Biomedical subjects

Chao-Hsien Kuo

Publications and source records attributed to Chao-Hsien Kuo.

8 recordsLinked to original sources

PubMed2006

Disorder effect on the focus image of sonic crystals in air.

When acoustic waves propagate in two-dimensional sonic crystals composed of parallel rigid cylinders in air, anisotropic band gaps, such as a partial gap and deaf band, forbid the waves within certain frequency regions from propagating along certain directions, thus forming a stable imaging focus effect. If the introduced disorder has not destroyed the original anisotropic band gap, this unique effect still exists, although the focused image becomes blurred. Once the sample reaches complete disorder, the anisotropic band gap is destroyed, and this effect also disappears.

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PubMed2005

Gravity waves over topographical bottoms: comparison with experiment.

The propagation of water surface waves over one-dimensional periodic and random bottoms is investigated by the transfer matrix method. For the periodic bottoms, the band structure is calculated, and the results are compared to the transmission results. When the bottoms are randomized, the Anderson localization phenomenon is observed. The theory has been applied to an existing experiment [J. Fluid Mech. 186, 539 (1988)]]. In general, the results are compared favorably with the experimental observation.

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PubMed2004

Optical transmission of photonic crystal structures formed by dielectric cylinders: evidence for non-negative refraction.

By a rigorous numerical simulation based on the standard multiple scattering theory, we investigate optical transmission in photonic crystal structures, formed from dielectric cylinders embedded in parallel in a uniform medium. In contrast to previous conjectures, the results indicate that the imaging effect of a flat photonic crystal slab, which has been interpreted as a signature of negative refractive effects, is caused by a tunneling or self-guiding effect in the presence of partial band gaps.

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PubMed2004

Electromagnetic energy and energy flows in photonic crystals made of arrays of parallel dielectric cylinders.

We consider electromagnetic propagation in two-dimensional photonic crystals, formed by parallel dielectric cylinders embedded a uniform medium. The frequency band structure is computed using the standard plane-wave expansion method, and the corresponding eigenmodes are obtained subsequently. The optical flows of the eigenmodes are calculated by a direct computation approach, and several averaging schemes of the energy current are discussed. The results are compared to those obtained by the usual approach that employs a group velocity calculation. We consider both the case in which the frequency lies within passing band and the situation in which the frequency is in the range of a partial band gap. The agreements and discrepancies between various averaging schemes and the group velocity approach are discussed in detail. The results indicate that the group velocity can be obtained by an appropriate averaging method. Existing experimental methods are also discussed.

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PubMed2004

Negative-refraction-like behavior revealed by arrays of dielectric cylinders.

We investigate the electromagnetic propagation in two-dimensional photonic crystals, formed by parallel dielectric cylinders embedded in a uniform medium. The transmission of electromagnetic waves through prism structures is calculated by the standard multiple scattering theory. The results demonstrate that, in certain frequency regimes and when the propagation inside the scattering media is not considered, the transmission behavior mimics the negative refraction expected for a left-handed material. This feature may illusively lead to the conclusion that a negative refraction is observed and it obeys Snell's law of negative refraction. Possible implications for current experimental and theoretical studies of negative refraction are also discussed.

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PubMed2004

Guiding optical flows by photonic crystal slabs made of dielectric cylinders.

We investigate the electromagnetic propagation in two-dimensional photonic crystals, formed by parallel dielectric cylinders embedded in a uniform medium. The frequency band structure is computed using the standard plane-wave expansion method, while the propagation and scattering of the electromagnetic waves are calculated by the multiple scattering theory. It is shown that within partial band gaps, the waves tend to bend away from the forbidden directions. Such a property may render novel applications in manipulating optical flows. In addition, the relevance with the imaging by flat photonic crystal slabs will also be discussed.

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PubMed2004

Propagation inhibition and localization of electromagnetic waves in two-dimensional random dielectric systems.

We rigorously calculate the propagation and scattering of electromagnetic waves by rectangular and random arrays of dielectric cylinders in a uniform medium. For regular arrays, the band structures are computed and complete bandgaps are discovered. For random arrays, the phenomenon of wave transmission and scattering is investigated and compared in two scenarios: (1) Wave propagating through the array of cylinders; this is the scenario which has been commonly considered in the literature, and (2) wave transmitted from a source located inside the ensemble. We show that within complete band gaps, results from the two scenarios are similar. Outside the gaps, however, there could be a distinct difference, that is, wave transmission can be inhibited by disorders in the first scenario, but such an inhibition may not prevail in the second scenario.

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PubMed2004

Band gaps in the propagation and scattering of surface water waves over cylindrical steps.

Here we investigate the propagation and scattering of surface water waves in the presence of arrays of bottom-mounted cylindrical steps. Both periodic and random arrangements of the steps are considered. The wave transmission through the arrays is computed using the multiple scattering method based upon a recently derived formulation. For the periodic case, the results are compared to the band structure calculation. We demonstrate that complete band gaps can be obtained in such a system. Furthermore, we show that the randomization of the location of the steps can significantly reduce the transmission of water waves. Comparison with other systems is also discussed.

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