campbell@gnu.ai.mit.edu (nobody:*:-2:60001:I. N. Cognito:/:) (05/07/91)
I just got an interesting little piece of plastic today. It's a
piece of PVDF (acid resistant) plastic sold under the brand name of Kynar.
The interesting feature of this little piece of plastic is that it is both
pyroelectric and piezoelectric.
Pyroelectric means that if any heat or infrared light strikes it,
the plastic starts generating a voltage from one side to the other. It can
detect a man from about 50 feet away and is used in burglar alarms for that
purpose.
Piezoelectric is where it really shines. If it undergoes stress,
vibration, or just about any movement, it also has a voltage. This is
reversible so that if you apply a voltage, it wiggles. It can be used as
a touch switch (the sample I was sent was about .5" X 1", enough to generate
about .5 volts when I tapped with a fairly resistive multimeter attached). You
can just tap the table and it picks up the vibrations. In fact, we had a hard
time zeroing it out (stand still and don't move or it will pick you up from
changes in heat or vibration).
This stuff can be used as fans. You can use the little (~$1) pieces
for switches. Because it senses vibration, you got to have a way to have a
true 'continuous' switch. Their literature suggests that you cement two pieces
on either side of a solid metal strip and apply electricity to one so that it
vibrates while the other is hooked to sensors. When anything touches the metal,
it changes the resonant frequency and the sensor can detect this.
As far as total voltage goes, I expected to have to measure in terms
of microvolts and to have to amplify it, but the range on this stuff is the
same as a lot of decent quality analog-to-digital convertors.
In my own project, I want to construct a touch screen. I looked at the
wire and surface acoustic wave methods and decided that they vastly
overcomplicated/raised the expense of the project. With this stuff, I can use
a sheet of glass and mount sensors around the edges. By timing how long it
takes for a vibration to reach a particular sensor, I can easily triangulate
the exact position where the wave occurred. If I also watch how large the
vibration peaks are, I might be able to even have a crude estimate of the
amount of force applied, so position and pressure make a difference.campbell@gnu.ai.mit.edu (nobody:*:-2:60001:I. N. Cognito:/:) (05/08/91)
I tried to drop the address and let you guys place with the corporate
bureaucracy, but NO! You want me to just tell you flat out and not let you go
through the same hassles I did! :-)
Samples: They have kits and samples available, for a price. I had to
pull some politics, but it is definitely possible to get a free sample out
of them if you pull the right strings.
Kits available:
Basic design kit ($50): microphone, speaker, switch, IR detector, and
acoustic pickup demo
Switch Kit ($50): limit, impact, soft-contact, wake-up, infrared,
magnetic (reed) and snap-action switches
Vibration sensor kit and accelerometer ($149): Demonstrates the advantages
over the traditional sensors in this range.
Motion Sensor ($25): self contained subassembly w/ sensor, electronics, and
LED indicator.
Bimorph actuator ($95): optical shutters, deformable mirrors, and
micropositioner and air flow generation applications.
Piezo Cable KIT ($05): For large area sensing areas. Has a long cable attached
instead of a short, small sensor.
IR sensor Kit ($199): Demonstrates detecting infrared human body, car sensors,
flame sensors, night vision, and ballistics.
Sheets available:
Size 9microns 28microns 52microns 110microns
(cmXcm)
15X15 $55 $45 $55 $65
15X30 $110 $90 $110 $130
30cmXcontinuous rolls also available
Special orders can be made for Ni, Ag, Cr, Cu, Au, Al, NiCr, Pd, and ITO
coatings. Standard is NiCu. BTW, ITO is transparent.
Ag metallization (thick)
Size Thickness
cmXcm 28 52 110
15X15 $45 $55 $65
15X30 $90 $110 $130
30cm continuous also available.
Small electrodes:
size (mmXmm) thickness (micrometers) price each
40X15 28 $.50
40X15 52 $.60
70X15 28 $1.00
70X15 52 $1.20
85X22 28 $2.00
85X22 52 $2.40
165X22 28 $4.00
165X22 52 $4.80
They attach leads to anything for about $2 and have lots of other stuff,
but this should give you a good estimate on price.
The company I have (there are a couple others) is
Atochem North America
Piezo Film Sensor Division
PO Box 799
Valley Forge, PA 19482-0799
Tech line: 215 666 3547
Regional sales offices:
East Coast:
PO Box 799
Valley Forge, PA 19482
215 666 3500 Fax: 215 666 3509
Midwest:
801 E. Ogden Avenue
Suite 1160
Naperville, IL 60563-2865
708 961 2922 Fax: 708 961 2994
West Coast:
172 Big Valley Road
Folsom, CA 95630
916 983 8644
Fax: 916 983 0479
Europe:
Atochem Piezo Film Ltd.
22 Ridge Way
Hillend Industrial Park
Dunfermline, Fife
Scotland, KY115JN
0383-825063 Telex: 72465 CHACOM G (Syrinx) Fax: 0383-825070
Teflon is not the same as Kynar. Kynar is PVDF, which can be treated with
magnetic systems to make it perform as a piezoelectric substance. They did
that back in the early 70's, but it didn't really show up on the market
until the early 80's. Teflon could be treated the same way, but they also
tried lots of ceramics and didn't have much luck with anything else, but
then Teflon is a new material. Any chemists willing to do take-home work?