Seismic Sensor based on Diamagnetic Levitation

Why levitation requires a gradient (spatial variation) in the magnetic field.


9/22/02 Visit to Meredith's
Field Visualization
Chris' Pages
Pencil Leads
Meredith summary by Chris 2/05/03


Meredith and David Lamb and James Spottiswoode have made all made great progress with the development of a seismic sensor based on diamagnetic levitation.  Recently (June, 2002) James has found that certain pencil leads are diamagnetic, which raises the possibility of a plentiful supply of diamagnetic graphite.

I've played around a bit more with this in mind, as indicated in the photograph and mpeg movies below.

I am using 10 rare-earth magnets from Forcefield.  These are 1/4 " diameter by 1 " long rods that are magnetized through the diameter rather than from one end to the other.  Two of the magnets are broken in two and they are arranged on a metal plate in two rows as in the figure below.

Note that I have left a gap in the center so that a flag can be suspended from the graphite rod.

I've had mixed success with pencil leads.  I've been trying Pentel Hi Polymer.  I had some old packages of 0.7 x 60 mm HB, 0.5 x 60 mm HB and F, and 0.3 x 60 mm HB around the house that I found would levitate.  I purchased additional 0.9, 0.7, and 0.5 mm in identical packages from Office Max yesterday and found that only the 0.5 mm leads would levitate.  I suppose this property may vary for different manufactured batches of leads.

I super glued two of the 0.7 mm leads together with a 2 mm overlap to extend their length to nearly 120 mm (I tried end-to-end gluing with out success).  An mpeg of this arrangement is shown here.  Not too exciting.  The low mass results in a frequency greater than 1 Hz.

I then tried one of the 1/8 " diameter spectrographic rods that Meredith Lamb gave me.  This worked better and yielded a period of about 1 second.  See mpeg here

I would like to figure out how to extend the period, and I have yet to make a photo detector, although I now have some plans, kindly provided by Chris Chapman.

Continued 6/17/02