Backscattered Power Level Research Articles

Fiber Optic Refractive Index Distributed Multi-Sensors by Scattering-Level Multiplexing With MgO Nanoparticle-Doped Fibers

In this work, we present the architecture of a multiplexed refractive index (RI) sensing system based on the interrogation of Rayleigh backscattering. The RI sensors are fabricated by fiber wet-etching of a high-scattering MgO nanoparticle-doped fiber, without the need for a reflector or plasmonic element. Interrogation is performed by means of optical backscatter reflectometry (OBR), which allows a detection with a millimeter-level spatial resolution. Multiplexing consists of a simultaneous scan of multiple fibers, achieved by means of scattering-level multiplexing (SLMux) concept, which uses the backscattered power level in each location as a diversity element. The sensors fabricated have sensitivity in the order of 0.473-0.568 nm/RIU (in one sensing point) and have been simultaneously detected together with a distributed temperature sensing element for multi-parameter measurement. An experimental setup has been prepared to demonstrate the capability of each sensing region to operate without cross-talk, while operating multi-fiber detection.

Efficiency measurement of the flexible on-body antenna at varying levels of stretch in a reverberation chamber.

Flexible antennas have the potential to transform wearable and fabric-based wireless sensing technologies. The antenna discussed in this study is part of a sensing system that uses the back-scattered power level as the decision metric. For a good wireless sensor, it is necessary to offer a feasible read range and maintain good distinctions in the back-scattered power levels between the different states (i.e. level of stretch) of the antenna. Moreover, effects due to human body proximity should be minimised. For these reasons, the radiation efficiency is a crucial parameter to investigate. This study presents the radiation efficiency measurement of the proposed flexible knitted 'Bellyband' antenna at two different levels of stretch in a reverberation chamber. This work validates the reverberation chamber measurements through comparison with simulations and anechoic chamber measurements at 900 MHz. Moreover, this work demonstrates how the approach can be used to quantify bellyband antenna efficiency in the vicinity of a human body. Finally, the efficiency results were used to predict the read range of Bellyband radio frequency identification technology.

Design of Non-Orthogonal Multiple Access Enhanced Backscatter Communication

Backscatter communication (BackCom), which allows a backscatter node (BN) to communicate with the reader by modulating and reflecting the incident continuous wave from the reader, is considered a promising solution to power the future Internet-of-Things. In this paper, we consider a single BackCom system, where multiple BNs are served by a reader. We propose using the power-domain non-orthogonal multiple access (NOMA), i.e., multiplexing the BNs in different regions or with different backscattered power levels, to enhance the spectrum efficiency of the BackCom system. To better exploit power-domain NOMA, we propose setting the reflection coefficients for multiplexed BNs to be different. Based on this considered model, we develop the reflection coefficient selection criteria. To illustrate the enhanced system with the proposed criteria, we analyze the performance of the BackCom system in terms of the average number of bits that can be successfully decoded by the reader for the two-node pairing case and the average number of successful BNs for the general multiplexing case. Our results show that NOMA achieves the much better performance gain in the BackCom system as compared to its performance gain in the conventional system, which highlights the importance of applying NOMA to the BackCom system.

Impact of Rayleigh backscattering on Stimulated Brillouin Scattering threshold evaluation for 10 Gb/s NRZ-OOK signals

At bit rates comparable with the Brillouin shift, i.e. higher than 10 Gbit/s, the signal and the Brillouin backscattered spectra partially overlap. This implies an interaction between different scattering phenomena occurring through out the optical fiber. In particular we believe that an evaluation of how Rayleigh backscattered components of the modulated signal are subjected to Stokes gain is required. This interaction may lead to an increased backscattered power, which in turn will affect Brillouin threshold estimation. We experimentally verified a decrease of Stimulated Brillouin Scattering (SBS) threshold for 10 Gb/s NRZ-OOK signals with respect to theoretical predictions. Simulations carried out with a numerical model of SBS, accounting for Rayleigh contributions, well predict measured backscattered power levels. On the other hand we also experimentally verified that this SBS threshold decrease does not degrade transmission system performance. Indeed, measured BER curves put into evidence a penalty reduction for signal powers just before the saturation regime, which should be usefully taken into consideration in optical systems power budget planning.

A Novel Conformal RFID-Enabled Module Utilizing Inkjet-Printed Antennas and Carbon Nanotubes for Gas-Detection Applications

This letter introduces for the first time the integration of a conformal radio frequency identification (RFID) antenna with a single-walled carbon nanotube (SWCNT) composite in a chipless RFID node for toxic gas detection. The electrical performance characterization of the inkjet-printed SWCNT film is also reported for the first time up to 1 GHz. The whole module is realized by inkjet printing on a low-cost paper-based substrate, and the RFID tag is designed for the European UHF RFID band. The electrical conductivity of the SWCNT film changes in the presence of very small quantities of toxic gases like ammonia and nitrogen oxide, resulting in the variation of the backscattered power level, which can be easily detected by the RFID reader to realize reliable wireless toxic gas sensing.

Theoretical estimation of the temperature dependence of backscattered ultrasonic power for noninvasive thermometry

The backscattered signal received from an insonified volume of tissue depends on tissue properties, such as attenuation, velocity, density, and backscatter coefficient and on the characteristics of the transducer at the insonified volume. Analysis of scattering in response to a burst of insonification showed that the temperature dependence of backscattered power was dominated by the effect of temperature on the backscatter coefficient. The temperature dependence of attenuation had a small effect on backscattered power. Backscattered power was independent of effects of temperature on velocity. These results were seen in the analysis of two types of inhomogeneity: 1) an aqueous scatterer in a water-based medium and 2) a lipid-based scatterer in the same water-based medium. The temperature dependence of the backscatter coefficient was inferred assuming that the backscatter coefficient was proportional to the scattering crosssection of a small scatterer. Backscattered power increased nearly logarithmically with temperature over the range from 37° to 50°C. Our model predicted a change of 5 dB for the lipid scatterer and a change of up to 3 db for the aqueous-based scatterer over that temperature range. For situations in which temperature dependence of the backscattered power can be calibrated, it may be possible to use the backscattered power level to track temperature distributions in tissue.

Turbulence scattering layers in the middle‐mesosphere observed by the EISCAT 224‐MHz radar

Spectral measurements of signals scattered from altitudes well below 70 km have for the first time been obtained with the EISCAT 224‐MHz radar. Observations with the antenna pointing away from the vertical at times show spectral power distributions departing markedly from those expected from collision‐dominated incoherent scatter theory. Separated peaks in the spectra occur in regions of abrupt shear in the velocity of the neutral wind within the scattering volume. Anomalously large backscattered power levels are sometimes observed in the vicinity of such shears at altitudes near 68 km. It is unlikely that these echoes are due to incoherent (Thomson) scatter. Instead, it is proposed that the abrupt velocity shears develop neutral turbulence in narrow layers and that these layers cause the enhanced backscatter. Calculations of the expected backscatter power levels at 224 MHz for incoherent scatter and for turbulence scatter show that the turbulence component can be the dominant one at heights below about 68 km if the potential refractive index gradient and the turbulence energy dissipation rates are large enough.

A modification event of the auroral E region as studied with EISCAT and other diagnostics

Highly enhanced backscattered power levels were measured with EISCAT during a modification experiment with a powerful HF heater. They occurred sporadically when the heater frequency was close to the local plasma frequency and very regularly during a time period when the heater frequency was definitely below the local plasma frequency (overdense heating). In this latter time interval the background electron density in the E region was enhanced due to particle precipitation. From the fact that the enhanced power levels were observed only with the Tromsø antenna looking along the magnetic field line and not with the remote antennas, it was concluded that the artificially created irregularities are pancake‐shaped, with the plane of the pancakes perpendicular to the magnetic field. Several processes which may be responsible for the excitation of these irregularities are discussed, and simultaneous results from other ground‐based experiments are presented.

An explanation of enhanced radar backscattering from flooded forests

Abstract A simpie structural backscatter model for a forest stand, suitable for use with L-band HH polarized radar imagery, is used to explain the increased level of backscattering observed from flooded forests. Measurements made of relative levels of backscatter from SIR-B image data of a flooded Australian forest are consistent with an interpretation based upon scattering mechanisms involving both the tree components and the understorey or forest floor. The change in Fresnel power reflection coefficient of the ground with flooding is advanced as the cause of the enhancement in backscattered power levels.

The modification of X and L band radar signals by monomolecular sea slicks

One methyl oleate and two oleyl alcohol surface films were produced on the surface of the North Sea under comparable oceanographic and meteorological conditions in order to investigate their influence on X and L band radar backscatter. Signals are backscattered in these bands primarily by surface waves with lengths of about 2 and 12 cm, respectively, and backscattered power levels in both bands were reduced by the slicks. The reduction was larger at X band than at L band, however, indicating that shorter waves are more intensely damped by the surface films. The oleyl alcohol film caused greater attenuation of short gravity waves than the film of methyl oleate, thus demonstrating the importance of the physicochemical properties of films on the damping of wind‐generated gravity capillary waves. Finally, these experiments indicate a distinct dependence of the degree of damping on the angle between wind and waves. Wind‐generated waves traveling in the wind direction are more intensely damped by surface films than are waves traveling at larger angles to the wind.

Rayleigh backscattering theory for single-mode optical fibers

The theory of backscattering in single-mode optical fibers is described through use of a correlation function for the refractive-index fluctuation in the fiber. A simple formula for the backscattered power is derived using two correlation functions for the Booker–Gordon and Gaussian models. The zeroth-order approximation of the formula, in which the correlation length is much smaller than the spot size of the waveguide mode, coincides with Brinkmeyer’s model. The backscattered power at the input end of single-mode fiber is compared with that for multimode fiber. It is also shown that the backscattered power level at the input end is lower by approximately 55 dB than the input power level.

Experimental investigation of variation of backscattered power level with numerical aperture in multimode optical fibres

Experiments have been performed to determine how the backscattered power level varies with numerical aperture. It is found that graded-index fibres are more sensitive to such variations than step-index fibres. By taking into account the dependence of the Rayleigh scattering coefficient on numerical aperture, the experimental results agree well with theory.

Relationship between Hurricane Surface Winds and L-Band Radar Backscatter from the Sea Surface

High-altitude, airborne, L-band synthetic aperture radar (SAR) data were collected in Hurricane Gloria on 28 and 30 September 1976. The backscattered power levels (proportional to the surface scattering coefficient) averaged over a few square kilometers of surface area were found to vary with surface wind speed and the angle of the wind relative to the radar. Comparisons between the backscatter from the eye and eye-wall regions of the hurricane were made with low-level aircraft wind measurements that were nearly coincident in space and time. The SAR has the potential advantage over other radar types because of its higher spatial resolution. It also appears to have the ability to penetrate rainfall, with a reduction in the echo from the surface. One difference when compared with higher frequency microwave radars is a decrease in the sensitivity of the backscatter to changes in wind speed. This dependence of L-band radar backscatter on surface winds suggests that the winds associated with hurricanes can be measured with airborne or spaceborne radars.