US4249043A — Electret transducer backplate, electret transduce…

Claim 1

Independent Claim 138 words

An electret transducer including a backplate and an electret foil diaphragm mounted over a face of the backplate, wherein the backplate is moulded from a thermo-softening plastics material rendered electrically conducting by electrically conducting particles distributed therethrough, the backplate is provided with protruding portions accurately moulded on said face of the backplate and protruding a predetermined distance from said face and the diaphragm is in contact with the protruding portions and out of contact with the rest of the face of the backplate, the hardness of the material of the backplate is greater than 40 units as measured in the "Shore D" hardness test, and the flexural rigidities of the backplate and of the diaphragm are such that, in use, the deflection of the diaphragm is at least twenty times as great as the deflection of the backplate.

Claim 2

Dependent Claim 138 words

An electret transducer including a backplate and an electret foil diaphragm mounted over a face of the backplate, wherein the backplate is moulded from a thermo-softening plastics material rendered electrically conducting by electrically conducting particles distributed therethrough, the backplate is provided with protruding portions accurately moulded on said face of the backplate and protruding a predetermined distance from said face and the diaphragm is in contact with the protruding portions and out of contact with the rest of the face of the backplate, the hardness of the material of the backplate is greater than 40 units as measured in the "Shore D" hardness test, and the flexural rigidities of the backplate and of the diaphragm are such that, in use, the deflection of the diaphragm is at least twenty times as great as the deflection of the backplate.

Claim 3

Dependent Claim 16 words

A backplate as claimed in claim 1 in which the electrically conducting particles are carbon particles.

Claim 4

Dependent Claim 14 words

A backplate as claimed in claim 2 in which the plastics material is polypropylene.

Claim 5

Dependent Claim 17 words

A backplate as claimed in claim 1 in which a metal termination is moulded into the backplate.

Claim 6

Dependent Claim 25 words

A backplate as claimed in claim 1 in which the backplate is formed with an integral stem extending from the rear face of the backplate.

Claim 7

Dependent Claim 13 words

A backplate as claimed in claim 1 in which the backplate is cup-shaped.

Claim 8

Dependent Claim 24 words

An electret transducer as claimed in claim 1 wherein the protruding portions comprise a plurality of pimples distributed over said face of the backplate.

Claim 9

Dependent Claim 25 words

A transducer as claimed in claim 1 in which the diaphragm is mounted on the inner side of the backplate and the backplate is foraminous.

Claim 10

Dependent Claim 19 words

A transducer as claimed in claim 8 in which the casing of the transducer is formed by the backplate.

Claim 11

Dependent Claim 126 words

An electret transducer including a backplate and a diaphragm mounted over a face of the backplate, wherein the backplate is moulded from polypropylene rendered electrically conducting by carbon particles distributed therethrough, the backplate is provided with protruding portions accurately moulded on said face of the backplate and protruding a predetermined distance from said face and the diaphragm is in contact with the protruding portions and out of contact with the rest of the face of the backplate, a plurality of holes are provided in the backplate extending from said face through the backplate, the flexural rigidity of the backplate and of the diaphragm are such that, in use, the deflection of the diaphragm is at least twenty times as great as the deflection of the backplate.

Claim 12

Dependent Claim 126 words

An electret transducer including a backplate and a diaphragm mounted over a face of the backplate, wherein the backplate is moulded from polypropylene rendered electrically conducting by carbon particles distributed therethrough, the backplate is provided with protruding portions accurately moulded on said face of the backplate and protruding a predetermined distance from said face and the diaphragm is in contact with the protruding portions and out of contact with the rest of the face of the backplate, a plurality of holes are provided in the backplate extending from said face through the backplate, the flexural rigidity of the backplate and of the diaphragm are such that, in use, the deflection of the diaphragm is at least twenty times as great as the deflection of the backplate.

Claim 13

Independent Claim 132 words

A method of making an electret transducer including the steps of: moulding a backplate from a thermo-softening plastics material rendered electrically conducting by electrically conducting particles distributed therethrough, the backplate having protruding portions accurately moulded on a face of the backplate and protruding a predetermined distance from said face and having a hardness greater than 40 units as measured in the "Shore D" hardness test, and mounting an electret foil diaphragm over said face of the backplate with the diaphragm in contact with the protruding portions and out of contact with the rest of the face of the backplate, the flexural rigidities of the backplate and of the diaphragm being such that, in use, the deflection of the diaphragm is at least twenty times as great as the deflection of the backplate.

Claim 14

Independent Claim 132 words

A method of making an electret transducer including the steps of: moulding a backplate from a thermo-softening plastics material rendered electrically conducting by electrically conducting particles distributed therethrough, the backplate having protruding portions accurately moulded on a face of the backplate and protruding a predetermined distance from said face and having a hardness greater than 40 units as measured in the "Shore D" hardness test, and mounting an electret foil diaphragm over said face of the backplate with the diaphragm in contact with the protruding portions and out of contact with the rest of the face of the backplate, the flexural rigidities of the backplate and of the diaphragm being such that, in use, the deflection of the diaphragm is at least twenty times as great as the deflection of the backplate.

Claim 15

Dependent Claim 45 words

A method as claimed in claim 11 which the step of mounting the electret foil diaphragm on the backplate comprises the steps of heating an electret foil, subsequently bonding the electret foil to a retaining ring and securing together the retaining ring and the backplate.

Claim 16

Dependent Claim 56 words

A method as claimed in claim 12 in which the steps of heating the electret foil and bonding the foil to a retaining ring comprise the steps of heating a plate, placing the electret foil on the plate and bonding the retaining ring to the foil with an adhesive while the foil is on the plate.

Claim 17

Dependent Claim 25 words

A method as claimed in claim 12 in which the temperature to which the electret foil is heated is of the order of 45° C.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1984-02-03	1984-08-04	1985-02-03	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1988-02-03	1988-08-04	1989-02-03	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1992-02-03	1992-08-04	1993-02-03	$7700.00	Window Closed / Lapsed

Electret transducer backplate, electret transducer and method of making an electret transducer

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