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Would a superconducting material...

drkitten said:
Um, Wikipedia is hardly an authority on cutting-edge physics.
Click to expand...

OK :)

http://www.lucent.com/minds/transistor/history.html

http://www.webopedia.com/TERM/T/transistor.html

http://www.williamson-labs.com/480_xtor.htm

http://electronics.howstuffworks.com/diode4.htm

ETA:I wouldn't call transistors cutting edge physics, having been around since the late 40s/early 50s or so (check the first link, they invented it :-)

Another edit, because the the first link doesn't go to the page I wanted (and to correct spelling;)

From the FAQ page of first link -

A semiconductor is a unique material with physical properties somewhere in between a conductor like aluminum and an insulator like glass. Examples include germanium, the semiconductor used for the first transistors, and silicon, the basic material in the integrated circuit. Researchers exploited the unique properties of a semiconductor to create the transistor effect--that is, the ability to change its conductivity properties using an electric current.
 
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A transistor is not merely a simple switch. Certainnly it can be used as one, and it is used as a simple switch in computer circuits. Those links only address their use in computer circuits where they are used as switches.

When used in their linear regime, transistors can be used as an amplifier for continuous time signals (analog signals). Your computer speakers, car stereo, home theater, I-Pod would not work if transistors could only be used as simple switches.

The same goes for vacuum tubes. The first computers used vacuum tubes, the same ones used in audio amplifiers. I have a few tube-based flip-flops in my junk collection that use the same 12AX7 dual triodes that are used in my guitar amplifiers.

Here's a page that describes the linear operation of a transistor:

http://fourier.eng.hmc.edu/e84/lectures/ch4/node5.html

The 'input' to the circuit is Vbe, which causes a current Ibe to flow into the base of the transistor. In response, a collector current Ic flows into the collector of the transistor. The magnitude of Ic is related to Ib by the current gain of the transistor beta:

Ic = beta * Ib

Beta is a number larger than 1, and betas of >100 are very common. So for a small amount of input current, we get a large amount of output current through the collector of the transistor. Since we get more out than we put in, we have amplified our base current, so we're using the transistor as an amplifier, not a switch.

The page goes on to say the transistor can be operated in three regimes:

1. Linear region (what I have just described; the transistor is used as an amplifier)

2. Cutoff region (Vbe is low so there is no base current. Ic is essentially zero so the collector current is 'cut off'. Another way to think about cutoff is that the transistor is switched off.

3. Saturation region: Ib is at or above the value at which collector current no longer increases. We can drive more Ib but Ic will remain at its maximum value. Another way to think about it is the transistor is fully switched on.

When used as a switch, a transistor goes in between saturation and cutoff; fully on or fully off, just like a switch.

The same thing goes for vacuum tubes, FET's, and several other semiconductor devices. SCR's, IGBT's, etc. are exclusively used as semiconductor switches, but those are meant for high power, not for computer circuits. Besides, no one even mentioned IGBT's so why am I even talking about them?
 
bjb said:
A transistor is not merely a simple switch. Certainnly it can be used as one, and it is used as a simple switch in computer circuits. Those links only address their use in computer circuits where they are used as switches.

SNIP

Besides, no one even mentioned IGBT's so why am I even talking about them?
Click to expand...

Those links were to show that they were semiconductors. Your of course correct. Most of the early uses were as amps (I remember the transistor radios I had as a youngster, long before home computers were even thought possible I'd say).

Of course most transistors used today are integrated into the CPU of the computers we use to use this forum (and such things) where they are used as on/off switches. Still through the use of semiconductors though;-)

Maybe you mentioned Insulated Gate Bipolar Transistors (IGBTs) because they are transistors ;)
 
Well, I had a whole reply typed but realized it's already been covered. So I deleted it. That was easy.
 
bjb said:
A transistor is not merely a simple switch.
Click to expand...
Yes, I know that. Being a computer geek, i don't tend to think of them as anything else.

That said, nothing anyone has posted has invalidated the fact transistors are not exclusively semiconductors; and that superconducting transistors exist.
 
luchog said:
Yes, I know that. Being a computer geek, i don't tend to think of them as anything else.

That said, nothing anyone has posted has invalidated the fact transistors are not exclusively semiconductors; and that superconducting transistors exist.
Click to expand...

Do you have a link to info on a transistor that is constructed of superconductive material, for other than the leads or perhaps the case?

The "Transistor Effect" is one caused by the properties of semiconductors to vary their resistance (via a voltage or signal input on the base in the case of standard transistors). Unless there is Superconductive material that can be semi-conductive at the same time, I don't see how the PNP or NPN regions can be both semi and super conductive. I'm sure (as I've found in other threads on other electronic devices) that there have been many advances in transistor design/manufacturing that I'm unaware of. And I won't deny the possibility, but so far no evidence has been provided to convince me that such a device is in existence.

I could easier conceive the idea of a superconductive material designed so that it could be made to go from a no conductive state to a superconductive state, acting as a pure switch. Having the varying resistance that allows transistors to act as amplifiers is a harder concept for me to grasp.

Anyway, I'd love to read about these superconductive transistors, and I eagerly await a link :-)
 
I don't know anything about these. If they count as what I think of as transistors, I'd guess that they might operate less like traditional junction transistors (the NPN and PNP kind) and more like field-effect transistors (FETs, used in just about all digital circuitry nowadays). I'd be interested to know what's going on in this area, it sounds -- begging y'all's pardon -- cool.
 
a few key concepts being overlooked

Folks
apparently many have not actually worked with superconductors or devices that use a superconductor. When you speak of high temp superconductors it is a relative term, normal YBCO used in SQUID's does not become superconductive until about 78K, optimum is from about 68 to 76 Kelvin... The critical temp is about 82-84K, meaning that you do not have zero resistance until the device is cooled below that critical temp. Further superconductors when fabricated into devices such as SQUID's, thin films shaped like a donut, cannot be directly connected to...as soon as you do you have a thermal loss pathway, critical temp is violated and you are back to a predictive material. The essence of a super cooled superconductor below it's critical temp is that there is now ZERO resistance...0... none...The loop cannot be connected to directly... you must use non contact, inferred measurement techniques or other attributes...for instance.. a superconducting loop when subjected to the smallest magnetic field imaginable will do what?.. remember zero resistance, a loop moving thru a magnetic field or some flux change.. causes a supercurrent...proportional to the magnitude of the magnetic field. but you cannot touch, or connect anything to the superconductor, as soon as you do...you lose the elusive property... so you find ways of inferring what is going on inside the superconducting loop by building next to it a device for instance that would be affected by this supercurrent flowing thru the loop.. hence the Josephson junction. but even that must be kept below the critical temperature...and then all the electronics for picking up the voltage changes and the wires etc must all be inside a good vacuum, typically at least 10 -5 torr. A SQUID at 74Kelvin with it's tuned electronics is so sensitive to magnetic fields that phase locked loops and other electronic means are needed to remove all the stray flux other than that which you desire to measure... a typical SQUID can detect magnetic fields 1/1000 that of the earths mag field. it can detect the DC magnetic field of a leaf as it dies, as the electrical nerve pathways decrease as the leaf dies. they are so sensitive that using a device laden helmet over a human head can record the most sublime of changes of human thought or pain or any stimulus desired. But they are also very difficult to implement or integrate into useful devices because of the very nature of the principles behind it. as we know from previous bright minds that figured out there are quantum effects that cannot be directly observed or measured because that effect affects the outcome/measurement... superconductors are the same...you cannot connect directly to them without thereby changing and losing the desired unique property of superconductance...the super current!!! there is very little if any design criteria out there today that dictates how circuits can be made to directly utilize the supercurrent that flows at the speed of light with ZERO resistance!! of and did I mention all the problems of the structures that make up the special nature of a superconductor material?? The problems are a mile long...the yield of a decent 35 micron diameter by 2 micron thick superconductor loop is about 10%...as soon as it is created it wants to destroy itself...the purity is critical... the level of oxygen to the .0001% is critical to maintain the properties. the slightest oxidation and it will not superconduct. They are not stable at room temperature.. and should be kept if at all possible at their critical operating temp of ~75Kelvin...just three or four temperature cycles to room ambient temps and back down.. will kill the junction.structure etc.
and by High temp superconductors... they are referring to a whopping high temp of 125K versus the current 75K typical...
 
LarsLuthor said:
Folks
apparently many have not actually worked with superconductors or devices that use a superconductor. When you speak of high temp superconductors it is a relative term, normal YBCO used in SQUID's does not become superconductive until about 78K, optimum is from about 68 to 76 Kelvin... The critical temp is about 82-84K, meaning that you do not have zero resistance until the device is cooled below that critical temp. Further superconductors when fabricated into devices such as SQUID's, thin films shaped like a donut, cannot be directly connected to...as soon as you do you have a thermal loss pathway, critical temp is violated and you are back to a predictive material. The essence of a super cooled superconductor below it's critical temp is that there is now ZERO resistance...0... none...The loop cannot be connected to directly... you must use non contact, inferred measurement techniques or other attributes...for instance.. a superconducting loop when subjected to the smallest magnetic field imaginable will do what?.. remember zero resistance, a loop moving thru a magnetic field or some flux change.. causes a supercurrent...proportional to the magnitude of the magnetic field. but you cannot touch, or connect anything to the superconductor, as soon as you do...you lose the elusive property... so you find ways of inferring what is going on inside the superconducting loop by building next to it a device for instance that would be affected by this supercurrent flowing thru the loop.. hence the Josephson junction. but even that must be kept below the critical temperature...and then all the electronics for picking up the voltage changes and the wires etc must all be inside a good vacuum, typically at least 10 -5 torr. A SQUID at 74Kelvin with it's tuned electronics is so sensitive to magnetic fields that phase locked loops and other electronic means are needed to remove all the stray flux other than that which you desire to measure... a typical SQUID can detect magnetic fields 1/1000 that of the earths mag field. it can detect the DC magnetic field of a leaf as it dies, as the electrical nerve pathways decrease as the leaf dies. they are so sensitive that using a device laden helmet over a human head can record the most sublime of changes of human thought or pain or any stimulus desired. But they are also very difficult to implement or integrate into useful devices because of the very nature of the principles behind it. as we know from previous bright minds that figured out there are quantum effects that cannot be directly observed or measured because that effect affects the outcome/measurement... superconductors are the same...you cannot connect directly to them without thereby changing and losing the desired unique property of superconductance...the super current!!! there is very little if any design criteria out there today that dictates how circuits can be made to directly utilize the supercurrent that flows at the speed of light with ZERO resistance!! of and did I mention all the problems of the structures that make up the special nature of a superconductor material?? The problems are a mile long...the yield of a decent 35 micron diameter by 2 micron thick superconductor loop is about 10%...as soon as it is created it wants to destroy itself...the purity is critical... the level of oxygen to the .0001% is critical to maintain the properties. the slightest oxidation and it will not superconduct. They are not stable at room temperature.. and should be kept if at all possible at their critical operating temp of ~75Kelvin...just three or four temperature cycles to room ambient temps and back down.. will kill the junction.structure etc.
and by High temp superconductors... they are referring to a whopping high temp of 125K versus the current 75K typical...
Click to expand...
A-freakin'-mazing!

Thanks for that LarsLuthor. Do you do some kind of advanced work with SQUIDS, or do you know all that just as a side interest?

You taught me more about the subject in one post than I had learned in years of trying to keep up with the related science. Why can't others on the "bleeding edge" be so concise?:)

WOW.:eye-poppi

Cheers,
Dave
 
if you only knew how much more there was..

CaveDave
I actually have to be kind of vague since some of this technology is being used by the NSA...I will give you a hint... there are a certain set of audio tapes that a certain past president had erased....and by integrating a SQUID device, for those not aware, Superconducting Quantum Interference Device, to a set of XY motors and some control software a SQUID was successfully used to recover the very smallest of remaining magnetic dipoles on those tapes....with amplifiers and other software the voices were recovered. They now know what was on those erased tapes!! One of our gov't agencies also uses controlled magnetic fields specially aligned and imparted to a special ink used on all the new currency... the ink is screened on and the sheets are then subjected to an oriented magnetic field while the ink is dried..locking that orientation into place,,,, the angle is not known for each batch but recorded so that when the secret service suspects counterfeting that is really good they can simply scan the bills with a SQUID device such as the Neocera Inc Magma C10 or C20 and read the orientation of the individual ferrite particles! Most folks have no idea of all the controls and levels of protection now integrated to our currency... this is one of them. The Magma C20's original purpose was to be able to find shorts inside of an electrical device such as a CPU, molded chipset, silicon etc...because when you energize the short circuit with an AC current and just a few micro amps of current you generate a magnetic field around the entire length of the circuit. You then scan the entire area mapping the B field, magnetic field intensity. when done that magnetic field image is transformed using traditional Maxwellian transforms to create the orthogonal electric field which is converted to the electric pathway... this image is then overlaid to the circuits design and it is easy to find where the current is flowing outside of the designed path. All this without any damage to the device, no cross sectioning or other destructive processes and has a precision of approximately 10 microns. This whole wonderful capability is made possible by a superconducting loop that is extremely sensitive to any and all magnetic fields...both the induced type, using the Frequency locked AC and any stray DC fields... for instance when scanning if the hood is left up and several feet away you move a 10 inch crescent wrench you can see the DC field sway, it is even worse if there is an elevator anywhere within a few hundred feet... the mass of steel moving creates a magnetic flux and this can be detected on the DC side...but the electronics are so designed to remove stray fields or to simply lock to a specific frequency.
 
LarsLuthor said:
CaveDave
I actually have to be kind of vague since some of this technology is being used by the NSA...I will give you a hint... there are a certain set of audio tapes that a certain past president had erased....and by integrating a SQUID device, for those not aware, Superconducting Quantum Interference Device, to a set of XY motors and some control software a SQUID was successfully used to recover the very smallest of remaining magnetic dipoles on those tapes....with amplifiers and other software the voices were recovered. They now know what was on those erased tapes!!
Click to expand...
I had long known that erased information on almost any medium left some traces, but I didn't know SQUIDS could be used to recover it in such a delicate manner. I assume the X-Y positioning and the 10 micron range resolution would allow statistical analysis to pull the signal out of the noise and recover the original analog recording.

One of our gov't agencies also uses controlled magnetic fields specially aligned and imparted to a special ink used on all the new currency... the ink is screened on and the sheets are then subjected to an oriented magnetic field while the ink is dried..locking that orientation into place,,,, the angle is not known for each batch but recorded so that when the secret service suspects counterfeting that is really good they can simply scan the bills with a SQUID device such as the Neocera Inc Magma C10 or C20 and read the orientation of the individual ferrite particles! Most folks have no idea of all the controls and levels of protection now integrated to our currency... this is one of them.
Click to expand...
They have publicized a dozen or so security features in the new currency, and I knew there had to be a dozen or more not revealed. I trust you have not broken any confidentiality agreements by revealing that.:) Such a sensitive detection method would serve well to locate counterfeits.
Now, if we could use the technology to prevent identity theft and create secure ID cards, a huge business opportunity would blossom.

The Magma C20's original purpose was to be able to find shorts inside of an electrical device such as a CPU, molded chipset, silicon etc...because when you energize the short circuit with an AC current and just a few micro amps of current you generate a magnetic field around the entire length of the circuit. You then scan the entire area mapping the B field, magnetic field intensity. when done that magnetic field image is transformed using traditional Maxwellian transforms to create the orthogonal electric field which is converted to the electric pathway... this image is then overlaid to the circuits design and it is easy to find where the current is flowing outside of the designed path. All this without any damage to the device, no cross sectioning or other destructive processes and has a precision of approximately 10 microns.
Click to expand...
Cool. I have for years wanted to build a probe to track down the component on a PCB that was drawing too much current, but haven't gotten past the need to surround the conductor or impose a varying signal over the DC. I guess if I had a few (or few hundred) grand to blow this would be doable.

This whole wonderful capability is made possible by a superconducting loop that is extremely sensitive to any and all magnetic fields...both the induced type, using the Frequency locked AC and any stray DC fields... for instance when scanning if the hood is left up and several feet away you move a 10 inch crescent wrench you can see the DC field sway, it is even worse if there is an elevator anywhere within a few hundred feet... the mass of steel moving creates a magnetic flux and this can be detected on the DC side...but the electronics are so designed to remove stray fields or to simply lock to a specific frequency.
Click to expand...
Sort of the DC or low frequency (magnetic) version of the person moving in the room or truck on the road changing the reception on a TV or radio in a weak signal area. Or capacitive detection of movement and presence.

I assume these detect static flux as opposed to a moving detector or varying field being required.

I bet it would be fun to work with you as your technician.

You continue to amaze (and educate) me.

Cheers,
Dave

ETA: Are SQUIDS the same devices the military uses (boom mounted on a large airplane) to detect submarines by the distortion of the earth's field, or was that an older generation of detector? IIRC they had to be at liquid nitrogen temps to work.
 
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