Mass damping- another use (non f1)

[TheMinister]

Hi all,
Not sure if this is the appropriate forum for this but I figured taking technologies from F1 into similar uses is close enough. If it's not, admins feel free to move me somewhere else.

Anyway, some friends and I want to build a STEM- a scanning tunneling electron microscope http://en.wikipedia.org/wiki/Scanning_t ... microscope.
It'd be easier to read the wikipedia explanation than for me to try and explain it.

There are a few sites detailing how they can be made on the cheap, but one problem remains- removing vibrations.

The guys who first built one and won a nobel prize for it used levitating magnets, which seems rather far fetched.

I was thinking about various ways of removing any vibrations from the ground etc, and I think using mass damping might be just what is needed.

Wikipedia has a lot about active mass damping, but that seems wildly overcomplicated for what I want to do. I was thinking something working along the same basic principles as the mass damper system that renault ran some years back would be better.

Basically I want to have a mass suspended and supported on spring, as they did. The only difference is, my experiment will go on the mass, which should have less vibrations than the ground supporting the springs.

I think (although I'm far from certain) that I might find the mass bouncing up and down at it's own natural frequency, which would ruin the point of putting the microscope on it in the first place. How did renault get around this problem?

Or have I just wildly misunderstood how a mass damper on springs works?

Any feedback would be greatly appreciated, or alternate methods of creating a vibration-free platform.

Thanks all,
TheMinister

[Ciro Pabón]

Well, I know Michelson and Morley used a stone slab on a tub filled with mercury, pretty simple, but I don't know if this is enough for atomic size "steadiness".

It was good enough for oscillations the size of a light wave. I know they had to wait for the traffic to subside to be able to carry the experiments (at 2 a.m.) and I know that the stone slab was huge.

AFAIK, mass dampers (in buildings) don't elliminate oscillations, they compensate for them and don't allow them to "run wild", but they have a "time lag" anyway.

EDIT: I just reread quickly the relevant sections of the experiment (On the relative motion of Earth and the luminiferous Ether) and this is what they say, just in case:



They claim that, in principle, they could detect (and thus, hold steady the table) changes of "1/100th the size of a fringe".

[Jersey Tom]

You want to build an electron microscope? Good luck.

With regard to mass dampers.. they're common. You can likely find them in most system dynamics textbooks. If I recall correctly (its been a while) the idea is by tuning that mass and springrate you can adjust the transmissability curve of the system.. and make something like a bandstop filter such that in a few frequency areas you can really drive the transmissability down to zero.

You have to have some insight into your system though and where noise will be coming from.

[ReubenG]

If you want to use mass damping to remove vibrations from the base of a machine, you need to use additional smaller masses and springs other than the large mass on which the machine is actually bolted. The idea is that external vibrations ( at certain frequencies) will be preferrentially transmitted into the additional masses (these are the vibration absorbers, or "mass dampers") rather than becoming vibrations of the large mass on which the machine is mounted. Problem - using this method only works if you know the frequency of the external vibrations: the large mass will experience the least oscillation at the natural frequency of the smaller mass and spring. So you need to do some experiments to find out what the troublesome frequencies in your site are.

[Nikko2]

When I did my MSc. My yag laser used to sit on a anti vibration table. It was an off the shelf item and by all accounts a very expensive bit of kit.

I couldnt give you any details unfortunately as I have slept since then.

I am sure google will help.