Frequency selective detecting system for detecting alternating magnetic fields
 A system for detecting an AC magnetic field of a desired frequency using a magnetic sensing element of the parametrically excited second harmonic oscillator, in which a reference signal having a repetition period substantially equal to the repetition period of the AC magnetic field is adopted for synchronous detection of the detected output of the magnetic sensing element, and in which a current proportional to the intensity of a noise magnetic field is applied to the oscillation winding of the magnetic sensing element to lessen the influence of the noise magnetic field to greatly improve the SN ratio of the detected signal. 
Kokusai Denshin Denwa Kabushiki Kaisha
G
G01R
inventional
Yoshinao Kazuomi Teruji Shizuo
Iwamoto Yamamura Watanabe Suzuki