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Dusty plasma environments, such as aircraft sheaths and rocket exhaust plumes, significantly affect the propagation of electromagnetic (EM) waves. In this study, the Mie theory and the dyadic Green method were used to calculate the Mie scattering cross section, Debye scattering cross section of the surrounding Debye cloud, and Mie–Debye coherence cross section formed by the two scattering fields. We propose that the Mie–Debye model should be regarded as a whole particle, and the dusty plasma can be simplified by assuming that it is composed of Mie–Debye spherical models of different densities. These assumptions were combined with the scattering characteristics of the microscopic Mie–Debye model and Monte Carlo method to analyze the propagation characteristics of EM waves in dusty plasma. [ABSTRACT FROM AUTHOR]

Calibration isan important step in measuring the electromagnetic scattering from a target. Metal spheres are usually selected as calibrators in the calibration process. However, real spherical calibrators are not perfect spheres, which cause calibration errors due to their geometric irregularity and thus affect the radar cross section (RCS) prediction accuracy for the target. A method of estimation and compensation based on high-resolution range profiles (HRRPs) of calibrators is proposed. First, the scattering of a real-world spherical calibrator is measured using the sweep-angle and the sweep-frequency strategies. Then, the error curves are obtained by comparing the HRRPs of the real-world calibrator and its theoretical solutions at each incident angle, which are also used to compensate the RCS error of the real-world spherical calibrator. Finally, the corrected RCS of the calibrator is adopted to access the accurate RCS of the target being tested. The results of simulation and testing show that the proposed method reduces the root mean square error of the RCS of the target by 40%, which demonstrates the effectiveness of the presentedmethod. [ABSTRACT FROM AUTHOR]

When electromagnetic (EM) coupling exists, false peaks occur periodically in high-resolution range profile (HRRP). These false peaks restrict the improvement of the success rate of the target recognition based on HRRPs. Therefore, identifying these false peaks and removing them is crucial, but has not been thoroughly investigated in the open literature. This letter first studies the EM coupling mechanism in a multiobject system according to the iterative physical optics theory. Then, templates to match the false peaks are constructed based on the established EM coupling theory. Next, cross correlation is performed to recognize and remove the false peaks. To verify the presented method, a metallic multitriangle model is used. The simulation results show that the proposed method can remove the false peaks and find the accurate locations of the metallic triangles. Finally, the practicability of the method is proved through experimental measurement results. [ABSTRACT FROM AUTHOR]

Chaff cloud is a passive jammer that is widely used in many tactical applications. It contains huge numbers of metallic fibers to produce a strong echo. However, electromagnetic (EM) scattering estimation for the chaff cloud is a challenging task since complex EM coupling between chaff elements needs to be taken into account. Actually, if the distance and the angle between two chaff elements are large enough, the EM coupling becomes ignorable. This letter presents an estimation method of the EM coupling radius to designate a region, out of which EM coupling effect can be ignored. A current attenuation formula is first proposed to indicate the relationship between the induced surface currents of any two chaff elements. Using Dijkstra's algorithm, we then find the coupling paths with the weakest attenuation. The EM coupling radius is finally determined by measuring the distance between two ends of the selected paths. Simulation results show that the averaged EM coupling radius is 3.7 times wavelength of the radar in our discussions. [ABSTRACT FROM AUTHOR]

The electromagnetic (EM) scattering properties of the chaff cloud in airflow are rarely addressed in previous works. To deal with this issue, two types of the chaff clouds in airflow are first established based on aerodynamics theories. Then, the K-means algorithm is utilized to divide the chaff cloud into several parts according to the elements’ number density. Meanwhile, the EM transmission property of each part is extracted with the help of the method-of-moments (MoM). Based on this, the vector radiative transfer (VRT) method is introduced to estimate the bistatic scattering coefficients of the established chaff clouds with 40 million elements, which takes into account the radiation pattern of the transmitting antenna and the EM coupling between chaff elements. To speed up the VRT program, parallel computing technologies are adopted. Besides, the verifications of the VRT method are proposed by performing simulations with a numerical method and conducting experiments. Comparative investigations indicate that the results predicted by the proposed VRT method have a good agreement with experimental ones with an error of less than 10%. [ABSTRACT FROM AUTHOR]

In this work, a cooperative optical Internet of Underwater Things (IoUT) system with hybrid decode-amplify-forward (HDAF) strategy is first proposed and investigated over the aggregated underwater wireless optical communication (UWOC) channel. The impacts of absorption, scattering and the misalignment caused by spatial spreading in the sea, which are modeled by the beam spread function (BSF), as well as the oceanic turbulence on the underwater optical links are all included to describe the practical channel characteristics. With the help of Gauss-Hermite and Gauss-Legendre quadrature numerical methods, the closed-form expressions of the average bit error ratio (ABER) and outage probability for this cooperative optical HDAF-IoUT system are derived and verified by the Monte Carlo (MC) simulations. Furthermore, numerical analyses are offered to explore the effects of water type, turbulence strength, relay location and power allocation scheme on this HDAF-IoUT system. The performance of this optical system over the mixture Exponential Generalized Gamma (EGG) channel is also given for comparison. The obtained results indicate that the optical HDAF-IoUT system is superior to the IoUT system with fixed amplify-and-forward (FAF) strategy, and has a better performance when the relay is close to the middle position for a fixed power allocation scheme. This work is beneficial for the cooperative system design in IoUT network. [ABSTRACT FROM AUTHOR]

In the past, most of the transient electromagnetic (EM) analyses focused on the scattering from the target. The transient scattering from rough surface was rarely studied, especially for the layered rough surface. When the target is above the rough surface, it needs to solve the composite transient scattering from the rough surface and the target above it. In this article, we mainly focus on the time-domain (TD) analysis for transient scattering from the target and layered rough surface based on time-domain ray tracing (TDRT) modeling. Applying geometrical optics (GO), the multiple bounces of the transient EM waves between layered rough surfaces and target are traced to obtain the incident field of the irradiated surfaces. Then considering the particularity of the layered rough surface, we modify TD Gordon integral and reduce the TD physical optics (TDPO) integral to closed-form expressions to improve the computing efficiency. To demonstrate the efficiency and accuracy of the proposed algorithm, the transient scattering simulations of the composite model involving target and layered rough surface are compared with frequency-domain ray tracing (FDRT) with inverse fast Fourier transform (IFFT), as well as the results obtained by the multilevel fast multipole algorithm (MLFMA) of FEKO in conjunction with IFFT (IFFT-MLFMA). The characteristics of transient scattering from the composite model are further studied to show the physical phenomenon of scattering mechanisms. Specifically, the transient scattering from the composite model for different parameters is simulated for sensitivity investigation of the transient scattering to the variations in the related parameters. [ABSTRACT FROM AUTHOR]

In this article, a theoretical study is carried out to seek an approach to remotely measure the thickness of the oil film. It is known that it is difficult to probe the oil thickness using a microwave radar due to the fact the dielectric constant of oil is very small compared with seawater for microwave frequencies. While in the range of terahertz (THz) electromagnetic (EM) wave frequency, the dielectric constants of oil and seawater are comparable, resulting in the THz EM fields scattered from the air–oil interface and those from the oil–water interface can produce constructive and destructive interference with the variation in the oil film thickness. Based on this principle, the sensitivity of the THz EM wave to the oil thickness is investigated in this work. First, the oil–seawater two-layer medium is equivalent to a single-layer medium by an equivalent dielectric constant model. Then, the THz EM scattering from the oil-covered sea surface is simulated using the first-order small slope approximation method (SSA-1) and the obtained equivalent dielectric constant. Meanwhile, the influences caused by the damping effect of the oil film, the reduction for friction velocity, and the change in equivalent permittivity on the normalized radar cross section (NRCS) are analyzed. The numerical results show that the NRCSs of THz frequencies are more sensitive to the change in oil thickness than that of microwave frequencies. This property makes the THz EM wave have the potential to probe the thickness of the oil film. [ABSTRACT FROM AUTHOR]

A new electromagnetic (EM) calculation model, the inhomogeneity zonal medium model (IZMM) (based on the physical optics (PO) method), is proposed to calculate and analyze the EM scattering characteristics of hypersonic vehicle covered with a plasma sheath. First, the flow field of the plasma sheath is divided into nonuniform calculation subregions with different spacing sizes. The shape of the external flow field of the aircraft is modeled by fitting with a paraboloid and circular platform with different radii. Then, the electron density, temperature, and pressure distribution are obtained by collecting data from different points in the flow field of the sheath. Finally, a piecewise PO method is used to calculate the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath from $L$ -band to $X$ -band. The numerical results show that the EM scattering characteristics of a target spacecraft covered with a plasma sheath can be described more accurately by using zoned medium model simulation. Under different flying conditions, the BRCS of hypersonic vehicle covered with a plasma sheath appears to be reduced to different degrees in the $S$ -band and the band range of 7–11 GHz, and a large attenuation of BRCS occurs in the head area of the aircraft. The research results enrich the EM modeling method of hypersonic vehicles, overcome some shortcomings of the existing PO method, and provide technical support and innovative ideas for the accurate analysis of the EM scattering characteristics of hypersonic targets. [ABSTRACT FROM AUTHOR]

Time-domain physical optics (TDPO) contour integral representations are developed for backscattered near fields from a perfectly conducting surface illuminated by a dipole source. The proposed representations are derived from the TDPO surface integral representations by introducing two theorems: surface gradient and surface divergence theorems. The proposed representations are free from singularities for all the source/observer positions in which the dipole antenna is located. In addition, the time-domain physical theory of diffraction is introduced to modify the physical optical field considering the effect of the edge diffraction. Numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

The role of cluster scattering on electron transport properties of ZnMgO/ZnO heterostructures considering three- and five-valley conduction band models was investigated with an ensemble Monte Carlo program developed by us. The cluster scattering is modeled as an elastic collision, in which the electrons confined in ZnO well are scattered by MgZnO clusters. The interface roughness scattering, dislocation scattering, alloy disorder scattering, and phonon scattering are also taken into account in the simulation. For both energy band models, it is found that Mg composition fluctuation ( $\eta $ ), the cluster size ( $\xi $ ), and the 2-D electron gas sheet density (Ns) have a great impact on low-field mobility owing to the cluster scattering. But the low-field mobility of five-valley is slightly smaller than that of three-valley due to the increased total scattering. A further comparison of velocity-field transport characteristics shows that the cluster scattering is prevailing at low temperature, and it significantly decreases the electron drift velocity for both energy band models. Moreover, the threshold electric fields of these two models are both enhanced by approximately 10 kV/cm at 10 K with cluster scatteringconsidered. This paper is beneficial for designing ZnMgO/ZnO heterostructure devices. [ABSTRACT FROM AUTHOR]

This letter focuses on scattering from rough sea surface covered by insoluble oil. Oil film damps the capillary wave of the rough sea surface, which leads to a smooth profile of the contaminated sea. We investigate this phenomenon using a highly efficient iterative model based on physical optics (PO) and Huygens' equivalence principle. PO is used to calculate the scattering from the oil film and underlying rough sea surface. The Huygens equivalence principle and iterative strategy are employed to evaluate the coupled scattering between the oil film and rough sea surface. The scattering of contaminated rough sea surface based on the iterative model is compared with those using the method of moments as well as computational time and memory requirements. Then, the influence of some important parameters, such as wind speed, oil thickness, incident wave frequency, and oil coverage, on scattering is investigated and discussed in detail. [ABSTRACT FROM PUBLISHER]

The high-field electron transport properties of ZnMgO/ZnO heterostructures considering multisubband conduction were systematically investigated with an ensemble Monte Carlo program developed by us. Electronic band structures were obtained by first-principles calculations using density functional theory, which provides more accurate parameters to calculate the electronic states and transport characteristics of 2-D electron gas. Wave functions and energy levels describing the subband structure were achieved to determine the 2-D scattering rates by solving the Schrödinger and Poisson equations self-consistently. The highest electron mobility gained at room temperature was approximately 4.23\times 10^\mathrm 2 cm2/Vs. The negative differential mobility was observed with a threshold electric field of approximately 80 kV/cm. The peak drift velocity of the Zn0.694Mg0.306O/ZnO heterostructure at 200 KV was about 2.011\times 10^8 cm/s. This paper benefits the development of high-performance ZnMgO/ZnO heterostructure devices. [ABSTRACT FROM AUTHOR]

This paper presents a feasible and efficient scattering model of the time-varying complex sea surface process to the field of sea spike modeling. To describe the phenomena of sea spikes as well as the “super events” from realistic sea clutter, wedges are posited on the two-scale sea surface to provide an approximate simulation of the breaking waves. The scattering of the wedge and multiple reflections that occur from the sea and wedges are considered in ray tracing for a large HH/VV ratio. With this technique, we obtained the time sequence of the time-varying sea surface and identified the spiking events in the background. Sea clutter properties with breaking waves are compared with that of the sea. Results indicate that spiking events are more likely to occur in the sea with breaking waves. The probability distribution function (PDF) curve of the sea surface with breaking waves has a heavy trail in the large amplitude region. The decorrelation time of the sea with breaking waves is significantly longer compared with the sea without breaking waves, particularly, for HH polarization. The spike properties of sea clutter in different wind speeds and resolutions are also investigated. Results show that spike events are more likely to happen under a high sea state and radar resolution. The Doppler spectrum of the sea with breaking waves showed remarkable improvement for both polarizations. All simulation results indicate that the proposed scattering model effectively stimulates sea clutter with a low grazing incident angle and explains the physical mechanism of the sea spikes. [ABSTRACT FROM PUBLISHER]

Abstract: The scattering of an axicon-generated Bessel beam (AGBB) by a sphere is investigated. An analytical formula for the calculation of Beam Shape Coefficients (BSCs) of an AGBB is first derived according to the Integral Localized Approximation (ILA). After the verification of BSCs by the comparison of the reconstructed field using BSCs with the original field obtained from the definition, the far-field scattered intensity is evaluated, and the rainbow produced by AGBB is also studied. The effect of angle on the far-field scattered intensity and the first rainbow is analyzed in detail. Such investigation could provide a useful tool for the research on radiation forces and torques, which is important in optical tweezers and the related optical manipulation applications. [Copyright &y& Elsevier]