261 research outputs found
Transmission and Reflection Properties of Composite Double Negative Metamaterials in Free Space
Cataloged from PDF version of article.We report free space transmission and the first reflection
measurements of a composite double negative (DNG) metamaterial,
also known as a left-handed material (LHM). The metamaterial
composes of the split-ring-resonators and discontinuous
thin wires. Very high transmission values of the metamaterial are
observed within a frequency range for which both effective permeability
and permittivity are expected to be negative
Investigation of localized coupled-cavity modes in two-dimensional photonic band gap structures
Cataloged from PDF version of article.We present a detailed study of the localized
coupled-cavity modes in 2-D dielectric photonic crystals. The
transmission, phase, and delay time characteristics of the various
coupled-cavity structures are measured and calculated. We observed
the eigenmode splitting, waveguiding through the coupled
cavities, splitting of electromagnetic waves in waveguide ports,
and switching effect in such structures. The corresponding field
patterns and the transmission spectra are obtained from the finite-difference-time-domain
(FDTD) simulations. We also develop
a theory based on the classical wave analog of the tight-binding
(TB) approximation in solid state physics. Experimental results
are in good agreement with the FDTD simulations and predictions
of the TB approximation
Effect of picosecond strain pulses on thin layers of the ferromagnetic semiconductor (Ga,Mn)(As,P)
The effect of picosecond acoustic strain pulses (ps-ASP) on a thin layer of
(Ga,Mn)As co-doped with phosphorus was probed using magneto-optical Kerr effect
(MOKE). A transient MOKE signal followed by low amplitude oscillations was
evidenced, with a strong dependence on applied magnetic field, temperature and
ps-ASP amplitude. Careful interferometric measurement of the layer's thickness
variation induced by the ps-ASP allowed us to model very accurately the
resulting signal, and interpret it as the strain modulated reflectivity
(differing for probe polarizations), independently from dynamic
magnetization effects.Comment: 6 pages, 5 figure
Negative Refraction and Left-handed electromagnetism in Microwave Photonic Crystals
We demonstrate negative refraction of microwaves in metallic photonic
crystals. The spectral response of the photonic crystal, which manifests both
positive and negative refraction, is in complete agreement with band-structure
calculations and numerical simulations. The negative refraction observed
corresponds to left-handed electromagnetism and arises due to the dispersion
characteristics of waves in a periodic medium. This mechanism for negative
refraction is different from that in metamaterials.Comment: 13 pages, 4 figure
Determination of in vitro rumen digestibility and potential feed value of tiger nut varieties
Tiger nut (Cyperus esculentus L.), or chufa, is a plant that is found in nature and is cultivated for its edible tubers. The purpose of this study was to determine the chemical composition, nutritive value, and in vitro digestibility of three tiger nut varieties using the in vitro gas production technique. These varieties were Sarışeker (yellow), Introduction 1, and Balyumru (brown). Rumen fluid was obtained from two cannulated Holstein animals. Time-dependent in vitro gas production was monitored at 3, 6, 9, 12, 24, 48, 72, and 96 hours of incubation. The varieties differed in dry matter (DM), crude ash (CA), ether extract (EE), neutral detergent fibre (NDF), and non-fibre carbohydrate (NFC) content (P <0.05). They also differed in the instantaneous volume of gas produced and in time-dependent gas production. Balyumru produced more gas at the onset of incubation than Introduction 1 and Sarışeker. However, over time, the gas produced by digestion of Introduction 1 exceeded the other two varieties. The amounts of gas produced at each time-point were intercorrelated. It is recommended that these results should lead to further evaluation in in vivo studies.
Keywords: chemical composition, energy content, in vitro gas productio
Transmission and reflection properties of composite metamaterials in free space
We measured transmission and reflection from SRRs, thin wires, and composite metamaterials in free space. X-band measurement exhibits high transmission magnitude for frequencies where both SRR and wire have effective negative permeability and permittivity, respectively. © 2000 Optical Society of America
Photonic band-gap effect, localization, and waveguiding in the two-dimensional Penrose lattice
We report experimental observation of a full photonic band gap in a two-dimensional Penrose lattice made of dielectric rods. Tightly confined defect modes having high quality factors were observed. Absence of the translational symmetry in Penrose lattice was used to change the defect frequency within the stop band. We also achieved the guiding and bending of electromagnetic waves through a row of missing rods. Propagation of photons along highly localized coupled-cavity modes was experimentally demonstrated and analyzed within the tight-binding approximation
Photonic band gaps and localization in two-dimensional metallic quasicrystals
We report on experimental observation of photonic stop bands in two-dimensional metallic Penrose lattice. We investigated the defect characteristics, and observed strongly localized cavity modes below the plasma frequency. The absence of the translational symmetry allowed to change the defect frequencies and localization properties of the defect modes. Propagation of photons along highly localized coupled-cavity modes was experimentally demonstrated in quasiperiodic metallic structures
Investigation of localized coupled-cavity modes in two-dimensional photonic bandgap structures
We present a detailed study of the localized coupled-cavity modes in 2-D dielectric photonic crystals. The transmission, phase, and delay time characteristics of the various coupled-cavity structures are measured and calculated. We observed the eigenmode splitting, waveguiding through the coupled cavities, splitting of electromagnetic waves in waveguide ports, and switching effect in such structures. The corresponding field patterns and the transmission spectra are obtained from the finite-difference-time-domain (FDTD) simulations. We also develop a theory based on the classical wave analog of the tight-binding (TB) approximation in solid state physics. Experimental results are in good agreement with the FDTD simulations and predictions of the TB approximation
Subwavelength resolution in a two-dimensional photonic-crystal-based superlens
The experimental and theoretical demonstration of a single-beam negative refraction and a superlensing effect in 2D photonic crystals was reported. As such, negative refraction was observed for the incidence angles of >20°. This broad angle range was used to demonstrate the superlensing effect, where the electromagnetic waves emitted from a point source were focused on the other side of the PC
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