Xref: utzoo sci.electronics:8124 rec.ham-radio:13818 sci.astro:5420 sci.physics:9893 sci.chem:534
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!zephyr.ens.tek.com!tektronix!sequent!rjk
From: rjk@sequent.UUCP (Robert Kelley)
Newsgroups: sci.electronics,rec.ham-radio,sci.astro,sci.physics,sci.chem
Subject: Re: Trying to build a fluxgate magnetometer -- help!
Summary: see Scientific American, Feb 1968, page 124
Keywords: proton free-precession magnetometer
Message-ID: <22842@sequent.UUCP>
Date: 6 Oct 89 19:54:24 GMT
References: <1914@sactoh0.UUCP> <28601@buckaroo.mips.COM> <1363@calvin.EE.CORNELL.EDU>
Reply-To: rjk@sequent.UUCP (Robert Kelley)
Followup-To: sci.electronics
Organization: Sequent Computer Systems, Inc
Lines: 14

In _The_Amateur_Scientist_ section of Scientific American, Feb 1968, page 124,
there's a description of a differential magnetometer capable of detecting a
minimum difference in field strength of 3e-5 oersted.  The magnetic field of
the earth causes protons in water molecules to precess at a rate of about 2025 Hz.
The article describes a device consisting of two bottles of water with coils
wound around them, and a high-gain (2e6) tuned amplifier.  A dc current is passed
through both coils to align the magnetic dipoles, then the current is removed and
the amplifier is connected to the coils.  A beat frequency proportional to the
difference in the magnetic fields at each bottle is heard at the output of the
amplifier.

It might be interesting to build a more modern version of the system described
in the article.  Another installation of _The_Amateur_Scientist_ describes another
NMR setup and suggests adding ferric nitrate to the water.  Why?