Hi John and all readers,

Your new web picture of the Colorado School of Mines, EPICS
group titled the "leadheads" diamagnetic seismometer was a real
attention getter, mainly for the induced curiosity with the additional
end magnets they added thereon.  The obvious small size of the
unit; and its relatively low cost are quite noteworthy also.

http://www.jclahr.com/science/psn/epics/reports/index.html

Both varieties of magnet sizes seem to be available via
Forcefield/Wondermaget.  The gold plated rod cylinder magnet
(1" length x 1/4" in diameter) seems to be only available via a
email inquiry to them; as its likely in a very limited supply.  Write
too:  ff@wondermagnet.com, or, forcefld@verinet.com

while the 1/4" x 1/4" x 1/2" magnet is shown via:

http://www.wondermagnet.com/dev/magnet25.html

The magnets polaritys should be noted.  The cylinder magnets
polarity is that they are polarized through the diameter and
not per half the length.  I.e; one side of the length is the north
pole and the other side is the south pole.  The small end magnets
are conventional in that 1/2 the length is one pole, and the other
half is the opposite pole.

The magnet layout with the poles marked as such below is the
only way one could have success.  In particular the end magnets
have to be arranged per the pic below.  If they are reversed,
the diamagnetic spectrographic rod, wants to escape the
containment, and/or not stabilize.

magnet layout 

If one observes the end magnets orientations on the diamagnetic
mass; the end magnets setup can both illustrate a inverted
pendulum (non-stable) and a regular hanging pendulum in its
response to the far left and right end magnets (1/4"x1/4"x1/2")
polarity changes.  The actual gauss across the magnets is in the
averaging neighborhood of  7K.  Both magnets are rated MGOe
45, which is about the strongest commercially made.

I did make up a magnet assembly like they used to test the
period.  I was most amazed that the natural period was around
6 seconds when leveled and stabilized!  All of the previous
known similar designs with the same gold plated cyclinders only;
averaged from one to ~ three seconds, in their physically induced
offsets, for testing the natural undampened periods.  The 6 second
period should do quite well with "P" & "S" wave detection for its
unknown true distance range of sensitivy and quake magnitude.
The 6 period is not to be distracted, as with most all seismometers
they are subject to "L" or Love wave horizontal displacements; and
the "L" wave phase could show up on seismograms with this; as
with some other horizontal seismometer designs to varying degrees.

Chris Chapman of the UK, has previously made mention of the
use of end magnets in other magnet layout designs, but it is most
interesting that the designers independantly came up with this
also, as it quite definitely extends the period, while also seemingly
slightly increasing the amount of diamagnetic lift (diamagnetic
repulsion of the graphite from the magnet/s).  This is a very good
additional observational application which makes it quite unique!

On the subject of dampening for the same illustrated design; the
amount of aluminum foil and its placement location on the
spectrographic rod "may not" (?); be sufficient for near critical dampening;
nor positioned to where the best effects can occur.  The strongest
fields will be near the joined lengthwise magnets; although some dampening
will also occur between the rows of magnets.  Eddy current dampening in
itself is a study where a mix of possible material and magnets can vary the
results.  It could be that for the "leadheads" graphite rod, they could simply
add additional outer rings of aluminum foil to attain somewhat better
dampening; nor would they have to be attached to the upright optical
flag they already have.  I would suggest a review of James Spottiswoode's
extensive web site with its text and photographs at:

http://www.jsasoc.com/diamagnetic_suspension_seismomet.htm

It should also be noted, that some varietys of common pencil refill leads
are quite diamagnetic, and this was first noted by James.  There is a
list of some tested commercially available pencil leads at:

http://www.jclahr.com/science/physics/diamag/seismo/leads.html

Perhaps a main point in applying aluminum foil/leaf wrapping for eddy
current dampening is that at some loop juncture of its wrapping/s; the
wrapped foil edges should make positive bridging contact to allow a full
diameter loop conduction of its eddy current dampening use.  If it doesn't,
the eddy current flow will not be as effective.   One might entertain the
thought of using various electrically conductive glues, resins, paint....if
the specific area's  mechanical aluminum contacts, are in question.

Congratulations to the "Leadheads" group for their innovative work and
effort; as it has contributed significantly with the prospect of using
diamagnetic seismometers!


Take care, Meredith Lamb
1/4/2002

meredithlamb at earthlink dot net

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