Finding expansion speed of a piezoelectric actuator

[Samson4]

Does anyone know how to find the "expansion" speed of a piezoelectric actuator? I tried displacement x frequency in hertz x 2 x 60 x 60 and then converted from um to miles. I'm getting 16> mph or an actuator that displaces 20um at 200,000 hertz.

I thought these things moved fast, approaching the speed of sound fast.

 

[Bystander]

http://www.piceramic.com/piezo-technology/properties-piezo-actuators.html

 

[nasu]

There is no reason to expect the particle velocity approaching the speed of sound.