# Experiments with Three-Plate "Capacitors". Center Plate Being a Coil

#### epsolutions

Sep 7, 2019
96
I am investigating the interaction between capacitors and coils arranged in a stack. The configurations I intend to try are illustrated in the diagram below. There is an assumption that the input is bipolar, as if from the push-pull amplifier. The signal is any audio sine wave. Dielectric not shown. I visualise the effects in the following way.

A - First half cycle: Inner plate goes high. Second half: outer plates go low. Net potential constant. (No coil)

B - Same as above, but coil is loaded with a resistor to emit an EM field. My question here is how the R value affects the potential between coil and plates, or other behavior of the circuit.

C - Same as above, but the coil is fed direct from the signal source in series with the transformer primary. This eliminates the prior load resistor, but the coil's voltage remains at line level. Potential is in effect halved.

D - Center tapped transformer. First half cycle: Coil goes high while plates go low (simultaneous). Second half: this reverses. Potential is halved.

Any correction or advice on my reasoning so far would be greatly appreciated.

I would also like to understand the effect of each configuration upon the signal source with regard to loading or reflection issues, etc. Or perhaps some ideas on different ones to try.

#### Nanren888

Nov 8, 2015
622
Just trying to understand the configuration: This coil in the middle, is it a pancake spiral coil, with the left, red connection to the centre end and the right, black connection to the outside end, that is different ends of the coil?
Where does the resistor connect?
.
Any hints of what the aim is?

#### epsolutions

Sep 7, 2019
96
Thank you for asking. Yes, it is a pancake coil wired as you describe, or the other way around. I am not sure if the polarity matters in terms of interaction with the two cap plates.

According to my thinking, the resistor in diagram B would be on the "low" side so the coil always remains positive relative to the plates. Is that correct? One of my questions is what factors to consider when determining the value of that resistor.

At this point, I am just trying to understand the differing electrodynamics of each configuration in preparation for bench work. I was hoping someone might help by briefly commenting on each one.

#### Martaine2005

May 12, 2015
4,558
A coil doesn’t have polarity.
I have no idea what you are try to achieve or investigate.
Can you explain what you are trying to investigate in more detail please.

Martin

#### epsolutions

Sep 7, 2019
96
I would like to understand the electrodynamics of each of the four configurations in my OP. I am retired now and this is just a learning exercise for me. By "polarity" I was referring to the magnetic field surrounding the coil. Thank you for your interest.

#### Nanren888

Nov 8, 2015
622
Sure. I understood your use of the word "polarity". Simply that I had guessed the wiring direction the wrong way round. Understood.
.
I guess you have a coil, an inductor with a distributed capacitance to the capacitor plates. Quite a lot will depend on the actual parameters, I guess.
Do you have access to any modelling software? Might want to give it a search.
.
My reason for asking about the aim, and I guess that of others, was that this seems a bit of an unusally arrangement.
To be interesting, I guess you are imagining that resonances might exist and somewhere near the frequencies you might operate this at? Yet you show it connected to a sound card, suggesting low frequencies, in turn suggesting rather large plates and coils?
.
I'm not sure how interested you are in the electrical, circuit-wise behaviour, versus the spatial fields.
It seem that in each configuration, the uppper and lower plates are connected together. So, in a circuit-sense it's just equivalent to a capacitor with one plate and one pancake coil.
In a spatial sense you have a coil with a plate above and below. Seemingily wanting to align the electric and magnetic fields vectors. Generally these tend to end up at right angles in most useful EM devices.So, again, not sure what the aim is.
.
So, A is a capacitor. Electrically, the two plates are irrelevant, just makes it a little smaller for the same capacitance.
B would seem to be likely equivalent to a coil with distributed capacitance. At low frequencies the plate is just a conductor, presuming it is not large compared to an electrical wavelength. So, a coil, with distributed capacitance, a transmission-line model? Loaded with a resistor? So some current flows.
.
What's the feed? Sinusoindal?

C appears to replace the resistor with a large? split inductance formed by what used to be the transformer.

So D seems pretty equivalent, just a shuffle of the components, so given no compoenent changes, the effective inductance changes.
.
So, amusing academic exercise. Not really something that I'm qualified to do, so maybe someone will correct any mistakes I made.
But, still wondering why?

A quick google search suggests that my comments echo some of those over on all about circuits where someone seems to have had discussion going for some time.
Did you get to a resonable understanding of the point made there, also, that is the plates are small compared to the electrical wavelength, that is the frequency is low, the circuit reduces, simplifies?
.
If you found some suitable modelling software you might be able to wrap some sort of genetic algorithm round it and generate numerous novel configurations for discussion.

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#### epsolutions

Sep 7, 2019
96
Thank you for your comments. What I am investigating is possible interaction between the coil and plates as you correctly surmise. I do not have any suitable modelling software, but once I get a few opinions to help guide me I will bench test various frequencies and voltages.

The general idea is to maximze the voltage potential between the outer and inner plates at any point within a single cycle. This is why I am interested in the various configurations shown in my OP and phase relationships.

#### Martaine2005

May 12, 2015
4,558
Sorry, do you mean hold maximum through the zero crossing too?.
Are you trying to build a voltage source from your ipod earphone output?.

Martin

#### Nanren888

Nov 8, 2015
622
The general idea is to maximze the voltage potential between the outer and inner plates at any point within a single cycle.

"at any point"? passive components, sinusoid in - sinusoid out, sinusoidal everywhere.
So, I presume you mean amplitude.

Not obvious what good comes from a high voltage on a capacitor.

Large ratio on the transformer?
Feed it to create resonance.
Might want to check out series and parallel resonance.
.
Some of it might be easier at higher frequency.
Watch out for those high voltages.
.

#### epsolutions

Sep 7, 2019
96
"at any point"? passive components, sinusoid in - sinusoid out, sinusoidal everywhere.
So, I presume you mean amplitude.

.

Electrical potential between the plates changes in distribution and polarity according to phase. Net amplitude remains constant, but depending upon the circuit, distribution is not necessarily even or balanced given that three charged "surfaces" are involved.

#### Nanren888

Nov 8, 2015
622
Not sure that there is anything magic coming form the "three".
Enjoy.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,825
Wonderful! I did sh!t like this when I was a kid, trying to figure out how things "electronical" worked. Of course, way back then, I didn't have a personal computer with a sound card to play with. No one did, because they hadn't been invented yet. So, one of the very first pieces of test gear I bought with money earned from my newspaper route was a Heathkit variable frequency oscillator. That was right after I purchased a kit Vacuum Tube Volt Meter (VTVM) made by RCA. Can't do any experiments without measurements, right?

Well, that kept me busy for awhile, but I soon realized that what I really needed was an oscilloscope, because once you introduce capacitors and inductors into your experimental circuits, phase becomes important. Ahem. About the only thing I knew about phase was gleaned from books I borrowed from the library, so further experiments didn't happen overnight. I was almost ready to graduate high school before I had saved enough money purchase a kit EICO 460K oscilloscope, about 1961.

I never did any experiments with homemade parallel plate capacitors, with or without a pancake inductor between the plates, although I did construct a high-voltage parallel plate capacitor using aluminum foil, rubber cement, and window glass. This was supposed to be the resonating capacitor for the primary of a Tesla coil, but I was stymied by my inability to wind the secondary. And I had no means to measure the resonant frequency of the primary, although much later I did acquire a Heathkit grid-dip meter that would have measured to within a few kilohertz... probably gud enuf fer amatoor werk.

So fast forward past high school graduation, the Viet Nam war, ten years of part-time study ending in a BEE degree in 1978 and I was ready to face the world with a bona fide engineering degree. I spent the next thirty-something years working as an electrical engineer for companies with United States Government contracts, usually something for the Department of Defense or Homeland Security. I retired to Florida in December 2016 and have been looking for something to do ever since... maybe some projects employing Microchip PIC microprocessors.

My latest idea is a toilet seat alarm, to remind men to put the seat down for women in their house. Seems like this simple task of lowering the toilet seat is abhorrent to most women. Germs, perhaps? I have installed self-lowering toilet seats that lower gently instead of with a bang, but wife says that's not good enough. I have to be responsible for seeing that the seat is down before she needs to use it. Hence the need for some sort of reminder that the seat is still up before I exit the bathroom. Urinating from a standing position over a lowered toilet seat is NOT an option, no matter how good my aim might be.

So, I bought a bunch of ball-in-cylinder tilt switches, made in China of course, from Amazon. Advertisement blurb says they are intended to interface with Arduino Uno microcontrollers. Well, they are simple on/off switches... why wouldn't they interface with an Arduino input port?

Problem is, these switches are very sensitive to an exact vertical orientation before the switch will close. Not that easy to get installed correctly on the bottom of the toilet seat. Plus, I need some way to know that the toilet seat is raised and someone is present (or not) before sounding an alarm.

This contraption must be battery powered, perhaps with a pair of AA NiMH rechargeable cells. And it needs an audible alarm (like smoke detectors have) to signal when the battery voltage is low, and an alarm to signal when the toilet seat is left up and no one is nearby to lower it. But this latter alarm must also be triggered if the seat is up and someone approaches the seat. And it should turn itself off for awhile, to save battery energy, if the "seat up" condition isn't corrected within a certain time interval.

Lots of design decisions to consider before actually soldering anything together. Plus I need to search the Internet because someone has probably already solved this "problem" cheaper, better, and simpler than whatever I might come up with. I am thinking a magnet and a magnetic reed switch might be a better seat-position sensor than a ball-in-cylinder tilt switch... some experiments are necessary.

So, my advice to @epsolutions is to get some test equipment together and start building your experiment. Keep careful notes of your setups, the voltages and/or currents you measure, and what you think it all means. Make sure your results are reproducible by others "skilled in the art" as well as, later, by yourself.

By all means, obtain a modern digital storage oscilloscope to allow you to make simultaneous measurements of wave forms in two or more circuit locations. A good sinusoidal oscillator is recommended for the kind of experiments you want to do. I recommend that you purchase or build a Wien Bridge oscillator for this purpose. If your experiments wander into the realm of radio frequencies, a stable RF oscillator would be necessary.

Good luck in your retirement! And always remember that electronics is supposed to be FUN!

Hop -- AC8NS

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