New Type of Flux‐Gate Magnetometer

The use of an ordinary toroidal core without air‐gap as a flux‐gate magnetometer has been overlooked. A magnetometer using such a core as the field‐sensitive element with semicircularly wound and differentially connected second‐harmonic detector windings has been developed. The semicircle portions of a nickel‐iron‐alloy ring core act here like two separate cores (corresponding to the two parallel nickel‐iron‐alloy strips or scrolls of conventional forms of flux‐gate elements), as far as second‐harmonic flux components are concerned. By using tape‐wound or laminated (washer‐type) Supermalloy cores having i.d.‐o.d. ratios in the range from 0.85 to 0.98, a sensitivity of 1000 μamp/oe or 1 v/oe can be achieved. Such ``ring‐core flux‐gate elements'' make it possible to: (1) use ultrathin, ⅛‐mil tape and correspondingly high excitation frequencies, 10–40 kc/sec, (2) make ``point measurements'' by reducing the core diameter to 0.5 in., or less, (3) minimize the magnetizing‐current requirements, (4) obtain linear...