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Re: Unusual capacitor dielectrics
>Original Poster: Jacob Roberto <jroberto-at-ieway-dot-com>
>
>I've noticed that pure water has a dielectric constant of 80 (about 40 times
>higher than that of polyethylene). Would it be practical to build capacitors
>that use water as the dielectric?
Its been done. Do you realy want to play in puddles? Not very stable,
physicaly or chemicaly.
>Also, what about barium titanate capacitors? Barium tatanate has a *huge*
1200
>dielectric constant. It isn't exactly easy to find, but "barium titanate,
Yea, too kewl. BaTiO is everywhere! Just listen for the "beeeeep" of
Peizo-disks.
I must check-out the ceramic vendors, to see what it will cost for them to
make me some disks. Titanium Dioxide has an Eff of 100, and I think is
pretty common in ceramic and paint pigments, and might be a very cost
effective kilo-volt range cap material.
>Does anyone know the puncture voltage and RF losses of pure water and barium
>titanate???
It varies according to your ability! The electric field results in a force
tensor in the crystal. An oscillating field will obvously result in acoustic
signals. Your "Q" will depend on physical design. The capacitor disk mounts
should be at the primary frequency acoustic nodes, with hard rubber.
No contacting metal plates to vibrate & heat, but sputtered aluminum or
silver ink electrodes. Each plate seperate from its neighbor, unless you
want to press and glue the whole stack, and DC polarize, load it or stress
it, which will also lessen the hysteresis loss.
I've put 100's of volts across around 3 mil piezo-disks (the $1 ubiquitous
ones) they go "snap" and fracture. AC voltage, at various resonant modes of
far less will heat and kill them, especialy if something touches them. At
Tesla coil frequencies, the resonace will be thickness (mm-thick disks), but
the rep-rate of sub-KHz could excite large-diameter (several inch across)
thick disks!
As you approach mechanical resonance, the 'capacitor' can become inductive,
with its motional or acoustic inductance thousands of Henries! (for very
high-Q values.) You may eventual come to the conclusion I have, that a
softball-sized shell, constructed from two interlocking curved surfaces,
like a tennis-ball, one curve of peizo-ceramic and the other of ferrite,
could form a resonator with interesting properties, centered in the Tesla
coil 2ndary. Mechanical resonace at the spark impulse rate, and
electro-magnetic resonace in 10's - 100's of KHz.
You can buy the powder from peizo-ceramics vendors on the web, or ceramics
dealers. The cm-thick 3" disks from ultrasonic cleaners may work well for
thousands of volts DC, BUT NOT AT 40 KHz RESONANCE!
Check this stuff out for us! I would condsider a high-TiO2 ceramic, with
less acoustic problems than the BaTiO:ZrO stuff. Ceramic and paint supply
will be far cheaper (but less pure) than chemical houses.