arXiv subjects

Yang Hao

Publications and source records attributed to Yang Hao.

45 records · Page 3Linked to original sources

arXiv2007

Magnification of Subwavelength Field Distributions at Microwave Frequencies Using a Wire Medium Slab Operating in the Canalization Regime

Magnification of subwavelength field distributions using a wire medium slab operating in the canalization regime is demonstrated using numerical simulations. The magnifying slab is implemented by radially enlarging the distance between adjacent wires, and the operational frequency is tuned to coincide with the Fabry-Perot resonance condition. The near-field distribution of a complex-shaped source is canalized over an electrical distance corresponding roughly to $3λ$, and the distribution details are magnified by a factor of three. The operation of the slab is studied at several frequencies deviating from the Fabry-Perot resonance.

physics.class-ph↗

arXiv2007

Accurate Modelling of Left-Handed Metamaterials Using Finite-Difference Time-Domain Method with Spatial Averaging at the Boundaries

The accuracy of finite-difference time-domain (FDTD) modelling of left-handed metamaterials (LHMs) is dramatically improved by using an averaging technique along the boundaries of LHM slabs. The material frequency dispersion of LHMs is taken into account using auxiliary differential equation (ADE) based dispersive FDTD methods. The dispersive FDTD method with averaged permittivity along the material boundaries is implemented for a two-dimensional (2-D) transverse electric (TE) case. A mismatch between analytical and numerical material parameters (e.g. permittivity and permeability) introduced by the time discretisation in FDTD is demonstrated. The expression of numerical permittivity is formulated and it is suggested to use corrected permittivity in FDTD simulations in order to model LHM slabs with their desired parameters. The influence of switching time of source on the oscillation of field intensity is analysed. It is shown that there exists an optimum value which leads to fast convergence in simulations.

cond-mat.other↗

arXiv2006

Experimental study of the sub-wavelength imaging by a wire medium slab

An experimental investigation of sub-wavelength imaging by a wire medium slab is performed. A complex-shaped near field source is used in order to test imaging performance of the device. It is demonstrated that the ultimate bandwidth of operation of the constructed imaging device is 4.5% that coincides with theoretical predictions [Phys. Rev. E 73, 056607 (2006)]. Within this band the wire medium slab is capable of transmitting images with λ/15 resolution irrespectively of the shape and complexity of the source. Actual bandwidth of operation for particular near-field sources can be larger than the ultimate value but it strongly depends on the configuration of the source.

cond-mat.mtrl-sci↗

arXiv2006

Accurate modeling of left-handed media using finite-difference time-domain method and finite-size effects of a left-handed medium slab on the image quality revisited

The letter contains an important message regarding the numerical modeling of left-handed media (LHM) using the finite-difference time-domain (FDTD) method which remains at the moment one of the main techniques used in studies of these exotic materials. It is shown that conventional implementation of the dispersive FDTD method leads to inaccurate description of evanescent waves in the LHM. This defect can be corrected using the spatial averaging at the interfaces. However, a number of results obtained using conventional FDTD method has to be reconsidered. For instance, the accurate simulation of sub-wavelength imaging by the finite-sized slabs of left-handed media does not reveal the cavity effect reported in [Phys. Rev. Lett. 92, 107404 (2004)]. Hence the finite transverse dimension of LHM slabs does not have significant effects on the sub-wavelength image quality, in contrary to previous assertions.

cond-mat.mtrl-sci↗

arXiv2006

UWB On-Body Radio Channel Modelling Using Ray Theory and Sub-band FDTD Method

This paper presents the ultra-wideband (UWB) on-body radio channel modelling using a sub-band Finite-Difference Time-Domain (FDTD) method and a model combining the uniform geometrical theory of diffraction (UTD) and ray tracing (RT). In the sub-band FDTD model, the frequency band (3 - 9 GHz) is uniformly divided into 12 sub-bands in order to take into account the material frequency dispersion. Each sub-band is simulated separately and then a combination technique is used to recover all simulations at the receiver. In the UTD/RT model, the RT technique is used to find the surface diffracted ray path while the UTD is applied for calculating the received signal. Respective modelling results from two-dimensional (2-D) and three-dimensional (3-D) sub-band FDTD and UTD/RT models indicate that antenna patterns have significant impacts on the on-body radio channel. The effect of different antenna types on on-body radio channels is also investigated through the UTD/RT approach.

cond-mat.other↗

arXiv2006

Spatially dispersive finite-difference time-domain analysis of sub-wavelength imaging by the wire medium slabs

In this paper, a spatially dispersive finite-difference time-domain (FDTD) method to model wire media is developed and validated. Sub-wavelength imaging properties of the finite wire medium slabs are examined. It is demonstrated that the slab with its thickness equal to an integer number of half-wavelengths is capable of transporting images with sub-wavelength resolution from one interface of the slab to another. It is also shown that the operation of such transmission devices is not sensitive to their transverse dimensions, which can be made even comparable to the wavelength. In this case, the edge diffractions are negligible and do not disturb the image formation.

physics.optics↗

arXiv2006

Modelling of Wave Propagation in Wire Media Using Spatially Dispersive Finite-Difference Time-Domain Method: Numerical Aspects

The finite-difference time-domain (FDTD) method is applied for modelling of wire media as artificial dielectrics. Both frequency dispersion and spatial dispersion effects in wire media are taken into account using the auxiliary differential equation (ADE) method. According to the authors' knowledge, this is the first time when the spatial dispersion effect is considered in the FDTD modelling. The stability of developed spatially dispersive FDTD formulations is analysed through the use of von Neumann method combined with the Routh-Hurwitz criterion. The results show that the conventional stability Courant limit is preserved using standard discretisation scheme for wire media modelling. Flat sub-wavelength lenses formed by wire media are chosen for validation of proposed spatially dispersive FDTD formulation. Results of the simulations demonstrate excellent sub-wavelength imaging capability of the wire medium slabs. The size of the simulation domain is significantly reduced using the modified perfectly matched layer (MPML) which can be placed in close vicinity of the wire medium. It is demonstrated that the reflections from the MPML-wire medium interface are less than -70 dB, that lead to dramatic improvement of convergence compared to conventional simulations.

cond-mat.mtrl-sci↗

arXiv2005

Sub-wavelength imaging at optical frequencies using canalization regime

Imaging with sub-wavelength resolution using a lens formed by periodic metal-dielectric layered structure is demonstrated. The lens operates in canalization regime as a transmission device and it does not involve negative refraction and amplification of evanescent modes. The thickness of the lens have to be an integer number of half-wavelengths and can be made as large as required for ceratin applications, in contrast to the other sub-wavelength lenses formed by metallic slabs which have to be much smaller than the wavelength. Resolution of $λ/20$ at 600 nm wavelength is confirmed by numerical simulation for a 300 nm thick structure formed by a periodic stack of 10 nm layers of glass with $ε=2$ and 5 nm layers of metal-dielectric composite with $ε=-1$. Resolution of $λ/60$ is predicted for a structure with same thickness, period and operating frequency, but formed by 7.76 nm layers of silicon with $ε=15$ and 7.24 nm layers of silver with $ε=-14$.

cond-mat.mtrl-sci↗

arXiv2005

Sub-wavelength imaging by wire media

Original realization of a lens capable to transmit images with sub-wavelength resolution is proposed. The lens is formed by parallel conducting wires and effectively operates as a telegraph: it captures image at the front interface and the transmit it to the back interface without distortion. This regime of operation is called canalization and is inherent in flat lenses formed by electromagnetic crystals. The theoretical estimations are supported by numerical simulations and experimental verification. Sub-wavelength resolution of $λ/15$ and 18% bandwidth of operation are demonstrated at gigahertz frequencies. The proposed lens is capable to transport sub-wavelength images without distortion to nearly unlimited distances since the influence of losses to the lens operation is negligibly small.

cond-mat.mtrl-sci↗