[scientizscht (OP)]

Hello!

What is the efficiency of piezoelectricity?

E.g. if I have a 10 Newton force applied constantly to a piezoelectric element, how much energy or voltage I can produce?

[alancalverd]

Not a lot. Most piezoelectric materials are hard, so your 10N force won't move very far.

Work = force x distance

Energy out = work in x efficiency

The efficiency of the first few microns of movement can be very high - it's good enough for spark ignition of gas lighters and even jet engines - but the effect depends on recoverable elastic distortion of the piezo element, and the mechanism for delivering repeated non-destructive impulses tends to be "clunky". 

[Bored chemist]

Hello!

What is the efficiency of piezoelectricity?

E.g. if I have a 10 Newton force applied constantly to a piezoelectric element, how much energy or voltage I can produce?

Probably less energy than if you apply it to a shelf or a table.

Also if you read up on the subject, you find things like
"The voltage sensitivity has dropped 11% simply by changing the cable."
from
https://www.bksv.com/media/doc/bb0694.pdf


A reasonable "ballpark" answer would be "millivolts"

[alancalverd]

There's a lot of good stuff here

https://www.americanpiezo.com/piezo-theory/generators.html

[scientizscht (OP)]

Translation: Piezoelectric materials give off no energy under continuous force.

How can we generate energy from a continuous force then?

[Bored chemist]

What do you mean?
Do you mean like the wind pressing on a sail or like a weight on a shelf?

Hint; shelving does not require batteries.

[evan_au]

How can we generate energy from a continuous force then?

You don't use a force as input, you use energy as an input.
- Piezoelectric materials can translate mechanical energy into electrical energy.
- Or if there is no external electrical circuit, piezoelectric materials represent their electrical potential (an electrical "force") as a mechanical force. In this mode, they can be quite efficient, provided you don't damage them.

To create a continuous electrical energy into an electrical circuit, you need to apply continuous mechanical input.
- Without exceeding the elastic limit of the material
- You can do this with repeated taps
- Or cyclic forces
- The electrical circuit can rectify and filter this cyclic voltage to DC (if that's what you want)

[Hayseed]

Efficiency is relative.  The first telegraph give efficiency for communications, but was not efficient electrically.

Piezoelectricity has a great future.  The dynamic can emit EM waves.  For the first time, we have short, efficient, low frequency transmitting antennas.   Frequencies of 30 kHz to 30 MHz have had some amazing results.  It seems, that antenna length is not that important as once thought.

I predict deep range metal detectors using piezoelectricity.  Big business.

[Bored chemist]

For the first time, we have short, efficient, low frequency transmitting antennas. 

Have you are reference for that?

[Hayseed]

BC....Sorry, not directly.  There have been several reports on phys.org.  and others.

Try searching for piezo antennas and direct antenna modulation.

If you can't find it, let me know.  I have read several reports over the last several years.  I didn't save the links.