11,186 research outputs found
Distributed opto-mechanical analysis of liquids outside standard fibers coated with polyimide
The analysis of surrounding media has been a long-standing challenge of
optical fiber sensors. Measurements are difficult due to the confinement of
light to the inner core of standard fibers. Over the last two years, new sensor
concepts have enabled the analysis of liquids outside the cladding boundary,
where light does not reach. Sensing is based on opto-mechanical, forward
stimulated Brillouin scattering interactions between guided light and sound
waves. In most previous works, however, the protective polymer coating of the
fiber had to be removed first. In this work, we report the opto-mechanical
analysis of liquids outside commercially available, standard single-mode fibers
with polyimide coating. The polyimide layer provides mechanical protection but
can also transmit acoustic waves from the fiber cladding towards outside media.
Comprehensive analysis of opto-mechanical coupling in coated fibers that are
immersed in liquid is provided. The model shows that forward stimulated
Brillouin scattering spectra in coated fibers are more complex than those of
bare fibers, and strongly depend on the exact coating diameter and the choice
of acoustic mode. Nevertheless, sensing outside coated fibers is demonstrated
experimentally. Integrated measurements over 100 meters of fiber clearly
distinguish between air, ethanol and water outside polyimide coating. Measured
spectra are in close quantitative agreement with the analytic predictions.
Further, distributed opto-mechanical time-domain reflectometry mapping of water
and ethanol outside coated fiber is reported, with a spatial resolution of 100
meters. The results represent a large step towards practical opto-mechanical
fiber sensors
Force-induced acoustic phonon transport across single-digit nanometre vacuum gaps
Heat transfer between bodies separated by nanoscale vacuum gap distances has
been extensively studied for potential applications in thermal management,
energy conversion and data storage. For vacuum gap distances down to 20 nm,
state-of-the-art experiments demonstrated that heat transport is mediated by
near-field thermal radiation, which can exceed Planck's blackbody limit due to
the tunneling of evanescent electromagnetic waves. However, at sub-10-nm vacuum
gap distances, current measurements are in disagreement on the mechanisms
driving thermal transport. While it has been hypothesized that acoustic phonon
transport across single-digit nanometre vacuum gaps (or acoustic phonon
tunneling) can dominate heat transfer, the underlying physics of this
phenomenon and its experimental demonstration are still unexplored. Here, we
use a custom-built high-vacuum shear force microscope (HV-SFM) to measure heat
transfer between a silicon (Si) tip and a feedback-controlled platinum (Pt)
nanoheater in the near-contact, asperity-contact, and bulk-contact regimes. We
demonstrate that in the near-contact regime (i.e., single-digit nanometre or
smaller vacuum gaps before making asperity contact), heat transfer between Si
and Pt surfaces is dominated by force-induced acoustic phonon transport that
exceeds near-field thermal radiation predictions by up to three orders of
magnitude. The measured thermal conductance shows a gap dependence of
in the near-contact regime, which is consistent with acoustic
phonon transport modelling based on the atomistic Green's function (AGF)
framework. Our work suggests the possibility of engineering heat transfer
across single-digit nanometre vacuum gaps with external force stimuli, which
can make transformative impacts to the development of emerging thermal
management technologies.Comment: 9 pages with 4 figures (Main text), 13 pages with 7 figures
(Methods), and 13 pages with 6 figures and 1 table (Supplementary
Information
Bridges Structural Health Monitoring and Deterioration Detection Synthesis of Knowledge and Technology
INE/AUTC 10.0
Hybrid dispersion laser scanner.
Laser scanning technology is one of the most integral parts of today's scientific research, manufacturing, defense, and biomedicine. In many applications, high-speed scanning capability is essential for scanning a large area in a short time and multi-dimensional sensing of moving objects and dynamical processes with fine temporal resolution. Unfortunately, conventional laser scanners are often too slow, resulting in limited precision and utility. Here we present a new type of laser scanner that offers ∼1,000 times higher scan rates than conventional state-of-the-art scanners. This method employs spatial dispersion of temporally stretched broadband optical pulses onto the target, enabling inertia-free laser scans at unprecedented scan rates of nearly 100 MHz at 800 nm. To show our scanner's broad utility, we use it to demonstrate unique and previously difficult-to-achieve capabilities in imaging, surface vibrometry, and flow cytometry at a record 2D raster scan rate of more than 100 kHz with 27,000 resolvable points
Damage identification in structural health monitoring: a brief review from its implementation to the Use of data-driven applications
The damage identification process provides relevant information about the current state of a structure under inspection, and it can be approached from two different points of view. The first approach uses data-driven algorithms, which are usually associated with the collection of data using sensors. Data are subsequently processed and analyzed. The second approach uses models to analyze information about the structure. In the latter case, the overall performance of the approach is associated with the accuracy of the model and the information that is used to define it. Although both approaches are widely used, data-driven algorithms are preferred in most cases because they afford the ability to analyze data acquired from sensors and to provide a real-time solution for decision making; however, these approaches involve high-performance processors due to the high computational cost. As a contribution to the researchers working with data-driven algorithms and applications, this work presents a brief review of data-driven algorithms for damage identification in structural health-monitoring applications. This review covers damage detection, localization, classification, extension, and prognosis, as well as the development of smart structures. The literature is systematically reviewed according to the natural steps of a structural health-monitoring system. This review also includes information on the types of sensors used as well as on the development of data-driven algorithms for damage identification.Peer ReviewedPostprint (published version
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 [...
Review: optical fiber sensors for civil engineering applications
Optical fiber sensor (OFS) technologies have developed rapidly over the last few decades, and various types of OFS have found practical applications in the field of civil engineering. In this paper, which is resulting from the work of the RILEM technical committee “Optical fiber sensors for civil engineering applications”, different kinds of sensing techniques, including change of light intensity, interferometry, fiber Bragg grating, adsorption measurement and distributed sensing, are briefly reviewed to introduce the basic sensing principles. Then, the applications of OFS in highway structures, building structures, geotechnical structures, pipelines as well as cables monitoring are described, with focus on sensor design, installation technique and sensor performance. It is believed that the State-of-the-Art review is helpful to engineers considering the use of OFS in their projects, and can facilitate the wider application of OFS technologies in construction industry
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