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watson.fawkes
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Quote: Originally posted by Rosco Bodine  | | You are failing to account for the leakage current. There is a makeup current flow which has to be occurring, and surpassing the leakage current in
value in order for a sufficient gate charge potential to be maintained, or increased, and the only path for that current flow is through the air gap.
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You're still wrong about a current across an air gap, and you're grasping at straws now. If you put a
resistor across a capacitor, it discharges the capacitor, removing the field across the capacitor. This eventually turns off the MOSFET when the
potential difference drops below the device's threshold voltage. So, even if the electric field was initially large enough to turn on the MOSFET, it
eventually turns off. How long that takes will depend a lot on the geometry of the device. Initial charge rearrangement from antenna to gate is almost
instantaneous. Charge rearrangement across the resistor formed by the gate insulation takes a lot, lot longer.
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franklyn
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I have 4 ionizers made by 3 different manufacturers in my home that eject ions into the air.
www.enotes.com/topic/Biefeld%E2%80%93Brown_effect
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Rosco Bodine
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@watson.fawkes, Keep talking. You are coming up with examples which support my belief that current is flowing across the air gap, and your example of
a bleeder resistor across a capacitor is illustrative of the reality of a non-idealized real world capacitor being in actuality parallel with a
resistance which represents the leakage path through its not quite perfect dielectric. There is also an inductance in series which is a small value
as well, so the capacitor may be regarded only in theory and for most practical purposes is only stipulated to be an idealized
capacitor, behaving only as a capacitance in a circuit since the capacitance parameter is what predominates. Capacitors in high voltage power
suppplies often have a bleeder resistor across their terminals as a safety measure to assure faster "self-discharge" of the capacitor when the
equipment is turned off. Otherwise, there is an electrocution hazard presented by a slowly decaying residual potential left residing across that
capacitor. Conversely the effect while the capacitor is wished to be charged to its required potential in powered on operation, a "makeup current"
must be supplied to the parallel RC device pair to offset the dissipation loss caused by the parasitic resistance of the bleeder resistor across the
capacitor.
http://en.wikipedia.org/wiki/Electric_current
Anyway, I said earlier that I have not put this scenario through its experimental paces to see what final conclusions are reasonable. It would be
easy enough to test to see by experiment if the switching on of the MOSFET through whatever mechanism across the airgap will hold steady in its ON
condition if the "transmitting" test lead is simply clamped in a fixed position with respect to the "antenna" lead to the Gate. What occurs during the
time elapsing thereafter will tell the tale for what is occuring. A variable capacitor would make an electrically and functionally equivalent
substitute
for the fingertip and airgap and antenna so this would be a convenient test device for series connection of the Gate lead
to the positive battery terminal with the variable capacitor interposed in series.
If the ON condition for the MOSFET maintains steady or even gradually increases, then clearly the leakage current for the Gate is being exceeded by
conductance of the air. And if the MOSFET gradually turns off (even though the "transmitter" lead is still present), then the transient charge
accumulation which first turned ON the MOSFET could reasonably be explained as a transient having originated from the induced current flow caused by
the initial establishment of capacitive coupling through the airgap, a coupling which was transiently conducting only during the establishment of the
field across that airgap.
If ....., now there is a another heck of a word huh. 
Please somebody confirm that my proposed experiment is valid .....since reportedly I'm so ignorant and arrogant and lazy it could be considered
presumptuous of me not to run this proposal past my betters just to confirm whether or not I'm right thinking about something as complicated as a
science experiment
Damn, I'm getting so senile and feeble minded I've misplaced my Americium 241 ....and I'm thinking it might make an interesting cosmic ray enhancing
addendum to this proposed experiment
[Edited on 9-1-2012 by Rosco Bodine]
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Morgan
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I have used a tiny negative ion generator not much bigger than the nine volt battery it runs on to charge my electrophorus from time to time. Funny
too how much of a charge you can put/store in acrylic.
As an aside, I wish I could find a way to store and prevent the charge from leaking with my simple leyden jars charged with a piece of PVC tubing and
paper towel. So far have managed a 13 inch spark. But I wonder if playing with more dielectrics or by using some characteristics/concepts of the
mosfet I could improve on things? Under the 4 liter LDPE bottle is a sheet of teflon and scattered about other sheets/squares of acrylic,
polycarbonate, and PVC to prevent premature arcing. The teflon also seems to help increase the spark distance the best, it's also one of the most
negative substances in the triboelectric scale. You can hear it crackle as I charge up the Leyden jar. It's really hard to construct a capacitor that
will hold such high voltage without it leaking as fast as you can charge it with these simple means. I have also tried layering under the leyden jar,
using the various dielectric plastic sheets I have. The bottle is filled with water and a combination of NaCL and Epson salt.
Electrophorus made from a Garrard Turntable.AVI
http://www.youtube.com/watch?v=4k0haLECQVY
Thirty Three Centimeter Spark from a Simple Experiment.AVI
http://www.youtube.com/watch?v=KMQYp218a-Q
Still sparking twenty minutes later.
http://www.youtube.com/watch?v=9Po35g23fYI&feature=relat...
http://www.youtube.com/watch?v=8biE3uP_nOI
Fellow gets shocked making a Liichtenberg Figure "I told you, I told you" ha
Making Electron Trees with a Linear Accelerator
http://www.youtube.com/watch?NR=1&v=xoKloJwmLjI
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watson.fawkes
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| Quote: Originally posted by Rosco Bodine | | It would be easy enough to test to see by experiment if the switching on of the MOSFET through whatever mechanism across the airgap will hold steady
in its ON condition if the "transmitting" test lead is simply clamped in a fixed position with respect to the "antenna" lead to the Gate.
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By all means do the experiment. Limit yourself to the 12 volts you've initially proposed. Beware that you
may well be in the triode operation region of your MOSFET and it may well not saturate (the "ON condition"). And you'll likely need a transistor with
a low threshold voltage to even see that. But I'll be waiting for you to prove your original claim: | Quote: Originally posted by Rosco Bodine | | There has to be a transfer of electrons through the air in the experiment I described in order to accumulate the charge on the Gate.
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It seems like you're going to need a femto-ammeter on the opposite terminal in order to show there's a
current flow through the air. How do you propose to measure this air-current?
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Rosco Bodine
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This has been interesting discussion, and after thinking about the circuit scenario I described for the MOSFET, I am going to concede you are correct
about the electrostatically induced dipole being what accounts for the MOSFET being switched ON by the simple approach of an ungrounded fingertip
within inches of the Gate. There is actually a series combination of two electrostatic fields and capacitances set up in that scenario I have
described for the MOSFET. As for 12 volts effecting enough potential through inches approaching a foot or more of airgap to be the operative stimulus
for direct charge transfer....no it would not be working that way at 12 volts, maybe a few thousand volts would do the trick but not 12 volts. You
are correct that something entirely different is occuring as the principal causation and mechanism. Whatever low level natural ionization of air is
available would not allow sufficient conductivity at a distance of several inches for a potential of 12 volts through what would be gigaohms plus of
resistance. An occasional wayfarer ion traversing that path would not overcome the leakage current, more importantly would not provide the sudden
pileup of observable potential being observed, sufficient to switch on a MOSFET. That only leaves field effect or elves. I looked carefully and no
elves were discovered. Induced electrostatic charge is indeed what would account for the observed behavior of the MOSFET.
Essentially the antenna formed by the Gate lead antenna is electrically isolated by the MOS structure at the device end and isolated by "space" or
airspace at the free end.
The same effect but on smaller scale is occuring for the "antenna" as is occuring for the turntable disk having the teflon handle as shown in video
for the electrophorus, with each end of the wire antenna having differing charge corresponding to the upper and lower faces of the turntable disk ,
with the discharge corrresponding to a much lower signal level but sufficient signal to turn on a MOSFET which would require under 2 volts. So
basically the experiment
with the MOSFET and a test lead is a microscale analogue of the electrophorus demonstration where the output observed is a D'Arsonval meter reading
for a MOSFET conducting current rather than a discharge spark crackling through the air.
Anyway, it can be seen the effect even at low voltages of signal level that interesting things can happen, clearly including the sudden appearance of
electrostatic fields involving and traversing and permeating airgaps, solid conductors, and solid semiconductive and capacitive structures....and the
mobility of ions and/or the mobility of elementary particles would be aligned according to their polarity in such a system providing ion mobility as
the OP was referencing. Cells having a porous barrier of a favorable level of permeability placed between opposite charged electrodes can be used to
keep separated the anionic and cationic products of an electrolytic reaction or an electrostatic separation, and a gelled medium through viscosity can
also be used to present a resistance path to inhibit mobile separated components from easily recombining.
About the proposed experiment with the variable capacitor.
It is predicted the MOSFET would already be turned ON simply by the approach of the positive test lead to clip onto the terminal of the variable
capacitor. MOSFETs are easily excitable .....if they even think they are going to be getting some and especially if they see it coming .....it's just
too much for them and they get turned on......but all too soon the thrill is gone
Something I would still assert is that Kirchoff's laws or some abstract translation thereof does still apply. You would still have conservation of
energy, there would not be a something from nothing "energy transfer" occurring and the books would have to be balanced concerning the "induced
current" as a transient drain felt in the battery which is ultimately the supplier of the charge contained in the current flow.
[Edited on 10-1-2012 by Rosco Bodine]
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watson.fawkes
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| Quote: Originally posted by Rosco Bodine | This has been interesting discussion, and after thinking about the circuit scenario I described for the MOSFET, I am going to concede you are correct
about the electrostatically induced dipole being what accounts for the MOSFET being switched ON by the simple approach of an ungrounded fingertip
within inches of the Gate. [...] So basically the experiment
with the MOSFET and a test lead is a microscale analogue of the electrophorus demonstration where the output observed is a D'Arsonval meter reading
for a MOSFET conducting current rather than a discharge spark crackling through the air. |
Indeed. This is the
principle of operation behind solid-state electrometers, a modern version of the old gold-leaf electroscope. The basic version uses a "naked gate"
connection from the gate of a FET to the antenna. Circuits for these can be as simple as a single transistor, a couple of resistors, a meter, and a
battery. If you want quantitative measurements, though, it's easier to use a FET-input op amp that's optimized for this. I found the LMC6001 with a search for "electrometer amplifier". Notably, this part comes only in DIP packaging, not SMD, because there are special geometric
requirements on nearby conductors (shielding, grounding, etc.) for the part to achieve its rated accuracy. | Quote: | | Something I would still assert is that Kirchoff's laws or some abstract translation thereof does still apply. You would still have conservation of
energy, there would not be a something from nothing "energy transfer" occurring and the books would have to be balanced concerning the "induced
current" as a transient drain felt in the battery which is ultimately the supplier of the charge contained in the current flow.
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Sure. It's Maxwell's equations that are relevant here. The battery does work on the system by moving charge
around. To analyze that, look at the Poynting vector, which represents energy flux in the electromagnetic field.
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gregxy
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Ignoring leakage and tunneling etc, the current that flows through the insulator in a capacitor is called the "displacement current" and is equal to
eps*dE/dt. There are no particles carrying the current, but it does act to preserve conservation of current (Kirchhoff's current law) throughout the
circuit.
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Rosco Bodine
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It is actually pretty amazing that there is so much charge mobility evident at such a low potential as 12 volts inducing an electrostatic field across
a foot distance through the air. Fields can reach out some distance though, and are definitely elastic. Magnetic fields can have a surprising reach
also. I have watched rare earth magnets of less than an ounce in weight maintain coupling through a merged and stretched field across a distance of
several feet. Increasing the separation past a limiting distance will cause the merged fields to break, snapping just like a rubber band stretched
past the elastic limit. And the separation gap must be reduced to a certain distance before the separate fields will interact and couple and merge to
reenforce again. There exists a hysteresis effect for the differing make and break distances for coupled fields. When the field coupling is initially
established on the "make" there is an avalanche effect and an exponential increase in field coupling which is probably what accounts for the "pileup"
of charge that would be sufficient to switch on a MOSFET.
[Edited on 11-1-2012 by Rosco Bodine]
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Morgan
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Just some field tidbits.
How to make a very sensitive jam jar magnetometer by Robert Cobain
http://www.eaas.co.uk/cms/index.php?option=com_content&v...
Radio-Micrometer
http://physics.kenyon.edu/EarlyApparatus/Thermodynamics/Radi...
[Edited on 11-1-2012 by Morgan]
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Morgan
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Possibly of interest/tidbits.
Experiments Demonstrate Nanoscale Metallic Conductivity in Ferroelectrics
"From an applied perspective, the ability to use only an electric field as a knob that tunes both the magnitude of metallic conductivity in a
ferroelectric and the type of charge carriers is particularly intriguing."
http://www.sciencedaily.com/releases/2012/01/120109155944.ht...
http://www.ornl.gov/info/press_releases/get_press_release.cf...
The dielectric constant of PZT can range from 300 to 3850 depending upon orientation and doping.[1]
http://en.wikipedia.org/wiki/Lead_zirconate_titanate
[Edited on 12-1-2012 by Morgan]
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ScienceSquirrel
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Thread Pruned
13-3-2012 at 05:14 |
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