Cross Sections For Targets Research Articles

Anisotropic hypocycloid inspired 3-bit digital coding metasurface for radar cross section reduction

Abstract Recently, researchers have realized various exotic electromagnetic control devices using the coded metasurfaces, sparking a broad investigation into the phase or amplitude-based encoding method, as well as their combination, in the field of metasurface design. In this paper, to evaluate the influence of random mutual coupling between the adjacent element on the scattering performance of metasurface, and also to minimize the backward radar cross section (RCS) of metal plate targets, a novel encoding approach combining the reflection phase and element-form has been proposed. During the implementation process, an anisotropic hypocycloid inspired 3-bit digital coding metasurface was designed. It consists of 9 different element-forms, with each capable of providing 7 phase states. Simulation results demonstrate that the random mutual coupling introduced by the proposed elements does not significantly affect the RCS performance of the metasurface. With a good polarization insensitivity property for both linearly and circularly polarized waves, the designed 3-bit digital coding metasurface can achieve more than 20 dB RCS reduction at 10 GHz, while simultaneously transmitting additional information by encoding the element forms. The good consistency between theoretical simulation and sample testing unequivocally validates the precision of the design, this paper may serve as a useful reference for expanding the design methods of metasurfaces.

Analysis of multi-photon quantum radar cross section for targets in atmospheric medium

Analysis of multi-photon quantum radar cross section for targets in atmospheric medium

Absolute Calibration of a UAV-Mounted Ultra-Wideband Software-Defined Radar Using an External Target in the Near-Field

We describe a method to calibrate a Software-Defined Radar (SDRadar) system mounted on an uncrewed aerial vehicle (UAV) with an ultra-wideband (UWB) waveform operated in the near-field region. Radar calibration is a prerequisite for using the full capabilities of the radar system to retrieve geophysical parameters accurately. We introduce a framework and process to calibrate the SDRadar with the UWB waveform in the 675 MHz–3 GHz range in the near-field region. Furthermore, we present the framework for computing the near-field radar cross section (RCS) of an external passive calibration target, a trihedral corner reflector (CR), using HFSS software and with consideration for specific antennas. The calibration performance was evaluated with various distances between the calibration target and radar antennas. The necessity for the knowledge of the near-field RCS to calibrate SDRadar was demonstrated, which sets this work apart from the standard method of using a trihedral CR for backscatter radar calibration. We were able to achieve approximately 0.5 dB accuracy when calibrating the SDRadar in the anechoic chamber using a trihedral CR. In outdoor field conditions, where the ground rough surface scattering effects are present, the calibration performance was lower, approximately 1.5 dB. A solution is proposed to overcome the ground effect by elevating the CR above the ground level, which enables applying time-gating around the CR echo, excluding the reflection from the ground.

K-X rays induced by helium-like C ions in thick target atoms of different metals

The physical process and experimental phenomena of the interaction between highly charged heavy ions and atoms are very complex, particularly in the intermediate energy region, because of the limitation of accelerator and existing theoretical analysis, less systematic researches, incomplete atomic data, and not so high accuracy. The research of celestial element X-ray data is more scarce and the research of X-ray data of celestial elements is even more scarce. Helium-like C ions with 15–55 MeV kinetic energy provided by the HI-13 MV series accelerator of the China Institute of Atomic Energy are used to bombard Fe, Ni, Nb and Mo thick targets. The HpGe detectors are used to measure the K-X ray emission, and the corresponding K-X ray emission cross sections are obtained. Due to the different ionization degrees of the shell layers of various target atoms, the branching intensity ratio of K<sub><i>β</i> </sub>to K<sub><i>α</i></sub> X rays emitted by Helium-like C ions interacting with Fe and Ni target atoms decreases with the increase of the kinetic energy of the incident ions, while the branching intensity ratio of K-X rays emitted by Nb and Mo target atoms does not change significantly. The K-X ray emission cross section of target atom is calculated by using the formula of thick target cross section, and compared with the results of different theoretical models and proton. The results show that with the increase of the kinetic energy of helium-like C ions, the total emission cross section of the K<sub><i>β</i> </sub>and K<sub><i>α</i></sub> X ray emitted from Fe and Ni target atoms are most consistent with the BEA correction model considering multiple ionization, and the total emission cross section of K<sub><i>β</i> </sub>and K<sub><i>α</i></sub> X ray emitted from Nb and Mo target atoms are closest to the theoretical values of PWBA model. When the energy of proton is the same as that of single nucleon C ion, the cross section of K-X ray produced by proton is about three orders of magnitude smaller than that produced by helium-like C ion.

Measurement of nuclide production cross sections for proton-induced reactions on [formula omitted]Ti and 93Nb at 0.8 and 3.0 GeV

The nuclide production cross sections for proton-induced reactions on natTi and 93Nb at 0.8 and 3.0 GeV were measured using an activation technique at Japan Proton Accelerator Research Complex. A total of 27 and 94 nuclide production cross sections for the natTi(p,X) and 93Nb(p,X) reactions were obtained, respectively. Cross sections of the natTi(p,X)44Sc, 93Nb(p,X)52Mn, 93Nb(p,X)69mZn, 93Nb(p,X)82mRb, 93Nb(p,X)85mY, 93Nb(p,X)87mY, 93Nb(p,X)90mY, 93Nb(p,X)91mNb, 93Nb(p,X)92mNb, and 93Nb(p,X)93mMo reactions were successfully measured for the first time. In addition, the cross sections of the natTi(p,X)46Sc, 93Nb(p,X)73As, 93Nb(p,X)85Y, and 93Nb(p,X)87Y reactions above about 1 GeV were firstly measured. The present data were compared with the results from nuclear reaction models in PHITS and data retrieved from Japanese Evaluated Nuclear Data Library High Energy file 2007 (JENDL/HE-2007). As the nuclear reaction models, Liège IntraNuclear Cascade (INCL), two versions of JAERI Quantum Molecular Dynamics, and Jet AA Microscopic Transport Model coupled with an evaporation process were applied. The prediction accuracy of JENDL/HE-2007 was the best for the 7Be production cross section of both targets. As an overall trend, underestimation of INCL and all of the models were confirmed for the natTi(p,X) and 93Nb(p,X) reactions, respectively.

Activation cross section for the [formula omitted] and [formula omitted] reactions on 103Rh, 48Ti and 52Cr from reaction threshold up to 25 MeV energy region

Activation and off-line γ-ray spectrometric methods were used to measure the ground and isomeric state (n,2n) reaction cross section for 103Rh at two different neutron energies. The standard 27Al (n,α)24Na reference reaction was used to normalise neutron flux. The proton beam from the 14UD BARC-TIFR Pelletron facility in Mumbai, India, was utilised to create high-energy quasi-monoenergetic neutrons via the 7Li (p,n) reaction. Statistical model calculations including the level density, pre-equilibrium and optical potential model were performed using the TALYS (ver. 1.95) and EMPIRE (ver. 3.2.3) reaction codes. In addition, because of considerable discrepancies in measured data, the literature (n,p) reaction cross section of 52Cr and 48Ti targets were examined theoretically in the present work. The measured cross sections are discussed and compared with the latest evaluated data of the FENDL-3.2b, CENDL-3.2, TENDL-2019, JENDL-5.0, and ENDF/B-VIII.0 libraries, and experimental data based on the EXFOR compilation. The theoretical investigation of the (n,2n) reaction cross section was performed for the ground and isomeric state for the first time from reaction threshold to 25 MeV energies. The experimental data corresponding to the ground, isomeric state and isomeric ratio were reproduced consistently by the theoretical calculations. The present experimental results are good with certain literature data and theoretical values.

Anion-substitution interfacial engineering to construct C@MoS2 hierarchical nanocomposites for broadband electromagnetic wave absorption

Developing an effective strategy to regulate the interfacial properties of hierarchical structure is of great significance for preparation of high-performance electromagnetic wave absorption (EMA) materials. Ion-substitution can change intrinsic structure and properties of a materials, but its effect on the interfacial properties of hierarchical structure remained to be explored. Herein, we first constructed a C@MoS2 hierarchical structure via simple hydrothermal reaction, then used the ion-substitution strategy to replace the S atoms in MoS2 with O, F and Se, and finally obtained anion-substituted hierarchical structure (C@X-MoS2, X = O, F, Se). The results show that ion-substitution destroys the MoS2 crystal structure and realizes tunable dielectric properties of C@MoS2, which leads to further enhancement of overall interfacial polarization. After optimization, the absorption strength and width of C@O-MoS2 has been significantly improved. The minimum reflection loss (RLmin) reaches −62.17 dB, and the maximum effective absorption bandwidth (EABmax) is 7.0 GHz. The simulation results show the obtained absorbent can greatly reduce the radar cross section of target, indicating it has broad application potential. Therefore, this work provides a novel method for regulation of EMA performance of hierarchical structure and preparation of high-performance absorbents.

Reducing radar cross section of flat metallic targets using checkerboard metasurface: Design, analysis, and realization

Aiming at the large-scale application of metasurface in the field of radar stealth, we present a hybrid resonance-based and dispersion substrate integrated checkerboard metasurface (CMS) for reducing the radar cross section (RCS) of flat metallic targets. Considering the frequency-dependent characteristics of such a dispersion material, a pair of single and dual resonant artificial magnetic conductor meta-atoms with the modified “crusades-like” cell topologies is employed to maximize the operating bandwidth; besides, a comprehensive and thorough investigation on the resonance mechanism is conducted in this paper to provide an intuitive physical insight of meta-atoms’ reflection responses. By comparing the predicted results with simulations, the quasi-periodic effect is introduced to explain the frequency shift of 10 dB RCS reduction bandwidth. In the implementation procedure, a prototype of the designed RCS reducer with a total dimension of 180 × 180 mm2 is fabricated and measured, the 10 dB RCS reduction bandwidth of theoretical simulation and experimental measurement are basically consistent, and the performance improvement of 8 dB RCS reduction in the experimental results can be attributed to the dispersion effects of the dielectric substrate. With a better figure of merit, our efforts may serve as a useful exemplar for the economical CMS architecture in radar evasive applications.

Echo grid integration: A novel method for preprocessing multibeam water column data to quantify underwater gas bubble emissions

AbstractWater column imaging multibeam echo sounder systems (MBESs) are a promising technology for quantitative estimates of the gas bubble volume flow within large gas seepage areas. Considerable progress has been made in recent years toward applicable calibration methods for MBESs as well as developing inversion models to convert acoustically measured backscattering cross sections to gas bubble volume flow. However, MBESs are still not commonly used for quantitative gas flow assessments. A reason for this is the absence of published processing methods that demonstrate how MBES data can be processed to quantitatively represent bubble streams. Here, we present a novel method (echo grid integration) that allows for assessing the aggregated backscattering cross section of targets within horizontal water layers. This derived value enables quantifying bubble stream gas flow rates using existing acoustic inversion methods. The presented method is based on averaging geo‐referenced volume backscattering coefficients onto a high‐resolution 3D voxel‐grid. The results are multiplied with the voxel volume to represent measurements of the total backscattering cross‐section within each voxel cell. Individual gridded values cannot be trusted because the beam pattern effects cause the values of individual targets to “smear” over multiple grid‐cells. The true aggregated backscattering cross‐section is thus estimated as the integral over the grid‐cells affected by this smearing. Numerical simulation of MBES data acquisition over known targets assesses the method's validity and quantify it's uncertainty for different, realistic scenarios. The found low measurement bias (< 1%), and dispersion (< 5%) are promising for application in gas flow quantification methods.

Multi-fold high-order cumulants based CFAR detector for radar weak target detection

As an important detection means, radar is widely used in target monitoring field. However, due to the small radar cross section (RCS) of stealthy or small target and the complex detection environment, the target echo signal is usually submerged in the environmental clutter. Then the target detection based on Pulse-Doppler radar shows the characteristics of weak signal detection. In this paper, the multi-fold high-order cumulant (HOC) on the radar range-Doppler (R-D) map is proposed to elevate the detection performance of the weak target signal, which can effectively eliminate the noise. Then the processed signal is sent to the CFAR detector to estimate the targets' range and velocity. Although HOC has been used in radar signal detection, the detection algorithm was mainly done on the processed signal after one-fold HOC. We propose a construction method of multi-fold HOC using a set of delay vectors to further eliminate residual noise after one-fold HOC processing. Our proposed multi-fold HOC can be seen as a data preprocessing method, which can also be applied to other detection algorithm to further improve its detection performance. Simulation results show that the proposed multi-fold HOC based CFAR algorithm can greatly reduce SNR required for signal detection, and has an advantage in radar weak signal detection.

Measurements of electron bremsstrahlung double-differential cross sections for solid targets down to low photon energies: No polarization contribution

The authors measured the bremsstrahlung double-differential cross sections for some solid thin-film elemental targets by kilovolt electron impact down to low photon energies. The results definitely show that there is no polarization bremsstrahlung contribution in solid-target experiments.

Estimating number of group targets arranged in linear array via forward‐backward matrix pencil method

AbstractAn efficient number estimation method is proposed for target detection by using the forward‐backward matrix pencil method. Compared with the traditional parameter estimation methods, the proposed method can work well even for sparse signals. At first, the radar cross section of the group targets arranged in linear array is obtained at some certain angles or frequencies. Then, the Hankel‐Toeplitz matrix is constructed from the known radar echoes, and the singular value decomposition is performed on this matrix. Finally, the number of the group targets arranged in linear array can be accurately estimated by setting an appropriate threshold to select the singular value with a large proportion. In addition, the influence of different signal‐to‐noise ratios (SNR) on the estimation results is also discussed. In order to enhance the accuracy, several groups of different echoes are used to estimate the number of group targets jointly. The simulation results demonstrate that the proposed method is effective and accurate in estimating the number of group targets arranged in linear array. Moreover, the estimation result of the proposed method in this paper is not affected by the noise, which shows that this method has better robustness.

МИКРОВОЛНОВЫЕ ПОЛЯРИЗАТОРЫ НА ОСНОВЕ ПЕЧАТНЫХ ДИФРАКЦИОННЫХ РЕШЕТОК МЕАНДРОВОГО ТИПА

The problem of printed gratings application is considered as converters of electromagnetic wavespolarization and polarizing modulators. Two directions in development of antenna engineering areconsidered in this paper. In each of them the scattering fields control of an antenna arrays allows essentiallyto expand functionalities of radio engineering sets. The first direction is the creation of auxiliarydepolarizing reflectors for two-mirror reflector antennas and folded lenses. In addition, in meanderlinepolarizers based on printed gratings, it is possible to constructively realize the necessary phase distributions of the field on their surfaces. Thus, it becomes possible to use such meanderline polarizers to createmultifunctional microwave antenna radomes. The second direction is connected to application ofantenna arrays for a reduction of a radar cross section of the radar-tracking targets. Transformation ofa field polarization by an antenna array allows to achieve both these purposes. In an aspect of high costand complexity of arrays experimental researches as a method of the analysis the mathematical simulationis selected. Besides, it is shown that introduction of impedance loads in the construction of the reradiatingelements of the printed grating opens additional possibilities for controlling the field scatteredby it. Thus, meanderline polarizers with improved characteristics can be realized on the basis ofmicrostrip-pin gratings. The given results can be used for choosing the most of rational electrodynamicstructure geometry variant at decision of particular problems by antennas engineering. The possible flatarrays based on printed complicated shape elements application area is also discussed and it's shownthese arrays are the very attractive type for controllable radioelectronic covers designing at microwaves.Some numerical results presented prove the possibility of a printed arrays application as smartcovers microwave modules.

14.77 MeV neutron-induced nuclear reaction cross sections for zinc, yttrium, and molybdenum targets* *S. D. Dhole and V. N. Bhoraskar gratefully acknowledge the financial assistance given by SERB-DST, New Delhi sanction number: EMR/2017/002497 for research in the field of neutron-induced nuclear reactions.

The cross sections for neutron-induced nuclear reactions on natural zinc, yttrium, and molybdenum targets were measured at a neutron energy of 14.77 ± 0.17 MeV using the activation technique, offline gamma-ray spectrometry, and a detailed covariance analysis. The uncertainty in the statistical model calculations of cross sections for the (n, 2n), (n, p), (n, α), and (n, γ) reactions with natural zinc, yttrium, and molybdenum at neutron energies from 13 to 17 MeV was calculated using the TALYS-1.96 nuclear code. The measured cross sections of the present study were compared with the experimental cross sections reported in the EXFOR database, the cross sections were calculated with the TALYS-1.96 and EMPIRE-3.2.3 nuclear codes and the evaluated nuclear data from the TENDL-2019, JENDL-5, and ENDF/B-VIII.0 libraries.

Computation of Voxel-by-Voxel Dose Rates in Patients for Proton Pencil Beam Dose Delivery

<h3>Purpose/Objective(s)</h3> Proton beam radiotherapy is most commonly delivered using the pencil beam scanning (PBS) technique. However, the vast majority of clinical outcome data is based on patients treated with the passive scattering technique. The overall dose distributions delivered with these techniques are fairly similar, with an advantage in conformity noted for PBS. Major differences between these two modalities can be observed in the temporal dose delivery pattern. The passive scattering technique uniformly delivers dose across the cross section of the entire target simultaneously, while the dose in PBS is delivered point-by-point, resulting in a much higher local instantaneous dose rate. Recent studies have shown that ultra-high dose rate (FLASH) irradiations can change the biological response to radiation. This work presents an analytical tool to compute voxel-wise maximum dose rates for clinical PBS treatment plans. <h3>Materials/Methods</h3> The scripting environment of our treatment planning system was used to develop software to compute dose rate distributions for clinical pencil beam scanning treatment plans. The basis of the computation is an accurate model of the delivery timing properties of the accelerator and scanning system. The minimum temporal resolution supported is 1 ms. This captures the timing of single spots but excludes the beam pulse structure of our cyclotron (ns). With the timing model and a given spot map we compute the average dose rate over a time interval of interest for each voxel. The latter is an input parameter determined by the user. To validate the tool, test beams in a simple solid water geometry were generated in the treatment planning system and corresponding dose rate distributions produced. Single point measurements with custom-made diode and electronics were used to verify computations against experimentation for a range of proton energies and depths. <h3>Results</h3> For dose rate calculations recording the maximum value observed in any 1 ms time interval during the field's delivery, we observe peak values of 186 Gy/min and 273 Gy/min for 110 MeV and 150 MeV protons, respectively. On average, the agreement of calculations and measurements was -0.9% with a standard deviation of 4.1%. <h3>Conclusion</h3> The software enables accurate local instantaneous dose rate calculations for clinically deliverable treatment plans. This may be important to use as a basis to better understand clinical results. In addition to standard PBS treatments, the observed dose rates may be relevant when considering the out of field areas in FLASH treatments.

Spherical Harmonic-Based Anisotropic Point Scatterer Models for Radar Applications Using Inverse Optimization

High-performance computing-based electromagnetic (EM) emulators are used to simulate real-time complex EM wave interactions between multiple radar targets, transmitters, and receivers. The radar cross section (RCS) of the radar targets are required to be stored as a table; however, the needed storage size increases dramatically with the angle and frequency sampling density. In this article, we present an innovative approach of constructing a concise spherical harmonic-based anisotropic point scatterer model that the emulators can use as part of the computations. The point scatterer model is constructed directly from the precomputed RCS data. First, we use only the monostatic RCS data and compute the spherical harmonic-based monostatic point scatterer model by solving a linear least-squares problem which has a group sparsity constraint. Then, we further compute the spherical harmonic-based bistatic point scatterer model using the full bistatic RCS data. The problem is formulated as a bilinear least-squares problem. The problem is solved using the normalized iterative algorithm, which linearly solves two parameters in a back and forth manner. The results show that the point scatterer model can effectively represent the bistatic RCS data of a radar target.

Study on Quantum Radar Detection Probability Based on Flying-Wing Stealth Aircraft

The development of quantum radar technology presents a challenge to stealth targets, so it is necessary to study the quantum detection probability. In this study, an analytical expression of the quantum radar cross section (QRCS) for complex targets is presented. Based on this QRCS expression, a calculation method for the detection probability for quantum radar is creatively proposed. Moreover, a self-designed flying-wing stealth aircraft is adopted to obtain the detection probability distributions of the conventional radar and the quantum radar in different directions. As revealed by the result of this study, the detection probabilities of the quantum radar and the conventional radar are significantly different, and the detection probability of the quantum radar has obvious advantages in most regions with a certain distance.

A Novel Design of Microwave Absorbers Based on Multilayered Composite Materials for Reduction of Radar Cross Section

Reduction of radar cross section (RCS) for targets can be achieved by different approaches and coating absorbing materials at the surfaces of targets is one of widely used methods because of its flexibility and good effect. In the work, we put forward a novel method of reducing the RCS based on the design of multilayer composite absorbing materials. The transmission line theory and particle swarm optimization (PSO) are used to guide the design and analysis, and two kinds of designs, i.e., Type IV and Type VII, are selected finally. Simulation experiments show that the designs are insensitive to the incident angles and polarizations of incident EM wave, which is required for being coated at the surfaces of real objects. Also, the designed absorbing materials are very thin and have an ultra-wide frequency band. The bandwidth of Type-IV design can reach 14.6314.63 GHz, ranging from 3.373.37 to 18.018.0 GHz, while Type-VII design can cover the frequency range from 2.02.0 to 18.018.0 GHz, which represents the major part of radar’s frequency range. The designed absorbing materials are coated at the surface of a perfectly-electric-conducting (PEC) cylinder to validate the effectiveness of the materials, and good results have been obtained.

An improved theoretical method for determining the mean D-T neutron energies in large solid angle sample

ABSTRACT Neutron energy of deuterium-tritium (D-T) generator plays an important role for the application of nuclear energy and nuclear technology. Based on the deuterium energy losing in tritiated titanium (T-Ti) target and differential cross sections of D-T reaction, an improved theoretical formula for calculating the mean neutron energy irradiating a large solid angle sample was proposed. Besides that, the mean neutron energy was discussed under the actual experimental conditions. The results were compared to the reported ratio values of 90Zr(n,2 n)89m+gZr to 93Nb(n,2 n)92mNb reaction cross sections (‘Zr/Nb’ ratio methods) and published theoretical calculated results, respectively. The relative deviations between present work and the ‘Zr/Nb’ ratio methods are below 0.5% and a higher precision was obtained compared with previous published theoretical method. The present work lays a foundation for the application of D-T neutron source in nuclear technology such as nuclear reaction cross section measurement, calibration of neutron detector, and neutron irradiation tests, etc.

Dynamic screening and two-center effects in neutral and partially dressed ion-atom collisions

In collisions involving projectiles with bound electrons, partial or total screening of their nuclear charge must be considered. Accordingly, a projectile dynamic effective charge, as a function of the collision momentum transfer, is included in the state-of-the-art continuum distorted wave with eikonal initial state model. This correction, applied in the exit channel, recovers a two-center description from collisions with neutral projectiles. Also, an improvement of both target and projectile ionization double differential cross sections is achieved, especially at the binary encounter and electron capture to the continuum peaks. The results calculated by our analytical model are shown in accordance with previous theoretical and experimental work.