Also see: Sensors -Anti-Shoplifting Garmet Tags - Electronic Alarm Systems (EAS).
The eBay seller (ttshungary)
is offering these for $20 + $10 for shipping. The
appear to be would tape type toroidal cores with a plastic
case. The core is 28mm OD, 20mm ID, 5mm high with a
rectangular cross section leading me to think they are wound
tape. The plastic case is: 30.5mm OD, 17.5mm ID and
The fluxmeter is a device that integrates the magnetic lines to come of with the total strength of a magnet.Handbook_for_Electrical_Engineers 1917 edited by Harold Pender - dead beat galvanometer
See: Helmholtz Coilx\Sensitive Research Inst Co Fluxmeter
Electricity and Magnetism for Advanced Students 1920 by Sydney George Starling - equations for ballistic galvo fluxmeter.
2020 June - noticed a number of quack AKS Long Range Metal Detectors where the pitch is pure snake oil. But I did find an interesting web page with some real information.
Geotech Technology for Treasure Hunting - where a number of topics include a list of related patents.
Magnetometers - Patents - Proton Precession (Wiki) magnetometers are very sensitive, but also expensive. It's possible to home brew them, but a lot of work. Typically used in professional Archaeology and treasure hunting.
Geophysics - Patents -
DC PM Motors
Flux Gate Patents
Magnetic Locators (only ferrous, includes gradiometer)
Metal Locators (All metals)