Selective remote excitation of complex structures using time reversal in audible frequency range

2019 ◽  
Vol 146 (4) ◽  
pp. 2510-2521
Author(s):  
Maxime Farin ◽  
Claire Prada ◽  
Julien de Rosny
Keyword(s):  
Time Reversal ◽  
Complex Structures ◽  
Frequency Range ◽  
Audible Frequency

Simulation of Fabry-Perot Resonance for 3D Printable Complex Holey Acoustic Metamaterials

2020 ◽  
Author(s):  
Sanjay Ravichandran ◽  
Xin Wu ◽  
Yutai Su ◽  
Jing Shi
Keyword(s):  
Resonance Condition ◽  
Simulation Method ◽  
Complex Structures ◽  
Sound Waves ◽  
Acoustic Metamaterials ◽  
Frequency Range ◽  
Acoustic Metamaterial ◽  
Fabry Perot ◽  
Audible Frequency ◽  
Sub Wavelength

Abstract An acoustic metamaterial is a kind of material that is artificially designed in such a way that it can manipulate, control and direct sound waves. To date, various designs for acoustic metamaterials in the imaging applications have been proposed. However, these designs are generally simple due to the restriction from conventional manufacturing methods. By taking advantage of the additive manufacturing (AM) techniques, many complex acoustic metamaterials could be realized. However, the research on the complex structures for imaging applications has been very limited. In this paper, various 3D printable holey structured metamaterials with only one aperture are proposed, and the application possibility for sub-wavelength acoustic imaging in the audible frequency range is investigated. By using numerical simulation method, the effect of transmission properties of incident evanescent waves is analyzed to see whether these waves can completely transmit through the metamaterial. The phenomenon of Fabry-Perot resonances (FPR) that occur inside the hole for five different aperture shapes which are air-filled is studied, and the possibility of operating in a broadband resonance condition for the five designs are analyzed. These results can also be used to obtain valuable information for realizing a broadband acoustic hyperlens, which is an emerging application of 3D printable acoustic metamaterials.

SIMP for Complex Structures

2016 ◽  
Vol 846 ◽  
pp. 535-540
Author(s):  
David J. Munk ◽  
David W. Boyd ◽  
Gareth A. Vio
Keyword(s):  
Natural Frequencies ◽  
Dynamic Loads ◽  
Topology Optimisation ◽  
Complex Structures ◽  
Structural Failure ◽  
Frequency Range ◽  
Aerodynamic Loading ◽  
Frequency Excitation ◽  
Wing Structure ◽  
Lifting Surfaces

Designing structures with frequency constraints is an important task in aerospace engineering. Aerodynamic loading, gust loading, and engine vibrations all impart dynamic loads upon an airframe. To avoid structural resonance and excessive vibration, the natural frequencies of the structure must be shifted away from the frequency range of any dynamic loads. Care must also be taken to ensure that the modal frequencies of a structure do not coalesce, which can lead to dramatic structural failure. So far in industry, no aircraft lifting surfaces are designed from the ground up with frequency optimisation as the primary goal. This paper will explore computational methods for achieving this task.This paper will present a topology optimisation algorithm employing the Solid Isotropic Microstructure with Penalisation (SIMP) method for the design of an optimal aircraft wing structure for rejection of frequency excitation.

Reduction of Vibrations in Complex Structures With Viscoelastic Neutralizers: A Generalized Approach

1995 ◽  
Author(s):  
J. J. de Espíndola ◽  
C. A. Bavastri
Keyword(s):  
General Procedure ◽  
Linear Optimization ◽  
Sound Radiation ◽  
Complex Structures ◽  
Frequency Range ◽  
Optimization Scheme ◽  
Modal Theory ◽  
Equivalent Quantity ◽  
Invariant Structures ◽  
Time Invariant

Abstract A general procedure for the optimization of the parameters of dynamic neutralizes is presented. It can be applied to the minimization of the vibration response and sound radiation of linear strutures subjected to excitations in a specified frequency range. Modal theory and generalized equivalent quantity concept for the neutralizers, introduced by Espíndola and Silva (1992), are applied to a non-linear optimization scheme. The proposed procedure can be applied to relaxed and time invariant structures. It is not dependent on the struture complexity and the degree of discretization adopted. In such conditions, a significant reduction in computing work is achieved, if compared with the more traditional methods.

Reduction of Vibrations in Complex Structures With Viscoelastic Neutralizers: A Generalized Approach and a Physical Realization

1997 ◽  
Author(s):  
J. J. de Espíndola ◽  
C. A. Bavastri
Keyword(s):  
General Procedure ◽  
Linear Optimization ◽  
Complex Structures ◽  
Frequency Range ◽  
Optimization Scheme ◽  
Modal Theory ◽  
Equivalent Quantity ◽  
Invariant Structures ◽  
Structure Complexity ◽  
Time Invariant

Abstract A general procedure for the optimization of the parameters of dynamic neutralizers is reviewed. It can be applied to the minimization of the vibration response and sound radiation of linear structures subjected to excitations in a specified frequency range. Modal theory and generalized equivalent quantity concept for the neutralizers, introduced by Espíndola and Silva (1992), as applied to a non-linear optimization scheme, are also reviewed for clarity. That proposed procedure can be applied to relaxed and time invariant structures. It is not dependent on the structure complexity and the degree of discretization adopted. In such conditions, a significant reduction in computing work is achieved, if compared with the more traditional methods. Experimental results are compared with numerical ones.

scholarly journals Student Sensor Lab at Home: Safe Repurposing of Your Gadgets

2020 ◽  
Vol 2 (1) ◽  
pp. 7
Author(s):  
Alexander N. Kalashnikov ◽  
Ali Elyounsi ◽  
Alan Holloway
Keyword(s):  
Learning Experience ◽  
Electronic Devices ◽  
Frequency Range ◽  
High Quality ◽  
Potential Harm ◽  
Electronic Circuitry ◽  
Conventional Teaching ◽  
Audible Frequency ◽  
Periodic Safety ◽  
At Home

The COVID-19 pandemic imposed various restrictions on the accessibility of conventional teaching laboratories. Enabling learning and experimenting at home became necessary to support the practical element of students’ learning. Unfortunately, it is not viable to provide or share a fully featured sensor lab to every student because of the prohibitive costs involved. Therefore, repurposing electronic devices that are common to students can bring about the sought-after practical learning experience without the hefty price tag. In distinction to the conventional lab instruments, however, consumer-grade devices are not designed for use with external sensors and/or electronic circuitry. They are not professionally maintained, do not undergo periodic safety tests, and are not calibrated. Nevertheless, nearly all modern computers, laptops, tablets or smartphones are equipped with high-quality audio inputs and outputs that can generate and record signals in the audible frequency range (20 Hz–20 kHz). Despite cutting off the direct currents completely, this range might be sufficient for working with a variety of sensors. In this presentation we look at the possibilities of making sure that such repurposing by design prevents any potential harm to the learner and to her or his personal equipment. These features seem essential for unsupervised lone experimenting and avoiding damage to expensive devices.

A New Analyzer for the Audible Frequency Range

1933 ◽  
Vol 5 (1) ◽  
pp. 62-62 ◽  
Author(s):  
H. H. Hall ◽  
D. G. Clifford
Keyword(s):  
Frequency Range ◽  
Audible Frequency
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