50 research outputs found
A novel directional coupler utilizing a left-handed material
A novel directional coupler with a left-handed material (LHM) layer between
two single-mode waveguides of usual material is introduced. The coupling system
is analyzed with the supermode theory. It is shown that such a LHM layer of
finite length can shorten significantly the coupling length for the two
single-mode waveguides. A LHM layer with two slowly tapered ends is used to
avoid the reflection loss at the ends.Comment: 3 pages, 2 figure
Imaging Studies of Characteristics for a Slab of a Lossy Left-handed Material
The characteristics of an imaging system formed by a slab of a lossy
left-handed material (LHM) are studied. The transfer function of the LHM
imaging system is written in an appropriate product form with each term having
a clear physical interpretation. A tiny loss of the LHM may suppress the
transmission of evanescent waves through the LHM slab and this is explained
physically. An analytical expression for the resolution of the imaging system
is derived. It is shown that it is impossible to make a subwavelength imaging
by using a realistic LHM imaging system unless the LHM slab is much thinner
than the wavelength.Comment: 15 pages, 10 figure
Interaction between negative and positive index medium waveguides
The coupling between negative and positive index medium waveguides is
investigated theoretically in this paper. A coupled mode theory is developed
for such a waveguide system and its validity is verified. Interesting phenomena
in the coupled waveguides are demonstrated, which occur in the case when the
negative index medium waveguide in isolation guides its mode backward. A new
type of coupled mode solution that varies exponentially with the coupling
length is found in the special case when the propagation constants of two
individual waveguides are nearly the same. A coupler operating in this case is
insensitive to the coupling length, and its coupling efficiency can reach 100%
as long as the coupling length is long enough. However, when the propagation
constants of the two individual waveguides differ greatly, the coupled mode
solution is still a periodic function of the coupling length, but the coupled
power is output backward. In addition, the modes in the composite waveguide
system are also studied using the coupled mode theory, and their fundamental
properties are revealed.Comment: 7 page
Finite-size effects of a left-handed material slab on the image quality
The characteristics of an imaging system formed by a left-handed material
(LHM) slab of finite length are studied, and the influence of the finite length
of the slab on the image quality is analyzed. Unusual phenomena such as surface
bright spots and negative energy stream at the image side are observed and
explained as the cavity effects of surface plasmons excited by the evanescent
components of the incident field. For a thin LHM slab, the cavity effects are
found rather sensitive to the length of the slab, and the bright spots on the
bottom surface of the slab may stretch to the image plane and degrade the image
quality.Comment: changes in the content and the title, and also the figure
Structure Analysis for Tunnel Longitudinal Deformation Based on Segment Dislocation Mode
AbstractAccording to tunnel structure around joints, tunnel longitudinal deformation is analyzed and a three-dimensional finite element model is built based on segment dislocation mode. Tunnel structure stress analysis is conducted from two aspects of segment in the shear and bolt in the tension. The analysis results show: (1) Segment shear model. When segment dislocation reaches 0.03mm, the principal stressÏ1 exceeds 3.0Mpa which is over concrete's tensile strength. Therefore, when convex tenon and concave tenon generate shear, there must be horizontal slipping and bolt is tensioned. (2) Bolt tension model. When joint opening value reaches 2mm, bolt stress exceeds 640Mpa, which is bolt's yield strength. When joint opening value reaches 6mm, which is the waterproof control standard for tunnel, bolt stress reaches 688.7Mpa, which is less than bolt's failure strength. The subway tunnel's structure safety should be controlled from the perspective of waterproof
Abnormal phenomena in a one-dimensional periodic structure containing left-handed materials
The explicit dispersion equation for a one-dimensional periodic structure
with alternative layers of left-handed material (LHM) and right-handed material
(RHM) is given and analyzed. Some abnormal phenomena such as spurious modes
with complex frequencies, discrete modes and photon tunnelling modes are
observed in the band structure. The existence of spurious modes with complex
frequencies is a common problem in the calculation of the band structure for
such a photonic crystal. Physical explanation and significance are given for
the discrete modes (with real values of wave number) and photon tunnelling
propagation modes (with imaginary wave numbers in a limited region).Comment: 10 pages, 4 figure