Methods and apparatus for EMI shielding

#This invention relates to methods of manufacturing electromagnetic interference (“EMI”) shields and the EMI shields produced thereby.

#As used herein, the term EMI should be considered to refer generally to both EMI and radio frequency interference (“RFI”) emissions, and the term electromagnetic should be considered to refer generally to electromagnetic and radio frequency.

#During normal operation, electronic equipment generates undesirable electromagnetic energy that can interfere with the operation of proximately located electronic equipment due to EMI transmission by radiation and conduction. The electromagnetic energy can be of a wide range of wavelengths and frequencies. To minimize the problems associated with EMI, sources of undesirable electromagnetic energy may be shielded and electrically grounded. Shielding is designed to prevent both ingress and egress of electromagnetic energy relative to a housing or other enclosure in which the electronic equipment is disposed. Since such enclosures often include vent openings and gaps or seams between adjacent access panels and around doors, effective shielding is difficult to attain, because the gaps in the enclosure permit transference of EMI therethrough. Further, in the case of electrically conductive metal enclosures, these gaps can inhibit the beneficial Faraday Cage Effect by forming discontinuities in the conductivity of the enclosure which compromise the efficiency of the ground conduction path through the enclosure. Moreover, by presenting an electrical conductivity level at the gaps that is significantly different from that of the enclosure generally, the gaps can act as slot antennae, resulting in the enclosure itself becoming a secondary source of EMI.

#The above and further advantages of this invention may be better understood by referring to the following description, taken in conjunction with the accompanying drawings, in which:

#FIG. 1 is a schematic drawing of a conventional aluminum air filter;

#FIG. 2 is a schematic drawing of a partial cross-section of an aluminum honeycomb substrate and a frame for the conventional aluminum air filter;

#According to the present invention, honeycomb filters used for airflow and EMI shielding can have improved airflow and durability through the use of a metallized dielectric honeycomb substrate and a frameless filter design. Metallized dielectric honeycomb substrate utilized in a reduced frame design can also be used to provide even greater durability along with increased airflow.

#FIG. 4 shows in perspective view, a cross-section of one embodiment of a metallized dielectric honeycomb filter 50. The metallized dielectric honeycomb filter 50 includes a dielectric honeycomb substrate 52 and a conductive layer 54. As used herein, the term honeycomb refers to a two-dimensional array of apertures of arbitrary cross-section. The aperture cross-section can be any shape, such as hexagonal, circular, elliptical, square, rectangular, triangular, rhomboidal, or other, and combinations thereof. The dielectric honeycomb substrate 52 is selected to provide significantly improved resiliency as compared to conventional aluminum honeycomb filters. Due to the improved resiliency, the dielectric honeycomb substrate 52 is much less likely to be deformed permanently under load or impact conditions that can be encountered during assembly and normal operation. By minimizing the possibility of deforming through the use of the dielectric honeycomb substrate 52, much of the rework required to fix damaged aluminum honeycomb filters in order to maintain proper airflow through the filter is thereby eliminated.

#The dielectric honeycomb substrate 52 can be made out of any dielectric material, such as plastic. For example, some materials that can be used for the dielectric honeycomb substrate 52 are acrylonitrile-butadiene-styrene (ABS), polycarbonates, polysulfones, polyamides, polypropylenes, polyethylene, and polyvinyl chloride (PVC). Additionally, other dielectric materials may be used such as fiberglass and paper products, such as aramid (e.g., Kevlar®) sheets, and aramid fiber paper. Dielectric honeycomb substrates are commercially available. For example, Kevlar® honeycomb cores (e.g., Ultracor part no. PN UKF-85-1/4-1.5), carbon honeycomb cores (e.g., Ultracor part no. UCF-145-3/8-0.8) are commercially available from Ultracor Inc., located in Livermore, Calif., Aramid fiber honeycomb cores (e.g., Hexcel part no. PN HRH-10), fiberglass honeycomb cores (e.g., Hexcel part no. HRP) are commercially available from Hexcel Corp., located in Danbury, Conn., and polypropylene honeycomb cores (e.g., Plascore part no. PP30-5) are commercially available from Plascore, Inc., located in Zeeland, Mich.