Thomas Dick 
To: psnlist 
Sent: Tue, 10 Jul 2012 15:50
Subject: Re: diamagnetic levitation seismometer possibility
=20
On 7/9/2012 9:34 AM, chrisatupw@....... wrote:=20
From: Bob McClure bobmcclure90@............
                               =20







I, too, have carried out diamagnetic levitation experiments similar to thos=
e by Meredith Lamb. Although the large amplitude motion looks smooth and fr=
ictionless, what I concluded for very small amplitudes, such is not the cas=
e. The supporting magnetic field has small-scale roughness, and the levitat=
ed graphite tends to hung up in the hills and valleys of the resulting forc=
e.=20

I don't understand this. I would only expect 'field roughness' to show up f=
or linear motions comparable to the levitation height, of 1/2 to 1 mm, NOT =
for tiny movements of ~100 nano metres.=20
    One problem that I had with levitating graphite was due to it's propens=
ity to pick up lint, hairs and dust. These can and do effect a very light s=
lider. Another problem is the extremely high field gradients at the edges o=
f the magnets picks up magnetic and paramagnetic dust only too easily. I cl=
ean magnets using a roll of PVC tape - you stick it onto the surface and th=
en peel it of with the rubbish attached.=20































































Chris & all ...

All of you seem locked in on the material being the problem ... and you may=
 be correct. But what if,  the "change" you are "seeing" and blaming on the=
 field roughness is being induced by  earth's magnetic field or from other =
radiations from space. I suggest shielding could be an issue. Some of you m=
ight remember a seismic unit I created years ago using a large horseshoe sh=
aped magnet dampened with oil. That setup was affected by the 200 watt 10 m=
eter amateur radio repeater I was operating at the time.=20

Hi Tom,=20














    You do have to shield the unit from any air movements VERY carefully. A=
lso from solar / heat radiation.The 'slider' only weighs 2 to 3 gm, so it i=
s quite easy to upset it! Strong radio signals can interfere with the elect=
ronics if they are not shielded well enough. I was using Si photocells, whi=
ch are fairly resistant to interference. The magnetic levitation enables th=
e armature to be suspended freely.  It just 'floats in mid air' with 1/2 to=
 1 mm clearance over the magnets. I didn't see anything comparable to Bob's=
 problems.=20
    The principle difficulty is designing / adjusting / trimming the field =
'suspension dish' and the armature to give a usefully long period. From mem=
ory, the longest period that I got was about 8 seconds. This would still re=
quire a specialist VLF boost amplifier to get periods of out to about 20 se=
conds. It might be more practical to choose a period of 3~4 seconds, which =
is much easier to attain.=20

    Regards,=20

    Chris























Thomas Dick <dickthomas01@.............>

To: psnlist <psnlist@..............>

Sent: Tue, 10 Jul 2012 15:50

Subject: Re: diamagnetic levitation seismometer possibility

 

On 7/9/2012 9:34 AM, chrisatupw@....... wrote: 

From: Bob McClure bobmcclure90@......... 

            &nb=
sp;            =
       
























=




I, too, have carried out diamagnetic levitation experiments similar to=
 those by Meredith Lamb. Although the large amplitude motion looks smooth a=
nd frictionless, what I concluded for very small amplitudes, such is not th=
e case. The supporting magnetic field has small-scale roughness, and the le=
vitated graphite tends to hung up in the hills and valleys of the resulting=
 force. 




I don't understand this. I would only expect 'field roughnes=
s' to show up for linear motions comparable to the levitation height, of 1/=
2 to 1 mm, NOT for tiny movements of ~100 nano metres. 


    One problem that I had with levitati=
ng graphite was due to it's propensity to pick up lint, hairs and dust.&nbs=
p;These can and do effect a very light slider. Another problem is the =
extremely high field gradients at the edges of the magnets picks up magneti=
c and paramagnetic dust only too easily. I clean magnets using a roll of PV=
C tape - you stick it onto the surface and then peel it of with the rubbish=
 attached. 















































































































































































Chris & all ...



All of you seem locked in on the material being the problem ... and you may=
 be correct. But what if,  the "change" you are "seeing" and blaming o=
n the field roughness is being induced by  earth's magnetic field or f=
rom other radiations from space. I suggest shielding could be an issue. Som=
e of you might remember a seismic unit I created years ago using a large ho=
rseshoe shaped magnet dampened with oil. That setup was affected by the 200=
 watt 10 meter amateur radio repeater I was operating at the time. 



Hi Tom, 








































    You do have to shield the unit from =
any air movements VERY carefully. Also from solar / heat radiation.The =
;'slider' only weighs 2 to 3 gm, so it is quite easy to upset it! Stro=
ng radio signals can interfere with the electronics if they are not shielde=
d well enough. I was using Si photocells, which are fairly resistant t=
o interference. The magnetic levitation enables the armature to be suspende=
d freely.  It just 'floats in mid air' with 1/2 to 1 mm clearance over=
 the magnets. I didn't see anything comparable to Bob's problems. 


    The principle difficulty is designin=
g / adjusting / trimming the field 'suspension dish' and the armature to gi=
ve a usefully long period. From memory, the longest period that I got was a=
bout 8 seconds. This would still require a specialist VLF boost amplifier t=
o get periods of out to about 20 seconds. It might be more practi=
cal to choose a period of 3~4 seconds, which is much easier to attain. 



 


    Regards, 


 


    Chris