Showing papers by "David R. Smith published in 2019"
TL;DR: The origins of localized plasmon resonances in few-nanometricre or sub-nanometre gaps between metal nanoparticles and metal films are discussed, as well as recent experimental observations and potential future directions.
Abstract: Ultrathin dielectric gaps between metals can trap plasmonic optical modes with surprisingly low loss and with volumes below 1 nm3. We review the origin and subtle properties of these modes, and show how they can be well accounted for by simple models. Particularly important is the mixing between radiating antennas and confined nanogap modes, which is extremely sensitive to precise nanogeometry, right down to the single-atom level. Coupling nanogap plasmons to electronic and vibronic transitions yields a host of phenomena including single-molecule strong coupling and molecular optomechanics, opening access to atomic-scale chemistry and materials science, as well as quantum metamaterials. Ultimate low-energy devices such as robust bottom-up assembled single-atom switches are thus in prospect.
476 citations
TL;DR: This paper proposes a mathematical model for massive MIMO systems with DMAs and discusses their constraints compared to ideal antenna arrays, characterize the fundamental limits of uplink communications with the resulting systems and proposes two algorithms for designing practical DMAs for approaching these limits.
Abstract: Massive multiple-input–multiple-output (MIMO) communications are the focus of considerable interest in recent years. While the theoretical gains of massive MIMO have been established, implementing MIMO systems with large-scale antenna arrays in practice is challenging. Among the practical challenges associated with massive MIMO systems are increased cost, power consumption, and physical size. In this paper, we study the implementation of massive MIMO antenna arrays using dynamic metasurface antennas (DMAs), an emerging technology which inherently handles the aforementioned challenges. Specifically, DMAs realize large-scale planar antenna arrays and can adaptively incorporate signal processing methods such as compression and analog combining in the physical antenna structure, thus reducing the cost and power consumption. First, we propose a mathematical model for massive MIMO systems with DMAs and discuss their constraints compared to ideal antenna arrays. Then, we characterize the fundamental limits of uplink communications with the resulting systems and propose two algorithms for designing practical DMAs for approaching these limits. Our numerical results indicate that the proposed approaches result in practical massive MIMO systems whose performance is comparable to that achievable with ideal antenna arrays.
102 citations
TL;DR: It is demonstrated that the flexibility in beamforming supported by the metasurface antennas can be used to achieve low spatial correlation and high SNR gain in clustered MIMO channels, leading to a significant improvement of the channel capacity.
Abstract: We propose a spatial multiplexing system using reconfigurable cavity-backed metasurface antennas. The metasurface antennas consist of a printed cavity with dynamically tunable metamaterial radiators patterned on one side and fed by multiple radio frequency ports on the other side (each port representing one communication node), forming a shared aperture. By individual tuning of the radiators, the antennas can generate steerable, concurrent beams that can be adapted to the properties of multiple-input-multiple-output (MIMO) channels. In this paper, we present a $2\times 2$ MIMO system with simulated metasurface antennas as transmit and receive antennas operating at 5.9 GHz. We demonstrate that the flexibility in beamforming supported by the metasurface antennas can be used to achieve low spatial correlation and high SNR gain in clustered MIMO channels, leading to a significant improvement of the channel capacity. Numerical studies show 2.36-fold, 2.11-fold enhancements of capacity in MIMO channels with one and two clusters, respectively, compared with an MIMO system consisting of linear dipoles. The MIMO system based on the metasurface antennas can be low cost, low profile, and low power. The metasurface antenna thus has potential applications in small cell networks requiring high data rate under bandwidth, energy, and cost constraints.
65 citations
TL;DR: This paper presents a new technique called the transverse spectrum deconvolution range migration algorithm allowing us to carry out reconstructions that are both faster and more accurate than with conventional Fourier domain processing techniques.
Abstract: The growing need for high-performance imaging tools for terrorist threat detection and medical diagnosis has led to the development of new active architectures in the microwave and millimeter range. Notably, multiple-input multiple-output systems can meet the resolution constraints imposed by these applications by creating large, synthetic radiating apertures with a limited number of antennas used independently in transmitting and receiving signals. However, the implementation of such systems is coupled with strong constraints in the software layer, requiring the development of reconstruction techniques capable of interrogating the observed scene by optimizing both the resolution of images reconstructed in two or three dimensions and the associated computation times. In this paper, we first review the formalisms and constraints associated with each application by taking stock of efficient processing techniques based on spectral decompositions, and then, we present a new technique called the transverse spectrum deconvolution range migration algorithm allowing us to carry out reconstructions that are both faster and more accurate than with conventional Fourier domain processing techniques. This paper is particularly relevant to the development of new computational imaging tools that require, even more pronouncedly than in the case of conventional architectures, fast image computing techniques despite a very large number of radiating elements interrogating the scene to be imaged.
35 citations
TL;DR: In this article, an analytical forward model describing the metamaterial elements as coupled dipoles is integrated into the ML pipeline to jointly learn optimal sampling and measurement processing strategies for a given task.
Abstract: We address the fundamental question of how to optimally probe a scene with electromagnetic (EM) radiation to yield a maximum amount of information relevant to a particular task. Machine learning (ML) techniques have emerged as powerful tools to extract task-relevant information from a wide variety of EM measurements, ranging from optics to the microwave domain. However, given the ability to actively illuminate a particular scene with a programmable EM wavefront, it is often not clear what wavefronts optimally encode information for the task at hand (e.g., object detection, classification). Here, we show that by integrating a physical model of scene illumination and detection into a ML pipeline, we can jointly learn optimal sampling and measurement processing strategies for a given task. We consider in simulation the example of classifying objects using microwave radiation produced by dynamic metasurfaces. By integrating an analytical forward model describing the metamaterial elements as coupled dipoles into the ML pipeline, we jointly train analog model weights with digital neural network weights. The learned non-intuitive illumination settings yield a higher classification accuracy using fewer measurements. On the practical level, these results are highly relevant to emerging context-aware systems such as autonomous vehicles, touchless human-interactive devices or within smart health care, where strict time constraints place severe limits on measurement strategies. On the conceptual level, our work serves as a bridge between wavefront shaping and tunable metasurface design on the physical layer and ML techniques on the processing layer.
32 citations
01 Jul 2019
TL;DR: In this paper, a planar waveguide is used to convey optical radiation between a grating coupler and a metasurface hologram to form a multicolor holographic image in free space.
Abstract: Various examples of out-of-plane multicolor waveguide holography systems, methods of manufacture, and methods of use are described herein. In some examples, a multicolor waveguide holography system includes a planar waveguide to convey optical radiation between a grating coupler and a metasurface hologram. The grating coupler may be configured to couple out-of-plane optical radiation of three different color incident at three different angles into the planar waveguide. The combined multicolor optical radiation may be conveyed by the waveguide to the metasurface hologram. The metasurface hologram may diffractively decouple the three colors of optical radiation for off-plane propagation to form a multicolor holographic image in free space.
31 citations
TL;DR: In this paper, an analytic model of a coax-fed planar cavity-backed metasurface antenna for radiation pattern synthesis is presented, where the metamaterial elements are arranged in an aperture and radiated with proper weights at their locations.
Abstract: We present an analytic model of a coax-fed planar cavity-backed metasurface antenna for radiation pattern synthesis. The metasurface antenna consists of a printed cavity loaded with metamaterial elements which is excited by a coaxial connector. Each metamaterial element radiates a portion of the reverberating fields in the cavity, contributing to an overall beam pattern. To synthesize a desired pattern, the elements need to be arranged in an aperture and radiate with proper weights at their locations. The weight of each element is jointly determined by the geometry of the cavity and the metamaterial element’s resonant response. To predict and achieve the required weights, we first provide a full analytic description of the interaction of the cavity and the metamaterial elements. After verifying the analytical model through numerical simulations, we utilize it in an iterative scheme to solve for the metasurface structure that generates a prescribed pattern. Using the outlined procedure, three different antennas are designed, fabricated, and examined in experiments. Excellent agreement between measured and designed patterns is demonstrated, verifying the proposed analysis and synthesis process. Cavity-backed metasurface antennas with either static or dynamically reconfigurable radiation patterns may find application in communications, imaging and sensing.
25 citations
TL;DR: In this article, the authors examined non-local optical effects in small gaps and its effect on the optical response of a coaxial metamaterial in the mid-IR, including spectral shifts and boosted transmittance of the cutoff epsilon-near zero mode.
Abstract: With advances in nanofabrication techniques, extreme-scale nanophotonic devices with critical gap dimensions of just 1–2 nm have been realized. Plasmons in such ultranarrow gaps can exhibit nonlocal response, which was previously shown to limit the field enhancement and cause optical properties to deviate from the local description. Using atomic layer lithography, we create mid-infrared-resonant coaxial apertures with gap sizes as small as 1 nm and observe strong evidence of nonlocality, including spectral shifts and boosted transmittance of the cutoff epsilon-near-zero mode. Experiments are supported by full-wave 3-D nonlocal simulations performed with the hybridizable discontinuous Galerkin method. This numerical method captures atomic-scale variations of the electromagnetic fields while efficiently handling extreme-scale size mismatch. Combining atomic-layer-based fabrication techniques with fast and accurate numerical simulations provides practical routes to design and fabricate highly-efficient large-area mid-infrared sensors, antennas, and metasurfaces. Nonlocality is typically studied in simplified 2D or symmetric 3D structures and the ability to perform nonlocal simulations for complex 3D structures is lacking. Here the authors examine non-local optical effects in small gaps and its effect on the optical response of a coaxial metamaterial in the mid-IR.
24 citations
Posted Content•
TL;DR: This work presents a model for DMAs which accounts for the configurable frequency selective profile of its metamaterial elements, resulting in a spectrally flexible hybrid structure for MIMO-OFDM receivers operating with bit-constrained analog-to-digital converters (ADCs).
Abstract: The combination of orthogonal frequency modulation (OFDM) and multiple-input multiple-output (MIMO) systems plays an important role in modern communication systems. In order to meet the growing throughput demands, future MIMO-OFDM receivers are expected to utilize a massive number of antennas, operate in dynamic environments, and explore high frequency bands, while satisfying strict constraints in terms of cost, power, and size. An emerging technology to realize massive MIMO receivers of reduced cost and power consumption is based on dynamic metasurface antennas (DMAs), which inherently implement controllable compression in acquisition. In this work we study the application of DMAs for MIMO-OFDM receivers operating with bit-constrained analog-to-digital converters (ADCs). We present a model for DMAs which accounts for the configurable frequency selective profile of its metamaterial elements, resulting in a spectrally flexible hybrid structure. We then exploit previous results in task-based quantization to show how DMAs can be configured to improve recovery in the presence of constrained ADCs, and propose methods for adjusting the DMA parameters based on channel state information. Our numerical results demonstrate that the DMA-based receiver is capable of accurately recovering OFDM signals. In particular, we show that by properly exploiting the spectral diversity of DMAs, notable performance gains are obtained over existing designs of conventional hybrid architectures, demonstrating the potential of DMAs for MIMO-OFDM setups in realizing high performance massive antenna arrays of reduced cost and power consumption.
24 citations
02 Jul 2019
TL;DR: The numerical results demonstrate that, in addition to their simplicity and low cost, properly configured DMAs can achieve downlink sum-rate performance which is comparable with the fundamental limits of multi-user MIMO systems.
Abstract: Massive multiple-input multiple-output (MIMO) is a promising technique to enable orders of magnitude improvement in spectral and energy efficiency by utilizing a large number of antennas. Despite its theoretical gains, the implementation of large-scale antenna arrays faces many practical challenges in hardware cost, power consumption, and physical size. In this work, we study downlink massive MIMO systems in which the base stations (BSs) are equipped with dynamic metasurface antennas (DMAs). DMAs can realize low-cost, power-efficient, planar, and compact antenna arrays. We first formulate a mathematical model for DMA-based downlink massive MIMO systems. Then, we characterize the achievable sum-rate for the resulting systems and design an efficient alternating algorithm to dynamically configure DMA weights to maximize the achievable sum-rate. Our numerical results demonstrate that, in addition to their simplicity and low cost, properly configured DMAs can achieve downlink sum-rate performance which is comparable with the fundamental limits of multi-user MIMO systems.
20 citations
Princeton Plasma Physics Laboratory1, Columbia University2, University of California, Irvine3, Princeton University4, General Atomics5, University of Wisconsin-Madison6, Lawrence Livermore National Laboratory7, Oak Ridge National Laboratory8, University of Illinois at Urbana–Champaign9, University of California, Davis10, Massachusetts Institute of Technology11, University of São Paulo12, University of California, Los Angeles13, University of Tennessee14, University of Washington15, Los Alamos National Laboratory16, Lehigh University17, Johns Hopkins University18
Posted Content•
TL;DR: In this article, the design, fabrication, and experimental characterization of a two-dimensional, dynamically tuned, metasurface aperture is presented, emphasizing its potential performance in computational imaging applications.
Abstract: We present the design, fabrication, and experimental characterization of a two-dimensional, dynamically tuned, metasurface aperture, emphasizing its potential performance in computational imaging applications. The dynamic metasurface aperture (DMA) consists of an irregular, planar cavity that feeds a multitude of tunable metamaterial elements, all fabricated in a compact, multilayer printed circuit board process. The design considerations for the metamaterial element as a tunable radiator, the associated biasing circuitry, as well as cavity parameters are examined and discussed. A sensing matrix can be constructed from the measured transmit patterns, the singular value spectrum of which provides insight into the information capacity of the apertures. We investigate the singular value spectra of the sensing matrix over a variety of operating parameters, such as the number of metamaterial elements, number of masks, and number of radiating elements. After optimizing over these key parameters, we demonstrate computational microwave imaging of simple test objects.
TL;DR: It is shown that two spatially separated or overlapped holographic images can be produced with two orthogonally polarized beams, incorporated into a binary computer generated hologram (CGH).
Abstract: We propose and experimentally demonstrate a polarization-selective waveguide hologram at optical wavelengths, based on an all-dielectric metamaterial multilayer system. We show that two spatially separated or overlapped holographic images can be produced with two orthogonally polarized beams, incorporated into a binary computer generated hologram (CGH). These two images can be combined into a single 3D stereoscopic image observable using linearly or circularly polarized glasses. The two polarized beams can also be utilized to construct radially and azimuthally polarized "vortex" beams. The fundamental and first higher-order TM and TE modes of an optical waveguide are used to guide the two polarization states with distinct propagation constants. The two guided waves act as spatially distinct reference waves such that the integrated, on-chip hologram can distinguish the two and provide two independent images corresponding to the two polarizations. Polarization selective waveguide holograms can be used in a diverse set of applications, from chip-scale displays and augmented reality (AR) to optical trapping.
TL;DR: In this paper, a compensatory waveguide feed layer is proposed to suppress grating lobes in metasurface antennas, which can result from an unwanted periodic magnitude response that accompanies an ideal phase pattern.
Abstract: Metasurface antenna arrays, formed by tiling multiple metasurface subapertures, offer an alternative architecture to electrically large beamsteering arrays often used in radar and communications. The advantages offered by metasurfaces are enabled by the use of passive, tunable radiating elements. While these metamaterial elements do not exhibit the full range of phase tuning as can be obtained with phase shifters, they can be engineered to provide a similar level of performance with much lower power requirements and circuit complexity. Due to the limited phase and magnitude control, however, larger metasurface apertures can be susceptible to strong grating lobes which result from an unwanted periodic magnitude response that accompanies an ideal phase pattern. In this work, we combine antenna theory with analytical modeling of metamaterial elements to mathematically reveal the source of such grating lobes. To circumvent this problem, we introduce a compensatory waveguide feed layer designed to suppress grating lobes in metasurface antennas. The waveguide feed layer helps metasurface antennas approach the performance of phased arrays from an improved hardware platform, poising metasurface antennas to impact a variety of beamforming applications.
15 Dec 2019
TL;DR: In this article, a dynamically reconfigurable metasurface antenna (DMA) is used for computational through-wall imaging using a single-feed, electrically large microstrip line, loaded with individually addressable metamaterial radiators.
Abstract: We present a study of computational through-wall imaging using a dynamically reconfigurable metasurface antenna (DMA). The DMA consists of a single-feed, electrically-large microstrip line, loaded with individually addressable metamaterial radiators. Each metamaterial resonator is integrated with a diode, enabling it to be switched on (radiating) or off (non-radiating) by an externally applied voltage. By switching subsets of the array of elements on or off, spatially diverse radiation patterns are formed that are scattered by the wall and structures beyond the wall. Images can be reconstructed from these measurements, using a combination of range migration algorithms and wall compensation algorithms, with minimal frequency bandwidth requirements; even single frequency measurements are possible in conjunction with the DMA. We investigate imaging through a variety of wall materials at K-band frequencies (18-26.5 GHz), including homogeneous media with known properties and inhomogeneous materials such as plywood. We further investigate single-frequency performance against full-bandwidth measurements. The DMA used here is electrically large in one dimension, over which many spatially diverse measurements can be taken. By scanning the DMA in the perpendicular direction, full two-dimensional scans can be acquired with minimal cost and time, making the one-dimensional DMA attractive as the basis for future through-wall scanning systems.
TL;DR: This is the first time the context of implementing simulation modelling recommendations in a health care setting, using a validated framework, has been examined and may provide valuable insights to increase the uptake of healthcare modellingRecommendations in service planning.
Abstract: Background: Advanced physiotherapist-led services have been embedded in specialist orthopaedic and neurosurgical outpatient departments across Queensland, Australia, to ameliorate capacity constraints. Simulation modelling has been used to inform the optimal scale and professional mix of services required to match patient demand. The context and the value of simulation modelling in service planning remain unclear. We aimed to examine the adoption, context and costs of using simulation modelling recommendations to inform service planning. Methods: Using an implementation science approach, we undertook a prospective, qualitative evaluation to assess the use of discrete event simulation modelling recommendations for service re-design and to explore stakeholder perspectives about the role of simulation modelling in service planning. Five orthopaedic and neurosurgical services in Queensland, Australia, were selected to maximise variation in implementation effectiveness. We used the consolidated framework for implementation research (CFIR) to guide the facilitation and analysis of the stakeholder focus group discussions. We conducted a prospective costing analysis in each service to estimate the costs associated with using simulation modelling to inform service planning. Results: Four of the five services demonstrated adoption by inclusion of modelling recommendations into proposals for service re-design. Four CFIR constructs distinguished and two CFIR constructs did not distinguish between high versus mixed implementation effectiveness. We identified additional constructs that did not map onto CFIR. The mean cost of implementation was AU$34,553 per site (standard deviation = AU$737). Conclusions: To our knowledge, this is the first time the context of implementing simulation modelling recommendations in a health care setting, using a validated framework, has been examined. Our findings may provide valuable insights to increase the uptake of healthcare modelling recommendations in service planning.
TL;DR: This work explores two distinct processing schemes: incoherent processing of intensity data, obtained using asynchronous receivers and inspired by optical ghost imaging works, and coherent processing with synchronized array elements, and improves resolution and image quality.
Abstract: The correlation-based synthetic aperture radar imaging technique, termed radar coincidence imaging, is extended to a fully multistatic multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) configuration. Within this framework, we explore two distinct processing schemes: incoherent processing of intensity data, obtained using asynchronous receivers and inspired by optical ghost imaging works, and coherent processing with synchronized array elements. Improvement in resolution and image quality is demonstrated in both cases using numerical simulations that model an airborne MIMO SAR system at microwave frequencies. Finally, we explore methods for reducing measurement times and computational loads through compressive and gradient image reconstruction using phaseless data.
Patent•
10 Jun 2019TL;DR: In this article, a single frequency, or very narrow frequency band, microwave imaging system is described, which includes an array transmitter, an array receiver and a computing device that receives signals detected from the array receiver, transforms the signals received by the array receivers into independent spatial measurements, constructs an image using the independent spatial measurement, and outputs a reconstructed image.
Abstract: A single frequency, or very narrow frequency band, microwave imaging system is described herein. A microwave imaging system can include an array transmitter; an array receiver; and a computing device that receives signals detected from the array receiver, transforms the signals received by the array receiver into independent spatial measurements, constructs an image using the independent spatial measurements, and outputs a reconstructed image. The array transmitter and the array receiver may each have a plurality of independently controllable metasurface resonant elements.
Patent•
04 Apr 2019TL;DR: In this article, a MIMO communication system with a first antenna comprising a first cavity, a plurality of RF ports for generating a feed wave within the first cavity and a first plurality of sub-wavelength artificially structured material elements as arranged on a surface of the second cavity as RF radiators is presented.
Abstract: A MIMO communication system is provided. The system may include a first antenna comprising a first cavity, a first plurality of RF ports for generating a feed wave within the first cavity, and a first plurality of sub-wavelength artificially structured material elements as arranged on a surface of the first cavity as RF radiators. The first antenna is configured to generate a plurality of radiation patterns respectively corresponding to the first plurality of ports. The system may also include a second antenna comprising a second cavity and a second plurality of sub-wavelength artificially structured material elements arranged on a surface of the second cavity.
TL;DR: This work presents a method based on the electromagnetic variational principle that applies to media that can be described as collections of point dipoles, as most metamaterials are, and demonstrates its efficacy by designing highly efficient, non-perturbative, multiplexing devices.
Abstract: A fundamental challenge has plagued computer-generated volumetric holography since its inception: design methods are available only in the perturbative limit, but this poses serious limitations on efficiency and the amount of multiplexing achievable. Given the recent progress in highly tailorable artificial media, such as metamaterials, the need for general and robust design techniques grows. We present a method based on the electromagnetic variational principle that applies to media that can be described as collections of point dipoles, as most metamaterials are. We demonstrate its efficacy by designing highly efficient, non-perturbative, multiplexing devices.
01 Feb 2019
TL;DR: The proposed cost-effective integration strategy is designed for Microwave antennas, such as Ku-band andKu-band satellite communications (SATCOM), and this will consider the optimal sizing of the ESS in combination with the solar system in order to minimize investment and operational costs, while ensuring a continuous and efficient operation of the antenna.
Abstract: in this paper, a cost-effective design technique of a combined photovoltaic solar system, with electrical energy storage (ESS) for remote areas wireless long-term communication integration system is presented and discussed. Solar systems are the only possible solutions for supplying the required power to the communication infrastructure, i.e. antennas, in remote areas with no access to the electricity grid. However, due to the intermittency of solar power production support from ESS is required. As such, in periods of solar generation excess, the ESS is charged with the extra energy, whereas, in periods of solar generation scarcity the ESS is discharged to provide the load. The sizing of the overall solar-ESS system should be carefully carried out, by considering important aspects, such as installation and maintenance costs, operational requirements and related constraints, i.e. desired level of reliability and efficiency. The proposed cost-effective integration strategy is designed for Microwave antennas, such as Ku-band and Ku-band satellite communications (SATCOM), and this will consider the optimal sizing of the ESS in combination with the solar system in order to minimize investment and operational costs, while ensuring a continuous and efficient operation of the antenna.
04 Sep 2019
TL;DR: In this paper, a 3D printed holographic metasurface antenna for beam-focusing applications at 10 GHz within the X-band frequency regime was demonstrated. And the authors demonstrated that using a dual-material 3D printer leveraging a biodegradable conductive polymer material (Electrifi) and polylactic acid (PLA) to print the dielectric substrate, high-fidelity beam focusing can be achieved within the Fresnel region of the antenna.
Abstract: We demonstrate a 3D printed holographic metasurface antenna for beam-focusing applications at 10 GHz within the X-band frequency regime. The metasurface antenna is printed using a dual-material 3D printer leveraging a biodegradable conductive polymer material (Electrifi) to print the conductive parts and polylactic acid (PLA) to print the dielectric substrate. The entire metasurface antenna is 3D printed at once; no additional techniques, such as metal-plating and laser etching, are required. It is demonstrated that using the 3D printed conductive polymer metasurface, high-fidelity beam focusing can be achieved within the Fresnel region of the antenna. It is also shown that the material conductivity for 3D printing has a substantial effect on the radiation characteristics of the metasurface antenna.
TL;DR: A ray-tracing analysis of a smart motion detector based on a dynamically reconfigurable metasurface antenna based on an array of metamaterial radiators excited by a single-port waveguide or cavity is presented.
Abstract: We present a ray-tracing analysis of a smart motion detector based on a dynamically reconfigurable metasurface antenna (DMA). A DMA consists of an array of metamaterial radiators excited by a single-port waveguide or cavity. By incorporating simple switchable components into each element and addressing them individually, DMAs can generate a myriad of spatially distinct radiation patterns and alter them as a function of an applied voltage. These patterns have the potential to probe all regions of a room or set of rooms and detect motion, even when operating over an extremely narrow bandwidth. Through the acquisition of time-resolved measurements, the DMA sensor can retrieve temporal signatures and distinguish between different sources of movements. We investigate this sensing paradigm using a ray tracing simulation. We first replicate the trends obtained from recent experiments using our simulation platform to ensure that numerical ray tracing generates data that is a faithful representation of the real-life physics. We then demonstrate that temporal signals obtained in this manner carry information about the nature of the movement. Specifically, by using power spectra and filtering, we are able to extract features that correspond to specific motion patterns. These results constitute the first step toward incorporating DMAs into a smart sensor equipped with learning algorithms that can distinguish between human and non-human motion with high fidelity.
01 Mar 2019
TL;DR: It is shown that using the concept of computational frequency-diverse imaging and quasi-random measurement bases, high-fidelity images of objects can be retrieved without the need for any mechanical scanning apparatus and phase shifting circuits.
Abstract: In this paper, we review modern advances in microwave and millimeter-wave computational frequency-diverse imaging, and submillimeter-wave radar systems. We first present a frequency-diverse computational imaging system developed by Duke University for security-screening applications at K-band (17.5-26.5 GHz) frequencies. Following, we show a millimeter-wave spotlight imaging concept and its conceptual integration with the K-band system as interesting example of sensor fusion. We also demonstrate the application of computational frequency-diverse imaging for polarimetric imaging and phase retrieval problems. We show that using the concept of computational frequency-diverse imaging and quasi-random measurement bases, high-fidelity images of objects can be retrieved without the need for any mechanical scanning apparatus and phase shifting circuits. Increasing the frequency-band of operation, we also demonstrate a 340 GHz radar developed by the Jet Propulsion Laboratory and its application for standoff detection. We demonstrate a new technique to characterize the point-spread-function (PSF) of radars operating at submillimeter-wave frequencies.
Posted Content•
TL;DR: In this paper, the authors proposed a method to enable an optical amplification of coherent Raman spectroscopy signals by converting a spectral frequency shift imparted by an impulsive coherent-raman excitation to a change in a probe pulse transit time, which is detected through the phase of a radio frequency electronic signal measured at a harmonic of the probe pulse train.
Abstract: We introduce the first method to enable an optical amplification of a coherent Raman spectroscopy signal called radio frequency Doppler Raman spectroscopy. Doppler Raman measurements amplify the optical signals in coherent Raman spectroscopy by converting a spectral frequency shift imparted by an impulsive coherent Raman excitation to a change in a probe pulse transit time. This transit time perturbation is detected through the phase of a radio frequency electronic signal measured at a harmonic of the probe pulse train. By exploiting this new capability to scale the signal of a coherent Raman spectroscopic signal, we open the potential to detect very weak Raman spectroscopy signals that are currently not observable due to limits of illumination intensity imposed by laser damage to the specimen.
TL;DR: This work presents an edge detector able to detect obstacles at 15 different locations with an average efficiency of 97% and minimal crosstalk and calls this class of devices that can integrate a vast number of distinct optical functions with high efficiency symphotic.
Abstract: Autonomous navigation systems rely on the collection and processing of large datasets with advanced and memory-intensive algorithms. The requirements in terms of computing power and energy consumption can be significant. In this work, we propose a passive electromagnetic structure that can reduce the computational load by detecting edges (obstacles) in the far field. This is accomplished by probing the scene and processing its scattering on the physical layer, at the speed of light in the medium. By using a recently developed inverse design method, we present an edge detector able to detect obstacles at 15 different locations with an average efficiency of 97% and minimal crosstalk. We call this class of devices that can integrate a vast number of distinct optical functions with high efficiency symphotic.