Dear Mr. Chua,

Firstly, are you sure there are no other natural frequencies lower than
your desired frequency? I think it can depends on the design of your
flexures. if your thickness is small, z-axis mode will come in before
your actuation mode. hence, when you are actuating your resonator,
coupling between modes occurs due to fabrication flaws will divert some
of the energy to the z-axis causing it to vibrate in procession motion.
thus you notice small displacement in your actuation axis but its
atcually a coupling motion which takes the shape of an ellipse. I hope
this make sense to you. thank you.

Leow Kok Wah
Department of Mechanical and Production Engineering
Nanyang Technological Univeristy of Singapore

Chua Bee Lee wrote:

> Dear All,
>         I have been working on folded beams resonators using square
> waves
> to drive them. As I adjusted the driving frequency towards the
> resonance
> value, I observed resonance at smaller amplitudes  at lower
> frequencies
> prior to the one that I was expecting. I would appreciate if someone
> can
> provide some insight on that.
>
>         Thank you.
>         CHUA Bee Lee
>         Department of Mechanical and Production Engineering
>         National University of Singapore
>