Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2000-04-26
2002-04-30
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C033S361000, 24
Reexamination Certificate
active
06380735
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic sensor of orthogonal flux-gate type which can detect the intensity and direction of a magnetic field and a manufacturing method for such a sensor.
Recently, there have been ever-increasing demands for small-size inexpensive magnetic sensors with high precision which can detect the intensity of a magnetic field as well as the direction of the magnetic field, and these sensors are used for detection sensors for magnetic markers on a road related to an automobile assist cruise and advanced high way system, magnetic sensors used for electronic compasses and navigation systems on vehicle equipment, measuring magnetic sensors for a magnetic field of live body such as the heart, and detection magnetic sensors for use in non-destructive inspection for steel, etc.
With respect to conventional magnetic sensors of this type, examples thereof include: Hall elements, MR elements, MI elements, superconducting quantum interference devices (SQUID), magnetic sensors of parallel or orthogonal flux-gate type, etc. Among these, the Hall elements are poor in sensitivity, and MR elements, MI elements, etc. are inferior in that since a single element cannot detect the direction of a magnetic field, a plurality of them need to be installed. In contrast, magnetic sensors of both parallel and orthogonal flux-gate types are able to detect the intensity and direction of a magnetic field even when installed as a single sensor. Moreover, these sensors are superior in the linear property, temperature characteristic and resolution of the detection output, and in particular, from the viewpoint of detection precision, attention has been focused on those of orthogonal flux-gate type because of their high precision.
FIG. 1A
is an explanatory drawing that shows the principle of an element of orthogonal flux-gate type;
FIG. 1B
is an explanatory drawing that shows a magnetic flux formed in the core;
FIG. 2
is an explanatory drawing that shows the operation thereof; and
FIG. 3
are waveform diagrams showing an exciting current, a degree of magnetization in the core length direction and an output voltage of the detection coil, in the case when detection for a magnetic field is made by using the element shown in FIG.
1
A.
Reference numeral
21
is a bar-like conductor made by a conductive material,
22
is a cylindrical core made by a soft magnetic material,
23
is a detection coil, and
25
is a high-frequency power source. The bar-like conductor
21
is placed coaxially with the core
22
through the inside of the core
22
, and the bar-like conductor
21
is connected to the high-frequency power source
25
. When the magnetic sensor of this type is placed with the axial line of the bar-like conductor
21
and the core
22
aligned in parallel with the direction of a magnetic field to be measured, the magnetic flux inside the magnetic field to be measured is attracted toward the core
22
side as illustrated in FIG.
2
(
a
), so that a magnetic path is formed through the core
22
.
When an exciting current I
Ex
having a sine-wave as shown in
FIG. 3
is flowed through the rod-like conductor
21
, the peripheral face of the core
22
is magnetized as indicated by arrow in FIG.
2
(
b
) so that the exciting current I
EX
is allowed to increase from a state shown in FIG.
3
(
a
), and when it reaches a maximum value as shown in FIG.
3
(
b
), the magnetization of the core
22
reaches a saturated state so that the magnetic flux of the magnetic field to be measured is separated from the core
22
and aligned in parallel with the bar-like conductor
21
. In this state, the degree of magnetization of the core
22
in the length direction drops in a manner as shown in
FIG. 3
, and the output (voltage) of the detection coil
23
increases at a position where the rate of change in the magnetization in the length direction is great, and at a position where the rate of change in the exciting current I
EX
is great and when the current I
Ex
reaches a maximum value or a minimum value, the output (voltage) of the detection coil
23
becomes zero.
During the state in which the exciting current I
EX
decreases from the maximum value and reaches the zero-crossing point, as shown in FIG.
2
(
c
), the magnetic flux of the magnetic field to be measured is again allowed to pass through the core
22
. When the direction of the exciting current I
Ex
is reversed, the peripheral face of the core
22
is magnetized in a reverse direction to the circumferential direction as indicated by arrow in FIG.
2
(
d
) and the exciting current I
EX
decreases to reach a minimum value, the magnetization of the core
22
is again allowed to reach a saturated state; thus, the magnetic flux of the magnetic field to be measured is aligned in parallel with the axial line of the core
22
. During this state, the output of the detection coil
23
repeats changes in which it becomes greater in the area where the exciting current I
EX
is great while it becomes zero when the exciting current I
EX
reaches the minimum value, with the result that it has a change corresponding to 2 cycles in response to a change in the exciting current I
EX
corresponding to one cycle.
In other words, the exciting current is allowed to flow through the cylinder-shaped core
22
made of a soft magnetic material so as to excite it in the circumferential direction periodically so that the magnetization in the length direction of the core
22
is switched; thus, the relationship between the core
22
and the magnetic field to be measured is changed from FIG.
2
(
a
) to FIG.
2
(
b
), from FIG.
2
(
b
) to FIG.
2
(
c
) and from FIG.
2
(
c
) to FIG.
2
(
d
). In this state, the density of the magnetic flux, which resides around the detection coil
23
, is allowed to change so that, as illustrated in
FIG. 3
, an output voltage (the phase of the output voltage) corresponding to the intensity (direction) of the magnetic field to be measured is obtained from the detection coil
23
.
In an element of such an orthogonal flux-gate type, the flux distribution formed by the exciting current I
EX
flowing through the rod-like conductor
21
is shown by FIG.
1
B. In other words, the magnetic fluxes are formed not only in the core
22
(indicated by a broken line s in the Figure), but also in the circumferential direction (indicated by a broken line t in the Figure) of a space outside the core
22
. As a result, most of them only excite the space, and the magnetic flux fails to concentrate the magnetic field on the core
22
, resulting in degradation in magnetic efficiency and wasteful consumption of the exciting current I
EX
. Moreover, in the element of orthogonal flux-gate type, since the detection coil
23
is an indispensable member, one portion of the magnetic fluxes (the broken line t in the Figure), generated in the space outside the core
22
, come to reside around the detection coil
23
, causing an exciting signal to be mixed with the detection output and resulting in degradation in the S/N ratio and resolution. Furthermore, the actual construction of the element of orthogonal flux-gate type is complex as compared with the Hall elements, MR elements, etc., although it is schematically shown in
FIGS. 1A and 2
so as to show the principle thereof; therefore, another problem is that it is difficult to miniaturize the construction.
Here, Japanese Patent Application Laid-Open No. 10-90381(1998) has proposed a magnetic detection element shown in FIG.
4
.
FIG. 4
is a schematic view that shows the constriction of the conventional magnetic detection element disclosed by the above-mentioned patent application, in which a bar-like conductor
61
made of a copper wire is coated with an insulating layer
62
, and inserted into a soft magnetic tube
63
coaxially, and one end of the bar-like conductor
61
is connected to a ground conductor
65
through a conductor
64
. In such a conventional magnetic detection element, a great change in impedance is generated by utilizing a frequency in the vicinity of a re
Aurora Reena
Patidar Jay
Sumitomo Special Metals Co. Ltd.
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