GB2376804A

GB2376804A - Electromagnetic interference shield with waveguides

Info

Publication number: GB2376804A
Application number: GB0208173A
Authority: GB
Inventors: Dale R Kopf
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 2001-04-20
Filing date: 2002-04-09
Publication date: 2002-12-24
Also published as: GB0208173D0

Abstract

An electromagnetic interference shield for electronic equipment comprises waveguides in the form of aperture cells 42 moulded from conductive plastics. These are attached to a sheet, e.g. of metal, or they may be moulded integrally with a conductive plastics sheet.

Description

APERTURE CELL FOR ELECTROMAGNETIC INTERFERENCE SHIELDING FIELD OF THE INVENTION [0001] The invention relates generally to electromagnetic interference (EMI) shielding in electronic systems.

BACKGROUND OF THE INVENTION [0002] The operation of electronic circuitry used in many electronic devices is often accompanied by unwanted stray electromagnetic radiation. Stray electromagnetic radiation or"noise"can interfere with the performance of surrounding devices. Consequently, it is important to shield electronic devices to reduce electronic noise emanating from those devices.

Redundant arrays of inexpensive or independent storage devices (RAID) are being employed by the mass storage industry to provide variable capacity storage. RAID systems use interconnected disk drives to achieve the desired capacity of mass storage. With this approach, a disk drive of one capacity may be manufactured and packaged with the same or different capacity drives to provide the required storage capacity. RAID systems eliminate the need to manufacture disk drives individually designed to meet specific storage requirements. Each disk drive in a RAID system is usually housed in an individual module for handling and installation. The modules slide into and out of a larger enclosure that houses the array of disk drives and provides the sockets, plug-ins and other connections for the electrical interconnection of the drives. Controllers orchestrate the interconnection and control access to selected disk drives for data reading and writing operations.

Each module includes a plastic housing and, in most cases, some type of metal EMI shielding. Metal shielding is often constructed as metal plates, panels, partial enclosures and the like positioned within or about the housing.

The metal attenuates stray electronic signals emanating from the module as well as stray signals coming from surrounding modules. The degree of attenuation increases with the amount, placement and composition of metal shielding. A closed metal box, for example, would provide excellent shielding. The housing, however, must also permit sufficient air flow to cool the device during operation.

Hence, there must be adequate openings in the housing and the shielding to provide the necessary degree of cooling air flow.

] Air flow openings in EMI shields are typically round, square or hexagonal. As the frequencies of the electromagnetic radiation/noise increased, the size of the openings was decreased as much as possible while increasing the length of the openings to provide waveguides that attenuate as much of the electromagnetic radiation as possible while still allowing sufficient cooling air flow. These waveguides have been formed by stacking sheets of metal with concentric openings, machined or molded metal that is significantly thicker than sheet metal and drawn sheet metal tubes pressed into a sheet metal plate.

SUMMARY OF THE INVENTION [0006] In one embodiment, the invention is directed to a molded conductive plastic aperture cell for use in electromagnetic interference (EMI) shielding. In another embodiment, the invention is directed to an EMI shield that includes a conductive sheet and a plurality of molded waveguides electrically connected to and extending away from the sheet.

DESCRIPTION OF THE DRAWINGS [0007] Fig. 1 is a perspective view of an enclosure for a disk drive or other electronic circuitry in which the front and rear portions of the enclosure are constructed as an EMI shield.

[0008] Fig. 2 is a perspective view of the front of a housing for a group of individual device modules, such as the disk drive modules used in RAID data storage systems. The electronic device in one or more of the modules may be housed in an enclosure like the one illustrated in Fig. 1.

[0009] Fig. 3 is a perspective view of the rear of the housing of Fig. 2.

Fig. 4 is a close-up perspective view of the rear corner of the device module of Fig. 1 showing one embodiment of an EMI shield in which molded aperture cells are used to attenuate electromagnetic radiation while allowing air flow through the shield.

] Fig. 5 is a detailed perspective view of one of the aperture cells of Fig.

4.

[0012] Fig. 6 is a plan view of the aperture cell of Fig. 5.

] Fig. 7 is a section view of the aperture cell of Fig. 5 taken along the line 7-7 in Fig. 6.

] Fig. 8 is a perspective view of an alternative embodiment of the invention in which the cell/sheet assembly is molded or cast as an integral unit to form interchangeable shielding modules.

DETAILED DESCRIPTION OF THE INVENTION [0015] Fig. 1 illustrates an enclosure 10 for a disk drive or other electronic circuitry in which the front panel 12 is constructed as an EMI shield. A multiplicity of openings 14 are formed along front panel 12 and rear portions 13 of enclosure 10. As described in more detail below, openings 14 function as air flow passages for cooling and as waveguides for EMI shielding. Some type of ejector latch 15 is typically used on front panel 12 to facilitate the installation and removal of enclosure 10 in a group housing unit such as the one described below for Figs. 2 and 3.

A waveguide is a structure that transmits electromagnetic radiation above a certain "cut-off" frequency. If the electromagnetic radiation is below the cut-off frequency, then the waveguide rapidly attenuates the signals. If the electromagnetic radiation is above the cut-off frequency, then the signals pass readily through the waveguide. Waveguide as that term is used in this Specification and in the Claims refers broadly to any structure forming an opening that will attenuate electromagnetic radiation.

Figs. 2 and 3 illustrate one example of a data storage system 18 with which the invention can be used. Referring to Figs. 2 and 3, data storage system 18 includes a group of individual device modules 20 and 22, such as the disk drive modules used in a RAID data storage systems, housed in a housing 24. Fig. 2 shows the front of housing 24. Fig. 3 shows the rear of housing 24.

The electronic device in each module 20 and 22 is housed in an enclosure like

the one illustrated in Fig. 1 in which the front panel and rear portions are constructed as an EMI shield. System 18 may also include, for example, power supplies 26 and 28, battery back-up units 30 and 32, cooling fan modules 34 and 36 and input/output modules 38 and 40. Power supplies 26 and 28 provide the necessary electrical power for system 18. Battery back-up units 30 and 32 provide an alternative power source in the event of a failure of one or more of the power supplies 26 and 28. Fan modules 34 and 36 circulate air through housing 24 to cool the components. The input/output modules 38 and 40 enable the system components to communicate with external devices. The front panels and other parts of the enclosures for power supplies 26 and 28 and battery back-ups 30 and 32 might also be constructed as EMI shields using the structures of the present invention.

[0018] The details of one embodiment of the waveguide structure of the present invention will now be described with reference to Figs. 4-7. Fig. 4 is a close-up perspective view of the rear corner of the device module enclosure 10 of Fig. 1. Figs. 4-7 show one embodiment of an EMI shield in which molded aperture cells 42 provide the waveguide structure that defines openings 14 used to attenuate electromagnetic radiation while allowing air flow through the shield.

Fig. 5 is a detailed perspective view of one aperture cell 42 pressed into a conductive sheet 44. Fig. 6 is a plan view of the aperture cell of Fig. 5. Fig. 7 is a section view of aperture cell 42 taken along the line 7-7 in Fig. 6.

Referring to Figs. 4-7, a multiplicity of aperture cells 42 are pressed into or otherwise affixed to a conductive sheet 44. Each aperture cell 42 defines an air flow opening 14 and acts as a waveguide to attenuate electromagnetic radiation. In the embodiment shown in the Figures, aperture cells 42 are each molded from a conductive material and pressed into holes punched in conductive sheet 44. Although aperture cells 42 and sheet 44 may be formed from any suitable conductive material, it is expected that cells 42 will usually be molded plastic and sheet 44 will usually be a metal sheet. Aperture cells 42 may be pressed, welded, fastened, bonded or otherwise secured in sheet 44. Each aperture cell 42 is, preferably, electrically connected to sheet 44

to improve the overall ability of the assembly to attenuate electromagnetic radiation. A low impedance electrical connection between cells 42 and sheet 44 will help optimize attenuation and thereby improve the shielding effect of the cells/sheet assembly. If cells 42 are formed from a highly conductive material, then a tight press fit of the cells into sheet 44 should be sufficient to provide the necessary electrical connection. It may be desirable to metalize less conductive cell materials at the joint to help ensure a good electrical connection.

The particular geometry of openings 14 in cells 42 may be selected as necessary or desirable to help optimize performance for any particular application and need not be limited to the circles, rectangles or hexagons typical of conventional waveguides. Non-uniform shapes, particularly three dimensionally non-uniform sha pes, are expected to have the greatest attenuation effect and, therefore, are the presently preferred shapes. Molded cells 42 are also suitable

for use with more complex waveguide shapes like those described in patent I (, b C-ILOE I-7Lt., 3) application attorney docket no. 10002526 filed April 20, 2001 IL and titled Electromagnetic Interference Shield, which is incorporated herein by reference. The cell/sheet assembly might also be molded or cast as an integral unit to form interchangeable shielding modules 46 such as those illustrated in Fig. 8 or to form customized complete shielding enclosures.

While aperture cells 42 may be any conductive material suitable for EMI shielding, it is expected that plastic or some other type of moldable or castable material will be used to more easily manufacture the desired shapes.

The aperture cell waveguide of the present invention offers the shielding engineer added flexibility over known shielding structures. The aperture cell can be used to implement almost any three dimensional aperture/waveguide that might be desired. The invented molded aperture cell shielding may also provide a cost effective alternative to stacked sheet metal concentric aperture or tube type waveguides. Using drawn sheet metal tubes pressed into a metal sheet may be less expensive where only a single sheet is needed, but there is little flexibility in these structures when unique aperture geometries and structures are needed.

] The present invention has been shown and described with reference to the foregoing exemplary embodiments. Other embodiments are possible. It should be understood, therefore, that the invention is to be construed broadly within the scope of the following claims.

Claims

CLAIMS What is claimed is: 1 1. An electromagnetic interference shield, comprising a conductive sheet 2 and a plurality of molded waveguides electrically connected to and extending away 3 from the sheet.

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2. The shield of Claim 1, wherein each waveguide comprises a discrete 2 elongated aperture cell secured to the sheet.

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3. The shield of Claim 2, wherein each aperture cell comprises a molded 2 conductive plastic body having an opening therethrough.

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4. The shield of Claim 2, wherein each aperture cell is pressed into a hole in 2 the sheet.

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5. The shield of Claim 1, wherein each waveguide comprises a molded 2 conductive plastic waveguide.

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6. The shield of Claim 1, wherein the sheet and the waveguides are molded 2 together as an integral unit.

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7. An aperture cell for use in electromagnetic interference shielding, the cell 2 comprising an elongated body of molded conductive plastic having an opening 3 therethrough.

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8. The cell of Claim 7, wherein the opening is characterized by a non- 2 uniform three dimensional shape.

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9. An electromagnetic interference shield, comprising a metal sheet and a 2 plurality of discrete elongated molded conductive plastic aperture cells secured to the 3 sheet.

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10. An electromagnetic interference shielding module, comprising a sheet of 2 conductive plastic and an array of conductive plastic waveguides molded together as 3 an integral unit.

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11. An electromagnetic interference shielded electronic module, comprising: 2 an electronic device capable of generating electromagnetic radiation; and 3 a housing at least partially enclosing the electronic device, the housing having a 4 plurality of walls at least one of which comprises a conductive sheet and a plurality of 5 molded waveguides electrically connected to and extending away from the sheet 6 towards an exterior of the housing.

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12. The shield of Claim 11, wherein each waveguide comprises a discrete 2 elongated aperture cell secured to the sheet.

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13. The shield of Claim 12, wherein each aperture cell comprises a molded 2 conductive plastic body having an opening therethrough.