A Noisy SAR Image Fusion Method Based on NLM and GAN

The unavoidable noise often present in synthetic aperture radar (SAR) images, such as speckle noise, negatively impacts the subsequent processing of SAR images. Further, it is not easy to find an appropriate application for SAR images, given that the human visual system is sensitive to color and SAR images are gray. As a result, a noisy SAR image fusion method based on nonlocal matching and generative adversarial networks is presented in this paper. A nonlocal matching method is applied to processing source images into similar block groups in the pre-processing step. Then, adversarial networks are employed to generate a final noise-free fused SAR image block, where the generator aims to generate a noise-free SAR image block with color information, and the discriminator tries to increase the spatial resolution of the generated image block. This step ensures that the fused image block contains high resolution and color information at the same time. Finally, a fused image can be obtained by aggregating all the image blocks. By extensive comparative experiments on the SEN1–2 datasets and source images, it can be found that the proposed method not only has better fusion results but is also robust to image noise, indicating the superiority of the proposed noisy SAR image fusion method over the state-of-the-art methods.     

Complementary electric-LC resonator antenna for WLAN applications

In this paper, a metamaterial antenna based on complementary electric-LC (CELC) resonator is proposed. The antenna consists of slot-loaded ELC on the ground plane as the main antennas radiating element and excited by a microstrip line. The CELC resonator is characterized by single-negative magnetic moment excited by coupling between the microstrip transmission line and slot-loaded CELC. The peak realized gain and efficiency of 2.63 dB and 86 % are obtained, respectively, at resonance frequency. Simulation and measurement results are presented to validate the design. The antenna is suitable for WLAN applications (2.39–2.48 GHz).     

Ultrasound simulation of real-time temperature estimation during radiofrequency ablation using finite element models

Radiofrequency ablation is the most common minimally invasive therapy used in the United States to treat hepatocellular carcinoma and liver metastases. The ability to perform real-time temperature imaging while a patient is undergoing ablation therapy may help reduce the high recurrence rates following ablation therapy. Ultrasound echo signals undergo time shifts with increasing temperature due to sound speed and thermal expansion, which are tracked using both 1D cross correlation and 2D block matching based speckle tracking methods. In this paper, we present a quantitative evaluation of the accuracy and precision of temperature estimation using the above algorithms on both simulated and experimental data.A finite element analysis simulation of radiofrequency ablation of hepatic tissue was developed. Finite element analysis provides a method to obtain the exact temperature distribution along with a mapping of the tissue displacement due to thermal expansion. These local displacement maps were combined with the displacement due to speed of sound changes and utilized to generate ultrasound radiofrequency frames at specified time increments over the entire ablation procedure. These echo signals provide an ideal test-bed to evaluate the performance of both speckle tracking methods, since the estimated temperature results can be compared directly to the exact finite element solution. Our results indicate that the 1D cross-correlation (CC) method underestimates the cumulative displacement by 0.20 mm, while the underestimation with 2D block matching (BM) is about 0.14 mm after 360 s of ablation. The 1D method also overestimates the size of the ablated region by 5.4% when compared to 2.4% with the 2D method after 720 s of ablation. Hence 2D block matching provides better tracking of temperature variations when compared to the 1D cross-correlation method over the entire duration of the ablation procedure. In addition, results obtained using 1D cross-correlation diverge from the ideal finite element results after 7 min of ablation and for temperatures greater than 65 °C.In a similar manner, experimental results presented using a tissue-mimicking phantom also demonstrate that the maximum percent difference with 2D block matching was 5%, when compared to 31% with the 1D method over the 700 s heating duration on the phantom.     

机载多天线系统电磁兼容性研究

为了在有限计算机资源条件下快速解决机载平台中多天线系统的电磁兼容(EMC)问题,基于电场积分方程(EFIE),实现自动分层的多层快速多极子方法(MLFMA).针对天线问的近场耦合特性,采用任意天线间的隔离度代替传统隔离度,使得隔离度计算结果更加合理.同时采用BiCGStab(l)结合近场预条件方法进行求解,进一步提高MLFMA的综合效率.最后实例计算并分析波音747飞机模型上多根超短波天线的辐射方向图和宽频带内天线间的隔离度.数值结果表明方法准确有效.     

Analysis of graphene based optically transparent patch antenna for terahertz communications

With and without multi walled carbon nanotube (MWCNT) loaded graphene based optically transparent patch antennas are designed to resonate at 6 THz. Their radiation characteristics are analyzed in 5.66–6.43 THz band. The optically transparent graphene is deployed as the patch and ground plane of the antennas, which are separated by a 2.5 μm thick flexible polyimide substrate. By shorting the microstrip line and ground plane of the antenna with a MWCNT via, the return loss of the antenna is improved. The peak gain of 3.3dB at 6.2 THz and a gain greater than 3dB in 5.66–6.43 THz band is obtained for antenna loaded without MWCNT. Both the antennas achieved a −10dB impedance bandwidth of 12.83%. Gain, directivity and radiation efficiency of the proposed antennas are compared with conventional transparent patch antennas and graphene based non-transparent antennas. The antenna structures are simulated by using finite element method based electromagnetic simulator-Ansys HFSS.     

Design of a Compact Millimeter-Wave Microstrip Antenna with Wide Bandwidth and Broad Beamwidth

Design of a novel compact millimeter-wave microstrip antenna with wide bandwidth and broad beamwidth is presented. In the structure, multiple layers and a parasitic element as well as a coupling aperture are used to achieve wideband, while a conducting cylinder and the coupling aperture are used to obtain broad beamwidth. Finally, phased array with eight present elements has been designed as an example. Compared to traditional microstrip antennas and arrays, present antenna and array are of smaller dimension and broader beamwidth as well as wider bandwidth.     

Modeling of coupling loss in ultra-compact SOI microring resonators

Ultra-compact microring resonators, made of high index contrast (HIC)-silicon on insulator (SOI) materials, have become key optical devices in integrated photonics systems. Both computer simulations and actual experiments have showed that coupling loss was a significant contributor to the total losses in ultra-compact microring resonators. In this paper, a computable model derived from step approximation method was present to theoretically determine the coupling loss. Excellent matching results between the model and literatures were achieved. The proposed model can be applied to evaluate the coupling loss for microring resonators with various geometries and guide the design of low loss optical devices based on ultra-compact microring resonators.     

Optical matching layer structures in evanescent coupling photodiodes at a wavelength of 1.55μm： physics,design and simulation

We have studied the optical matching layers (OMLs) and external quantum efficiency in the evanescent coupling photodiodes (ECPDs) integrating a diluted waveguide as a fibre-to-waveguide coupler, by using the semi-vectorial beam propagation method (BPM). The physical basis of OML has been identified, thereby a general designing rule of OML is developed in such a kind of photodiode. In addition, the external quantum efficiency and the polarization sensitivity versus the absorption and coupling length are analysed. With an optical matching layer, the absorption medium with a length of 30μm could absorb 90% of the incident light at 1.55μm wavelength, thus the total absorption increases more than 7 times over that of the photodiode without any optical matching layer.     

An analysis of small aperture multimode horn as quasi-optical Gaussian beam radiator

In this paper a small aperture multimode horn is analysed by full-wave method and the coupling efficiency to Gaussian fundamental mode is calculated. The coupling efficiency of exceeding 0.98 is obtained over 4 GHz bandwidth. This horn may be used to connect waveguide with quasi-optical element in millimeter wave system and also may be used as an element in imaging array.     

Theoretical and practical limits of superdirective antenna arrays

Some applications as Wireless Power Transfer (WPT) require compact and directive antennas. However, Electrically Small Antennas (ESAs) have low efficiencies and quasi-isotropic radiation patterns. Superdirective ESA arrays can be an interesting solution to cope with both constraints (the compactness and the directivity). In this paper, the theoretical and practical limits of superdirective antennas will be presented. These limits can be summarized by the directivity sensitivity toward the excitation coefficients changes and the radiation efficiency decrement as the inter-element decreases. The need for negative resistances is also a practical limit for transforming these arrays into parasitic ones. The necessary trade-offs between the antenna total dimensions (the number of elements and the inter-element distance) and the attainable directivity and efficiency are also analyzed throughout this paper.     

Interaction of valence band excitations and terahertz TE-polarized cavity modes

The strong coupling of THz radiation and material excitations has potential to improve the quantum efficiency of THz devices. In this paper, we investigate a simple structure delivering THz polaritons and antipolaritons based on valence band transitions. The approach can improve the quantum efficiency of THz based devices based on TE mode in the strong coupling regime of THz radiations and intervalence bands transitions in a GaAs/AlGaAs quantum well. A Nonequilibrium Many Body Approach for the optical response beyond the Hartree–Fock approximation is used as input to the effective dielectric function formalism for the polariton/antipolariton problem. The energy dispersions relations in the THz range are obtained based on simplified analytical approximation.     

点缺陷二维光子晶体波导的出射光集束

光子晶体器件在高密度集成光通信中有广泛的应用,为解决光子晶体波导出射光场的空间控制,采用时域有限差分法分析光子晶体波导结构的缺陷传播特性,提出基于点缺陷优化波导结构,通过在波导出射口两侧加上点缺陷,出射光方向性有显著提高,实现三点光源干涉系统的光集束。模拟结果表明缺陷态越靠近能带结构中央,共振腔的耦合效率越高;相反,缺陷态越靠近能带结构边缘位置,则共振腔耦合效率越低,因此,选取禁带区域四分之一处对应的点缺陷,可以有效实现波导出射的光集束。     

Analysis on effect of low dielectric permittivity on indium-doped tin oxide based optically transparent terahertz patch antenna

Indium-doped tin oxide based optically transparent rectangular patch antennas are designed to resonate at 750 GHz; one on the glass substrate and the other on the polyimide substrate. Characteristics of both the transparent antennas such as impedance bandwidth, radiation efficiency, directivity and gain are analyzed and compared. Polyimide substrate has a lower dielectric permittivity than the glass substrate. The effect of low dielectric permittivity substrate on the radiation characteristics of the terahertz transparent patch antenna is analyzed. The transparent antenna on polyimide substrate is shown to have gain greater than 3.97dB in 714–795 GHz. The proposed transparent antennas are designed and simulated by using finite element method based electromagnetic solver, Ansys–HFSS.     

The noise factor of receiver coil matching networks in MRI

In typical MRI applications the dominant noise sources in the received signal are the sample, the coil loop and the preamplifier. We hypothesize that in some cases (e.g. for very small receiver coils) the matching network noise has to be considered explicitly. Considering the difficulties of direct experimental determinations of the noise factor of matching networks with sufficient accuracy, it is helpful to estimate the noise factor by calculation. A useful formula of the coil matching network is obtained by separating commonly used coil matching network into different stages and calculating their noise factor analytically by a combination of the noise from these stages. A useful formula of the coil matching network is obtained. ADS simulations are performed to verify the theoretical predictions. Thereafter carefully-designed proof-of-concept phantom experiments are carried out to qualitatively confirm the predicted SNR behavior. The matching network noise behavior is further theoretically investigated for a variety of scenarios. It is found that in practice the coil matching network noise can be improved by adjusting the coil open port resonant frequency.     

多铁性磁电器件研究进展

多铁性材料可以实现力、电、磁等多物理场之间的相互耦合,在小尺寸、快速响应和低功耗的磁电器件领域具有重要的应用前景.在应用需求的推动下,以具有磁电耦合效应的多铁性材料为基础的磁电器件在设计、微纳加工和性能优化等方面的研究取得了持续的进展.本文简要介绍了基于磁电耦合效应的几种原型器件的最新进展,包括可调谐电感、滤波器、磁电存储器、能量回收器、磁电传感器和磁电天线等,分析总结了各种磁电器件的工作原理及其性能表现,讨论了当前多铁性磁电器件研究所面临的问题和挑战,并提出了改进磁电器件性能的研究方向.     

电磁带隙微带天线馈源阵设计

 针对阵列天线在大反射面馈电中的应用,设计一种基于电磁带隙（EBG）结构的馈源阵列。在深入研究EBG结构带隙特性的基础上,制作一个基于EBG结构的六边形7元微带天线阵,并对其性能进行了实测和分析。结果表明：EBG结构可以有效抑制天线阵元之间的互耦,改善天线匹配及圆极化特性;基于EBG结构的六边形馈源阵列较无EBG结构性能有较大提高,适用作反射面天线的焦平面馈电阵。     

Flashlamp-pumped Nd:KGW laser at repetition rates up to 50 Hz

4+ :YAG passive element. Energies up to 1.1 J and 550 mJ, respectively, are obtained with a total efficiency close to 3%. Received: 29 May 1996     

Coplanar waveguide-fed compact planar ultra-wideband antenna with inverted L-shaped and extended U-shaped ground for portable communication devices

To simultaneously cover multiple wireless services and protocols, the antenna in communication devices should operate over a wide and ultra-wide frequency band. The use of wide/ultra-wideband antennas not only lessens the number of antennas necessary to cover multiple frequency bands but also decreases the system complexity, size, and costs. To operate over the ultra-wide frequency band, in this paper a CPW-fed small antenna is reported for portable communication devices. The anticipated antenna comprises a bow-tie-shaped patch and two ground planes. One inverted L-shaped and one extended U-shaped ground plane are asymmetrically placed with the main radiator which helps the antenna prototype to realize a functional band of 3.05 – 11.25 GHz (VSWR ≤ 2). In the functional band, the studied antenna accomplished a maximum peak gain of 4.98 dBi and maximum efficiency of 94.4%. Moreover, it exhibits symmetric omnidirectional radiation patterns and good time-domain behavior. The lucrative characteristics such as simple design, very small size (24.5 × 20 mm²), ultra-wide operating band, good gain and efficiency, stable radiation characteristics, and good time-domain characteristics make it a potential candidate to be used in portable communication devices.     

平面天线在场效应晶体管太赫兹探测器中的应用

为了提高场效应晶体管太赫兹探测器的响应度并降低噪声等效功率,需要对探测器集成平面天线的结构进行合理设计与优化,本文对集成平面天线结构的场效应晶体管太赫兹探测器的研究进行了深入调研。首先,对场效应晶体管太赫兹探测器的工作原理进行了分析,介绍了集成平面天线如何解决耦合太赫兹波效率低的问题。然后,介绍了一些常用的平面天线结构,包括偶极子天线、贴片天线、缝隙天线、grating-gate和其他类型的结构,比较了各种天线的性能以及引入后对太赫兹探测器响应度的影响。通过对比不同天线结构的探测器响应度和噪声等效功率等参数指标,发现:采用平面天线结构之后,场效应晶体管太赫兹探测器的响应度有了大幅度的提升,各种类型的天线对探测器响应度都有不同程度的提升。本文着重介绍了几种集成于场效应晶体管的平面天线结构,包括各种天线的性能和研究进展,最后分析了场效应晶体管太赫兹探测器存在的问题和发展趋势。     

Active Frequency-Tune Beam-Scanning Leaky-Wave Antenna Arrays

X-band active beam-scanning leaky-wave antenna arrays, including 1 × 1,1 × 2 and 1 × 4 prototypes, have been demonstrated. These antennas integrated one or several microstrip leaky-wave antenna elements with a single varactor-tuned HEMT VCO as an active source. Measured results on experimental antennas indicate that the beam scanning angle of the 1 × 1 antenna close to 40° can be achieved and the scanning range of 1 × 2 and 1 × 4 antenna arrays are both close to 32°. Furthermore, reflected wave due to the open end of each leaky-wave antenna element has been suppressed by the symmetric configuration of this antenna array and the antenna efficiency increases. When comparing with the measured radiation pattern of the single element antenna, we found that the 1 × 2 and 1 × 4 antenna arrays can effectively suppress the reflected power by more than 5.5 dB and 10.5 dB, respectively, at 10.2GHz. The power gain are more than 2 dB and 3.16 dB higher than the single element antenna with a measured EIRP of 18.67 dBm.