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Browse Prior Art Database

INTEGRATED EMC VENT AND HEATSINK

IP.com Disclosure Number: IPCOM000008185D
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2002-May-24
Document File: 3 page(s) / 110K

Publishing Venue

Motorola

Related People

Thomas Paul Groves: AUTHOR [+2]

Abstract

The principle uses the natural height, length and breadth of natural or forced air convection cooling fms used in the cooling of electronic assemblies to form a matrix of waveguides operating beyond their cut off frequency. This may then be used to provide attenuation to tf. fields when the heatsink assembly forms a vent in an electrically screened enclosure. Figure 1 illustrates a typical example of an enclo- sure utilizing such a device.

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M-LA Technical Developments

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INTEGRATED EMC VENT AND HEATSINK

by Thomas Paul Groves and Malcolm John Perry

  The principle uses the natural height, length and breadth of natural or forced air convection cooling fms used in the cooling of electronic assemblies to form a matrix of waveguides operating beyond their cut off frequency. This may then be used to provide attenuation to tf. fields when the heatsink assembly forms a vent in an electrically screened enclosure. Figure 1 illustrates a typical example of an enclo- sure utilizing such a device.

  The equations for cut off frequency and attenuation with respect to the wave-guide length, shape and maximum aperture dimensions are well documented in standard texts on this topic and should be con- sulted if a high level of accuracy is required in the design. However, as a rough guide for the purpose of this article the following equations will be useful for the majority of designs.

For h-equencies less than one tenth of the cut off frequency the attenuation will be approximately

    (r = (27 x/y) - 10 log n where a = attenuation in dR
x = length of the waveguide y = the longest dimension of the waveguide aperture
n = total number of waveguides formed by the matrix

Note that this equation neglects any attenuation due to reflection terms. In practice the additional

attenuation gained from these reflection terms gives a useful margin to any design based on the above.

Cut off frequency for rectangular waveguides is approximate...