Search results for " sensor"
showing 10 items of 1714 documents
Hydrogen sensor based on a palladium-coated fibre-taper with improved time-response
2006
Abstract We report an experimental study of the response of a hydrogen sensor, based on a palladium-coated tapered optical fibre, at different temperatures in the range −30 to 80 °C. We have studied the transmission, the time-response and the initial response velocity, being able to correlate these measurements with the pressure–composition isotherms of the Pd–H system and its phase transitions. Heating of the palladium layer optically with an auxiliary laser diode permits to improve the sensor's time-response at low temperatures.
A portable NMR sensor to measure dynamic changes in the amount of water in living stems or fruit and its potential to measure sap flow.
2014
Nuclear magnetic resonance (NMR) and NMR imaging (magnetic resonance imaging) offer the possibility to quantitatively and non-invasively measure the presence and movement of water. Unfortunately, traditional NMR hardware is expensive, poorly suited for plants, and because of its bulk and complexity, not suitable for use in the field. But does it need to be? We here explore how novel, small-scale portable NMR devices can be used as a flow sensor to directly measure xylem sap flow in a poplar tree (Populus nigra L.), or in a dendrometer-like fashion to measure dynamic changes in the absolute water content of fruit or stems. For the latter purpose we monitored the diurnal pattern of growth, ex…
Ultrasonic Guided Wave Inspection of Bonded Lap Joints: Noncontact Method and Photoelastic Visualization
2001
The main topic of this paper is the nondestructive inspection of adhesively bonded lap joints by using ultrasonic guided (plate) waves. A noncontact, couplant-free method that employs capacitive air-coupled transducers is demonstrated for the inspection of thin aluminum joints with dimensions typical of aircraft fuselage and wing panels. Two types of bond defects, disbonded regions and regions of poorly cured (low-cohesive-strength) adhesive, are successfully detected by measuring the amplitude decrease of selected plate waves leaking from one adherend to the other one through the bondline. It is shown that proper choice of the vibrating mode structure, in terms of cross-sectional displacem…
ZnO/polyaniline composite based photoluminescence sensor for the determination of acetic acid vapor
2020
In this study, we report a novel ZnO/polyaniline (PANI) nanocomposite optical gas sensor for the determination of acetic acid at room temperatures. ZnO nanorods, synthesized in powder form were coated by PANI (ZnO/ PANI) by chemical polymerization method. The obtained nanocomposites were deposited on glass substrate and dried overnight at room temperature. Structure and optical properties of ZnO/PANI nanocomposite have been studied by using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, diffuse reflectance and photoluminescence spectroscopy. Tests towards acetic acids were performed in the range of concentrations 1–13 ppm. The adsorption of acetic a…
Nitrogen-doped carbon dots embedded in a SiO2 monolith for solid-state fluorescent detection of Cu2+ ions
2017
We describe the simple fabrication of SiO2 sol-gel monoliths embedding highly luminescent carbon nanodots (CDs) sensitive to metal ions. The pristine CDs we synthesize display an intense dual emission consisting in two fluorescence bands in the green and violet region, and we demonstrate that this photoluminescence is substantially unchanged when the dots are incorporated in the SiO2 matrix. The emission of these CDs is quenched by interactions with Cu2+ ions, which can be used to detect these ions with a detection limit of 1 μM. The chromophores remain accessible to diffusing Cu2+ ions even after embedding CDs in the sol-gel monolith, where their detection capabilities are preserved. Such …
Gamma irradiation of graphene quantum dots with ethylenediamine: Antioxidant for ion sensing
2020
Due to the low consumption of chemicals, the absence of toxic residual side products, the procedure simplicity and time-saving aspects, gamma irradiation offers advantages over the classical chemical protocols. We successfully employed gamma irradiation in order to introduce N-atoms in Graphene Quantum Dots (GQDs). By irradiating GQDs water dispersions in the presence of isopropyl alcohol and ethylenediamine, at doses of 25, 50 and 200 kGy, we attached amino groups onto GQDs in a single synthetic step. At the same time, a chemical reduction is achieved, too. Selected conditions induced incorporation of N-atoms within GDQs atomic lattice (around 3 at%), at all applied doses. Additionally, th…
Photoelectrochemical Bisphenol S Sensor Based on ZnO‐Nanoroads Modified by Molecularly Imprinted Polypyrrole
2019
Molecularly imprinted polymers are important tools for the design of sensors and other molecular recognition based analytical systems. In this paper the development of a photoelectrochemical sensor for selective bisphenol determination is reported. The sensor is based on a glass/ZnO/MIP‐Ppy structure consisting of glass modified by a ZnO layer (glass/ZnO), which is functionalized by molecularly imprinted conducting polymer polypyrrole (MIP‐Ppy). The sensitivity of the sensor to bisphenol is in the range of 0.7–12.5 µm. Selectivity tests to other bisphenolic compounds are performed. Some aspects of a photoinduced response mechanism in glass/ZnO/MIP‐Ppy nanostructures are predicte…
Application of Room Temperature Photoluminescence From ZnO Nanorods for Salmonella Detection
2014
ZnO nanorods grown by gaseous-disperse synthesis are confirmed by XRD analysis to have the wurtzite crystal structure. The obtained crystallites, as found from SEM studies, are 57 +/- 9 nm in diameter and 470 +/- 30 nm long on the average. Two emission bands of photoluminescence from ZnO nanorods observed at room temperature are centered at 376 and 520 nm. A biosensitive layer is prepared by immobilization of anti-Salmonella antibodies from liquid solutions on the ZnO surface. Immobilization of the biosensitive layer onto ZnO nanorods is found to increase the intensity of PL. After further reaction with Salmonella antigens (Ags), the PL intensity is found to decrease proportional to Ag conc…
Quantum sensor networks as exotic field telescopes for multi-messenger astronomy
2020
Multi-messenger astronomy, the coordinated observation of different classes of signals originating from the same astrophysical event, provides a wealth of information about astrophysical processes with far-reaching implications. So far, the focus of multi-messenger astronomy has been the search for conventional signals from known fundamental forces and standard model particles, like gravitational waves (GW). In addition to these known effects, quantum sensor networks could be used to search for astrophysical signals predicted by beyond-standard-model (BSM) theories. Exotic bosonic fields are ubiquitous features of BSM theories and appear while seeking to understand the nature of dark matter…
Hypersensitive tunable Josephson escape sensor for gigahertz astronomy
2020
Sensitive photon detection in the gigahertz band constitutes the cornerstone to study different phenomena in astronomy, such as radio burst sources, galaxy formation, cosmic microwave background, axions, comets, gigahertz-peaked spectrum radio sources and supermassive black holes. Nowadays, state of the art detectors for astrophysics are mainly based on transition edge sensors and kinetic inductance detectors. Overall, most sensible nanobolometers so far are superconducting detectors showing a noise equivalent power (NEP) as low as 2x10-20 W/Hz1/2. Yet, fast thermometry at the nanoscale was demonstrated as well with Josephson junctions through switching current measurements. In general, det…