Natural Science Forum / Physics / General Physics / July 2008

I've got one trapped inside a bar magnet, that's much easier. I call it
the Androcles effect.

Is it a neural tube you speak about somekind of telepathy ;)

I am really most curious how fast two objects with an interchanged
magnetic field will be aware of that the other one is gone.

I understand that Einsteins light postulate will prevent this to be
done faster than light, if magnetic field somehow had action over
great distances or am i wrong?

"Trapped magnetic flux" inside a superconductor does indeed occur.
However, the trapping is not perfect.  The superconductivity can break
down in small patches, and allow some of the magnetic flux to pass
through ("via flux vortices").  Thus, superconductors are not
necessarily a perfect magnetic container.  I did an experiment on this
very subject when I was an undergraduate.

CM

Al, what you are describing is a primitive form of an oil well logging
sensor, although these measure many more parameters than simply
temperature (stimulated back scatter analysis being just one of about
a dozen contained sensors). These are lowered by cable down a well
shaft often to well depths between 3,000 and 20,000 feet. Methods of
supplying energy to the sensor assembly vary, as do the mechanisms
that convey measurement data to the surface in real-time. Early
versions had their power supplied by the suspension cable, and
returned their data through a technique that employed the walls of the
well and the suspension cable as a crude coax, and used vhf radio as
the data transmission media.  This worked well on relatively shallow
holes. As wells became deeper and probes became more sopisticated,
this system became obsolute.  When I last lost connection with these
projects, the then current technology focused on the use of a
umbelical cable fixed to the suspension cable, that contained to small
coaxial cables.  The first one supplied power and control commands to
the sensor, the second was used for the transmission of measurement
data and sensor status to the surface which was displayed in real time
to the operator, and in 1985 was still being captured on
instrumentation recorders.  Where the technology has gone since 1985,
I can't say with any degree of certainty.

My connection was that I designed the displays for these types of
systems, based on the availability of down-time from working on
defense systems.  The connection here is that during those years I
worked for Ratheon.  Ratheon owned two Geophysical oriented firms,
Seismic Services Corporation, and a company named Birdwell.  Birdwell
had a specialty in well logging sensors and recorders. Later, Raytheon
merged the operations of Seismic Services (oil exploration) and
Birdwell, well logging.  A few years later, Ratheon became
disenchanted with the geophysical business, and sold Seismic Services
to Schlumberger  (Not a smart move in my book.)

Harry C.

On Jul 19, 10:25 pm, "Timo A. Nieminen" <t...@physics.uq.edu.au>
wrote:

Not really, but one would have to examine the configuration to be
sure.  There is some magnetic field "transmission" in the near field
but it would have to be separated from EM components.

Look. I know MIT just invented "magnetic power transmission" and
everybody is oooing and ahhhing!  Bollocks!  Bunkies, it's called
magnetic induction and it's been around for a LONG time!

Absolutely.  A DC field does indeed proceed out into space when turned
on, but carries only one bit of  information so it's hardly a
'transmission"!

Not so. Generally inductive pickups work differently from loop
antennas. Antennas are designed to work with EM waves. An inductive
pickups is designed to work with ONLY a changing magnetic field.  But
let me point out here that there is a certain advantage to inductive
transmission.  While EM waves fall off as r squared induction falls
off only as r. A loop around a long solenoid has the same output
voltage no matter how large you make it!   Magnetic fields can indeed
be picked up at large distances with properly sensitive apparatus. A
common application some time ago was tapping of telephone
conversations using inductive pickups at considerable distance from
the wires. [which is why it's always funny when people think they
heard "clicks" that mean their phone is tapped by the CIA!]

Bottom line: Magnetic "transmission" is just plain old magnetic
induction!  Period.