Abstract: 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.

Abstract: A character pattern recognition method and apparatus for recognizing an unknown character pattern in accordance with a correlation between the unknown character pattern and each known standard character pattern, in which the unknown character pattern is temporarily stored in a magnetic thin plate in a form of a magnetic domain pattern. The magnetic domain pattern is modified by varying the bias magnetic field on the magnetic thin plate to provide a modified unknown character pattern emphasizing the feature of the unknown character pattern stored in the magnetic thin plate. The modified unknown character pattern is compared with each known modified feature enhanced standard character pattern to obtain the correlation.

Abstract: A magnetic bubble transmission system in which a magnetic bubble is retained in a magnetic thin plate under an appropriate bias magnetic field applied to said magnetic thin plate in a direction perpendicular thereto and in which said magnetic bubble is transmitted by reducing and restoring the intensity of the bias magnetic field. A single conductor line is disposed in close contact with the magnetic thin plate. Magnetic patterns magnetostatically coupling with the magnetic bubble are disposed along the conductor to develop at least one desired transmission path of the magnetic bubble line in such a manner that their width are monotoneously reduced at regular intervals in the desired transmission path of the magnetic bubble. The intensity of the bias magnetic field in the area extending along said conductor line is reduced and restored by a pulse current flowed in the conductor line. The transmission step of the magnetic bubble can be controlled by changing the level of the pulse current.

Abstract: A magnetism detecting system, in which reference magnetic fields sequentially scan many radial scanning lines obtained by dividing a plane to be detected at regular intervals of a desired angle with respect to an origin positioned at the common intersecting point of said scanning lines. At least one parametrically excited second harmonic oscillator detects the direction and magnitude of a magnetic field to be detected along each of the scanning lines. A display device is provided for scanning and displaying the plane with respect to the origin in synchronism with the scanning of each of the scanning lines. A detected output is applied to the display device when the magnetic field to be detected and the reference magnetic field coincides with each other in direction and in magnitude.