Heat conversion by using piezzo effect

[Kysmett]

What about the U of Chicago's discovery of negative resistance displayed in crossed carbon polymers?  Could that somehow be used to reduce the diode bias voltage?

[Charlie Brown ARN]

My first response to googleing: crossed carbon polymers negative resistance was   http://wings.buffalo.edu/academic/department/eng/mae/cmrl/Apparent%20negative%20electrical%20resistance%20in%20carbon%20fiber%20composites.pdf    I heard that PDFs were hard on some people's browsers so proceed accordingly. The negative resistance was carefully called apparent rather than true even though with regression analysis ~whatever~ it graphed through 00 , the orgin and was of negative slope. Current going through it heated it, a strong point for realistic evaluation. It had low resistance in AC circuits to MHz frequencies. Semiconductor properties were mentioned. It is an offering of the new discipline of structual electronics.  I am curious about the materials use as an electroplating cathode.

Aloha, Charlie

[swankpower]

I have found some schottky diodes with Vf=375mV made by Agilent...they are quite expensive, but they are quite low threshold voltage.


added minutes later...
from Agilent's website
"The HSCH-534x family of low barrier Beam Lead Schottky diodes are ideally suited for mixer and detector applications from 1-26GHz. These products are suitable for applications that require guaranteed RF tested performance. Vbr=4V. Max. (Vf)=375mV. Max leakage Current (Ir)=400nA. "

[swankpower]

I don't exactly understand why higher voltage generating piezos cannot be used. I can only understand this in an OPEN AIR situation where at ambient pressure and temperature there is a maximum pressure which can be exerted on such a piezo, thus limiting voltage....But if you have a container with the piezo enclosed with larger voltage, you should be able to 'tune' the pressure in the closed container to where the piezo has just enough pressure on it where it is in disequilibrium causing it to push in and out, NOT just push in and stay in. Please forgive me if I forget something completely obvious, as I am not an expert in piezoelectrics.

[Kysmett]

I have done some basic piezo work.  The voltage is produced by a change in shape.  The pressure in a chamber exerts its force universally on the material, so while the pressure is increasing the material compresses.  But it won't decompress unless the pressure is relieved.  So you end up with a direct correlation of votage proportional to the change in shape wich is proportional with the change in pressure.  You would have to oscilate the pressure to get a continuous voltage out.  Otherwise you get a voltage while you set the pressure, but then the material settles at equilibrium with its new environment and voltage drops.

If I am wrong, either in my assesment of the material or that of your idea, please let me know.  I am always ready to learn something new.