Guishan Yuan

General conformal transformation method based on Schwarz-Christoffel approach

A general conformal transformation method (CTM) is proposed to construct the conformal mapping between two irregular geometries. In order to find the material parameters corresponding to the conformal transformation between two irregular geometries, two polygons are utilized to approximate the two irregular geometries, and an intermediate geometry is used to connect the mapping relations between the two polygons. Based on these manipulations, the approximate material parameters for TE and TM waves are finally obtained by calculating the Schwarz-Christoffel (SC) mappings. To demonstrate the validity of the method, a phase modulator and a plane focal surface Luneburg lens are designed and simulated by the finite element method. The results show that the conformal transformation can be expanded to the cases that the transformed objects are with irregular geometries.

A design method to change the effective shape of scattering cross section for PEC objects based on transformation optics

A design method was proposed for transforming the scattering cross sections shape of PEC objects to other arbitrary shapes based on transformation optics. The parameters of the transformer which is a kind of metamaterial being tightly covered to the original PEC object can be determined by the transformation expressions derived in the paper. With the method, the virtual PEC objects with their definite shape of the scattering cross section can be produced visually through the original PEC objects with a designed transformer. The validation was made by comparing the distribution of electromagnetic field of the PEC objects with and without transformer by means of finite-element method. Some examples are also given for demonstrating the effectiveness of the method.

Design method to enhance the transmittance of a structured lens based on nonperiodic sampling

On the basis of the work of Chen, Zhou, Luo, and Du [Opt. Lett. 33, 753-755 (2008)], we propose a new method using nonperiodic sampling to design a high-transmittance structured lens. The sizes of the holes are decided by the phase requirements, and the holes are arranged with a fixed interval in the vertical direction while a variable interval in the horizontal direction. With this design method, holes can be arranged more compactly and the fill factor of the holes can be increased effectively. Numerical simulation is performed through the finite-difference time-domain method, and the results indicate that the transmittance of the lens climbs to 73.6%, which reaches almost 3.5 times that achieved in the above-mentioned work. Meanwhile, the simulated focal length agrees well with the theoretical design result with the error of 1.1% and the full width at half maximum of the focal spot is obtained similar to 1.16 times of the diffraction limit

Frequency tunable electromagnetic metamaterial based on mechanical movement method

A frequency tunable electromagnetic metamaterial is proposed based on mechanical movement method. Two rings are etched against each other on two separate substrates and the two substrates can be adjusted to move relatively. Thus, the resonant frequency can be modulated due to the changed coupling capacitance between the rings according to equivalent circuit theory. Simulation results show that the transmissions (S21) can be continuously adjusted, and the retrieved effective parameters based on simulated scattering parameters reveal that the negative permittivity is available and the negative permittivity frequency region can be tuned downward or upward by slipping the rings either along or perpendicular to the gaps directions. By combining frequency modulations in the two directions, resonant frequency can be shifted from 6.2 GHz to 8.7 GHz, which has realized an efficient modulation in a broad frequency range. The proposed tunable metamaterial has potential applications to design dual band, multi-band antennas and frequency reconfigurable antennas.