Resonance of HV Stressed Cap - Picture This Time

It sounds like an interesting research problem in electroacoustics; I don't know that you will find a simple answer for free on the Internet. Here is a paper that seems related:

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bitrex
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Ah!

You won't be applying electrostatic stress that way, because the 20kV (+/-) is shielded by the "AC" electrodes.

Simple enough: bias the AC with the DC. No need for those other tubes.

Making that change, I don't know if it would vary. It would figure that stiffness changes slightly with the DC "preloading". Which might be most pronounced in a porous polycrystalline part, as compared to a single crystal. I would expect the change to be small, maybe within a percent, not like the large effect you get with a varactor tuned oscillator or something.

In general, the resonant frequency is going to be given by some dimension of the part (like the thickness of the hoop), and the speed of sound in that medium. Nothing to do with [optical] refractive index.

Though, you can define the acoustic index of refraction in a perfectly analogous way, and use that; but, since there's no ultimate speed of sound as there is a speed of light, it's always relative to some arbitrary medium. It also varies with mode (transverse, shear, longitudinal..).

Tim

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Reply to
Tim Williams

Doesn't matter, the electric field from those is very, very weak because it goes through air (k = 1) and is shielded by the other electrodes. Any coupling would be incidental (a few pF) and equivalent to coupling it in at the AC terminals.

This is easy: attach an inductor to resonate with the terminal capacitance, and a transformer (or drive it as a series resonant tank) to couple your power source (amplifier, switching inverter, etc.) to it.

If you mean something more specific by "pulsing" than just making it ring, there are some ways to do that (e.g., key the oscillator so it goes in tone bursts), but also not (e.g., trying to drive it with a square wave for mechanical actuator use, trying to get bandwidth above the mechanical resonant frequency).

Could be right.

Tim

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Tim Williams

What if the HVDC was replaced by a half-wave rectified AC, so the outer tube was always negative?

I believe that is the way piezo transformers work.

Given the HV is now pulsed, I assume low voltage AC would appear across the Titanate electrodes. This would remain isolated from the HVAC.

The objective would then be to pulse the Titanate cap at its self-resonant frequency.

So the question is, does the superimposed HVAC alter the self-resonance of the Titanate cap, and if so, to what degree?

What are the determining factors?

I tried tapping the Titianate with a screwdriver and watching on a CRO. Looks like it rings at around 20KHz, but that seems low.

The part was originally from a sonobouy.

Any advice or comments??

David King

Reply to
dking

Based upon the replies to my previous question, I have revised my question and added a cross-sectional drawing for clarification.

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What I would like to know is if applying electrostatic stress to the Titanate dielectric would alter the resonant frequency of the cap.

The "cap" is the Barium Titanate cylinder with sintering on the inner and outer surfaces.

If there is such an effect, can anyone suggest where I might find the formulae to predict the resonance?

Thank you.

David King

Reply to
dking

I have redrawn the device based upon your recommendations.

The mylar to provide better coupling, and the center tube eliminated.

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The object would be to see a resonant signal across the output and common.

David King

Reply to
dking

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