العنوان البديل: Research on Radio Wave Propagation Prediction Model of Vehicle-Mounted Ultrashort Wave Radio.

المؤلفون: 李敏¹, 张光硕¹, 徐至江¹, 谢红星¹, 路宏敏¹

المصدر: Electronic Science & Technology. 2023, Vol. 36 Issue 7, p64-69. 6p.

مصطلحات موضوعية: *RADIO wave propagation, *ANTENNA radiation patterns, *MACHINE learning, *STANDARD deviations, *RANDOM forest algorithms, *INTELLIGENT transportation systems, *TELECOMMUNICATION satellites

الملخص (بالإنجليزية): Given the problem that the communication distance and quality of the vehicle-mounted ultrashort wave radio are affected by ground attachments and topography in the actual combat environment, a radio wave propagation prediction model of vehicle-mounted ultrashort wave radio is established based on ray tracing and machine learning. The integrated modeling of armored combat vehicle and vehicle antenna is established to obtain the antenna radiation pattern, and combined with electronic images, the radio wave propagation simulation model based on ray tracing technology is established. Based on the machine learning algorithm of the random forest and data results for the simulation model, the radio wave propagation prediction model based on the random forest was established. Compared with traditional classical radio wave propagation models such as the Egli and Okumura-Hata models, the radio wave propagation prediction model based on the random forest has higher accuracy. The root mean square error reaches 2.190 1 dB, and the coefficient of determination reaches 0.960 1. It can accurately predict radio wave propagation in the tactical communication environment. [ABSTRACT FROM AUTHOR]

Abstract (Chinese): 针对实战环境中车载超短波电台通信距离和质量受地面附着物和地形地貌影响的问题,文中基于射线追踪和机器学习,建立了车载超短波电台电波传播预测模型。采用装甲车辆与车载天线的一体化建模获得车载天线辐射方向图,融合电子地图,建立了基于射线追踪技术的电波传播仿真模型。利用随机森林机器学习算法和仿真模型的数据结果,建立了基于随机森林的电波传播预测模型,并与经典电波传播模型如Egli模型和Okumura-Hata模型进行对比。结果显示,基于随机森林的电波传播模型预测精度更高,均方根误差达到2.190 1 dB,决定系数达到0.960 1,可准确预测战术通信环境中的电波传播情况。 [ABSTRACT FROM AUTHOR]

المؤلفون: LI Tianjie¹, WU Gensheng¹, YUAN Zhishan², YIN Fuqiang¹, GU Yunfeng¹ gu_yunfeng@sina.com

المصدر: Journal of Synthetic Crystals. Dec2022, Vol. 51 Issue 12, p2022-2030. 9p.

مصطلحات موضوعية: *PHONONIC crystals, *ELASTIC wave propagation, *SILICONE rubber, *FINITE element method, *CRYSTAL models, *PHONONS

مستخلص: In this paper, a new phononic crystal structure with periodic units consisting of four tungsten vibrators wrapped by silicone rubber coating is designed. The dispersion curve, vibration mode and transmission loss spectrum of the structure were calculated by finite-element method(FEM). The results show that the bandgap range of this structure is 18. 85 ~225. 28 Hz, which is consistent with the frequency attenuation range of transmission loss spectrum, and can effectively suppress the propagation of elastic waves of 20 ~200 Hz in phononic crystals. By analyzing the vibration mode corresponding to the point on the dispersion curve, the formation mechanism of the bandgap is explained. The influence of the notch angle of the phononic crystal plate and the longitudinal and transverse spacing between the phonons on the bandgap was discussed in this paper. The results show that as the notch angle decreases, the lower boundary of the bandgap remains almost unchanged, and the upper boundary of the bandgap rises, thus increasing the width of the bandgap. As the transverse or longitudinal spacing between the vibrators increases, the lower and upper boundaries of the bandgap rise, and the width of the bandgap increases, thus the bandgap of the phononic crystal model is optimized. At the same time, the notch design of the phononic crystal plate save the material and reduce the weight of the structure. [ABSTRACT FROM AUTHOR]

المؤلفون: Xudong Gu, Binbin Ni, Wei Xu, Shiwei Wang, Bin Li, Ze-Jun Hu, Fang He, Xiangcai Chen, Hong-Qiao Hu

المصدر: 地球与行星物理论评, Vol 55, Iss 1, Pp 15-23 (2024)

مصطلحات موضوعية: whistler wave monitoring equipment, antarctic great wall station, space weather, vlf wave propagation, chinese meridian project, Geophysics. Cosmic physics, QC801-809, Astrophysics, QB460-466

الوصف: A system for the detection of very low frequency (VLF) electromagnetic waves has been developed by Wuhan University (WHU) with the Polar Research Institute of China (PRIC), and has been successfully deployed by PRIC at the Great Wall Station (GWS, 62.22°S, 58.96°W) in Antarctica, as part of the Phase II of Chinese Meridian Project. The system has a dynamic range of ~110 dB and a timing accuracy of ~100 ns, and hence can provide observational data at sufficient resolution to contribute to space physics and space weather research. This paper reports initial measurements of the WHU VLF (Meridian Project-Phase II ID：OCHCH_WHWM01) wave detection system at GWS, to demonstrate performance of the system. Data from nearly one year of routine operation indicate that the system is effective in recording the dynamic change of ground-based VLF transmitter signals from North America and Europe. The characteristics of VLF transmitter signals observed at GWS during X-class solar flares are consistent with results from previous studies. The VLF data exhibited a good correlation in space and time with measurements of magnetospheric electron deposition during geomagnetic storms, as detected in the south Atlantic anomaly (SAA) region. The WHU VLF system additionally provides data on the wide-band whistler waves as excited by lightning discharge, the spectrum of which exhibits a distinctive dispersion structure. The unique position of GWS in Antarctica provides the opportunity to obtain observational data on VLF waves which can be used to investigate multiple aspects of space physics, including the propagation of whistler waves in polar regions, lower ionosphere disturbance, lightning discharge, and radiation belt electron precipitation from the radiation belts. These measurements are of critical importance in monitoring near-Earth space weather.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/2097-1893Test

الوصول الحر: https://doaj.org/article/55839fb7c4b842e4a364873657e0e488Test

المؤلفون: YU Aiping, CHEN Zhehan, WU Xiaoman, MAO Feiteng, CHEN Xuandong

المصدر: Journal of Henan University of Science & Technology, Natural Science; 12/25/2023, Vol. 44 Issue 6, p70-76, 7p

مصطلحات موضوعية: ACOUSTIC emission, ACOUSTIC wave propagation, HIGH strength concrete, FAST Fourier transforms, CONCRETE, ATTENUATION coefficients

مستخلص: The application of acoustic emission (AE) in concrete faces great challenges due to complex material parameters of concrete materials and the rapid attenuation characteristics of acoustic emission wave. In order to clarify the influence of concrete strength level on acoustic emission wave propagation characteristics and create conditions for evaluating concrete damage by acoustic emission technology, the acoustic emission technology was used to study the propagation behavior of acoustic emission waves in concrete with different strength levels through parameter analysis and fast Fourier transform. The results show that the attenuation coefficients of AE energy in C30, C40 and C50 concrete are 0.013 94, 0.010 67 and 0.005 68, respectively, and the higher the strength is, the smaller the attenuation is. The benchmark wave speeds are 3 966 m/s, 4 193 m/s and 4 411 m/s, respectively, and the higher the intensity, the faster the wave speed. The frequency distribution tends to shift from high frequency to low frequency with the increase of propagation distance, but the signal attenuation and frequency deviation of concrete with high strength are slower. The signal wave types received within 500 mm and outside 500 mm are different, which is not conducive to the acoustic emission monitoring. When monitoring the acoustic emission of concrete, the sensor spacing should be within 500 mm to ensure the monitoring accuracy. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Henan University of Science & Technology, Natural Science is the property of Editorial Office of Journal of Henan University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

العنوان البديل: A Through-the-Wall Radar Imaging Composite Delay Time Algorithm for Wall with Unknown Parameters Based on Refraction Static Correction.

المؤلفون: 李家强^1,2 ljq@nuist.edu.cn, 刘　然², 徐才秀³, 陈金立^1,2, 陈焱博², 朱艳萍²

المصدر: Telecommunication Engineering. 5/28/2021, Vol. 61 Issue 5, p582-588. 7p.

مصطلحات موضوعية: *PROBLEM solving, ELECTROMAGNETIC wave propagation, RECEIVING antennas, TRANSMITTING antennas, ELECTROMAGNETIC waves, CLUTTER (Radar)

الملخص (بالإنجليزية): In the practical application of through-the-wall radar, the wall generally consists of two layers of different media and the parameters of the wall are unknown. The problem of image defocusing and displacement of the target behind multi-layered wall will arise when the target is directly imaged. To solve this problem, a composite delay time method based on refraction static correction is proposed to focus the image of the target behind the wall. Firstly, the method reads the echo data of each receiving antenna to determine the refraction echo time of the electromagnetic wave, and then obtains the time delay overdetermined equations through the basic refraction equation. Solving the overdetermined equations can obtain the propagation delay of the electromagnetic wave in the outer wall. The propagation delay of the electromagnetic wave in the inner wall is estimated by the difference between the adjacent transmitting antenna and the adjacent receiving antenna. The propagation delay in each channel is added successively and then the backward jection proalgorithm is used for imaging. Finally, the imaging position accuracy, image entropy and target clutter ratio of the algorithm are analyzed to demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Abstract (Chinese): 在穿墙雷达实际应用中,墙体一般由两层不同介质构成,且各层墙体参数未知。若对墙后目 标直接成像,会产生目标散焦或位置偏移。针对该问题,提出了基于折射波静校正的合成延迟时方 法对墙后目标进行聚焦成像。首先读取每根接收天线回波数据确定电磁波的折射回波时刻,通过基 本折射方程得到延迟时超定方程组,解此超定方程组可得电磁波在外层墙体内的传播时延,再运用 相邻发射天线和相邻接收天线延迟时之差估计内层墙体中电磁波的传播时延,最后各个通道内传播 时延依次相加后运用后向投影算法获得目标精确成像。对成像位置精度、图像熵,以及输入输出目 标杂波比等性能的分析和比较证明了该算法的有效性。 [ABSTRACT FROM AUTHOR]

: Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: Junjun LI, Mengfei YU, Guofu LI, Zheng WANG, Jian GONG, Junke GAO

المصدر: Meitan kexue jishu, Vol 51, Iss 9, Pp 121-128 (2023)

مصطلحات موضوعية: low permeability coal seam, aerospace solid propellant, high-energy gas fracturing, stress wave propagation, attenuation law, pressure in the borehole wall, permeability enhancement, Mining engineering. Metallurgy, TN1-997

الوصف: Coal reservoirs with high gas content and low permeability seriously restrict the efficient production of coal and coalbed methane. It is necessary to fracture and enhance the permeability of coal reservoirs. Aerospace solid propellant deflagration can generate a large amount of high-energy gas to impact coal reservoirs, which can achieve the purpose of fracturing and enhancing permeability of coal reservoirs. To study the characteristics of aerospace solid propellant for fracturing coal, a solid propellant for fracturing and permeability enhancement of coal reservoir was firstly researched and developed based on the formula of civil aerospace solid propellant, was, and its performance, sensitivity, pressure and temperature resistance were tested. The aerospace solid propellant fracturing test was then carried out using simulated coal samples, and the borehole wall pressure and strain within the simulated coal samples were monitored during the test. Finally, the destruction characteristics of simulated coal samples were analyzed according to the test results. The results shown that the aerospace solid propellant had good performance, with the advantages of waterproof, pressure resistant, and no CO generation, which could be adapted to the underground environment of coal mine. During the test, the time curve of the borehole wall pressure shown the stages of rapid pressure rise, slow pressure rise, and nonlinear pressure drop, in which the rise time of the borehole wall pressure was about 18 ms. The peak pressure in the borehole was low and unevenly distributed. The peak pressure in the middle of the borehole was 118.1 MPa, and the peak pressure at the bottom of the borehole was 85.3 MPa. Stress wave generated in simulated coal sample during aerospace solid propellant fracturing was composed of compressive and tensile phases with low intensity, long duration and slow decay with distance. The aerospace solid propellant fracturing technology was dominated by the quasi-static action of high-energy gas, with high utilization of stress wave energy. The research results provide a reference for the application of aerospace solid propellant in the field of coalbed methane mining.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/0253-2336Test

الوصول الحر: https://doaj.org/article/0506482e34824614a615bdf0de3620c7Test

العنوان البديل: A Random Forest-based LOS / NLOS Base Station Identification Method. (English)

المؤلفون: 戢静红, 张振宇, 邓平

المصدر: Telecommunication Engineering; 10/28/2023, Vol. 63 Issue 10, p1596-1602, 7p

مصطلحات موضوعية: MEASUREMENT errors, RANDOM forest algorithms, MACHINE learning, RADIO waves, RADIO wave propagation

الملخص (بالإنجليزية): The cellular mobile communication environment is complex and volatile,and the Non-Line-ofSight(NLOS) propagation of radio waves inevitably occurs between base stations and mobile stations,which causes a significant increase in the distance measurement error between base stations and mobile stations and leads to a sharp decrease in localization performance. In order to accurately identify Line-of-Sight (LOS) and NLOS base station signals, a Random Forest-based LOS / NLOS base station identification method is proposed. By analyzing the correlations between the measured distances of mobile stations and each base station receiver and the localization errors,the LOS / NLOS measured distances are selected as features for classifier training, and then the classifier is used for the identification of LOS / NLOS base stations. Simulation results show that the correct recognition rate of NLOS base stations by the method reaches more than 90%,and better localization performance is achieved. [ABSTRACT FROM AUTHOR]

Abstract (Chinese): 蜂窝移动通信环境复杂多变,在基站和移动台之间不可避免会出现电波的非视距(NonLine-of-Sight,NLOS)传播,使基站和移动台之间的距离测量误差显著增大,导致定位性能急剧下降。 为了准确识别出视距(Line-of-Sight,LOS) 与非视距传播的基站信号,提出了一种基于随机森林的 LOS / NLOS 基站识别方法,通过分析移动台与各基站接收机测量距离与定位误差之间的相关性,选 择 LOS / NLOS 测量距离作为特征进行分类器训练,再将分类器用于 LOS / NLOS 基站的识别。 仿真结 果表明,该方法对 NLOS 基站的正确识别率达到 90% 以上,能取得较好的定位性能。 [ABSTRACT FROM AUTHOR]

: Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

العنوان البديل: Forward simulation of electromagnetic waves in coal gangue model based on improved bidirectional peak-valley search algorithm. (English)

المؤلفون: 史翔予, 司垒, 王忠宾, 魏东, 顾进恒

المصدر: Journal of Mine Automation; Oct2023, Vol. 49 Issue 10, p87-95, 9p

مصطلحات موضوعية: FINITE difference time domain method, ELECTROMAGNETIC wave propagation, MAXWELL equations, ELECTROMAGNETIC waves, SEARCH algorithms

الملخص (بالإنجليزية): Realizing automatic recognition of coal gangue content during the top coal caving process is an important goal of fully mechanized mining automation. The existing methods for automatic recognition of coal gangue content have problems such as low accuracy and real-time performance. The coal gangue mixture generated during the top coal caving process is a three-phase medium formed by coal, gangue, and air. The electrical parameters of each phase medium are different. The propagation features of electromagnetic waves are also different in different components of the mixed three-phase medium. There is a significant difference in the dielectric constant between coal blocks and gangue. By studying the electrical parameters of coal gangue mixtures with different gangue contents, new ideas and methods can be provided for automatic recognition of gangue content in top coal caving working faces. In order to explore the electrical differences of coal gangue mixtures with different gangue contents, a bidirectional peak-valley search algorithm based on the divide and conquer strategy is proposed. Based on this algorithm, a multiphase discrete random medium model of coal gangue is established. Based on the Maxwell equations and their constitutive relationship equations, the electromagnetic wave forward simulation of the established model is performed using the finite difference time domain method. The analysis shows that after improving the bidirectional peak-valley search algorithm based on the divide and conquer strategy, there is a clear phase interface between the coal, gangue, and air phases in the coal gangue multiphase discrete random medium model. Moreover, there is a greater degree of dispersion of each phase and no aggregation phenomenon. Therefore, the local medium can also reflect the overall electrical parameters, which can meet the requirements of the medium model for electromagnetic wave forward modeling. The forward simulation results indicate the following points. ① The frequency of the excitation signal will affect the amplitude of the transmitted wave. In the 12 GHz range, the higher the frequency of the excitation signal, the greater the amplitude of the transmitted wave. Low frequency will reduce the robustness of the signal, and the excitation frequency should be higher than 2 GHz. ② The gangue content of the coal gangue mixture is positively correlated with the overall equivalent dielectric constant of the medium. The higher the gangue content, the greater the propagation loss of the electromagnetic wave signal. The smaller the amplitude of the signal received by the receiving plane, the longer the time it takes for the electromagnetic wave signal to penetrate the medium. There is a significant difference between different gangue contents, which can be used as a basis for the gangue content recognition of fully mechanized top coal caving. [ABSTRACT FROM AUTHOR]

Abstract (Chinese): 实现放顶煤过程煤矸含量自动识别是综采自动化的重要目标, 现有煤矸含量自动识别方法存在准确 性、实时性较低等问题。放顶煤过程产生的煤矸混合物是由煤、矸石和空气形成的三相介质, 各相介质的电性参 数不同, 在不同组分的混合三相介质中, 电磁波的传播特性也不同。煤和矸石相对介电常数差异明显, 通过研究 不同含矸率煤矸混合物的电性参数, 可为放顶煤工作面含矸率自动识别提供新的思路和方法。为了探究不同含 矸率煤矸混合物的电性差异, 提出了一种基于分治策略的双向峰−谷搜索算法, 基于该算法建立了煤矸多相离散 随机介质模型, 基于麦克斯韦方程组及其本构关系方程, 利用时域有限差分法对所建立的模型进行电磁波正演模 拟。分析表明, 基于分治策略改进双向峰−谷搜索算法后, 煤矸多相离散随机介质模型中的煤、矸石、空气三相之 间不仅存在明显的相界面, 且各相离散程度更大, 不存在聚集现象, 因此局部介质也能体现整体的电性参数, 能够 满足电磁波正演的介质模型需求。正演模拟结果表明：① 激励信号的频率会影响透射波的幅值, 在 12 GHz 范围 内, 激励信号频率越高, 透射波幅值越大；频率过低会降低信号的鲁棒性, 激励频率应高于 2 GHz。② 煤矸混合物 的含矸率与介质整体的等效介电常数呈正相关。含矸率越高, 电磁波信号的传播损耗越多, 接收平面接收到的信 号幅值越小, 电磁波信号穿透介质所用的时间越长。不同含矸率之间呈现明显的差异性, 可以用作综采放顶煤含 矸率识别的依据。 [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

المؤلفون: YANG Zhiyong, HOU Peng, JIANG Wenge, YANG Lei, ZUO Xiaobiao, GENG Dongbing, ZHU Zhongzheng, LI Hua

المصدر: Journal of Aeronautical Materials; Oct2023, Vol. 43 Issue 5, p84-96, 13p

مصطلحات موضوعية: ACOUSTIC models, ABSORPTION of sound, ACOUSTIC field, ACOUSTIC wave propagation, DEGREES of freedom, SIMULATION methods & models

مستخلص: Acoustic liner is an important component to reduce engine noise. In this work, the modal sound source characteristics of the pipeline under different flow fields were calculated and used as the input boundary for the background flow field calculation and sound propagation calculation of the Actran software, thereby establishing the sound propagation model. The influences of four structural parameters on the sound absorption effect of the muffler plate hole diameter, hole spacing, honeycomb height, and muffler plate thickness in the single-DOF acoustic liner and the double-DOF acoustic liner were studied respectively. The simulation results show that both degrees of freedom acoustic liners exhibit the phenomenon that the smaller the perforation diameter, the better the sound absorption performance within a certain range of hole diameter. The effects of hole spacing, honeycomb height, and muffler thickness on the sound absorption performance are varied with frequency, the double-DOF acoustic liner above 2500 Hz has large dissipation power and good sound absorption effect. Through the contrast verification in the flow tube test, the transmission loss of the acoustic liner of different structures under different excitation sources is compared, and a reasonable and credible simulation method is obtained. [ABSTRACT FROM AUTHOR]

: Copyright of Journal of Aeronautical Materials is the property of Editorial Board of Journal of Aeronautical Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

العنوان البديل: Design and Verification of C Band Broadband Thin-Film Bulk Acoustic Wave Filter. (English)

المؤلفون: 蒋世义, 蒋平英, 马晋毅, 陈彦光, 徐 阳, 刘 娅, 徐 溢

المصدر: Piezoelectrics & Acoustooptics; Aug2023, Vol. 45 Issue 4, p535-539, 5p

مصطلحات موضوعية: WAFER level packaging, ACOUSTIC filters, SOUND waves, MICROELECTROMECHANICAL systems, INSERTION loss (Telecommunication), ACOUSTIC wave propagation, STRUCTURAL optimization

الملخص (بالإنجليزية): The design method of a miniaturized C band broadband thin-film bulk acoustic wave filter suitable for bumped wafer level packaging with three-dimensional stacking is introduced, and the process validation is carried out. The design of thin-film bulk acoustic wave filter with a relative bandwidth of more than 5% was realized through scandium doping, material parameter extraction and structural model optimization of the piezoelectric film. The filters are fabricated by the surface silicon based micro-electro-mechanical systems(MEMS) process and bumped wafer level packaging. A C band broadband thin-film bulk acoustic wave filter with a nominal frequency of 5 800 MHz, insertion loss of less than 2.8 dB, stopband suppression of greater than 40 dBc and a size of only 1.0 mm×1.0 mm×0.35 mm has been developed. [ABSTRACT FROM AUTHOR]

Abstract (Chinese): 介绍了一种适用于三维堆叠的凸点式晶圆级封装的小型化C波段宽带薄膜体声波滤波器的设计方法, 并进行了工艺验证。通过对压电层薄膜进行钪掺杂、材料参数提取、结构模型优化实现了相对带宽大于 5% 的薄膜体声波滤波器设计。通过表面硅基微机电系统 (MEMS)工艺制备与凸点式晶圆级封装实现滤波器制备。研制出标称频率 5800 MHz、插入损耗小于 2.8 dB、阻带抑制大于 40 dBc、体积仅 1.0 mm×1.0 mm×0.35 mm 的C波段宽带薄膜体声波滤波器。 [ABSTRACT FROM AUTHOR]

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