High pressure low impedance electrostatic transducer

• US 5,450,498 A
• Filed: 07/14/1993
• Issued: 09/12/1995
• Est. Priority Date: 07/14/1993
• Status: Expired due to Fees

• Current Assignee: Sound Cheers Limited
• Original Assignee: University of British Columbia
• Inventors: Whitehead, Lorne A.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Le, Huyen D.
• Application Number:
  US08/091,009
• Time in Patent Office: 790 Days
• Field of Search: 381/191, 381/113, 381/116, 381/174, 381/168, 29/594
• US Class Current: 381/191
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: G01H 11/06 by electric means
• CPC Class Codes: H02N 1/006 of the gap-closing type H02N1/004 takes precedence

Abstract

An electrostatic transducer in which two sheets are separated by a gas-filled gap. The sheets have conductive surfaces for imposing electric fields within the gap when an electrical potential is applied across the sheets. A flexible positioning mechanism between the sheets maintains the gap at a desired time-averaged thickness. The gap is made up of a plurality of thick regions and a plurality of thin regions. Both regions have a total projected area which is a substantial portion of the total area of one of the sheets. The average thickness of the gap in the thick regions is at least ten times greater than the gap'"'"'s average thickness in the thin regions. The electrostatic field energy of the electric fields is concentrated in the thin regions.

Claims

1. An electrostatic transducer having an intended operating frequency range and comprising:

(a) first and second sheets separated by a gas-filled gap, each of said sheets having a conductive surface for imposing electric fields within said gap;

(b) flexible positioning means disposed between said sheets for maintaining a desired average thickness of said gap;

said gap comprising a plurality of thick regions and a plurality of thin regions, wherein;

(i) said thin regions have a total projected area comprising a substantial portion of one of said sheets'"'"' total area;

(ii) said thick regions have a total projected area also comprising a substantial portion of one of said sheets'"'"' total area;

(iii) said gap has an average thickness in said thick regions at least ten times greater than said gap'"'"'s average thickness in said thin regions; and

,

(iv) means for concentrating said electric fields'"'"' electrostatic field energy in said thin regions;

wherein;

(c) said gas has a gas pressure in said gap;

(d) said gap thickness in said thin regions is less than or equal to the Paschen minimum distance for said gas and said gas pressure;

(e) said sheets have;

(i) a component z_gap of net mechanical impedance per unit area due to pressure changes required to compress and rarefy said gas within said gap;

(ii) a component z_mass of net mechanical impedance per unit area due to said sheets'"'"' mass;

(f) said gap thickness in said thick regions is sufficiently large that said component z_gap has a magnitude of the same order as, or less than the magnitude of said component z_mass at frequencies within said transducer'"'"'s intended operting frequency range;

(g) each of said thin regions have a width less than the width at which gas glow into and out of said thin regions can substantially increase said transducer'"'"'s net mechanical impedance per unit area at frequencies within said transducer'"'"'s intended operating frequency range;

(h) said positioning means has a net mechanical impedance per unit area z_pos ; and

(i) z_pos has a magnitude of the same order as, or less than the magnitude of said component z_mass for frequencies within said transducer'"'"'s intended operating frequency range.

2. An electrostatic transducer as defined in claim 1, wherein said positioning means comprises an elastomeric material.

3. An electrostatic transducer as defined in claim 2, wherein:

(a) said gas has a gas pressure in said gap; and

,

(b) said transducer further comprises means for equalizing said gas pressure in said gap with a gas pressure external to said transducer, at frequencies substantially below said transducer'"'"'s intended operating frequency range.

4. An electrostatic transducer as defined in claim 3, wherein one of said sheets comprises an elastomeric material bearing a conductive coating, said coating having a thickness less than that which significantly impede flexibility of said coated sheet.

5. An electrostatic transducer as defined in claim 4, wherein said conductive surface on at least one of said sheets is coated with a thin ceramic for electrically isolating said surface from said gap.

6. An electrostatic transducer having an intended operating frequency range and comprising:

(a) first and second sheets separated by a gas-filled gap, each of said sheets having a conductive surface for imposing electric fields within said gap;

(b) flexible positioning means disposed between said sheets for maintaining a desired average thickness of said gap;

said gap comprising a plurality of thick regions and a plurality of thin regions, wherein;

(i) said thin regions have a total projected area comprising a substantial portion of one of said sheets'"'"' total area;

(ii) said thick regions have a total projected area also comprising a substantial portion of one of said sheets'"'"' total area;

(iii) said gap has an average thickness in said thick regions at least ten times greater than said gap'"'"'s average thickness in said thin regions; and

,

(iv) means for concentrating said electric fields'"'"' electrostatic field energy in said thin regions;

wherein;

(c) said gas has a gas pressure in said gap;

(d) said gap thickness in said thin regions is less than or equal to the Paschen minimum distance for said gas and said gas pressure;

(e) said positioning means has a net mechanical impedance per unit area z_pos ;

(f) said sheets have a component z_mass of net mechanical impedance per unit area due to said sheets'"'"' mass; and

,

(g) z_pos has a magnitude of the same order as, or less than the magnitude of said component z_mass for frequencies within said transducer'"'"'s intended operating frequency range.

7. An electrostatic transducer having an intended operating frequency range and comprising:

(a) first and second sheets separated by a gas-filled gap, each of said sheets having a conductive surface for imposing electric fields within said gap;

(b) flexible positioning means disposed between said sheets for maintaining a desired average thickness of said gap;

said gap comprising a plurality of thick regions and a plurality of thin regions, wherein;

(i) said thin regions have a total projected area comprising a substantial portion of one of said sheets'"'"' total area;

(ii) said thick regions have a total projected area also comprising a substantial portion of one of said sheets'"'"' total area;

(iii) said gap has an average thickness in said thick regions at least ten times greater than said gap'"'"'s average thickness in said thin regions;

(iv) means for concentrating said electric fields'"'"' electrostatic field energy in said thin regions;

wherein;

(c) said gas has a gas pressure in said gap;

(d) said gap thickness in said thin regions is less than or equal to the Paschen minimum distance for said gas and said gas pressure;

(e) each of said thin regions have a width less than the width at which gas flow into and out of said thin regions can substantially increase said transducer'"'"'s net mechanical impedance per unit area at frequencies within said transducer'"'"'s intended operating frequency range;

(f) said positioning means has a net mechanical impedance per unit area z_pos ;

(g) said sheets have a component z_mass of net mechanical impedance per unit area due to said sheets'"'"' mass; and

,

(h) z_pos has a magnitude of the same order as, or less than the magnitude of said component z_mass for frequencies within said transducer'"'"'s intended operating frequency range.

8. An electrostatic transducer having an intended operating frequency range and comprising:

(a) first and second sheets separated by a gas-filled gap, each of said sheets having a conductive surface for imposing electric fields within said gap;

(b) flexible positioning means disposed between said sheets for maintaining a desired average thickness of said gap;

said gap comprising a plurality of thick regions and a plurality of thin regions, wherein;

(i) said thin regions have a total projected area comprising a substantial portion of one of said sheets'"'"' total area;

(ii) said thick regions have a total projected area also comprising a substantial portion of one of said sheets'"'"' total area;

(iii) said gap has an average thickness in said thick regions at least ten times greater than said gap'"'"'s average thickness in said thin regions;

(iv) means for concentrating said electric fields'"'"' electrostatic field energy in said thin regions;

wherein;

(c) said gas has a gas pressure in said gap;

(d) said sheets have;

(i) a component z_gap of net mechanical impedance per unit area due to pressure changes required to compress and rarefy said gas within said gap;

(ii) a component z_mass of net mechanical impedance per unit area due to said sheets'"'"' mass;

(e) said gap thickness in said thick regions is sufficiently large that said component z_gap has a magnitude of the same order as, or less than the magnitude of said component z_mass at frequencies within said transducer'"'"'s intended operating frequency range;

(f) said positioning means has a net mechanical impedance per unit area z_pos ; and

(g) z_pos has a magnitude of the same order as, or less than the magnitude of said component z_mass for frequencies within said transducer'"'"'s intended operating frequency range.

9. An electrostatic transducer as defined in claim 8, wherein each of said thin regions have a width less than the width at which gas glow into and out of said thin regions can substantially increase said transducer'"'"'s net mechanical impedance per unit area at frequencies within said transducer'"'"'s intended operating frequency range.

10. An electrostatic transducer as defined in claim 8, wherein said gap thickness in said thin regions is less than or equal to about twice the Paschen minimum distance for said gas and said gas pressure.

11. An electrostatic transducer having an intended operating frequency range and comprising:

(a) first and second sheets separated by a gas-filled gap, each of said sheets having a conductive surface for imposing electric fields within said gap;

(b) flexible positioning means disposed between said sheets for maintaining a desired average thickness of said gap;

said gap comprising a plurality of thick regions and a plurality of thin regions, wherein;

(i) said thin regions have a total projected area comprising a substantial portion of one of said sheets'"'"' total area;

(ii) said thick regions have a total projected area also comprising a substantial portion of one of said sheets'"'"' total area;

(iii) said gap has an average thickness in said thick regions at least ten times greater than said gap'"'"'s average thickness in said thin regions;

(iv) means for concentrating said electric fields'"'"' electrostatic field energy in said thin regions;

wherein;

(c) said gas has a gas pressure in said gap;

(d) each of said thin regions have a width less than the width at which gas flow into and out of said thin regions can substantially increase said transducer'"'"'s net mechanical impedance per unit area at frequencies within said transducer'"'"'s intended operating frequency range;

(e) said positioning means has a net mechanical impedance per unit area z_pos ;

(f) said sheets have a component z_mass of net mechanical impedance per unit area due to said sheets'"'"' mass; and

,

(g) z_pos has a magnitude of the same order as, or less than the magnitude of said component z_mass for frequencies within said transducer'"'"'s intended operating frequency range.

12. An electrostatic transducer as defined in claim 11, wherein said gap thickness in said thin regions is less than or equal to about twice the Paschen minimum distance for said gas and said gas pressure.

13. An electrostatic transducer having an intended operating frequency range and comprising:

(a) first and second sheets separated by a gas-filled gap, each of said sheets having a conductive surface for imposing electric fields within said gap;

(b) flexible positioning means disposed between said sheets for maintaining a desired average thickness of said gap comprising a plurality of thick regions and a plurality of thin regions, wherein;

(i) said thin regions have a total protected area comprising a substantial portion of one of said sheets'"'"' total area;

(ii) said thick regions have a total protected area also comprising a substantial portion of one of said sheets'"'"' total area;

(iii) said gap has an average thickness in said thick regions at least ten times greater than said gap'"'"'s average thickness in said thin regions;

(iv) means for concentrating said electric fields'"'"' electrostatic field energy in said thin regions;

wherein;

(c) said gas has a gas pressure in said gap;

(d) said positioning means has a net mechanical impedance per unit area z_pos ;

(e) said sheets have a component z_mass of net mechanical impedance per unit area due to said sheets'"'"' mass; and

,

(f) z_pos has a magnitude of the same order as, or less than the magnitude of said component z_mass for frequencies within said transducer'"'"'s intended operating frequency range.

14. An electrostatic transducer as defined in claim 13, wherein said gap thickness in said thin regions is less than or equal to about twice the Paschen minimum distance for said gas and said gas pressure.

15. An electrostatic transducer having an intended operating frequency range and comprising:

(a) first and second sheets separated by a gas-filled gap, each of said sheets having a conductive surface for imposing electric fields within said gap;

(b) flexible positioning means disposed between said sheets for maintaining a desired average thickness of said gap;

said gap comprising a plurality of thick regions and a plurality of thin regions, wherein;

(i) said thin regions have a total projected area comprising a substantial portion of one of said sheets'"'"' total area;

(ii) said thick regions have a total projected area also comprising a substantial portion of one of said sheets'"'"' total area;

(iii) said gap has an average thickness in said thick regions at least ten times greater than said gap'"'"'s average thickness in said thin regions;

(iv) means for concentrating said electric fields'"'"' electrostatic field energy in said thin regions;

wherein;

(c) said gas has a gas pressure in said gap;

(d) said gap thickness in said thin regions is less than or equal to the Paschen minimum distance for said gas and said gas pressure;

(e) said sheets have;

(i) a component z_gap of net mechanical impedance per unit area due to pressure changes required to compress and rarefy said gas within said gap;

(ii) a component z_mass of net mechanical impedance per unit area due to said sheets'"'"' mass;

(f) said gap thickness in said thick regions is sufficiently large that said component z_gap has a magnitude of the same order as, or less than the magnitude of said component z_mass at frequencies within said transducer'"'"'s intended operating frequency range;

(g) said positioning means has a net mechanical impedance per unit area z_pos ; and

(h) z_pos has a magnitude of the same order as, or less than the magnitude of said component z_mass for frequencies within said transducer'"'"'s intended operating frequency range.

16. An electrostatic transducer having an intended operating frequency range and comprising:

(a) first and second sheets separated by a gas-filled gap, each of said sheets having a conductive surface for imposing electric fields within said gap;

(b) flexible positioning means disposed between said sheets for maintaining a desired average thickness of said gap;

said gap comprising a plurality of thick regions and a plurality of thin regions, wherein;

(i) said thin regions have a total projected area comprising a substantial portion of one of said sheets'"'"' total area;

(ii) said thick regions have a total projected area also comprising a substantial portion of one of said sheet'"'"' total area;

(iii) said gap has an average thickness in said thick regions at least ten times greater than said gap'"'"'s average thickness in said thin regions;

(iv) means for concentrating said electric fields'"'"' electrostatic field energy in said thin regions;

wherein;

(c) said gas has a gas pressure in said gap;

(d) said sheets have;

(i) a component z_gap of net mechanical impedance per unit area due to pressure changes required to compress and rarefy said gas within said gap;

(ii) a component z_mass of net mechanical impedance per unit area due to said sheets'"'"' mass;

(e) said gap thickness in said thick regions is sufficiently large that said component z_gap has a magnitude of the same order as, or less than the magnitude of said component z_mass at frequencies within said transducer'"'"'s intended operating frequency range;

(f) said positioning means has a net mechanical impedance per unit area z_pos ;

(g) z_pos has a magnitude of the same order as, or less than the magnitude of said component z_mass for frequencies within said transducer'"'"'s intended operating frequency range; and

,

(h) each of said thin regions have a width less than the width at which gas flow into and out of said thin regions can substantially increase said transducer'"'"'s net mechanical impedance per unit area at frequencies within said transducer'"'"'s intended operating frequency range.

17. An electrostatic transducer as defined in claim 16, wherein said gap thickness in said thin regions is less than or equal to about twice the Paschen minimum distance for said gas and said gas pressure.