Need Kynar or Piezoelectric Film
erco
Posts: 20,256
Anybody have a source or sample? I need about a 3" square piece. Digikey has sample sheets over $100 each, too rich for my blood. Basically I need a drum head kinda membrane that outputs voltage when deflected by a slight pressure, not quite a microphone but close. Any thoughts? I think standard flex sensors are small pieces of this film laminated in plastic, but I need a much bigger piece for the sensitivity I need.
Comments
http://www.ebay.com/itm/Epson-Piezo-Pro-Clear-Film-17-x-100-S042017-/121990994699
2.
3. Profit!
-Phil
https://www.parallax.com/product/30056
aren't Kynar, but the vibration tabs like this one are:
https://www.parallax.com/product/605-00004
There is a difference in output. As I'm sure you know, flex sensors provide a constant output, while piezo film sensors act like any other piezo device, providing an output only during a physical change of its surface properties, such as bending.
In general, the larger the sheet of this stuff, the less easy it is to work with. It all needs a bias of some kind, such as the moment mass on the end of some versions of the vibra tab. It acts as an amplifier to what is usually a very small produced voltage.
You might actually have better luck attaching one of these smaller tabs, with or without the little weight, to a bigger flexible sheet, such as very thin surgical rubber. Let the rubber pick up the vibrations, which in turn will activate the sensor.
These are the people that sell the sensorized version of Kynar film:
http://www.meas-spec.com/piezo-film-sensors/piezo-film-elements.aspx
If you are working on a product prototype that could yield sales orders for them, you might consider contacting an application engineer there, and discuss what you might need.
You can get the raw film from many places, such as Ridout plastic. But you really don't want to be trying to turn into these into useful sensors, and bonding electrical terminals to it.
(I don't know if the stuff Phil linked to is actually Kynar, or just some film Epson used to sell for printing silkscreen positives. The type of printer used is an Epson piezo printer, piezo as in the technology used in the printhead. Phil could elaborate if this is Kynar film, and if it is, as long as you don't get into a bidding war, a low-ball price might be worth it.
@Gordon: Yup, I saw that, and already requested meas-tech to contact me. Yup, it's for a prototype. Ohhhh, something big is afoot at ercolabs!
Thank you both, my good men!
Also looking at thin film speakers & such to see if that may be a source. Dangit, I used to have the perfect size sample of real Kynar at Mattel from 20 years back, but that got lost in the shuffle.
That old and it might not be any good now anyway. I had some samples from the mid to late 80s that oxidized or were otherwise affected by age/atmosphere/whatever. I had sheets of uncoated pieces, and on all of them, they took on a kind of tarnished look. It was impossible to bond any kind of wires to it, and expect a decent electrical connection. I threw it all away.
One of the samples I had was the infamous speaker/microphone sheet. The trick with that was suspending it in such a way that allowed for mechanical freedom. What happens is that the sheet won't produce an output at any place it's mechanically attached to a support.
Not knowing your application or price point, perhaps you might also want to consider something like this:
http://www.worthpoint.com/worthopedia/edmund-scientific-co-1960s-musicvision-3-items
Combine a small front surface mirror mounted on a thin sheet of silicone rubber, a 40 cent laser, and a photodetector with the proper lens, and you have a very good microphone, thump sensor, or vibration sensor that can fit into a very small space. Unlike MusicVision, which was intended to reflect colored light into the room or onto a screen, it would have the advantage of being able to be made into a sealed unit.
http://www.meas-spec.com
I used one of their sensors for measuring heart rate with it stuck to the chest and attached to a tiny radio transmitter.
http://www.ebay.com/itm/5-Piezo-Film-Transducer-PVDF-Fluoropolymer-Vibra-Tabs-50mV-g-Audio-Sensor-Mass-/111946572300
I just need a big piece of film for my application, which is a toy. It may be a bad sign that it is hard to find. Most things get cheaper and more available as time goes by, but that isn't the case here.
The only alternative materials I can use for this project are Unobtainium and Byzanium.
$42 Film and $75 speaker
I need to cut a hole in the middle. Wonder if that would ruin...?
Piezo technology is used heavily and is pretty cheap. This stuff is speciality -- hence the name of the company that promotes it -- and it is expensive. I've never used anything large; just the small tabs that can be attached to bigger things. When those bend and deflect, the material acts as an amplifier for the film, making the signal even more pronounced. Usual concept of mechanical advantage, and all that.
Seems kinda funny that here's a whole replacement 7" touch screen for $1.76 and I can hardly find piezo film that size under $100.
http://www.ebay.com/itm/Replacement-Digitizer-Touch-Screen-Lens-Panel-Glass-For-7inch-Tablet-MID-LO-/162051763867
Good old carbon telephone mics were exactly a "membrane that outputs voltage when deflected by a slight pressure".
I guess my question is do yo need a pressure sensor, basically a DC coupled device.
Or something more percussive, an AC coupled device ?
There must be ways to do this capacitively, or magnetically.
Mechanically arranging that might be an issue. Can you use the PCB the accelerometer is soldered to as the membrane?
I'm gobsmacked that one Vibratab is $6 or more on Ebay: http://www.ebay.com/itm/PVDF-Fluoropolymer-Piezo-Film-Tab-Vibratab-50mV-g-Audio-Transducer-/261758457949
Or at best, 5 for $27: http://www.ebay.com/itm/5-Piezo-Film-Transducer-PVDF-Fluoropolymer-Vibra-Tabs-50mV-g-Audio-Sensor-Mass-/111946572300
How much could that tiny piece of film cost? I'm surprised China isn't selling ten for a buck. What that country needs is a good 10-cent sensor.
At $2.50, Parallax's Vibratab is a conspicuous value: https://www.parallax.com/product/605-00004
But that's moot since their cheapest shipping option is $12.71. Pretty sad since they would easily fit into an envelope and mail for 47 cents.
-Phil
At commercial quantities, you will be able to get the tabs for much less. Your application does not require the mass, so no need to look at those. Any factory in China would be able to build a jig for attaching the wire terminals, so all you need to spec is the basic film. You don't need to guestimate prices on the much more expensive versions with wires or terminals already struck on.
I wish I still had some tabs that I could send you, because in 30 minutes of playing with these, your brain will kick into high gear with the possibilities. For experimenting, you can attach the stuff to various things using duct tape. No doubt you'll attach some to your forehead, and then slap it.
At one time, I created a "kitchen band" for an intended article for Make (my editor left the magazine, and I went on to other things). I connected these tabs to plastic forks, paper dishes, the underside of plastic cups, everything. It's all good, and every one of them detected the thumps, bumps, thwacks, and whacks I threw at them.
There's also this:
http://robotoid.com/appnotes/sensors-laser-fiber-whiskers.html
though it can be so sensitive, that even air movement in the room will trigger it. You'd mount a fiber optic ring around the periphery of the membrane, and set the sensitivity so low that it'll only react to definite concussions of the membrane.
This plan first appeared in an older book I did in '88. I then discovered several people had applied for patents related to sensors based on lasers and fiber optics. Most of those should be expired by now, but you'll want to check. This method may cost < $1 in quantity. I know you know where to find cheap lasers... For the fiber optics, you'll need to raid that light fountain sculpture you bought from Spencer Gifts for Mrs. Erco's birthday last year.
My son was about 6 or 7 when we saw Star Trek: First Contact in the theaters. In it, there are some borgs that have penlight lasers stuck to the side of their heads.
Days after we saw the movie, and as as a joke, my son waited until it was dark, and his mother and I were out in the living room watching TV. He strapped a penlight laser over his ear with a pair of headphones, and then slowly came into the room, borg style. My wife literally shot to the ceiling. If she had cat claws, would have clung there for the rest of the night!
Anyway, you're probably right about the lasers -- they consume too much power anyway. The piezo solution will draw in the single digit milliamps.
What I have is a piece of original Penwalt "kynar" film, 28µ NiAl plated, about 3" x 5.5". Not corroded. You'll need copper tape with conductive adhesive (e.g. 3M #1181) to make the contacts. (Penwalt became Amp, then in 1998 they were bought out by Meas-Spec, then in 2014 Meas-Spec became a subsidiary of TE Connectivity. Unlike many other such chains of acquisition, they did retain the technical depth.)
How sensitive do you need? ...and would these work? ... awhile back I bought one hundred 15mm (12kHz) piezo discs for less than $6...
Yow!
I remember them. It's nice to know that the firm is still in business.
Gordon, your book? Which edition?
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erco, new problem. Your robots are busy packing for a visit some place.
Great call Beau! I have a pile of 25mm disks I've been using for experiments. As you showed, very sensitive. I used those on my Knock Box a few years back. Likely too sensitive here since this is on a mobile robot application, it will be moving and vibrating by itself. I need to isolate impacts. Might be a matter of tuning. I won't rule anything out!
Attaching several useful piezo links here which I found in my web searches. Might help someone else. Like Duane, I see this forum as useful place to store info.
http://www.imagesco.com/articles/piezo/piezo06.html
http://www.imagesco.com/piezoelectric/
https://solarbotics.com/download.php?file=487
https://www.steminc.com/PZT/en/
http://www.meas-spec.com/contact/distributordetail.aspx?r=650&t=690&s=128
Until the forum software gets upgraded again or reorganised again. Each time we seem to lose heaps of info