This paper presents a modified version of minimum description length (MDL) method, referred as multifrequency MDL (FMDL), for scatterers enumeration before using the multiple signal classification (MUSIC) algorithm in microwave imaging applications. The inclusion of data from multiple frequencies should make an attempt to reduce the error in number estimation due to noise and multiple scattering. Data fusion in multiple frequencies is performed based on two schemes called averaging and maximization rules. The solution for MDL criterion which is a minimum for one frequency is not likely to be the solution for other frequencies, so by averaging the MDL criterion over the total frequencies or by maximization of the solution for each frequency, we can achieve the correct source number. Furthermore, a whitening step before applying FMDL method is employed to compensate the aspect limitations of the measured data due to the limited number of antennas. The superiority of the proposed FMDL approach with respect to the other competing methods is confirmed by both the numerical examples and the Institut Fresnel experimental dataset. The results indicate that the FMDL yields more accurate estimate of the targets number specially for the cases of low SNR values and very colsely spaced scatterers.

A meshless method for fast solution of the electromagnetic scattering problem related to arbitrary shaped radially inhomogeneous cylinders is proposed. This is an important problem since radially inhomogeneous circular cylinders are common in various engineering applications, and deformations such as notches, grooves and noncircular holes on such cylinders are required for different purposes. This approach is basically an extension of the previously proposed method, which is based on Fourier series representation of the electric field on boundaries. In the original method, a multilayer cylinder with arbitrary shaped homogeneous layers is considered, and accordingly, the general solution of the cylindrical wave equation in homogeneous medium is used. Here we modify the method by considering the general solution in radially inhomogeneous medium, and derive compact expressions for the field.

A substrate integrated waveguide circular cavity (SIWCC) bandpass filter is developed using printed circuit board technology. A circular cavity structure using TM₁₁₀ mode was employed in the design of the filter to operate at the frequency of 4.75 GHz, which is in the C-band frequency range. The filter was designed based on double-layer elements comprising a substrate integrated circular cavity (SICC) and a transmission line (TL) that produce single-mode resonance. In the proposed structure, circular resonators consisting of vias and a rectangular patch at the top layer are combined into a circular substrate integrated waveguide (SIW) structure. To achieve the desired resonance frequency, a triangle probe is etched at both sides of the microstrip line feeding section. The proposed structure is put in a conducting box to prevent radiation to the outside and eliminate radiation loss. Furthermore, the desired centre frequency and bandwidths of the passbands can be obtained by adjusting the dimension of the filter. To prove the concept, the filter structure is fabricated using Rogers RO₄₃₅₀B^TM circuit materials with a dielectric constant of ε_r = 3.48 and height of the substrate of 1.52 mm. The design was simulated using Ansoft HFSS simulator and measured using a vector network analyser. Simulation and fabrication results are compared for verification. The proposed SIWCC bandpass filter has potential applications in satellites and wireless communication systems.

In a probabilistic approach, the performance of the control is characterized by statistical indi-cators such as the Probability of Detection (PoD) which describes the probability of detecting a defect of a given size knowing that it is present in the inspected structure. In this paper, an experimental analysis and simulation using FEM of the eddy current testing on three-dimensional riveted structure is performed on small fatigue cracks to identify and quantify probability of detec-tion curves. The PoD curves are plotted in terms of characteristic dimensions of the defect (depth, length, orientation, etc.) and are dependent on a number of factors including material, geometry, defect type, operator, and environmental effects.

The recent growth of terahertz (THz) applications has sparked interest in the design of novel electromagnetic structures for this frequency regime. One of the structures is the THz absorber, used in sensing and imaging applications. Metamaterial based designs are commonly used to achieve the desired absorption characteristics. Absorbers whose spectra can be tuned by changing the temperature are a subclass in the broad family of THz absorbers that are used for temperature sensing. In the beginning years, single band temperature tunable absorbers were designed, and at present the focus has shifted to the design of multi-band temperature tunable absorbers. Absorbers with six tunable bands have already been proposed. In this paper an octa-band temperature tunable terahertz metamaterial absorber is proposed, whose unit cell consists of four orthogonally placed tapered triangular structures connected by a ring resonator on top of an InSb dielectric substrate. At 210K it is observed that the structure's absorption spectra are: 98.7% at 1.026 THz, 79.5% at 1.245 THz, 90.4% at 1.301 THz, 95.2% at 1.442 THz, 97.44% at 1.585 THz, 96.4% at 1.644 THz, 97.1% at 1.756 THz, and 90.4% at 2.071 THz. The temperature sensitivities of the proposed structure in eight of its absorption bands are 10.3 GHz/K, 8.22 GHz/K, 7.96 GHz/K, 7.02 GHz/K, 6.44 GHz/K, 6.17 GHz/K, 5.5 GHz/K, and 3.2 GHz/K, respectively. Thus, the proposed design can have practical applications in terahertz temperature sensing applications.

This paper describes a theoretical characterization of a Transverse Electric (TE)-polarized vortex beam antenna in the microwave range. The main body of the antenna consists of a cylindrical waveguide that is excited by a traveling-wave current ring feeder. A new design of the feeder is proposed. Closed-form formulas are obtained for the fields and the antenna input impedance following a conventional derivation based on the electric vector potential. A detailed dispersion analysis is used for accurate evaluation of the relevant spectrum and propagation properties. The effectiveness of the theoretical derivations is validated via full-wave numerical simulations.

As ionosphere is one of the most prominent sources of error, ionospheric TEC and scintillation studies are necessary for improving the performance of a navigation system. In this paper, the behavior of the correlation coefficient (ρ) between Rate of TEC Index (ROTI) and amplitude scintillation index (S₄) over low latitude station Hyderabad (Latitude: 17.44° (deg.) N, Longitude: 78.74° (deg.) E) for different seasons is analyzed. Also, the analysis is extended for nearly same longitude stations like Trivandrum, Bangalore, Bhopal, Delhi and Shimla for the higher values of total K_p index for 60 days (most disturbed 5 days per month). For Trivandrum (lowest latitude station), it is observed that both S₄ and ROTI are high as compared to Bangalore, Bhopal, Delhi, and Shimla. It is found that there is a good correlation between the temporal variations of ROTI with S₄ after post sunset hours. The confidence intervals for computed correlation coefficients at 95% confidence level are also given.

Non-contact vital sign detection using radar is relevant for many applications. In search and rescue missions in disaster-stricken areas, this technology can be used to non-invasively detect live survivors on the ground. However, in a very large disaster area, a fast and effective detection approach is required. This need has suggested radar mounted on a flying platform such as a drone as the most feasible approach. This task is challenging, since human respiration is weak, and the signal recorded is easily affected by disturbances such as noise and movement of the platform. Therefore, in this study, we propose a signal processing technique to deal with this problem. Human respiration signals modulate a hyperbolic pattern recorded by moving radar because of distance projection, leading us to applying sequential image processing steps and hyperbolic pattern reconstruction to extract respiration signals. A Fourier transform is then applied to seek the respiration frequency component. The results of laboratory experiments show that the proposed method can detect human respiration. As an important note, the flying speed of the platform should be determined carefully to cope with slow human respiration.

Cherenkov radiation (CR) is a promising method to generate high-power terahertz (THz) electromagnetic (EM) waves, which are highly desired in numerous practical applications. For the purpose of economy energy, naturally occurred materials with flat surface (e.g. graphene), which can support highly-confined surface-plasmon-polariton (SPP) modes, have been proposed to construct high-efficiency terahertz CR source; however, these emerging materials cannot be easily fabricated nor flexibly designed. Here, we propose a designer-SPP metamaterial scheme to pursue terahertz CR. The metamaterial is a structure-decorated metal surface, which is compatible with planar fabrication, and can support SPP-like EM modes in terahertz frequencies, also named as designer SPP. Due to the structure dependence of designer SPP, its dispersions can be flexibly designed by changing the structure geometries as well as choosing proper dielectric medias. Numerical results clearly demonstrated this scheme. Our proposal may promise future high-efficiency and intense THz source with design flexibilities.

Fluorescence confocal laser scanning endomicroscopy is a novel tool combining confocal microscopy and endoscopy for in-vivo subcellular structure imaging with comparable resolution as the traditional microscope. In this paper, we propose a three-channel fluorescence confocal microscopy system based on fiber bundle and two excitation laser lines of 488nm and 650nm. Three fluorescent photomultiplier detecting channels of red, green and blue can record multi-color fluorescence signals from single sample site simultaneously. And its ability for in-vivo multi-channel fluorescence detection at subcellular level is verified. Moreover, the system has achieved an effective field of view of 154μm in diameter with high resolution. With its multi-laser scanning, multi-channel detection, flexible probing, and in-vivo imaging abilities it will become a powerful tool in bio-chemical research and diagnostics, such as the investigation of the transport mechanism of nano-drugs in small animals.

In this paper, the effectiveness for inferring the responses to electromagnetic threats of the finite difference time domain method combined with a multi-conductor, multi-shield and multi-branched cable harness transmission line solver is validated by comparing simulation results with measurements performed on an equipped cockpit partially made by carbon fiber composite. A complete lightning indirect effects and high-intensity radiated field testing campaign was carried out in this cockpit within the scope of the European research and technology project Clean Sky 2 whose main goal is to reduce the aviation environmental impact by, for instance, building low-weight aircrafts with the increasing use of carbon fiber. Simulations are performed with EMA3D and MHARNESS obtaining very good agreement with measurements for a variety of observables and in a wide frequency range, thus proving the predictive capacity of these numerical methods for estimating the electromagnetic behavior of complex structures.

In this article, a novel dual-band multi-port compact rectenna design for RF energy harvesting is proposed. An E-shaped coaxial fed microstrip antenna combined with an inverted L-shaped structure is used to achieve a dual-band operation at 0.9 GHz (GSM900) and 2.4 GHz (WiFi) frequency bands with gains of 0.8 dBi and 4.4 dBi, respectively. A shorting post is incorporated in the design, which restricts the antenna size to 50 mm x 47 mm, making the overall rectenna compatible with any sensor nodes. Further, a compact rectifier circuit covering both the frequency bands is designed to obtain a conversion efficiency up to 50% for an input power as low as -20 dBm. The matching circuit ensures that the nonlinear impedance of the rectifier matches with that of the antenna under varying operating conditions. Finally, the rectennas designed are combined and arranged together to form a cubical structure to produce an output voltage as large as 0.5 V for an input power of -20 dBm. With 360˚ coverage and orthogonal polarization reception, the cubical antenna arrangement ensures improved harvesting efficiency making the proposed design suitable for powering low power IoT devices.

In this paper, two microstrip antennas with a U-slot on the patch are presented for base station applications to provide simultaneous communications for uplink and downlink respectively. The intended antennas are expected to operate in triple bands, i.e., to cover GSM and LTE bands. The three designated bands for uplink antenna are from 823 MHz to 830 MHz for lower band, 1.738 GHz to 1.761 GHz for middle band and 2.321 GHz to 2.355 GHz for upper band. Similarly, the antenna which is designed for downlink operates in three bands from 872 MHz to 880 MHz for lower band, 1.81 GHz to 1.85GHz for middle band, and 2.338 GHz to 2.375 GHz for upper band. These frequency band(s) satisfy the requirements of GSM850, GSM1800, and LTE2300 bands. Comparisons among designed, simulated and measured results are presented. Isolation parameters and the Envelope Correlation Coefficient (ECC) values of Multiple Input Multiple Output (MIMO) antenna in all specified bands are also presented.

The performance of direction-of-arrival (DOA) estimation algorithms degrades when a partly calibrated array is adopted due to the existing unknown gain-phase uncertainties. In addition, the spatial discretized searching grid also limits the performance improvement and effectiveness of subspace-based DOA estimation algorithms, especially when the true angles do not lie on the grid points which is referred to the off-grid problem alike. In this paper, a self-calibration DOA estimation algorithm is proposed which solves the array calibration and off-grid problems simultaneously. Firstly, the signal model for a partly calibrated array with gain-phase uncertainties is established. To suppress the off-grid errors, an optimization problem for joint parameters estimation is constructed by substituting the approximation of the steering vector into a newly constructed objective function. The alternative minimization (AM) algorithm is employed to calculate the joint DOA and gain-phase uncertainty estimations. Within each iteration step of the optimization problem, a closed-form solution is derived that guarantees the convergence of the proposed algorithm. Furthermore, the Cramer-Rao bound (CRB) for the partly calibrated arrays with unknown gain-phase uncertainties is also derived and analyzed in the paper. Simulation results demonstrate the effectiveness of the proposed algorithm.

An efficient field-to-circuit hybrid method is presented for the electromagnetic interference (EMI) analysis of penetrated wire of an electronic device excited by ambient wave, which consists of finite-difference time-domain (FDTD) method, transmission line (TL) equations, Thevenin's theorem, and circuit analysis method. The significant feature of this method is that it can avoid modelling the structures of penetrated wire and terminal circuit directly on the premise of guaranteeing sufficient accuracy. At first, the whole model of penetrated wire of an electronic device is decomposed into external and internal regions according to the shielded enclosure of the device. Then, the FDTD method combined with TL equations is applied to build the coupling model of external transmission line with the shielded enclosure and extract the equivalent circuit model of an external region based on Thevenin's theorem, which is further imported into the internal region as excitation source. Finally, the EMI analysis of internal region is executed by constructing the transmission parameter matrices of the two-port cascade network, which is contributed by the penetration node, internal transmission line and terminal circuit. Then the interference response on terminal circuit can be obtained. Numerical simulations have been taken into account to verify the the accuracy and efficiency of this field-to-circuit hybrid method by comparing with the traditional FDTD method.

A novel optically-switched antenna is proposed, in which a photodiode is embedded into an antenna radiator. In order to avoid the high loss problem in series structures for the integration of photodiodes and patch antenna, a photodiode parallel structure with sensitive radio frequency response is selected for the design. The status of the antenna while at work can be effectively adjusted by illumination. Its reflection coefficient and radiation gain vary with the exposure of photodiode to light illumination and non-illumination state. The simulation and experiment of this design at 1.52 GHz produce an obvious effect on light control with a maximum 6.6 dB gain variation on omnidirectional pattern. It is thus deemed suitable for speed measurement and occlusion detection in remote wireless sensor networks and other applications.

A dual-mode hyperspectral imager using field of view scanning needs no moving macro parts. It could work in dual-mode (macro imaging and micro imaging) and is equipped with a conjugated camera for quick object-selection and focusing. By adjusting the imaging lens and achieving the image clarity on the conjugated camera, we could find the correct location and focusing of the ROIs simultaneously instead of inefficiently checking the hyperspectral image after the whole scanning process. The whole system was applied to the study of spectral characteristics of blood oxygen in human hands and the microscopic identification of algae, showing a great potential of clinical and marine applications of our system.

In order to overcome the problem of high voltage loss rate caused by the increase of current harmonics due to dead-time effect and the decrease of average potential output of inverter in the control process of the interior permanent magnet synchronous motor (IPMSM) for electric vehicles, a dead-time compensation control method based on an extended Kalman filter (EKF) and a neural network bandpass filter (NNBPF) is proposed. Firstly, from the mechanism of dead-time effect, the problems and causes of dead-time effect are analyzed. Secondly, the extended Kalman filter combining feedback and prediction function is used to filter the d- and q-axis currents of the motor, so as to solve the problem that zero current polarity is difficult to judge in the traditional dead-time compensation process. Thirdly, the high-order harmonics due to dead-time effect in the d- and q-axis currents are extracted by using the neural network band-pass filter, and the dead-zone compensation is carried out after the amplitude phase adjustment. Finally, the effectiveness of the proposed dead zone compensation method is proved by comparing no dead-time compensation with the dead-time compensation strategy proposed in this paper. The experimental results show that the proposed dead-time compensation method can effectively suppress the current harmonics, reduce the current distortion, reduce the voltage loss rate to 0.04%, improve the voltage utilization ratio, and effectively improve the operating performance and endurance of electric vehicles.

In practice, the amplitude and phase excitations of array elements undergo random errors that lead to unexpected variations in the array radiation patterns. In this paper, the technique of the clustered array elements with discretized amplitude excitations is used to minimize the effect of random amplitude excitation errors and restore the desired array patterns. The most important feature of the proposed technique is its implementation in the design stage which may instantly count for any errors in the amplitude excitations. The cost function of the used optimizer is constrained to prevent any undesirable increase in the sidelobe levels due to unexpected excitation errors. Moreover, the error occurrences on the element amplitude excitations are considered to be either randomly over the whole array aperture or regionally (i.e., error affecting only a part of the array elements that located in a particular quadrant of the array aperture). Simulation results fully verify the effectiveness of the proposed technique.

The (6k±1)th harmonics exist in the extended electromotive force estimates due to the influence of the inverter nonlinearities and the flux spatial harmonics in the process of sensorless control of permanent magnet synchronous motor (PMSM), which give rise to the (6k)th harmonic in the rotor position estimate. A method of rotor position observation based on the time delay signal cancellation-frequency locked loop (DSC-FLL) is proposed to improve the sensorless control system of PMSM. The equivalent back EMF information is obtained by using the sliding mode observer, and the harmonic component in the specified back EMF observation value is filtered by using the delay signal elimination operator in the two-phase static coordinate system. The frequency locking loop is designed to track the rotor position information online, so as to improve the observation accuracy of the rotor position information. The model of sensorless control system of PMSM based on DSC-FLL is established, and compared with the model of sensorless control system of PMSM based on arctangent function. The results show that after adopting the method of rotor position observation based on DSC-FLL, the high harmonic in back EMF is suppressed, the error of rotor position fluctuation observation reduced, and the error of rotation speed observation reduced. The observation accuracy of rotor position information is significantly improved.