[hpsdr] [Hpsdr] Call for Comments - ALEX

[Henry Vredegoor]

Hi Chris, Ray, All,

Very interesting data Ray!

Never I have dug this deep into the physical and theoretical aspects of
shielding, I only saw different applications of aluminum and steel for
shielding in pro communications equipment. One thing I noticed was indeed
the use of always much thicker shielding thickness in case of aluminum and I
wondered why.

Now I do know why! (A little more.....)
Thank you for your explanation and information!

73's,

Henry.


> -----Original Message-----
> From: Ray Anderson [mailto:ray.anderson at xilinx.com] 
> Sent: woensdag 25 juli 2007 20:36
> To: Henry Vredegoor; hpsdr at hpsdr.org
> Cc: Ray Anderson
> Subject: RE: [Hpsdr] Call for Comments - ALEX
> 
> 
> 
> 
> >Is there any data on how thick the aluminum shielding would 
> have to be
> to
> >provide the same magnetic shielding as say 1 mm. thick steel plate?
> 
> Here are the skin depths for Copper, Aluminum and Steel (in 
> inches) for
> several frequencies.
> 
>  Frequency        Skin Depth             Skin Depth            Skin
> Depth
>                   (Copper)                (Aluminum)          
>   (Steel)
>    60Hz            0.335                   0.429              
>      0.034
>   100Hz            0.26                    0.333              
>      0.026
>    1kHz            0.082                   0.105              
>      0.008
>   10kHz            0.026                   0.033              
>      0.003
>  100kHz            0.008                   0.011
> 0.0008
>    1MHz            0.003                   0.003
> 0.0003
>   10MHz            0.0008                  0.001
> 0.00008
> 
> 
> The absorption  attenuation is 8.69 dB per skin depth (so if you want
> 50dB attenuation you need about 5.75 skin depths of thickness, that
> would be 5.75mil of aluminum or 0.46mil of steel).
> 
> You can see from the data that you need 12.5 times the thickness of
> aluminum as compared to steel for the equivalent magnetic 
> shielding. The
> lower the frequency you want to shield the thicker the 
> material needs to
> be for the same shielding effectivness.
> 
> Also note that the total effective attenuation is greater 
> since there is
> also a reflection loss besides the absorption loss. Aluminum has more
> reflection loss than steel (at 10MHz steel has about 50 dB loss while
> aluminum has around 80dB). Below about 10MHz the reflection loss
> predominates, above 10 MHz the absorption loss predominates.
> 
> So at 10MHz .46mil of steel has a total of about 100dB loss while
> 5.75mil of aluminum would have about 130dB. Increase the 
> steel thickness
> to the same as we have for aluminum and then the total steel shielding
> loss would be a theoretical 675 dB!. At higher frequencies the
> absorption loss increases and the reflection loss decreases.
> 
> As with all things it is an engineering tradeoff.
> 
> -Ray  WB6TPU
> 
>  
> 


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