Have you looked into Hall Effect Sensors? Have a look at this article: <a href="http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/77/29325/01325161.pdf?arnumber=1325161" target="_blank">http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/77/29325/01325161.pdf?arnumber=1325161</a> <a href="http://ieeexplore.ieee.org/iel5/77/29325/01325161.pdf?arnumber=1325161" target="_blank">http://ieeexplore.ieee.org/iel5/77/29325/01325161.pdf?arnumber=1325161</a> and this one: <a href="http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=RSI****000077000008086101000001&idtype=cvips&gifs=yes" target="_blank">http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=RSI****000077000008086101000001&idtype=cvips&gifs=yes</a> <a href="http://link.aip.org/link/?RSI****/77/086101/1" target="_blank">http://link.aip.org/link/?RSI****/77/086101/1</a> and this one: Quite a bit elaborated.. The magnetic field is measured by 3 orthogonal axes of Hall effect probes. <a href="http://www.adc9001.com/do***ents/company/publications/papers/magnetic_field.pdf" target="_blank">http://www.adc9001.com/do***ents/company/publications/papers/magnetic_field.pdf</a>