# How does a cantilever have a torsional mode in micro size?

1. May 29, 2012

### Tah

Hi,

My question is how does a microcantilever have a torsional resonant mode.

We generally study a longitudinal mode, not so much considering the torsional mode.

The man who replied to my question said

"It's because of the material it is made from. Torsional modes can be induced in two ways. Firstly an asymmetric force or secondly a symmetric force on an crystalline structure which is asymmetric. "

But I still have a difficulty in understanding that meaning.

Can anyone describe it much easier?

2. May 29, 2012

### Studiot

Take a ruler and hold it on your desk so that it forms a cantilever over the edge.

Now press down at the end but in the middle of the ruler.

The ruler deflects in bending as expected.

You will find, however, that if you push down on one side or the other at the end the ruler also twists.

Now imagine your ruler is softer one side than the other (perhaps it has the steel insert one side).
This time distribute your pressure across the end of the cantilver instead of at a point.

Again your ruler twists a bit as well as deflecting, this time because of the different structural properties along each side.

3. May 29, 2012

### Tah

Thanks Studiot

Your explanation is very easy to understand.

Could you explain a little bit more about your example with resonant frequency?

Microcantilever has four different oscillating modes in response to the resonance frequency.

Thank you.