Vibro acoustic cover using expanded PTFE composite
An acoustically reactive composite can include an expanded polytetrafluoroethylene (ePTFE) membrane formed of a highly fibrillated ePTFE microstructure with an elastomer fully impregnated within the ePTFE membrane. The composite can have an acoustic loss of less than 7 dB at 1 kHz and a water entry pressure (WEP) of at least 20 PSI. A layered assembly for protecting an acoustic device can include an acoustically reactive composite as described above and an adhesive layer arranged to define an acoustic cavity. An acoustic device can incorporate an acoustically reactive composite or layered assembly as described above, with the acoustically reactive composite or layered assembly arranged to span an acoustic cavity proximate to a transducer of the acoustic device.
1. An acoustically reactive composite, comprising:
an expanded polytetrafluoroethylene (ePTFE) membrane comprising a highly fibrillated porous microstructure; and
an elastomer fully impregnated within the ePTFE membrane and substantially filling the porous microstructure to form the composite, wherein;
the composite has an acoustic loss of less than 7 dB at 1 kHz; and
the composite has a water entry pressure (WEP) of at least 20 PSI.
2. The acoustically reactive composite of claim 1 , wherein:
the ePTFE membrane comprises a microstructure of substantially only fibrils fused at crossover points.
3. The acoustically reactive composite of claim 1 , wherein:
the composite has a water entry pressure of at least 70 PSI.
4. The acoustically reactive composite of claim 1 , wherein:
the composite has an acoustic loss of less than 2 dB at 1 kHz.
5. The acoustically reactive composite of claim 1 , wherein:
the composite has a resonance peak greater than about 16 kHz.
6. The acoustically reactive composite of claim 1 , wherein:
the ePTFE membrane has a mass per area of between about 0.5 grams/m 2 and about 6.0 g/m 2 .
7. The acoustically reactive composite of claim 1 , wherein:
the composite is nonporous.
8. The acoustically reactive composite of claim 1 , wherein:
the elastomer comprises at least 20% of the composite by weight.
9. The acoustically reactive composite of claim 1 , wherein the ePTFE membrane is substantially free of nodes.
10. The acoustically reactive composite of claim 1 , wherein the ePTFE membrane has a thickness of less than about 5 microns.
11. The acoustically reactive composite of claim 1 , wherein the ePTFE membrane has a Matrix Tensile Strength of about 655 MPa in a longitudinal direction and about 310 MPa in a transverse direction.
12. The acoustically reactive composite of claim 1 , wherein the composite has a first side and a second side and further comprises a layer of elastomer on at least one of said first and second side.
13. The acoustically reactive composite of claim 12 , wherein the layer of elastomer is formed of the elastomer fully impregnated within the ePTFE membrane.
14. A layered assembly for protecting an acoustic device, the layered assembly comprising:
an expanded polytetrafluoroethylene (ePTFE) membrane comprising a highly fibrillated porous microstructure, the ePTFE membrane having a first side and a second side;
an elastomer fully impregnated within the ePTFE membrane and substantially filling the porous microstructure to form an acoustically reactive composite and
an adhesive layer connected with the acoustically reactive composite on the first side of the acoustic membrane and defining an acoustic cavity.
15. The layered assembly of claim 14 , wherein the adhesive layer is a first adhesive layer, and further comprising a second adhesive layer on the second side of the acoustic membrane, the second adhesive layer defining an acoustic channel aligned with the acoustic cavity, wherein the first adhesive layer is configured to connect the layered assembly with the acoustic device, and the second adhesive layer is configured to connect the layered assembly with a housing containing the acoustic device.
16. An acoustic device, comprising:
an acoustic device comprising a transducer;
an acoustic cavity proximate to the transducer; and
an acoustically reactive composite layer spanning the acoustic cavity between the transducer and an exterior environment, wherein:
the acoustically reactive composite layer comprises an expanded polytetrafluoroethylene (ePTFE) membrane comprising a highly fibrillated porous microstructure; and
an elastomer fully impregnated within the ePTFE membrane and substantially filling the porous microstructure to form the composite, wherein;
the composite layer has an acoustic loss of less than 7 dB at 1 kHz; and
the composite layer has a water entry pressure (WEP) of at least 20 PSI.
17. The acoustic device of claim 16 , wherein the composite layer has an acoustic resonance peak greater than about 16 kHz.
18. The acoustic device of claim 16 , wherein the composite layer has an acoustic loss of less than 2 dB at 1 kHz.
19. The acoustic device of claim 16 , further comprising an adhesive layer connecting the composite layer with the acoustic device.
20. The acoustic device of claim 19 , wherein the adhesive layer connecting the composite layer with the acoustic device is a first adhesive layer positioned on a first side of the composite layer, and further comprising:
a housing containing the acoustic device, the housing having an acoustic channel aligned with the acoustic cavity; and
a second adhesive layer connecting the composite layer with the housing.