Acoustic attenuation materials

Abstract

Acoustic attenuation materials are described that comprise outer layers of a stiff material sandwiching a relatively soft elastic material therebetween, with means such as spheres, discs or wire mesh being provided within the elastic material for generating local mechanical resonances that function to absorb sound energy at tunable wavelengths.

1 . An acoustic attenuation material comprising outer layers of a stiff material sandwiching a relatively soft elastic material therebetween, and wherein means are provided within said elastic material for generating local mechanical resonances.  
     
     
         2 . A material as claimed in  claim 1  wherein said resonance generating means comprises a rigid material located within said elastic material.  
     
     
         3 . A material as claimed in  claim 2  wherein said rigid material has a volume filling ratio within said elastic material of from about 5% to 11%.  
     
     
         4 . A material as claimed in  claim 2  wherein said resonance generating means comprise a plurality of individual solid particles located within said elastic material.  
     
     
         5 . A material as claimed in  claim 4  wherein said solid particles are spheres.  
     
     
         6 . A material as claimed in  claim 4  wherein said solid particles are discs.  
     
     
         7 . A material as claimed in  claim 2  wherein said rigid material comprises a wire mesh.  
     
     
         8 . A material as claimed in  claim 7  wherein said material is generally planar and said wire mesh lies in the plane of said material.  
     
     
         9 . A material as claimed in  claim 7  wherein means are provided for supporting said mesh.  
     
     
         10 . A material as claimed in  claim 9  wherein said material includes a surrounding frame member and means are provided for securing said mesh to said frame member.  
     
     
         11 . A material as claimed in  claim 10  wherein said securing means comprise elastic connection members.  
     
     
         12 . A material as claimed in  claim 2  wherein said rigid material comprises a plurality of wire mesh segments.  
     
     
         13 . A material as claimed in  claim 12  wherein a plurality of frame members are provided between said segments, and wherein means are provided for elastically connecting said segments to said frame members.  
     
     
         14 . A material as claimed in  claim 1  wherein said stiff outer layers are formed of gypsum, aluminum, cement, plywood, paperboard, polymer materials or any other stiff building materials.  
     
     
         15 . A material as claimed in  claim 1  wherein said elastic material is selected from foam or foam-like materials, natural and synthetic rubber and rubber-like materials, fiberglass, elastic polymer materials and the like.  
     
     
         16 . A material as claimed in  claim 2  wherein said rigid material is a metal.  
     
     
         17 . An acoustic attenuation material comprising two outer layers of a stiff material sandwiching a layer of relatively soft elastic material therebetween, and a plurality of solid particles disposed throughout said elastic material.  
     
     
         18 . A material as claimed in  claim 17  wherein said solid particles are spheres.  
     
     
         19 . A material as claimed in  claim 17  wherein said solid particles are discs.  
     
     
         20 . A material as claimed in  claim 17  wherein the dimensions and material of said particles, and the thickness and material of said elastic layer, are chosen so as to define a plurality of local mechanical resonances at a frequency to be attenuated.  
     
     
         21 . A material as claimed in  claim 20  wherein said frequency is in the range of 100 to 200 Hz.  
     
     
         22 . An acoustic attenuation material comprising two outer layers of a stiff material sandwiching a layer of relatively soft elastic material therebetween, and a wire mesh disposed throughout said elastic material.  
     
     
         23 . A material as claimed in  claim 22  wherein said wire mesh is parallel to said outer layers.  
     
     
         24 . A material as claimed in  claim 22  wherein the dimensions and material of the mesh, and the thickness and the material of the elastic layer, are chosen so as to define a plurality of local mechanical resonances at a frequency to be attenuated.  
     
     
         25 . A material as claimed in  claim 24  wherein said frequency is in the range 100 to 200 Hz.  
     
     
         26 . A method of forming an acoustic attenuation material comprising: 
 (c) providing two outer layers of a stiff material sandwiching a layer of an elastic material, and    (d) providing means within said elastic layer for generating local mechanical resonances at the frequency to be attenuated.    
     
     
         27 . A method as claimed in  claim 26  wherein said resonance generating means comprises a plurality of solid particles.  
     
     
         28 . A method as claimed in  claim 27  wherein the attenuation frequency is varied by selecting the dimensions, shape and material of the solid particles, and the thickness and material of the elastic layer.  
     
     
         29 . A method as claimed in  claim 26  wherein said resonance generating means comprises a wire mesh.  
     
     
         30 . A method as claimed in  claim 29  wherein the attenuation frequency is varied by selecting the dimensions, shape and material of the solid particles, and the thickness and material of the elastic layer.