Capacitive-type displacement and pressure sensitive transducer

Claim 1

An air-filled electro-acoustical transducer producing a voltage output proportionately responsive to displacement pressures of preselected acoustic wave frequencies, the transducer comprising: a plurality of elongate members of substantially equal length sandwiched in a loose contact one with the other whereby substantial transducer lengths can be extrudably formed, said transducer having a length greater than the wave length of a particular preselected frequency of interest, said plurality of sandwiched members including: an outer casing member providing an enclosure formed of elongate upper and lower flexible walls and end walls, said upper and lower walls having electrically-conductive inner surfaces and being displaceable responsively to said wave pressures acting only on their outer surfaces, a central electrically-conductive solid plate member disposed axially of said casing member flexible walls and having irregular upper and lower air-trapping surfaces and aperatures for permitting passage of said air transversely through said plate member, said plate member further having sufficient mass for remaining substantially stationary relative to said flexible wall displacements, and a sheet-like member formed of permanently-polarized dielectric material disposed co-extensively between said stationary plate-like member and each of said upper and lower flexible walls for establishing a voltage potential between said member and said walls, and voltage-output means coupled to the conductive surfaces of said plate member and said walls, said output means including a resistance member of sufficient value for assuring a voltage output proportional to the flexible wall displacements produced by said preselected frequency of interest.