Re: FDC ground plane thickness

[Gerard Visser <gvisser@indiana.edu>]

Hi Dan,
	Ok, sorry I didn't do this test till now. I just measured it, I find 
that the sheet resistance _per_ _side_ is 1.18 Ohms per square. In other 
words if both sides are considered then it is 0.59 Ohms per square. This 
was measured on a 235 x 10.5 mm strip with a 4-wire method at 0.497A 
test current.
	This seems fairly low, I would assume that it will be fine. It is 
important to ensure good contact to both sides of the material at 
sufficiently large portions of the perimeter. Especially important that 
one side does not wind up floating, that could create a noise/coupling 
issue.
	The above sheet resistance, together with the properties of the cathode 
plane, could now be put into an electromagnetic simulation of the 
cathode strip as a transmission line, to determine its characteristic 
impedance and to look at crosstalk (including determination of the 
ground plane voltage, which would give crosstalk into the next layers 
cathode strips). I don't think I have the CAD tools required to do this. 
Perhaps Fernando has access to something. It should be pursued, but I 
don't expect any results of this will indicate that the materials of 
either cathode plane or ground plane need to be changed.

	Gerard

p.s. The sheet resistance above is consistent with a thickness of 2.3E-8 
m = 230 Angstroms. So it makes sense.

Daniel S. Carman wrote:
> 
> Gerard,
> 
> When you were here at JLab last, Brian Kross gave you a sample of
> double-sided aluminized mylar.  The mylar was 6.3 microns thick and
> the aluminum deposited on each side was a few hundred angstroms
> thick.  This is the material that we are nominally planning to use
> for our ground planes on the ends of each FDC package and in
> between each cathode.  Have you thought about the suitability
> of this material to fulfill this purpose?
> 
> 
> 				Regards,
> 
> 					Daniel
> 
> 
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