A broadband artificial magnetic conductor (AMC) metasurface for radar cross section reduction is proposed.Modified Jerusalem cross unit and quasi-circular unit can achieve effective reflection phase difference of 180 • (±37 • ) within a wide frequency range from 8.95 to 17.3 GHz.The broadband metasurface consists of chessboard-arranged 3 × 3 block arrays, and each block array is composed of 4 × 4 AMC units.The proposed AMC metasurface is applied to a microstrip antenna for reducing RCS.The measurement results show that the low RCS antenna can obtain 10 dB RCS reduction from 7.93 to 17.5 GHz.The relative bandwidth is 75.2%, and the maximum reduction value is 30.2 dB.Also, radiation performance of the antenna is well maintained.
This paper presents a high-precision Runge-Kutta (RK) method for solving transmission line equations. This method adopts high-order Taylor expansion in space, which improves the approximation accuracy of spatial differentiation. Compared with the traditional finite element time-domain method, when the number of samples per wavelength is the same, RK method has higher precision. At the same time, according to the Taylor model, researchers use RK method to solve transmission line equation in the external field excitation. The correctness and high precision of the RK method are verified by numerical examples of our study.
Abstract This paper analyzes the cause of the overshot of the signal measured by D-dot sensor, and points out that the second-order RLC equivalent circuit model can explain the overshot Taking the asymptotic conical antenna as an example, the inductance L of the second-order model is obtained by using CST simulation and Pspice parameter scanning method. The first-order model and the second-order model are used to calculate the electric field waveform. Under the given conditions, the first-order model is used to obtain the electric field waveform, the waveform overshot is serious, the maximum overshoot reaches 27%, while the second-order model is used to improve the ringing phenomenon, And the maximum overshoot is reduced to 5%.The results show that the second-order model is more accurate than the first-order model and can improve the precision of electric field measurement using D-dot sensor.
Abstract The shielding efficiency of coaxial cable is characterized by its anti-interference ability in electromagnetic environment. The testing methods include three-axis method, GTEM chamber method, line injection method, power absorption clamp method, reverberation chamber method and so on. In practical application, it is found that the shielding performance of the cable under high altitude electromagnetic pulse (HEMP) does not accord with the shielding efficiency measured by the cable. While a typical multi-layer shielded cable is selected as the test object, a test method is designed and tested under electromagnetic simulator, and then the test results are verified and extended by CST simulation. Finally, the reason of this phenomenon is analysed theoretically, which has important reference significance for the prediction and testing of shielding efficiency of cable in HEMP environment.
Industrialization has resulted in the discharge of a certain amount of lead (Pb) from industrial sources causing damage risk to water quality and human health. Adsorption is an effective technique to remove Pb, and biochar has been widely studied owing to its advantages of low cost and high adsorption capacity. This review summarizes the influence of raw materials and modification methods on the adsorption capability of biochar. The adsorption isotherms and kinetics of biochar were summarized, and the main Pb removal mechanisms were studied systematically. In addition, the challenges and future perspectives were discussed comprehensively. It is expected that the review could provide insightful fundamentals for the experimental research and practical applications of biochar.
As an important ecological security barrier in China, the ecological environment of Tibet has aroused widespread concern domestically and overseas. Landfills are a major solid waste treatment approach in Tibet but also cause severe environmental pollution. To date, there are no studies related to the pollution risk of landfills in Tibetan areas. This study investigated the pollution levels, ecological risk, health risk, and possible pollution sources of eight heavy metals in the soils around a landfill site in Lhasa, Tibet. The results indicated that the concentrations of heavy metals in soil were relatively low, only cadmium (Cd), arsenic (As), copper (Cu), chromium (Cr), zinc (Zn), nickel (Ni), and lead (Pb) were 1–2 times higher than the corresponding background value. The values of the single pollution index and geo-accumulation index show that the study area is most seriously polluted by Cd and As. Based on the Nemerow pollution index and the pollution load index, over 83.3% and 8.33% of soil sampling sites had light and moderate contamination levels. According to the results of potential ecological risk evaluation, the potential ecological risk of heavy metals in soil was very low, and only one out of the 72 sampling sites exhibited considerable ecological risk. Cd, As, and mercury (Hg) served as the dominant ecological risk contributors and contributed over 45.0%, 14.1%, and 18% of the ecological risk. The results of the health risk evaluation showed that adults have a higher risk of cancer (1.73 × 10−5), while the non-carcinogenic risk for adults was low. Waste disposal activities and construction activities have a significant influence on soil heavy metal concentrations, causing a higher pollution level in the southeast part of the landfill site in Lhasa.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
