7,240 research outputs found
Time Reversal to Localise Multiple Partial Discharges in Power Cables
The paper studies the suitability of the electromagnetic time reversal (EMTR) technique to localise multiple sources of partial discharges (PD) in power cables. In particular, the localisation of two PDs in a homogeneous power line is investigated both in the presence or absence of noise. The investigation, which is based on numerical simulations, shows that an EMTR-based PD localisation method is able to localise two PDs occurring simultaneously in a line using only a measurement at one observation point (OP), indiscriminately collecting the direct and reflected signals coming from the two PD sources. The EMTR procedure to localise multiple PD sources, using a Transmission Line Matrix model digital twin for the time reversal simulations, is described and the challenges that must be addressed to develop an EMTR-based device for the on-line location of multiple PDs
are discussed
Structural Health Monitoring of Large Structures Using Acoustic Emission-Case Histories
Acoustic emission (AE) techniques have successfully been used for assuring the structural integrity of large rocket motorcases since 1963 [...
Locating Multiple Soft Faults in Wire Networks Using An Alternative DORT Implementation
International audienceDecomposition of the time reversal operator (DORT) was recently applied to the problem of detection and location of soft faults in wire networks and proved effectual when dealing with a single fault, even in the case of complex network configurations. In this paper, the case of location of multiple faults is addressed, first proving that the standard DORT formulation does not allow to take a clear decision about the individual position of each fault. An alternative version of the DORT, based on an updating procedure, is presented and demonstrated to enable accurate and selective location of multiple soft faults. The proposed procedure is also shown to allow estimating the reflection coefficient of each fault, thus giving access to their severity
Computational polarimetric microwave imaging
We propose a polarimetric microwave imaging technique that exploits recent
advances in computational imaging. We utilize a frequency-diverse cavity-backed
metasurface, allowing us to demonstrate high-resolution polarimetric imaging
using a single transceiver and frequency sweep over the operational microwave
bandwidth. The frequency-diverse metasurface imager greatly simplifies the
system architecture compared with active arrays and other conventional
microwave imaging approaches. We further develop the theoretical framework for
computational polarimetric imaging and validate the approach experimentally
using a multi-modal leaky cavity. The scalar approximation for the interaction
between the radiated waves and the target---often applied in microwave
computational imaging schemes---is thus extended to retrieve the susceptibility
tensors, and hence providing additional information about the targets.
Computational polarimetry has relevance for existing systems in the field that
extract polarimetric imagery, and particular for ground observation. A growing
number of short-range microwave imaging applications can also notably benefit
from computational polarimetry, particularly for imaging objects that are
difficult to reconstruct when assuming scalar estimations.Comment: 17 pages, 15 figure
DYNAMIC MAGNETIC EFFECTS IN AMORPHOUS MICROWIRES FOR SENSORS AND CODING APPLICATIONS
This work is devoted to the study of the dynamic properties of magnetic amorphous wires,
in particular, glass-coated microwires, which have small diameters (5-30 microns), outstanding
soft magnetic behaviour with a high permeability and low coercivity, yet, possess a well-defined
magnetic structure.
First part of my PhD research has been devoted to the investigation of a bi-stable
magnetisation reversal in glass-coated amorphous microwires. In contrast to traditional
approaches, where characteristics of the magnetisation reversal are analysed as a consequence of
the eddy current effect, l have applied stochastic methods for modelling the remagnetisation
reversal in the microwires with axial anisotropy. While the eddy current approach, widely
discussed in literature, was based on the single domain model, proposed stochastic approach
takes into account a multi-domain state of studied samples. A modified stochastic Neel-Brown
model of the magnetisation reversal has been proposed enabling the explanation of number of
characteristic parameters of the microwires with axial magnetisation. Such important parameters
of Barkhausen discontinuity as a mean switching field and a standard deviation of the switching
field distribution have been investigated experimentally for understanding the influence of
extrinsic factors such as a slew rate of the alternating magnetic field on applications operation.
A deep understanding of the remagnetisation process in amorphous the microwires with
axial anisotropy was successfully applied in development of a new type of the remote magnetic
interrogation system. My reading system allows the large Barkhausen jump to be detected
without actual contact between the magnetic microwire and the magnetic field detector.
Experiments show that the detection will be possible at a distance of approximately 100-150 mm
from the detecting sensor. A very low cost and easily repetitive amorphous microwires with axial
anisotropy are . incontrovertibly best materials for Electronic Article Surveillance (EAS)
applications.
During the study of the microwires with axial anisotropy and development of the
application based on them, I took part in the investigation of unusual coding methods of the
amorphous microwires using a localised laser annealing treatment. This treatment produces a
multi-pulse code within the wire and therefore adds to the information contained within the wire,
improving reliability and security. I developed and used a magnetic interrogation system
allowing an accurate and reliable test and analysis of the studied samples.
The second part of my PhD research has included investigations of microwires with
circumferential and helical anisotropies. The main interest in these materials is due to their
applications for high-performance magnetic and stress sensors. Within this research project, the
microwires with circumferential/helical anisotropy have been studied in a broad range of
frequencies. A number of dynamic effects have been experimentally obtained and analysed. In
particular, a detailed investigation of dynamic circular hysteresis (10kHz-300kHz) has been
carried out allowing explanation of different behaviour of the materials with
circumferential/helical anisotropy at different frequencies. The experimental curves are proposed
to be analysed in terms of field dependence of characteristic permeabilities: domain wall
displacements (reversible and irreversible) and magnetisation rotation. It was established that
these permeabilities have different field behaviour. That explains different MI patterns at
relatively low frequencies (less than a few MHz) and relatively high frequencies (more than 10
MHz).
Further, some special features of the Magneto-Impedance effect in the microwires with a
circumferential anisotropy such as off-diagonal impedance and microwave impedance have been
considered. In this research, the former presents a considerable interest for development of linear
magnetic sensors and the latter can find application in tuneable microwave materials and
devices. As a result of this study several types of linear, bi-directional MI sensors were
developed. I also developed new MI sensing approaches (such as off-diagonal response) and a
new high performance detection technique allowing us to improve sensitivity, bandwidth, and
linearity at low cost and simple construction ..
The last part of the PhD research has been devoted to an investigation of the stress-impedance
in the ultra high-frequency (UHF) band (300MHz-3 GHz). Based on the experimental
investigation, a new type of a stress-sensitive composite material is proposed. The microwave
effective permittivity of such material depends on mechanical stresses. These composite
materials opens up new possibilities for remote monitoring of stress with the use of microwave
"free-space" techniques. This kind of composite material can be characterised as a "sensing
medium", which images the mechanical stress distribution inside construction or on its surface
Technology applications
A summary of NASA Technology Utilization programs for the period of 1 December 1971 through 31 May 1972 is presented. An abbreviated description of the overall Technology Utilization Applications Program is provided as a background for the specific applications examples. Subjects discussed are in the broad headings of: (1) cancer, (2) cardiovascular disease, (2) medical instrumentation, (4) urinary system disorders, (5) rehabilitation medicine, (6) air and water pollution, (7) housing and urban construction, (8) fire safety, (9) law enforcement and criminalistics, (10) transportation, and (11) mine safety
- …