U.S. patent application number 12/681527 was filed with the patent office on 2013-02-14 for magneto-impedance element and magneto-impedance senor including detection coil..
This patent application is currently assigned to Aichi Steel Corporation. The applicant listed for this patent is Yoshinobu Honkura, Michiharu Yamamoto. Invention is credited to Yoshinobu Honkura, Michiharu Yamamoto.
Application Number | 20130038323 12/681527 |
Document ID | / |
Family ID | 40526244 |
Filed Date | 2013-02-14 |
United States Patent
Application |
20130038323 |
Kind Code |
A1 |
Honkura; Yoshinobu ; et
al. |
February 14, 2013 |
MAGNETO-IMPEDANCE ELEMENT AND MAGNETO-IMPEDANCE SENOR INCLUDING
DETECTION COIL.
Abstract
A magneto-impedance element includes a magnetic sensitive member
having a form of a line, whose electromagnetic characteristics vary
depending on an external magnetic field, a pulse current flowing
from one to another end portion thereof in an axial direction. A
conductive layer is arranged on an insulating layer provided on an
outer surface of the magnetic sensitive member. A connection
portion, electrically connecting the magnetic sensitive member and
the conductive layer, is arranged on the other end portion in the
axial direction of the magnetic sensitive member. A detection coil,
outputting an induced voltage corresponding to an intensity of an
external magnetic field acting on the magnetic sensitive member
when the pulse current flows in the magnetic sensitive member, is
wounded around the conductive layer. A direction of the pulse
currents flowing in the magnetic sensitive member and in the
conductive layer are opposite each other.
Inventors: |
Honkura; Yoshinobu; (Aichi,
JP) ; Yamamoto; Michiharu; (Aichi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Honkura; Yoshinobu
Yamamoto; Michiharu |
Aichi
Aichi |
|
JP
JP |
|
|
Assignee: |
Aichi Steel Corporation
Tokai-shi, Aichi
JP
|
Family ID: |
40526244 |
Appl. No.: |
12/681527 |
Filed: |
October 2, 2008 |
PCT Filed: |
October 2, 2008 |
PCT NO: |
PCT/JP2008/067946 |
371 Date: |
June 9, 2010 |
Current U.S.
Class: |
324/244 |
Current CPC
Class: |
G01R 33/18 20130101;
G01R 33/063 20130101 |
Class at
Publication: |
324/244 |
International
Class: |
G01R 33/02 20060101
G01R033/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2007 |
JP |
2007-258578 |
Claims
1: A magneto-impedance element comprising: a magnetic sensitive
member having the form of a line, whose electromagnetic
characteristics vary depending on a magnetic field acting from the
outside, and in which a pulse current flows from one end portion
thereof to the other end portion in an axial direction; a
conductive layer arranged on an insulating layer provided on an
outer surface of the magnetic sensitive member; a connection
portion arranged at the other end portion in an axial direction of
the magnetic sensitive member to electrically connect the magnetic
sensitive member and the conductive layer to each other; and a
detection coil wounded around the conductive layer unidirectionally
to output an induced voltage corresponding to an intensity of the
external magnetic field acting on the magnetic sensitive member
when the pulse current flows in the magnetic sensitive member,
wherein a direction of the pulse current flowing in the magnetic
sensitive member and a direction of the pulse current flowing in
the conductive layer are opposite to each other.
2: The magneto-impedance element according to claim 1, wherein the
magnetic sensitive member is formed to have a circular section, the
conductive layer is formed to have a cylindrical shape, and the
conductive layer is arranged coaxially with the magnetic sensitive
member.
3: The magneto-impedance element according to claim 1, wherein the
magnetic sensitive member is composed of an amorphous magnetic
material.
4: The magneto-impedance element according to claim 1, wherein the
conductive layer is a plated film or a sputtered film made of
copper or aluminum.
5-6. (canceled)
7: A magneto-impedance sensor comprising: the magneto-impedance
element according to any one of claims 1 to 4; a pulse generator
which generates the pulse current input to the magnetic sensitive
member; and a sample-and-hold circuit which is connected to the
detection coil and samples and holds the induced voltage output
from the detection coil when the pulse current flows.
Description
TECHNICAL FIELD
[0001] The present invention relates to a magneto-impedance element
and a magneto impedance sensor having good linearity.
BACKGROUND ART
[0002] As a conventional magnetic sensor (hereinafter referred to
as an MI sensor) using a magneto-impedance element (hereinafter
referred to as an MI element), for example, a magnetic sensor
having a detection coil wound around an amorphous wire is known.
Patent Document 1 discloses a MI sensor which causes a pulse
current to pass through an amorphous wire and measures a first
pulse of an induced voltage output from a detection coil to make it
possible to sensitively detect an external magnetic field Hex. The
MI element is also called a giant magneto-impedance element or a
GMI element. The MI sensor is also called a giant magneto-impedance
sensor or a GMI sensor. [0003] Patent Document 1: Japanese
Unexamined Patent Application Publication No. 2000-258517
[0004] As will be described below, a principle of magnetic field
detection by the MI element will be explained with reference to
FIG. 10.
[0005] As shown in the drawing, when a pulse current I passes
through an amorphous magnetic wire 91, a magnetic field H is caused
in a circumferential direction by the pulse current I. An induced
voltage (dH/dt) is output from a detection coil 95. In the case
where an external magnetic field Hx is applied in the state that
the pulse current I flows, spins arranged in a circumferential
direction of the amorphous magnetic wire 91 resonate and shake by
.theta.. An induced voltage (dM.theta./dt) generated by the spin
resonance .theta. is output to the detection coil 95 overlapping
the induced voltage (dH/dt). More specifically, in application of
an external magnetic field Hx, an induced voltage
(dH/dt+dM.theta./dt) is output.
[0006] FIG. 11 is a waveform chart showing an output of an induced
voltage to a pulse current of the MI sensor using the MI element.
This is a waveform chart 101 showing a time variation of induced
voltage in damped oscillation output from a detection coil when the
pulse current I flows in application of the external magnetic field
Hx.
[0007] FIG. 12 shows a waveform chart 102 showing a time variation
in induced voltage caused only by the pulse current I without
applying the external magnetic field Hx with respect to a peak
characteristic of the first pulse in the waveform chart 101, a
waveform chart 103 and a waveform chart 104, each showing a time
variation in induced voltage when the external magnetic field Hx is
applied (+Hx and -Hx).
[0008] As shown in FIG. 12, times (t) for zero crossing of the
induced voltages when the first pulses damped in the waveform
charts 102 to 104 are not equal to each other and have a phase
difference. With respect to time t1 at which zero crossing is
caused only by the pulse current I without applying an external
magnetic field, time at which zero crossing occurs when an external
magnetic field +Hx is applied is given by t1+.DELTA.ta to cause a
delay (.DELTA.ta). When an external magnetic field -Hx is applied,
the time for zero crossing is given by t1-.DELTA.tb, the zero
crossing time is earlier (.DELTA.tb).
[0009] As a result, when the external magnetic field changes in
polarity from +Hx to -Hx (FIG. 12), it is found that time at which
an output voltage of the detection coil reaches a peak varies as
zero crossing time varies. The present inventors devotedly studied
the cause, and conceived the followings.
[0010] There is a phase difference in peak time between a time
variation waveform of an output voltage by dH/dt which is a
component caused by a pulse current and a time variation waveform
of an output voltage by dM.theta./dt which is a component varying
(changing) depending on an external magnetic field. For this
reason, an induced voltage waveform generated in the detection
coil, which is a combination of two waveforms, has a phase
difference with respect to peak time of an output voltage generated
by dH/dt which is a component caused by the pulse current. A peak
voltage of a time variation waveform in output voltage by
dM.theta./dt which is a component varying depending on the external
magnetic field rises with an increase in external magnetic field.
For this reason, a phase difference of an induced voltage waveform
generated in the detection coil which is a combination of two
waveforms is supposed to be changed with respect to peak time of an
output voltage generated by dH/dt as the external magnetic field
changes.
[0011] As will be described below, a known magneto-impedance sensor
(hereinafter arbitrarily referred to as a MI element) uses the fact
that a peak value of an output voltage of the detection coil is in
proportion to an external magnetic field parallel to a magnetic
sensitive member used in a magneto-impedance element (hereinafter
arbitrarily referred to as a MI element).
[0012] In the MI sensor using the current MI element, on the basis
of time t1 at which the pulse current rises as shown in FIG. 6
(described later), an analog switch is turned on-off for a short
period of time at predetermined timing t2 at which a peak value is
supposed to be given in an induced voltage waveform generated in
the detection coil to detect a peak value of an output voltage
generated in the detection coil corresponding to an external
magnetic field. In this case, when a predetermined input current
waveform and an output voltage waveform corresponding to the input
current waveform are present, a sampling time .DELTA.t is obtained
by subtracting rise time t1 of the pulse current from a
predetermined timing t2 at which a peak value is supposed to be
given in the output voltage waveform (.DELTA.t=t2-t1).
[0013] In general, time at which an external magnetic field is
applied such that a sampling time .DELTA.t is fixed in the absence
of an external magnetic field (102 in FIG. 12) is also
measured.
[0014] For this reason, when time at which an output voltage of the
detection coil reaches a peak is varied by an external magnetic
field as shown in FIG. 12, if the external magnetic field is
applied, voltages are sampled at a timing deviated from time at
which the output voltage reaches a peak value, so that sensitivity
and linearity are deteriorated because the output voltage
drops.
[0015] With a change in material characteristic of an electric
resistance or the like of a magnetic sensitive member with a change
in temperature, a pulse current flowing in the magnetic sensitive
member changes. When the pulse current changes, a circumferential
magnetic field H caused by the pulse current varies as a matter of
course. Therefore, the circumferential magnetic field H caused by
the pulse current independently of magnetization (M) of the
magnetic sensitive member is varied by the change in temperature.
According to this, deterioration in linearity and drift of an
original point (in this example, a peak value of an output voltage
generated without applying a magnetic field) occur.
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0016] However, a conventional magnetic sensor disadvantageously
requires a feedback coil (not shown) wounded around an amorphous
magnetic wire 91 and a feedback circuit (not shown) to supply a
current to the feedback coil in order to improve linearity. As a
result, a circuitry becomes complex and the magnetic sensor may be
large. When the feedback circuit is omitted, a sufficient detection
accuracy may not be obtained. In order to drive the feedback coil
and the feedback circuit, a power consumption disadvantageously
increases.
[0017] In particular, for a magnetic sensor installed in, for
example, a cellular phone or the like to measure direction, both a
function which can detect a magnetic field at a high accuracy by
improving the linearity and a function which achieves a low power
consumption by simplifying a circuitry are required.
[0018] The present invention is made in consideration of the
problems in the conventional magneto-impedance sensor, and has an
object to provide a magneto-impedance element and a
magneto-impedance sensor which are good in linearity and
temperature characteristic without using a feedback circuit.
Means for Solving the Problems
[0019] According to a first aspect of the present invention, a
magneto-impedance element includes a magnetic sensitive member
having the form of a line, whose electromagnetic characteristics
vary depending on a magnetic field acting from the outside, and in
which a pulse current flows from one end portion thereof to the
other end portion in an axial direction; a conductive layer
arranged on an insulating layer provided on an outer surface of the
magnetic sensitive member; a connection portion arranged at the
other end portion in an axial direction of the magnetic sensitive
member to electrically connect the magnetic sensitive member and
the conductive layer to each other; and a detection coil wounded
around the conductive layer to output an induced voltage
corresponding to an intensity of the external magnetic field acting
on the magnetic sensitive member when the pulse current flows in
the magnetic sensitive member, wherein a direction of the pulse
current flowing in the magnetic sensitive member and a direction of
the pulse current flowing in the conductive layer are opposite to
each other.
Effect of the Invention
[0020] An effect of the present invention will be then described
below.
[0021] In the present invention, a conductive layer is formed
around a magnetic sensitive member, and the magnetic sensitive
member and the conductive layer are connected to each other by the
connection portion. In this manner, the direction of a pulse
current flowing in the magnetic sensitive member and a direction of
a pulse current flowing in the conductive layer are opposite to
each other. For this reason, a magnetic field caused outside of the
magnetic sensitive member by the pulse current flowing in magnetic
sensitive member and a magnetic field caused outside of the
conductive layer by the pulse current flowing in the conductive
layer cancel out. In this manner, in an induced voltage output from
the detection coil, dH/dt which is a component caused by the pulse
current supposed to cause deterioration in linearity or the like
can be weakened, and only dM.theta./dt which is a component varying
depending on an external magnetic field can be detected.
[0022] For this reason, linearity between the external magnetic
field and the induced voltage can be improved. Since a feedback
coil and a feedback circuit need not to be arranged, power
consumption can be reduced.
[0023] As described above, according to the present invention, a
magneto-impedance element which is good in linearity can be
provided without using a feedback circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic view of a magneto-impedance element
according to Embodiment 1.
[0025] FIG. 2 is a schematic sectional view of the
magneto-impedance element according to Embodiment 1.
[0026] FIG. 3 is a conceptual diagram showing directions of pulse
current flowing in a magnetic sensitive member and a conductive
layer according to Embodiment 1.
[0027] FIG. 4 is a diagram of the magnetic sensitive member
extracting from FIG. 3.
[0028] FIG. 5 is a diagram of the conductive layer extracting from
FIG. 3.
[0029] FIG. 6 is a diagram showing a relationship between a pulse
current flowing in the magnetic sensitive member and an induced
voltage output to a detection coil according to Embodiment 1.
[0030] FIG. 7 is a circuit diagram of a magneto-impedance sensor
according to Embodiment 1.
[0031] FIG. 8 is a waveform chart showing an output characteristic
of the detection coil with respect to a pulse current according to
Embodiment 1.
[0032] FIG. 9 is a diagram showing a manufacturing process of the
magneto-impedance element according to Embodiment 1.
[0033] FIG. 10 is a diagram showing an operational principle of a
magneto-impedance element according to a conventional example.
[0034] FIG. 11 is a waveform chart showing an output characteristic
of a detection coil with respect to a pulse current according to a
conventional example.
[0035] FIG. 12 is a waveform chart of a first pulse output from the
detection coil and is also a waveform chart obtained when an
external magnetic field is set to be +Hx, 0, and -Hx (G) according
to a conventional example.
BEST MODE FOR CARRYING OUT THE INVENTION
[0036] A preferable embodiment according to the present invention
described above will be described below.
[0037] In the present invention, the magnetic sensitive member is
formed to have a circular section, the conductive layer is formed
to have a cylindrical shape, and the conductive layer is preferably
arranged coaxially with the magnetic sensitive member.
[0038] In this case, in comparison with a magnetic sensitive member
having a noncircular section or a magnetic sensitive member not
coaxial with a conductive layer, a magnetic field caused by a pulse
current and radiated to the outside of the conductive layer can be
made almost zero. In this manner, in the induced voltage output
from the detection coil, dH/dt is almost eliminated, and only
dM.theta./dt which is a component varying depending on an external
magnetic field can be detected.
[0039] The magnetic sensitive member preferably is made of an
amorphous magnetic material. The amorphous magnetic material can be
preferably used as a magnetic sensitive member according to the
present invention because the amorphous magnetic material has a
property (magneto-impedance effect) in which electromagnetic
characteristics change depending on the magnitude of a magnetic
field acting from the outside.
[0040] Some of the amorphous magnetic material are made of a
CoFeSiB-based alloy.
[0041] The CoFeSiB-based alloy is a soft magnetic material, the
magnetic characteristics of which largely change depending on the
magnitude of a magnetic field acting from the outside, and is a
low-magnetostrictive material, thereby to be preferably used as the
magnetic sensitive member according to the present invention.
[0042] The magnetic sensitive member is made of a known material
having the above characteristics, or is made of a CoMSiB-based
amorphous alloy or a Fe--Si-based amorphous alloy.
[0043] The conductive layer may preferably be a plated film or a
sputtered film, made of copper or aluminum, respectively.
[0044] In this case, by using a plating method or a sputtering
method, a thin conductive layer can be easily formed.
[0045] According to a second aspect of the present invention, a
magneto-impedance element includes an amorphous magnetic wire to
which a pulse current is supplied, a conductive layer arranged on
an insulating layer provided on an outer surface of the amorphous
magnetic wire, and a connection portion formed of a conductor which
electrically connects the amorphous magnetic wire to the conductive
layer on one end face of the amorphous magnetic wire
[0046] In contrast to a conventional structure in which a detection
coil is wounded around an amorphous magnetic wire, in the present
invention, a conductive layer is arranged on an insulating layer
provided around the amorphous magnetic wire, the amorphous magnetic
wire serving as a conductor and the conductive layer are
electrically connected to each other to make a direction of a pulse
current flowing in the amorphous magnetic wire and a direction of a
pulse current flowing in the conductive layer reversed. For this
reason, the effect described above (described in "Effect of the
Invention") can be obtained.
[0047] The magneto-impedance sensor according to the present
invention includes the magneto-impedance element, a pulse generator
which generates the pulse current to be input to the magnetic
sensitive member, and a sample-and-hold circuit which is connected
to the detection coil and samples and holds the induced voltage
output from the detection coil when the pulse current flows.
[0048] In this case, unlike in a conventional magneto-impedance
sensor, since a feedback coil and a feedback circuit to cancel out
an external magnetic field need not to be arranged, a power
consumption of the magneto-impedance sensor can be reduced.
[0049] A giant magnet impedance element (magneto-impedance element)
according to the present invention includes a substrate made of a
nonmagnetic material, a coaxial core having, as an axis, an
amorphous magnetic wire (magnetic sensitive member) to which a
pulse current is applied, and a detection coil formed around the
coaxial core.
[0050] As the non-magnetic substrate, an insulating alumina-based
ceramics, a semiconductor silicon wafer, a conductive metal, or the
like can be preferably used.
[0051] The coaxial core includes an amorphous magnetic wire
(magnetic sensitive member) and a conductive layer arranged on an
insulator (insulating layer) provided around the amorphous magnetic
wire (magnetic sensitive member). In the coaxial core, the
amorphous magnetic wire (magnetic sensitive member) and the
conductive layer are electrically connected to each other on one
end face of the coaxial core by a conductor (connection
portion).
[0052] An input electrode terminal is constituted of an electrode
terminal connected to the amorphous magnetic wire (magnetic
sensitive member) and an electrode terminal connected to the
conductive layer.
[0053] With this configuration, when a pulse current flows in the
amorphous magnetic wire (magnetic sensitive member), the pulse
current flowing in the amorphous magnetic wire (magnetic sensitive
member) flows into a conductor (connection portion) of the end face
of the coaxial core, then the pulse current flows in the conductive
layer in a direction opposite to a direction of the pulse current
flowing in the amorphous magnetic wire (magnetic sensitive member)
in the conductive layer around the amorphous magnetic wire
(magnetic sensitive member).
[0054] Therefore, a circumferential magnetic field +H caused by a
pulse current I flowing in the amorphous magnetic wire (magnetic
sensitive member) and a circumferential magnetic field -H caused by
a pulse current flowing in the conductive layer cancel out. As a
result, in a detection coil 5, an induced voltage (dH/dt) is not
generated by the pulse current I.
[0055] The insulator of the coaxial core is provided to surely
insulate the amorphous magnetic wire with the conductive layer, and
is made of inorganic material such as a glass film to coat the
amorphous magnetic wire or an SiO.sub.2 film formed by a CVD
method, or an organic material having an insulating property, such
as an epoxy resin.
[0056] The conductive layer of the coaxial core is made of a plated
film such as a copper plating or an aluminum plating, a sputtered
film made of copper or the like, or a thin film formed by a PVD
method or a CVD method. The conductive layer is preferably made of
a nonmagnetic material. With a magnetic conductive layer, the
conductive layer itself is magnetized by a circumferential magnetic
field formed by a current flowing in the conductive layer, which
causes noise generation, deterioration of the linearity of the
sensor, and decrease in an S/N ratio.
[0057] The connection portion which electrically connects one end
face of the coaxial core may be formed by the plated film, the
sputtered film, or bonding of gold or the like.
[0058] The detection coil includes a lower coil including a
plurality of lower conductive films arranged on a flat surface of a
substrate and an upper coil including a plurality of upper
conductive films formed on an outer surface of the insulator formed
to include the coaxial core, and arranged on the surface of the
lower coil and in the same direction as that of the lower
conductive films.
[0059] Both the ends of the detection coil are connected to the
output electrode terminals.
[0060] The lower conductive films and the upper conductive films
are formed by sputtered films made of a conductive metal such as
copper or aluminum, thin films formed by a PVD method or a CVD
method, or plated films.
[0061] The insulator including the coaxial core made of an
inorganic material such as an SiO.sub.2 formed by a CVD method and
an organic material having insulating property, such as an epoxy
resin.
EMBODIMENTS
Embodiment 1
[0062] A magneto-impedance element and a magneto-impedance sensor
according to an embodiment of the present invention will be
described below with reference to FIGS. 1 to 9.
[0063] FIG. 1 is a schematic view of a magneto-impedance element
10, and FIG. 2 is a sectional view of the magneto-impedance element
10. FIG. 3 is a schematic diagram showing a flowing direction of a
pulse current I.
[0064] As shown in FIG. 1, the magneto-impedance element 10
includes a magnetic sensitive member 1 having the form of a line
and electromagnetic characteristics variable under the influence of
a magnetic field acting from the outside, in which a pulse current
I flows from one end portion 1a to the other end portion 1b in an
axial direction.
[0065] A conductive layer 3 is arranged on an insulating layer 2
provided on an outer surface of the magnetic sensitive member
1.
[0066] A connection portion 4 which electrically connects the
magnetic sensitive member 1 and the conductive layer 3 to each
other is arranged on the other end portion 1b in the axial
direction of the magnetic sensitive member 1.
[0067] Furthermore, a detection coil 6 which outputs an induced
voltage corresponding to intensity of an external magnetic field
acting on the magnetic sensitive member 1 when the pulse current I
flows in the magnetic sensitive member 1, is wounded around the
conductive layer 3.
[0068] As shown in FIG. 3, a direction of the pulse current I
flowing in the magnetic sensitive member 1 and a direction of the
pulse current I flowing in the conductive layer 3 are opposite to
each other.
[0069] As shown in FIG. 1, the magneto-impedance element 10
includes a first electrode 7a connected to the one end portion 1a
of the magnetic sensitive member 1 and a second electrode 7b
connected to the conductive layer 3. A pulse voltage is applied
between the first electrode 7a and the second electrode 7b. A
detection coil 6 is arranged between a contact portion 7c where the
second electrode 7b is in contact with the conductive layer 3, and
the connection portion 4.
[0070] FIG. 1 is a diagram showing an outline of the giant
magneto-impedance element 10 (magneto-impedance element 10).
[0071] On a flat surface of a substrate 9 consisting of a
nonmagnetic silicon wafer, the giant magneto-impedance element 10
has the amorphous magnetic wire 1 (magnetic sensitive member 1)
coated with a glass film 2 (insulating layer 2) having an
insulating property, the conductive layer 3 formed by copper
plating, a coaxial core (20) configured by the conductor 4
(connection portion 4) formed by a copper plating which
electrically connects the amorphous magnetic wire 1 (magnetic
sensitive member 1) and the conductive layer 3, an insulator 5
(outside insulating layer 5) made of an epoxy resin configured to
include the coaxial core (20), and the detection coil 6 formed to
extend from the flat surface of the substrate 9 to an outer surface
of the insulator 5 (outside insulating layer 5).
[0072] An input electrode terminal includes an electrode terminal
7A from which a pulse current (I) is supplied to the amorphous
magnetic wire 1 (magnetic sensitive member 1) and an electrode
terminal 7B to which the pulse current (I) returns from the
conductive layer 3.
[0073] The magneto-impedance element 10 also has an output
electrode terminal 8.
[0074] In this case, a diameter and a length of the magnetic
sensitive member 1 (amorphous magnetic wire) are 7 .mu.m and 1.5
mm, respectively, a CoFeSiB alloy is used as a composition of the
amorphous magnetic wire, and the insulating layer 2 made of the
glass film has a thickness of 1 .mu.m. A thickness of the outside
insulating layer 5 is 2 .mu.m, and the detection coil 6 is coated
with an epoxy resin. Thicknesses of the conductive layer 3 and the
connection portion 4 are 2 .mu.m each.
[0075] A winding number of the detection coil 6 is 30 turns.
[0076] As described above, although the magnetic sensitive member 1
has the form of a line, a diameter of 7 .mu.m and a length of 1.5
mm, a conceptual view in which the magnetic sensitive member 1 is
shortened in an axial direction is shown in FIG. 1.
[0077] The members other than the amorphous magnetic wire
preferably made of a nonmagnetic material because of the same
reason as stated above about the conductive layer.
[0078] As shown in FIG. 2, the magnetic sensitive member 1 is
formed to have a circular section, the conductive layer 3 is formed
cylindrically and coaxially with the magnetic sensitive member
1.
[0079] More specifically, an outer surface 12 of the magnetic
sensitive member 1 is coated with the insulating layer 2, and the
insulating layer 2 is coated with the conductive layer 3. The
conductive layer 3 is coated with the outside insulating layer 5,
and the detection coil 6 is wounded around the outside insulating
layer 5.
[0080] The reason why the structure is used will be explained with
reference to FIGS. 4 and 5. FIG. 4 is a diagram explaining only the
magnetic sensitive member 1 shown in FIG. 3, and FIG. 5 is a
diagram explaining only the conductive layer 3. As shown in FIG. 4,
the pulse current I flows in the magnetic sensitive member 1 to
generate a magnetic field H1 outside of the magnetic sensitive
member. An intensity of the magnetic field H1 caused by the pulse
current I at a position being a distance r from the center of the
magnetic sensitive member 1 can be expressed by
H1=.mu..sub.0I/2.pi.r as the magnetic sensitive member 1 has a
circular section.
[0081] As shown in FIG. 5, a magnitude of the pulse current I
flowing in the conductive layer 3 is equal to that of the pulse
current I flowing in the magnetic sensitive member 1, and a
direction of the pulse current I flowing in the conductive layer 3
and a direction of the pulse current I flowing in the magnetic
sensitive member 1 are opposite to each other. For this reason, the
magnetic field H2 caused by the pulse current I at a position being
the distance r from the center of the conductive layer 3 can be
expressed by H2=-.mu..sub.0I/2.pi.r as the conductive layer 3 is
arranged cylindrically and coaxially with the magnetic sensitive
member 1. For this reason, as shown in FIG. 3, when the magnetic
sensitive member 1 is arranged inside of the conductive layer 3,
the magnetic field H1 caused outside of the magnetic sensitive
member 1 by the pulse current I flowing in the magnetic sensitive
member 1 and the magnetic field H2 caused outside of the conductive
layer by the pulse current I flowing in the conductive layer 3
cancel out to satisfy H1+H2=0.
[0082] As shown in FIG. 5, inside the conductive layer 3, a
magnetic field Hin caused by the pulse current I becomes 0. For
this reason, as shown in FIG. 3, the magnetic sensitive member 1
arranged inside of the conductive layer 3 is not influenced by a
magnetic field generated by the conductive layer 3.
[0083] More specifically, with the structure in FIG. 3, the
magnetic sensitive member 1 is not influenced by the magnetic field
generated by the conductive layer 3, and a magnetic field caused by
the pulse current I is not radiated to the outside of the
conductive layer 3.
[0084] As described above, the magnetic field H1 caused outside of
the magnetic sensitive member 1 by the pulse current I flowing in
the magnetic sensitive member 1 is canceled out by the magnetic
field H2 caused outside of the conductive layer 3 by the pulse
current I flowing in the conductive layer 3 (see FIGS. 4 and 5).
For this reason, a component dH/dt obtained by a magnetic field H
(=H1+H2) caused by the pulse current I is not output from the
detection coil 6, and only a component dM.theta./dt obtained by
magnetization M.theta. generated by a spin s is output.
[0085] An example of waveform of an induced voltage output from the
detection coil 6 is shown in FIG. 6. In this manner, when the pulse
current I flows in the magnetic sensitive member 1, magnetization
M.theta. largely changes. For this reason, an induced voltage
dM.theta./dt is output to the detection coil 6 as shown in FIG.
6.
[0086] The magnetic sensitive member 1 according to this embodiment
is made of an amorphous magnetic material made of a CoFeSiB-based
alloy.
[0087] A magneto-impedance sensor 11 using the magneto-impedance
element 10 of the embodiment will be described below.
[0088] As shown in FIG. 7, the magneto-impedance sensor 11 includes
the magneto-impedance element 10, a pulse generator 200 which
generates the pulse current I input to the magnetic sensitive
member 1, and a sample-and-hold circuit 400 which is connected to
the detection coil 6 and samples and holds an induced voltage
dM.theta./dt output from the detection coil 6 when the pulse
current I flows. A detection timing can be set to times t2 and t5
in voltage waveforms P1 and P1' in FIG. 6 depending on at rise time
or fall time of the pulse current I. At this time, voltages V1 and
V1' can be detected.
[0089] Also R11 in the magneto-impedance element represents a
resistance of the magnetic sensitive member 1 as an equivalent
resistance.
[0090] FIG. 8 is a waveform chart obtained when the first pulse P1
is measured by the magneto-impedance sensor 11 according to the
embodiment. A waveform obtained when an external magnetic field Hex
acting on the magneto-impedance sensor 11 being +2 G is represented
by 112, and a waveform obtained when the external magnetic field
Hex being 0 G is represented by 111. A waveform obtained when the
external magnetic field Hex being -2 G is represented by 113. A
pulse current in measurement is 180 mA, and a pulse duration time
is 50 ns. A rise time and a fall time are 5 ns each.
[0091] As is apparent from FIG. 8, in the case of the external
magnetic field Hex=0, as shown in the waveform chart 111, an output
voltage of the detection coil 6 transits at almost 0 mV. In this
manner, it is understood that a noise voltage generated by a
circumferential magnetic field H caused by the pulse current I
flowing in the magnetic sensitive member 1 is completely
eliminated.
[0092] The waveform chart 112 of the external magnetic field Hex=+2
G and the waveform chart 113 of the external magnetic field Hex=-2
G are symmetric, and zero crossing times (t) coincide with each
other. As a result, an excellent linearity between an output
voltage and an external magnetic field is obtained.
[0093] A manufacturing process of the magneto-impedance element 10
will be explained with reference to FIG. 9.
[0094] FIG. 9 is a diagram showing steps in manufacturing the
magneto-impedance element 10 shown in FIG. 1 and a longitudinal
sectional view.
[0095] A lower coil 61 constituted by a lower conductive film
having a thickness of about 2 .mu.m is formed on a flat surface of
the substrate 9 made of alumina-based ceramics by copper
plating.
[0096] An insulating layer 51 made of an SiO.sub.2 film is formed
by a CVD method to insulate the lower coil 61 from the conductive
layer 3 of the coaxial core 20. Then, an insulating layer 52 made
of an epoxy resin is formed by coating.
[0097] The coaxial core 20 including the magnetic sensitive member
1 (amorphous magnetic wire), the insulating layer 2 (glass film),
and the conductive layer 3 (copper plating) is fixed on the
insulating layer 52.
[0098] A connection portion 4 is formed by a copper-sputtered film
to electrically connect the magnetic sensitive member 1 (amorphous
magnetic wire) and the conductive layer 3 on the end face of the
coaxial core 20, and the insulating layer 53 of an SiO.sub.2 film
is formed by a CVD method.
[0099] An insulating layer 54 of an SiO.sub.2 film layer is formed
on an upper portion of the coaxial core 20 by a CVD method, an
upper coil 62 constituted by an upper conductive film having a
thickness of about 2 .mu.m is formed by a copper plating, and the
spiral coil 6 is spirally formed by the lower coil 61 and the upper
coil 62.
[0100] The upper coil 62 is coated with the insulating layer 55 of
a SiO.sub.2 film by a CVD method.
[0101] Advantages of the magneto-impedance element 10 and the
magneto-impedance sensor 11 according to the embodiment will be
explained.
[0102] In the embodiment, as shown in FIG. 1, the conductive layer
3 is formed around the magnetic sensitive member 1, and the
magnetic sensitive member 1 and the conductive layer 3 are
connected to each other by the connection portion 4. In this
manner, a pulse current having the same magnitude as that of the
pulse current flowing in the magnetic sensitive member 1 flows in
the conductive layer 3 in a direction opposite to the pulse current
flowing in the magnetic sensitive member 1. For this reason, a
magnetic field caused outside of the magnetic sensitive member 1 by
the pulse current flowing in the magnetic sensitive member 1 and a
magnetic field caused outside of the conductive layer 3 by the
pulse current flowing in the conductive layer 3 cancel out with
each other outside of the conductive layer 3, and a magnetic field
is held inside of the magnetic sensitive member. In this manner, in
the induced voltage output from the detection coil, dH/dt which is
a component caused by the pulse current is weakened, and only
dM.theta./dt which is a component varying depending on the external
magnetic field can be mainly detected.
[0103] For this reason, the linearity and temperature
characteristic of the external magnetic field and the induced
voltage can be improved. Since a feedback coil and a feedback
circuit need not to be arranged, power consumption can be
reduced.
[0104] As shown in FIG. 2, the magnetic sensitive member 1 is
formed to have a circular section, the conductive layer 3 is formed
cylindrically and coaxially with the magnetic sensitive member
1.
[0105] In this case, in comparison with the magnetic sensitive
member 1 having a noncircular section or the magnetic sensitive
member 1 arranged not coaxially with a conductive layer 3, a
magnetic field H caused by the pulse current I and radiated to the
outside of the conductive layer 3 can be made almost zero. In this
manner, in the induced voltage output from the detection coil 6,
dH/dt is almost eliminated, and only dM.theta./dt which is a
component varying depending on the external magnetic field can be
detected.
[0106] Furthermore, the conductive layer 3 is a plated film or a
sputtered film made of copper or aluminum.
[0107] In this case, by using a plating method or a sputtering
method, the thin conductive layer 3 can be easily formed.
[0108] The magneto-impedance sensor of the embodiment, as shown in
FIG. 7, includes the magneto-impedance element 10, the pulse
generator 200, and the sample-and-hold circuit 400.
[0109] In this case, unlike in a conventional magneto-impedance
sensor, since a feedback coil and a feedback circuit need not to be
arranged so as to cancel an external magnetic field, a power
consumption of the magneto-impedance sensor can be reduced.
[0110] A magneto-impedance element is referred to as an MI element.
An element manufactured based on the same configuration as in the
magneto-impedance element is also referred to as a giant
magneto-impedance element or a GMI element.
[0111] A magneto-impedance sensor is also referred to an MI sensor,
a giant magneto-impedance sensor, or a GMI sensor.
* * * * *