143 research outputs found
Ghost line waves
Time-harmonic electromagnetic plane waves in anisotropic media can exhibit
complex-valued wavevectors (with nonzero real and imaginary parts) even in the
absence of material dissipation. These peculiar modes, usually referred to as
"ghost waves," hybridize the typical traits of conventional propagating and
evanescent waves, displaying both phase accumulation and purely reactive
exponential decay away from the direction of power flow. Their existence has
been predicted in several scenarios, and has been recently observed
experimentally in the form of surface phonon polaritons with complex-valued
out-of-plane wavevectors propagating at the interface between air and a natural
uniaxial crystal with slanted optical axis. Here, we demonstrate that ghost
waves can arise also in lower-dimensional flat-optics scenarios, which are
becoming increasingly relevant in the context of metasurfaces and in the field
of polaritonics. Specifically, we show that planar junctions between isotropic
and anisotropic metasurfaces can support "ghost line waves" that propagate
unattenuated along the line interface, exhibiting phase oscillations combined
with evanescent decay both in the plane of the metasurface (away from the
interface) and out-of-plane n the surrounding medium. Our theoretical results,
validated by finite-element numerical simulations, demonstrate a novel form of
polaritonic waves with highly confined features, which may provide new
opportunities for the control of light at the nanoscale, and may find potential
applications in a variety of scenarios, including integrated waveguides,
nonlinear optics, optical sensing and sub-diffraction imaging.Comment: 19 pages, 5 figures. Some typos fixe
Vocal Folds Disorders Detection and Classification in Endoscopic Narrow-Band Images
The diagnosis of vocal folds (VF) diseases is error- prone due to the large variety of diseases that can affect them. VF lesions can be divided in nodular, e.g. nodules, polyps and cysts, and diffuse, e.g. hyperplastic laryngitis and carcinoma. By endoscopic examination, the clinician traditionally evaluates the presence of macroscopic formations and mucosal vessels alteration. Endoscopic narrow-band imaging (NBI) has recently started to be employed since it provides enhanced vessels contrast as compared to classical white-light endoscopy. This work presents a preliminary study on the development of an automatic diagnostic tool based on the assessment of vocal cords symmetry in NBI images. The objective is to identify possible protruding mass lesions on which subsequent vessels analysis may be performed. The method proposed here is based on the segmentation of the glottal area (GA) from the endoscopic images, based on which the right and the left portions of the vocal folds are detected and analyzed for the detection of protruding areas. The obtained information is then used to classify the VF edges as healthy or pathological. Results from the analysis of 22 endoscopic NBI images demonstrated that the proposed algorithm is robust and effective, providing a 100% success rate in the classification of VF edges as healthy or pathological. Such results support the investment in further research to expand and improve the algorithm presented here, potentially with the addition of vessels analysis to determine the pathological classification of detected protruding areas
Independent Manipulation of Heat and Electrical Current via Bifunctional Metamaterials
Spatial tailoring of the material constitutive properties is a well-known
strategy to mold the local flow of given observables in different physical
domains. Coordinate-transformation-based methods (e.g., transformation optics)
offer a powerful and systematic approach to design anisotropic,
spatially-inhomogeneous artificial materials ("metamaterials") capable of
precisely manipulating wave-based (electromagnetic, acoustic, elastic) as well
as diffusion-based (heat) phenomena in a desired fashion. However versatile
these approaches have been, most designs have so far been limited to serving
single-target functionalities in a given physical domain. Here we present a
step towards a "transformation multiphysics" framework that allows independent
and simultaneous manipulation of multiple physical phenomena. As a proof of
principle of this new scheme, we design and synthesize (in terms of realistic
material constituents) a metamaterial shell that simultaneously behaves as a
thermal concentrator and an electrical "invisibility cloak". Our numerical
results open up intriguing possibilities in the largely unexplored phase space
of multi-functional metadevices, with a wide variety of potential applications
to electrical, magnetic, acoustic, and thermal scenarios.Comment: 31 pages, 7 figures, 2 table
Spectral-domain method of moments for the modal analysis of line waveguides
A rigorous full-wave modal analysis based on the method of moments in the
spectral domain is presented for line waveguides constituted by two-part
impedance planes with arbitrary anisotropic surface impedances. An integral
equation is formulated by introducing an auxiliary current sheet on one of the
two half planes and extending the impedance boundary condition of the
complementary half plane to hold on the entire plane. The equation is then
discretized with the method of moments in the spectral domain, by employing
exponentially weighted Laguerre polynomials as entire-domain basis functions
and performing a Galerkin testing. Numerical results for both bound and leaky
line waves are presented and validated against independent results, obtained
for isotropic surface impedances with the analytical Sommerfeld-Maliuzhinets
method and for the general anisotropic case with a commercial electromagnetic
simulator. The proposed approach is computationally efficient, can accommodate
the presence of spatial dispersion, and offers physical insight into the modal
propagation regimes.Comment: 10 pages, 13 figure
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