Abstract: A method and apparatus are disclosed for measuring the magnetic properties of magnetic materials by generating flux lines through a balanced magnetic core and through a magnetic sample placed adjacent to the core. Increased sensitivity is accomplished through a modulation of the flux in the magnetic core which is measured and subsequently demodulated to yield an electrical signal corresponding to the magnetic properties of the material being tested.

Abstract: A magneto-optic Kerr effect hysteresis loop measuring apparatus is provided which employs a pair of pole-pieces of the same magnetic polarity providing a high and uniform magnetic field strength in the gap between the oppositely disposed faces of the pole-pieces. The spot on the product which is to be nondestructively tested is placed in the gap between the pole-pieces in a region of uniform saturating magnetic field. A laser beam having a high polarization ratio is directed along an incident path with a spot on the surface of the product to be nondestructively tested, and a reflected beam is processed in a Kerr effect detector to provide hysteresis loop data. This data is capable of providing information sufficient to determine the squareness of the hysteresis loop and the coercivity of high coercivity material being nondestructively tested.

Abstract: A degaussing head is mounted on a tape drive transport unit adjacent to a rotating reel of tape. The degaussing head is selectively energized by a signal indicating that the tape is to be erased. Preferably, the degaussing head takes the form of an E-shaped iron core driven by a coil supplied with attenuated DC current. The degaussing head is mounted on the door of the tape drive transport cabinet in such a manner that when the door is closed the legs of the degaussing head orthogonally span the tape in the reel to provide an attenuated alternating magnetic field for bulk erasing the tape as it is rotated past the head.

Abstract: Apparatus is disclosed for bulk erasing magnetic tapes spirally wound on a carrier. A pair of magnetic structures are spaced apart by an air gap of sufficient width to receive the tape carrier. Circuitry is provided for producing a rotating magnetic field in the air gap substantially parallel with the tape. Preferably, the magnetic structures take the form of multi-legged iron cores. The cores are mounted so that corresponding legs on opposing cores have the same magnetic polarity. A phase shifter circuit is adapted to supply currents 90.degree. out of phase with one another to selected pairs of legs in the cores to create a rotating magnetic field in the air gap.