Backscattered Power Research Articles

Backscatter Efficiency Modeling of Inductive Links Applied to Wireless Power Transfer Systems

In this paper, we analyze the backscatter response of inductive link-based wireless power transfer systems. This analysis leads to a model that predicts the power levels received back on the primary side of the inductive link. The proposed model considers the inductive link characteristics as the magnetic coupling factor, the quality factors of the inductors, and the impedance matching at the secondary side, but also accounts for the equivalent on-resistance of the switch used to apply the response on the secondary side. The modeling of the backscattering response can be helpful to choose design variables of the system such as the duty cycle of the response and the size of the switching transistors. Moreover, the estimation of the reflected power can be used to specify the receiver sensitivity on the primary side. The model is validated with experimental results on two different inductive links: one using only FR4-printed inductors with a PIN diode acting as backscatter switch and the other using a CMOS fully integrated wireless power receiver. The measured backscattered power in both cases agrees with the predicted values.

Soil Moisture and Vegetation Water Content Retrieval Using QuikSCAT Data

Climate change and hydrological cycles can critically impact future water resources. Uncertainties in current climate models result in disagreement on the amount of water resources. Soil moisture and vegetation water content are key environmental variables on evaporation and transpiration at the land–atmosphere boundary. Radar remote sensing helps to improve our estimate of water resources spatially and temporally. This work proposes a backscattered power formulation for the Ku-band. Li et al. (2010) retrieved soil moisture and vegetation water content values using Windsat data and simultaneous collocated QuikSCAT backscattered power are used to estimate different parameters of backscatter formulation. These parameters are used to estimate soil moisture and vegetation water content using QuikSCAT power everywhere and every day during the summer season. The 2-folded cross validation method is used to evaluate the performance of soil moisture and vegetation water content retrieval. A relatively large correlation is observed between vegetation water content using WindSat and QuikSCAT data in land classes of Evergreen Needleleaf, Evergreen Broadleaf, Deciduous Broadleaf, and Mixed Forests. Similarly, the retrieved soil moisture using QuikSCAT in areas with bare surface fraction of greater than 60% shows relatively high correlation with WindSat values. QuikSCAT satellite collects data over land globally almost every day. Therefore, QuikSCAT data can be used to generate a global map of soil moisture and vegetation water content daily from 2000 to 2009.

Anisotropy and Spatial Heterogeneity in Quantitative Ultrasound Parameters: Relevance to the Study of the Human Cervix

Imaging biomarkers based on quantitative ultrasound can offer valuable information about properties that inform tissue function and behavior such as microstructural organization (e.g., collagen alignment) and viscoelasticity (i.e., compliance). For example, the cervix feels softer as its microstructure remodels during pregnancy, an increase in compliance that can be objectively quantified with shear wave speed and therefore shear wave speed estimation is a potential biomarker of cervical remodeling. Other proposed biomarkers include parameters derived from the backscattered echo signal, such as attenuation and backscattered power loss, because such parameters can provide insight into tissue microstructural alignment and organization. Of these, attenuation values for the pregnant cervix have been reported, but large estimate variance reduces their clinical value. That said, parameter estimates based on the backscattered echo signal may be incorrect if assumptions they rely on, such as tissue isotropy and homogeneity, are violated. For that reason, we explored backscatter and attenuation parameters as potential biomarkers of cervical remodeling via careful investigation of the assumptions of isotropy and homogeneity in cervical tissue. Specifically, we estimated the angle- and spatial-dependence of parameters of backscattered power and acoustic attenuation in the ex vivo human cervix, using the reference phantom method and electronic steering of the ultrasound beam. We found that estimates are anisotropic and spatially heterogeneous, presumably because the tissue itself is anisotropic and heterogeneous. We conclude that appropriate interpretation of imaging biomarkers of cervical remodeling must account for tissue anisotropy and heterogeneity.

ISR Spectra Simulations With Electron‐Ion Coulomb Collisions

AbstractIncoherent scatter radars (ISR) rely on Thomson scattering of very high frequency or ultrahigh frequency radio waves off electrons in the ionosphere and measure the backscattered power spectra in order to estimate altitude profiles of plasma density, electron temperature, ion temperature, and ion drift speed. These spectra result from the collective behavior of coupled ion and electron dynamics, and, for most cases, existing theories predict these well. However, when the radar points nearly perpendicular to the Earth's magnetic field, the motion of the plasma across the field lines becomes complex and Coulomb collisions between electrons and ions become important in interpreting ISR measurements. This paper presents the first fully kinetic, self‐consistent, particle‐in‐cell simulations of ISR spectra with electron‐ion Coulomb collisions. We implement a grid‐based Coulomb collision algorithm in the Electrostatic Parallel Particle‐in‐Cell simulator and obtain ISR spectra from simulations both with and without collisions. For radar directions greater than 5° away from perpendicular to the magnetic field, both sets of simulations match collisionless ISR theory well. For angles between 3° and 5°, the collisional simulation is well described by a simplified Brownian motion collision process. At angles less than 3° away from perpendicular the Brownian motion model fails, and the collisional simulation qualitatively agrees with previous single particle simulations. For radar directions exactly perpendicular to the magnetic field the simulated collisional spectra match those from the Brownian motion collision theory, in agreement with previous single particle simulations.

Forest Above-Ground Biomass Estimation Using Single-Baseline Polarization Coherence Tomography with P-Band PolInSAR Data

Forest above ground biomass (AGB) extraction using Synthetic Aperture Radar (SAR) images has been widely used in global carbon cycle research. Classical AGB inversion methods using SAR images are mainly based on backscattering coefficients. The polarization coherence tomography (PCT) technology which can generate vertical profiles of forest relative reflectivity, has the potential to improve the accuracy of biomass inversion. The relationship between vertical profiles and forest AGB is modeled by some parameters defined based on geometric characteristics of the relative reflectivity distribution curve. But these parameters are defined without physical characteristics. Among these parameters, tomographic height (TomoH) is considered as the most important one. However, TomoH only corresponds to the highest volume relative reflectivity, which is lower than the actual forest height, affecting the accuracy of forest height and AGB inversion. In this paper, we introduce a new parameter, the canopy height (Hac), for AGB inversion by analyzing the vertical backscatter power loss. Then, we construct an inversion model based on the combination of the new parameter (Hac) and other parameters from the tomographic profile. The P-band polarimetric SAR datasets of the European Space Agency (ESA) BioSAR 2008 campaign acquired over Krycklan Catchment are selected for the verification experiment at two different flight directions. The results show that Hac performs better in estimating forest height and AGB than TomoH does. The inversion root mean square error (RMSE) of the proposed method is 18.325 t ha−1, and the result of using TomoH is 21.126 t ha−1.

Artificially controlled backscattering in single mode fibers based on femtosecond laser fabricated reflectors

A novel method to artificially control the backscattering of the single-mode fiber (SMF) is proposed and investigated for the first time. This method can help to fabricate a high backscattering fiber (HBSF), such as by fabricating reflectors in every one meter interval of an SMF based on the exposure of the femtosecond laser beam. The artificially controlled backscattering (ACBS) can be much higher than the natural Rayleigh backscattering (RB) of the SMF. The RB power and ACBS power in the unit length fiber are derived according to the theory of the RBS. The total relative power and the relative back power reflected in the unit length of the HBSF have been simulated and presented. The simulated results show that the HBSF has the characteristics of both low optical attenuation and high backscattering. The relative back power reflected in the unit length of the HBSF is 25dB larger than the RB power of the SMF when the refractive index modulation quantity of the reflectors is 0.009. Some preliminary experiments also indicate that the method fabricating reflectors to increase the backscattering power of the SMF is practical and promising.

A New Scatter Particle and Mixture Fluid for Preparing Blood Mimicking Fluid for Wall-Less Flow Phantom.

Background:To examine the blood flow and detection of the issues related to it by medical ultrasound, it is extremely important to have suitable blood mimicking fluid (BMF) to be used in vitro and to have a movable or portable Doppler flow phantom to use it as a standardizing tool. As known, the main drawbacks of the currently commercial BMF used in the research studies are high in cost and the long time needed for preparation, which is at least 5–7 h. Moreover, there are only two common scatter particles using in BMF as suspension materials such as nylon (Orgasol) and polystyrene. Thus, we need to prepare BMF with both a new mixture fluid and new scatter particle to be as a reflecting factor of ultrasonic waves, for evaluating the speed of sound of the blood flow in the same method like in the research study of ultrasound with relatively low-cost and less consuming time of preparation. However, both the acoustical and physical features of the Doppler flow phantom components (BMF and tissue mimicking material) must correspond the features of the human tissues to make the examination significance. In addition, the BMF must also represent the hemodynamic features of real human blood.Methods:In this experiment, a new adequate ternary mixture liquid for preparation of BMF applied and suspended with a new scatter particle material, this scatter particle material called poly (4-methylstyrene), it used to be adequate with the mixture density and for saving neutrally buoyant. This BMF was prepared for use in the test objects or Doppler flow phantom. The poly (4-methylstyrene) particles were applied for suspension in a mixture liquid or fluid based on three items, which were distilled water, propylene glycol (PG), and polyethylene glycol (PEG) (200 Mw). The diameter of poly (4-methylstyrene) particles is 3–8 μm, which determined by specific sieve in a unit of μm, and the density is 1.040 g/ml.Results:Speed of sound, viscosity, density, Backscatter power and attenuation features of mixture fluid or liquid which used for preparing a BMF were measured, discussed, and agreed with draft International Electrotechnical Commission values.Conclusions:There are three various types of ternary items of mixture fluid (water, PG, and PEG [200 Mw]), and a new type of scatter particle material poly (4-methylstyrene) was utilized for preparing the BMF. The scatter particles and mixture fluid prepared and measured at a temperature that simulates the body temperature 37°C. Moreover, one of the advantages of this new blood that is being cheaper than the commercially available BMF products because the PG and the polyethylene glycol (200 Mw) are much cheaper and more available than glycerol and the Dextran that used usually. In addition, new BMF needs less time for preparation compared to the commercial one.

A fast convolution based waveform model for conventional and unfocused SAR altimetry

In this paper we derive a closed-form solution to generate a backscatter power representation for both unfocused synthetic aperture radar altimetry and conventional altimetry signals in the frequency/slow-time domain. This new approach involves fast convolutions and leads to a fast numerical computational model which uses very few approximations. The transform back to the range-time/doppler frequency domain is then made numerically.Two retrackers based on this Signal Model Involving Numerical Convolution (SINC) are constructed for conventional and synthetic aperture radar altimetry and are named SINC2 and SINCS respectively. Output from retracking are the epoch t0 with respect to the tracking reference point, the significant wave height and the backscattering cross section at normal incidence σ0.Main benefits of the SINC model are its flexibility, the possibility to use the real point target response (PTR) or more complex representations of the height probability density function of scattering sea surface elements (PDF), and its fast computation speed to retrack the waveforms.The retrackers are applied to CryoSat-2 reduced SAR (RDSAR) and unfocused SAR waveforms. The RDSAR SINC2 retracker is only ten percent slower than the commonly used MLE3 retracker, which is a minor slowdown compared to the benefits of the SINC model. The SAR processing including the SINCS retracking procedure is three times slower than the RDSAR processing including retracking with SINC2.Model and algorithms are validated on both synthetic data generated by Monte-Carlo simulations and on real datasets. SAR SAMOSA+ results accessible through the ESA G-POD SARvatore service serve as a reference. Cross-validation shows higher agreement between SAR SAMOSA+ and SAR SINCS sea level anomaly and lower agreement between SAR SAMOSA+ and RDSAR SINC2, with accuracy of −0.1 cm for SAR SINCS and 1.7 cm for RDSAR SINC2. Instead, the accuracy of significant wave height, 4.9 cm and 3.9 cm for SAR and RDSAR and of backscatter coefficient, 0.16 and 0.12 dB in SAR and RDSAR, are comparable.Cross-validation results shows for sea level anomaly and significant wave height a higher precision of SAR SINCS and a lower precision of RDSAR SINC2, with precision of 0.92 cm and 6.6 cm for SAR SINCS and 1.96 cm and 12.6 cm for RDSAR SINC2 in sea level anomaly and significant wave height respectively. Instead, the precision of the backscatter coefficient is higher in RDSAR SINC2 than in SAR SINCS, and is 0.014 and 0.016 dB.In summary the new open ocean retrackers are a viable alternative recommended for both reduced and unfocused SAR processing in open ocean.

Spaceborne PolSAR Tomography for Forest Height Retrieval

Synthetic aperture radar (SAR) data with polarization diversity and multibaseline acquisition has the capability to resolve the structural information of the target. Three-dimensional (3-D) imaging using SAR tomography is an advance and recent technology that focuses on backscattered echoes not only in the 2-D plane defined by the azimuth and range coordinates, but also in cross-range direction. Forests act as a semitransparent media for radar wavelengths, and thus allow us to gather the vertical distribution of this volumetric scatterer. This paper investigated the potential of polarimetric SAR tomography (PolTomSAR) to retrieve the scatterer distribution of forest area using C-band Radarsat-2 spaceborne SAR dataset. Teak patch of Haldwani forest was chosen as the test site to validate the robustness of TomoSAR algorithms. Fourier, beamforming, Capon, Capon like, and polarimetric capon were implemented in this study and backscatter power variations with their corresponding vertical profile for a particular azimuth bin were derived and analyzed. It was observed that Fourier suffered from high sidelobes that were reduced by beamforming and Capon. Limitations of beamformer were highlighted and well resolved by Capon. However, both beamforming and Capon yielded low backscattering power at different height levels. The Capon-like algorithm substantially improved the backscatter intensity at different forest height levels. Polarimetric capon surpassed the Capon algorithm and was able to estimate better heights by incorporating various polarization channels. Height map was generated for fully polarimetric Capon and validated with the ground truth data.

Validity of the Kirchhoff approximation for the scattering of electromagnetic waves from dielectric, doubly periodic surfaces.

Accuracy of Kirchhoff approximation (KA) for rough-surface electromagnetic wave scattering is studied by comparison with accurate numerical solutions in the context of three-dimensional dielectric surfaces. The Kirchhoff tangent plane approximation is examined without resorting to the principle of stationary phase. In particular, it is shown that this additional assumption leads to zero cross-polarized backscattered power, but not the tangent plane approximation itself. Extensive numerical results in the case of a bisinusoidal surface are presented for a wide range of problem parameters: height-to-period, wavelength, incidence angles, and dielectric constants. In particular, this paper shows that the range of validity inherent in the KA includes surfaces whose curvature is not only much smaller, but also comparable to the incident wavelength, with errors smaller than 5% in total reflectivity, thus presenting a detailed and reliable source for the validity of the KA in a three-dimensional fully polarimetric formulation.

Tornado identification and forewarning with very high frequency windprofiler radars

The ability of very high frequency (VHF) (~50 MHz) windprofilers to measure backscatter, winds and turbulence in the troposphere and the lower stratosphere gives them a unique perspective not available with many other remote sounding radar techniques. This capability has been utilized to study the environment of 31 tornadoes generated in the provinces of Ontario and Quebec in Canada over an 11‐year period. Tornadoes were mostly of Enhanced Fujita (EF) types EF0 to EF2, with one being EF3. Focus is on events which produced visible damage. Signals detected show characteristics demonstrating new informative—and potentially predictive—capabilities. A large enhancement in backscattered power immediately above the common volume of the radar and the tornadic supercell, reaching to the tropopause and beyond, when coupled with radar measurements of strong turbulence and wind speeds, provides good radar evidence of tornadic activity.

Expansion of major urban areas in the US Great Plains from 2000 to 2009 using satellite scatterometer data

A consistent dataset delineating and characterizing changes in urban environments will be valuable for socioeconomic and environmental research and for sustainable urban development. Remotely sensed data have been long used to map urban extent and infrastructure at various spatial and spectral resolutions. Although many datasets and approaches have been tried, there is not yet a universal way to map urban extents across the world. Here we combined a microwave scatterometer (QuikSCAT) dataset at ~1km posting with percent impervious surface area (%ISA) data from the National Land Cover Dataset (NLCD) that was generated from Landsat data, and ambient population data from the LandScan product to characterize and quantify growth in nine major urban areas in the US Great Plains from 2000 to 2009. Nonparametric Mann-Kendall trend tests on backscatter time series from urban areas show significant expanding trends in eight of nine urban areas with p-values ranging 0.032 to 0.001. The sole exception is Houston, which has a substantial non-urban backscatter at the northeastern edge of the urban core. Strong power law scaling relationships between ambient population and either urban area or backscatter power (r2 of 0.96 in either model) with sub-linear exponents (β of 0.911 and 0.866, respectively) indicate urban areas become more compact with more vertical built-up structure than lateral expansion to accommodate the increased population. Increases in backscatter and %ISA datasets between 2001 and 2006 show agreement in both magnitude and direction for all urban areas except Minneapolis-St. Paul (MSP), likely due to the presence of many lakes and ponds throughout the MSP metropolitan area. We conclude discussing complexities in the backscatter data caused by large metal structures and rainfall.

On the potential of Polarimetric SAR Interferometry to characterize the biomass, moisture and structure of agricultural crops at L-, C- and X-Bands

Polarimetric SAR Interferometry (Pol-InSAR) has shown great promise for estimating the height of agricultural crops through the inversion of a scattering model of the plant canopy and the soil. The inversion also provides estimates of model parameters describing the microwave attenuation within the canopy and the relative scattering contributions from canopy and soil surface.Here, we investigate how vegetation characteristics including biomass, water content (VWC) and canopy structure are related to these parameters and provide a first assessment of the potential of estimating such characteristics using Pol-InSAR time series in L-, C- and X-Bands.The overall attenuation for maize is positively related to total VWC in L- and C-Bands. Furthermore, larger attenuation in VV than HH points toward the existence of anisotropic propagation effects due to vertical orientation of the stalks.Conversely, for wheat in C- and X-Bands there is no consistent relation between attenuation loss and VWC. Rather, structural changes occurring within the plant growth cycle appear to have an appreciable polarization-dependent effect on the observed attenuation changes.In addition, the estimated normalized volume backscattering power NVP (a measure of the relative scattering contribution from the canopy compared to the underlying soil) is associated with wet biomass. However, the contrasting sign of this relation (negative for maize in L- and C-Bands; positive for wheat in C- and X-Bands) indicates again the role of crop structural properties in the Pol-InSAR measurements. For instance, the NVP for maize in L- and C-Bands appears to decrease with increasing biomass due to the increasingly important double bounce ground-stalk scattering contribution as plants become taller and thicker.Overall, these results indicate the sensitivity of the Pol-InSAR parameters to canopy structure and biomass; this sensitivity is however dependent, amongst others, on crop type and radar frequency. When choosing an appropriate baseline/frequency configuration, the Pol-InSAR attenuation loss and NVP may complement the information of the estimated crop height, especially if the latter shows very little variation over the plant growth cycle (e.g. as for wheat).

Experimental assessment of an RFID-based crack sensor for steel structures

The use of welded steel cover plates had been a common design practice to increase beam section capacity in regions of high moment for decades. Many steel girder bridges with cover plates are still in service. Steel girder bridges are subject to cyclic loading, which can initiate crack formation at the toe of the weld and reduce beam capacity. Thus, timely detection of fatigue cracks is of utmost importance in steel girder bridge monitoring. To date, crack monitoring methods using in-house radio frequency identification (RFID)-based sensors have been developed to complement visual inspection and provide quantitative information of damage level. Offering similar properties at a reduced cost, commercial ultra-high frequency (UHF) passive RFID tags have been identified as a more financially viable option for pervasive crack monitoring using a dense array of sensors. This paper presents a study on damage sensitivity of low-cost commercial UHF RFID tags for crack detection and monitoring on metallic structures. Using backscatter power as a parameter for damage identification, a crack sensing system has been developed for single and multiple tag configurations for increased sensing pervasiveness. The effect on backscatter power of the existence and stage of crack propagation has been successfully characterized. For further automation of crack detection, a damage index based on the variation of backscatter power has also been established. The tested commercial RFID-based crack sensor contributes to the usage of this technology on steel girder bridges.

Abstract 889: A comparison between quantitative ultrasound and histology in heterogeneous tumor structure

Abstract Background: To investigate how QUS (Quantitative Ultrasound) maps reflect regional variations in heterogeneous tumor microstructure, we compared like-regions of QUS effective scatterer diameter (ESD, μm) and effective acoustic concentration (EAC, dB/cm) maps to whole-slice, virtual histology sections stained for vascular, cellular and other microstructural features. Methods: An ectopic model of murine colorectal carcinoma (CT26) was implanted in 7 mice (BALB/c). US radiofrequency data were acquired for the longitudinal plane of tumors in vivo (SSI, Aixplorer, SL15-4 probe, research mode) on days 6 and 14 after start of therapy with an anti-angiogenic (AA: n = 3) or placebo (P: n = 4). The AA used is Pazopanib, an oral tyrosine kinase inhibitor of VEGF receptors 1/-2/-3, platelet-derived growth factor receptors (PDGFR) -alfa/-beta, and c-KIT. A daily dose of 2 mg of AA, diluted in 100µl of solution, was administered per os. Average backscattered power spectra were calculated (FFT, 512 pts, Rectangular gated RF), normalized with respect to a reference phantom and corrected for attenuation (0.4 dB/cm/MHz). ESD and EAC were mapped (2 x 2 mm blocks, with 75% axial and lateral overlap). Tumors were excised and marked to conserve orientation and approximate position relative to US imaging plane. Whole-slice, histological sections were prepared with fluorescent immunohistochemical markers at D6 and D14 for invasive assessment of cell nuclei, apoptosis and vascular endothelium. The Number of Nuclei (NU), the % area of Apoptosis (AP) and % area of Vascular (VA) marker were calculated with image analysis processing for each 333µm by 333µm region of histological sections. QUS and histological maps of each tumor were manually segmented and coregistered using an affine registration method so that matched regions could be compared. Results: The absolute value of the non-parametric Spearman correlation coefficient (RS) was computed separately for each mouse to study the correlation between histological parameters and QUS parameters. Two mice of the AA group showed a moderate correlation (0.4<=RS<0.6) between NU and EAC. Only one mouse in the P group showed strong correlation (0.6<=RS) for [AP vs. ESD], [AP vs. EAC], [VA vs. ESD] and [VA vs. EAC]. The other tumors (1 from AA group and 3 from P group) showed poor correlation (RS<0,4). Additional data is available from 14 other mice (7 from AA group and 7 from P group) and will be analyzed to more fully investigate correlation between the QUS parameters and the histological parameters. Conclusions: This original technique to compare QUS parameter maps and whole slice histology analysis shows a promising evolution for this non-invasive imaging technique. Complete results on 21 mice will be presented in April. Citation Format: Jerome Griffon, Delphine Le Guillou-Buffello, Oumeima Laifa, Alexandre Dizeux, Micheal Oelze, Lori Bridal, Michele Lamuraglia. A comparison between quantitative ultrasound and histology in heterogeneous tumor structure [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 889. doi:10.1158/1538-7445.AM2017-889

Depth-Resolved Backscatter and Differential Interferometric Radar Imaging of Soil Moisture Profiles: Observations and Models of Subsurface Volume Scattering

Microwave observations of soils at L- to X -band are commonly interpreted in terms of surface scattering. However, recent observations of the backscatter and the differential interferometric response indicate that subsurface volume scattering may often be more important than generally thought. The dependence of the subsurface backscatter and interferometric return on soil moisture remains poorly understood as most observations are indirect in that they are confounded with the surface contribution. Here, we aim to elucidate the impact of soil moisture on subsurface volume scattering by employing depth-resolved observations at C -band with a depth resolution of 5–10 cm, thus isolating the subsurface contribution. For the sandy soil analyzed in the experiment, the volumetric subsurface backscattered power is strongly affected by soil moisture (>15 dB): It appears to be governed by the local soil moisture content (local dielectric constant and its spatial variability) and the soil moisture content above (absorption). When the soil moisture changes, the observed interferometric response is consistent with the notion that the subsurface return is mainly governed by the changing optical path through the soil. By modeling and inverting this relation of the interferometric phase to soil moisture, we derive the first spatially continuous estimates of soil moisture profiles based on the clutter. These findings indicate the potential of depth-resolved observations to provide direct, spatially extensive information about the vertical variability of soil moisture, and to inform models of the subsurface response.

Quantifying Backscatter Anisotropy Using the Reference Phantom Method.

Acoustic properties can be exploited to infer and evaluate tissue microstructure. However, common assumptions are that the medium of interest is homogeneous and isotropic, and that its underlying physical properties cause diffuse scattering. In this paper, we describe how we developed and tested novel parameters designed to address isotropy/anisotropy in backscattered echo signal power in complex biological tissues. Specifically, we explored isotropy/anisotropy in backscattered power in isotropic phantoms (spherical glass beads), an anisotropic phantom (dialysis phantom with rodlike fibers), and an in vivo human tissue with well-described anisotropy (bicep muscle). Our approach uses the reference phantom method to compensate for system transfer and diffraction losses when electronically beamsteering a linear array transducer. We define three parameters to quantify the presence and orientation of anisotropic scatterers, as well as address magnitude of anisotropy. We found that these parameters can detect and sense the degree of anisotropy in backscatter in both phantoms and bicep muscle. Bias of the summary anisotropy parameters, induced through a speed of sound mismatch of sample media and reference phantom, was less than 0.2 dB if the speed of sound was within ±20 m/s of the sample media. In summary, these new parameters may be useful for testing the assumption of isotropy as well as providing more detailed information about the underlying microstructural sources of backscatter in complex biological tissues.

Investigations of Backscattering Effects in Optical Fibers and Their Influences on the Link Monitoring

In this paper, first, we employed the coupled-mode theory to investigate the backscattering power characteristics of Rayleigh backscattering (RB) and stimulated Brillouin scattering (SBS) both synchronously and precisely. We discovered how the RB and SBS power changed with pump powers and fiber lengths. The scattering power curves with different pump powers could be divided into three regions. The first was called “the linear region of RB,” in which the pump power was mainly converted into RB and the RB power grew linearly with pump powers. The second region was called “the stimulation region of Brillouin scattering,” in which the power was mainly converted into SBS. In “the gain-saturated region,” when the pump power was much higher than the SBS threshold, both the RB and SBS power were gain-saturated. We also obtained the power curves with different fiber lengths. The power curves were helpful to set up proper launch powers in practical engineering applications, such as optical time-dome reflectometry systems and distributed fiber sensors. Then, we verified our theoretical results by experiments. Finally, according to the measurements and numerical solutions of the coupled-mode equations, we discussed the application of backscattering and gave advice for pump power selections in different fiber link monitoring systems.

Power coupling characteristics between FBG and back-scattering signals

The property and compatibility between fiber Bragg grating (FBG) and back-scattering signals are investigated by employing optical time domain reflectometry. We compare the power spectrums of spontaneous Brillouin scattering (SpBS), simultaneous Brillouin scattering (SBS) and Rayleigh scattering (RS), and coupling mechanism between FBG and back-scattering signal is explored. Experimental results show that the region of FBG contributes to the backscatter power and causes the desired reflection, and the power peak of FBG in SBS power spectrum is the sharpest among back-scattering light power spectrums and broadens with the decrease of spatial resolution. Moreover, the FBG-based method is used to find the location of temperature or stain event for scatter-based distributed sensors.

First observations of electron gyro-harmonic effects under X-mode HF pumping the high latitude ionospheric F-region

We provide the first experimental evidence of the sensitivity of phenomena induced by extraordinary (X-mode) polarized HF high power radio waves to pump frequency stepping across the fifth electron gyro-harmonic (5fce) from below to above. The results were obtained at the EISCAT (European Incoherent Scatter Scientific Association) HF heater facility near Tromsø under effective radiated powers of 456–715MW, when the HF pump wave was transmitted into the magnetic zenith. We have analyzed the behavior and intensities of various spectral lines in the narrowband stimulated electromagnetic emission (SEE) spectra observed far from the heater, HF-enhanced plasma and ion lines (HFPL and HFIL) from EISCAT UHF incoherent scatter radar spectra, and artificial field-aligned irregularities from CUTLASS (Co-operative UK Twin Located Auroral Sounding System) observations, depending on the frequency offset of the pump field relative to the 5fce. At pump frequencies below 5fce the narrowband SEE spectra exhibited very intense so-called stimulated ion Bernstein scatter (SIBS), accompanied by other spectral components, associated with stimulated Brillouin scatter (SBS), which are greatly suppressed and disappeared in the vicinity of 5fce and did not reappear at fH>5fce. As the pump frequency reached 5fce, the abrupt enhancements of the HFPL and HFIL power, the appearance of cascade lines in the plasma line spectra, and the onset of increasing CUTLASS backscatter power occurred. That is opposite to the ordinary mode (O-mode) effects in the vicinity of 5fce. The X-mode pumping at frequencies below and in the vicinity of the fifth electron gyro-harmonic clearly demonstrated an ascending altitude of generation of induced plasma and ion lines from the initial interaction height, whereas for O-mode heating the region of interaction descended. The observations are consistent with the coexistence of the electron acceleration along and across the geomagnetic field at fH<5fce, while only very strong electron acceleration along the magnetic field was observed at fH≥5fce.