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A Wideband Planar Aperture Array Using Interconnected Crossed Rings
摘要： A 5:1 frequency bandwidth aperture array antenna based on a new planar structure is reported. Dual polarization is implemented with high cross-polarization discrimination over ±45? scan angle from zenith. It is a low-loss cost effective approach using minimum dielectric materials. In the proposed planar antenna array design, a mutual coupled interconnected ring structure is used which extends the operational frequency band to the region where the element separation can be considerably greater than half a wavelength, unlike the previously reported interconnected array structures. Hence the total number of elements can be reduced for a speci?ed aperture size. The dual polarization have coincident-phase centers and in the implemen-tation reported here two low noise ampli?ers on the same board are integrated with a pair of dual polarized elements to form an active array. A 10 by 10 element array prototype of the design has been manufactured and the measured results con?rm it as a low cost, high performance front-end solution.
关键词： Aperture antennas,Phased arrays,Planar arrays,Radio astronomy
更新于2025-09-23 15:21:21
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Effective spin physics in two-dimensional cavity QED arrays
摘要： We investigate a strongly correlated system of light and matter in two-dimensional cavity arrays. We formulate a multimode Tavis–Cummings (TC) Hamiltonian for two-level atoms coupled to cavity modes and driven by an external laser ?eld which reduces to an effective spin Hamiltonian in the dispersive regime. In one-dimension we provide an exact analytical solution. In two-dimensions, we perform mean-?eld study and large scale quantum Monte Carlo simulations of both the TC and the effective spin models. We discuss the phase diagram and the parameter regime which gives rise to frustrated interactions between the spins. We provide a quantitative description of the phase transitions and correlation properties featured by the system and we discuss graph-theoretical properties of the ground states in terms of graph colourings using Pólya’s enumeration theorem.
关键词： cavity arrays,Jaynes–Cummings,Dicke,ground states of spin systems,Tavis–Cummings models,frustrated spin models,quantum Monte Carlo
更新于2025-09-23 15:21:21
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Broadband light harvesting for highly efficient hot-electron application based on conformal metallic nanorod arrays
摘要： The utilization of nonradiative decay of surface plasmons (SPs) in the form of hot electrons in metallic nanostructures has a great potential for applications in photovoltaics, photocatalysis, photodetection, and surface imaging. Unfortunately, the metallic nanostructures usually support only narrowband plasmon resonances; moreover, the hot-electron thermalization loss during the transport to Schottky interface and the confined momentum space for hot-electron injection into semiconductor together result in an inefficient internal quantum process. In this study, we propose and experimentally demonstrate a broadband super absorber based on the metallic nanorod arrays (NRs). Optically, the average absorption across the entire visible band is up to 0.8, which is over 16-fold enhancement of the planar reference. Electrically, the hot electrons are controlled to be preferentially generated near Schottky interface within the mean free path, relieving the severe hot-electron thermalization loss. Moreover, the three-dimensional Schottky junction provides much increased hot-electron momentum space for injection at the vertical surface. These optical and electrical benefits lead to over 30-fold enhancement in the IPCE (incident photon-to-electron conversion efficiency) relative to the reference. The IPCE can be up to 10.9% at Eph = 3.1 eV, which is close to the limit of the thick-film single-barrier hot-electron devices. The conformal NRs system provides a promising strategy to simultaneously improve the hot-electron generation, transport and collection efficiencies and could be an outstanding candidate for efficient hot-electron optoelectronic and photocatalysis systems.
关键词： hot electron,surface plasmons,nanorod arrays,broadband absorber
更新于2025-09-23 15:21:21
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DIAMAGNETO-DIELECTRIC ANISOTROPIC WIDE ANGLE IMPEDANCE MATCHING LAYERS FOR ACTIVE PHASED ARRAYS
摘要： In this paper, we present the full process of designing anisotropic metamaterial (MM) wide angle impedance matching (WAIM) layers. These layers are used to reduce the scan losses that occur in active phased arrays for large scanning angles. Numerical results are provided to show the improvement in performances that such layers can ensure. The proposed anisotropic MM-WAIM layers achieve an improvement of about 1 dB of more radiated power at θ = 70? from broadside, in a 13% of fractional bandwidth on the azimuthal plane φ = 90?. Weaker improvements are obtained in the other azimuthal planes, however keeping the active re?ection coe?cient below ?9 dB for all azimuthal planes up to θ = 60? and up to θ = 70? o?-axis for planes φ = 45?, 90? in the whole operational band.
关键词： scan losses,wide angle impedance matching,anisotropic metamaterial,active phased arrays,impedance matching
更新于2025-09-23 15:21:21
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PATTERN SYNTHESIS FOR LARGE PLANAR ANTENNA ARRAYS USING A MODIFIED ALTERNATING PROJECTION METHOD
摘要： A pattern synthesis approach based on a modi?ed alternating projection method for large planar arrays is presented in this paper. In the alternating projection method, pattern synthesis problem is considered as ?nding the intersection between two sets: the speci?cation set and the feasible set. The former contains all the patterns that want to be obtained, while the latter contains all the patterns that can be realized. An element belongs to both sets is a solution to the problem. In this paper, a modi?ed projection operator which varies with the iteration number is introduced because the conventional alternating projection method is known to su?er from low convergence rate and/or trapping on local optimum depending on the starting point. When the planar array has a nonuniform element layout, the unequally spaced elements are interpolated into virtual uniform elements with an interpolation of the least square sense. Then the synthesis problem is converted to the problem of a uniform array. Finally, several examples are presented to validate the advantages of the proposed method. Results show that the modi?ed method is fast and obtains better results than the conventional one.
关键词： modi?ed alternating projection method,interpolation,planar antenna arrays,nonuniform element layout,pattern synthesis
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Arrays of Si Field Emitter Individually Regulated by Si Nanowires High Breakdown Voltages and Enhanced Performance
摘要： We fabricate Si field emitter arrays (FEAs) with integrated Si nanowire current limiters and investigate a method to enable higher voltage operation, which can potentially increase achievable current densities. In this work, we focus on the dielectric breakdown occurring in the vicinity of the nanopillar. A deeper etch is shown to increase the breakdown voltage but at the expense of poorer field emission characteristics possibly due to the loss of mechanical support or increased surface states.
关键词： field emitter arrays,Silicon,breakdown voltage,current limiters
更新于2025-09-23 15:21:21
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Autofocusing with out-of-band phase conjugation
摘要： Electromagnetic phase conjugation provides an appealing path towards communication and target localization in dynamic media such as the Earth’s atmosphere. However, realizing phase conjugation-based devices has proven difficult because of the inherent complexity of systems that employ receivers and transmitters working on the same band. In this letter we propose the concept of out-of-band phase conjugation in which the frequency of the phase conjugated wave is an integer multiple of the incident wave frequency. Remarkably, the out-of-band phase conjugated wave maintains the autofocusing property that makes phase conjugation so powerful and opens the door to imaging technology effective in random and dynamic media.
关键词： Phase Conjugation,Retrodirective Arrays,Metasurface,Active Metamaterial,Time Reversal
更新于2025-09-23 15:21:21
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An Optoelectronic Pulse Drive for Quantum Voltage Synthesizer
摘要： An optoelectronic pulse drive system based on commercially available telecoms optoelectronic components and a field-programmable gate array has been developed. In order to allow the use of ac-coupled optoelectronic components, a method of adding and subtracting complementary pulses was developed. The system was used to drive a Josephson junction array to synthesize quantum-accurate voltage waveforms. These waveforms will be used in voltage waveform metrology applications. Results from the synthesis of sinusoidal unipolar voltage waveforms from 3 to 300 kHz are presented. The margin of operation was measured and shown to require an optical pulse height stability better than 0.15 mW. The use of delta–sigma code with repeated sections, suitable for a quantum voltage digitizer was also examined. A test code corresponding to a delta–sigma feedback loop rate of 250 MHz was used to synthesize a 3.125 kHz sinusoidal waveform.
关键词： Josephson arbitrary waveform synthesizer,optoelectronics,metrology,Josephson arrays,measurement,voltage measurement
更新于2025-09-23 15:21:21
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Highly ordered Au-decorated Ag nanorod arrays as an ultrasensitive and reusable substrate for surface enhanced Raman scattering
摘要： For surface-enhanced Raman spectroscopy (SERS) substrates, complexity of the fabrication process, sensitivity and stability are factors that need to be considered. We report a simple and novel method for preparing an effective substrate that greatly enhances SERS signals. The SERS substrate is fabricated by selectively electroless deposition of Ag nanoparticles in the highly ordered porous anodized aluminum oxide (AAO) template and then etching it to form Ag nanorod bundles structure, so that the Raman enhancement occurs in the gap between the nanorods and the top of the nanorod bundle, which is verified by finite element analysis. A peculiarity of this method is that this is the first time to synthesize Ag nanorod arrays structure by using it. The results indicated that this prepared substrate has special micro-nano structure and when rhodamine 6 G is selected as the detection reagent, the detection limit is as low as 10?16 M with excellent recyclability. This outstanding array structure has a promising practical application in SERS field.
关键词： Reproducibility,Electroless deposition,Micro-nano structure,SERS,Ag nanorod arrays
更新于2025-09-23 15:21:21
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Low-temperature-dependent growth of titanium dioxide nanorod arrays in an improved aqueous chemical growth method for photoelectrochemical ultraviolet sensing
摘要： The growth of titanium dioxide nanorod arrays (TNAs) in aqueous solutions containing titanium butoxide and hydrochloric acid can be controlled by regulating the temperature from 115 to 150 °C as an adjustable physical parameter. The transparent colloidal solution of titanates is clouded on the basic growth of TNAs when heated at a certain temperature using an improved aqueous chemical growth method in a clamped Schott bottle. The structural, optical and electrical properties of grown TNAs films were thoroughly investigated and discussed. The distinct and high-intensity peaks observed in the X-ray diffraction pattern and Raman spectra of the grown TNAs show the rutile phase with high crystal quality. The crystallite size, diameter size, and thickness of TNAs decrease with decreasing growth temperature. The prepared TNAs were used to detect 365 nm ultraviolet (UV) photon energy (750 μW/cm2) in a photoelectrochemical cell structure with a maximum photocurrent of 26.31 μA and minimum photocurrent of 3.48 μA recorded for TNAs grown at 150 °C and 115 °C, respectively. The size, structural properties, charge transfer resistance, and electron lifetime play a key role in determining the UV sensing characteristics of the TNAs. Results show that TNAs are very promising in fabricating a UV sensor with a high response at 0 V bias even at a low growth temperature of 115 °C.
关键词： Photoelectrochemical ultraviolet sensing,Titanium dioxide nanorod arrays,Rutile phase,Aqueous chemical growth method,UV sensor
更新于2025-09-23 15:21:21