Showing papers by "Qun Wu published in 2013"

Electronically Radiation Pattern Steerable Antennas Using Active Frequency Selective Surfaces

Abstract: This paper proposes a novel method of building electronically beam steerable antenna system using active frequency selective surfaces (AFSS) The design methods and special principals of the active frequency selective surfaces built for this kind of antenna are studied The antenna system is fabricated and experimentally investigated The front-to-back ratio is more than 30 dB with the a null point of -59 dB The gain can be promoted to be 70 dBi Furthermore, multi-beam functionality is achieved and the amplitudes of the beams can be controlled

Polarization manipulation based on electromagnetically induced transparency-like (EIT-like) effect

Abstract: We proposed, designed and fabricated a high transparency of metasurface-based polarization controller at microwave frequencies, which consists of orthogonal two pairs of cut wires. The high transmission and the strong dispersion properties governed by electromagnetically induced transparency-like (EIT-like) effects for both incident polarizations make our device efficiently manipulating the polarization of EM waves. In particular, the proposed polarization device is ultrathin (~0.017λ), as opposed to bulky polarization devices. Microwave experiments are performed to successfully demonstrate our ideas, and measured results are in reasonable agreement with numerical simulations.

Automatic Design of Broadband Gradient Index Metamaterial Lens for Gain Enhancement of Circularly Polarized Antennas

Abstract: A broadband gradient index (GRIN) metamaterial lens for gain enhancement of circularly polarized antennas has been automatically designed, fabricated and investigated. The GRIN metamaterial lens consists of an isotropic dielectric plate with a corresponding distribution of deep-subwavelength drill holes each with the same diameter. Such drill holes have a negligible in∞uence on both the polarization state and the spectral response of the electromagnetic wave transmitting through the resulting GRIN metamaterial lens. Therefore, the GRIN metamaterial lens is polarization-insensitive and can e-ciently transform spherical waves into planar waves over a very broad frequency range keeping the initial polarization states (e.g., linear or circular) scarcely changed. In the following we have derived analytical formulas that enable the setup of distribution rules

Total transmission and total reflection of electromagnetic waves by anisotropic epsilon-near-zero metamaterials embedded with dielectric defects

Abstract: In this paper, the transmission of the electromagnetic waves in the waveguide filled with the anisotropic epsilon-near-zero (ENZ) metamaterials with dielectric cylindrical defects embedded is investigated. The anisotropy is taken into consideration, and the sandwich structure is put forward to achieve total transmission and total reflection. Despite of the anisotropy and the impedance mismatch compared with the matched impedance zero-index metamaterials, both the analytical and the numerical results show that the total reflection and the total transmission can be achieved. Furthermore, some factors that own potential effects on the transmission of the electromagnetic waves are also discussed, and it is interesting to find that the radius of the embedded dielectric cylindrical defect could greatly affect the bandwidth of total transmission and total reflection. By removing the dependence on isotropy and impedance matching, our work can facilitate the applications of the ENZ metamaterials in the waveguide.

Low-Loss Magnetic Metamaterial at THz Frequencies by Suppressing Radiation Losses

Abstract: We propose an effective way to reduce losses of the magnetic metamaterial by suppressing radiation losses. The numerical simulations unveil that the losses reduction of the magnetic metamaterial is achieved by placing a split ring resonator (SRR), twisted at an angle of 180° with respect to the existing SRR owing to suppression of the radiation damping caused by residual currents in the SRR metamaterial. This leads to a remarkable increase in the figure of merit (FOM) of the proposed system compared to the single SRR. The dependence relationship between the loss property of the proposed system and the coupling interaction is also theoretically investigated in detail. Results show that when the distance between SRRs changes, the negative permeability effect and the FOM value correspondingly change due to the different cancellation of residual currents in each SRR. On the other hand, a different SRR configuration that the dielectric medium is added to the SRR metamaterial is conceived. This leads to in a finite bandwidth deviated from the resonance frequency where the SRR's loss performance is dramatically improved due to suppression of the radiation losses. These results open up new prospects for study of the unique effects associated with low-loss and negative index materials at THz frequencies.

An ultra-low loss split ring resonator by suppressing the electric dipole moment approach

Abstract: We propose an efiective way to realize the ultra-low loss in a split ring resonator (SRR) by suppressing the electric dipole moment approach. To tremendously reduce the loss, the loss mechanism of the SRR is theoretically analyzed in detail. The nonuniform current distribution on the SRR loop results in the residual electric dipole moment and thus brings the high radiation losses. Three difierent SRR conflgurations that the lumped capacitor, the distributed capacitor and the dielectric medium are incorporated into the SRR metamaterial are conceived, by which the uniform current distribution can be observed. This leads to in a flnite bandwidth deviated from the resonance frequency where the SRR's loss performance dramatically improves owing to suppression of the residual electric dipole moment. The proposed the loss reduction mechanism has potential applications in negative and zero index metamaterials, especially at THz frequencies and in the optical regime.

An overview of cancer treatment by terahertz radiation

Abstract: Cancer claimed the death of over 7.6 million people each year all over the world. Many attempts have being practiced in clinical applications, yet some new technologies are believed to make up for the shortcomings of existing methods. Some latest advances have aroused interests in terahertz imaging and the biological effect as promising diagnostic methods for cancer. This review, however, taps into the biological effects of terahertz radiation as well as the possible mechanism to reveal the potentials and prospects of THz in cancer treatment.

Study of a novel compact rectenna for wireless energy harvesting

Abstract: A compact novel topology rectenna system is presented. The proposed rectenna is developed by decomposition a rectenna topology into two function parts, and then re-combination the two parts into a new topology to reach a very compact system size. The operation mechanism of the proposed novel topology rectenna is explained and analyzed. In addition, the proposed architecture is uni-planar, robust and compact, which lead to an easy design and realization at the required frequency ranges with a very low cost. A 2.45 GHz rectenna system is designed and measured to show their microwave performances.

A zero index metamaterial lens for gain enhancement of patch antenna and H-plane horn antenna

Abstract: A zero index metamaterial lens (ZIML) is proposed in this paper for antenna directivity and gain enhancement. The zero index metamaterial (ZIM) is constructed from both electric metamaterial with near-zero permittivity and magnetic metamaterial-modified split ring resonator (MSRR)-with near-zero permeability. The ZIM unit cell is numerically simulated in CST MWS. The scattering parameters show that there is a wide pass band where both permittivity and permeability are small enough to achieve wave collimation. Particularly, both of the two parameters are of the same value of 0.25, which not only obtains near-zero refractive index but also makes the relative characteristic impedance to be 1 and match that of air. A patch antenna and an H-plane horn antenna are also implemented to examine the directivity and gain enhancement ability of the ZIML. The E-plane radiation patterns are both sharpened greatly. The gain enhancement of patch antenna and H-plane horn antenna are 6.6 dB and 4.3 dB, respectively. The universality of the ZIML for both patch antenna and H-plane horn antenna indicates a more flexible application of the ZIML compared with traditional ones.

Two-dimensions beam scanning reflectarray antenna

Abstract: In this paper a two-dimensions beam scanning reflectarray antenna, which is formed by novel active elements with varactor diodes loaded, is proposed and demonstrated. The active element allows continuous tuning of the scatter wave's phase over a 360 deg range by adjusting the bias voltage of the varactor diodes, and it has a quasi-linearity phase distribution versus the capacitance characteristics. Besides, this element is only applied to the TE mode incident wave. The full wave analysis results show that the main radiation beam can be controlled to arbitrary directions with a less than 0.5 deg azimuth error by varying the bias voltage of each tunable element. And the performance of the antenna, such as maximum gain, side lobe levels, polarization and aperture efficiency are presented as well.

Design of electromagnetic refractor and waveguide bends using complementary medium

Abstract: Based on the theory of transformation optics and concept of complementary medium, a kind of electromagnetic refractor and wave splitter using homogeneous metamaterials with negative refraction index is proposed. The operating mechanisms are described and constitutive tensors of the complementary medium are derived. Full wave simulations are performed to confirm the functionality of the proposed devices. Simulation and calculation results verified that this approach can be further utilized to design novel waveguide bends structure with different cross section width and angle using homogeneous metamaterials with negative refraction index, in addition, the simulations results show that nearly all the energies are transmitted and there is no wave fronts distortion when wave transmits through the bend.

Automatic design and fabrication of broadband circular-polarized gradient index metamaterial lens

Abstract: An automatic design and fabrication method for a broadband circular-polarized gradient index metamaterial (GIM) lens is proposed. There two key points: Firstly, the GIM lens consists of isotropic dielectric plate with deep-subwavelength through-holes, which have very little influence on the polarization states of incident waves; Secondly, the analytical formulas for the distribution rules of the through-holes on the plate is derived. This method is numerically and experimentally validated.

A high-efficiency measurement system for the complex permittivity characterization of materials at UHF band

Abstract: A fast and high-efficiency test approach for the complex permittivity characterization of flaky materials in UHF band is presented in this paper. A planar microstrip resonance sensor with two test ports is designed, simulated and optimized. In this approach, only two parameters are required to test for the determination of complex permittivity, namely, resonant frequency and 10 dB bandwidth. Experimental and measured results show that this approach is characterized by convenient test procedure, high efficient data collection, and higher accuracy for fast measurement of the complex permittivity for different type of flaky materials.