Patent No. 4591788 Magnetic field sensing device
Patent No. 4591788 Magnetic field sensing device (Mohri, et al., May 27, 1986)
Abstract
A magnetic field sensing device for sensing low levels of magnetic intensity is composed of a ribbon-shaped strip of amorphous magnetic material having at least one twist along the length thereof between the ends of the strip. Subsequent to imparting the desired number of twists to the strip, the strip is supported in the twisted condition. The device is capable of generating a pulse in response to the presence of an external magnetic field similar to the Wiegand wire effect.
Notes:
Magnetic
field sensing device. Filed September 1982, granted May 1986. Says it is capable
of detecting magnetic fields in the .001 Hz to 6 Hz frequency range. Basically
just detects that the magnetic field is there and sounds like something from
a Junior High or High School general science class demonstration.
BACKGROUND
OF THE INVENTION
The present invention is directed to a magnetic field sensing device and more
specifically to a twisted, ribbon-shaped strip of amorphous magnetic material
which is supported in the twisted condition and exhibits an effect similar to
a Wiegand effect.
A Wiegand wire is a bistable magnetic device having specific characteristics
obtainable by processing a thin ferromagnetic wire to form a central relatively
"soft" core portion and an outer relatively "hard" magnetized shell portion
with relatively low and high coercivities respectively. Such a bistable ferromagnetic
wire is disclosed in the Wiegand U.S. Pat. No. 3,820,090, granted June 25, 1974
and entitled "Bistable Magnetic Device". The magnetized shell portion is operable
for magnetizing the core portion in a first direction, the magnetization of
the core portion is reversible by application of a separate magnetic field and
the shell portion is operable to remagnetize the core portion in a first direction
upon removal of the separate magnetic field. As a result of the changing magnetic
field, there is a net change in the flux outside of the wire and an appropriately
placed pick-up coil will generate a pulse-shaped voltage having a peak value
and a narrow width with no relation to the changing rate of the magnetic field.
Thus, the Wiegand wire is useful as a magnetic sensor. However, a conventional
Wiegand wire is capable of only being able to detect a fairly high external
magnetic field.
German Offenlegungsschrift No. 28 06 249 discloses a transmitter for emitting
an electrical signal during the magnetic reversal of a ferromagnetic wire within
a coil wherein the wire is kept under tensile stress and/or torsional stress.
Comments