User:Circuit dreamer/Negative resistance

New suggestions for improving the Negative resistance article







Some history in retrospective
In the end of 2006, I made a major edit of the existing article by presenting a new fresh viewpoint at the negative resistance phenomenon. My idea was to unveil the mystery of this strange, odd and unrecognized phenomenon, to show in a human friendly manner that there was nothing mystic, magic and supernatural behind it... Circuit-fantasist (talk) 09:18, 13 January 2009 (UTC)

Now, two years later, as I can see, I have not succeeded in doing that:( No one has appreciated my insights into the phenomenon although they are unique and based only on human common sense; instead, there are only negative reactions to them. I can understand these Wikipedians as I know people do not like someone to express own ideas even if they are more than obvious. This upsets their mental equilibrium and they react to this "intervention" trying to redress the "balance". The sorry truth is that people do not prefer to use their own brains; contrary, they like "nameless" facts or speculations expressed by famous reputable persons even when they have not explained anything. People adopt willingly, use and benefit from nobody's ideas. I have known this truth from my experience since, being an individualist who has own philosophy about circuit phenomena, I have been bearing the reactions of people around me through my life. I have even reserved a special page (Why creative persons are unhappy) about these human "phenomenon" in Circuit idea wikibook.

As I can see, the idea behind the (reasonable) suggestions above that are expressed through these two years is: "Let some super-expert in this area get the absolute true from some completely reputable sources and write it fully encyclopedically". It sounds wonderful but...no one has still done it... just because the simple fact - there are not such experts, the true is hidden and there are not such sources! There are only capable wikipedians that can rewrite the article encyclopedically... but they do not like to do it. What do we do then?

Of course, it would be wonderful if there were such nice places on the web where to get the absolute truth from. And, more generally speaking, it would be wonderful, if we live in a well-arranged and a predictable world where all is clear and we know exactly what to do. For example, then we, ordinary human beings, will know whether or not we should fall in love and whom to fall in love:) Also, if you have graduated a reputable university and then if you are a reputable professor, you will know all the secrets of electronic circuits and will show them to students, etc. Unfortunately:) or maybe fortunately, I think:), quite frequently there is not any logic in our world... and exactly this feature is its charm! I am 54-years old man and I know I should not fall in love but I have fallen in love with woman that I have never supposed. I have not graduated a reputable university but I have managed to reveal the secrets of electronic circuits while for thousands graduates from such universities circuit phenomena look like "black magic". I am (still:) not a reputable professor but I reveal the secrets of electronic circuits to my students while thousands professors do not show the truth about circuits as just they do not know it. Further, I know I should not devote myself to this thankless task - revealing the ideas behind circuits and I should not contribute the non-profit Wikipedia and Wikibooks; instead, I have to write dull (pseudo)scientific articles to climb up the academic ladder. And finally, I know I should not expose my new insights into negative resistance phenomenon on this page and I should not take up rewriting, restructuring and tiding it up as this initiative will bring about me only troubles; instead I should place them on my site of circuit-fantasia.com or in Circuit idea or in papers or a book...everywhere only not here...but yet I resume here this discussion...

Doing that, I do not cherish the hope that some reputable professionals will support me; instead, I expect sooner they will try to depress me and to kill my enthusiasm (I recommend a list of sophisticated "idea-killing" techniques to help them:) I can understand all these people - reputable engineers, designers, lecturers, authors. It is pity for them to realize they have spent a lot of money to educate and then many years of time to apply their knowledge... and now to realize they do not actually know the truth about the phenomenon. Only imagine how a famous old professor that has been teaching circuitry to the poor students decade of years on end will react if he/she realizes the naked truth?!? Can you guess what he/she will do after reading these speculations? I can... Circuit-fantasist (talk) 15:13, 11 January 2009 (UTC)

The great voltage compensation idea
(see also the discussion about the relevant Circuit idea story)





I think revealing the secret of circuits with voltage compensation is my first great achievement in teaching analog electronics (saying circuits with voltage compensation I mean op-amp circuits with parallel negative feedback or, in other words, all these popular op-amp inverting circuits with parallel negative feedback - an inverting amplifier, an integrator, a differentiator, a logarithmic converter, etc.) I grasped this powerful, intuitive  and extremely simple idea in the end of 80s and from then I have been creating a great many various materials, in order to popularize it. Finally, I decided to generalize all my insights about the great idea into one "philosophical" story and started a discussion in Circuit idea wikibook a month ago. Well, here is the secret of these legendary circuits:

General idea. Circuits with voltage compensation consist of three components connected in series: a passive Element 1, a passive Element 2 and a "helping" voltage source VH. The Element 1 converts the exciting (input) voltage V into a current I and the Element 2 converts back the current into a voltage drop VE2; we need it... but it disturbs the current. So, the "helping" voltage source VH compensates the "disturbing" voltage drop VE2 by adding the same voltage to the exciting voltage source V; as a result, the Element 2 is "neutralized" and the current depends only on the exciting voltage and the Element 1. If we need a current output, we connect the current load in the place of the Element 2; if we need a voltage output, the compensating voltage VH can serve as a perfect "mirror" output voltage - powerful, grounded and inverting.

Implementation. Most of the circuits with voltage compensation are implemented as op-amp circuits with parallel negative feedback where the op-amp (including the power supply) serves as a "helping" voltage source. It compensates the "disturbing" voltage drop across the Element 2 by adding the same voltage VH = VE2 to the exciting voltage source V. The compensating voltage is negative with respect to the ground; so, all these op-amp circuits are inverting. Circuit-fantasist (talk) 15:14, 11 January 2009 (UTC)



Another great idea: negative impedance
I have finally realized how to expose the great idea of negative impedance by using lucid explanations based on human common sense and intuition. IMO, in the beginning, we have to show in the most general way what the ordinary "positive" resistance is and what the odd negative resistance is by comparing the two electrical attributes. For this purpose, we may reason as folows.

What a "positive" impedance is...
In electrical circuits, passive elements (resistors, capacitors and inductors) impede current by their inherent resistance, capacitance and inductance (impedance is the combination of them). As a result, voltage drops appear across the passive elements that represent the energy losses in them. Passive elements absorb this energy from the exciting electrical source: resistors dissipate energy from them to outside environment while capacitors and inductors accumulate energy into themselves. For the purposes of this article it is no matter if passive elements dissipate or accumulate energy; it is only important they absorb energy.









''I cannot stop using a funny analogy to picture these properties (don't worry, I will not place it in the main article:) You know, in every society, there are such bad people that steal. Some of them spend immediately what they have stolen while others steal up the swag. But for us (the victims) it is no matter if they spend or store the swag; for us it is only important that we have lost our property:(''

In circuitry, we may connect elements in series or in parallel or mixed. For example, if we connect a resistor R in series with a load (Fig. 3a), a voltage drop VR = R.I that is proportional to the current appears across the resistor. If we connect a capacitor or an inductor, voltage drops changing through time appear across them.

Conversely, if we connect the resistor R in parallel with the load (Fig. 3b), a current IR = VL/R that is proportional to the voltage flows through the resistor. If we connect a capacitor or an inductor, currents changing through time flow through them. Circuit-fantasist (talk) 15:14, 11 January 2009 (UTC)

Let's see the graphoanalytical interpretation of the circuit operation by superimposed IV curves on Fig. 4. When the input current/voltage varies, the crossing operating point slides over an IV curve representing the "positive" resistance. It is a real IV curve having a positive slope and passing through the origin of the coordinate system.



...and what a "negative" impedance is
Elements with "negative" impedance do the opposite - they inject energy into electrical circuits. While passive elements with "positive" impedance absorb energy from the input source (they are loads), the elements with "negative" impedance add energy to the input source (they are sources). While voltage drops appear across "positive" elements, negative elements produce voltage; while "positive" elements sink current, negative elements produce current. Only, they are not ordinary, steady sources; they are varying sources (voltage sources whose voltage across them depends on the current through them or current sources whose current depends on the voltage across them).









Above (Fig. 3), we connected the "positive" resistor R in series with the load; so, a voltage drop VR = R.I that is proportional to the current appeared across the resistor. Let's now connect a negative resistor -R in series with the load (Fig. 5a). As a result, a voltage VH = VR = R.I that is proportional to the current appears across the negative resistor. Only, while above the resistor R detracts the voltage V from the input voltage (V is a voltage drop), here the negative resistor -R adds the same voltage V to the input voltage (here V is a voltage). The element named "resistor" is really a resistor while the "negative resistor" here is actually a voltage source, whose voltage is proportional to the current passing through it. If we connect a negative capacitor or a negative inductor, voltages changing through time appear across them (the negative elements generate these voltages).

''A negative resistor can be a voltage source, whose voltage is proportional to the current passing through it (a two-terminal current-controlled voltage source). This is a current-driven negative resistor.''

Contrary, if we connect the negative resistor in parallel with the load (Fig. 5b), the same current as above IR = VL/R that is proportional to the voltage drop across the load flows through the negative resistor. However, while above the resistor R sinks the current from the input current (diverts it from the load current), here the negative resistor -R ads the same current to the input current (injects an additional current into the load). If we connect a capacitor or an inductor, currents changing through time flow through them.

'' A negative resistor can be also a current source, whose current is proportional to the voltage across it (a two-terminal voltage-controlled current source). This is a voltage-driven negative resistor.''

Let's see the graphoanalytical interpretation of the circuit operation by superimposed IV curves on Fig. 6. When the input current/voltage varies, the voltage/current source representing the negative "resistor" changes its voltage/current. As a result, its IV curve moves and the crossing operating point slides over a new dynamic IV curve representing the negative resistance. It is not a real IV curve; it is an artificial, imaginary IV curve having a negative slope and passing through the origin of the coordinate system.

Circuit-fantasist (talk) 10:55, 24 January 2009 (UTC)



How to create the simplest current-driven negative impedance element...
Negative impedance elements are wonderful... but there is only a little problem:) with them - there are not such elements in nature; there are only ordinary, passive elements with "positive" impedance. So, we have to make them... and this is the most interesting part of this discussion. Well, how do we create negative impedance elements?

The idea is extremely simple, clear and intuitive; it is so plain that it is even... invidious:) Only, I don't know why I needed years of time to realize it as all we need to grasp it is only our human common sense! I began thinking about negative resistance phemomenon in the early 90s... and realize this simple truth only in the end of 2008! Why the simplest things in this world are the most unintelligible and ununderstandable? But let's begin thinking!

Well, we have an element with "positive" impedance (a resistor, a capacitor or an inductor) but we need an element with negative impedance (a negative resistor, a negative capacitor or a negative inductor). A voltage drop appears across the "positive" element that depends on the current passing through it in a some definite way (linear, non-linear or time-dependent); the same voltage (depending in the same way on the current) has to appear across the negative element. What do we have to do then?

...without using a negative feedback...
''I cannot stop relying again on the funny analogy above to extract the solution (don't worry, I will not place it in the main article:) Imagine there are bad people that steal but we need good people with the opposite behavior (to grant instead to steal), in order to "neutralize" the wickedness of the bad people. But imagine there are not such people; so, we have to create them. For this purpose, we take some bad person as an "original" and make an inverse "copy" of his/her behavior. The paradox is that, in order to make goodness, we need wickedness! But what do we do if there are not good people:)?''



Of course, we have only to "copy" the voltage drop across the "positive" element and to "insert" this voltage into the circuit so that to "help" the input voltage source! All we need to do this donkey work is only a bare voltage follower (including its power supply) - Fig. 5! In this arrangement, the voltage drop across the "positive" element PE2 is the "original"; the voltage across the negative element NE2 is the "mirror copy".

Eureka! We have invented the simplest technique for creating a negative impedance; we know already what the simplest negative impedance element contains:

The simplest element with negative impedance consists only of two components: an element with "positive" impedance and a voltage follower that is the actual negative impedance element.

Note the "positive" impedance element is necessary but it does not belong to the negative impedance element in this arrangement (compare with the 2-terminal negative impedance element below):

Let's look at this idea from another viewpoint. The current-driven negative impedance element is actually a current-controlled voltage source with a specific relation between the voltage and current (linear, non-linear or time-dependent). So, it has to measure in some way the current flowing through it and to convert it to a voltage according to the desired function. For this purpose, the negative impedance element needs a functional current-to-voltage converter and the positive impedance element serves exactly as such an exotic converter.

The simplest negative impedance element exploits the available "positive" impedance element as a functional current-to-voltage converter.

Is there a feedback in this arrangement? There is only a slight positive feedback as we have not a large amplification. Let's consider it. When we increase the input voltage V, the current increases and the voltage drop VPE begins increasing as well. The voltage follower copies and adds it to the input voltage. As a result, the current increases thus incrasing the voltage drop.

We just need a bare voltage follower; it might be a poor transistor amplifier with amplification 1... but it has to amplify exactly 1 time. The only way of doing that is the ubiquitous negative feedback... Circuit-fantasist (talk) 07:12, 13 January 2009 (UTC)





...by using a negative feedback.
Of course, negative feedback is the most perfect technique for making voltage followers. In this arrangement (Fig. 6), we have made an op-amp compare its output voltage VNE (by subtracting) with the voltage drop VPE2 across the positive element and change it so that the difference between them is always (almost) zero. As a result, the op-amp output voltage is a copy of the voltage drop across the positive element. Note the op-amp may have a bare single-ended input as its input voltage - the difference VPE2 - VNE, is measured regarding to the ground.



Putting into practice the simplest negative impedance element
The amazing feature of this arrangement is that negative impedance "neutralizes" the same positive one; as a result, the whole combination of the two elements has zero total impedance. This is the most important use of the negative impedance phenomenon - to destroy, remove, annihilate, neutralize the ordinary positive impedance by an equivalent negative one. For example, all the circuits with voltage compensation (op-amp inverting circuits) exploit this technique (see below). Accordingly, there is zero voltage drop across this zero impedance element and the famous virtual ground (great circuit phenomenon) appears above the positive element 2. The virtual ground represents the result of the "neutralization".



In order to see the benefits of using the simplest negative impedance element, let's discover a well-known problem from circuitry - how to make perfect voltage sources with zero internal resistance. Real voltage sources have some internal resistance; in addition, there is some line resistance between the source and the line. As a result, the load voltage droops when the source is loaded as disturbing voltage drops appear across the internal and line resistances. That is why, in electronics, we frequently need voltage sources and conductors having zero internal "positive" resistance.

The classical solution is to buffer the imperfect voltage source by a powerful voltage follower. But we have to place the buffer at the end of the line, near the load; frequently, this is just impossible. What do we do then?

The more exotic and sometimes, more useful solution is to compensate the internal resistance by an equivalent negative resistance. For this purpose, we might use the simplest negative resistor that we have created above, i.e., a transimpedance amplifier with resistor Ri (the internal resistance). In this arrangement (Fig. 7), the op-amp compensates the voltage drop across the "positive" resistance Ri by adding the same voltage in series to the input voltage source.



Comparing the general ideas...
A month ago, I started a discussion about the great voltage compensation idea in Circuit idea wikibook. I used Christmas holidays to rationalize all I have known and collected about this great phenomenon through years. On December 31, at the top of the New Year, strolling along the park, thinking aloud and recording my thoughts about the voltage compensation idea, I gained suddenly a new insight into this great phenomenon. I realized that the "helping" voltage source in this arrangement acts actually as an element with negative impedance and more particularly, in all the op-amp circuits with parallel negative feedback (op-amp inverting circuits), the combination of the op-amp and the power supply acts as a negative impedance element!





Look again t Fig. 1 and Fig. 8 to compare the two great ideas and to convince yourself that they are absolutely identical.

Voltage compensation (see the copy of Fig. 1 on the left) means to compensate the "disturbing" voltage drop VE2 across the passive Element 2 by adding the same voltage to the exciting voltage source V by a "helping" voltage source. As a result, the Element 2 is "neutralized" and the current depends only on the exciting voltage and the Element 1.

Negative impedance (Fig. 8) means to compensate the "disturbing" voltage drop VE2 across the Element 2 with "positive" impedance by adding the same voltage to the exciting voltage source V by a "mirror" element with negative impedance. As a result, the "positive" impedance Element 2 is "neutralized" again and the current depends only on the exciting voltage and the Element 1. Now, don't you think negative impedance is voltage compensation and v.v., voltage compensation is negative impedance?

In electronic circuits with voltage compensation, the compensating voltage source acts as a negative impedance element and v.v., in electronic circuits with negative impedance, the negative impedance element acts as a compensating voltage source.

'In all the circuits with voltage compensation, there are two elements connected in series: one with "positive" impedance and other with the same but negative one. The total impedance of this combination is zero.'



...and the specific op-amp implementations




Now, should I convince you very much that in all these popular op-amp inverting circuits the op-amp, in combination with the power supply, acts actually as a negative impedance element? See for example the legendary circuits of transimpedance amplifier, inverting amplifier, diode antilogarithmic converter, capacitive differentiator and inductive integrator (Fig. 9). All they contain various elements (a resistor, a diode, a capacitor and an inductor) acting as Element 1 from the generalized voltage compensation circuit (Fig. 1), an ordinary "positive" resistor R acting as Element 2, an op-amp and a power supply. Here, the combination of the op-amp and the power supply acts as a negative resistor with negative resistance -R that "neutralizes" the "positive" resistance R (the negative resistor -R adds as much voltage as it loses across the positive resistor R).





Or see another legendary circuit - the capacitive op-amp inverting integrator (Fig. 10). Here, the combination of the op-amp and the power supply acts as a negative capacitor with negative capacitive reactance that "neutralizes" the "positive" capacitive reactance (the negative capacitor adds as much voltage as it accumulates in the positive capacitor).

Similarly, in the circuit of the op-amp inverting logarithmic converter (Fig. 11), the op-amp acts as a negative diode; it adds a forward voltage VF to the input voltage instead to subtract a voltage drop from the input voltage. In the circuit of the op-amp inverting inductive differentiator (Fig. 12) the op-amp acts as a negative inductor, etc. So, we may generalize this great insight into op-amp inverting circuits with negative feedback as a final conclusion:

'In op-amp circuits with parallel negative feedback (op-amp inverting circuits), the combination of the op-amp and the power supply acts as a negative impedance element. It is a "mirror" copy of the positive impedance element connected between the op-amp's output and the inverting input. The two elements (the "positive" and the negative one) are connected in series so that the total impedance of this combination is zero.'



What does this viewpoint mean?
Just imagine what this negative impedance viewpoint at op-amp inverting circuits means! Now, negative impedance does not look already as a "black magic"; it is not already that mystic, odd, strange, exotic and ununderstandable circuit phenomenon! No one can already take unfair advantage of it as it is an everyday phenomenon that we may see in every circuit with parallel negative feedback! We have unveiled the mystery of negative impedance; we are just the boy from Andersen's story who says, "The King is naked!":)



What the problem is
Finally, we have arrived at the most interesting part of our discussion. Here, we will unveil the mystery of the conventional negative impedance elements - the so called negative impedance converters (NIC). IMO, they are the most interesting, odd, strange and even "mystic" electronic circuits, which are still unexplained; they are real nightmares for students and for their teachers:) I have not still met some "human-friendly" explanations of this legendary circuit on the web or in the books (if you have found, let me know). Even the famous Mr. Horovitz has not explained (although mentioned) it in his bestseller The Art of Electronics (see page 251). Instead, he has afforded this opportunity to his students; maybe, he had hoped they would help him:)?

Well, what the problem is? We have already made the simplest element with negative impedance (Fig. 5). Then, why do we need another negative impedance element?

See again Fig. 7 where we have used a transimpedance amplifier to make a perfect voltage source with zero internal resistance. Thes solution seems perfect but it has one great disadvantage: the op-amp needs a third wire to measure the internal voltage drop; sometime this is impossible (in the case of compensating the internal resistance) or inconvenient (in the case of compensating the line resistance). What do we do then?

The general idea
Obviously, we have to create a more sophisticated 2-terminal negative impedance element so that we can insert it at any place along the line. How do we make it? Maybe, the funny analogy above will give a hint to us?

'' Well, imagine the bad person acting as an "original" is far away and we cannot observe his/her behavior, in order to make an inverse "copy". What do we do then? Of course, we may take another bad person that is near at hand as an "original" and make again an inverse "copy" of his/her behavior. But now it has to be 2 times bigger "copy", in order to "neutralize" the wickedness of the two bad persons!



Let's use this clever trick to create a true 2-terminal negative impedance element for the same purpose - to make a perfect voltage source with zero internal resistance. Now, we need two components (Fig. 13): an additional near resistor with "positive" resistance R = Ri and a voltage amplifier with amplification K = 2 (including its power supply). The amplifier produces two times higher voltage; half the voltage compensates the voltage drop across the near resistor R = Ri; the other half the voltage compensates the voltage drop across the remote resistor Ri. As a result, the total internal resistance is zero.

Eureka again! We have invented another clever technique for creating a negative impedance; we have already known what the negative impedance element contains:

The element with negative impedance consists of two components: an element with "positive" impedance and a doubling voltage amplifier.

It is a paradox but it is true: Every element with negative impedance contains an element with the same "positive" impedance.

As above, this current-driven negative impedance element is actually a current-controlled voltage source with a specific relation between the voltage and current (linear, non-linear or time-dependent). It needs a functional current-to-voltage converter to measure the current flowing through it. Above, we used the accessible "positive" impedance element as such an exotic converter. Here, we have not such an element; so, we connect another identical "positive" impedance element (a duplicate) acting as such a converter.



The implementation


We have to make the op-amp produce two times higher output voltage than the "mirror" voltage drop across the "copy" resistor R = Ri. The op-amp will do this "magic", if we make it compare 1/2 of its output voltage with the "mirror" voltage drop across the "copy" resistor. For this purpose, let's connect a voltage divider consisting of two equal resistors R between the op-amp output and the non-inverting input (Fig. 14).



General idea






Implementation






Revealing the truth about Deborah Chung's "apparent negative resistance"
(see also the relevant Circuit idea story)

In this section I will unveil the mystery behind the Chung's experiment - the greatest misconception in the area of the negative resistance phenomena. For a start, I have placed here a few demonstrative drawings to provoke your imagination. Do not take them to heart; maybe there are some mistakes there:) Circuit-fantasist (talk) 17:12, 8 January 2009 (UTC)

The motivation
A week ago, I received an email from Robert Michaels; he said he was impressed by my discussions about the negative resistance phenomenon. He has made the observation that diodes and other components in conventional circuits, which are known to generate negative resistance also generate undesireable thermal losses in heat (inefficiency) and he has supposed that Chung's apparent negative resistance findings in carbon fiber may be WITHOUT any thermal losses. But here I would like to say that he provoked my interest in Chung's "apparent negative resistance" as he was speaking about it with respect.

Realizing the naked truth
I read closely the section and the old discussion about this scientific sensation where I found interesting speculations (e.g., the "bridge" and "transresistance" viewpoints). For my great surprise, I did not find any negative resistanse in this arrangement - neither absolute nor differential! I did not find even the more ordinary dynamic resistance in this arrangement; imagine there was only an odd carbon-fiber network having an ordinary, bare, "19th century" ohmic resistance! I had the feeling I was seeing some of Edison's carbon microphone experiments... Circuit-fantasist (talk) 07:35, 9 January 2009 (UTC)

Presenting the carbon fiber network as a bridge circuit
Finally, I realized this exotic carbon fiber arrangement acts as some kind of bridge circuit formed by two kinds of resistances - steady carbon fiber resistances R and varying contact resistances Rc (you may find also the same "bridge viewpoint" in the old discussion). In some way (for now unrecognized), it turned out they were connected in the opposite bridge legs. By the way, a long time ago I was impressed by this remarkable feature of the bridge circuit - to reverse the output voltage. It can do that because the output voltage is a differential quantity. It is "flying"; it is the difference between the two grounded voltages - VR and VRc. Depending on the proportion between R and Rc, this difference may be zero (R = Rc), positive (R > Rc) or negative (R < Rc). And, if we assume the current IIN is the input quantity and the voltage VOUT is the output quantity, we may think of this device as a zero, a positive or... a "negative" transresistance converter:) But this is not a negative resistance; this is not even a resistance; it is the more abstract transresistance (you may find also the same "transresistance viewpoint" in the old discussion)! Circuit-fantasist (talk) 08:28, 9 January 2009 (UTC)



How the carbon fiber network does this "magic"
Once revealed the general idea behind this experiment (to be more precise, the absence of any idea) I loosed any interest in thinking about it. I knew what the carbon fiber network actually did but yet.. it was a great challenge to understand how the carbon fiber tangle did this "magic". And I began thinking again... Circuit-fantasist (talk) 08:47, 10 January 2009 (UTC)

No pressure is applied




Well, let's look at Fig. 20 and begin thinking together. The two laminae are connected to each other by great number of contact resistances Rc; you may think of the central cross area as a kind of cube. The current flows from the top lamina that is positive to the bottom lamina that is negative. So, the upper point B is positive and the lower point D is negative; the output voltage VOUT has a positive polarity as it is shown on the picture. The "resistance" is positive: R = VOUT/IIN > 0.



A big pressure is applied




Now, let's look at Fig. 21 and continue thinking together. Now, a big pressure is applied; so, the two laminae are connected to each other by great number of zero contact resistances. In this case, the central cross area is a flat grid. The current goes into the left side of the grid, turns to the bottom and goes out from the bottom side of the grid. In this situation, the point D stays closer to the positive terminal of the input voltage source and the point B stays closer to the negative terminal. So, the point D is more positive than the point D and the output voltage VOUT has a negative polarity as shown on the right picture. As a result, like Professor Chung, we might draw a wrong conclusion that the "resistance" is "negative": R = -VOUT/IIN < 0 and to begin making a stir.

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A moderate pressure is applied
Finally, we may suppose there is some middle pressure between the extreme limits when the output voltage VOUT is zero. The "resistance" is zero as well: R = VOUT/IIN = 0.

Conclusions
Then, what has Professor Deborah Chung actually observed? What has she done? Let's try to answer...

It is clear she has made some kind of exotic bridge circuit depending on applied pressure. Indeed, this carbon fiber arrangement can serve as an odd voltage-to-voltage converter, a current-to-voltage converter or as a (poor) pressure-to-voltage converter (a pressure sensor). But IMO, there are no any benefits of using it; contrary, there are many losses... Only see in Google how many people are involved in this useless discussion and how much efforts, time and money are wasted... It is a pity to see how people relying more on "reputable" sources than on their own human common sense are misleaded!

There is not any connection between this experiment and the negative resistance phenomenon.

There is not any apparent, absolute, differential or even dynamic resistance in this arrangement; there is only ordinary, bare, "19th century" ohmic resistance.

Chung's carbon fiber network behaves actually as an odd bridge circuit depending on the applied pressure (like the ordinary tensometric bridge circuit).

It seems Chung's experiment is the greatest misconception in the area of the negative resistance phenomena.

Circuit-fantasist (talk) 08:51, 9 January 2009 (UTC)

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