JP2000236192A - Electromagnetic interference shield - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic interference(EMI) shield, capable of achieving desired EMI shield and characteristics of air flow. SOLUTION: An EMI shield, containing a metal plate 46 and array of metal wave guides 42 stretched from the metal plate 46, is provided. The wave guides 42 are generally constituted as circular or rectangular tubes, fixed to holes of the metal plate 46 and act as wave guides for EMI shield and paths of air flow. A shield can be manufactured by using individual plates and tubes, which are bonded or fixed to the plates or manufactured as an collectively formed component, where the tubes are extruded from the plate. Shields where the plates and the tubes are assembled can be stacked in the order upwardly (or arranged laterally), in response, as necessary, for achieving a desired EMI shield and the characteristics of air flow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates generally to electromagnetic interference (EMI) shielding in electronic systems, and more particularly to EMI shielding in disk drive arrays and similar data storage products.

[0002]

BACKGROUND OF THE INVENTION The operation of electronic circuits used in many electronic devices can be accompanied by unwanted stray electromagnetic radiation. Stray electromagnetic radiation or "noise" can interfere with the operation of surrounding equipment. As a result, it is important to shield electronic devices from electronic noise.

[0003] The mass storage industry uses redundant arrays of inexpensive or independent storage devices (RAID) to implement variable capacity storage. RAID systems use interconnected disk drives to achieve a desired mass storage capacity. With this approach, a disk drive of a certain capacity can be manufactured and combined with drives of the same or different capacities to achieve the required storage capacity. RAID systems eliminate the need to manufacture individually designed disk drives to meet special storage requirements. Each disk in RAID system
Drives are usually housed in separate modules for operation and installation. The module fits into and is removed from a larger housing that houses an array of disk drives and provides sockets or plug-in or other connections for electrical interconnection of the drives. For data read and write operations, a controller coordinates the interconnect to control access to the selected disk drive.

[0004] Each module includes a plastic housing and in most cases some type of metal E
Includes MI shield. Metal shields are often configured as metal plates, panels, partial enclosures, etc. positioned in or around the housing. The metal attenuates stray electronic signals exiting the module as well as stray signals entering around the module. The degree of attenuation increases with the amount and placement of the metal shield. For example, a closed metal box provides an excellent shield. However, the housing must also allow sufficient airflow to cool the device during operation. Therefore, there must be adequate openings in the housing and shield to provide the required degree of cooling airflow. Array storage products, such as the aforementioned RAID systems, include new "Fibre Channel" serial connectivity protocols and their high operating frequencies, so they design and create enclosures that provide adequate EMI shielding and cooling airflow. It becomes more difficult to do. One solution to the problem of providing an effective balance between EMI attenuation and low resistance to airflow is one of the solutions described in "An I I," which is incorporated herein by reference in its entirety.
No. 09 / 232,270 entitled "mproved EMI / RF Shielded Ventilation Device". Patent application Ser. No. 09 / 232,270 describes a relatively thick metal ventilation panel with a number of holes passing through the panel. This hole acts as a waveguide that attenuates electromagnetic radiation while allowing cooling air flow to provide EMI shielding. The panels can be made using a thixotropic injection molding process as described in patent application Ser. No. 09 / 232,270, or the panels can be die cast or machined from solid metal blocks. Or you can.
It has been found that due to the number and proximity of the holes, the production of such ventilation panels by die casting is difficult and thixotropic molding and machining can be expensive.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an EMI shield capable of achieving desired EMI shield and airflow characteristics.

[0006]

SUMMARY OF THE INVENTION The present invention provides an EMI comprising a metal plate and an array of metal waveguides extending from the metal plate.
Targets shields. The waveguide is generally configured as a circular or rectangular tube, fixed in a hole in a metal plate, and
It serves as an I-shield waveguide and airflow path. EM
The I-shield can be manufactured using a separate plate and a tube glued or secured to the plate, or as an integral part of the tube extruded from the plate. As needed to achieve the desired EMI shielding and airflow characteristics,
The combined plate and tube shields can be stacked on top of each other (or side by side). Such a new E
Incorporating MI shield design and manufacturing techniques into the manufacture of electronic device housings, modules, and other enclosures minimizes manufacturing costs by reducing raw materials, using conventional machinery, and reducing manufacturing and assembly time. It is expected to help.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
1 shows a housing 10 for an electronic circuit such as a disk drive configured as a shield. On the entire front panel 12,
A plurality of openings 14 are formed. As will be described in more detail below, the opening 14 serves as a passage for cooling airflow and as a waveguide for EMI shielding. The term waveguide, as used in this specification and in the claims, refers to any structure that constitutes a hole that attenuates electromagnetic radiation broadly. An air flow opening 16 is formed along the rear of the housing 10. As will be described later with reference to FIGS. 2 and 3, a front panel 12 is provided to facilitate attachment and detachment of the group of housing units to and from the housing 10.
Some type of ejector latch 15 is used above.

FIGS. 2 and 3 show one example of a data storage system 18 in which the present invention can be used. FIG.
Referring to and 3, data storage system 18 includes a group of individual device modules 20 and 22, such as disk drive modules used in a RAID data storage system housed in housing 24. FIG.
Indicates a front portion of the housing 24. FIG. 3 shows the rear part of the housing 24. The electronics within each module 20 and 22 are housed in a housing 10 similar to that shown in FIG. 1 where the front panel 12 is configured as an EMI shield. The system 18 also includes, for example, power supplies 26 and 28, battery backup units 30 and 3
2, including cooling fan modules 34 and 36, and input / output modules 38 and 40. Power supplies 26 and 2
8 provides the necessary power for the system 18. Battery backup units 30 and 32 are powered by power supply 26
And 28 provide an alternate power source in the event that one or more of the devices fail. Fan modules 34 and 36
Circulates air through the housing 24 to cool the components. Input / output modules 38 and 40 allow system components to communicate with external devices.
Further, the front panels 12 of the power supplies 26 and 28 and the battery backups 30 and 32 are configured as EMI shields.

FIG. 4 shows one embodiment of the front panel 12 that defines the opening 14 using a tubular waveguide insert 42. Referring to FIG. 4, holes 44 are formed in metal plate 46.
Is formed. The circular metal tube 42 is inserted into the hole 44 and held. FIG. 5 shows the pipe 42, the hole 44, and the plate 46. Hole 44 in the upper left portion of FIG. 5 was left empty to show details of these components. Next, FIG.
Referring to FIG. 7, the tube 42 is preferably flared along the outside of one end 48, and the holes 44 are chamfered on the front surface 50 to help properly position and retain the tube on the plate 46. Is done. The interior of the tube 42 at the end 48 creates a flat (rather than conical) inner diameter of the tube up to a small beveled transition region 49, as best shown in FIG. 6, to provide a more uniform opening. be able to. Tube 42
Any suitable technique may be used to weld, tighten, glue, or secure in the bore 44.

In an alternative embodiment of the front panel 12,
The tubular waveguide 52 is extruded or formed directly from the metal plate 46 as shown in FIGS.

In the third embodiment of the present invention shown in FIG. 10, the aforementioned plate / tube assembly, designated by reference numeral 54 in FIG. 10, is used to achieve the desired waveguide and airflow characteristics. Stacked on top of or beside each other as needed. This embodiment may be particularly useful with the tube design shown in FIGS. 8 and 9, where the length of the tube 52 is limited by the thickness and ductility of the plate 46.

In the fourth embodiment of the invention shown in FIG. 11, a square tube 56 is used.

The size and shape of the tubes 42, 52 and 56 will depend on the EMI shielding and airflow requirements of the particular device, module and system in which the panel will be used. The shielding effectiveness of panel 12 is determined by the design principles of the waveguide. Waveguides are structures that carry electromagnetic radiation above a certain "cut-off" frequency. If the electromagnetic radiation is below the cutoff frequency, the waveguide will
Attenuates the signal rapidly. If the electromagnetic radiation is higher than the cutoff frequency, the signal will easily pass through the waveguide.

In the case of a circular waveguide as shown in FIGS. 1 to 10, the cutoff frequency is determined by the following equation (1).

Fc (Hz) = 6.9 × 10 9 / d (1)

Where d is the diameter of the waveguide in inches. The shield effectiveness S is then determined by equation (2).

S (dB) = 32 × t / d (2)

Where d is the diameter of the waveguide in inches, and t is the length of the waveguide in inches. When multiple waveguides are used, as in the present invention, the shielding effectiveness depends on the size and number of waveguides. If waveguides of the same size are all densely arranged, the shielding effectiveness is determined by the following equation (3).

S (dB) = (32 × t / d) −10 log (n) (3)

Here, n is the number of diagonal waveguide openings. For a more detailed explanation of waveguide design principles, see
Henry W., incorporated herein by reference for further background. "NOISE R" by Henry W. Ott
EDUCTION TECHNIQUES IN ELECTRONIC SYSTEMS '', Wiley
-Seen in Interscience (2d ed. 1986).

It can be seen that long and narrow waveguides provide the greatest shielding effectiveness and higher cutoff frequency. Long and narrow waveguides, of course, have a low capacity as an airflow path. One example of a set of waveguide dimensions suitable for use as the front panel of a disk drive module is described in patent application Ser.
No. 2,270. Patent Application No. 09/23
No. 2,270, for example, each waveguide is 5 mm × 5 mm
Equipped with 36 × 10 mm square waveguides on diagonal lines
The I-shield and airflow panel provide a 47% airflow opening, a cutoff frequency of 22,940 MHz,
It discloses having dB shielding effectiveness. 1
A larger waveguide of 0 mm x 10 mm x 20 mm
The single-piece panel has an open area of 72% of the larger airflow, but the cutoff frequency and shielding effectiveness are
Only 11,016 MHz and 28 dB. These are just two examples of the various size, shape and density variables that can be used. The size, shape and density of the waveguide will depend on the EMI shielding and airflow requirements of the particular device, module and system.

The plate 46 and the waveguide 42 are formed by the Otto “NOISE REDUCTION TECHNIQUES IN ELECTRONIC SYSTEM”.
S "should be made of a suitable material such as a metal as described in Wiley-Interscience (2d ed. 1986).
The thickness of plate 46, tubes 42 and 52 will depend on the technology used to manufacture the plate and tube. The new design takes into account the "skin effect" where high frequency electromagnetic radiation is attenuated mainly along the outer surface of the waveguide. Thus, at the high frequencies of equipment using the Fiber Channel connectivity protocol, effective EMI shielding can be achieved using very thin wall waveguides.

Although the present invention has been shown and described with reference to the above embodiments, it will be understood that other forms and details can be made without departing from the spirit and spirit of the invention. The foregoing data storage system 18 and components of the system 18 represent just one of many types of electronic circuits and systems in which the present invention can be used. The present invention is not limited to a front panel of a housing such as a module. Also, the structure of the shield device of the present invention and the techniques for manufacturing such a device may require a separate module for the housing or cabinet or space of the system as necessary or desirable for effective EMI shielding and cooling airflow. On the side, top, bottom or back of the housing. Waveguides are not limited to circular or rectangular tubes that extend straight from the plate. Other cross-sectional shapes can be used, and in some applications, it may be necessary or desirable for the tube to extend from the plate at an angle other than 90 °.

The embodiments of the present invention have been described in detail above. Hereinafter, examples of each embodiment of the present invention will be described.

[Embodiment 1] A metal plate (46) having a plurality of holes (44) penetrating therethrough, fixed to the plate (46),
A plurality of metal waveguides (42, 52 or 56) extending from said plate (46) at the locations of said holes.

[Second Embodiment] The shield according to the first embodiment, wherein the waveguide (42, 52 or 56) includes a tube (42, 52 or 56).

[Embodiment 3] The plate (46) has a surface (50).
Embodiment 1 wherein the waveguide (42, 52 or 56) extends from the plate (46) substantially perpendicular to the plane (50). shield.

[Embodiment 4] The waveguide (42 or 5)
6. Shield according to embodiment 1, characterized in that 6) is a separate part attached to the plate (46).

[Embodiment 5] The shield according to embodiment 1, wherein the waveguide (52) is an integral part of the plate (46).

[Embodiment 6] A first and a second metal plate (46) arranged in parallel with each other and having a plurality of holes (44) penetrating therethrough, and the first plate (46) at a position of the hole. ) Extending to said second plate (46), passing through said plate (46) and forming an aperture therebetween, a first plurality of metal waveguides (42, 52 or 56); and said second plate. (46) the first plurality of metal waveguides (42, 5);
2 or 56) and a second plurality of metal waveguides (42, 52 or 56) extending oppositely.

[Embodiment 7] An electromagnetic interference shield housing (1) having a plurality of walls arranged to form a closed area
0) wherein at least one of said walls (12) has a metal plate (46), said metal plate (46) comprising a plurality of holes (44) therethrough and said holes (44). A plurality of thin-walled metal tubes (42, 52 or 56) secured to said metal plate and extending from said metal plate (46) towards said closed area.
Electromagnetic interference shield housing (10).

[Embodiment 8] The plate (46) has a surface (50).
The shield according to claim 7, characterized in that the tube (42, 52 or 56) extends from the plate (46) substantially perpendicular to the plane (50).

[Embodiment 9] An electronic module (20 or 22) which is electromagnetically shielded and has an electronic device capable of generating electromagnetic radiation and a plurality of walls at least partially surrounding the electronic device. Housing with (10)
Wherein at least one of the walls has a metal plate (46), the metal plate (46) having a plurality of holes (44) therethrough.
And a plurality of metal waveguides (42, 52 or 5) fixed to the holes (44) and extending inward from the metal plate (46).
(6) An electronic module (20) comprising: a housing having:

[0034]

As described above, desired EMI shielding and airflow characteristics can be achieved by using the present invention.

[Brief description of the drawings]

FIG. 1 is a perspective view of a housing for an electronic circuit such as a disk drive in which a front panel is configured as an EMI shield.

FIG. 2 is a front perspective view of a housing of a group of individual device modules, such as a disk drive module used in a RAID data storage system.

FIG. 3 is a rear perspective view of the housing of FIG. 2;

FIG. 4 shows an E in which a tubular waveguide is glued or fixed to a metal plate.
FIG. 2 is a detailed perspective partial cutaway view of the front panel of FIG. 1 showing one embodiment of an MI shield.

5 is a detailed perspective view of the metal plate and the tubular waveguide insert of the shield of FIG. 4 showing the hole without the tube and the hole with the tube.

6 is an end view of the tubular waveguide insert of FIG.

FIG. 7 is a side view of the tubular waveguide insert of FIG.

FIG. 8 shows an EM in which a tubular waveguide is extruded from a metal plate.
FIG. 6 is a front view of a second embodiment of the I shield.

FIG. 9 shows an EM in which a tubular waveguide is extruded from a metal plate.
FIG. 9 is a rear view of the second embodiment of the I-shield.

FIG. 10 is a perspective view of a third embodiment of an EMI shield in which two of the shields shown in FIGS. 8 and 9 are stacked side by side;

FIG. 11 is a perspective view of an EMI shield having a rectangular waveguide.

[Explanation of symbols]

 10: Electromagnetic interference shield housing 20, 22: Electronic module 42, 52, 56: Metal waveguide 44: Hole 46: Metal plate 50: Surface

Claims (1)

[Claims] 1. An electromagnetic interference shield comprising: a metal plate having a plurality of holes therethrough; and a plurality of metal waveguides fixed to the plate and extending from the plate at the positions of the holes.