🚀 go-pugleaf

In article <13404@creare.COM>, kwg@creare.COM (Kent Goeking) writes:
|> 
|>    I would like to know if there are any materials that demonstrate negative
|>    resistance on the macroscopic scale.  I am aware of this behavior in tunnel
|>    diodes but I wonder if it might not occur in other structures. 
|> 
|>    For example, it seems plausible to me that the conductivity (albeit small)
|>    of a dielectric material may be sensitive to the electric field in unusual
|>    ways.  If leakage currents are primarily carried along grain boundaries then
|>    perhaps if the material was piezoelectric, under a field these current paths
|>    might become more restricted due to increased internal stresses.  Hence the
|>    resistance would increase with applied field.  A plot of V vs I in this case
|>    would have negative slope and thus Ohms law would be rewritten V=-IR.
|> 
|>    Anyone know of such a material?  Is it possible to design some sort of
|>    composite?  Not sure what applications it would be good for but sure would
|>    be a unique capability.


		Gallium arsenide has a negative resistance region in its
		drift velocity / electric field characteristic which has
		been exploited to make two-terminal microwave oscillators
		-- the Gunn diode (nothing but a contact on either end of
		a piece of GaAs) is one example.

		I'm no longer up to date in the area, but I believe two
		terminal oscillators are still the only choice for 60 GHz+
		frequencies -- especially when efficiency is not a major
		concern.

		-Arun

		
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|> -- 
|> ^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~
|> Kent Goeking (kwg@creare.com)| "We are continually faced with a series of
|> Creare Inc., P.O. 71         |  opportunities brilliantly disguised as
|> Hanover, New Hampshire 03755 |  insoluble problems"  - John W. Gardner

-- 
Arun Rao, PhD
Senior Research Scientist
Recognition & Information Processing Group
Eastman Kodak Company
901 Elmgrove Road, Rochester, NY 14653-5722