- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Generation of High-Power, Reversed-Cherenkov Wakefield Radiation in a Metamaterial Structure
摘要： We present the first demonstration of high-power, reversed-Cherenkov wakefield radiation by electron bunches passing through a metamaterial structure. The structure supports a fundamental transverse magnetic mode with a negative group velocity leading to reversed-Cherenkov radiation, which was clearly verified in the experiments. Single 45 nC electron bunches of 65 MeV traversing the structure generated up to 25 MW in 2 ns pulses at 11.4 GHz, in excellent agreement with theory. Two bunches of 85 nC with appropriate temporal spacing generated up to 80 MW by coherent wakefield superposition, the highest rf power that metamaterial structures ever experienced without damage. These results demonstrate the unique features of metamaterial structures that are very attractive for future high-gradient wakefield accelerators, including two-beam and collinear accelerators. Advantages include the high shunt impedance for high-power generation and high-gradient acceleration, the simple and rugged structure, and a large parameter space for optimization.
关键词： high-power microwaves,reversed-Cherenkov radiation,wakefield acceleration,electron bunches,metamaterial structure
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - Krakow, Poland (2018.10.16-2018.10.18)] 2018 IEEE International Conference on Imaging Systems and Techniques (IST) - A Newton-Conjugate-Gradient Method in L <sup>p</sup> Banach Spaces for Three-Dimensional Microwave Imaging
摘要： Microwave imaging is a diagnostic technique for inspecting dielectric and conducting materials based on electromagnetic scattering. Although usually developed with reference to two-dimensional configurations (tomography), it allows a quite 'natural' extension to three-dimensional targets. In this paper, a full-wave three-dimensional approach is developed. The inverse scattering problem is solved, in a regularized way, by using a Newton-conjugate-gradient method. The main novelty concerns the nonconventional framework in which the approach is developed, i.e., the Lp Banach spaces. The paper describes the mathematical formulation of the method. Moreover, numerical results are reported and discussed in order to assess the capabilities and limitations of the proposed technique.
关键词： Banach spaces,inverse problems,Newton schemes,Imaging techniques,conjugate gradient method,microwaves
更新于2025-09-23 15:22:29
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Gyroton with the Corrugated Resonator
摘要： A new type of high-power electronic device—a gyroton with a corrugated resonator—is described and investigated. Spatial bunching of the electron beam does not occur in this device, however, highly efficient electron beam power conversion into the rotating electromagnetic field power is possible. The rectilinear electron beam deviates from the axis by the slow TM11 wave, then it gives up longitudinal energy to the same wave with more than 78% efficiency, and an output power up to 30 MW. The developed mathematical model of the interaction of the relativistic electron beam with an irregular circular waveguide and resonator fields presented in this article can be used to calculate and optimize the processes occurring in various microwave electronic devices, such as gyrotrons, gyrotons, TWT, Gyro-TWT, and BWT.
关键词： corrugated resonator,high-power microwaves,gyroton,rotating field,irregular waveguide
更新于2025-09-23 15:22:29
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Dynamically Steered Maser Action of Rydberg Excitons in Cu <sub/>2</sub> O
摘要： The Rydberg excitons in Cu2O are a promising candidate for realization of solid state maser. The highly excited states, unique to this crystal, provide the necessary energy level transitions for emission of microwaves. The achievement of population inversion is facilitated by exceptionally long lifetimes of excitons and their strong coupling to external field. Moreover, due to the strong Stark shift of excitonic energy levels, one can tune the emission wavelength on demand.
关键词： Rydberg excitons,microwaves,maser
更新于2025-09-23 15:22:29
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NUMERICAL ESTIMATION OF THE COMPLEX REFRACTIVE INDEXES BY THE ALTITUDE DEPENDING ON WAVE FREQUENCY IN THE IONIZED REGION OF THE EARTH ATMOSPHERE FOR MICROWAVES INFORMATION AND POWER TRANSMISSIONS
摘要： The phase and group refractive indexes of microwaves in the ionosphere region of the earth atmosphere are very important for both the researching theoretical problems and practical problems in wireless information transmission (WIT) and wireless power transmission (WPT). So far, there have been many attempts devoted to discussing and determining characterizations of earth atmosphere’s ionosphere region including the refractive indexes of microwaves concerning their velocities in ionized region, unfortunately due to the complicated features of the ionosphere region leading to research task facing many challenges. Up to recent, there is still a lack of systematic numerical data of complex refractive index by altitude depending on high frequencies of the electromagnetic waves in the ionosphere region. This paper outlines some theoretical analyses and discussions of some theoretical aspects of the complex refractive index in atmosphere’s ionized region more in detail. Based on conductivities data and the complex relative permittivity by altitude determined previously, the numerically estimated data of complex refractive indexes by the altitude from 100 km up to 1000 km at the di?erent frequencies are also shown and discussed.
关键词： wireless information transmission,refractive index,microwaves,ionosphere,wireless power transmission
更新于2025-09-23 15:21:21
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[OSA CLEO: Applications and Technology - San Jose, California (2015..-..)] CLEO: 2015 - Photonic generation of linearly-chirped microwave waveform with tunable center frequency and time-bandwidth product
摘要： A novel approach is presented to generate linearly-chirped microwave waveforms with tunable center frequency and expandable time-bandwidth product (TBWP). Different types of waveforms are demonstrated and the maximum measured TBWP is up to ~166.4.
关键词： Radio frequency photonics,Microwaves,Mode-locked lasers
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting - Boston, MA, USA (2018.7.8-2018.7.13)] 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting - Phase Retrieval in Frequency-Diverse Imaging
摘要： We demonstrate a phaseless computational frequency-diverse imaging system at K-band frequencies. The integration of the phase retrieval concept with computational frequency-diverse imaging is achieved by leveraging a gradient-descent based Wirtinger Flow algorithm. Using the developed phaseless imaging system, imaging of complex-shaped targets, such as the letters of the word “DUKE”, is shown, and it is observed that the phaseless reconstructed images are on par with the complex-based reconstructions.
关键词： computational imaging,phase retrieval,microwaves,imaging,phaseless
更新于2025-09-19 17:15:36
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[IEEE 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting - Boston, MA, USA (2018.7.8-2018.7.13)] 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting - Computational Millimeter-wave Spotlight Imaging using Holographic Metasurface Antennas
摘要： In this paper, a spotlight imaging system integrated with a frequency-diverse aperture is presented for security-screening applications. The spotlight imager consists of holographic metasurface antennas that can dynamically be tuned to radiate spotlight patterns allowing the extraction of high-resolution images from a constrained field-of-view (FOV). The spotlight aperture operates at a single frequency, 75 GHz, within the W-band frequency regime (75 – 110 GHz) and is used for the identification of threat objects while the frequency-diverse aperture operates at K-band frequencies (17.5 – 26.5 GHz) and is used for detection purposes, determining the constrained FOV to be imaged using the spotlight imager at high resolution.
关键词： spotlight,metamaterial,metasurface,millimeter-wave,microwaves,imaging,focusing
更新于2025-09-19 17:15:36
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - Buried tunnel junction current injection for InP-based nanomembrane photonic crystal surface emitting lasers on Silicon
摘要： Microwave backscatter from vegetated surfaces is influenced by vegetation structure and vegetation water content (VWC), which varies with meteorological conditions and moisture in the root zone. Radar backscatter observations are used for many vegetation and soil moisture monitoring applications under the assumption that VWC is constant on short timescales. This research aims to understand how backscatter over agricultural canopies changes in response to diurnal differences in VWC due to water stress. A standard water-cloud model and a two-layer water-cloud model for maize were used to simulate the influence of the observed variations in bulk/leaf/stalk VWC and soil moisture on the various contributions to total backscatter at a range of frequencies, polarizations, and incidence angles. The bulk VWC and leaf VWC were found to change up to 30% and 40%, respectively, on a diurnal basis during water stress and may have a significant effect on radar backscatter. Total backscatter time series are presented to illustrate the simulated diurnal difference in backscatter for different radar frequencies, polarizations, and incidence angles. Results show that backscatter is very sensitive to variations in VWC during water stress, particularly at large incidence angles and higher frequencies. The diurnal variation in total backscatter was dominated by variations in leaf water content, with simulated diurnal differences of up to 4 dB in X- through Ku-bands (8.6–35 GHz). This study highlights a potential source of error in current vegetation and soil monitoring applications and provides insights into the potential use for radar to detect variations in VWC due to water stress.
关键词： Agriculture,vegetation water content (VWC),microwaves,hydrology,water stress,diurnal differences,radar,vegetation
更新于2025-09-16 10:30:52
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Multiple scattering enabled superdirectivity from a subwavelength ensemble of resonators
摘要： An ensemble of resonators arranged on a subwavelength scale is usually considered as a bulk effective medium, known as a metamaterial, and can offer unusual macroscopic properties. Here, we take a different approach and limit ourselves to the study of only a few number of such elementary components and demonstrate that they still offer uncommon opportunities. Typically, owing to the multiple scattering and the phase shift that the resonances offer, we observe ?elds that vary at scales completely independent of the wavelength in free space. By smartly tuning the resonance frequencies, we can design at will the complex current distribution in those resonators. This way, we design a superdirective antenna, i.e., an antenna that is surprisingly more directive than its size would foreshadow. This approach is veri?ed numerically and experimentally in the context of microwaves, but this applies to any wave ?eld where subwavelength resonators exist.
关键词： metamaterials,superdirectivity,microwaves,subwavelength resonators,multiple scattering
更新于2025-09-16 10:30:52