Design of a Variable Thickness Plate to Focus Bending Waves

2012 ◽  
Author(s):  
Noah H. Schiller ◽  
Sz-Chin Steven Lin ◽  
Randolph H. Cabell ◽  
Tony Jun Huang
Keyword(s):  
Numerical Simulations ◽  
Thin Plate ◽  
Traveling Waves ◽  
Variable Thickness ◽  
Focal Point ◽  
Frequency Range ◽  
Additional Energy ◽  
Broad Frequency Range ◽  
Bending Waves ◽  
Energy Dissipated

This paper describes the design of a thin plate whose thickness is tailored in order to focus bending waves to a desired location on the plate. Focusing is achieved by smoothly varying the thickness of the plate to create a type of lens, which focuses structure-borne energy. Damping treatment can then be positioned at the focal point to efficiently dissipate energy with a minimum amount of treatment. Numerical simulations of both bounded and unbounded plates show that the design is effective over a broad frequency range, focusing traveling waves to the same region of the plate regardless of frequency. This paper also quantifies the additional energy dissipated by local damping treatment installed on a variable thickness plate relative to a uniform plate.

Incorporating Compressional and Shear Wave Types Into Fuzzy Structure Models for Plates

1995 ◽  
Author(s):  
Judith L. Rochat ◽  
Victor W. Sparrow
Keyword(s):  
Thin Plate ◽  
Shear Waves ◽  
Wave Theory ◽  
Structure Theory ◽  
Detailed Knowledge ◽  
Bending Waves ◽  
Incident Plane ◽  
Dependent Mass ◽  
Mass Spring ◽  
Bending Wave

Abstract Although realistic complex structures are usually difficult to model theoretically, fuzzy structure theory enables one to produce such a model without a detailed knowledge of the entire structure. Using the theory established by Pierce et al. [A. D. Pierce, V. W. Sparrow, and D. A. Russell, J. Vib. Acoust. (to be published), also ASME 93-WA/NCA-17.] regarding fundamental structural-acoustic idealizations for structures with imprecisely known or fuzzy internals, the effects that fuzzy attachments have on different wave types in a primary (or master) structure are examined in this paper. In the theory by Pierce et al., the primary structure that undergoes vibrations is a thin plate mounted in an infinite baffle. On one side of the plate are fuzzy attachments, represented as an array of attached mass-spring-dashpot systems, which are excited by an incident plane pulse. This known theory explains the effects of these attachments on bending waves in the plate. In this paper, the theory is extended to isolated compressional and shear waves in a plate. While studying this new problem, it is discovered that coupling effects occur when the plate and attachment properties are not uniform in the direction perpendicular to the wave propagation. Hence, unlike the bending wave theory which models a finite thin plate with point attached oscillators, the new wave type theory uses a thin plate infinite in one direction with line attached oscillators also infinite in the same direction. For both the compressional and shear waves, it is found that the fuzzy attachments add an apparent frequency dependent mass and damping to the plate. These results are similar to those for the bending wave theory.

Silicon Pillars as Resonators in an Acoustical Metamaterial

2014 ◽  
Author(s):  
Bernard Bonello ◽  
Rémi Marchal ◽  
Rayisa Moiseyenko ◽  
Yan Pennec ◽  
Bahram Djafari-Rouhani ◽  
...  
Keyword(s):  
Thin Plate ◽  
Lamb Waves ◽  
Mass Density ◽  
Resonant Mode ◽  
Ultrasonic Technique ◽  
Frequency Range ◽  
Negative Mass ◽  
Laser Ultrasonic ◽  
Compressional Mode ◽  
Bending Modes

We have investigated the propagation of Lamb waves in structures made of either an isolated resonant pillar or a set of pillars arranged in a line on a thin plate. The resonators as well as the plate are made of silicon. FEM computations show that two bending modes and one compressional mode are unambiguously identified in the frequency range of interest (0–10 MHz). We used a laser ultrasonic technique to map both the amplitude and the phase of the normal displacements on top of the pillars and at the surface of the sample. When the frequency is tuned to a resonant mode, either compressional or bending, the pillars vibrate 180° out-of-phase with respect to the Lamb waves, resulting in a negative modulus or negative mass density respectively.

Propagation of bending waves in a thin plate with an ensemble of randomly located holes of non-canonical form

2020 ◽  
Vol 18 (0) ◽  
Author(s):  
Ya. I. Kunets' ◽  
V. V. Matus ◽  
V. O. Mishchenko ◽  
V. V. Porokhovs'kyi
Keyword(s):  
Thin Plate ◽  
Canonical Form ◽  
Bending Waves

scholarly journals An Analysis of the Elements of an all Sky Survey

1985 ◽  
Vol 112 ◽  
pp. 405-410
Author(s):  
Edward T. Olsen ◽  
Anatoly Lokshin ◽  
Samuel Gulkis
Keyword(s):  
Observation Time ◽  
Frequency Resolution ◽  
Frequency Range ◽  
Broad Frequency Range ◽  
Sky Survey ◽  
Microwave Signals ◽  
Celestial Sphere

One component of the NASA search for microwave signals of extraterrestrial intelligent origin will be an all sky survey at a significantly low limiting flux over a broad frequency range. We are currently designing an overall strategy which will permit this survey to be: (1) carried out using existing antennas in less than 3 years of observation time, (2) uniform in sensitivity (within 0.5 db) over the celestial sphere for any given frequency, and (3) complete to 6×10−23 W/m2 or better over the frequency range 1.2GHz⩽ν⩽10GHz with a frequency resolution of 32 Hz.

scholarly journals Pre-selection of the candidate fields for deep imaging of the epoch of reionization with SKA1-low

2020 ◽  
Vol 499 (3) ◽  
pp. 3434-3444
Author(s):  
Qian Zheng ◽  
Xiang-Ping Wu ◽  
Quan Guo ◽  
Melanie Johnston-Hollitt ◽  
Huanyuan Shan ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Low Frequency ◽  
Far Field ◽  
Frequency Range ◽  
High Quality ◽  
Average Surface ◽  
Square Kilometre Array ◽  
Broad Frequency Range ◽  
Deep Imaging ◽  
Selection Of

ABSTRACT The Square Kilometre Array (SKA) will be the first low-frequency instrument with the capability to directly image the structures of the epoch of reionization (EoR). Indeed, deep imaging of the EoR over five targeted fields of 20 sq deg each has been selected as the highest priority science objective for SKA1. Aiming at preparing for this highly challenging observation, we perform an extensive pre-selection of the ‘quietest’ and ‘cleanest’ candidate fields in the southern sky to be suited for deep imaging of the EoR using existing catalogues and observations over a broad frequency range. The candidate fields should meet a number of strict criteria to avoid contaminations from foreground structures and sources. The candidate fields should also exhibit both the lowest average surface brightness and smallest variance to ensure uniformity and high-quality deep imaging over the fields. Our selection eventually yields a sample of 7 ‘ideal’ fields of 20 sq deg in the southern sky that could be targeted for deep imaging of the EoR. Finally, these selected fields are convolved with the synthesized beam of SKA1-low stations to ensure that the effect of sidelobes from the far-field bright sources is also weak.

Determination of dynamic properties of elastomers over broad frequency range

1983 ◽  
Vol 23 (2) ◽  
pp. 158-164 ◽  
Author(s):  
G. M. Smith ◽  
R. L. Bierman ◽  
S. J. Zitek
Keyword(s):  
Dynamic Properties ◽  
Frequency Range ◽  
Broad Frequency Range

Simulating Acoustic Engine Performance Over a Broad Frequency Range

2011 ◽  
Author(s):  
Koen Vansant ◽  
Rapha\agl Hallez ◽  
Hadrien B\aeriot ◽  
Michel Tournour ◽  
Gert Massa ◽  
...  
Keyword(s):  
Engine Performance ◽  
Frequency Range ◽  
Broad Frequency Range
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