In order to locate the faint sources in the lightning discharge, an improved broadband VHF observation system is developed. Both the system configuration and locating algorithm are specially designed to locate weak radiation sources from background noise. The proposed system consists of seven broadband omnidirectional antennas in “L”shape and runs in continuous acquisition mode. An electromagnetic time reversal method designed in frequency domain is applied to locate the radiation sources. Two metrics have been introduced to distinguish between actual lightning sources and noise event. Numerical simulations and field calibration are carried out to test the system's performance in locating weak sources. Moreover, the performance on spatial resolution, robustness, and the ability of multi-source localization are investigated. Finally, this system is applied to map the propagation of the upward positive leader (UPL) from a classical triggered lightning with time resolution 0.128 μs. The results prove that the proposed system could well depict the whole progression of UPL until its extinction, and the advantages of the proposed seven antennas array in retrieving weak radiations are presented in detail.

In this letter, the complex frequency shifted (CFS) perfectly matched layer (PML) is developed for the unconditionally stable finite-difference time-domain method based on weighted Laguerre polynomials for periodic structures. To verify the validity of the presented method, a numerical example of scattering from periodic structures is given. Numerical results show that, compared with the traditional PML, the CFS-PML is more effective in absorbing the evanescent waves, and has about 32 dB improvement in terms of the maximum relative error and much lower reflection error for the late-time.

Electronic equipment brings great convenience to daily life but also causes a lot of electromagnetic radiation pollution. Therefore, there is an urgent demand for electromagnetic wave-absorbing materials with a low thickness, wide bandwidth, and strong absorption. This work obtained a high-performance electromagnetic wave absorption system by adding conductive carbon spheres (CSs) to the CH₃NH₃PbI₃ (MAPbI₃) absorber. In this system, MAPbI₃, with strong dipole and relaxation polarization, acts dominant to the wave absorber. The carbon spheres provide a free electron transport channel between MAPbI₃ lattices and constructs interfacial polarization loss in MAPbI₃/CS. By regulating the content of CSs, we speculate that this increased effective absorption bandwidth and reflection loss intensity are attributed to the conductive channel of the carbon sphere and the interfacial polarization. As a result, when the mass ratio of the carbon sphere is 7.7%, the reflection loss intensity of MAPbI₃/CS reaches −54 dB at 12 GHz, the corresponding effective absorption bandwidth is 4 GHz (10.24–14.24 GHz), and the absorber thickness is 2.96 mm. This work proves that enhancing conduction loss and interfacial polarization loss is an effective strategy for regulating the properties of dielectric loss-type absorbing materials. It also indicates that organic-inorganic hybrid perovskites have great potential in the field of electromagnetic wave absorption.

For high efficient analysis of an obliquely incident plane wave on periodic structures, one-step leapfrog locally one-dimensional finite-difference time-domain (LOD-FDTD) method is proposed in this letter. Firstly, by applying the LOD scheme into the improved split-field algorithm, unconditional stability can be achieved. And then, by introducing three auxiliary variables, the one-step leapfrog implementation for the LOD scheme is derived. Finally, the implementation of the convolutional perfectly matched layer (CPML) for the proposed method is derived. At last, numerical results are given to verify the accuracy and efficiency of the proposed method.

A novel approximate method based on the Kirchhoff-type circuit for frequency-selective surface (FSS) analysis is presented in this paper. Instead of splitting up the array element and solving a higher order impedance/admittance matrix equation in the periodic moment method, the equivalent transmission line method is adopted to obtain analytical solutions of the normalized receiving current (or magnetic current) distribution for pattern functions. The impedance/admittance elements and transmission coefficients can then be analytically calculated using Munk's scheme. The proposed method can be applied to generic FSS elements composed of relatively narrow straight slots/strips. The revision scheme of the equivalent transmission line lengths is proposed to account for discontinuity effects at corners of the element. The transmission coefficients of the six biplanar symmetric hybrid radomes are computed to verify the accuracy and efficiency of the presented method.

D-dot sensors can realize the non-contact measurement of transient electric fields, which is widely applied to electromagnetic pulse (EMP) measurements with characteristics of the wide frequency band, high linearity, and good stability. In order to achieve accurate calibration of D-dot sensors in the laboratory environment, this paper proposed a new calibration method based on system identification. Firstly, the D-dot sensor can be considered as a linear time-invariant (LTI) system under corner frequency, thus its frequency response can be characterized by the transfer function of a discrete output error (OE) model. Secondly, based on the partial linear regression of the transfer function curve, the sensitivity coefficient of the D-dot sensor is obtained. By increasing the influence weight of low-frequency components, this proposed method has better calibration performance when the waveform is distorted in the time domain, and can artificially adapt to the operating frequency range of the sensor at the same time.