scholarly journals Sound Localization through Multi-Scattering and Gradient-Based Optimization

Mathematics ◽  
2021 ◽  
Vol 9 (22) ◽  
pp. 2862
Author(s):  
Feruza Amirkulova ◽  
Samer Gerges ◽  
Andrew Norris
Keyword(s):  
Sound Localization ◽  
Focal Point ◽  
Incidence Angle ◽  
Analytic Form ◽  
Acoustic Lens ◽  
Gradient Based ◽  
Sound Amplification ◽  
Inverse Designs ◽  
Incident Waves ◽  
Localization Region

A gradient-based optimization (GBO) method is presented for acoustic lens design and sound localization. GBO uses a semi-analytical optimization combined with the principle of acoustic reciprocity. The idea differs from earlier inverse designs that use topology optimization tools and generic algorithms. We first derive a formula for the gradients of the pressure at the focal point with respect to positions of a set of cylindrical scatterers. The analytic form of the gradients enhances modeling capability when combined with optimization algorithms and parallel computing. The GBO algorithm maximizes the sound amplification at the focal point and enhances the sound localization by evaluating pressure derivatives with respect to the cylinder positions and then perturbatively optimizing the position of each cylinder in the lens while incorporating multiple scattering between the cylindrical scatterers. The results of the GBO of the uni- and multi-directional broadband acoustic lens designs are presented including several performance measures for the frequency dependence and the incidence angle. A multi-directional broadband acoustic lens is designed to localize the sound and to focus acoustic incident waves received from multiple directions onto a predetermined localization region or focal point. The method is illustrated for configurations of sound hard and sound soft cylinders as well as clusters of elastic thin shells in water.

scholarly journals Fluctuation of magnitude of wave loads for a long array of bottom-mounted cylinders

2019 ◽  
Vol 868 ◽  
pp. 244-285 ◽  
Author(s):  
Xiaohui Zeng ◽  
Fajun Yu ◽  
Min Shi ◽  
Qi Wang
Keyword(s):  
Incidence Angle ◽  
Local Maximum ◽  
Destructive Interference ◽  
Horizontal Distance ◽  
Wave Loads ◽  
Wave Load ◽  
Intrinsic Mechanism ◽  
Fluctuation Phenomenon ◽  
Analytical Formulae ◽  
Incident Waves

For wave loads on cylinders constituting a long but finite array in the presence of incident waves, variations in the magnitude of the load with the non-dimensional wavenumber exhibit interesting features. Towering spikes and nearby secondary peaks (troughs) associated with trapped modes have been studied extensively. Larger non-trapped regions other than these two are termed Region III in this study. Studies of Region III are rare. We find that fluctuations in Region III are regular; the horizontal distance between two adjacent local maximum/minimum points, termed fluctuation spacing, is constant and does not change with non-dimensional wavenumbers. Fluctuation spacing is related only to the total number of cylinders in the array, identification serial number of the cylinder concerned and wave incidence angle. Based on the interaction theory and constructive/destructive interference, we demonstrate that the fluctuation characteristics can be predicted using simple analytical formulae. The formulae for predicting fluctuation spacing and the abscissae of every peak and trough in Region III are proposed. We reveal the intrinsic mechanism of the fluctuation phenomenon. When the diffraction waves emitted from the cylinders at the ends of the array and the cylinder concerned interfere constructively/destructively, peaks/troughs are formed. The fluctuation phenomenon in Region III is related to solutions of inhomogeneous equations. By contrast, spikes and secondary peaks are associated with solutions of the eigenvalue problem. This study of Region III complements existing understanding of the characteristics of the magnitude of wave load. The engineering significances of the results are discussed as well.

The Gradient of Total Multiple Scattering Cross-Section and Its Application to Acoustic Cloaking

2020 ◽  
Vol 28 (04) ◽  
pp. 1950016
Author(s):  
Feruza A. Amirkulova ◽  
Andrew N. Norris
Keyword(s):  
Parallel Computing ◽  
Multiple Scattering ◽  
Cross Section ◽  
Optimization Algorithm ◽  
Analytic Form ◽  
Scattering Cross Section ◽  
Thin Shells ◽  
Scattering Cross ◽  
Total Scattering Cross Section ◽  
Gradient Based

We derive a formula for the gradients of the total scattering cross-section (TSCS) with respect to positions of a set of cylindrical scatterers. The analytic form enhances modeling capability when combined with optimization algorithms and parallel computing. As application of the method, we consider a gradient-based minimization of TSCS for a set of cylindrical obstacles by incrementally repositioning them so that they eventually act as an effective cloaking device. The gradient-based optimization algorithm reduces the TSCS by evaluating its derivative with respect to the cylinder positions and then perturbatively optimizing the position of each cylinder in the cloaking device while taking into account acoustic multiple scattering between the cylinders. The method is illustrated for clusters of hard cylinders and sets of elastic thin shells in water.

scholarly journals Security Paper Design with Frequency-Selective Structure for X-Band Electromagnetic Detection System

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Sang-Hwa Lee ◽  
Min-Sik Kim ◽  
Jong-Kyu Kim ◽  
Jong-In Lim ◽  
Ic-Pyo Hong
Keyword(s):  
Detection System ◽  
Incidence Angle ◽  
Multiple Antenna ◽  
Silver Ink ◽  
Electromagnetic Detection ◽  
X Band ◽  
Plain Paper ◽  
Specific Frequency ◽  
Frequency Selective ◽  
Incident Waves

This study designed and fabricated a frequency-selective structure-based security paper for the electromagnetic detection system of a security gate, which aims to prevent leakage of confidential documents. When a functional paper embedded with a frequency-selective pattern that selectively reflects a specific frequency is being leaked out of a security zone, the electromagnetic detection system receives and detects the intensity of the electromagnetic wave reflected from the security paper passing through an antenna gate, which transmits/receives RF signals. A stable detection performance of the security paper can be ensured by improving the incidence angle stability for incident waves and reducing the reflection loss. This study designed a frequency-selective structure with stable frequency reflection properties at the X-band by utilizing a Jerusalem cross structure. The proposed design was realized using the screen printing technique, which could implement a circuit, to print silver ink on a plain paper. To verify the applicability of the frequency-selective structure-based security paper, an RF detection system with a multiple antenna array was constructed and the intensity of the received signals was measured. The measurement was performed for various scenarios, and the result showed that the proposed security paper was well detected.

Broadband acoustic lens design using the principle of reciprocity and gradient-based optimization

2020 ◽  
Vol 148 (4) ◽  
pp. 2605-2605
Author(s):  
Feruza Amirkulova ◽  
Samer Gerges ◽  
Andrew N. Norris
Keyword(s):  
Lens Design ◽  
Acoustic Lens ◽  
Gradient Based

Migration/inversion for incident waves synthesized from common-shot data gathers

Geophysics ◽  
2007 ◽  
Vol 72 (6) ◽  
pp. W17-W31 ◽  
Author(s):  
Norman Bleistein
Keyword(s):  
Wave Equation ◽  
Incidence Angle ◽  
Plane Waves ◽  
Data Sets ◽  
Amplitude Wave ◽  
Data Set ◽  
Data Synthesis ◽  
Single Wave ◽  
Incident Waves ◽  
Domain Source

Wavefield synthesis is a process for producing reflection responses from more general sources or from prescribed incident waves by combining common-shot data gathers. Synthesis can provide surveywide data sets, similar in that regard to common-offset data gathers, but with the added advantage that each synthesized data set is a solution to a single wave equation. A common-offset data set does not have this last feature. Thus, synthesized data sets can be processed by true-amplitude wave-equation migration. The output is then known to be true amplitude in the same sense as is the output of Kirchhoff inversion. That is, the peak amplitude is proportional to the ray-theoretic reflection coefficient at a determinable specular incidence angle multiplied bythe area under the frequency-domain source signature and scaled by [Formula: see text]. Alternatively, the Kirchhoff inversion of synthesized data has a Beylkin determinant that is expressed in terms of the ray-theoretic Green’s function amplitude. This is in contrast to 3D common-offset inversion, wherein the Beylkin determinant is most difficult to compute. We present a theory of data synthesis and true-amplitude migration/inversion based on the application of Green’s theorem to the ensemble of common-shot gathers and prescribed more general sources or prescribed incident waves. Specific examples include delayed-shot line sources and incident dipping plane waves at the upper surface. We also discuss two cases in which waves are prescribed at depth, back-projected to the upper surface, and then used to generate a synthesized data set.

Design of Acoustic Metamaterials Using Gradient Based Optimization

2018 ◽  
Author(s):  
Feruza A. Amirkulova ◽  
Andrew N. Norris
Keyword(s):  
Large Scale ◽  
Optimization Problems ◽  
Optimization Algorithms ◽  
Analytic Form ◽  
Parallel Optimization ◽  
Acoustic Metamaterials ◽  
Function Calls ◽  
Gradient Based ◽  
Scale Optimization ◽  
Solution Accuracy

We derive formulas for the gradients of the total scattering cross section (TSCS) with respect to positions of a set of cylindrical scatterers. Providing the analytic form of gradients enhances modeling capability when combined with optimization algorithms and parallel computing. This results in reducing number of function calls and time needed to converge, and improving solution accuracy for large scale optimization problems especially at high frequencies and with a large number of scatterers. As application of the method we design acoustic metamaterial structure based on a gradient-based minimization of TSCS for a set of cylindrical obstacles by incrementally re-positioning them so that they eventually act as an effective cloaking device. The method is illustrated through examples for clusters of hard cylinders in water. Computations are performed on Matlab using parallel optimization algorithms and a multistart optimization solver, and supplying the gradient of TSCS.

Inverse Design Framework with Invertible Neural Networks for Passive Vibration Suppression in Phononic Structures

2021 ◽  
pp. 1-18
Author(s):  
Manaswin Oddiraju ◽  
Amir Behjat ◽  
Mostafa Nouh ◽  
Souma Chowdhury
Keyword(s):  
Neural Networks ◽  
Vibration Suppression ◽  
Inverse Design ◽  
Design Framework ◽  
Learning Approaches ◽  
The Novel ◽  
Forward Prediction ◽  
Higher Dimensional ◽  
Gradient Based ◽  
Inverse Designs

Abstract Automated inverse design methods are critical to the development of metamaterial systems that exhibit special user-demanded properties. While machine learning approaches represent an emerging paradigm in the design of metamaterial structures, the ability to retrieve inverse designs on-demand remains lacking. Such an ability can be useful in accelerating optimization-based inverse design processes. This paper develops an inverse design framework that provides this capability through the novel usage of invertible neural networks (INN). We exploit an INN architecture that can be trained to perform forward prediction over a set of high-fidelity samples, and automatically learns the reverse mapping with guaranteed invertibility. We apply this INN for modeling the frequency response of periodic and aperiodic phononic structures, with the performance demonstrated on vibration suppression of drill pipes. Training and testing samples are generated by employing a Transfer Matrix Method. The INN models provide competitive forward and inverse prediction performance compared to typical deep neural networks (DNN). These INN models are used to retrieve approximate inverse designs for a queried non-resonant frequency range; these inverse designs are then used to initialize a constrained gradient-based optimization process to find a more accurate inverse design that also minimizes mass. The INN initialized optimizations are found to be generally superior in terms of the queried property and mass compared to randomly-initialized and inverse DNN-initialized optimizations. Particle Swarm Optimization with INN-derived initial points is then found to provide even better solutions, especially for the higher-dimensional aperiodic structures.

scholarly journals Self-focusing effect in Au-target induced by high power pulsed laser at PALS

2008 ◽  
Vol 26 (3) ◽  
pp. 379-387 ◽  
Author(s):  
L. Torrisi ◽  
D. Margarone ◽  
L. Laska ◽  
J. Krasa ◽  
A. Velyhan ◽  
...  
Keyword(s):  
Focal Point ◽  
Incidence Angle ◽  
Pulsed Laser ◽  
Target Surface ◽  
Step Motor ◽  
Linear Processes ◽  
Ion Energy ◽  
Focusing Effect ◽  
Self Focusing ◽  
Plasma Measurements

AbstractSelf-focusing effects, induced by ASTERIX pulsed laser at PALS Laboratory of Prague, have been investigated. Laser was employed at the third harmonics (438 nm) and intensities of the order of 1016 W/cm2. Pure Au was used as thin target and irradiated with 30° incidence angle. An ion energy analyzer was employed to detect the energy-to-mass ratio of emitted ions from plasma. Measurements were performed by changing the focal point position with a high spatial resolution step-motor. Results demonstrated that non linear processes, due to self-focusing effects, occurs when the laser beam is focused at about 200 µm in front of the target surface. In such conditions, a new ion group, having high charge state and kinetic energy, is produced because of the increment in temperature of the laser-generated plasma.

Integrating perspectives: How the development of second-personal competence lays the foundation for a second-personal morality

2020 ◽  
Vol 43 ◽  
Author(s):  
John Corbit ◽  
Chris Moore
Keyword(s):  
Empirical Evidence ◽  
Developmental Process ◽  
Focal Point ◽  
Personal Information ◽  
Personal Competence ◽  
Triadic Interactions ◽  
Personal Morality ◽  
Integrative Process

Abstract The integration of first-, second-, and third-personal information within joint intentional collaboration provides the foundation for broad-based second-personal morality. We offer two additions to this framework: a description of the developmental process through which second-personal competence emerges from early triadic interactions, and empirical evidence that collaboration with a concrete goal may provide an essential focal point for this integrative process.

CBED Shadow Images and Cs:Aberration Measurement

1982 ◽  
Vol 40 ◽  
pp. 696-697
Author(s):  
R. W. Carpenter ◽  
I.Y.T. Chan ◽  
J. M. Cowley
Keyword(s):  
Focal Point ◽  
Spherical Aberration ◽  
Optic Axis ◽  
Wide Angle ◽  
Caustic Surface ◽  
Convergent Beam

Wide-angle convergent beam shadow images(CBSI) exhibit several characteristic distortions resulting from spherical aberration. The most prominent is a circle of infinite magnification resulting from rays having equal values of a forming a cross-over on the optic axis at some distance before reaching the paraxial focal point. This distortion is called the tangential circle of infinite magnification; it can be used to align and stigmate a STEM and to determine Cs for the probe forming lens. A second distortion, the radial circle of infinite magnification, results from a cross-over on the lens caustic surface of rays with differing values of ∝a, also before the paraxial focal point of the lens.

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