Beam Broadening Research Articles

Analysis of Receiving Beam Broadening and Detection Range of LiDAR Based on Diffractive Optical System

Analysis of Receiving Beam Broadening and Detection Range of LiDAR Based on Diffractive Optical System

DDMA-MIMO Observations With the MU Radar: Validation by Measuring a Beam Broadening Effect

The phased-array radar, basically developed with the defense systems, has mainly utilized for the atmospheric radar and the wind profiling radar in the field of meteorological remote sensing, and recently it has also applied to the weather radar for research purposes. As a further development of phased-array technology, the “Multiple-Input Multiple-Output (MIMO) technique,” which has been developed in the field of communication systems, has been applied to radars. With the MIMO radar, it is possible to create a virtual antenna aperture plane beyond the actual antenna and to reduce the actual antenna size compared to that of the conventional antenna while maintaining the angular resolution. This effect is expected to reduce costs, which is one of the major hurdles in expanding phased array radars instead of parabolic antenna systems. In order to confirm the effect, an experimental observation was performed using the MU radar which is a VHF-band phased array atmospheric radar with multi-channel receivers. The MIMO technique requires orthogonal waveforms on each transmitter to identify the transmitted signals with multiple receivers, and various methods are known to realize orthogonality. In this paper, we focus on the “ Doppler Division Multiple Access (DDMA)” MIMO technique, with which slightly different frequencies are selected as transmit waveforms to separate in each receiver in the Doppler frequency domain. The observation results by measuring a beam broadening effect with the MU radar indicate that it will be a key technique for the atmospheric radar in the near future.

Novel Beamforming Approach for Secure Communication in UDN to Maximize Secrecy Rate and Fairness Security Assessment

With an unprecedented amount of sensitive data and private information generated by mobile devices, security becomes critical for the emerging ultradense network. The conventional approach of encryption is not suitable to provide desired level of security as a result of increased scalability. Thus, physical layer protection is stressed to ensure secure transmission to users in dense environment. In this paper, we examine the security challenges of high speed users for ultradense network under dense picocells deployment. Initially, we consider a dense condition where users are randomly distributed within the picocell. Targeting the problem of security for vehicular users, we propose a beam broadening (BB) and beam merging (BM) techniques that ensure reliable transmission between source and destination. We prove the effectiveness of proposed approach through mathematical and simulation analysis that guarantees high QoS and secure communication. Based on the above formulations, we examine the reliability and potential capability of BB and BM with the measurement of fairness security assessment (FSA). Numerical results demonstrate that BM and BB can achieve higher value of secrecy rate and FSA, in comparison to conventional beamforming. To end this, the complexity analysis is performed in terms of beam generations as a function of speed of user.

Beam Broadening Measured in Transmission Mode at Low Electron Energies in a Scanning Electron Microscope

The broadening of the electron beam in the sample has to be considered when performing scanning transmission electron microscopy (STEM) at low primary electron energies. This work presents direct measurements of the beam broadening in a range of materials. The experimental results are compared with the theoretical model by Gauvin and Rudinsky that uses the concept of anomalous diffusion to obtain an analytical equation for the beam broadening.

Robust LCMV Beamformer for Direction of Arrival Mismatch Without Beam Broadening

In this work, we propose a new and efficient algorithm to mitigate the signal look direction error problem in adaptive beamforming without broadening the main beam. The algorithm exploits a reference lobe in the region of signal look direction error. This reference lobe is the main beam of the generalized sidelobe canceller when there is no direction of arrival mismatch for the desired signal. The desired pattern is forced to follow the reference beam in the region of signal look direction error by utilizing multiple additional constraints. Simulations are performed in MATLAB to check and test the validity of the proposed algorithm on the basis of different scenarios.

The Influence of Beam Broadening on the Spatial Resolution of Annular Dark Field Scanning Transmission Electron Microscopy

The spatial resolution of aberration-corrected annular dark field scanning transmission electron microscopy was studied as function of the vertical position z within a sample. The samples consisted of gold nanoparticles (AuNPs) positioned in different horizontal layers within aluminum matrices of 0.6 and 1.0 µm thickness. The highest resolution was achieved in the top layer, whereas the resolution was reduced by beam broadening for AuNPs deeper in the sample. To examine the influence of the beam broadening, the intensity profiles of line scans over nanoparticles at a certain vertical location were analyzed. The experimental data were compared with Monte Carlo simulations that accurately matched the data. The spatial resolution was also calculated using three different theoretical models of the beam blurring as function of the vertical position within the sample. One model considered beam blurring to occur as a single scattering event but was found to be inaccurate for larger depths of the AuNPs in the sample. Two models were adapted and evaluated that include estimates for multiple scattering, and these described the data with sufficient accuracy to be able to predict the resolution. The beam broadening depended on z 1.5 in all three models.

涡旋光束在湍流大气中的光束扩展

涡旋光束在湍流大气中的光束扩展

Influence of Beam Broadening on the Accuracy of Radar Polarimetric Rainfall Estimation

Abstract The quantitative estimation of rain rates using meteorological radar has been a major theme in radar meteorology and radar hydrology. The increase of interest in polarimetric radar is in part because polarization diversity can reduce the effect on radar precipitation estimates caused by raindrop size variability, which has allowed progress on radar rainfall estimation and on hydrometeorological applications. From an operational point of view, the promises regarding the improvement of radar rainfall accuracy have not yet been completely proven. The main reason behind these limits is the geometry of radar measurements combined with the variability of the spatial structure of the precipitation systems. To overcome these difficulties, a methodology has been developed to transform the estimated drop size distribution (DSD) provided by a vertically pointing micro rain radar to a profile given by a ground-based polarimetric radar. As a result, the rainfall rate at the ground is fixed at all ranges, whereas the broadening beam encompasses a large variability of DSDs. The resulting DSD profile is used to simulate the corresponding profile of radar measurements at C band. Rainfall algorithms based on polarimetric radar measurements were taken into account to estimate the rainfall into the radar beam. Finally, merit factors were used to achieve a quantitative analysis of the performance of the rainfall algorithm in comparison with the corresponding measurements at the ground obtained from a 2D video disdrometer (2DVD) that was positioned beside the micro rain radar. In this method, the behavior change of the merit factors in the range is directly attributable to the DSD variability inside the radar measurement volume, thus providing an assessment of the effects due to beam broadening.

Beam Broadening in Transmission EBSD

Beam Broadening in Transmission EBSD

Thickness-Dependent Beam Broadening in Transmission EBSD

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Thermally induced polarizabilities and dipole moments of small tin clusters

We study the influence of thermal excitation on the electric susceptibilities for Sn(6) and Sn(7) clusters by molecular beam electric deflection and Monte-Carlo simulations in conjunction with quantum-chemical calculations. At low temperatures (40 K), no field-induced broadening of the Sn(6) and Sn(7) cluster beams are observed, in agreement with vanishing permanent electric dipole moments due to their centro-symmetrical ground states. The electric polarizabilities of Sn(6) and Sn(7), as inferred from the field-induced molecular beam deflection, are in good agreement with the quantum-chemical predictions. At elevated temperatures of 50-100 K, increased polarizabilities of about 2-3 Å(3) are obtained. Also, we found indications of a field-induced beam broadening which points to the existence of permanent dipole moments of about 0.01-0.02 D per atom at higher temperatures. These results cannot be explained by thermal excitations within a harmonic oscillator model, which would yield a temperature-independent polarizability and fluxional, but not permanent, dipole moments. We analyze this behavior by Monte-Carlo simulations in order to compute average temperature-induced electric dipole moments. For that purpose, we developed a novel technique for predicting observables sampled on the quantum-chemical potential energy surface by an umbrella sampling correction of Monte-Carlo results obtained from simulations utilizing an empirical potential. The calculated, fluxional dipole moments are in tune with the observed beam broadenings. The cluster dynamics underlying the polarizability appear to be intermediate between rigid and floppy molecules which leads to the conclusion that the rotational, not the vibrational temperature seems to be the key parameter that determines the temperature dependence of the polarizability.

Antenna Beam Broadening in Multifunction Phased Array Radar

of element pattern, mutual coupling between elements, phase quantization, amplitude and phase error and elements failure rates on array pattern are discussed. Target angle measurement and side lobe cancelling, in order to reduce jamming power through side lobes, is illustrated in this antenna. Also antenna beam width is broadened with dierent methods and compared with narrow beam characteristics. It is shown that, for special broadening factors, beam broadening may lead to a better coverage and power eciency relative to narrow beam antenna.

Impacts of Beam Broadening and Earth Curvature on Storm-Scale 3D Variational Data Assimilation of Radial Velocity with Two Doppler Radars

Abstract The radar ray path and beam broadening equations are important for assimilation of radar data into numerical weather prediction (NWP) models. They can be used to determine the physical location of each radar measurement and to properly map the atmospheric state variables from the model grid to the radar measurement space as part of the forward observation operators. Historically, different degrees of approximations have been made with these equations; however, no systematic evaluation of their impact exists, at least in the context of variational data assimilation. This study examines the effects of simplifying ray path and ray broadening calculations on the radar data assimilation in a 3D variational data assimilation (3DVAR) system. Several groups of Observational System Simulation Experiments (OSSEs) are performed to test the impact of these equations to radar data assimilation with an idealized tornadic thunderstorm case. This study shows that the errors caused by simplifications vary with the distance between the analyzed storm and the radar. For single time level wind analysis, as the surface range increases, the impact of beam broadening on analyzed wind field becomes evident and can cause relatively large error for distances beyond 150 km. The impact of the earth’s curvature is more significant, even for distances beyond 60 km, because it places the data at the wrong vertical location. The impact of refractive index gradient is also tested. It is shown that the variations of refractive index gradient have a very small impact on the wind analysis results. Two time series of 1-h-long data assimilation experiments are further conducted to illustrate the impact of the beam broadening and earth curvature on all retrieved model variables. It is shown that all model variables can be retrieved to some degrees in all data assimilation experiments. Similar to the wind analysis experiments, the impacts of both factors are not obvious when radars are relatively close to the storm. When the radars are far from the storm (especially beyond 150 km), overlooking beam broadening degrades the accuracy of assimilation results slightly, whereas ignoring the earth’s curvature leads to significant errors.

The Impact of Beam Broadening on the Quality of Radar Polarimetric Data

Abstract The impact of beam broadening on the quality of radar polarimetric data in the presence of nonuniform beam filling (NBF) is examined both theoretically and experimentally. Cross-beam gradients of radar reflectivity Z, differential reflectivity ZDR, and differential phase ΦDP within the radar resolution volume may produce significant biases of ZDR, ΦDP, and the cross-correlation coefficient ρhv. These biases increase with range as a result of progressive broadening of the radar beam. They are also larger at shorter radar wavelengths and wider antenna beams. Simple analytical formulas are suggested for estimating the NBF-induced biases from the measured vertical and horizontal gradients of Z, ZDR, and ΦDP. Analysis of polarimetric data collected by the KOUN Weather Surveillance Radar-1988 Doppler (WSR-88D) demonstrates that frequently observed perturbations of the radial ΦDP profiles and radially oriented “valleys” of ρhv depression can be qualitatively and quantitatively explained using the suggested NBF model.

Characterization of microstructures with sizes from the sub-nm to the μm-range by extended small-angle neutron scattering

Conventional SANS facilities cover scattering vectors q between about 0.01 and 3 nm −1 and are well suited for analyzing microstructures in materials with sizes from 1 to about 100 nm. At the Geesthacht neutron facility (GeNF), this range has been greatly extended. Larger values of q (up to 25 nm −1) are made accessible at the pin-hole facility SANS-2 by means of a second area detector, which can be rotated around the sample. Smaller q-values down to 10 −3 nm −1 can be covered at the SANS-2 by means of the beam broadening (BB) technique. With the use of a double-crystal diffractometer (DCD) still smaller q-values down to 10 −4 nm −1 become accessible. Investigations of extremely small structures (cluster with radii of only 0.3 nm), and extremely large ones (creep pores in ceramics with size up to some μm) are presented.

Variations in the Probe Beam Broadening with Operating Conditions in ESEM: Monte-Carlo Simulations and Edx Measurements

Abstract An understanding of the scattering of an electron beam as it passes through a volume of low pressure gas is of critical importance for users of Low Vacuum and Environmental Scanning Electron Microscopes (LV-SEM & ESEM respectively) The ‘skirting’ of the primary beam as a result of scattering is of particular importance in X-ray microanalysis where scattered electrons, falling onto the sample away from the probe beam, can adversely affect the spatial resolution of the X-ray signal. A number of studies have attempted to quantify the width of the probe beam experimentally and hence determine optimum microscope operating parameters. Theoretical and computational work modelling the interactions of the beam with the gas have suggested that the shape of the probe beam can be modelled by some form of Gaussian. Experimental measurements, however, suggest that the probe has a skirted form rather than a Gaussian one.

Joint use of double crystal diffractometry, beam broadening and conventional SANS for analysis of creep pore formation in liquid-phase sintered alumina

The formation of pores during creep initiates the failure of ceramic materials used for high-temperature applications. Thus, the determination of pore sizes and their number densities is of key importance in obtaining an understanding of the failure mechanisms. In former investigations it was shown that small-angle neutron scattering (SANS) and beam broadening (BB) are powerful experimental techniques for the investigation of pore size distribution. In this paper it is noted that in addition to these methods complementary high resolution SANS experiments have to be performed in order to determine pore size distributions reliably in the size range from a few nanometers to several micrometers. The evolution of such pore size distributions have been observed during the creep of liquid-phase sintered alumina.

The Application of a Model Function Describing Beam Broadening to Elemental Analysis of Rapidly Varying Concentration Gradients

As microanalysis by X-ray spectrometry in STEM is increasingly applied in materials science, a particular set of problems is being identified in which beam spreading in the sample and the associated concept of the X-ray spatial resolution are crucial to the interpretation of experimental data. These problems include the investigation of solute segregation to, or depletion near, grain boundaries, the determination of composition profiles across dendrite cell walls, especially in rapidly solidified material, composition determination in phase separated systems where the separation takes place on a fine scale, as for example in spinodal decomposition, and many other problems involving small precipitates or interfaces between phases. We intend to discuss beam spreading separately at this meeting. We propose the use of a model, parameterized function to describe beam spreading for application to the problems mentioned above. With this description, an analytic expression for the X-ray emission from a region of known or modeled composition variation can be obtained, being proportional to the convolution of the two functions describing the electron intensity distribution and the concentration variatioa For many simple cases this expression can be simply solved, either analytically or with the aid of a small computer or programmable calculator.

Laser Beam Broadening in Atmospheric Propagation

By using the Born approximation and the Gaussian model for the correlation of refractive index fluctuations in the atmosphere, an expression for the power in the first‐scattered field of the TEM∞ mode is obtained. It is demonstrated that the second‐scattered field does not contribute to beam broadening in the lowest‐order approximation. The total power in the first‐scattered field is found. The transverse profile of the scattered power is shown to be a function of a single parameter ΘL, which depends strongly on the ratio of the beam radius to the scale of turbulence a/lo. Values of lo and the mean square fluctuation of the refractive index (n12) are determined in an illustrative comparison with experimental data of the theoretical profile of a broadened beam.

LEED Beam Broadening as a Result of Sputtering Damage

Investigations of sputtering damage based only on changes in LEED intensities are unable to distinguish between lattice distortions resulting from bombardment atoms imbedded in the lattice and localized structural defects such as vacancies. Such a distinction can be made on the basis of beam broadening. The observed beam broadening due to bombardment of a clean annealed (100) nickel surface with 500-eV argon ions can be accounted for by assuming that a strain of 0.05 is introduced by occluded argon atoms. As a result of the finite beam width, plots of the intensity of the beam as a function of electron energy are affected by the mechanics of recording and reducing the data. It is shown that the correct intensity can be obtained regardless of beam width by superimposing plots of collector current versus electron energy for all values of the collector angle.