Abstract:
Enclosures and gasket assemblies for reducing EMI for computer systems and other electronic devices are disclosed. In an exemplary embodiment a gasket assembly for reducing EMI may comprise a soft core sizable to extend along at least the length of an opening in an EMI housing. The gasket assembly may also comprise a plurality of fingers positionable at spaced-apart positions along the entire length of the opening in the EMI housing, the plurality of fingers maintaining conductivity between mating surfaces of the EMI housing.

Description:
BACKGROUND 
   Operation of computer systems and other electronic devices may generate electromagnetic fields (EM fields) in the radio frequency (RF) spectrum. These energies, referred to as electromagnetic interference (EMI) may cause “noise” or otherwise degrade performance of other computer systems and electronic devices. Accordingly, computer systems and other electronic devices may be shielded to reduce emissions which cause EMI and disrupt the operation of other equipment. Computer systems and electronic devices may also be shielded against EMI caused by other equipment in order to function properly in the intended environment. 
   Filters have been developed to reduce emissions that cause EMI. However, EMI filters may require modifying the circuitry, can be expensive, and do not protect against EMI caused by other computer systems or electronic devices. Alternatively, shielding may be used to reduce emissions that cause EMI. Shielding may be accomplished by enclosing circuits or other sources of EMI. Shielding also protects against EMI caused by other computer systems or electronic devices. 
   EMI shielding may be accomplished by sealing openings in enclosure with foam gaskets. These foam gaskets work well if the mating surfaces of the enclosure are highly conductive (e.g., metal). However, the materials used for these enclosures may include zinc or other heavy metals, and therefore may be insulated to comply with Reduction of Hazardous Substances (RoHS) standards. Obviously, foam gaskets cannot pierce this insulating layer, thereby reducing its effectiveness for EMI shielding. 
   Although a metal gasket may be used to pierce the insulating layer, metal gaskets typically requires relatively high compressive forces in order to pierce the insulating layer. Accordingly, the enclosure has to be designed to resist these forces. Such a design increases manufacturing costs and the size/weight of the final product, all of which are undesirable in electronic devices. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front perspective view of an exemplary computer system which may implement EMI shielding. 
       FIG. 2  is a perspective view of two modules of the computer system shown in  FIG. 1  shown pulled apart from one another to illustrate the use of an exemplary enclosure and gasket assembly for EMI shielding. 
       FIG. 3  is a detailed perspective view of the two modules in  FIG. 2  showing the gasket assembly bonding the edges of enclosures. 
       FIGS. 4   a  and  4   b  are high-level cross-sectional views showing the mating surfaces of exemplary enclosures and gasket assembly (a) in an open position, and (b) in a closed position. 
       FIGS. 5   a  and  5   b  are other high-level cross-section views showing alternative embodiments of the gasket assembly wherein (a) the finger is positioned at least partially over the soft core, and (b) the finger is positioned adjacent the soft core. 
   

   DETAILED DESCRIPTION 
   Embodiments of an enclosure and gasket assembly are disclosed. The enclosure may include sheet metal or other conductive material (e.g., metalized plastic). Seams and other openings in the enclosure may be sealed with a gasket assembly. The enclosure and gasket assembly work together to reduce or altogether eliminate emissions that can cause EMI. The enclosure and gasket assembly do not require modifications to any circuitry, while reducing emissions and protecting against external EMI caused by the operation of other computer systems and/or other electronic devices. 
     FIG. 1  is a front perspective view of an exemplary computer system  100  which may implement EMI shielding. In one example, the computer system  100  may be a basic 8 processor system including eight separate modules  110   a - h . Each of the separate modules  110   a - h  may be enclosed and bonded together by a gasket assembly to provide effective EMI shielding (as better seen in  FIGS. 2 and 3 ). 
   In the basic 8 processor system, eight modules  110   a - h  are mounted in a chassis  120  in two rows of four each. Accordingly, each module  110   a - h  may be bonded to another module on the top (or bottom) and on at least one side. For example, module  110   a  is bonded to module  110   b  on the side and to module  110   e  on the bottom. Module  110   f  is bonded to modules  110   e  and  110   g  on the sides, and module  110   b  on the top. 
   It is noted, that the chassis  120  may be configured for any number of modules  110   a - h . For example, the chassis  120  may also be configured for a single row of four modules. Other configurations are also contemplated. In addition, the enclosure and gasket assembly may also be implemented for components within each of the separate modules and/or for the chassis  120  itself, and is not limited to use only between the modules  110   a - h , as will be readily appreciated by those having ordinary skill in the art after becoming familiar with the teachings herein. 
   Before continuing, it is noted that the embodiments of computer system  100  described herein are provided for purposes of illustration and are not intended to limit the enclosure and gasket assembly to use with any particular type or configuration of computer system or other electronic device. 
     FIG. 2  is a perspective view of two modules  110   a  and  110   b  of the computer system  100  shown in  FIG. 1  shown pulled apart from one another to illustrate the use of exemplary enclosures  130   a  and  130   b  (respectively) and gasket assembly  140  (respectively) for EMI shielding. The enclosures  130   a  and  130   b  may be made of sheet metal or other conductive material (e.g., metalized plastic). 
   In this illustration, gasket assembly  140  on enclosure  130   a  may be used to bond the edge  150  of enclosure  130   b  to enclosure  130   a . The other modules shown in  FIG. 1  (e.g., modules  110   a - h ) may be similarly provided with gasket assemblies for bonding the edges of the enclosures to one another on the sides, top, and/or bottom in the chassis  120 , as discussed above. 
   It is noted that the gasket assembly  140  may also be used to seal an opening in a single enclosure, and is not limited only to use between enclosures. For example, at least one opening formed between mating conductive surfaces (e.g., a door on an enclosure) may also be sealed for EMI. 
     FIG. 3  is a detailed perspective view of the two modules  110   a  and  110   b  in  FIG. 2  showing the gasket assembly  140  bonding the edges of enclosures  130   a  and  130   b . The gasket assembly  140  may include a soft core  142 , such as, but not limited to, mesh, elastomers, and fabric bonded to foam. The gasket assembly may also include a plurality of spaced-apart, strong, conductive fingers  144  as shown in the figures. 
   Poor conductivity through the gasket assembly  140  may reduce the effectiveness of the EMI shielding, and may even act as an EMI antenna, serving to transmit energy instead of reduce EMI. Therefore, the fingers  144  are readily compressible, but sufficiently strong so as to readily pierce any insulating layer that may be provided on the enclosure  130   a  and  130   b , as better seen in the illustration shown in  FIGS. 4   a  and  4   b . Accordingly, the fingers  144  serve to maintain conductivity between mating surfaces of the enclosures  130   a  and  130   b.    
     FIGS. 4   a  and  4   b  are high-level cross-sectional views showing the mating surfaces  152  and  154  of exemplary enclosures and gasket assembly (a) in an open position, and (b) in a closed position. The open position corresponds to an uncompressed state, e.g., as shown in  FIG. 2  where the finger  144  of gasket assembly  140  is not in contact with the mating surface  154  of the enclosure. The closed position corresponds to a compressed state, e.g., as shown in  FIG. 3  where the finger  144  of gasket assembly  140  is in contact with a mating surface  154 . 
   Although the finger  144  is shown positioned over the soft core  142  of gasket assembly  140 , other embodiments are also contemplated. For example, the finger  144  may be at least partially over the soft core  142  (e.g., extending half way over the soft core), as shown in  FIG. 5   a . Alternatively, the finger  144  may be positioned next to or otherwise adjacent the soft core  142 , as shown in  FIG. 5   b.    
   The gasket assembly  140  is also shown in  FIG. 4   b  with the finger  144  having pierced the insulating layer  160  of mating surface  154 . Accordingly, the gasket assembly  140  provides a low-impedance path for conducting current between mating surfaces  152  and  154  of the respective enclosures. At low frequencies the gasket assembly  140  may function as a resistor. At higher frequencies, the gasket assembly  140  may function as an inductor in series with a resistive load, or alternatively, as a shunt capacitor in parallel to a resistive load. 
   The gasket assembly  140  may also provide a wide functional frequency range. That is, the gasket assembly  140  provides good bonding of mating surfaces  152  and  154  of the enclosures to protect against emissions in the direct current (DC) through very high frequency (VHF) range. The soft core  142  of gasket assembly  140  may also provide bonding which reduces emissions in the VHF through microwave range. 
   It is noted that the exemplary embodiments discussed above are provided for purposes of illustration. Embodiments of the gasket assembly  140  described herein are not limited to use with any particular type or configuration of computer system. For example, gasket assembly  140  may be implemented with other computer systems, such as, e.g., a personal desktop or laptop computer. In addition, the gasket assembly is not limited to use with computer systems. For example, the gasket assembly  140  may also be implemented with any of a wide variety of other types of electronic devices or other EMI sources. It is also noted that the gasket assembly  140  may be implemented to shield against emissions which may cause EMI, as well as shielding against EMI caused by emissions from other computer systems or other electronic devices. 
   Still other embodiments are also contemplated. In addition to the specific embodiments explicitly set forth herein, other aspects and embodiments will be apparent to those skilled in the art from consideration of the specification disclosed herein. It is intended that the specification and illustrated embodiments be considered as examples only.