Chladni Plate ?? Wot ???

[Bluechip]

Hi Folks

Don't know quite where to put this, so I've poked it in here. In some ways it follows on from Bogs' post about 'lack of project posts', it's what I've been fooling around with today, ( no lickable slugs to be found )  

Not mine, I must add, but a similar arrangement. May interest some. Various modes of vibration on a flat plate. In my case 1/8" hard brass. Driven by a knacked 5" 20W speaker.

The sort of things retired electronic bods do .. found the brass plate for another job, remembered this Chladni stuff, and got no further on original caper.

Dave BC

[sbwhart]

Coor Dave thats cool:- I take it different frequencies generate a different pattern, is it sand or salt on the plate, I suppose different stuff produces different patterns at different frequencies, the more I think about it the more question I have 

Thanks

Stew

[Bluechip]

Stew

Yes, depends on frequency and, I would think, the plate stiffness. ( Young modulus) ??

I used salt.

Good fun, complete waste of time of course.  for me anyway.
At one time, the Boffins were working on mineral separation using an 'Acoustic Sieve', how far they got I don't know. If you have a column of mineral particles with different densities, you pulse it with sound at a particular frequency, and pretty much all the heavy stuff goes to the top IIRC, and the lighter stuff remains at the bottom of the column. Bit clever for the likes of me!!

Kept me amused for a couple of hours. Speaker was no use, torn cone, so it got sacrificed.

If you look for 'Chladni Plate' on Youtube, there are some other vids. with water etc.

Dave BC

[sbwhart]

Yes I can understand that done a lot of experimenting dispensing small units of sticky powder very accurately and yet keep the mix homogenous, had to give up in the end and revert to manual weighing.

Interesting little project though.

Stew

[Darren]

Is it the frequencies in the speaker coil causing magnetic fields which when passing through a non magnetic metal produces voltage current thingies...

[John Hill]

Is it the frequencies in the speaker coil causing magnetic fields which when passing through a non magnetic metal produces voltage current thingies...

Interesting question! 

Considering that salt is pretty much non magnetic I expect not in this case but if one was to use iron filings I would expect eddy currents in the conducting plate to have an effect on the pattern.   

Hmmmm, mix iron filings with salt and see if two interlocking patterns emerge.

[John Hill]

Yes I can understand that done a lot of experimenting dispensing small units of sticky powder very accurately and yet keep the mix homogenous, had to give up in the end and revert to manual weighing.

Stew

Very interesting Stew, closest I ever came was mixing milk powder with powdered coffee which by some magic prevented them going sticky and hard in the jar, which they both did if stored seperate in tropical conditions.

Ok, Ok....

[Bluechip]

Hi Folks

Nothin Electrickery about it. The salt stays where there is a 'Node' ie 'No displacement'.

I have seen it done with a violin bow on the edge of the plate .. no eddy currents, no nowt.

It's just like standing waves on a vibrating string.
Only in two dimensions instead of one.
Easier to alter the frequency with a signal generator. Or it is for me anyway. 'Bout as musical as a tortured cat.



Dave

[Darren]

Ahh, so simply resonations in the plate then?

[Bluechip]

Darren


That's it. If it was any deeper, there's no way I would have got there. 

Dave

[Brass_Machine]

Darren


That's it. If it was any deeper, there's no way I would have got there. 

Dave

Dave,

You got pictures/video of yours?

Eric

[Stilldrillin]

That`s a bit clever innit! 

I used to stand mesmerised at the pretty vibration patterns in the coolant puddle, at the end of milling m/c table.

(It still doesn`t take much to amuse me). 

David D

[Bluechip]

Eric,

Didn't take any pics. of mine. Just a rather corroded brass plate. I doubt if the salt pattern would show up very well. That, and my less than competent antics with the camera. Apparently it will take short video, but I've never tried it. Despite a lifetime in Digital Electronics, to my shame, I don't get on with the wretched thing. I used to do 35mm stuff quite a lot. Even did my own prints and enlarging, but this thing is a mystery to me. I just about take some reasonable stills, but that's my lot. So, in case anyone was interested, I grabbed a Youtube example.
Far better than anything I could have done.
I didn't set out to make a Chladni plate, a friend wanted a brass disc 6 1/2" OD with a 5" hole, it just struck me, being a hard plate it may well work. My mind wanders a bit. Nothing more pressing to do, so I got the old speaker, a 15W audio amp. and my Signal Generator, and played about a bit.
Speaker has now had it's magnet salvaged, the rest dumped, and the brass plate has been trepanned and collected. Pretty much it. I live a frantic life don't I?

Dave,

Why not watch vibration patterns? ... I like 'em. They're free, and rather more interesting and animated than eleven solid hours of golf on BBC2.

Dave BC

[HerbD]

Interesting.  Would the shape of the plate influence the patterns (at the same frequencies)?   Or for that matter would changes in size (thickness, linear dimensions (square, rectangle, circle), type of plate (steel, wood, plastic, copper, etc) change the pattern perhaps because of resonance?

[Looking around shop to see what I have to try it]

[sbwhart]

Interesting.  Would the shape of the plate influence the patterns (at the same frequencies)?   Or for that matter would changes in size (thickness, linear dimensions (square, rectangle, circle), type of plate (steel, wood, plastic, copper, etc) change the pattern perhaps because of resonance?

[Looking around shop to see what I have to try it]

Hi HerbD if you get anything cool don't forget 

Have fun

Stew

[dsquire]

Interesting.  Would the shape of the plate influence the patterns (at the same frequencies)?   Or for that matter would changes in size (thickness, linear dimensions (square, rectangle, circle), type of plate (steel, wood, plastic, copper, etc) change the pattern perhaps because of resonance?

[Looking around shop to see what I have to try it]

Hi HerbD 

A big W E L C O M E  to 

If you haven't already realized it 

Don't be shy, pull up a chair, grab a  and join in.

Tell us about some of your projects and interests and remember 

There is always someone around to answer most questions 


cheers

Don

[Bluechip]

Hi HerbD

Welcome from me too, ...  Chladni Plate  .. Try it. I remembered the thing from years ago, at Tech.
I have little idea whether it would work with softer material, as I said, I used a scrap sheet of hard brass. That did work. Not as good as the Youtube demo, but the patterns were there. Size of plate would matter. it works along the lines of a string instrument or organ pipe. As the frequency changes you come to one that is a 'multiple' of the plate size you have, and the pattern appears. Just like an organ pipe would have a resonant frequency. I am not the world's authority on the things by any means. I had a bit of a go 'cos I had some suitable stuff to hand.  And the time to play    .. It's what I do now ..

Dave BC

[HerbD]

Hear you Stew, just have to scavenge up some pieces