selective surface

Abstract: A newly proposed electronically antenna with a reconfigurable azimuth radiation pattern, has been experimentally investigated in this work. In this design a coaxial colinear (COCO) antenna is located in the middle of a cylinder shield as an omnidirectional source. The cylindrical shield is constructed with active band reflective unit cells. The antenna has been fabricated and measured. A tunable step of 18° is realized. Front-to-back ratio in the directivity pattern is about 20 dB with the depth of null point at −34 dB and the gain of the antenna can be promoted to 9.35 dB.