Acoustics – Sound-modifying means – Mechanical vibration attenuator
Patent
1998-04-01
2000-05-30
Dang, Khanh
Acoustics
Sound-modifying means
Mechanical vibration attenuator
181208, F16F 1500
Patent
active
060680814
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process to damp the amplitude of vibrations and the pressure wave radiated by a material which is exposed to mechanical and/or acoustic vibrations.
The present invention also relates to the material made by applying the process according to the invention.
When a wall is exposed to an incident pressure wave, or when it is vibrated by mechanical means, the incident pressure wave and/or the vibrations are transmitted through the structure of the material from the incident surface to its radiating surface.
The invention relates both to vibratory and acoustic waves as well as to the field of infrasonic and ultrasonic waves.
The aim of the invention is to reduce the amplitude of the waves transmitted by preventing a vibrating mechanical system from generating a vibro-acoustic wave in the surrounding environment, or by isolating a sound wave from another area, either to insulate a noisy piece of apparatus, or to protect a sensitive system from mechanical vibrations induced by the waves.
The damping obtained by means of the invention can reach some tens of decibels in the case of acoustic waves.
STATE OF THE ART
To reduce the acoustic energy transmitted by a wall, several known solutions are currently in use.
One known device consists in increasing the mass of the walls which separate the source of sound from the area to be protected.
This solution is efficient over a wide range of frequencies. Doubling the mass of the walls enables a gain of around 4 dB (decibels), but requires more space and greater mass. This solution is difficult to implement when a gain of several tens of decibels is required.
Another means to perform high acoustic insulation is to use multiple walls. For example, one double wall composed of a first wall, a volume of air or a resilient material and a second wall. Such a complex structure enables the acoustic insulation to be improved without over-increasing the mass, if the resilient material is of very low density. However, to use such a resilient complex structure requires substantial thickness.
It is also known to use a porous material to perform acoustic insulation. The energy contained in the incident acoustic wave is dissipated by increasing the apparent viscosity of the environment with respect to the air inside the material pores. This type of solution requires the pore size to be fully adapted to the main frequency components present in the noise spectrum, whose transmission or reflection are to be avoided. This solution also involves the use of relatively thick structures.
A foam-based material can be inserted between two rigid walls. The assembly acts as an isotropic structure whose technical properties are used merely to absorb part of the vibrations.
There is another solution to reduce the vibrations of structures which may cause acoustic radiation consisting in equipping the structures with viscoelastic walls able to damp the structures. This solution results in excess mass for a limited gain in performance.
SUBJECT OF THE INVENTION
A first subject of the invention consists in developing a process to enable substantial vibro-acoustic damping to be obtained by using a low density composite material.
A second subject of the invention consists in performing substantial acoustic insulation requiring relatively low excess mass.
A third subject of the invention consists in preventing the vibrating of a structure material.
To this end, the process according to the invention to damp the amplitude of vibrations radiated by the surface of a material exposed to vibrations, of mechanical and/or acoustic origin, uses a material made of an anisotropically-shaped heavy resilient structure having an inner geometry able to divert and localize the internal vibrations of the structure.
According to one characteristic of the invention, the modification of wave vibration direction is carried out from a direction substantially perpendicular to the incident surface to a substantially parallel direction parallel to or close to a parallel
REFERENCES:
patent: 3615961 (1971-10-01), Meyer
patent: 4828202 (1989-05-01), Jacobs et al.
patent: 5710396 (1998-01-01), Rogers
patent: 5895538 (1999-04-01), Hatayama et al.
Capdepuy Marc
Haddad Florent
Le Mehaute Alain
Artec Aerospace
Dang Khanh
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