🚀 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

		
|> 
|> 
|> 
|> 
|> -- 
|> ^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~
|> 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

In article <3485@eastman.UUCP> rao@kodak.com (Arun Rao) writes:
>From: rao@kodak.com (Arun Rao)
>Subject: Re: Negative resistance
>Date: 31 Jul 92 19:29:47 GMT
[much deleted]
>|> ^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~
>|> 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
Kent,  
  All of my email to you bounces.  Is there anyway you could get an email 
address that is connected to the network?  Somewhere in the internet, creare.
com may be connected, but the internet is not simply connected to your 
machine.

Joe
#,:::::::;,   ::            Joe Landman  Graduate Student (PhD),
#    ::       ::            Computational Solid State Physics.
#;:  ::       ::            Physics Dept., Wayne State Univ.   
#`::::; oe    ;:::; andman  666 Hancock Avenue, Detroit MI 48202 
#Internet: landman@hal.physics.wayne.edu landman@rhic2.physics.wayne.edu
#          kil@pandora.cs.wayne.edu  jland@ss0.eng.wayne.edu
#ATTnet: (313) 577-2720

In article <13404@creare.COM> kwg@creare.UUCP (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. 
<stuff deleted>
>   A plot of V vs I in this case
>   would have negative slope and thus Ohms law would be rewritten V=-IR.

Pedant's corner: dV/DI = -R -> (V-Vo) = -IR.  We don't need to add an extra 
                 sign stripe to resistors and all battery manufacturors can
                 breathe easy.

>   Anyone know of such a material?

Low pressure neon - like in a bulb or plasma pannel, or other similar stuff.
A gap of 1cm in vacuum has a very high resistance, but apply enough voltage
to get a discharge and it can go to less than 0.1 ohm.

Some pure superconductors can do funny things with flux lines.  I have
measured potential profiles along a conductor where the voltage gradient
along a specimen seems to change sign, though the overall trend is positive.
The flux lines due to the imposed magnetic field and those generated by the
current get driven about by the current, and this can lead to them busting 
out wherever they can.




-- 
Richard Kirk         Image Processing Group    Crosfield Electronics Ltd. U.K.
rak@crosfield.co.uk  0442-230000 x3361/3591    Hemel Hempstead, Herts, HP2 7RH

In article <13404@creare.COM> kwg@creare.UUCP (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. 

	The classic example is a neon lamp; resistance is high until
one reaches the breakover voltage, then it drops (because the gas
becomes ionized).  Some semiconductors have similar properties,
when they are undoped, because avalanche conduction makes new
charge carriers (and lowers the resistance).  

	John Whitmore

p.s. negative resistance is also  possible in some AC circuits, if
the right kinds of tricks are played... this is a kind of trick
for analyzing oscillator circuits.

	

In article <14979@suns3.crosfield.co.uk> rak@crosfield.co.uk (Richard Kirk) writes:
>From: rak@crosfield.co.uk (Richard Kirk)
>Subject: Re: Negative resistance
>Date: 3 Aug 92 08:41:58 GMT

[much deleted]
>Some pure superconductors can do funny things with flux lines.  I have

When I did some V vs I, and Jc measurements on thin film 123 material in 
1988, I encountered a negative resistance phenomenon for current densities 
below Jc.  I never looked into it further, and never gave it much thought (
we were trying to make the film growing reproducible...)

Joe

ps: Kent, this is the message I wanted to send you.  creare.com is not 
reachable from my machine.





>-- 
>Richard Kirk         Image Processing Group    Crosfield Electronics Ltd. U.K.
>rak@crosfield.co.uk  0442-230000 x3361/3591    Hemel Hempstead, Herts, HP2 7RH
#,:::::::;,   ::            Joe Landman  Graduate Student (PhD),
#    ::       ::            Computational Solid State Physics.
#;:  ::       ::            Physics Dept., Wayne State Univ.   
#`::::; oe    ;:::; andman  666 Hancock Avenue, Detroit MI 48202 
#Internet: landman@hal.physics.wayne.edu landman@rhic2.physics.wayne.edu
#          kil@pandora.cs.wayne.edu  jland@ss0.eng.wayne.edu
#ATTnet: (313) 577-2720

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.
|>
>
	ZnO2 based varistor materials have a negative resistance
	region. 

	- Anis