Research On Left-handed Material Theory And Its Applications

Focused on the hot spot in recent years in Electromagnetics— the left-handed material, this thesis is mainly composed of three parts: superlensing in two-dimensional photonic crystals, study on the Brewster angle in anisotropic left-handed material, and the design of a SRR loaded controllable waveguide filter.Begin with the basic concepts of photonics crystals and how to calculate photonic bands using plane wave expansion method, two types of negative refraction is studied in this part. A clear and explicit distinction between the concepts of negative refraction, negative refractive index, and superlensing is drawn. In virtue of FDTD method, both near field and far field imaging are displayed. Layered superlensing consisting of only triangular lattice photonic crystal is also studied and it exhibits more flexibility than the single layer counterpart. That is, the objective distance can be changed freely while keeping the image distance constant and vice versa. This is useful in the potential subwavelength imaging system.Brewster angle in anisotropic left-handed material is studied. When optical axis is perpendicular to the surface normal, it is found that the Brewster angle is decreased with the increase of frequency in the negative pass band. Experiments are performed to corroborate the conclusions. To further study this problem, the optical axis is rotated by an arbitrary angle. A striking phenomenon is discovered that the Brewster angle is always equal to the rotation angle. This is because the waves in the direction perpendicular to the optical axis become evanescent since the permittivity is positive while the permeability is negative in this direction. And hence zero reflection.A SRR loaded controllable waveguide filter is designed. Both theoretical calculation and numerical simulation are given. The stop band above the waveguide cut-off frequency can be controlled by tuning the varactors loaded between the arms of SRRs. Similarly, the pass band below the waveguide cut-off frequency can also be tuned by the same token. But the remarkable passband below the cut-off frequency is a negative pass-band which supports the propagation of backward waves i.e., the direction of the energy is anti-parallel to the direction of the wave vector.