scholarly journals Programmable nonreciprocal meta-prism

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sajjad Taravati ◽  
George V. Eleftheriades
Keyword(s):  
Three Dimensional ◽  
Frequency Component ◽  
Phase Shifters ◽  
Frequency Dependent ◽  
Spatial Decomposition ◽  
Spatial Frequencies ◽  
Digitally Controlled ◽  
Field Programmable ◽  
Lorentz Reciprocity Theorem ◽  
Spatially Variant

AbstractOptical prisms are made of glass and map temporal frequencies into spatial frequencies by decomposing incident white light into its constituent colors and refract them into different directions. Conventional prisms suffer from their volumetric bulky and heavy structure and their material parameters are dictated by the Lorentz reciprocity theorem. Considering various applications of prisms in wave engineering and their growing applications in the invisible spectrum and antenna applications, there is a demand for compact apparatuses that are capable of providing prism functionality in a reconfigurable manner, with a nonreciprocal/reciprocal response. Here, we propose a nonreciprocal metasurface-based prism constituted of an array of phase- and amplitude-gradient frequency-dependent spatially variant radiating super-cells. In conventional optical prisms, nonreciprocal devices and metamaterials, the spatial decomposition and nonreciprocity functions are fixed and noneditable. Here, we present a programmable metasurface integrated with amplifiers to realize controllable nonreciprocal spatial decomposition, where each frequency component of the incident polychromatic wave can be transmitted under an arbitrary and programmable angle of transmission with a desired transmission gain. Such a polychromatic metasurface prism is constituted of frequency-dependent spatially variant transistor-based phase shifters and amplifiers for the spatial decomposition of the wave components. Interesting features include three-dimensional prism functionality with programmable angles of refraction, power amplification, and directive and diverse radiation beams. Furthermore, the metasurface prism can be digitally controlled via a field- programmable gate array (FPGA), making the metasurface a suitable solution for radars, holography applications, and wireless telecommunication systems.

scholarly journals Programmable Nonreciprocal Meta-Prism

2021 ◽  
Author(s):  
Sajjad Taravati ◽  
George V. Eleftheriadees
Keyword(s):  
Three Dimensional ◽  
Frequency Component ◽  
Phase Shifters ◽  
Frequency Dependent ◽  
Spatial Decomposition ◽  
Spatial Frequencies ◽  
Digitally Controlled ◽  
Field Programmable ◽  
Lorentz Reciprocity Theorem ◽  
Spatially Variant

Abstract Optical prisms are made of glass and map temporal frequencies into spatial frequencies by decomposing incident white light into its constituent colors and refract them into different directions. Conventional prisms suffer from their volumetric bulky and heavy structure and their material parameters are dictated by the Lorentz reciprocity theorem.. Considering various applications of prisms in wave engineering and their growing applications in the invisible spectrum and antenna applications, there is a demand for compact apparatuses that are capable of providing prism functionality in a reconfigurable manner, with a nonreciprocal/reciprocal response. Here, we propose a nonreciprocal metasurface-based prism constituted of an array of phase-and amplitude-gradient frequency-dependent spatially variant radiating super-cells. In conventional optical prisms, nonreciprocal devices and metamaterials, the spatial decomposition and nonreciprocity functions are fixed and noneditable. Here, we present a programmable metasurface integrated with amplifiers to realize controllable nonreciprocal spatial decomposition, where each frequency component of the incident polychromatic wave can be transmitted under an arbitrary and programmable angle of transmission with a desired transmission gain. Such a polychromatic metasurface prism is constituted of frequency-dependent spatially variant transistor-based phase shifters and amplifiers for the spatial decomposition of the wave components. Interesting features include three-dimensional prism functionality with programmable angles of refraction, power amplification, and directive and diverse radiation beams. Furthermore, the metasurface prism can be digitally controlled via a field-programmable gate array (FPGA), making the metasurface a suitable solution for radars, holography applications, and wireless telecommunication systems.

scholarly journals Pure and Linear Frequency Converter Temporal Metasurface

2021 ◽  
Author(s):  
Sajjad Taravati ◽  
George V. Eleftheriades
Keyword(s):  
Frequency Conversion ◽  
Frequency Converter ◽  
Temporal Frequency ◽  
Extraordinary Wave ◽  
Phase Shifters ◽  
Linear Frequency ◽  
Telecommunication Systems ◽  
Digitally Controlled ◽  
Field Programmable ◽  
Invisibility Cloaks

Abstract Metasurfaces are ultrathin structures which are constituted by an array of subwavelength scatterers with designable scattering responses. They have opened up unprecedented exciting opportunities for extraordinary wave engineering processes. On the other hand, frequency converters have drawn wide attention due to their vital applications in telecommunication systems, health care devices, radio astronomy, military radars and biological sensing systems. Here, we show that a spurious-free and linear frequency converter metasurface can be realized by leveraging unique properties of engineered transmissive temporal supercells. Such a metasurface is formed by time-modulated supercells; themselves are composed of temporal and static patch resonators and phase shifters. This represents the first frequency converter metasurface possessing large frequency conversion ratio with controllable frequency bands and transmission magnitude. In contrast to conventional nonlinear mixers, the proposed temporal frequency converter offers a linear response. In addition, by taking advantage of the proposed surface-interconnector-phaser-surface (SIPS) architecture, a spurious-free and linear frequency conversion is achievable, where all undesired mixing products are strongly suppressed. The proposed metasurface may be digitally controlled and programmed through a field programmable gate array. This makes the spurious-free and linear frequency converter metasurface a prominent solution for wireless and satellite telecommunication systems, as well as invisibility cloaks and radars. This study opens a way to realize more complicated and enhanced-efficiency spectrum-changing metasurface.

scholarly journals Intruder colour and light environment jointly determine how nesting male stickleback respond to simulated territorial intrusions

2016 ◽  
Vol 12 (8) ◽  
pp. 20160467 ◽  
Author(s):  
Daniel I. Bolnick ◽  
Kimberly Hendrix ◽  
Lyndon Alexander Jordan ◽  
Thor Veen ◽  
Chad D. Brock
Keyword(s):  
Frequency Dependence ◽  
Three Dimensional ◽  
Light Environment ◽  
Depth Gradient ◽  
Frequency Dependent ◽  
Frequency Dependent Selection ◽  
Negative Frequency Dependent Selection ◽  
Colour Signals

Variation in male nuptial colour signals might be maintained by negative frequency-dependent selection. This can occur if males are more aggressive towards rivals with locally common colour phenotypes. To test this hypothesis, we introduced red or melanic three-dimensional printed-model males into the territories of nesting male stickleback from two optically distinct lakes with different coloured residents. Red-throated models were attacked more in the population with red males, while melanic models were attacked more in the melanic male lake. Aggression against red versus melanic models also varied across a depth gradient within each lake, implying that the local light environment also modulated the strength of negative frequency dependence acting on male nuptial colour.

scholarly journals Oscillatory and steady streaming flow in the anterior chamber of the moving eye

2019 ◽  
Vol 863 ◽  
pp. 904-926 ◽  
Author(s):  
M. Dvoriashyna ◽  
R. Repetto ◽  
J. H. Tweedy
Keyword(s):  
Anterior Chamber ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Frequency Component ◽  
Dominant Frequency ◽  
Point Of View ◽  
Dimensional Structure ◽  
Steady Streaming ◽  
Constant Height ◽  
Angular Amplitude

We study the flow induced by eye rotations in the anterior chamber (AC) of the eye, the region between the cornea and the iris. We model the geometry of the AC as a thin domain sitting on the surface of a sphere, and study both the simpler case of a constant-height domain as well as a more realistic AC shape. We model eye rotations as harmonic in time with prescribed frequency $\unicode[STIX]{x1D714}_{f}$ and amplitude $\unicode[STIX]{x1D6FD}$, and use lubrication theory to simplify the governing equations. We write the equations in a reference frame moving with the domain and show that fluid motion is governed by three dimensionless parameters: the aspect ratio $\unicode[STIX]{x1D716}$ of the AC, the angular amplitude $\unicode[STIX]{x1D6FD}$ and the Womersley number $\unicode[STIX]{x1D6FC}$. We simplify the equations under the physiologically realistic assumptions that $\unicode[STIX]{x1D716}$ is small and $\unicode[STIX]{x1D6FC}$ large, leading to a linear system that can be decomposed into three harmonics: a dominant frequency component, with frequency $\unicode[STIX]{x1D714}_{f}$, and a steady streaming component and a third component with frequency $2\unicode[STIX]{x1D714}_{f}$. We solve the problem analytically for the constant-height domain and numerically as the solution of ordinary differential equations in the more realistic geometry. Both the primary flow and the steady streaming are shown to have a highly three-dimensional structure, which has not been highlighted in previous numerical works. We show that the steady streaming is particularly relevant from the clinical point of view, as it induces fluid mixing in the AC. Furthermore, the steady flow component is the dominant mixing mechanism during the night, when the thermal flow induced by temperature variations across the AC is suppressed.

scholarly journals Emulator of a Boost Converter for Educational Purposes

Electronics ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 1883
Author(s):  
Paula Lamo ◽  
Ángel de Castro ◽  
Christian Brañas ◽  
Francisco J. Azcondo
Keyword(s):  
Current Mode ◽  
Boost Converter ◽  
Project Based Learning ◽  
Electronic Systems ◽  
Hardware In The Loop ◽  
Pulse Width Modulator ◽  
Digital Pulse ◽  
Digitally Controlled ◽  
Field Programmable ◽  
A Current

Project-based learning (PBL) is proposed for the development of a Hardware-in-the-Loop (HIL) platform and the design of its digital controller for an undergraduate course on Digital Electronic Systems. The objective for students is the design of a digitally controlled HIL Boost converter, a digital pulse-width modulator (DPWM) and a current mode controller, implemented in field-programmable gate array (FPGA) devices. To this end, the different parts of the project are developed and evaluated, maximizing the use of FPGA resources in the design of the HIL and DPWM blocks, and applying design techniques that minimize the use of the digital resources used in the design of the controller. Students are equipped with a new individualized educational experience, allowing them to test their technical competence and knowledge in an environment close to the reality of the industry.

scholarly journals Smart filtering of phase residues in noisy wrapped holograms

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Behnam Tayebi ◽  
Farnaz Sharif ◽  
Jae-Ho Han
Keyword(s):  
Iterative Algorithm ◽  
Intensity Distribution ◽  
Three Dimensional ◽  
Phase Unwrapping ◽  
Spatial Frequencies ◽  
Phase Map ◽  
Filtering Technique ◽  
Automatic Filtering ◽  
Simple Phase

Abstract Phase unwrapping is one of the major challenges in multiple branches of science that extract three-dimensional information of objects from wrapped signals. In several applications, it is important to extract the unwrapped information with minimal signal resolution degradation. However, most of the denoising techniques for unwrapping are designed to operate on the entire phase map to remove a limited number of phase residues, and therefore they significantly degrade critical information contained in the image. In this paper, we present a novel, smart, and automatic filtering technique for locally minimizing the number of phase residues in noisy wrapped holograms, based on the phasor average filtering (PAF) of patches around each residue point. Both patch sizes and PAF filters are increased in an iterative algorithm to minimize the number of residues and locally restrict the artifacts caused by filtering to the pixels around the residue pixels. Then, the improved wrapped phase can be unwrapped using a simple phase unwrapping technique. The feasibility of our method is confirmed by filtering, unwrapping, and enhancing the quality of a noisy hologram of neurons; the intensity distribution of the spatial frequencies demonstrates a 40-fold improvement, with respect to previous techniques, in preserving the higher frequencies.

scholarly journals An Integrated Front-end Circuit Board for Air-Coupled CMUT Burst-Echo Imaging

Sensors ◽  
2020 ◽  
Vol 20 (21) ◽  
pp. 6128
Author(s):  
Lei Ye ◽  
Jian Li ◽  
Hui Zhang ◽  
Dongmei Liang ◽  
Zhuochen Wang
Keyword(s):  
Imaging System ◽  
Signal To Noise Ratio ◽  
Three Dimensional ◽  
Ultrasonic Transducers ◽  
Circuit Board ◽  
Capacitive Micromachined Ultrasonic Transducers ◽  
Front End ◽  
Field Programmable ◽  
Good Potential ◽  
Dc Bias

To conduct burst-echo imaging with air-coupled capacitive micromachined ultrasonic transducers (CMUTs) using the same elements in transmission and reception, this work proposes a dedicated and integrated front-end circuit board design to build an imaging system. To the best of the authors’ knowledge, this is the first air-coupled CMUT burst-echo imaging using the same elements in transmission and reception. The reported front-end circuit board, controlled by field programmable gate array (FPGA), consisted of four parts: an on-board pulser, a bias-tee, a T/R switch and an amplifier. Working with our 217 kHz 16-element air-coupled CMUT array under 100 V DC bias, the front-end circuit board and imaging system could achieve 22.94 dB signal-to-noise ratio (SNR) in burst-echo imaging in air, which could represent the surface morphology and the three-dimensional form factor of the target. In addition, the burst-echo imaging range of our air-coupled CMUT imaging system, which could work between 52 and 273 mm, was discussed. This work suggests good potential for ultrasound imaging and gesture recognition applications.

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