An analytical approach for calculation of the dyadic Green's functions inside the rectangular cavity over a broad range of frequency is presented. Both vector potential and electric field dyadic Green's functions are considered. The method is based on the extraction of the Green's function at an imaginary wave number from itself to obtain a rapidly convergent eigenfunction expansion of the dyadic Green's function. The extracted term encompasses the singularity of the Green's function and are computed using spatial expansions. Results are illustrated for rectangular cavity up to 5 wavelengths in size with thousand of cavity modes obtained by the 6th order convergent expansion. It is shown that for an accurate and broadband simulation, the proposed method is many times faster than the Ewald method.

In this paper, we consider a MIMO wiretap system in wireless sensor networks (WSNs), where the confidential signal sent to the legitimate receive (Bob) may be eavesdropped by the eavesdropper (Eve). Assuming that only partial channel state information (CSI) can be obtained by the transmitter, we consider both worst case (WC) and outage-constrained (OC) robust secrecy optimizations. To solve the WC design, we propose to linearize these logarithmic determinant terms. After linearization, we tackle the CSI uncertainty using the Nemirovski lemma. Then, an alternating optimization (AO) algorithm is proposed to solve the reformulated problem. On the other hand, to solve the OC design, we transform the probabilistic constraint into safe and tractable reformulation by the Bernstein-type inequality (BTI) and large deviation inequality (LDI), and an AO algorithm is proposed. Numerical results are provided to demonstrate the performance of the proposed scheme.

This paper presents a multi-band annular ring antenna that is obtained from a single-layer probe-fed substrate integrated waveguide based on a graphene material, with three top plan slits. In order to create a multi-bands antenna, we conduct simulation of the antenna structure based on CST/HFSS, so we use parametric tuning to adjust TM modes. Simulations show a good results between the two methods (finite element method and integral method) CST and HFSS Simulators. The bandwidths for three modes are 340 GHz in first mode, 346 GHz in the second mode, and 104 GHz in the third mode. The simulation gains at TM₁₁, TM₀₂, and TM₁₂ are 8.2 dB, 8 dB, and 11 dB, respectively. The proposed antenna can be used in therahertz applications.

Accurate measurement of atmospheric particulate matter (PM) absorption coefficient is highly required for study of earth climate change and for monitoring of air quality. In addition, multi-wavelength measurements of PM absorption can provide information on the PM chemical composition (black carbon or brown carbon). A multi-wavelengths photoacoustic (MW-PA) spectrophone operating at 444, 532 and 660 nm was developed and deployed for filter-free characterization of wavelength-dependent optical properties of PM mass absorption coefficient (MAC) and absorption Ångström coefficient (AAC). It is worth noting that to date no any AAC of volcanic ashes determined by filter-free measurement have been reported. The developed MW-PA spectrophone was deployed to an intensive field campaign measurement of environmental PM in Grenoble (France). Side-by-side inter-comparison measurements of ambient PM showed a good correlation between the developed MW-PA spectrophone and a reference instrument aethalometer (Magee scientific, AE33).

This paper demonstrates a three-port coaxial fed antenna system for wireless local area network (WLAN) access points, consisting of two dipoles and a patch, radiating at 5.2 GHz with impedance bandwidth of 150 MHz. The antennas are designed for pattern diversity in the end-fire and broadside orientation with an individual gain of 4.5 dBi, which is further enhanced to 6 dBi after integrating with unit-cell structures. The gain enhancement for individual antennas is achieved by strategically integrating transmission type and reflective type sub-wavelength structures for patch and dipoles respectively. The realized ground plane is shared among the three antennas. The measured results show that the return loss of the antennas is unaffected by the unit-cell loading and has an isolation of less than 26 dB throughout the band and across the ports for a port-to-port distance of 0.25λ.

This paper provides a sound wireless power transfer (WPT) recharging solution for on-road automated guided vehicle (AGV) system. In this solution, multiple transmitting coils serve as power transmitters (TXs), and a receiving coil in AGV serves as a power receiver (RX). The multiple TXs are along a straight track for dynamic charging to AGV. The circuit model of multiple-TX and single-RX WPT system is first constructed based on circuit theory (CT), and then current-optimized scheme based on Lagrangian multiplier method is proposed to tune the currents in multiple TXs to maximize the power delivered to the load (PDL). The equal current (EC Case) flowing through each TX is compared with the optimal current (OC Case). Through contrastive analysis, the OC Case shows its advantages in PDL. Finally, the theoretical analysis results are confirmed by the results of full-wave electromagnetic simulation.

In recent years, through-wall imaging (TWI) has gained much research interest because of urgent needs of civilian, security, and defense applications. TWI based on compressive sensing (CS) method can produce high resolution, assuming that the wall parameters are known in prior. However, it is difficult to know the exact wall parameters in actual scenarios. With unknown wall parameters, the dictionary matrix is not a fixed one. Therefore, CS theory cannot be directly applied in the TWI. This paper presents a parametric sparse recovery method for TWI with unknown wall parameters. The original reconstruction problem is reformulated into a joint optimization one which can be solved with an alternating minimization algorithm. Specifically, the proposed method performs the wall parameter estimation and sparse image reconstruction in an iterative procedure. With the estimated wall parameter which is or close to the true one, the high fidelity and high-resolution image is obtained. Experimental simulations show that the proposed method can obtain an autofocus image and improve the image quality.

Because of the current commutation and the double salient pole structure of bearingless switched reluctance motors (BSRMs), the torque and suspension force have large ripples when traditional current control methods are used. According to the special structure of the double stator BSRM (DSBSRM), the direct decoupling of torque and suspension force is realized. Therefore, the DSBSRM can be controlled separately as a conventional 12/8 SRM and a four-poles active magnetic bearing. In order to achieve the suppression of the torque ripple and improve the robustness of speed, a direct torque control (DTC) strategy using second order sliding mode (SOSM) speed controller is proposed. In order to achieve the suppression of the suspension force ripple and rotor displacement chattering, a direct suspension force control (DSFC) strategy is proposed as well. Then the SOSM-DT/DSFC model is established by simulink. The results of simulation show that the torque ripple, suspension force ripple and rotor radial displacements of DSBSRM can be reduced respectively. Moreover, the proposed control strategy has better robustness and dynamic performance than traditional control strategy.

In the wireless power transfer system (WPT) via magnetically coupled resonance, the lateral misalignment between the transmission coil and the receiving coil may affect the mutual inductance, then the transfer efficiency may be decreased, and the output power may be fluctuated, which lead to an unstable system. In this paper, a calculation method of the mutual inductance of an asymmetrical two-coil structure is presented. Based on the mutual inductance calculation method, an optimization method of quasi-constant mutual inductance is proposed. The key parameters of each coil can be obtained by using the proposed method. The mutual inductance can be kept constant when the misalignment is changed. And the output voltage and efficiency are also nearly constant with different misalignments. Finally, the setup of the asymmetric two-coil WPT system via magnetically coupled resonance is designed. Calculation, simulation, and experimental results validating the proposed method are given.

A novel multi-mode resonator-fed filtering patch antenna with improved selectivity and bandwidth is proposed in this paper. Unlike well-known cascaded-resonator structure, the proposed filtering antenna shows five poles in the reflection coefficient response utilizing only one resonator. The gap-coupled radiating part introduces two gain zeros along each side of the gain response. Meanwhile, the dual-mode resonator feeding structure of the antenna will also produce another two gain zeros. All these four gain zeros highly improve the selectivity of the filtering antenna without increasing the number of coupling resonators. In addition, the bandwidth of the antenna is also considerably extended using this feeding structure. For validation, a prototype is designed, fabricated, and measured. The measured results agree well with the simulated ones.

A method based on the radial basis function neural network (RBFNN) is developed to fast establish the tropospheric refractivity profile model. Parameters of the RBFNN include SPREAD and the number of training samples is optimized. The actual measured data of meteorological station at Qingdao city in China are used as test data to evaluate the performance of RBFNN. The simulation results show that the root mean squared error (RMSE) has a minimum of 0.81 when SPREAD is 8.1. The simulated valuesagree well with the test data which is observed by using the sounding balloon method. Finally, the tropospheric refractivity profile model of a selected area is established by using two different simulation methods. This paper attempts to propose a method to fast establish the tropospheric refractivity profile model which providesanavailablemethod to correctthe atmospheric refractionerror in radar applications.

The resonant frequency of a magnetically coupled resonant wireless power transmission system is a core parameter that determines the performance of the system. However, how to obtain the variation law of the resonant frequency and the efficiency or output power of the system is still a difficult problem when the capacitance of each coil is changed. In this paper, a two-coil wireless power transmission system is taken as an object, and the expressions of the input impedance, frequency, efficiency, and output power are deduced. Based on these expressions, the relationships among frequency, efficiency, and output power are studied. It is concluded that there may be multiple resonant frequencies in a WPT system with the changes of capacitance. The system always features a maximum efficiency point and a maximum output power point. The frequencies of the two points are almost the same. These theories provide a feasible scheme for simultaneously achieving both a high efficiency and output power. Finally, a magnetically coupled resonant wireless power transmission system is designed and developed. Simulated and experimental results demonstrate the validity and correctness of the proposed method.

This letter proposes a compact single-layer balanced bandpass filter (BPF), which is realized by a new arrangement of eighth-mode substrate integrated waveguide (EMSIW) cavities. Under differential-mode (DM) operation, the half bisection topology of the proposed EMSIW filter can be equivalent to a quadruplet scheme based on four coupled EMSIW cavities. The negative cross coupling can be easily realized by the nature of the fringe electric fields of opened ends of EMSIW cavities. For the demonstration, a balanced EMSIW filter with the operating frequency at 2.4 GHz is designed, fabricated, and measured.

In this paper, a sensor based on a meta-surface absorber loaded with microfluidics is proposed foridentification of edible oil species and provides a non-destructive, rapid and convenient technology for the measured samples. First, a narrow-band absorber with absorption frequency of 9.887 GHz and Q value of 147, which is implemented with four W-shaped meander line resonators, is designed by Finite Element Method. Its corresponding electromagnetic resonance mechanism is explored to reveal absorption characteristics, build its corresponding equivalent circuit model and guide the design of the palindromic microfluidic channel. The sensor shows a high sensitivity of 500 MHz/ε'_r, and the corresponding sensing performance is experimentally validated by the fact that the distinguishableresonance absorption frequency shift is 461 MHz, 458 MHz, 449 MHz, 444 MHz and 436 MHz when rapeseed oil, corn oil, peanut oil, sesame oil, and olive oil are loaded into the microfluidic channel, respectively. The identificationis successfully achievedaccording to the resonance absorption frequency shift. Moreover, a good agreement between the simulated and measured results demonstrates that the proposed meta-surface-inspired sensor is a promising candidate to monitor and determine the quality of edible oil to some extent, and is relatively valuable to the modern agriculture and food industry.

The problem of ambiguity in defining effective dielectric permittivity is studied theoretically in application to a plane layered heterogeneous medium, compounded by two and more alternating homogeneous layers with different dielectric permittivities (water and glass), for the range of wavelengths from 1 to 10 cm. The effective permittivity for such a heterogeneous medium is usually determined by the phenomenological semi-empirical Braggeman's power rule, and the aim of the given investigation is validation of this rule by means of rigorous model of plane wave transmission and reflection. It is shown that the complex values of effective dielectric permittivity for a layered dielectric, determined by measuring its transmission and reflection coefficients, differ noticeably from one to another. It is also shown that in a wide frequency range, the Braggeman's formula gets as a close approximation only for such an effective dielectric permittivity, which is determined by a transmission coefficient.

Loss and temperature rise are important parameters for performance evaluation of bearingless switched reluctance machine. In this paper, a 12/8 outer-rotor single-winding bearingless switched reluctance motor (SWBSRM) is studied for its loss and temperature rise under high speed operation. Firstly, a 2D finite element model is established by using Ansoft Maxwell, and the magnetic flux density waveform and the variation law of different parts of the core are obtained. Furthermore, various losses including core loss and copper loss are coupled to the temperature field analysis module as a heat source. Thirdly, the thermal model is established by Motor-CAD, and the transient and stable temperature field is simulated and analyzed. Finally, the temperature field distributions of the core and windings are obtained.

In this paper, the Compressive Sampling Matching Pursuit Algorithm (CoSaMP) is applied to microwave reconstruction of a 2-dimensional non-sparse object. First, an adaptive discretization method, DistMesh method, is applied to discretize the image domain based on the region of interest. The dual-mesh method is able to provide denser and smaller discretized cells in more important areas of the object and larger cells in other areas, thereby providing more details in the interest domain and keeping the computational burden at a reasonable level. Another benefit of using the dual-mesh method is that it automatically generates size functions and adapts to the curvature and the feature size of the geometry. In addition, the size of each cell changes gradually. Next, the inverse scattering problem is solved in frame of Distorted Born Iterative Method (DBIM). During each iteration of DBIM, the near field scattering problem is modeled as a set of linear equations. Furthermore, a compressive sensing (CS) method called the Compressive Sampling Matching Pursuit Algorithm is applied to solve the nonlinear inverse problem. During this process, two innovative steps are applied. First, for the reconstruction of the non-sparse object, the signal input to our algorithm is processed via a wavelet transformation to obtain sparsity. Second, as the dual-mesh method discretizes more important cells in smaller sizes, these cells have high potential to be filtered by the threshold of CoSaMP. As a result, a regularization matrix is introduced to reduce the effect of size. Finally, we present numerical experiment results based on our dual-mesh method combined with the regularized CoSaMP algorithm.

In this paper, a simple approach for enhancing the gain of a planar dipole antenna using the concept of grounded metamaterial (MTM) has been proposed. In this regard, a magnetic metamaterial with Mu-very large (MVL) property has been utilised to increase the gain of the electric dipole source. A fully planar structure has been configured due to the placement of the metamaterial just over the ground plane. A significant amount of gain improvement (about 3.7 dB) of the dipole antenna can be attained using the metamaterial. In addition, a fair increase of fractional bandwidth by 2.2% has been obtained due to the loading of the metamaterial. A comparative study with respect to recently reported literature for the gain enhancement of planar dipole has also been discussed. The proposed antenna is a worthy candidate for wireless communication owing to the high gain, low profile, and wide bandwidth characteristics.

Underwater electric field is an important source of exposure for warship targets, so we try to track the ship's movement by measuring its underwater electric field in this paper. Considering the nonlinear distribution characteristics of underwater electric field, the unscented particle filter method is applied for tracking. First, the equivalent electric field model based on point-electrodes methods is studied. Second, the equivalent electric field model of a scaled ship is used as the electric field source, and the source's movement is tracked by measuring the three components of the underwater electric field induced by the source. To meet the requirements of mine applications,only one measuring node is used in the tracking process. Thenumerical simulation result shows that the target can be tracked stably within 200 meters of the measuring node. Finally, a sea trail experiment is carried out to examine the effectiveness of this method. In this experiment, the electric field source is composed by two graphite electrodes, and only the horizontal components of underwater electric field are measured. The results show that the tracking performance is good within 150 m of the measuring node.

As one of the important means in discriminating every mode in a high power microwave (HPM) multimode system, utilizing a mode-selective directional coupler to quantitatively analyze multi-modes and power measurement has been proposed. The first step of this method is to calibrate the coupling coefficients of each coupled mode in the HPM system. Moreover, the conventional calibrating method must make the corresponding single mode exciter or mode generator. In this manuscript, a different calibrating method is presented by measuring the output power from each output port of two back-to-back identical mode-selective couplers, including the backward wave power, then the coupling coefficients of each coupled mode can be calculated by combining and solving equations. In this way, it is not necessary to manufacture the single mode exciter or mode generator for each mode in the HPM system, and also to repeat iteration solution; therefore, this method is more precise, convenient, efficient, and has lower cost than the current other methods.