# Can I develop constant force (pressure) from piezoelectric crystal?

Can I develop constant force (pressure) from piezoelectric crystal applying constant voltage?

• What did your research show? What formulas did you find? What terms in the formulas indicated that force might not be sustained? Put all the info in your question - not scattered through the comments. – Transistor Jan 21 '18 at 14:09
• Unfortunately I didn't find any information for this use case. But this question bothers me for a long time. There is plenty of information about oscillating motion and AC voltage. Theoretically if we put a charge into crystal it will expand (contract) and remain in this state (as it is dielectric). So it can develop pressure on some object until we remove the charge from it. However I didn't find any implementation or theoretical basis to prove this. – cos Jan 21 '18 at 14:26
• Where is the theory you suggest that says a crystal will change? Ie do you have a source? – Solar Mike Jan 21 '18 at 14:40
• You need to specify a specific crystal and a specific force on a specific axis. Your question got flagged as LQ due to lack of details that can help you get an answer. – Sparky256 Jan 21 '18 at 21:39
• I read the following "Can piezo transducers be used as static and dynamic force sensors? Piezo transducers are not suitable for static force measurements because of charge leakage. They can be used effectively for transient force measurements lasting less than 0.1 second." which implies that static use is not practical. www.piezo.com/tech3faq.html – KalleMP Jan 22 '18 at 16:14

Yes, you can, however there is some change (call it creep or drift or relaxation) in the motion, logarithmically decreasing with time adding up to perhaps several perecent over hours. Here is the response to a 60$\mu\text m$ motion:

To get macroscopic motion from piezo elements there are a few techniques- such as stacking large number of elements, using mechanical amplification (as in benders) and "walking" or other motor techniques. The latter type of technique does not depend on the piezo to hold position so it will not have the same drift characteristic. Also it's common in high precision applications to close the loop with a feedback sensor.

Obviously you want to know, if the crystal deformation under constant DC voltage stays constant, Of course it's possible that the crystal breaks down with high enough voltage or with high enough external force.

There are some applications which need long time deformation. Examples:

• gas lasers are fine tuned (=the distance between the mirrors is adjusted) for precision measuring purposes by moving a mirror with a piezocrystal.
• mirror tilters for optical systems

Here's a datasheet of a mirror tilter.

http://www.piezo.com/catalog7C.pdf%20files/Cat7C.14&15.pdf

The specified frequency range starts from zero Hz, so the deformation can be constant.

I know little about the application of piezo electric sensor and actuators other than their common uses as phono record needles, tweeters, beepers and that I have used them on commercially built ultrasonic cutting presses. They also appear to be used as motors / actuators in camera focusing systems and binocular image stabilisation (where, on my Canon binoculars) they do a super job eliminating hand shake from the image.

Introduction to Piezoelectric Actuators Kenji Uchino, International Center for Actuators and Transducers, Penn State University, may be of some interest to you.

I found the link on Wikipedia's Amplified piezoelectric actuator and this makes the interesting statement:

As classical piezoelectric materials have a strain of 0.1%, it is practically impossible to reach significant stroke without displacement amplification (1 mm displacement would require 1 meter of piezoelectric material). The solution to reach middle range stroke is to use an amplification system.

• There are research projects using piezo actuators to relieve stress in the vertical stabilisers of fast jets; the stress during high g manouevres is enormous and causes deformation that subtly changes aerodynamic characteristics. For aircraft with electronic flight controls, that can cause issues. – Peter Smith Jan 21 '18 at 15:13