检索结果-内蒙古大学图书馆

Maximum Willis Coupling in Acoustic Scatterers

Physical Review Letters 2018年第25期120卷 254301-254301页

作者： Li Quan Younes Ra’di Dimitrios L. Sounas Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

Willis coupling in acoustic materials defines the cross-coupling between strain and velocity, analogous to bianisotropic phenomena in electromagnetics. While these phenomena have been garnering significant attention in recent years, to date their effects have been considered mostly perturbative. Here, we derive general bounds on the Willis response of acoustic scatterers, show that these bounds can be reached in suitably designed scatterers, and outline a systematic venue for the realistic implementation of maximally bianisotropic acoustic inclusions. We then employ these inclusions to realize acoustic metasurfaces for bending and steering of sound with unitary efficiency.

关键词： Acoustic metamaterials Acoustic wave phenomena Acoustics Mechanical & acoustical properties

来源：评论

学校读者我要写书评

暂无评论

Active Microwave Cloaking Using Parity-Time-Symmetric Satellites

引用

Physical Review Applied 2018年第5期10卷 054040-054040页

作者： Ahmed Kord Dimitrios L. Sounas Andrea Alù Department of Electrical and Computer Engineering the University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

In this paper, we present and study the dynamics of an active microwave cloaking technique that alleviates the trade-offs between loss, bandwidth, and size inherent in passive approaches. The presented cloak consists of a finite number of satellite antennas loaded with parity-time-symmetric lumped admittances, which, without external control, can track in real time the amplitude, frequency, and phase variations of the impinging signals and generate the required current distributions at the antennas to totally suppress the scattered waves, including reflections and shadows. We analytically derive the optimal density and frequency dispersion of the antenna satellites surrounding the object in order to achieve substantial reduction in the scattering crosssection over a wide bandwidth. We also investigate the conditions necessary to maintain the cloak stability and study its transient response for excitation with pulsed signals.

关键词： Cloaking Metamaterials Optical cloaking PT-symmetry Microwave techniques

来源：评论

学校读者我要写书评

暂无评论

Hyperbolic Sound Propagation over Nonlocal Acoustic Metasurfaces

引用

Physical Review Letters 2019年第24期123卷 244303-244303页

作者： Li Quan Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10016 USA Department of Electrical Engineering City College of The City University of New York New York 10031 USA

Hyperbolic metasurfaces, supporting extreme anisotropy of the surface impedance tensor, have recently been explored in nanophotonic systems for robust diffractionless propagation over a surface, offering interesting opportunities for subdiffraction imaging and enhanced Purcell emission. In acoustics, due to the longitudinal nature of sound transport in fluids, these phenomena are forbidden by symmetry, requiring the acoustic surface impedance to be inherently isotropic. Here we show that nonlocalities produced by strong coupling between neighboring impedance elements enable extreme anisotropic responses for sound traveling over a surface, supporting negative phase and energy velocities, as well as hyperbolic propagation for acoustic surface waves.

关键词： Acoustics Hyperbolic metamaterials Metamaterials

来源：评论

学校读者我要写书评

暂无评论

Angular-momentum selectivity and asymmetry in highly confined wave propagation along sheath-helical metasurface tubes

引用

Physical Review B 2019年第15期99卷 155425-155425页

作者： Yarden Mazor Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

Highly confined surface waves present unique opportunities to enhance light interactions with localized emitters or molecules. Hyperbolic dispersion in metasurfaces allows us to tailor and manipulate surface waves, enhancing the local density of states over broad bandwidths. So far, propagation on this platform was mainly studied in planar geometries, which facilitates the analysis but somehow limits the realm of possibilities. Here we show that “wrapping” hyperbolic metasurfaces into tubes may greatly enrich the wave propagation dynamics along their axis. This system shows strong interaction with fields and sources carrying optical angular momentum and pronounced field asymmetries, and opens pathways to valley-specific excitation and routing. In addition, we demonstrate that various parameter regimes enable strong spin/helicity momentum locking.

关键词： Angular momentum of light Hyperbolic metamaterials Light-matter interaction Surface plasmons Surfaces

来源：评论

学校读者我要写书评

暂无评论

Passive Acoustic Metasurface with Unitary Reflection Based on Nonlocality

引用

Physical Review Applied 2019年第5期11卷 054077-054077页

作者： Li Quan Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin Austin Texas 78712 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

Metasurfaces have introduced large flexibility in manipulating the impinging wavefront for light and sound by locally engineering the reflection and transmission coefficients based on generalized Snell’s laws. Local phenomena in each unit cell, however, are fundamentally limited in the level of efficiency with which anomalous wavefront transformations can be achieved. Here, we explore acoustic metasurfaces with suitably engineered nonlocality, obtained by coupling neighboring cells. We demonstrate that nonlocal passive metastructures can overcome the limitations of local designs, and mimic balanced gain and loss distributions, enabling unitary efficiency for extreme beam steering.

关键词： Acoustic metamaterials Acoustic wave phenomena Beam control Beam optics Light propagation, transmission & absorption

来源：评论

学校读者我要写书评

暂无评论

Parity-time Symmetry Based on Time Modulation

引用

Physical Review Applied 2020年第3期14卷 031002-031002页

作者： Huanan Li Hady Moussa Dimitrios Sounas Andrea Alù Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Department of Electrical Engineering City College of The City University of New York New York 10031 USA Department of Electrical and Computer Engineering Wayne State University Detroit Michigan 48202 USA Physics Program Graduate Center City University of New York New York New York 10016 USA

We leverage aperiodic temporal modulations and nonreciprocity to realize PT-symmetric phenomena without the need for gain and loss provided by external mechanisms. We develop our approach using a general coupled-mode framework, and verify our results via detailed simulations in a conservative electronic circuit, demonstrating wave phenomena such as scattering PT-phase transition and anisotropic transmission resonances in a Hermitian system. Our concept opens the possibility of implementing PT-symmetric phenomena without gain, with applications in sensing, communications, and a broad range of quantum physics.

关键词： Symmetry protected topological states Coupled oscillators Metamaterials PT-symmetry Cavity resonators Coupled mode theory S-matrix method in transport

来源：评论

学校读者我要写书评

暂无评论

Coupling Rendering and Generative Adversarial Networks for Artificial SAS Image Generation

Coupling Rendering and Generative Adversarial Networks for A...

引用

OCEANS

作者： Albert Reed Isaac D. Gerg John D. McKay Daniel C. Brown David P. Williamsk Suren Jayasuriya School of Electrical Computer & Energy Engineering Arizona State University Tempe AZ USA School of Electrical Engineering and Computer Science Pennsylvania State University State College PA USA Applied Research Laboratory Pennsylvania State University State College PA USA Graduate Program in Acoustics Pennsylvania State University State College PA USA NATO STO Centre for Maritime Research & Experimentation La Spezia Italy School of Arts Media & Engineering Arizona State University Tempe AZ USA

There is a growing demand for large-scale Synthetic Aperture Sonar (SAS) datasets. This demand stems from data-driven applications such as Automatic Target Recognition (ATR) [1]-[3], segmentation [4] and oceanographic research of the seafloor, simulation for sensor prototype development and calibration [5], and even potential higher level tasks such as motion estimation [6] and micronavigation [7]. Unfortunately, the acquisition of SAS data is bottlenecked by the costly deployment of SAS imaging systems, and even when data acquisition is possible, the data is often skewed towards containing barren seafloor rather than objects of interest. This skew introduces a data imbalance problem wherein a dataset can have as much as a 1000-to-1 ratio of seafloor background to object-of-interest SAS image chips.

关键词：

来源：评论

学校读者我要写书评

暂无评论

GNN-Based Point Cloud Maps Feature Extraction and Residual Feature Fusion for 3D Object Detection

GNN-Based Point Cloud Maps Feature Extraction and Residual F...

引用

IEEE International Conference on Robotics and Automation (ICRA)

作者： Wei-Hsiang Liao Chieh-Chih Wang Wen-Chieh Lin Graduate Degree Program of Artificial Intelligence National Yang Ming Chiao Tung University Hsinchu Taiwan Department of Electrical and Computer Engineering National Yang Ming Chiao Tung University Hsinchu Taiwan Mechanical and Mechatronics Systems Research Laboratories Industrial Technology Research Institute Hsinchu Taiwan Institute of Multimedia Engineering National Yang Ming Chiao Tung University Hsinchu Taiwan

LiDAR detection of long-range vehicles is challenging because very few and sparse points are measured in long distances and vehicles with similar shapes of targets could lead to false positives easily. To tackle these challenges, taking the environment information (HD maps) into account could be beneficial to predetermine where targets are more or less likely to appear. Compared with semantic maps, HD maps formed by point clouds provide much richer information from surrounding static objects and scenes. In this work, we construct a GNN-based feature extraction of point cloud maps to increase the receptive fields of learning map features. Our work is based on PVRCNN, the state-of-the-art LiDAR object detection method. With point-wise and voxel-wise features obtained from PVRCNN, residual feature fusion is proposed to fuse the features from PVRCNN and the map features from GNN. Our approach is evaluated on NuScenes dataset. It achieves a 24.78% average precision improvement for long-range objects at 40–50 meters, the farthest areas with ground truth annotation. Our approach also has a 4.22% reduction of false positives in the entire sensing areas.

关键词：

来源：评论

学校读者我要写书评

暂无评论

Scalable Numerical Embeddings for Multivariate Time Series: Enhancing Healthcare Data Representation Learning

arXiv

引用

arXiv 2024年

作者： Huang, Chun-Kai Hsieh, Yi-Hsien Chien, Ta-Jung Chien, Li-Cheng Sun, Shao-Hua Su, Tung-Hung Kao, Jia-Horng Lin, Che Taiwan Data Science Degree Program NTU Taiwan Department of Electrical Engineering NTU Taiwan Division of Gastroenterology and Hepatology NTU Hospital Taiwan Hepatitis Research Center NTU Hospital Taiwan Graduate Institute of Clinical Medicine College of Medicine NTU Taiwan Center for Advanced Computing and Imaging in Biomedicine NTU Taiwan Smart Medicine and Health Informatics Program NTU Taiwan

Multivariate time series (MTS) data, when sampled irregularly and asynchronously, often present extensive missing values. Conventional methodologies for MTS analysis tend to rely on temporal embeddings based on timestamps that necessitate subsequent imputations, yet these imputed values frequently deviate substantially from their actual counterparts, thereby compromising prediction accuracy. Furthermore, these methods typically fail to provide robust initial embeddings for values infrequently observed or even absent within the training set, posing significant challenges to model generalizability. In response to these challenges, we propose SCAlable Numerical Embedding (SCANE), a novel framework that treats each feature value as an independent token, effectively bypassing the need for imputation. SCANE regularizes the traits of distinct feature embeddings and enhances representational learning through a scalable embedding mechanism. Coupling SCANE with the Transformer Encoder architecture, we develop the Scalable nUMerical eMbeddIng Transformer (SUMMIT), which is engineered to deliver precise predictive outputs for MTS characterized by prevalent missing entries. Our experimental validation, conducted across three disparate electronic health record (EHR) datasets marked by elevated missing value frequencies, confirms the superior performance of SUMMIT over contemporary state-of-the-art approaches addressing similar challenges. These results substantiate the efficacy of SCANE and SUMMIT, underscoring their potential applicability across a broad spectrum of MTS data analytical tasks. Copyright © 2024, The Authors. All rights reserved.

关键词： Embeddings

来源：评论

学校读者我要写书评

暂无评论

Quasielectrostatic Wave Propagation Beyond the Delay-Bandwidth Limit in Switched Networks

引用

Physical Review X 2019年第3期9卷 031015-031015页

作者： Mykhailo Tymchenko Dimitrios Sounas Aravind Nagulu Harish Krishnaswamy Andrea Alù Department of Electrical and Computer Engineering The University of Texas at Austin 1 University Station C0803 Austin Texas 78712 USA Department of Electrical and Computer Engineering Wayne State University Detroit Michigan 48202 USA Department of Electrical Engineering Columbia University 1300 South West Mudd 500 West 120th Street New York New York 10027 USA Photonics Initiative Advanced Science Research Center City University of New York New York New York 10031 USA Physics Program Graduate Center City University of New York New York New York 10026 USA Department of Electrical Engineering City College of New York New York New York 10031 USA

The delay-bandwidth limit implies a stringent trade-off between the time delay, bandwidth, and propagation distance of an electromagnetic signal. Here, we show that temporal modulation can overcome this constraint, enabling extremely broadband wave propagation with close-to-zero group velocity dispersion in switched multipath electronic networks. Contrary to time-invariant waveguides, in which wave propagation implies a delicate balance between electric and magnetic stored energies, in such modulated networks the stored energy is largely electrostatic in nature. We show that in this case the phase and group velocities become independent of the properties of their constituent elements, and they are controlled only by the modulation scheme. Based on these findings, we provide practical designs of deeply subwavelength CMOS-compatible reciprocal and nonreciprocal microwave components, such as delay lines, phase shifters, couplers, and circulators. The obtained results also explicitly show that temporally modulated systems are not bound by constraints of time-invariant systems and can achieve arbitrarily large delay-bandwidth products.

关键词： Metamaterials

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：