20,575 research outputs found
Propagation and scattering of electromagnetic waves in complex environments
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (p. 231-236).by John H. Oates.Ph.D
Surface-Wave Dispersion Retrieval Method and Synthesis Technique for Bianisotropic Metasurfaces
We propose a surface-wave dispersion retrieval method and synthesis technique
that applies to bianisotropic metasurfaces that are embedded in symmetric or
asymmetric environments. Specifically, we use general zero-thickness sheet
transition conditions to relate the propagation constants of surface-wave modes
to the bianisotropic susceptibility components of the metasurface, which can
themselves be directly related to its scattering parameters. It is then
possible to either obtain the metasurface dispersion diagram from its known
susceptibilities or, alternatively, compute the susceptibilities required to
achieve a desired surface-wave propagation. The validity of the method is
demonstrated by comparing its results to those obtained with exact dispersion
relations of well known structures such as the propagation of surface plasmons
on thin metallic films. In particular, this work reveals that it is possible to
achieve surface-wave propagation only on one side of the metasurface either by
superposition of symmetric and asymmetric modes in the case of anisotropic
metasurfaces or by completely forbidding the existence of the surface wave on
one side of the structure using bianisotropic metasurfaces
Circuit model for diffuse multipath and electromagnetic absorption prediction in rooms
We present a room electromagnetics-based theory which primarily models the diffuse multipath components (DMC) power density with a simple circuit model, and afterwards includes the line-of-sight (LOS) component to predict the total exposure in a realistic environment. Given a human absorption cross section (ACS) and its location from a transmitter (Tx), the average whole-body specific absorption rate (SAR(wb)) can be determined by the proposed circuit model for ultra-wideband (UWB) and wireless local area network (WLAN) systems. The SAR(wb) in humans in a realistic office environment for both UWB and WLAN systems is investigated as part of application. The theory is simulated with the Advanced Design System (ADS) software, and excellent agreement between theoretical and simulated values are obtained in terms of relative errors (<2%). The model may be very useful for SAR(wb) prediction in realistic complex indoor environments
Joint Compressed Sensing and Manipulation of Wireless Emissions with Intelligent Surfaces
Programmable, intelligent surfaces can manipulate electromagnetic waves
impinging upon them, producing arbitrarily shaped reflection, refraction and
diffraction, to the benefit of wireless users. Moreover, in their recent form
of HyperSurfaces, they have acquired inter-networking capabilities, enabling
the Internet of Material Properties with immense potential in wireless
communications. However, as with any system with inputs and outputs, accurate
sensing of the impinging wave attributes is imperative for programming
HyperSurfaces to obtain a required response. Related solutions include field
nano-sensors embedded within HyperSurfaces to perform minute measurements over
the area of the HyperSurface, as well as external sensing systems. The present
work proposes a sensing system that can operate without such additional
hardware. The novel scheme programs the HyperSurface to perform compressed
sensing of the impinging wave via simple one-antenna power measurements. The
HyperSurface can jointly be programmed for both wave sensing and wave
manipulation duties at the same time. Evaluation via simulations validates the
concept and highlight its promising potential.Comment: Published at IEEE DCOSS 2019 / IoT4.0 workshop
(https://www.dcoss.org/workshops.html). Funded by the European Union via the
Horizon 2020: Future Emerging Topics - Research and Innovation Action call
(FETOPEN-RIA), grant EU736876, project VISORSURF (http://www.visorsurf.eu
A computational model for path loss in wireless sensor networks in orchard environments.
A computational model for radio wave propagation through tree orchards is presented. Trees are modeled as collections of branches, geometrically approximated by cylinders, whose dimensions are determined on the basis of measurements in a cherry orchard. Tree canopies are modeled as dielectric spheres of appropriate size. A single row of trees was modeled by creating copies of a representative tree model positioned on top of a rectangular, lossy dielectric slab that simulated the ground. The complete scattering model, including soil and trees, enhanced by periodicity conditions corresponding to the array, was characterized via a commercial computational software tool for simulating the wave propagation by means of the Finite Element Method. The attenuation of the simulated signal was compared to measurements taken in the cherry orchard, using two ZigBee receiver-transmitter modules. Near the top of the tree canopies (at 3 m), the predicted attenuation was close to the measured one-just slightly underestimated. However, at 1.5 m the solver underestimated the measured attenuation significantly, especially when leaves were present and, as distances grew longer. This suggests that the effects of scattering from neighboring tree rows need to be incorporated into the model. However, complex geometries result in ill conditioned linear systems that affect the solver's convergence
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