An 8 mm-band passive millimeter-wave imager BHU-2D has been developed by Beihang University. This imager is designed for detecting concealed weapons on human body. The imager adopts two-dimensional synthetic aperture interferometric radiometer (SAIR) technique which avoids the radiation risk to human body. Compared with scanning technique, SAIR technique could obtain images of a larger field of view (FOV) while achieving high imaging rate, which are necessary for security monitoring. In this paper, the imaging principle of SAIR is stated firstly. Secondly, background cancellation method designed for BHU-2D is interpreted. The technique is used to reduce the complexity as well as the dimensional requirements of the receiving elements. Thirdly, system configuration is illustrated in detail. Then external point source calibration method is introduced and discussed specifically for security check applications. Finally, imaging experiments on a person with concealed weapon are conducted by which the design and image calibration algorithms are verified. To conclude, experimental results prove that BHU-2D could be employed in security check applications.

The magnetic energy and inductance of current distributions on the surface of a torus are considered. Specifically, we investigate the in°uence of the aspect ratio of the torus, and of the pitch angle for helical current densities, on the energy. We show that, for a fixed surface area of the torus, the energy experiences a minimum for a certain pitch angle. New analytical relationships are presented as well as a review of results scattered in the literature. Results for the ideally conducting torus, as well as for thin rings are given.

Compressive Sensing (CS) is a recently developed technique, which can reconstruct the sparse signal with an overwhelming probability, even though the signal is sampled at highly sub-Nyquist rate. Based on the observation that the electromagnetic scattering structure (ESS) of a metal landmine is composed of two scattering centers, whose geometrical parameters are tightly related to its physical dimensions, a new physics-based landmine discrimination approach is proposed in this paper. Firstly, the approach uses the Multi-Measurement Iterative Pixel Discrimination method to reconstruct the landmine's ESS in noisy environments. Secondly, the geometrical parameters of the landmine's ESS are extracted from the sparse image. Thirdly, landmine discrimination is conducted according to the measured geometrical features and apriori knowledge. Finally, the field experimental results demonstrate the effectiveness of the proposed approach.

The purpose of this paper is to investigate the use of simulation technology for the analysis of wireless propagation channel in medical environments. In this paper, the channel modeling has been carried out by using an effective simulation platform, which combines full-wave Method of Moments and adaptive ray tracing technique. Base on this, the channel characteristics involving both large-scale and small-scale parameters of a wireless network deployed within a hospital environment can be estimated. Also, it is straightforward to predict the levels of electromagnetic field interference produced from the network infrastructure. The simulated results of four scenarios of medical environment, such as the patient room, the operating room, a particular level of the hospital, and the cardiac stress test room, with different wireless technologies used show the advantage and capability of the presented simulation approach.

A vector network analyzer (VNA) with a bulk current injection (BCI) probe is proposed to measure the transmission coefficient of a PCB. The purpose of developing such a measurement techniques is to predict the radiated emission for good correlation with the fully-anechoic chamber measured results. In this study, the proposed method is used to determine the radiated emission from a DC supply loop. Moreover, the proposed method can be further used to accurately predict the reduction of radiated emission from the improved DC supply loop. Electromagnetic simulations is also developed to confirm the accuracy of the proposed techniques.

In this paper, small dual layer spirals with several various ground structure are applied in the vicinity of the DDR3 high-speed circuit to achieve noise suppression characteristics up to 3.2 GHz region. For wider noise suppression bandwidth, the dual layer spirals with various ground structure, which provide high self resonance frequency (SRF) as well as inductance value, are implemented. The proposed dual layer spiral with various ground clearance dimension exhibits greater than 9 dB power noise suppression characteristics in the frequency range of interests and achieve about 50% voltage fluctuation reduction in time domain compare to the reference case model. To validate the effectiveness of the proposed model, sample PCB are fabricated and measured. It shows good agreement between the measured and simulated results up to 3.2 GHz.

Efficient and accurate modeling of electromagnetic structures is valuable in antenna analysis and design, and time domain solutions are at a premium over frequency domain in the case of ultra wide band signals or transients. Among the full wave electromagnetic methods in time domain the method of moments in time domain (MoM-TD) is very interesting. Such a method can be implemented, as for frequency domain, either resorting to a thin wire approximation or to a surface patch model. Depending on the structure to be analyzed one or the other is most convenient. For heterogeneous structures both implementations might be needed, and the problem of the attachment between a perfectly conducting thin wire and a perfectly conducting surface is hence relevant. In this paper attachment modes are introduced in MoM-TD. The solution is validated on a test case and against another numerical technique.

A biconical antenna has been developed for ultra-wideband sensing. A wide impedance bandwidth of around 115 % at bandwidth 3.73-14 GHz is achieved which shows that the proposed antenna exhibits a fairly sensitive sensor for microwave medical imaging applications. The sensor and instrumentation is used together with an improved version of delay and sum image reconstruction algorithm on both fatty and glandular breast phantoms. The relatively new imaging set-up provides robust reconstruction of complex permittivity profiles especially in glandular phantoms, producing results that are well matched to the geometries and composition of the tissues. Respectively, the signal-to-clutter and the signal-to-mean ratios of the improved method are consistently higher than 5 dB and 10 dB, corresponding to an average increase in image fidelity of more than 140% compared to conventional radar focusing technique.

A novel circularly polarized cavity-backed antenna (CBA) excited by crossed bowtie dipoles is presented in this paper. It is fed by a transition from a microstrip line to double-slot lines. The crossed dipoles consist of a top-loaded triangular and a filleted rhombic to achieve the required input impedance relations for circularly polarized radiation. After optimization, a simulated 3-dB axial-ratio bandwidth of 50% and a broadside gain in a range of 7 to 9 dBi are achieved while the standing wave ratio is kept below 2.

We report results continuing the research which looks at the influence of two different magnetic materials in a core construction on the transformation errors of a current transformer [1]. In this paper we consider the behaviour of two different magnetic materials in a core. They are joined in a different way to the previous study; not axially (one-by-one), but also radially (one inside the second). We have conducted 3D analyses of the electromagnetic field distribution for different cases of current transformers and carried out computations based on the finite-element numerical method. We compare the results with tests of real-life models.

Design of multiband antennas with low volume is of practical interest for the ever growing wireless communication industry. In this regard, the design of a small multi band microstrip patch antenna (MPA) for GSM900 (880-960 MHz), GSM1800 (1710-1880 MHz), GSM1900 (1850-1990 MHz), UMTS (1920-2170 MHz), LTE2300 (2305-2400 MHz), and Bluetooth (2400-2483.5 MHz) applications by using a genetic algorithm (GA) is proposed. The proposed GA method divides the overall patch area into different cells taking into account that cells have a small overlap area between them. This avoids optimized geometries with certain cells having only an infinitesimal connection to the rest of the patch. Therefore, the proposed method is robust for manufacturing. A shorting pin is also included for impedance matching. GA optimization combined with finite element method (FEM) is used to optimize the patch geometry, the feeding position and the shorting position. A prototype has been built showing good agreement with the simulated results. The optimized MPA has a footprint of 46 mm × 57 mm (0.138λ x 0.171λ at 900 MHz) and an air gap of 10 mm. It shows a reflection coefficient less than -10 dB at all six bands and can be useful for a base station antenna.

The element failure of antenna arrays increases the sidelobe power level. In this paper, the problem of antenna array failure has been addressed using Firefly Algorithm (FA) by controlling only the amplitude excitation of array elements. A fitness function has been formulated to obtain the error between pre-failed (original) sidelobe pattern and measured sidelobe pattern and this function has been minimized using FA. Numerical example of large number of element failure correction is presented to show the capability of this flexible approach.

The Split-Field Finite-Difference Time-Domain (SFFDTD) formulation is extended to periodic structures with Kerr-type nonlinearity. The optical Kerr effect is introduced by an iterative fixed-point procedure for solving the nonlinear system of equations. Using the method, formation of solitons inside homogenous nonlinear media is numerically observed. Furthermore, the performance of the approach with more complex photonic systems, such as high-reflectance coatings and binary phase gratings with high nonlinearity is investigated. The static and the dynamic behavior of the Kerr effect is studied and compared to previous works.

In this paper, electromagnetic scattering problems are analyzed using an electric field integral equation (EFIE) formulation that is based on loop-star basis functions so as to avoid low-frequency instability problems. Moreover, to improve the convergence rate of iterative methods, a block matrix preconditioner (BMP) is applied to the EFIE formulation which is based on loop star-basis functions. Because the matrix system resulting from the conventional method of moments is a dense matrix, a sparse matrix version of each block matrix is constructed, followed by the inversion of the resultant block sparse matrix using incomplete factorization. Numerical results show that the proposed BMP is efficient in terms of computation time and memory usage.

We propose a new architecture for array antennas able to achieve a high-gain performance by using a low number of elements and uniform-amplitude excitations. The solution is realized through a fast and deterministic design technique able to accurately emulate, by exploiting only the feeds' dimensions as degrees of freedom of the synthesis, `ideal' continuous aperture sources fulfilling at best the assigned directivity requirements. The given theory is supported by numerical examples concerning the synthesis of isophoric direct radiating arrays devoted to a multibeam coverage of Europe from a geostationary satellite.

We report synthesis of magnetic Fe₃O₄ nanoparticles (MNPs) based on two phase method and their application in organic light-emitting devices (OLEDs) as blend with emissive Polyfluorene (PFO) matrix. Two phase method allows to successively synthesizing oleic acid capped MPNs with 5-10 nm particle size. Colloidal MNPs can be easily mixed with emissive polymer solutions to obtain a blend for OLED application. The electroluminescence efficiency increases by doping with MNPs into emissive layer. Different dopant concentrations varied from 0.4% to 2% were monitored. It was observed that the electroluminescence increases up to 1% v/v doping ratio. The luminance of OLEDs increased from 15.000 cd/m² to 24.000 cd/m² in comparison pristine device with 1% MNP doped device.

Diagonal loading has been regarded as an efficient manner to tackle the finite sample effect or the steering vector imprecision problem on adaptive array beamforming. However, the reason of the robustness improvement by the loading factor is still unknown and rarely discussed. In this paper, we consider the finite sample effect and derive the approximated output signal-to-interference-plus-noise ratio (SINR) of minimum variance distortionless response (MVDR) beamformers with diagonal loading. The obtained SINR expression is more explicit and compact than the existing formulas in the literature. Based on the theoretical results, we investigate the effects of a loading factor on the output SINR of MVDR beamformers. The theoretical analysis shows the effectiveness of diagonal loading on alleviating finite sample effect. Moreover, the price of using diagonal loading is also discussed. Simulation results are presented for confirming the validity of the research work.

In this paper, we present a method for detecting anti-tank or anti-personnel landmines buried in the ground. A set of data generated by a ground penetrating radar is processed to remove the surface reflection and clutter, yielding signals for possible landmines. In order to detect landmines in the signals, features are computed and compared against a database, which contains those of various landmines. Three features are proposed to use; principal components from principal component analysis, Fourier coefficients and singular values from singular value decomposition method, each of which is chosen to represent each landmine uniquely. Detection is performed using Mahalanobis distance-based method. Examples show that the proposed method can effectively detect landmines in various burial condition.

In this paper a robust technique for the design of high performance directional couplers is proposed. It combines the advantages of wiggly coupled lines and slot-coupled lines but overcomes their main limitations. The key to this novel technique is a new corrugated slot that allows perfect compensation of the even and odd mode phase velocities and can be easily designed using Bloch-Floquet theory, yielding outstanding performance. To demonstrate the validity of the proposed technique, the design of two different wideband directional couplers is presented. The first design consists of a 10 dB asymmetric directional coupler with a one decade bandwidth (1.2-12 GHz) that exhibits a coupling accuracy of 10±0.6 dB, a return loss better than 23 dB and an isolation better than 28 dB across the complete frequency band. The second design consists of a symmetric quadature hybrid that operates over the complete UWB band (3.1 to 10.6 GHz) showing an amplitude and phase imbalance between the output ports lower than ±0.5 dB and ±0.7°, respectively.

Conventional equivalent source reconstruction methods (SRM) require both phase and amplitude information of the acquired field data. However, there are situations where the phase information is not available or impractical to obtain. Hence, the development of SRM using phaseless fields is important. In this paper, a novel iterative SRM based on phaseless electric fields is presented. The reconstructed equivalent current source can be electric, magnetic current, or both. They can fit the physical geometry of the radiator. Electric field integral equation (EFIE) is employed to build the relationship between the reconstructed current source and measured fields. It can precisely reproduce the original 3D radiation pattern with very good accuracy. To investigate the robustness and accuracy of the proposed approach, both strong and weakly-directional radiators are benchmarked.