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 Section 4:
DESIGN PHASE
4.1
Introduction. When NAVFAC authorization is received by the
Engineering Field Divison (EFD) for the design of a project requiring
Electromagnetic Interference (EMI) shielding, the Project Manager (PM) and the
Engineer-In-Charge/Architect-In-Charge (EIC/AIC) shall review the Facility
Study and BESEP to ensure that the shielding requirements are included. A
copy of the BESEP should be reviewed by the EFD's Design Branch with expertise
in EMI shielding to assure that the EMI shielding requirements are free from
ambiguities including the area (or areas) to be shielded, the type of
shielding required (Electromagnetic Compatibility (EMC), TEMPEST, High
Altitude Electromagnetic Pulse (HEMP), Hazards of Electromagnetic Radiation to
Personnel (HERP), Hazards of Electromagnetic Radiation to Ordnance (HERO), or
Hazards of Electromagnetic Radiation to Fuel (HERF)), whether both radiated
and conducted isolation is required, the decibels of attenuation required, and
the frequency range over which the shielding must cover. All comments or
questions on the BESEP should be sent the Naval Electronic Systems Engineering
Center (NAVELEXCEN) that prepared the BESEP. Also, the PM or EIC/AIC should
contact the Station to determine if any modifications to the BESEP are
required. The Synopsis and Scope of Work should reflect the need for EMI
shielding design expertise. The design team must have an EMI shielding
specialist with in-depth knowledge of design and construction of shielded
enclosures, and of shielding criteria including EMC and TEMPEST.
4.2
Predesign. Prior to negotiation of the design fee for the project
it is recommended that a predesign conference be held to discuss the project
requirements including the EMI shielding system. At the conference the
shielding requirements shall be presented including all special TEMPEST
requirements. The advantages and disadvantages of the various types of EMI
shielded enclosures shall be investigated so that a shielding system
compatible with the needs of the users is provided. The Station's
requirements for longevity, relocatability, maintainability and the
possibility for a change in the basic shielding requirements must be
investigated and determined.
4.3
Architectural Design. Various architectural design considerations
require special attention in an EMI shielded facility including EMI shielded
doors, coatings, finishes and fasteners. EMI shielded doors are recognized as
the "weak link" in the overall shielding system. Shielded doors come in
various configurations, single doors, double doors, standard or custom sizes,
but the number and size should be minimized. Neither the shielded enclosure
nor the doors should be exposed to the outside environment, both are
vulnerable to adverse environmental conditions and the shielding effectiveness
rapidly deteriorates if exposed to the outside environment. If the shielded
enclosure must open to the exterior, a weatherproof vestibule should be built
between the enclosure and the exterior. Doors that are used continuously
should be single doors. Double doors or larger openings should be used only
for equipment access since the shielding effectiveness of double doors is
difficult to maintain when the doors are in continuous use.
4.3.1
Comparison of Various Seals. To provide an EMI/RFI seal around
enclosure doors requires a good and continuous electrical contact between the
door and the door jamb. The seal can be made with RFI mesh gasket,
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