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Posted by Eeyore on June 2, 2008, 4:21 am
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Ken Maltby wrote:
> "Eeyore" wrote in message
> > Ken Maltby wrote:
> >> "Curlyque" wrote
> >>
> >> > Piezo crystals make small amounts of electricity when they vibrate.
> >> >
> >> > LEDs use small amounts of electricity.
> >> >
> >> > Would the typical vibrations around a home excite the crystals enough
> >> > to light LEDs, or would it just take too many crystals to be practical?
>
> >> >
> >> > Or is it just a stupid idea to begin with?
> >>
> >> It was my understanding that the crystals worked
> >> under compression, not simple vibration.
> >
> > Vibration can cause compression. Piezo devices have been used in audio
> > transducers for many many decades.
>
> True, with a design that creates that effect, like a record needle's
> movement against the piezo device, as the other end of the needle
> follows the groove of a record. Or the piezoelectro device(s) that
> formed the active part of some telephone handsets.
>
> For power generation, all the experiments I've read about use
> some form of direct compression. The most interesting used a
> number of pyramids of piezo devices ganged together. (Sorta
> like the way peltiers are formed into pyramids to reach lower
> temp.) Alternating pyramids and up side down pyramids form
> a layer that is compressed between top and bottom plates.
There are additionally some 'piezo transformers'. These are bar shaped (like
one leg of a tuning fork) and one end is excited to make it oscillate at
presumably its natural frequency, whilst power is taken out as a higher
voltage IIRC at the other end. The Japanese seemed to be into this. It's a
niche technology though.
Graham
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