Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
2002-06-14
2003-02-25
Martin, David (Department: 2841)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C361S816000, C361S799000, C361S753000, C361S818000
Reexamination Certificate
active
06525267
ABSTRACT:
BACKGROUND
The disclosures herein relate generally to computer systems and more particularly to sealing chassis enclosures used in such systems.
As the value and use of information continue to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Because of the lack of precision in many of today's high production manufacturing processes, mechanical parts designed to contact each other may not attain sufficient contact. Sufficient contact between the parts is necessary to simulate a homogeneous material or surface. This homogeneous surface allows the current to flow freely along the surface.
Electromagnetic fields inside the chassis or shielding case produce a current along the inside of the chassis. Emissions from the chassis occur when a current in the chassis passes over a discontinuity. A discontinuity may exist at a joint between two elements which do not have a tight, metal-to-metal (electrically conductive) seal. As the current attempts to travel around the discontinuity it produces a voltage across the discontinuity on the inside of the chassis that is also seen across the discontinuity on the outside of the chassis. The voltage on the outside of the chassis induces a current on the outside of the chassis that results in an electromagnetic field radiating outside of the chassis. This presents a problem of producing electromagnetic interference (EMI) between this component and others.
One method of addressing this problem in the past has been to insert an EMI gasket between the two conducting surfaces. The gasket interior may be composed of any of a number of compressible materials, and the gasket exterior is a layer of conductive material. As the two conducting surfaces come together, the surfaces compress the interior of the gasket, resulting in a conductive contact between the two surfaces through the conductive surface layer of the gasket. A problem with this solution involves the degree of contact that is created between the gasket and the surface. A certain level of compression force provided by the conducting surfaces is required to obtain reasonable and reliable gasket conductivity performance. Flat, square, D-shaped, or round-gaskets often do not create enough surface contact between a conducting surface and the gasket, and require increased compression forces in order to provide chassis closure that results in cosmetic distortion of the chassis. Typical industry design practice is to provide a groove in the chassis or shielding case to contain the gasket with a mating adjacent surface tongue applying closure force. The gasket normally is sized to be retained in the grove without adhesive. The applied compression force of the tongue expands the gasket to make contact with the bottom and sides of the groove as well as the tongue. The amount of force required closing the chassis or shielding case is influenced by the gasket design and selected materials.
Therefore, what is needed is a gasket that will increase conductivity at a reduced deflection force to provide easier chassis closure with less cosmetic distortion, and more efficient EMI shielding.
SUMMARY
One embodiment, accordingly, provides a chassis discontinuity seal that includes a gasket member comprising an elongated compressible material having a first density and including a peripheral surface. The peripheral surface has an interruption which defines an elongated portion of the gasket of a second density, less than the first density. A flexible sealing material covers the peripheral surface and spans the elongated portion of the gasket.
A principal advantage of these embodiments is that the gasket member enhances EMI containment by providing increased surface contact between the gasket and the two surfaces while requiring a low force to seal the two surfaces. The embodiments are also applicable to any shielding enclosure desiring to reduce compression force while maintaining high surface conductivity.
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Berry Chase
Worley Richard
Dell Products L.P.
Haynes and Boone LLP
Martin David
Vu Phuong T.
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