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Sensing touch on glass objects

more of a physics question:
is there an electromagnetic dimension that changes (and can be measured) when a person is touching a glass object?
the idear is to boolean the touch of different glass objects

Good question but I dont think so since glas counts to isolator materials. You would need to cover it with a small layer of material which changes capacity when touched. Depending on the objects I think optical or vibration sensors would work better and would be cheaper.

@tekcor if you mean optical as in watching for the hand, it wont work it has to be a tactile contact.
as for vibration sesors, you think it would have to be a precise/expensive one to sense a hand touch on a glass object?

was thinking about a plasma globe, found this:

if the glasses were plasma globes, could dielectric polarization be measured ?
at least with an optical sensor waiting for the gas to lite, maybe simpler ?

if you want the touches simply use an FTIR touchscreen you need bunch of IR leds and a webcam. supersimple and could be hidden easily

the idear is to boolean the touch of different glass objects
i.e. a glass sphere or a bottle

Ill read the plasma stuff later. For the optical thing… ir leds or lasers shining through the glass and a hidden camera/brightness sensor behind the object are calibrated accordingly. If the user touches the glass, the reflection or absorbtion can be measured. Similar to what microD said :)

This is cool… you shoulld be able to detect the currency change when the globe is touched. Maybe even how many fingers… But non-spherical objects might get tricky, as my flatmate said, because there is a certain amount of energy needed for the plasma lightning to overcome a certain radius. Too close causes it to light all the time and too far doesnt work at all. And its realy dangerous to work with those gases…

How about a piezo microphone stuck at the bottom of each object?

@zeos: ooooh yeees!! there are those laser microphones too http://en.wikipedia.org/wiki/Laser_microphone they record sound of a static glass too if someone touches that glass it would blow out loudly i guess
and they could be hidden more easily than a piezo mic

@microdee: Sounds great ;) Never used those laser mics…