Method for widening the reject-band in low-pass/band-pass filters by employing coupled C-shaped defected ground structure

Two new compact defected ground structure low-pass filters with broad stop-band and low insertion loss in the pass band are presented. The structures of these new microstrip low-pass filters are simple as they are composed of a pair of DGS-slots and an openstub. One filter is realised through the multi-layer method, and the second filter by cascading. With these configurations, two LPF with compact size, wide reject band and sharp transition from pass to stop-band are realised. The design formulas are derived by using an equivalent circuit model of coupled DGS resonators. Demonstration filters are designed, fabricated and tested. The experimental results show good agreement with theoretical results and demonstrate that the required characteristics of LPF could be simply obtained through the proposed methods. Finally a simple gap-method will be used in order to transform the LPF to BPF.     

Wideband multilayered microstrip antennas fed by coplanar waveguide-loop with and without via combinations

Coplanar waveguide (CPW)-loop fed wideband multilayered microstrip antennas with and without via combinations are presented. The antenna consists of two dielectric substrates, CPW-loop on the ground plane layer, main patch on the middle layer and four asymmetric parasitic patches on the upper layer. The feed consists of a CPW, a loop on a ground plane and a via between main patch and feeding strip on the ground plane layer. Using via, the gain flatness over the impedance bandwidth and return loss are improved. The proposed antenna with four feeding structures is also studied. The 10 dB return loss bandwidths of the antenna with and without via are 34% (3.12? 4.41 GHz) and 33.7% (3.18 ?4.47 GHz), respectively. The measured gain is >5.0 dBi over the impedance bandwidth.     

Analytical closed-form solutions for different configurations of parallel-coupled microstrip lines

Closed-form solutions are presented for the even- and odd-mode impedances of the parallel-coupled microstrip lines with different configurations. The first set of equations is for the conventional-coupled microstrip lines. The second set is for the parallel-coupled microstrip lines with a slotted ground plane and the third set is for the parallel-coupled microstrip lines with a slotted ground plane and a floating-potential conductor added to cover most of the slot in the ground plane. The solution is achieved using the conformal mapping technique, which also considers the effect of any fringe capacitor that has an impact on the impedance of the coupled lines. To validate the accuracy of the presented equations, a comparison is made with the available empirical solution (only for the conventional-coupled microstrip lines), a numerical solution (using Galerkin?s technique) and the full-wave electromagnetic solution using the software HFSS. The result of the comparison indicates the high accuracy of the presented equations over a wide range of design parameters. The difference between the calculated values using the derived equations and those from the full-wave electromagnetic analysis is ,5% for most of the cases. To validate the derived equations experimentally, they are used to design a 3 dB coupler. The result of measurements on the manufactured coupler confirms the accuracy of the presented equations.     

Influence of substitutional doping on the electronic properties of carbon nanotubes with Stone Wales defects: density functional calculations

Abstract

In this work, we implemented density function theory to investigate the structural and the electronic properties of nitrogen doped single walled carbon nanotube under different orientations of Stone Wales defect. We have found that, the doped defected structures are more stable than the non-doped defected structures. Furthermore, doping defected carbon nanotubes with a nitrogen atom has significantly narrowed the band gap and slightly shifted the Fermi level toward the conduction band. Moreover, nitrogen substitution creates new band levels just above the Fermi level which exemplifies an n-type doping. However, the induced band gap is indirect band gap compared to direct band gap as in pristine carbon nanotubes. Furthermore, the electronic and structural properties of nitrogen doped carbon nanotube with Stone Wales defects is crucially affected by the dopant site as well as the orientations of Stone Wales defects.     

Enhancement of Sensitivity of Microwave Planar Sensors With EBG Structures

A strategy to improve microstrip sensor performance for monitoring dielectric properties of materials is proposed. The method relies on the reduction of the wave group velocity to induce higher interaction between the sensor and the material. This is achieved by the design of periodic patterns in the sensor ground plane, which exhibit electromagnetic band gap (EBG) effects. The presence of these EBG structures turns out to be highly effective, inducing a noticeable decrease of the wave velocity. The sensitivity is defined and measured for different sensor configurations in order to quantify the improvements obtained. It is observed that, with the EBG structures, the residence time of the wave in the material under test is longer, and a substantial increase of the sensor sensitivity is obtained. EDICS Category-MICR     

Application of defect engineering to silicon Raman lasers and amplifiers

Silicon Raman lasers and amplifiers are the only silicon-based, monolithic device structures in which optical gain has been unambiguously observed. The main limitation on this gain is optical absorption due to free carriers, generated by two photon absorption. Here we explore a means to mitigate carrier effects via defect engineering. The optical and electrical properties of the defected silicon waveguides are modeled for both a uniform defect distribution and a remote, localized defect distribution. Simulation results indicate that a uniform defect distribution provides no improvement with any increase in net gain provided solely by surface modification. In contrast, for devices with remote defect volumes the reduction of carrier lifetime and limited optical absorption results in a significant improvement to net gain.     

Elimination of scan blindness with compact defected ground structures in microstrip phased array

A compact H-shaped defected ground structure (DGS) is applied to reduce the mutual coupling between array elements and eliminate the scan blindness in a microstrip phased array design. The proposed DGS is inserted between the adjacent E-plane coupled elements in the array to suppress the pronounced surface waves. A two-element array is measured and the results show that a reduction in mutual coupling of 12 dB is obtained between elements at the operation frequency of the array. The scan properties of microstrip phased arrays with and without DGS are studied by the waveguide simulator method. The analysis indicates that the scan blindness of the microstrip phased array can be well eliminated because of the effect of the proposed DGS. Meanwhile, the active patterns of the array centre element in 7 x 3 element arrays with and without the H-shaped DGS are simulated, and the results agree with those obtained by the waveguide simulator method.     

Application of defect engineering to silicon Raman lasers and amplifiers

Silicon Raman lasers and amplifiers are the only silicon-based, monolithic device structures in which optical gain has been unambiguously observed. The main limitation on this gain is optical absorption due to free carriers, generated by two photon absorption. Here we explore a means to mitigate carrier effects via defect engineering. The optical and electrical properties of the defected silicon waveguides are modeled for both a uniform defect distribution and a remote, localized defect distribution. Simulation results indicate that a uniform defect distribution provides no improvement with any increase in net gain provided solely by surface modification. In contrast, for devices with remote defect volumes the reduction of carrier lifetime and limited optical absorption results in a significant improvement to net gain.     

无通孔共面波导到微带的转换效应

分析了无通孔接地板对共面波导(CPW)至微带转换过渡的影响。计算和实验结果显示,如果在缩短其长度的同时加宽其宽度,可以有效地增加转换的带宽。通过等效电路做出了一定的解释,同时提供了简单的无通孔CPW至微带转换设计指导方法。     

Flexible ultrasonic transducer arrays for nondestructive evaluationapplications. I. The theoretical modeling approach

This paper presents the development of a theoretical modeling strategy to be used in the design of flexible ultrasonic transducer arrays. These new types of array device are intended for those applications where surface conformity is desirable. Such array structures allow much more efficient and effective coupling of acoustic energy between the transducer and test specimen than would have been otherwise possible with an equivalent rigid device. The objective of this work is to provide the transducer designer with a set of design tools that will permit the analysis of different material configurations and various transmit-receive aperture designs. Linear systems modeling is used to evaluate, and consequently optimize, the transduction performance, while a surface scattering model has been developed to facilitate the analysis of different transmit-receive aperture configurations. A theoretical modeling approach for flexible arrays is developed and where necessary, the validity confirmed by experimental measurement     

Application of on-wafer TRL calibration on the measurement ofmicrowave properties of Ba0.5Sr0.5TiO3films

A series of Al/Ba_0.5Sr_0.5TiO₃ (BST) /sapphire multi-layered coplanar waveguide (CPW) transmission lines of different geometries and thin-film configurations was fabricated. We employed an accurate on-wafer Through-Line-Reflect (TRL) calibration technique and quasi-TEM analysis to measure the dielectric constant, loss tangent, and tunability of BST thin films using this CPW structure. Experimental results show that the overall insertion loss is less than 3 dB/cm even at frequencies as high as 20 GHz, which is the lowest obtained to date for metal/BST CPW devices. This result indicates that, with optimized impedance matching, normal conductors are also possibly suitable for fabricating low-loss tunable phase-shifter devices     

Modified Calibration Coefficients of Two-Port CPW Standards with Superstrate Effects

Calibration standards are used for the calibration of a vector network analyzer to characterize the microwave components under test. For the direct characterization of coplanar waveguide components, two-port CPW open, short and line are proposed to complement the existing calibration techniques. The developed CPW standards are characterized in the frequency range of 10 MHz to 10 GHz. As these are planar structures, effects of small superstrates on the calibration coefficients of open and short are studied also. The CPW line has shown slight changes in impedance due to superstrates, whereas a few calibration coefficients of open and short standards showed dependence on superstrates. Similar observations are noted by improving the polynomial models of CPW open and short standards up to fifth and sixth order, respectively, which better matches for CPW standards. The reported results are helpful to estimate any change in the measurement uncertainty on using such calibration standards due to superstrates.     

基于数学形态学的分形维数计算及在轴承故障诊断中的应用

滚动轴承故障信号是一种典型的非线性信号,分形几何为描述轴承故障信号的特性提供了一个有力的分析工具。基于数学形态学的分形维数是在Minkowski-Boulingand维数基础上拓展的一种采用形态学操作计算分形维数的新方法。本文较详细的阐述了基于数学形态学的分维数计算方法,对比分析了与传统计盒维数方法的区别与联系,并对实际的滚动轴承正常、滚动体故障、内圈故障和外圈故障信号进行了分析,结果表明,基于数学形态学的分维数计算方法具有计算速度快,估计准确稳定的特点,为准确判断滚动轴承故障状态提供了一种快速有效的新方法。     

Edge-fed cavity backed patch antennas and arrays

A new edge-fed patch antenna that mitigates spurious radiation issues when thick substrates are used to create the antenna is presented. The radiator can be classified as an edge-fed cavity backed patch. Here, a thin substrate is used to develop the microstrip feed line, thereby ensuring the track widths are small and subsequently decreasing spurious feed radiation. The patch radiator utilises the thick substrate employed in the cavity ensuring reasonable return loss bandwidth can be achieved. A single element and a 2 x 2 array have been designed, fabricated and tested using the proposed technique and it has been shown that significant reduction in pattern distortion and increase in gain can be achieved compared to conventional edge-fed microstrip patch configurations. Because of the thin tracks used to feed the radiators, the new technique is very applicable to large arrays of microstrip patches where the area consumed by the distribution network must be minimised to ensure good radiation performance.     

Metamaterial-Based Compact Antenna with Defected Ground Structure for 5G and Beyond

In this paper, a unit cell of a single-negative metamaterial structure loaded with a meander line and defected ground structure (DGS) is investigated as the principle radiating element of an antenna. The unit cell antenna causes even or odd mode resonances similar to the unit cell structure depending on the orientation of the microstrip feed used to excite the unit cell. However, the orientation which gives low-frequency resonance is considered here. The unit cell antenna is then loaded with a meander line which is parallel to the split bearing side and connects the other two sides orthogonal to the split bearing side. This modified structure excites another mode of resonance at high frequency when a meander line defect is loaded on the metallic ground plane. Specific parameters of the meander line structure, the DGS shape, and the unit cell are optimized to place these two resonances at different frequencies with proper frequency intervals to enhance the bandwidth. Finally, the feed is placed in an offset position for better impedance matching without affecting the bandwidth The compact dimension of the antenna is 0.25 λL × 0.23 λL × 0.02 λL, where λL is the free space wavelength with respect to the center frequency of the impedance bandwidth. The proposed antenna is fabricated and measured. Experimental results reveal that the modified design gives monopole like radiation patterns which achieves a fractional operating bandwidth of 26.6%, from 3.26 to 4.26 GHz for |S11|<−10 dB and a pick gain of 1.26 dBi is realized. In addition, the simulated and measured cross-polarization levels are both less than −15 dB in the horizontal plane.     

Analysis of a digital microstrip optical switch: a novel method

A time domain analysis of an optically controlled digital microstrip switch for microwave integrated circuits on Si substrates is studied. A new model for high-frequency pulse propagation on a microstrip optical switch for different optical parameters is presented. A frequency-dependent macromodel for a microstrip line with a gap is implemented in Spice 3, taking into consideration high-frequency pulse dispersion, conductor and dielectric losses, metallization thickness, gap length, and different optical parameters such as optical energy, surface recombination velocities, and diffusion of generated carriers. In addition, the developed model has been used to optimize the switching frequency, gap length, level of optical power, and suitable substrate material parameters.     

Numerical exploration of plastic deformation mechanisms of copper nanowires with surface defects

Based on the molecular dynamics simulation, plastic deformation mechanisms associated with the zigzag stress curves in perfect and surface defected copper nanowires under uniaxial tension are studied. In our previous study, it has found that the surface defect exerts larger influence than the centro-plane defect, and the 45° surface defect appears as the most influential surface defect. Hence, in this paper, the nanowire with a 45° surface defect is chosen to investigate the defect’s effect to the plastic deformation mechanism of nanowires. We find that during the plastic deformation of both perfect and defected nanowires, decrease regions of the stress curve are accompanied with stacking faults generation and migration activities, but during stress increase, the structure of the nanowire appears almost unchanged. We also observe that surface defects have obvious influence on the nanowire’s plastic deformation mechanisms. In particular, only two sets of slip planes are found to be active and twins are also observed in the defected nanowire.     

Design and simulation of equilateral triangular microstrip antenna using particle swarm optimization (PSO) and advanced particle swarm optimization (APSO)

In this paper a new design is proposed in microstrip antenna family. In this paper, a review design of microstrip antenna design using particle swarm optimization (PSO) and advanced particle swarm optimization (APSO) has been presented which optimizes the parameters and both results are compared. This technique helps antenna engineers to design, analyze, and simulate antenna efficiently and effectively. An advanced PSO driven antenna has been developed to calculate resonant frequency of slit-cut stacked equilateral triangular microstrip antenna. The paper presents simplicity, accuracy and comparison of result between PSO and APSO.     

Compact microstrip band-pass filters based on semi-lumped resonators

A new design approach for compact microstrip band-pass filter based on semi-lumped resonators are proposed. The resonators, which are coupled through quarter wavelength meander lines acting as admittance inverters, are shunt connected to the line. They consist of parallel combination of a grounded (inductive) stub and a narrow metallic strip followed by a capacitive patch to ground. With this topology, the necessary degree of flexibility to design narrow and broad-band-pass filters with compact dimensions and good out-of-band performance was obtained. Another key advantage of the devices, as compared to previous lumped or semi-lumped element- based structures reported by the authors, is the absence of ground plane etching. To illustrate the potentiality of the proposed approach, a third-order (30% fractional bandwidth) and a nineth-order (35% fractional bandwidth) Chebyshev band-pass filters have been designed and fabricated. The measured frequency responses are very symmetric and exhibit low in-band losses as well as good out-of-band rejection up to approximately 3f_o. Filter dimensions are as small as 0.40lambda times 0.12lambda (third-order prototype) and 0.62lambda times 0.16lambda (nineth-order prototype), lambda being the guided wavelength at f_o. With these dimensions and performance, and the possibility to synthesise microstrip filters with controllable bandwidth over a wide margin, it is believed that the reported approach can be of actual interest for the design of planar filters at microwave frequencies.     

Influence of split ring resonators on the properties of propagating structures

The study of a 50 Omega microstrip line and microstrip resonators loaded with resonant elements called split-ring resonators (SRRs) is presented. The two different filtering phenomena observed lead to make an analogy with those observed when waveguides are loaded with these elements. So, in order to make this analogy, the different results obtained with the SRRs loaded in a propagating and an under cut-off waveguide are shown. Then, another technique to achieve and even improve these results is presented. The technique consists of using, respectively, a 50 Omega microstrip line and capacitive-gap-coupled microstrip resonators instead of the propagating and under cut-off waveguides. The numerical and experimental results obtained with the two structures (waveguides and microstrip lines) are compared and discussed. This study shows that the combination of SRRs with guiding structures helps in the design of compact structures, but an enhancement of the performances needs a better fabrication accuracy