68,589 research outputs found
On the Accuracy of Equivalent Antenna Representations
The accuracy of two equivalent antenna representations, near-field sources
and far-field sources, are evaluated for an antenna installed on a simplified
platform in a series of case studies using different configurations of
equivalent antenna representations. The accuracy is evaluated in terms of
installed far-fields and surface currents on the platform. The results show
large variations between configurations. The root-mean-square installed
far-field error is 4.4% for the most accurate equivalent representation. When
using far-field sources, the design parameters have a large influence of the
achieved accuracy. There is also a varying accuracy depending on the type of
numerical method used. Based on the results, some recommendations on the choice
of sub-domain for the equivalent antenna representation are given. In
industrial antenna applications, the accuracy in determining e.g. installed
far-fields and antenna isolation on large platforms are critical. Equivalent
representations can reduce the fine-detail complexity of antennas and thus give
an efficient numerical descriptions to be used in large-scale simulations. The
results in this paper can be used as a guideline by antenna designers or system
engineers when using equivalent sources
Technical design and commissioning of the KATRIN large-volume air coil system
The KATRIN experiment is a next-generation direct neutrino mass experiment
with a sensitivity of 0.2 eV (90% C.L.) to the effective mass of the electron
neutrino. It measures the tritium -decay spectrum close to its endpoint
with a spectrometer based on the MAC-E filter technique. The -decay
electrons are guided by a magnetic field that operates in the mT range in the
central spectrometer volume; it is fine-tuned by a large-volume air coil system
surrounding the spectrometer vessel. The purpose of the system is to provide
optimal transmission properties for signal electrons and to achieve efficient
magnetic shielding against background. In this paper we describe the technical
design of the air coil system, including its mechanical and electrical
properties. We outline the importance of its versatile operation modes in
background investigation and suppression techniques. We compare magnetic field
measurements in the inner spectrometer volume during system commissioning with
corresponding simulations, which allows to verify the system's functionality in
fine-tuning the magnetic field configuration. This is of major importance for a
successful neutrino mass measurement at KATRIN.Comment: 32 pages, 16 figure
Efficient full-wave modeling of radiative near-field interactions in semi-anechoic conditions
In this paper, a full-wave method to efficiently compute the electromagnetic interaction between two devices placed in semi-anechoic conditions is proposed. The aim of this research is the accurate and efficient reproduction of radiated immunity and emission tests in simulation. The employed technique relies on a single simulation (or measurement) of the radiation pattern of each device and allows an arbitrary relative position between the devices. The resulting procedure is practical, has a low computational cost, and shows good agreement with reference solutions
Polarization-maintaining reflection-mode THz time-domain spectroscopy of a polyimide based ultra-thin narrow-band metamaterial absorber
This paper reports the design, the microfabrication and the experimental characterization of an ultra-thin narrow-band metamaterial absorber at terahertz frequencies. The metamaterial device is composed of a highly flexible polyimide spacer included between a top electric ring resonator with a four-fold rotational symmetry and a bottom ground plane that avoids misalignment problems. Its performance has been experimentally demonstrated by a custom polarization-maintaining reflection-mode terahertz time-domain spectroscopy system properly designed in order to reach a collimated configuration of the terahertz beam. The dependence of the spectral characteristics of this metamaterial absorber has been evaluated on the azimuthal angle under oblique incidence. The obtained absorbance levels are comprised between 67% and 74% at 1.092 THz and the polarization insensitivity has been verified in transverse electric polarization. This offers potential prospects in terahertz imaging, in terahertz stealth technology, in substance identification, and in non-planar applications. The proposed compact experimental set-up can be applied to investigate arbitrary polarization-sensitive terahertz devices under oblique incidence, allowing for a wide reproducibility of the measurements
Electronic modulation of infrared emissivity in graphene plasmonic resonators
Electronic control of blackbody emission from graphene plasmonic resonators
on a silicon nitride substrate is demonstrated at temperatures up to 250 C. It
is shown that the graphene resonators produce antenna-coupled blackbody
radiation, manifest as narrow spectral emission peaks in the mid-IR. By
continuously varying the nanoresonators carrier density, the frequency and
intensity of these spectral features can be modulated via an electrostatic
gate. We describe these phenomena as plasmonically enhanced radiative emission
originating both from loss channels associated with plasmon decay in the
graphene sheet and from vibrational modes in the SiNx.Comment: 17 pages, 6 figure
Superluminal, subluminal, and negative velocities in free-space electromagnetic propagation
In this Chapter the time-domain analysis of the velocity of the
electromagnetic field pulses generated by a spatially compact source in free
space is presented. Recent simulations and measurements of anomalous
superluminal, subluminal, and negative velocities are discussed. It is shown
that such velocities are local and instantaneous in nature and do not violate
either causality or special relativity. Although these effects are mainly
confined to the near- and intermediate-field zones, some of them seem
paradoxical and still lack adequate physical interpretation.Comment: This is an extended account (21 pages, 9 figures) of my previous
work: PRL 102, 02040
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