Highly Efficient Piezoelectric Ceramics

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  • #1
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does anyone work with piezoelectric ceramics or polymers

i need to know so real world numbers that i just cant seem to find i think this is due to the fact that i have no real clue as to what i am doing but i would like to
1 a base line number for efficiency as in one kilogram of pressure = how many watts volts
2 base line cost to produce; i read that there are cheap but i need some type of base line and i just can find this
3 base line compression of material to produce current
4 how to manage current
5 can piezoelectric materials be sandwiched between a layer of malleable but non conductive materials on top and non malleable but conductive materials on bottom to sort of manage the flow of electricity
 

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  • #3
xez
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Quickly here are a few partial responses. I could probably
find a lot more quantitative information later.

"1 a base line number for efficiency as in one kilogram of pressure = how many watts volts"
Well the wattage will be quite small; piezoelectrics
generate high voltages but very low currents. They are
electrically polarized dielectric insulators essentially, so
they work by mechanically separating charges but they
are usually not capable of generating a significantly large
current into any impedance. Usually you use either a
high input impedance voltage measurement circuit with
them, or for very wide bandwidths you might use some
electrical transmission line and load that's matched to
some value related to the impedance of your electronics
loads and maybe also relative to the impedance of the
piezo transducer if the design calls for that.

The actual sensitivity in joules or volts per force
applied etc. depends on the piezo material chosen,
the range of forces applied, the frequency spectrum of
the forces, the active area of the transducer etc.

"2 base line cost to produce; i read that there are cheap but i need some type of base line and i just can find this "

Well cheap is relative... if you're making something totally
custom and very mechanically/electrically intricate like a
256 sensor integrated array for ultrasound imaging,
that'll cost a bit, especially in low quantity. If you want
something like a piezo disc buzzer for a kid's toy in
quantity 100,000, yeah that'd be quite cheap. Talk with
some prospective manufacturers about your
application's design needs and production volumes / schedules to get a better idea.

3 base line compression of material to produce current

Well you don't "compress" the material to as an end user
to get it to produce an output. It just sits there in your
device at whatever ambient pressure/temperature is
normal for your application, and then added stresses
on top of the static levels will produce changes in the
electrical output. Since they're essentially electrostatic
devices in most applications, they don't really produce
a DC output, but they give you response indicating the
change in forces applied over some given timescale
from a small few seconds maximum down to nanoseconds
for some applications and designs.
Certainly being ceramic and fragile (somewhat) devices
there are limits of pressure/temperature/shock/electrical
energy input that they can be subjected to, so if you have
specific needs in these areas that are 'extreme' then
certainly consult an applications engineer so that you'll
get the best design performance for delta-pressure
sensitivity given your baseline environment.

"4 how to manage current" -- generally either
terminate it in some characteristic impedance of the
sensor, or just sense it as you would an electrometer --
high impedance buffer amplifier going to whatever your
other circuitry is.
If you're actively zapping the piezo electrically
to generate a mechanical impulse like a SONAR application
there are certainly applied energy / frequency /
impedance matching / resonance criteria you'll need to
sort out but those are highly application dependent.
Same deal for crystal oscillator applications or
acousto-optic modulators or whatever else...

"5 can piezoelectric materials be sandwiched between a layer of malleable but non conductive materials on top and non malleable but conductive materials on bottom to sort of manage the flow of electricity" --
Top? Bottom? Well depending on your transducer
design you can take the electrical outputs from various
physical places on the piezo... Generally it's between the
areas that receive the most strain from your mechanical
input... The contacts are generally made with contacts
that are either metal films that are evaporated / sputtered
on the ceramic, or they're painted-on conductive layers
of metallic type of inks, or they're some kind of specially
pressure-seated mechanical contacts, or with some
particular kinds of conductive cement or whatever..
Generally you specify the design of the transducer and
the contact locations and also do that in the context of
specifying or understanding the design for the
holding cell for the transducer so it's free to communicate
the mechanical stresses to the environment in an
appropriately efficient way as well as to protect the
electrical contacts and other areas of the cell / transducer
that shouldn't be exposed to the environment.
Generally unless you're talking about conductive rubber
or plastic most pliable materials are non-conductors.
If the transducer has built in "leads" or contact points
you're free to (and encouraged to) put non-conductive
materials all around the area of the surfaces of the
transducer to the extent that you want to environmentally
seal the element and its contacts from the environment.
Obviously you'll need the contact points themselves to
be bonded to your leads or circuit board or whatever
electrically, but anywhere except at that point you can
design your holder cell however you need to so that
the mechanical support / damping / resonance / coupling /
impedance transformation / whatever you need is
accomplished... Of course since it is a piezo material
stresses can cause voltages at other points on the surface
of the material and applied voltages at other points will
cause mechanical stresses...
It all depends on your design.. look at a piezo disc buzzer
it has both electrical contacts on top... whereas some
quartz crystals have contacts on opposite physical sides of
a slab of material... it just depends on your application's
design requirements.

What are you making, in what volumes, and what
are the primary design criteria?
 
  • #4
xez
174
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