The switching speeds of today's high speed electronic components create high frequencies which escape from (emissions), or enter (immunity), any openings in electronic enclosures. Interference control standards are mandated by various regulatory agencies in most industrialize markets to control the unwanted transmission or receiving of such high frequencies. In addition, it may be preferred engineering practice to control these emissions to assure proper equipment performance in both systems and groupings of electronic equipment such as in medical, instrumentation, process controls or other diagnostic situations.  

  When access panels, doors, ventilation, displays, etc. are required in an otherwise solid enclosure, precautions must be taken to eliminate the transmission of radio frequencies through such openings or slots.

Shielding gaskets assure tight RFI/EMI sealing of electronic enclosures containing high speed microprocessors.

 The graph below displays the maximum shielding effectiveness possible from a given size opening (slot) in an enclosure. 
 
 

Shielding Effectiveness vs. Frequency as a Function of Slot Length
It can be seen from the information above that the shielding effectiveness increases as the size of the opening is reduced. In order to achieve the same performance as a small opening, the slot must be coupled electrically across its opposing surfaces. This can be accomplished by using conductive fasteners or gaskets. Gaskets are usually the most common choice. They offer a continuous coupling along the full length of the slot while permitting the opposing surfaces to be separated easily for access to the components contained within. See the photo below.

Top view of electronic enclosure door with typical shielding gasket installation.