Microphone capable of cancelling mechanical generated noise

• US 4,127,749 A
• Filed: 03/31/1977
• Issued: 11/28/1978
• Est. Priority Date: 09/09/1976
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Yamamoto, Hiroshi, Atoji, Nobuhisa, Ibaraki, Satoru, Naono, Hiroyuki
• Primary Examiner(s): Stellar, George G.
• Application Number:
  US05/783,385
• Time in Patent Office: 607 Days
• Field of Search: 179/110 A, 179/121 D, 179/1 DM, 310/367, 310/800
• US Class Current: 381/170
• CPC Class Codes: H04R 17/025 using a piezoelectric polymer
• CPC Class Codes: H04R 31/00 Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor manufacture of microstructural arrangements of deformable or non-deformable structures in general B81C1/00182
• CPC Class Codes: H04R 7/16 Mounting or tensioning of diaphragms or cones
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF

Abstract

A microphone comprises a pair of electroacoustic transducing high polymer piezoelectric semi cylindrical shaped membranes having a single axis of elongation tangent to the curvature mounted in a housing facing each other. The membranes are electrically series connected to each other with a connection between the facing surfaces thereof and are of prescribed polarizations to generate an output which is substantially twice the voltage developed individually from each membrane when said membranes are caused to flex in opposite directions and substantially zero when said membranes are caused to flex in the same direction.

Claims

1. A noise-cancelling electroacoustic transducer comprising:

a pair of first and second high-polymer piezoelectric membranes each having electrically conductive, oppositely polarized surfaces and a single axis of elongation parallel to said surfaces; and

an electrically conductive support structure having an opening therethrough including opposed first side portions and opposed second side portions, each of the first side portions including opposed first and second curved perimetrical edges in the direction of the axis of said opening and each of said second side portions including straight perimentrical first and second parallel edges, said first and second membranes being held respectively in a part-cylindrical shape in spaced relation by the curvature of said first and second perimentrical edges of said first side portions and the straight perimetrical edges of said second side portions which the circumference of the part-cylindrical shape being parallel to said axis of elongation, the direction of curvature of said first and second perimetrical edges of said first side portions and the direction of polarization of said membranes being such that output voltages produced from the outer faces of said membranes in response to an impulse reinforce each other when they are flexed in opposite directions and cancel out each other when they are flexed in a same direction.

2. An electroacoustic transducer comprising:

a housing having a pair of opposed first and second apertures;

a spectacles-like structure having first and second conductive frames capable of taking the shape of an arch in said housing adjacent to said first and second apertures, respectively;

first and second high-polymer piezoelectric membranes each of which has been prepared by elongation in one direction and polarized in the direction of its thickness and coated with a conductive film on its opposite surfaces, said first and second membranes being adhesively secured to said first and second frame structures, respectively, to take the shape of an arch in a same direction with the direction of polarization being opposite to each other; and

the direction of arches and polarization of said membranes being such that when both membranes are caused to flex in opposite directions there developes an output which is substantially twice the amplitude of the signal developed from each membranes, and there develops substantially no output when said membranes are caused to flex in the same direction.

3. An electroacoustic transducer as claimed in claim 2, wherein said first and second membranes are arched in opposite directions and polarized in the same direction.

4. An electroacoustic transducer as claimed in claim 3, wherein said electrical connecting means comprises an open-ended conductive casing and said first and second membranes being in contact with the end of said conductive casing.

5. A noise-cancelling electroacoustic transducer comprising:

a housing having an opening therethrough including opposed first side portions and opposed second side portions, each of the first side portions including opposed first and second curved perimetrical edges in the direction of the axis of said opening and each of said second side portions including straight parallel perimetrical edges;

a pair of first and second high-polymer piezoelectric membranes each having electrically conductive, oppositely polarized surfaces and a single axis of elongation parallel to said surfaces, said first and second membranes being respectively held in a part-cylindrical shape in spaced relation by the curvature of said first and second perimetrical edges of said first side portions and the straight edges of said second side portions with the circumference of the part-cylindrical shape being parallel to said axis of elongation; and

means for electrically interconnecting the inner faces of said membranes so that electrical signals may be produced in response to an impulse from the outer faces of said membranes, the direction of curvature of said first and second perimetrical edges of said first side portions and the direction of polarization of said membranes being such that said electrical signals reinforce each other when they are flexed in opposite directions and cancel out each other when they are flexed in a same direction.

6. The electroacoustic transducer as claimed in claim 5, further comprising an acoustic absorber disposed in said housing.