Re: NEC-List: Wire Radi to printed conductor?

----- Original Message -----
From: "Chuck Counselman" <ccc_at_space.mit.edu>
To: <nec-list_at_gweep.ca>
Sent: Friday, May 10, 2002 1:23 PM
Subject: Re: NEC-List: Wire Radi to printed conductor?

> At 9:27 AM -0700 5/10/02, Alan Thomas wrote:
> >...the answer is in rho, the bulk resistivity property with respect to
> >cross-sectional area and length.
> >
> >I too am taken aback at the arbitrary approach to such conversions
> >and I don't believe it's correct. I don't see pi anywhere.
> >
> >This is interesting along those lines (no pun intended)- see the PCB
> >trace impedance calculator link:
> >http://www.polarinstruments.com/menu/home.html
>
>
> Since you mention "rho, the bulk resistivity property with respect to
> cross-sectional area and length," I suspect that you're thinking of
> the DC resistance of a conductor. Cross-sectional area is irrelevant
> at radio frequency (RF) for practical conductors.
>
> Since this is the NEC-List, I assumed that Wayne Shanks' question was
> about the RF inductance and capacitance per unit length of a thin
> cylindrical wire or thin flat strip in free space, and that
> resistance was negligible.
>
> Calculating PCB trace impedance at RF is beyond NEC. PCBs involve
> geometries and combinations of dielectric media and free space that
> NEC is unable to model.
>
> Nor is NEC able to calculate the DC resistance of a PCB trace.
>
> -Chuck.
> --
> The NEC-List mailing list <nec-list_at_gweep.ca>
> http://www.gweep.ca/mailman/listinfo.cgi/nec-list

Hi Chuck...

My question was to get a simple first order adjustment for simulating thin
straps in free space of width w by adjusting the radii of the NEC wires.
I know about the non-uniform current distribution in a thin strap. Again to
first order this is compensated for by an appropriate shift in conductor
radii. I know that conductor interactions will be modeled poorly; I will
just have to deal with that. My simulations are to get me close. I am
resigned to the fact that I will have to fine tune the physical prototype.

I guess there is a more broad question.

Can you simulate an arbitrary cross-section conductor, by simply matching
it's capacitance, inductance, and effective resistivity per unit length with
that of a cylindrical wire?
It sound correct to me.

Wayne S

-- 
The NEC-List mailing list <nec-list_at_gweep.ca>
http://www.gweep.ca/mailman/listinfo.cgi/nec-list