Electromagnetic Multi–Gaussian Speckle

Generalizing our prior work on scalar multi-Gaussian (MG) distributed optical fields, we introduce the two-dimensional instantaneous electric-field vector whose components are jointly MG distributed. We then derive the single-point Stokes parameter probability density functions (PDFs) of MG-distributed light having an arbitrary degree and state of polarization. We show, in particular, that the intensity contrast of such a field can be tuned to values smaller or larger than unity. We validate our analysis by generating an example partially polarized MG field with a specified single-point polarization matrix using two different Monte Carlo simulation methods. We then compute the joint PDFs of the instantaneous field components and the Stokes parameter PDFs from the simulated MG fields, while comparing the results of both Monte Carlo methods to the corresponding theory. Lastly, we discuss the strengths, weaknesses, and applicability of both simulation methods in generating MG fields.

Analysis of The Phase Velocities of (Pure, Slow And Fast ) Alfvèn Waves In The E Region of The Ionosphere For Low Latitudes

In this paper, (pure, slow, and fast) Alfvèn waves for the accepted conditions in Northern-hemisphere at E-region of ionospheric plasma were calculated with low latitudes by using Eq. (20,25-26) and the real geometry of Earth’s magnetic field, at hours 12.00 LT for the 1990 year which sunspot is maximum. One of the most important results of this study is to show analytically that the “MHD modes= (pure, slow and fast) Alfvèn waves” depend not only on the angle between the wave propagation vector (k) and the magnetic field (B) but also on the declination (D=It is the angle value between the direction of the sun's rays and the equatorial plane) and magnetic dip angle (I=It is the angle between real north and magnetic north). From the results obtained, the behavior of the magnitudes of the squares of the phase velocities of all MHD modes is consistent with the behavior of the distribution of electron density with low geographic latitude, even if the magnetic field vector is both perpendicular and parallel to the propagation vector of the wave. In parallel, the phase velocities of the waves are greater in summer than in winter. It has been determined that the propagation velocities of the fast and slow MHD mode in the magnetic equatorial trough region at (q = I) are very small, the energy is almost non-existent, but if q = 90 + I, the energy increases with latitude and is approximately maximum at the low latitude limit. It can be said that the minimum points are between 0-10 oN latitudes where the wave energies are the smallest, and the maximum points are between 20-30 oN latitudes the wave energies are the biggest.

Kinematical modeling of circular and elliptical polarization of the polarized light via screw transformation

In this paper, it is shown that the motion of a polarized light wave in an optical fiber has a special meaning that relates the scalar and vector part of the dual quaternion to the kinematics concept of a screw. We describe the circular and elliptical polarization of a light wave according to how the electric field vector varies in a projection onto a plane perpendicular to the propagation direction using the Clifford algebra of the dual quaternion. Also, we determine the circular-Rytov curve (CR ) and elliptical-Rytov curve (ER ), which described the paths traced out by the tip of the electric field vector as it propagates in space, related to the polarization state of the electric field ε. The elliptical and circular polarization states are expressed by using the four Stokes parameters and their matrix form. Furthermore, some motivating examples are given and visualized their images with the help of the MAPLE program.

Sudden Obstacle Appearance Detection by Analyzing Flow Field Vector for Small-Sized UAV

Achieving a reliable obstacle detection and avoidance system that can provide an effective safe avoidance path for small unmanned aerial vehicle (UAV) is very challenging due to its physical size and weight constraints. Prior works tend to employ the vision based-sensor as the main detection sensor but resulting to high dependency on texture appearance while not having a distance sensing capabilities. The previous system only focused on the detection of the static frontal obstacle without observing the environment which may have moving obstacles. On the other hand, most of the wide spectrum range sensors are heavy and expensive hence not suitable for small UAV. In this work, integration of different based sensors was proposed for a small UAV in detecting unpredictable obstacle appearance situation. The detection of the obstacle is accomplished by analysing the flow field vectors in the image frames sequence. The proposed system was evaluated by conducting the experiments in a real environment which consisted of different configuration of the obstacles. The results from the experiment show that the success rate for detecting unpredictable obstacle appearance is high which is 70% and above. Even though some of the introduced obstacles are considered to have poor texture appearances on their surface, the proposed obstacle detection system was still able to detect the correct appearance movement of the obstacles by detecting the edges.

Muscle Fatigue Revisited – Insights From Optically Pumped Magnetometers

So far, surface electromyography (sEMG) has been the method of choice to detect and evaluate muscle fatigue. However, recent advancements in non-cryogenic quantum sensors, such as optically pumped magnetometers (OPMs), enable interesting possibilities to flexibly record biomagnetic signals. Yet, a magnetomyographic investigation of muscular fatigue is still missing. Here, we simultaneously used sEMG (4 surface electrode) and OPM-based magnetomyography (OPM-MMG, 4 sensors) to detect muscle fatigue during a 3 × 1-min isometric contractions of the left rectus femoris muscle in 7 healthy participants. Both signals exhibited the characteristic spectral compression distinctive for muscle fatigue. OPM-MMG and sEMG slope values, used to quantify the spectral compression of the signals, were positively correlated, displaying similarity between the techniques. Additionally, the analysis of the different components of the magnetic field vector enabled speculations regarding the propagation of the muscle action potentials (MAPs). Altogether these results show the feasibility of the magnetomyographic approach with OPMs and propose a potential alternative to sEMG for the study of muscle fatigue.

FEM Analysis of Piezoelectric Resonator Polarization Process

The polarization of the piezoelectric resonator depends on the direction of the applied electric field. The direction of the applied electric field is determined by the shape of the resonator and the position of the electrodes. In case of resonators with electrodes incompletely covering their bases, an inhomogeneous electric field is generated, which results in an inhomogeneous polarization of the resonator. The resonator will be polarized in some places either in a direction other than the desired one or not polarized at all. The aim of this work is to analyze the polarization process on resonators with electrodes incompletely covering their bases. The physical description is given by the linear piezoelectric equations, the Gaussian equation for the description of the electric field and by Newton’s law of force. On this basis, a FEM model is developed and used to analyze the polarization process. The results of the calculation of the electric field vector distribution are presented. Finally, the areas are identified in which polarization in the desired direction is achieved in the resonator as well as the ones where no polarization occurs.

A Decoupled Calibration Method Based on the Multi-Output Support Vector Regression Algorithm for Three-Dimensional Electric-Field Sensors

Aiming at the problem that the measured accuracy of the electric field intensity which is affected by the coupling interference by sensor output signal from the component of a three dimensional electric field, the causes of the coupling error was analyzed, and a decoupled calibration method based on support vector regression algorithm for three-dimensional electric field sensor is proposed. The solution of the decoupled calibration matrix was regarded as a multi-objective optimization process, and the optimal decoupling calibration matrix was obtained by the ν-SVR algorithm. The complex inverse calculation of the matrix was avoided, and the calculation error was reduced. A rotary calibration device was designed to accurately measure the angle between the induction electrode of the sensor and the electric-field vector, and an accurate calculation model of the theoretical electric field was established. The experimental results showed that the error between the calculated and theoretical values of the electric-field components obtained by the proposed method were smaller than those obtained by the traditional inverse matrix calibration method, the accuracy of the calibration was improved, the rationality of the calibration method was proven, and the accuracy of the three-dimensional electric-field intensity measurements was further improved.

Improvement of the Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Inversion Code

A spectral line inversion code, Very Fast Inversion of the Stokes Vector (VFISV), has been used since 2010 May to infer the solar atmospheric parameters from the spectropolarimetric observations taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. The magnetic filling factor, the fraction of the surface with a resolution element occupied by magnetic field, is set to have a constant value of 1 in the current version of VFISV. This report describes an improved inversion strategy for the spectropolarimetric data observed with HMI for magnetic field strengths of intermediate values in areas spatially not fully resolved. The VFISV inversion code has been modified to enable inversion of the Stokes profiles with two different components: one magnetic and one nonmagnetic. In this scheme, both components share the atmospheric components except for the magnetic field vector. In order to determine whether the new strategy is useful, we evaluate the inferred parameters inverted with one magnetic component (the original version of the HMI inversion) and with two components (the improved version) using a Bayesian analysis. In pixels with intermediate magnetic field strengths (e.g., plages), the new version provides statistically significant values of filling fraction and magnetic field vector. Not only does the fitting of the Stokes profile improve, but also the inference of the magnetic parameters and line-of-sight velocity are obtained uniquely. The new strategy is also proven to be effective for mitigating the anomalous hemispheric bias in the east–west magnetic field component in moderate field regions.

Computer technology for interpreting vector measurements of the magnetic field

Computer technology is presented to solve the inverse problem of magnetic field vector measurements using software and algorithmic support for an automated system to interpret potential fields. The technology includes constructing a numerical model of the magnetic field of the studied area, forming an initial approximation model, assessing the depth of the sources and their magnetization. An approximation structure is used to describe the sources of anomalies (a set of uniformly magnetized polygonal prisms). To solve the problem, we used real vector measurements of the magnetic field by the components Xа, Ya, Zа, Та in the sections of Gruzsko South and Gruzsko Severnaya. Geologically, the area belongs to the central part of the Ukrainian Shield — the Kirovograd tectonic megablock. The area of work is confined to the Subotsko-Moshorin latitudinal fault zone. The possibility of comparing the results of the interpretation of anomalies on each profile by the components of the anomalous magnetic field increases the reliability of the geological interpretation of magnetic prospecting data compared to the interpretation of modular surveys. The presence of vector measurements greatly facilitates the ability to determine the parameters of anomalous objects, which makes it possible to obtain more reliable solutions to the inverse problem. The use of vector information makes it possible to localize geological sources more successfully, thereby reducing the amount of work.

Determination of the Brewster angle of the wave reflected from a plate with dielectric losses

In free space, the permittivity of materials is usually determined by the value of the Brewster angle using the angular dependences of the amplitude and phase of the wave reflected from the material plate. An expression corresponding to materials without dielectric and magnetic losses is used as a calculation model. Experimental studies of the parameters of the wave reflected from dielectric materials show the discrepancies with theoretical calculations known as deviations from the Fresnel laws. We present the results of determining the Brewster angle of the wave reflected from a plate made of a material with dielectric losses. The angular dependences of the amplitude and phase of the reflected wave were calculated using the numerical solution of the problem of falling at an arbitrary angle of a plane linearly polarized wave with an electric field vector lying in the plane of incidence on a plate of a dielectric material with complex values of the dielectric and magnetic permittivity. They were used to determine the angles corresponding to the minimum reflection coefficient depending on the dielectric losses of the plate material. The differences between the numerical calculations and the data obtained using the Brewster angle formula were noted, which increased with increasing dielectric losses of the material. From the condition that the modulus of the reflected wave amplitude is equal to zero, a different formula for calculating the Brewster angle for a material with losses is analytically obtained. The results of calculations using this formula coincided with the calculations for the reflected wave when solving the classical problem of the inclined incidence of a plane wave on a plate of a dielectric material in the framework of geometric optics. The results obtained can be used to determine the Brewster angle for a wave reflected from a plate with magnetic and dielectric losses.