50,755 research outputs found
Mathematical analysis of guided water waves
Projet IDENTIn this article, we present a detailed mathematical analysis of the phenomenon of water waves guided by the coast. We work with the mathematical model issued from the linearized theory of gravity waves. Our results mainly concern the existence, the number and the high and low frequency behaviours of the guided modes. These results point out a large variety of phenomena which are deeply influenced by the geometry of the coast. We obtain them with the help of the spectral theory of unbounded selfadjoint operators. Some numerical results are presented at the end of the paper to illustrate the theory
Stochastic band structure for waves propagating in periodic media or along waveguides
We introduce the stochastic band structure, a method giving the dispersion
relation for waves propagating in periodic media or along waveguides, and
subject to material loss or radiation damping. Instead of considering an
explicit or implicit functional relation between frequency and
wavenumber , as is usually done, we consider a mapping of the resolvent set
in the dispersion space . Bands appear as as the trace of
Lorentzian responses containing local information on propagation loss both in
time and space domains. For illustration purposes, the method is applied to a
lossy sonic crystal, a radiating surface phononic crystal, and a radiating
optical waveguide. The stochastic band structure can be obtained for any system
described by a time-harmonic wave equation
Fluid-loaded metasurfaces
We consider wave propagation along fluid-loaded structures which take the
form of an elastic plate augmented by an array of resonators forming a
metasurface, that is, a surface structured with sub-wavelength resonators. Such
surfaces have had considerable recent success for the control of wave
propagation in electromagnetism and acoustics, by combining the vision of
sub-wavelength wave manipulation, with the design, fabrication and size
advantages associated with surface excitation. We explore one aspect of recent
interest in this field: graded metasurfaces, but within the context of
fluid-loaded structures.
Graded metasurfaces allow for selective spatial frequency separation and are
often referred to as exhibiting rainbow trapping. Experiments, and theory, have
been developed for acoustic, electromagnetic, and even elastic, rainbow devices
but this has not been approached for fluid-loaded structures that support
surface waves coupled with the acoustic field in a bulk fluid. This surface
wave, coupled with the fluid, can be used to create an additional effect by
designing a metasurface to mode convert from surface to bulk waves. We
demonstrate that sub-wavelength control is possible and that one can create
both rainbow trapping and mode conversion phenomena for a fluid-loaded elastic
plate model.Comment: 13 pages, 10 figure
Explicit asymptotic modelling of transient Love waves propagated along a thin coating
The official published version can be obtained from the link below.An explicit asymptotic model for transient Love waves is derived from the exact equations of anti-plane elasticity. The perturbation procedure relies upon the slow decay of low-frequency Love waves to approximate the displacement field in the substrate by a power series in the depth coordinate. When appropriate decay conditions are imposed on the series, one obtains a model equation governing the displacement at the interface between the coating and the substrate. Unusually, the model equation contains a term with a pseudo-differential operator. This result is confirmed and interpreted by analysing the exact solution obtained by integral transforms. The performance of the derived model is illustrated by numerical examples.This work is sponsored by the grant from Higher Education of Pakistan and by the Brunel University’s “BRIEF” research award
Trapped modes in finite quantum waveguides
The Laplace operator in infinite quantum waveguides (e.g., a bent strip or a
twisted tube) often has a point-like eigenvalue below the essential spectrum
that corresponds to a trapped eigenmode of finite L2 norm. We revisit this
statement for resonators with long but finite branches that we call "finite
waveguides". Although now there is no essential spectrum and all eigenfunctions
have finite L2 norm, the trapping can be understood as an exponential decay of
the eigenfunction inside the branches. We describe a general variational
formalism for detecting trapped modes in such resonators. For finite waveguides
with general cylindrical branches, we obtain a sufficient condition which
determines the minimal length of branches for getting a trapped eigenmode.
Varying the branch lengths may switch certain eigenmodes from non-trapped to
trapped states. These concepts are illustrated for several typical waveguides
(L-shape, bent strip, crossing of two stripes, etc.). We conclude that the
well-established theory of trapping in infinite waveguides may be incomplete
and require further development for being applied to microscopic quantum
devices
Polarization-resolved sensing with tilted fiber Bragg gratings: theory and limits of detection
Polarization based sensing with tilted fiber Bragg grating (TFBG) sensors is
analysed theoretically by two alternative approaches. The first method is based
on tracking the grating transmission for two orthogonal states of linear
polarized light that are extracted from the measured Jones matrix or Stokes
vectors of the TFBG transmission spectra. The second method is based on the
measurements along the system principle axes and polarization dependent loss
(PDL) parameter, also calculated from measured data. It is shown that the
frequent crossing of the Jones matrix eigenvalues as a function of wavelength
leads to a non-physical interchange of the calculated principal axes; a method
to remove this unwanted mathematical artefact and to restore the order of the
system eigenvalues and the corresponding principal axes is provided. A
comparison of the two approaches reveals that the PDL method provides a smaller
standard deviation and therefore lower limit of detection in refractometric
sensing. Furthermore, the polarization analysis of the measured spectra allows
for the identification of the principal states of polarization of the sensor
system and consequentially for the calculation of the transmission spectrum for
any incident polarization state. The stability of the orientation of the system
principal axes is also investigated as a function of wavelength
Self-Evaluation Applied Mathematics 2003-2008 University of Twente
This report contains the self-study for the research assessment of the Department of Applied Mathematics (AM) of the Faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS) at the University of Twente (UT). The report provides the information for the Research Assessment Committee for Applied Mathematics, dealing with mathematical sciences at the three universities of technology in the Netherlands. It describes the state of affairs pertaining to the period 1 January 2003 to 31 December 2008
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