High-resolution Angle Research Articles

Elevation Angle Estimation in a Multipath Environment Using MIMO-OFDM Signals

It is challenging to estimate the elevation angle of low-altitude targets due to the multipath effect. Various signal processing techniques have been proposed to mitigate these effects, including the use of multi-frequency signals as opposed to single narrowband signals. However, the optimal type of multi-frequency signals and their effective utilization have not been thoroughly explored. Compressive sensing was also proposed as a high-resolution angle estimation method. But, that was conducted with narrowband signals. In this paper, we employ MIMO-OFDM signals along with a block sparse Bayesian learning fast marginalized (BSBL-FM) method. This combination allows for the effective processing of multi-frequency signals and provides high resolution estimates. The MIMO-OFDM approach represents radar signals in a block-sparse matrix form, and the BSBL-FM method leverages this sparsity to achieve high-resolution angle estimates. Simulation results demonstrate that our method can accurately estimate angles at extremely low altitudes where the elevation angle is less than 1 degree.

Terahertz angle sensor based on the asymmetry coupling of the square and L-shaped structure

This letter presents a terahertz angle sensor using a rectangular and double L-shaped structure. The structure unit of the sensor consists of a typical metal-medium structure, with the top metal pattern comprising a rectangle and a double L-shaped structure. At the same time, the bottom layer is made of polyimide, a dielectric material. By varying the position and number of L-shaped structures, a terahertz angle sensor based on a spring-shaped structure is created. The terahertz angle sensor achieves a Q value of 120.6 with a sensitivity of 3.45 GHz per degree. The terahertz angle sensor offers high-angle resolution and may find applications in terahertz communication, imaging, sensing, and other related fields.

A Miniatured Fully Integrated High Resolution and Accuracy Capacitive Angle Encoder

In this paper, a capacitive angle encoder monitored and sensed by ASIC with a sensitive structure fabricated by MEMS technology is proposed. The sensitive structure with a 27.5mm outer diameter is designed and optimized in a limited footprint to realize higher accuracy. After being fabricated by MEMS technology, it is integrated with an ASIC, realizing high fabrication accuracy and a small footprint at the same time. The ASIC is designed in an analog-digital hybrid architecture to achieve low power consumption as well as a small footprint. The analog part of the ASIC consists of a charge to voltage converter with capacitance cancellation array and a sigma-delta modulator (SDM) with a 3-bit quantizer. In the digital part of ASIC, the processor based on Cortex-M3 core is designed to perform angle calculation. The measurement result of the proposed angle sensor reveals that the power consumption is 250 mW from a single 5V supply, the bandwidth is over 130Hz, the resolution is 0.002° and the accuracy over the full range is 0.024°, indicating that the encoder has considerable potential for use in high-precision applications.

A high-resolution angle estimation method for distributed aperture arrays

A high-resolution angle estimation method for distributed aperture arrays

An Algorithm to Correct the Sensitivity Distribution of a Retarding Field Analyzer for Photoelectron Holography

Recently, we developed a retarding field analyzer (RFA) with high energy resolution and wide acceptance angles, which was installed at BL25SU in SPring-8, Japan. This apparatus enables us to measure photoelectron angular distributions (photoelectron holograms) with a solid angle of ±49° in a few minutes, and this approach is now being applied to measure the atomic arrangements of dopants and interfaces. However, correcting the sensitivity distribution of the measured images by the RFA is important in processing this data. The sensitivity distribution of the RFA is difficult to measure directly because it depends on the geometry of a sample, the kinetic energy of the photoelectrons, and so forth. Therefore, we developed an image processing algorithm to estimate the sensitivity distribution using spherical harmonics. This approach is more accurate than a Fourier transform and can efficiently correct the sensitivity distribution. Moreover, the algorithm can also be adopted in a wide variety of other applications in addition to RFA measurements.

Novel strategy for space group determination in real space

Traditional space group determination methods are all in reciprocal space, which involves ambiguous identification on some space groups which have glide plane and screw axes. The novel strategy herein for space group determination in real space is based on the atom resolution high angle annular dark field (HAADF) technology. Three HAADF images in three specific crystal zone axes are needed at most. The proposed strategy for space group determination is easy and effective.

Waveform Design and DoA-DoD Estimation of OFDM-LFM Signal Based on SDFnT for MIMO Radar

In comparison to orthogonal frequency division multiplexing (OFDM), the OFDM linear frequency modulation (OFDM-LFM) signal has similar time-bandwidth product, lower peak-to-average power ratio, and higher sensitivity to Doppler frequency shift, making it a promising candidate waveform for multiple-in multiple-out (MIMO) radar applications. However, the OFDM-LFM signal is unsatisfactory in practical applications due to the challenges in waveform design and its non-stationary property, which significantly degrades the performance of current high-resolution subspace techniques for direction of departure (DoD) and direction of arrival (DoA) angle estimation. In this paper, we first proposed a novel OFDM-LFM waveform design method based on the scale discrete Fresnel transform (SDFnT), which efficiently generates orthogonal LFM signals with unlimited number of subcarriers and can be convieniently implemented using the fast Fourier transform (FFT). Then, for angle estimation in OFDM-LFM MIMO radars, we presented a new scale discrete Fresnel transform multiple signal classification (SDFnT-MUSIC) method. By converting the steering vector into the chirp domain and making it non-time-vary, high resolution angle estimation for OFDM-LFM wideband signals can be achieved. Simulation results shows that the proposed waveform design method requires less computational time than conventional method based based on the fractional Fourier transform (FrFT), whereas the proposed DoA-DoD estimation method outperform the FrFT-MUSIC method in terms of computational complexity and target angle estimate performance.

Simultaneous Sparse Deconvolution

Increasing seismic resolution has been long pursued by the geophysical community, serving, among other applications, for more detailed interpretation of seismic clinoforms, better seismic inversion and quantitative interpretation. Sparse deconvolution methods play central role in this pursuit. However, although sparse methods have performed well for single seismic stack or acoustic inversion tasks, their application for multi-stack seismic volumes and consequent use in elastic inversion is still a challenging and ongoing research topic. The challenge is to obtain reflectivity volumes with high correlation between them. In this study, we present a new method to perform simultaneous sparse deconvolution (SSD) in a group of seismic volumes associated with different reflection angles. The proposed algorithm enforces co-localization of the spikes on the estimated reflectivity traces and additionally allows user control of the sparsity via hyperparameters. The method is validated in both synthetic and real datasets proving its co-localization capability and resulting in higher correlations between the reflectivity volumes, when compared to independent sparse deconvolution (ISD) of the seismic stacks. The resulting reflectivity volumes are, henceforth, better suited for downstream tasks such as high resolution amplitude versus angle (AVA) analysis, or input for high resolution elastic inversions.

Large-Scale and Broadband Silicon Nitride Optical Phased Arrays

Large-scale one-dimensional (1D) waveguide surface grating arrays enable smaller antenna pitches and larger apertures for the OPAs. However, broad wavelength tuning is required for wide-angle beam steering along the transverse θ direction for 1D waveguide antennas. High-resolution and wide-angle beam steerings at visible and NIR wavelengths have not been reported in previous studies. This study presents a large-scale SiNx nanophotonic phased array with an optical aperture of 2.3 mm × 2.3 mm, which is the largest OPA aperture produced in the visible and NIR bands thus far. Broad wavelength tuning from 650 nm to 1064 nm is employed to achieve small beam divergences of 0.03° – 0.054° in a wide steering range of 53.7°. The overall losses are accordingly analyzed with 3 dB bandwidth of 150 nm from 785 nm to 935 nm. Furthermore, with a supercontinuum laser illuminated on the OPA, more than 1000 resolvable spots merge together in the free space and form a fine strip of continuous line in the far-field projection with an FOV of >50°. This study demonstrates both high steering resolution and wide steering angle at wavelengths from visible to NIR on SiNx OPAs for the first time, to the best of our knowledge.

First Sidelobe Analysis of Spatial Spectrum for Distributed Dual mmWave Radars

This letter considers a distributed cascade of two millimeter-wave (mmWave) radars to achieve a large virtual aperture for high-resolution angle measurement. In order to explore the high sidelobe problem caused by distributed radars, we derive the general Bartlett spatial spectrum expression of the virtual array. Furthermore, we introduce four cases to describe the relationship between the radar spacing, the number of transmitters/receivers, and the sidelobe position of the spatial spectrum. Finally, numerical simulation and experiment examples are provided to verify the effectiveness of the analysis.

Interactive transformation mechanisms of multiple metastable precipitates in a Si-rich Al-Mg-Si alloy

ABSTRACT The precipitate evolution mechanism of the Al-Mg-Si alloys with a Si-rich composition have been a long-term challenge due to the complex transformation paths among multiple precipitates. In the present work, the interactive transformation process of multiple metastable precipitates in a Si-rich Al-Mg-Si alloy were thoroughly studied by atomic resolution high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), in-situ heating TEM and first-principles calculation. It was revealed that the β″ phase transforms simultaneously to various types of precipitates in the over-aged stage. Two different evolution paths are proposed. Firstly, the β″ phase transforms directly to the U1, U2 and β′ phases. Secondly, the U2 phase, as an intermediate phase, transforms to the U1, β′ and B′ phases during the prolonging aging. The formation and evolution of substructures, including the QP lattice and Al–Si columns, are the key for structural transformation of precipitates. During the severe over-aging, the evolution of precipitates is governed by the dissolution of small precipitates (β′ and B′ phases) and the growth of the large ones (U1 phase). These results provide scientific basis for both property improvement of the commercial Al-Mg-Si alloys and development of new 6xxx aluminum alloys.

Doping induced band renormalization in 122-type Fe-based superconductor

We study the electronic structure of a superconducting composition of 122-type Fe-based pnictide material, CaFe1.9Co0.1As2 employing high resolution angle resolved photoemission spectroscopy technique. The experimental results exhibit three bands close to Fermi level at Γ-point of the Brillouin zone among which only one band crosses the Fermi level. In the parent compound, CaFe2As2, all the three bands cross the Fermi level and form three hole pockets. While the destruction of Fermi pockets due to electron doping (Co-substitution dopes electrons into the system) is expected, we observe significant orbital selective band renormalization with respect to the parent compound. It appears that the effect of spin-orbit coupling is stronger in the doped compound.

Diffusion MRI Connections in the Octopus Brain.

Using high angle resolution diffusion magnetic resonance imaging (HARDI) with fiber tractography analysis we map out a meso-scale connectome of the Octopus bimaculoides brain. The brain of this cephalopod has a qualitatively different organization than that of vertebrates, yet it exhibits complex behavior, an elaborate sensory system and high cognitive abilities. Over the last 60 years wide ranging and detailed studies of octopus brain anatomy have been undertaken, including classical histological sectioning/staining, electron microscopy and neuronal tract tracing with injected dyes. These studies have elucidated many neuronal connections within and among anatomical structures. Diffusion MRI based tractography utilizes a qualitatively different method of tracing connections within the brain and offers facile three-dimensional images of anatomy and connections that can be quantitatively analyzed. Twenty-five separate lobes of the brain were segmented in the 3D MR images of each of three samples, including all five sub-structures in the vertical lobe. These parcellations were used to assay fiber tracings between lobes. The connectivity matrix constructed from diffusion MRI data was largely in agreement with that assembled from earlier studies. The one major difference was that connections between the vertical lobe and more basal supra-esophageal structures present in the literature were not found by MRI. In all, 92 connections between the 25 different lobes were noted by diffusion MRI: 53 between supra-esophageal lobes and 26 between the optic lobes and other structures. These represent the beginnings of a mesoscale connectome of the octopus brain.

Transmit-Receive Beamforming for Distributed Phased-MIMO Radar System

Distributed phased Multiple-Input Multiple-Output (phased-MIMO) radar system consisting of separated subarrays possesses a high angle resolution but with sharing high sidelobes. This paper therefore focuses on the design of a virtual low-sidelobe beampattern in distributed phased-MIMO radar. An iterative framework with respect to subarray layout and receive weighting coefficients is proposed to minimize beampattern Peak Sidelobe Level (PSL) accounting for practical position constraints as well as the mainlobe level restriction. In each iteration, an efficient cyclic optimization algorithm based on the Coordinate Descent (CD) framework is developed to seek for the subarray layout through splitting high dimensional layout optimization problem into multiple one-dimensional optimization problems, and the SemiDefinite Relaxation (SDR) technique and rank one approximation are explored to design weighting coefficients. Numerical simulations are provided to assess the performance of the proposed algorithms in term of the achieved beampattern under different constraints and parameter settings.

Reply to “Comments on ‘Combining Switched TMAs and FDAs to Synthesize Dot-Shaped Beampatterns”’

It is noted that the main innovation contained lies in the consideration of frequency diverse arrays (FDAs) feeding networks made up of time-modulating switches (hence, the term TMA-FDA) instead of phase shifters. This has the undoubted advantage of leveraging that RF switches have virtually zero insertion loss while offering high angle resolution and cost-efficiency.

High resolution graphene angle sensor based on ultra-narrowband optical perfect absorption

We propose and experimentally demonstrate high resolution angle sensors based on ultra-narrowband graphene perfect absorbers. Perfect absorption at wavelength of 1452.8 nm with absorption bandwidth of 0.8 nm is numerically demonstrated for a designed angle sensor based on single graphene absorber at normal incidence, and the angular width of the resonant absorption is only 0.05°. In the experiment, peak absorption over 95% with bandwidth about 2.8 nm is measured at normal incidence for a fabricated graphene sensor, and the device has a wavelength-angle sensitivity over 17 nm per degree which agrees well with the simulation result. Meanwhile, an optoelectronic angle sensor with high resolution and fast response by using an array of graphene absorbers is proposed. The demonstrated graphene angle sensors with ultra compact size and high resolution could be of valuable applications in many fields.

Dispersion of neutron spin resonance mode in Ba0.67K0.33Fe2As2 * *Project supported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0704200, 2018YFA0305602, 2017YFA0303100, and 2017YFA0302900), the National Natural Science Foundation of China (Grant Nos. 11822411 and 11961160699), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (CAS) (Grant Nos. XDB25000000 and XDB07020300), K.C.Wong Education

We report an inelastic neutron scattering investigation on the spin resonance mode in the optimally hole-doped iron-based superconductor Ba0.67K0.33Fe2As2 with Tc= 38.2 K. Although the resonance is nearly two-dimensional with peak energy E R ≈ 14 meV, it splits into two incommensurate peaks along the longitudinal direction ([H,0,0]) and shows an upward dispersion persisting to 26 meV. Such dispersion breaks through the limit of total superconducting gaps Δ tot = |Δk | + |Δ k+Q | (about 11–17 meV) on nested Fermi surfaces measured by high resolution angle resolved photoemission spectroscopy (ARPES). These results cannot be fully understood by the magnetic exciton scenario under s±-pairing symmetry of superconductivity, and suggest that the spin resonance may not be restricted by the superconducting gaps in the multi-band systems.

The role of thermodynamically stable configuration in enhancing crystallographic diffraction quality of flexible MOFs

SummarySingle-crystal X-ray diffraction (SCXRD) is a widely used method for structural characterization. Generally, low temperature is of great significance for improving the crystallographic diffraction quality. Herein we observe that this practice is not always effective for flexible metal-organic frameworks (f-MOFs). An abnormal crystallography, that is, more diffraction spots at a high angle and better resolution of diffraction data as the temperature increases in the f-MOF (1-g), is observed. XRD results reveal that 1-g has a reversible anisotropic thermal expansion behavior with a record-high c-axial positive expansion coefficient of 1,401.8 × 10−6 K−1. Calculation results indicate that the framework of 1-g has a more stable thermodynamic configuration as the temperature increases. Such configuration has lower-frequency vibration and may play a key role in promoting higher Bragg diffraction quality at room temperature. This work is of great significance for how to obtain high-quality SCXRD diffraction data.

Triboelectric bending sensor based smart glove towards intuitive multi-dimensional human-machine interfaces

Recent advances in human-machine interface (HMI) lead to a renewed interest in creating intuitive and immersive interaction. Here, we designed a simple-structured and high-resolution bending angle triboelectric sensor named bending-angle triboelectric nanogenerator (BA-TENG) to construct a glove-based multi-dimensional HMI. With the assistance of a customized print circuit board (PCB), the glove-based HMI exhibits high sensitivity and low crosstalk in real-time multi-channel finger motion sensing. The signal-to-noise ratio (SNR) is improved by 19.36 dB. By systematically extracting and analyzing the multi-dimensional signal features of the BA-TENG, intuitive multi-dimensional HMIs were realized for smart-home, advanced robotic control, and a virtual keyboard with user recognition functionality. The classification accuracy of the virtual keyboard for seven users reached 93.1% by leveraging the advanced machine learning technique. The proposed BA-TENG-based smart glove reveals its potential as a solution for minimalist-design and intuitive multi-dimensional HMI, promising in diversified areas, including the Internet of things (IoT), assistive technology, and intelligent recognition systems. • Development of high bending angle resolution triboelectric nanogenerator (BA-TENG) using PDMS and silicon rubber. • The signal-to-noise ratio (SNR) is improved by 19.36 dB with the assistance of a trans-impedance amplifier. • Multi-dimensional signal features are extracted, including valley ( V ), width ( W ), hold time ( H ), and time interval ( T ). • Light-brightness control, robotic hand control, and a virtual keyboard with user identification were achieved. • Machine learning technique (SVM) is used for user identification with an accuracy of 93.1%.

Detailed Morphologic Mapping and Traverse Planning for a Rover-based Lunar Sample Return Mission to Schrödinger Basin

Abstract Schrödinger basin, a 312 km diameter complex impact structure located near the lunar south pole, has been widely cited as a prime target for future lunar exploration. In 2020 NASA identified Schrödinger as a high-priority landing site for a 2024 mission supported by the Payloads and Research Investigations on the Surface of the Moon solicitation and the Commercial Lunar Payload Services program. Schrödinger basin hosts an uplifted peak ring that would provide a surface mission with access to materials that originated deep within the lunar crust, as well as material ejected from the larger South Pole–Aitken basin. Schrödinger basin also hosts well-preserved mare and pyroclastic deposits that could provide valuable insight into volcanic processes on the Moon. This study used high-resolution Wide Angle Camera and Narrow Angle Camera images from the Lunar Reconnaissance Orbiter, elevation data from the Lunar Orbiter Laser Altimeter, and spectral data from the Clementine mission to produce a high-resolution morphologic map of the basin center consisting of 10 distinct morphologic units. This new map was used to plan traverse paths for a rover mission to the region. The design requirements for this traverse were based on those originally developed for the multiagency Human-Enhanced Robotic Architecture and Capability for Lunar Exploration and Science (HERACLES) mission and the Canadian Space Agency Precursor to Humans And Science Rover concept. The proposed traverse path includes up to 20 sample collection stops with the goal of better understanding lunar chronology, lunar volcanism, and the impact cratering process.