- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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EFFICIENT LOCALIZATION ALGORITHM OF MIXED FAR-FIELD AND NEAR-FIELD SOURCES USING UNIFORM CIRCULAR ARRAY
摘要： An e?cient algorithm based on high-order cumulant is addressed for the scenarios where both far-?eld and near-?eld narrow-band signals may exist synchronously. The ?rst matrix built by four-order cumulant is utilized to estimate the two dimensional direction-of-arrivals (DOAs) using the orthogonal projection matrix of the signal subspace and the virtual steering matrix. Then, the second matrix built by four-order cumulant is decomposed to get the noise subspace using the eigen decomposition. Meanwhile, a virtual steering matrix is used to distinguish far-?eld signals (FFSs) from near-?eld signals (NFSs). And one-dimensional MUSIC algorithm is used to estimate the range of the NFSs. Compared to the TSMUSIC, the proposed algorithm can provide high resolution for the DOAs. In addition, there is higher accuracy for the DOA of NFS in the proposed algorithm than that in TSMUSIC and in TSMD. Simulation results are carried out to certify the performance of the proposed algorithm.
关键词： near-field signals,MUSIC algorithm,high-order cumulant,uniform circular array,far-field signals,DOA estimation
更新于2025-09-04 15:30:14
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2018) - Nagoya (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - THz Near- Field Imaging and Spectroscopy with Nanoscale Resolution
摘要： Scattering-type near-field microscopy can overcome the limits in spatial resolution present in conventional THz imaging and spectroscopy techniques. This talk shows how THz near-field imaging and THz-TDS with a spatial resolution <20 nm can be realized with our neaSNOM microscope and some of the possible applications.
关键词： THz-TDS,nanoscale resolution,neaSNOM microscope,THz near-field imaging
更新于2025-09-04 15:30:14
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Inverse photonic design of functional elements that focus Bloch surface waves
摘要： Bloch surface waves (BSWs) are sustained at the interface of a suitably designed one-dimensional (1D) dielectric photonic crystal and an ambient material. The elements that control the propagation of BSWs are defined by a spatially structured device layer on top of the 1D photonic crystal that locally changes the effective index of the BSW. An example of such an element is a focusing device that squeezes an incident BSW into a tiny space. However, the ability to focus BSWs is limited since the index contrast achievable with the device layer is usually only on the order of Δn≈0.1 for practical reasons. Conventional elements, e.g., discs or triangles, which rely on a photonic nanojet to focus BSWs, operate insufficiently at such a low index contrast. To solve this problem, we utilize an inverse photonic design strategy to attain functional elements that focus BSWs efficiently into spatial domains slightly smaller than half the wavelength. Selected examples of such functional elements are fabricated. Their ability to focus BSWs is experimentally verified by measuring the field distributions with a scanning near-field optical microscope. Our focusing elements are promising ingredients for a future generation of integrated photonic devices that rely on BSWs, e.g., to carry information, or lab-on-chip devices for specific sensing applications.
关键词： focusing elements,scanning near-field optical microscope,integrated photonic devices,Bloch surface waves,photonic design
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - A Computational and Experimental Investigation of λ/2 and λ/4 Sampling Step in Phaseless Planar Near-Field Measurements at 60GHz
摘要： While complex planar near-field measurements involve a formal sampling step requirement (less than 0.5λ, typically 0.45λ) phaseless planar near-field measurements with the two-scans technique do not. In phaseless measurements only the magnitude is measured; while the plane wave spectrum of the square of the magnitude has twice the bandwidth of the complex signal, the magnitude itself may have an even much larger bandwidth. However, the spectrum of the magnitude is not of significance for phaseless measurements with the two-scans technique where the measured magnitude is combined with an initial guess for the phase to form a complex signal. But this combined complex field may also have a plane wave spectrum that is broader than that of the measured complex signal and thus extend beyond the visible region of the spectral domain. This will happen if the initial guess for the phase does not fit properly to the measured magnitude; e.g. if the phase jumps by 180deg. at a point where the measured magnitude in non-zero. For this reason, the phaseless measurement may require a sampling step notably smaller than λ/2 to avoid aliasing effects in the visible region of the spectral domain. This work, based on experimental and simulated planar near-field measurements of a 60GHz horn, investigates the effect of the initial guess for the phase on the plane wave spectrum of the combined complex signal. Furthermore, it investigates the effect of the initial guess for the phase and different sampling steps on the phase retrieval, using the Iterative Fourier Technique, and thus on the resulting far-field radiation pattern.
关键词： measurements,magnitude-only,phaseless,near-field
更新于2025-09-04 15:30:14
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5D Parameter Estimation of Near-Field Sources Using Hybrid Evolutionary Computational Techniques
摘要： Hybrid evolutionary computational technique is developed to jointly estimate the amplitude, frequency, range, and 2D direction of arrival (elevation and azimuth angles) of near-field sources impinging on centrosymmetric cross array. Specifically, genetic algorithm is used as a global optimizer, whereas pattern search and interior point algorithms are employed as rapid local search optimizers. For this, a new multiobjective fitness function is constructed, which is the combination of mean square error and correlation between the normalized desired and estimated vectors. The performance of the proposed hybrid scheme is compared not only with the individual responses of genetic algorithm, interior point algorithm, and pattern search, but also with the existing traditional techniques. The proposed schemes produced fairly good results in terms of estimation accuracy, convergence rate, and robustness against noise. A large number of Monte-Carlo simulations are carried out to test out the validity and reliability of each scheme.
关键词： pattern search,interior point algorithm,parameter estimation,hybrid evolutionary computational techniques,genetic algorithm,near-field sources
更新于2025-09-04 15:30:14
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Nanoapertures without nanolithography
摘要： We propose and experimentally demonstrate the implementation of lithography-free nano-apertures on optical fibers. By sputtering metallic nanofilms onto the end face of step index fibers that contain central nano-channels, fiber-integrated nano-apertures are instantaneously implemented without the use of any kind of lithographic step. In accordance with simulations, the experiments show diffraction-limited nano-spots in the far-field at the location of the nano-aperture for sufficiently thick films. We reproducibly implement a series of devices by sputtering Al and Pt nano-films, reaching aperture diameters as small as 40 nm and showing spectrally broadband operation. Due to its simplicity, scalability and potential for large-scale production the nano-aperture enhanced fiber concept will be highly relevant for lab-on-a-fiber applications and for the development of future fiber-based nano-probes with high spatial resolutions.
关键词： lab-on-a-fiber,hybrid fibers,nanofabrication,scanning near-field optical microscopy (SNOM),nanoapertures
更新于2025-09-04 15:30:14
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The Sommerfeld ground-wave limit for a molecule adsorbed at a surface
摘要： Using a mid-infrared emission spectrometer based on a superconducting nanowire single-photon detector (SNSPD), we observe the dynamics of vibrational energy pooling of CO adsorbed at the surface of a NaCl crystal. After exciting a majority of the CO molecules to their first vibrationally excited state (v = 1), we observe infrared emission from states up to v = 27. Kinetic Monte Carlo simulations show that vibrational energy collects in a few CO molecules at the expense of those up to eight lattice sites away by selective excitation of NaCl’s transverse phonons. The vibrating CO molecules behave like classical oscillating dipoles, losing their energy to NaCl lattice-vibrations via the electromagnetic near-field. This is analogous to Sommerfeld’s description of the Earth’s influence on radio transmission by ground waves.
关键词： vibrational energy pooling,NaCl crystal,superconducting nanowire single-photon detector,electromagnetic near-field,Kinetic Monte Carlo simulations,Sommerfeld ground-wave limit,CO adsorbed
更新于2025-09-04 15:30:14