Semiconductor saturable absorber mirror (SESAM) based on InAs quantum dot (QD) material is important in designing fast mode-locked laser devices. A self-consistent time-domain travelling-wave (TDTW) model for the simulation of self-assembled QD-SESAM is developed. The 1-D TDTW model takes into consideration the time-varying QD optical susceptibility, refractive index variation resulting from the intersubband free-carrier absorption, homogeneous and inhomogeneous broadening. The carrier concentration rate equations are considered simultaneously with the travelling wave model. The model is used to analyze the characteristics of 1.3-μm p-i-n QD InAs-GaAs SESAM. The field distribution resulting from the TDTW equations, in both the SESAM absorbing region and the distributed Bragg reflectors, is obtained and used in finding the device characteristics including the modulation depth and recovery dynamics. These characteristics are studied considering the effects of QD surface density, inhomogeneous broadening, the number of QD absorbing layers, and the applied reverse voltage. The obtained results, based on the assumed device parameters, are in good agreement, qualitatively, with the experimental results.

By using parallel strip line fed printed dipole antennas as array elements, an omnidirectional antenna array and a wide angle sector coverage array operating in octave band are designed. A maximum deviation of ±1.25 dB from the omnidirectional pattern is achieved for the omnidirectional array, and the average gain of the antenna was measured as being 5 dB in the 1.35-2.7 GHz band. For the sector coverage array, a special reflector design is utilized to maintain a half power beam width of around 115° with a standard deviation of 14° in the aforementioned frequency band. The average gain of the sector coverage array was measured as 10 dB, thereby being almost three fold larger than the average gain of the omnidirectional array.

A fast low-frequency surface integral equation solver based on hierarchical matrix algorithm is proposed. First, the augmented electric field integral equation (A-EFIE) formulation is introduced to eliminate the low-frequency breakdown of traditional EFIE. To deal with large-scale problems, the low-frequency multilevel fast multipole algorithm (LF-MLFMA) is employed to construct a hierarchical (H-) matrix representation of the A-EFIE system matrix. Moreover, a recompression method is developed to further compress the H-matrix generated by LF-MLFMA. The H-matrix-based triangular factorization algorithm can be performed with almost linear computational complexity and memory requirement, which produces a fast direct solver for multiple right-hand-side (RHS) problems, and a good preconditioner to accelerate the convergence rate of an iterative solver. Numerical examples demonstrate the effectiveness of the proposed method for the analysis of various low-frequency problems.

A very compact triple band-notched multiple input multiple output antenna (MIMO) for ultra-wideband (UWB) communications is fabricated on a FR4 dielectric substrate having overall size of 18 x 21 x 0.8 mm³. The proposed antenna consists of two rectangular metal monopoles which are excited by 50-Ω microstrip lines on top of substrate, and a common protrude ground is at the bottom. To achieve low mutual coupling between radiating elements, a T-shaped stub is protruded from the ground plane. By etching two C-shaped slots on the radiating patches, band-notched functions at 5.15-6 GHz and 7.8-8.4 GHz are obtained. The third notch band from 3.3-3.7 GHz is realized by adding U-shaped metal strips to the ground. The measured and simulated results demonstrate that the proposed antenna offers good impedance bandwidth of |S₁₁| ≤ -10 dB from 2.8-12.2 GHz covering whole UWB band except at the designed notch bands, while giving less mutual coupling (|S₂₁|) of lower than -25 dB in the whole UWB band. The measured envelope correlation coefficient (ECC < 0.013), nearly constant gain and stable radiation patterns show that the proposed MIMO antenna is an appropriate candidate for portable UWB systems.

A dual-band two-element Multiple-Input-Multiple-Output (MIMO) antenna for Wireless Local Area Network (WLAN) applications is proposed in this paper. The MIMO antenna consists of two closely arranged symmetric monopole antennas with edge-to-edge distance of only 5.3 mm (0.044λ at 2.51 GHz). To enhance isolation, a decoupling network is inserted between the two antennas without increasing the footprint. The -10 dB impedance bandwidths in lower and higher frequency bands are 2.46-2.7 GHz and 5.04-5.5 GHz. Compared to previous works, the presented decoupling structure can obtain higher isolation over 30 dB in dual bands. Measured results agree well with the simulated ones.

A compact wideband circularly polarized square slot antenna for universal UHF RFID reader applications is proposed and tested. An L-shaped radiator at lower surface of the substrate is used to feed the proposed antenna. To achieve a broadband circular polarization (CP) and good performance, two rectangular stubs with different sizes are inserted at opposite corners of the square slot at the upper surface of the substrate. A small rectangular slit is used to improve the impedance matching of the proposed antenna. The antenna's measured <10-dB impedance bandwidth and measured 3-dB axial ratio bandwidth are 70.2% (660-1374 MHz) and 45.8% (796-1269 MHz), respectively. The proposed antenna has a dual circular polarization characteristic, wide impedance bandwidth, wide axial ratio, compact size, and maximum measured gain about 3.9 dBi. The total size of the proposed antenna is 120×120×1.6 mm³. Furthermore, the impedance bandwidth and axial ratio bandwidth of the proposed antenna cover the entire UHF RFID band easily. The proposed antenna is suitable for UHF RFID reader applications.

High power amplifier not only causes in-band intermodulation but also causes out-of-band harmonic distortion. For a wideband transmitter, harmonic distortion out of communication frequency can be restrained by a radio-frequency filter, but harmonic distortion in the communication frequency is difficult to restrain. In this paper, we develop harmonic memory proper to model harmonic distortion and then propose a digital harmonic canceling algorithm based on direct learning structure - nonlinear filtered-x ane projection algorithm (NFX-APA). Simulation and measurement results demonstrate that this novel digital canceling method can cancel harmonic effectively.

A new C-band monopole antenna is proposed for use in a CAPS-based vehicle monitoring system. This monopole antenna has highly omnidirectional main beam with low elevation angle and sufficient half-power beamwidth by using a cone-shaped ground plane. The impedance bandwidth defined by 10 dB return loss is 650 MHz (5.50-6.15 GHz), and the main beam elevation angle and the half-power beamwidth are about 20° and 40° at the operating frequency 5.885 GHz, respectively. The manufactured prototype has survived a long-distance terrestrial test across China, and the design requirements for the satellite link budget, volume, cost, etc. have been reached.

Eddy current testing (ECT) is known as an effective technology for inspecting surface and near surface defects in metallic components. It is well known that the amplitude of eddy current (EC) density decreases with increasing depth, which is referred to as skin effect. Skin depth is an important parameter that quantifies the speed of attenuation of EC in the depth direction and is closely related to the capability of ECT for detecting deeply hidden defects. It is found that the traditional formula for calculating skin depth derived under the assumption of uniform plane field excitation is not applicable to the cases of ECT with coils. The skin effect in component with flat surface excited by pancake coil has been investigated by the authors. The skin effect in conductive tube tested by bobbin coil and that in conductive bar tested by encircling coil are more complex. The paper studies the skin effect in these two cases. Finite element analysis shows that the attenuation of EC is not only due to the ohmic loss, but also influenced by the diffusion effects, the aggregation effect, and the combined cancellation/diffusion effect of EC. The skin depth of EC associated with bobbin coil is always smaller than that associated with uniform plane field excitation, whereas the skin depth of EC associated with encircling coil can be greater than that associated with uniform plane field excitation under certain conditions.

In the recently published article, Sood et al. (Progress in Electromagnetics Research M, Vol. 44, 3946, 2015) proposed a wide-angle ultra-thin metamaterial absorber structure for wideband applications. The reported unit cell was shown to have simulated wideband absorbivity FWHM bandwidth of 1.94 GHz i.e. from 5.05 GHz to 6.99 GHz. In this article, we prove that the reported structure is not an electromagnetic wave absorber. For the reported structure, we find that absorption is less than 22.3% over a operating bandwidth of 4 GHz to 8 GHz. It is demonstrated that the strong absorption was caused due to ignorance of cross-polarization effect rather than true absorption as they claimed.

This is the first communication reporting a compact broadband printed circular slot antenna with stair shaped ground plane in which bandwidth is enhanced mainly in the lower frequency band on adding 19 strips at regular space intervals in the partial ground plane. The impedance matching at specific band (7.1-8.4 GHz) takes place as a result of circular slot in the patch. The proposed structure is printed on an FR4 substrate with ε_r = 4.3 and 0.025 loss tangent over a compact volume of 20×25×1.5 mm³. The impedance bandwidth (S₁₁ < -10 dB) of the proposed antenna is 133.7 % (3.0-15.1 GHz). The antenna exhibits 4.9 dB peak gain and 74 % peak radiation efficiency in the operating band. Satisfactory results and such a simple and easy to fabricate design with compact space make the proposed antenna a suitable choice for UWB applications, 5.2/5.8 GHz WLAN bands, 3.5/5.5 GHz Wi-MAX bands, X band (8-12 GHz) and other wireless communication systems. Measured and simulated results are in good agreement, affirming the simulation process. Omnidirectional radiation patterns are generally observed in the operating band of the designed antenna.

The discovery of ``quasi-crystals,'' whose X-ray diffraction patterns reveal certain unusual features which do not conform with spatial periodicity, has motivated studies of the wave-dynamical implications of ``aperiodic order.'' This paper discusses various aperiodic configurations generated by Rudin-Shapiro (RS) sequences. These RS sequences constitute ones of the simplest conceivable examples of deterministic aperiodic geometries featuring random-like (dis)order. The scattering properties of aperiodically-ordered thinned 2-D patch arrays based on RS sequences are analyzed by using physical optics approximation. Compared to a periodic case, RS-based antenna array is found to have a substantial reduction in the magnitude of the backscattering component of the scattered signal with half of the elements and the same magnitude of specular reflection. This property is verified by illustrative numerical parametric studies.

This paper presents a broadband planar printed antenna comprising two dipoles with different lengths and a transition structure of microstrip (MS) to coplanar stripline (CPS). These two dipoles are serially connected through CPS. By adding trapezoid and stepped patches, the dipole elements are modified for enhancing the impedance matching of the antenna. In addition, a tapered transition is adopted in the CPS to achieve improved impedance matching. The current work shows a good agreement between measured and simulated results. The measured bandwidth is from 2.43 to 8.04 GHz for VSWR≤2, corresponding to 107.2% fractional bandwidth. Measured peak gain≥4.0 dBi is obtained in the whole operating band.

The problem of electromagnetic (EM) wave scattering on small particles is reduced to solving the Fredholm integral equation of the second kind. Integral representation of solution to the scattering problem leads to necessity to determine some unknown function contained in integrand of this equation. The respective linear algebraic system (LAS) for the components of this unknown vector function is derived and solved by the successive approximation method. The region of convergence of the proposed method is substantiated. The numerical results show rapid convergence of the method in the wide region of the physical and geometrical parameters of problem. Comparison of the obtained results with Mie type and asymptotic solutions demonstrates high degree of accuracy of the proposed method. The numerical results of scattering on particles of several forms and sizes are presented.

A new class of tri-band bandpass filter (BPF) is presented, and harmonic passband bandwidth can be independently controlled. In the implementation, three coupling paths are used to control the bandwidth of each passband. The first coupling path is two grounded vias which are utilized to realize coupling between two short-stub loaded resonators. And the first coupling path delivers signals at the first passband. Meanwhile, the second coupling path delivers signals at both the first and second passbands. And the third coupling path only delivers signals at the third passband. Using this method, both the frequency and bandwidth of each passband can be designed and tuned easily. In this filter design, the first harmonic passband can be adjusted separately and is independent of the fundamental passband. Two grounded vias improve flexibility and form a fundamental passband and harmonic passband independently controllable passband filter. For demonstration, a tri-band BPF with three passbands at 1.5 GHz, 2.5 GHz, and 3.5 GHz with insertion losses of 0.34, 0.76 and 1.08 dB is designed, fabricated and measured. So this proposed filter will be attractive in wireless communication systems.

A new microstrip-to-microstrip vertical transition structure for ultra-wideband (UWB) applications is proposed in this paper. The transition consists of a low impedance microstrip ring stub and a couple of slotline square multiple-mode resonators (MMRs) on the common ground plane. The low impedance microstrip ring stubs are realized by the connection of three single stubs in parallel, and the high-impedance section of slotline SIR is realized by the connection of four single stubs in series. The simulated and measured results are in good agreement, showing good wideband filtering performance with ultra-wideband fractional bandwidth.

In this paper, we present a straightforward numerical algorithm for visual image sequential motion detection based on half quadratic minimization method. To solve the optimization problem modeled for sequential motion detection, an auxiliary functional is introduced. The proposed algorithm is more efficient since the iterative computation is operate mainly on the current frame rather than the whole batch of images. As for the standard visual image sequences with RGB color representation, an intuitive way is to convert it to grayscale image to achieve an approximate motion detection with relatively low computational load. Instead, we propose an improved processing scheme for more accurate detection by utilizing the algorithm separately and then perform fusion on a higher level. Experiment results show that the proposed algorithm can successfully detect moving object in practical visual surveillance applications.

Light-sheet microscopy has attracted considerable attention since it is a fluorescence imaging technique with rapid optical sectioning capabilities for transparent sample. In our study, we report a new application based on light-sheet microscopy for exploratory investigating three-dimensional surface topography of opaque sample. Instead of using inelastic scattering fluorescent signal, our method utilizes the elastic scattering light from the surface of opaque sample, which is illuminated by a light sheet generated by a cylindrical lens. Through a simple structural modification by removing the fluorescent filter, the orthogonally imaging module can capture the elastic scattering image. As the opaque sample is scanned by a motorized stage, the light-sheet microscope acquires a serial of sectional images, which can be stitched to be a three-dimensional surface topography image. This method also offers the opportunity to visualize 3D fingerprint on micron level. Therefore, this technique may be useful in industry and biomedical field for the measurement of surface microstructure.

An approach to separate metallic and dielectric losses in ferroelectric capacitors in all range of tuning under control dc voltages (Udc) is considered. The procedure is based on measurements of the dc voltage dependencies of microwave losses (tanδt(Udc)) and capacitance (C(Udc)) for a set of capacitors with similar layout but with different nominals. Linear extrapolation of tanδt(C) dependencies at different control dc voltages to C = 0 allows to evaluate the dielectric losses tanδd as a function of the control dc voltage. The procedure of separation was performed for a set of sandwich metal/(Ba0:5Sr0:5)TiO3/metal capacitors. Capacitors parameters were measured at a frequency of 2 GHz in a range of electric field strength in ferroelectric of E = (0 - 30) V/μm. The intrinsic commutation quality factor of BSTO lm itself was estimated by the method proposed.