Magnetically permeable electrostatic shield

• US 5,360,941 A
• Filed: 10/28/1991
• Issued: 11/01/1994
• Est. Priority Date: 10/28/1991
• Status: Expired due to Fees

• Current Assignee: Cubic Automatic Revenue Collection Group (Cubic Corporation)
• Original Assignee: Cubic Automatic Revenue Collection Group (Cubic Corporation)
• Inventors: Roes, John B.
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): LEDYNH, BOT L
• Application Number:
  US07/784,457
• Time in Patent Office: 1,100 Days
• Field of Search: 174/35 R, 174/35 MS, 361/424, 219/10.55 R, 219/10.55 D, 428/35.8, 428/621
• US Class Current: 174/378
• CPC Class Codes: G06K 19/07327 Passive means, e.g. Faraday cages Faraday-type protection of electric circuits in general H05K9/00
• CPC Class Codes: H05F 1/02 by surface treatment
• CPC Class Codes: H05F 3/00 Carrying-off electrostatic charges from shoes A43B7/36; from living beings A61N1/14; from tyres B60C19/08; from vehicles B60R16/06; from aircraft B64D45/02; from large containers B65D90/46
• CPC Class Codes: H05K 9/0079 Electrostatic discharge protection, e.g. ESD treated surface for rapid dissipation of charges
• CPC Class Codes: Y10T 428/12535 with additional, spatially distinct nonmetal component

Abstract

A permeable electrostatic shielding method and apparatus is disclosed that is suitable for use in shielding portable electronic devices such as calculators, smart cards and radios. Such electronic devices require protection from the electrostatic discharge occurring when a user accumulates an electrostatic charge and contacts a conducting surface of the electronic device. The resulting electrostatic discharge creates capacitively-coupled voltage transients in the digital circuits within the electronic device. The present invention prevents local charge accumulation on the surfaces of such electronic devices, which transmit and receive electromagnetic radio waves, without blocking the electromagnetic radiation essential to device function. One embodiment of this permeable electrostatic shield is formed by depositing a conductive layer of controlled thickness comprising a plurality of closely-spaced conductors that are electrically connected at one end to form a practical electrostatic shield permeable to RF electromagnetic radiation above 15 MHz.

Claims

1. A magnetically permeable, electrostatically shielded device, comprising:

an electronic device;

a pouch-like container enclosing said electronic device;

the container comprising a non-conductive supporting surface of flexible material having a conductive shielding layer, said layer consisting essentially of at least one plurality of parallel conductive strips, each said strip having a first and a second end, with said first ends conductively joined to a conductive termination; and

said supporting surface being folded over upon itself and joined at the edges to form a pouch-like container.

2. The shielded device described in claim 1 wherein said supporting surface comprises at least one material selected from a group consisting essentially of aromatic polyamide, polyester, and polyethylene.

3. The shielded device described in claim 1 wherein said shielding layer comprises at least one material selected from a group consisting essentially of copper, silver, zinc, aluminum and gold.

4. The shielded device described in claim 1 wherein said conductive termination is conductively connected to a local ground potential.

5. The shielded device described in claim 1 wherein the spacing between said parallel conductive strips is uniform.

6. A magnetically permeable, electrostatically shielded device comprising an electronic device, an outer housing enclosing said device, said housing comprising a plurality of supporting walls joined together to form a box-like enclosure, each said wall having a non-conductive supporting surface and a conductive shielding layer consisting essentially of at least one plurality of parallel conductive strips, each said strip having a first and a second end, with said first end conductively joined to a conductive termination.

7. The shielded device described in claim 6 wherein each said conductive termination is conductively connected to a local ground potential.

8. The shielded device described in claim 6 wherein the spacing between said parallel conductive strips is uniform.

9. An electrostatically shielded device, permeable to electromagnetic radiation at a selected frequency, comprising:

an electronic device;

an outer container enclosing said electronic device;

the outer container comprising a single non-conductive supporting surface having a conductive shielding layer, said shielding layer consisting essentially of a continuous surface of conductive material, said conductive material having an electromagnetic skin penetration depth at said selected frequency, and said shielding layer having a thickness of less than the electromagnetic skin penetration depth for said material at said frequency;

the shielding layer comprising means for shielding against electrostatic discharge while permitting transmission of electromagnetic radiation at said selected frequency.

10. The shielded device described in claim 9 wherein said supporting surface is flexible.

11. The shielded device described in claim 10 wherein said supporting surface comprises at least one material selected from a group consisting essentially of aromatic polyamide, polyester, and polyethylene.

12. The shielded device described in claim 9 wherein said conductive material comprises at least one material selected from a group consisting essentially of copper, silver, zinc, aluminum and gold.

13. The device as claimed in claim 9, wherein the shielding layer has a thickness of less than 20% of the skin penetration depth.

14. The device as claimed in claim 13, wherein the shielding layer has a thickness of 10% of the skin penetration depth.