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# Shieldinhg effectiveness

- To: femm@yahoogroups.com
- Subject: Shieldinhg effectiveness
- From: emiliano.menghi@inwind.it
- Date: Tue, 24 Apr 2001 19:44:38 -0000
- User-agent: eGroups-EW/0.82

    Hi. I use femm to calculate shielding effectiveness of various
    material (such as alluminium, copper, iron, mumetal etc,) at 50 Hz,
    but i have some problem.
    My configuration is simple:
    A alluminium wire with 1000 A 50 Hz (r=7.1 mm)
    A dielectric around the wire (external radius r=16.5 mm)
    A tubolar shield around (external radius r= 19.5 mm)

    I use A=0 as boundary condition

    If i don't simulate the shield all is OK, but when i use for example
    an alluminum shield, i have these problems:

    1- Shielding effectiveness depends on the position of the boundary
    condition
    2- I compared femm results with real measures: in the measure setup
    the wire and the shield lenghts were 10 mt. The wire was grounded
    (for femm is grounded at infinity, i think)
    Results ( distance from wire: 20 cm)

    without shield
    B femm= 323 microT B measured=321

    with alluminium shield
    B femm= 101 microT B measured= 275 microT
    I in the shield femm= 200A measured=35 A
    with shield floating B measured= 303 microT
    Why?
    Is The problem, perhaps, the lenght of the wire (and the shield)
    infinite for femm and finite (10 mt) for the measure?
    Can i simulate with femm terminations of shield (floating or
    grounded)?
    Thanks and exuse me for my poor english

    Menghi Emiliano

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