Piezoelectric electro-acoustic transducer with non-uniform backing

Claim 2

In a piezoelectric electro-acoustic transducer comprising a diaphragm made of a flexible piezoelectric film material, a support means of a relatively stiff material supporting the edge of said diaphragm, a resilient backing member fitted to the diaphragm to impart at least one of a resiliency and tension to the diaphragm, and a base plate of a stiff material compressing the resilient backing member against said diaphragm, the improvement wherein the resilient backing member includes a locally protruded section for imparting to different parts of the flexible diaphragm different properties in respect of at least one of the resiliency and tension, said locally protruded section occupying less than the full width of said resilient backing member and locally increasing the thickness of said resilient backing member, such that said locally protruding section forms a local thickness discontinuity in said resilient backing member and a local change in the pressure of the resilient backing member against said diaphragm.

Claim 3

A piezoelectric electro-acoustic transducer as set forth in claim 1, wherein said resilient backing member includes a first slab-like portion extending the length and width of said resilient backing member but only part of the thickness thereof, said resilient backing member further including a second slab-like portion defining said locally protruded section and of lesser width and length than said first portion, said second slab-like portion being superimposed on said first slab-like portion between opposed portions of said support means, the maximum thickness of said resilient backing member being at least the total thickness of said superimposed first and second slab-like portions, the superimposed first and second slab-like portions defining a step in their uncompressed condition and tending to locally bulge, at said step, said diaphragm away from said base plate.

Claim 4

A piezoelectric electro-acoustic transducer as set forth in claim 2, wherein the locally protruded section is formed integrally with the resilient backing member.

Claim 5

A piezoelectric electro-acoustic transducer as set forth in claim 2, wherein the locally protruded section is formed separately from the remainder of the resilient backing member.

Claim 6

A piezoelectric electro-acoustic transducer as set forth in claim 2, in which said resilient backing member is of resilient polyurethane foam.

Claim 7

In a piezoelectric electro-acoustic transducer, the combination comprising: an edge support member of conductive material; a cover plate fixed to and extending inboard from said support member and having an opening therethrough well spaced inboard from said edge support member; a diaphragm made of a thin film of high molecular weight polymer material, said diaphragm film being flexible and having a piezoelectric characteristic, said film being covered on both sides with conductive layers serving as electrodes and being fixedly attached at its edge portions to said edge support member; a base plate of stiff material provided with openings, the peripheral edges of said base plate, diaphragm and edge support member forming a peripheral sandwich and including means therebetween for securing same together and for insulatingly spacing said diaphragm from said edge support and cover plate, such that said diaphragm extends along said cover plate in close spaced relation therefrom and across said opening in said cover plate; a resilient backing member of resilient film material disposed in a compressed state between said diaphragm and base plate, said resilient backing member in its said compressed state resiliently pressing the diaphragm toward the cover plate, said resilient backing member including a portion corresponding in size and location to said opening in said cover member and constituting a protruding section of said resilient backing member, said resilient backing member including a first slab-like portion extending the length and width of said resilient backing member but only a part of the thickness thereof, said resilient backing member further including a second slab-like portion defining said locally protruded section and of lesser width and length than said first portion, said second slab-like portion being superimposed on said first said slab-like portion between opposed portions of said edge support member, the thickness of said resilient backing member being at least the total thickness of said superimposed first and second slab-like portions, said first and second slab-like portions defining a step in an uncompressed condition and tending to locally bulge thereat said diaphragm away from said base plate and toward said opening in said cover plate.

Claim 8

In a piezoelectric electro-acoustic transducer, the combination comprising: an edge support member of conductive material; a cover plate fixed to and extending inboard from said support member and having an opening therethrough well spaced inboard from said edge support member; a diaphragm made of a thin film of high molecular weight polymer material, said diaphragm film being flexible and having a piezoelectric characteristic, said film being covered on both sides with conductive layers serving as electrodes and being fixedly attached at its edge portions to said edge support member; a base plate of stiff material provided with openings, the peripheral edges of said base plate, diaphragm and edge support member forming a peripheral sandwich and including means therebetween for securing same together and for insulatingly spacing said diaphragm from said edge support and cover plate, such that said diaphragm extends along said cover plate in close spaced relation therefrom and across said opening in said cover plate; a resilient backing member of resilient film material disposed in a compressed state between said diaphragm and base plate, said resilient backing member in its said compressed state resiliently pressing the diaphragm toward the cover plate, said resilient backing member including a portion corresponding in size and location to said opening in said cover member and constituting a protruding section of said resilient backing member, said resilient backing member including a first slab-like portion extending the length and width of said resilient backing member but only a part of the thickness thereof, said resilient backing member further including a second slab-like portion defining said locally protruded section and of lesser width and length than said first portion, said second slab-like portion being superimposed on said first said slab-like portion between opposed portions of said edge support member, the thickness of said resilient backing member being at least the total thickness of said superimposed first and second slab-like portions, said first and second slab-like portions defining a step in an uncompressed condition and tending to locally bulge thereat said diaphragm away from said base plate and toward said opening in said cover plate.

Claim 9

A piezoelectric electro-acoustic transducer as set forth in claim 6 including a thin perforate platelike member of stiff material carried by said cover plate over said opening in spaced protective relation with said protruding section of said diaphragm.