- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Performance enhancement of approximated model based near-field sources localisation techniques
摘要： Most of the existing near-field sources localisation methods are based on an approximated model. Making use of such an approximation brings degradation in the estimation accuracy. In this study, the authors propose a correction method to mitigate this problem and improve the estimation performance of the approximated model based methods. Simulation results show that the proposed technique can significantly improve the performance of the classical approximated model based near-field sources localisation methods.
关键词： approximated model,estimation accuracy,correction method,near-field sources localisation
更新于2025-09-23 15:21:21
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[IEEE 2018 IEEE 5G World Forum (5GWF) - Silicon Valley, CA, USA (2018.7.9-2018.7.11)] 2018 IEEE 5G World Forum (5GWF) - Feasibility and Challenges of Over-The-Air Testing for 5G Millimeter Wave Devices
摘要： The evolution from 1G through 5G cellular technologies has been fueled mainly by the insatiable need for speed, lower latency, high reliability and enhanced flexibility of use across the wireless ecosystem. Using multiple antennas in conjunction with complex modulation schemes has rendered each generation of cellular technology an enhanced version over its former counterpart. 5G technology aims to exploit previously unchartered higher millimeter wave (mmWave) frequencies & larger bandwidths towards realizing the goal of greater data throughput, while simultaneously enhancing data reliability and reducing latency. The small wavelength of mmWave signals makes it possible to design 5G devices using several multi-element phased array antennas with small element-element spacing. However, unlike the antenna designs of 2G/3G/4G devices, 5G multi-element antennas would be integrated with the radio frequency integrated circuit (RFIC) board of the 5G device. The tight integration between antennas and RFIC renders the antenna port of the device under test (DUT) inaccessible for physical connections using cables/connectors to test equipment. Since conducted testing with cables is not feasible anymore, radiated over-the-air (OTA) testing becomes mandatory for 5G mmWave device verification. This paper aims to assess the feasibility of candidate OTA test methods for 5G mmWave test requirements. The challenges of testing 5G mmWave devices over-the-air have been elucidated and alternative OTA test solutions for overcoming these challenges have also been discussed.
关键词： multi-probe anechoic chamber (MPAC),Multiple-input multiple-output (MIMO),compact antenna test range (CATR),far-field,near-field,antenna arrays
更新于2025-09-23 15:21:01
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Non-Lorentzian Local Density of States in Coupled Photonic Crystal Cavities Probed by Near- and Far-Field Emission
摘要： Recent theories proposed a deep revision of the well-known expression for the Purcell factor, with counterintuitive effects, such as complex modal volumes and non-Lorentzian local density of states. We experimentally demonstrate these predictions in tailored coupled cavities on photonic crystal slabs with relatively low optical losses. Near-field hyperspectral imaging of quantum dot photoluminescence is proved to be a direct tool for measuring the line shape of the local density of states. The experimental results clearly evidence non-Lorentzian character, in perfect agreement with numerical and theoretical predictions. Spatial maps with deep subwavelength resolution of the real and imaginary parts of the complex mode volumes are presented. The generality of these results is confirmed by an additional set of far-field and time-resolved experiments in cavities with larger modal volume and higher quality factors.
关键词： non-Lorentzian local density of states,Purcell factor,quantum dot photoluminescence,photonic crystal cavities,near-field hyperspectral imaging
更新于2025-09-23 15:21:01
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Topology Optimization-Based Inverse Design of Plasmonic Nanodimer with Maximum Near-Field Enhancement
摘要： The near-field enhancement factor is one of the most significant parameters to evaluate the performance of plasmonic nanostructures. Numerous efforts have been made to maximize the enhancement factor through optimizing the size, shape, and spatial arrangement of metallic nanostructures with simple geometries, such as disk, triangle, and rod. This work implements topology optimization to inversely design a metallic nanoparticle dimer with the goal of optimizing the near-field enhancement factor in its sub-10 nm gap. By optimizing the material layout within a given design space, the topology optimization algorithm results in a plasmonic nanodimer of two heart-shaped particles having both convex and concave features. Full-wave electromagnetic analysis reveals that the largest near-field enhancement in the heart-shaped nanoparticle dimer is originated from the greatest concentration of surface charges at the nano-heart apex. Inversely designed heart-, bowtie-, and disk-shaped nanodimers are fabricated by using focused helium ion beam milling with a “sketch and peel” strategy, and their near-field enhancement performances are characterized with nonlinear optical spectroscopies at the single-particle level. Indeed, the heart-shaped nanodimer exhibits much stronger signal intensities than the other two structures. The present work corroborates the validity and effectiveness of topology optimization-based inverse design in achieving desired plasmonic functionalities.
关键词： topology optimization,near-field enhancement,plasmonic nanostructures,inverse design,nonlinear optics
更新于2025-09-23 15:21:01
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An enhanced circular polarization near-field focused antenna array by director patches
摘要： This paper presents an enhanced circular polarization (CP) near-field focused (NFF) antenna array. There exist three advantages for the CP NFF antenna. First, this study provides an effective way to realize the CP and NFF simultaneously and do not need to design a specific patch shape for CP, which provides more freedom to change the patch shape for improving other performances. The effective way is arranging the element excitation according to maximum power transmission efficiency theory under the condition of a CP testing antenna. Second, the array element consists of a driven and director patches, and the director patches tilt the element beam from broadside direction to focal point, and then obviously enhance the electric field focusing gain. Third, the proposed array antenna achieves much less size of focal point by using much less element number than published papers. The curves for the impedance and axial ratio (AR) as function of frequency, focus width and depth are analyzed. The simulated and measured results basically agree.
关键词： antenna array,circular polarization (CP),near-field focused (NFF) antenna,director patch
更新于2025-09-23 15:21:01
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Simulational and experimental investigation on the wavefront sensing method based on near-field profile acquisition in high power lasers
摘要： This paper presents a novel wavefront sensing method based on near-field profile acquisition (NIA) to acquire the wavefront information. This method uses a cross mark at the focal plane of the spatial filter to directly obtain wavefront slope from the power spectral density (PSD) distribution of the output near-field profile. Principles of this method are introduced and the numerical simulation model is built. The influence of primary parameters on the measurement precision are analyzed and discussed. Based on the designed cross mark structure, an experiment is carried out in a multi-pass amplification high power laser and the wavefront of the pre-amplifier is reconstructed. Experimental results show that the difference between the reconstructed wavefronts by using the traditional Shack–Hartmann (SH) and the NIA wavefront sensing method is as small as 0.09 μm (peak-to-valley value).
关键词： Power spectral density,Near-field profile,Wavefront sensing,Wavefront
更新于2025-09-23 15:21:01
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Near-field radiative heat transfer between black phosphorus and graphene sheet
摘要： Low thermal conductivity of black phosphorus (BP) makes it difficult to cool BP-based electronic or optoelectronic devices. Therefore, developing a cooling strategy for BP-based nano devices is highly required. We theoretically study the near-field radiative heat transfer between BP sheets as well as between BP and graphene. We find that the heat transfer between BP sheets is determined by its electron doping. Plasmons excited by BP in different directions dominate the heat transfer for different electron doping. At optimum electron doping, heat transfer between the BP sheets increases significantly. The heat transfer between BP and graphene is dependent on both the electron doping of BP and chemical potential of graphene. Modulating the chemical potential of graphene can result in a strong coupling between graphene plasmons and BP plasmons, which will lead to a significant enhancement of heat transfer between BP and graphene. Our results are not only meaningful in controlling the heat transfer between BP-based structures but also helpful in developing cooling strategies for BP-based nano devices.
关键词： near-field radiative heat transfer,plasmons,graphene,black phosphorus,chemical potential,electron doping
更新于2025-09-23 15:21:01
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Apparent Spectral Shift of Thermally Generated Surface Phonon-Polariton Resonance Mediated by a Nonresonant Film
摘要： The physical origin of the spectral shift of a thermally generated surface phonon-polariton (SPhP) resonance of a silicon carbide (SiC) bulk mediated by a nonresonant film is explained. The local density of electromagnetic states (LDOS) in a nonresonant intrinsic silicon (Si) film due to thermal emission by SiC, derived using fluctuational electrodynamics, exhibits a local maximum near the SPhP-resonant frequency in addition to a lower frequency resonance generated by gap modes emerging in the vacuum gap separating the SiC and Si layers. Multiple reflections within the vacuum gap also induce a LDOS drop around the SPhP-resonant frequency. As a result, depending on the film thickness to vacuum gap ratio and the location where the LDOS is calculated in the film, the low-frequency resonance can dominate the LDOS, such that the SPhP resonance appears to be redshifted. A similar spectral behavior is observed on the monochromatic radiative heat flux absorbed by the Si film. It is shown that apparent spectral (red and blue) shifts of the SPhP resonance mediated by a nonresonant film are bounded by the transverse and longitudinal optical phonon frequencies of SiC. This work is of importance in applications involving dissimilar materials, such as thermophotovoltaics and thermal rectification, where gap modes may significantly disrupt flux resonance. Gap modes may also be at the origin of the resonance redshift systematically observed in near-field thermal spectroscopy.
关键词： local density of electromagnetic states,thermal emission,surface phonon-polariton,spectral shift,near-field thermal spectroscopy
更新于2025-09-23 15:21:01
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The Double PEC Wedge Problem: Diffraction and Total Far Field
摘要： Complex scattering targets are often made by structures constituted of wedges that may interact at near field. In this paper, we examine the scattering of a plane electromagnetic wave by two separated arbitrarily oriented perfectly electrically conducting wedges with parallel axes. The procedure to obtain the solution is based on the recently developed semianalytical method known as generalized Wiener–Hopf technique that allows a comprehensive mathematical model of the problem in the spectral domain avoiding multiple steps of interaction among separated objects. The numerical results are presented to validate the procedure in terms of spectral quantities, GTD/uniform theory of diffraction coefficients and total far fields for engineering applications. The structure is of interest in electromagnetic applications, in particular, to accurately predict path loss in propagation with diffraction phenomena.
关键词： electromagnetic diffraction,radar applications,wedges,propagation,electromagnetic shielding,wireless communication,Wiener–Hopf (WH) method,integral equations,EMC,near-field interactions,Antenna technologies
更新于2025-09-23 15:21:01
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New Perspectives in Breast Imaging || Near-Field Radar Microwave Imaging as an Add-on Modality to Mammography
摘要： According to global statistics, there is a high incidence of cancer in western countries; and, due to the limited resources available in most healthcare systems, it seems like one of the most feasible options to fight against cancer might be strict prevention policies—such as eliminating carcinogens in people’s daily lives. Nevertheless, early cancer detection and effective treatment are still necessary, and understanding their efficacy and limitations are important issues that need to be addressed in order to ultimately enhance patients’ survival rate. In the case of breast cancer, some of the problems faced by conventional mammography have been addressed in the literature; they include high rate of false-positive and false-negative results, as well as the possibility of overdiagnosis. New technologies, such as digital breast tomosynthesis (DBT), have been able to improve the sensitivity and specificity by using 3D imaging. However, the low contrast (1%) existing between tumors and healthy fibroglandular tissue at X-ray frequencies has been identified as one of the main causes of misdiagnosis in both conventional 2D mammography and DBT. Near-field radar imaging (NRI) provides a unique opportunity to overcome this problem, since the contrast existing between the aforementioned tissues is intrinsically higher (10%) at microwave frequencies. Moreover, the low resolution and highly complex scattering patterns of microwave systems can be enhanced by using prior information from other modalities, such as the DBT. Therefore, a multimodal DBT/NRI imaging system is proposed to exploit their individual strengths while minimizing their weaknesses. In this work, the foundation of this idea is reviewed, and a preliminary design and experimental validation of the NRI system, used as a DBT complement, is introduced.
关键词： breast cancer statistics,digital breast tomosynthesis,microwave imaging,antipodal Vivaldi antennas,near-field radar imaging,breast cancer detection
更新于2025-09-23 15:21:01