[rescue] Oh no! This poor Origin server.....

[Dave McGuire]

On Apr 1, 2004, at 11:16 PM, Phil Stracchino wrote:
>>   So...use it as a hypersensitive metal detector.  Not to find watches
>> on the beach, but to find coins under a thousand feet of water.
>
> Wow.  That sensitive?

   Yup.

>   How do you turn the output signal into location
> information?  (Or is this left as an exercise for the student?)

   Well, the frequency of the signal you get out of the kerosene cell 
can be, with a tiny bit of math, turned directly into an absolute 
measurement of the intensity of the local magnetic field.  Now build 
two identical units, stack one sensor atop the other, maybe 3-6 feet 
apart, mounted to a pole of some sort.  Suspend it so it always stands 
as close to vertical as you can manage.

   Now measure the *difference* between the two frequencies from the two 
sensors...Voila, a proton precession gradiometer...measuring the local 
field gradient.

   Now...Put this on a boat, and do a cartesian sweep pattern...plotting 
the gradient with false color or something like that on an X-Y grid.  
You will see a "bump" if you pass over something metallic, and with a 
little bit of math, you can calculate (at least I *think* you can 
calculate) the absolute distance between you and the object.

>>   Or use it to detect cars & trucks driving by, just for shits &
>> giggles.
>
> Unfortunately, I'd probably create a bigger signal just walking around
> the room, with all the metal in my leg.
>
> Then again, it *is* stainless steel, which is diamagnetic ....

   Indeed. :)

       -Dave

--
Dave McGuire          "PC users only know two 'solutions'...
Cape Coral, FL          reboot and upgrade."    -Jonathan Patschke