Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2000-03-29
2002-10-15
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S260000
Reexamination Certificate
active
06466012
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a MI element utilizing so-called magnetic impedance effect and more particularly to a magnetic sensor technique to construct a magnetic sensor head by two layers of thin film magnetic material having their axes of easy magnetization intersecting each other.
2. Description of the Related Art
There have already been magnetic sensors such as the magnetic resistance (MR) element utilizing a magnetoresistance effect, the sensor of flux-gate type and the magnetic field sensor utilizing a magnetic impedance effect.
The magnetic impedance effect utilizing magnetic field sensor has its head incorporated with a MI element to magnetically record various information and to read out such recorded information. The magnetic field sensor of this type may be more widely used for various applications, for example, as a multipolar magnetization sensor of a rotary encoder for robot control.
The MI element making a part of the magnetic field sensor is a magnetic sensor element utilizing a phenomenon (MI effect) that a surface effect causes the MI element to exhibit an impedance remarkably varying in response to an external magnetic field when the magnetic material forming this MI element is supplied with high frequency current.
There have already been various forms of MI element such as the cylindrical element formed by amorphous wire, the thin film element formed by sputtering amorphous material on a substrate and film laminated sensor formed by sputtering or plating appropriate magnetic material on a substrate. All of them are intended to be used as the micro-dimensioned head.
FIG. 7
of the accompanying drawings is a perspective view partially showing an example of well known MI element made of thin film magnetic material.
This MI element
10
comprises a glass substrate
11
and magnetic material
12
sputtered on a surface of said glass substrate
11
to form thin film.
The magnetic material
12
forming this MI element
10
has been subjected to a process of annealing in magnetic field or a process of sputtering in magnetic field so that its axis of easy magnetization Jm extends at right angles with respect to a direction corresponding to a path of high frequency current Iac (i.e., transversely of the magnetic material
12
).
When said MI element
10
made of thin film magnetic material is longitudinally supplied with high frequency current Iac, a magnetization vector oriented transversely of the MI element will be declined longitudinally of said MI element, a transverse magnetic permeability of said MI element will correspondingly vary and an impedance also will vary so far as said MI element is being applied with an external magnetic field Hex longitudinally thereof.
Variation in the transverse magnetic permeability due to the external magnetic field leads to variation in a depth of the surface effect exhibited by the MI element
10
.
Accordingly, simultaneous variation of electric resistance and inductance causes the impedance to remarkably vary in response to the external magnetic field Hex.
The MI element
10
of this type is incorporated in a self-oscillator circuit and operated as a magnetic field sensor.
In such application, a variation in the voltage amplitude of said self-oscillator circuit is detected as a variation in the impedance of the MI element
10
dependent on the external magnetic field Hex. This is based on a fact that said variation in the voltage amplitude of said self-oscillator circuit is proportional to said impedance of the MI element
10
and the oscillating frequency is modulated dependent on the external magnetic field Hex.
FIG. 8
is a graphic diagram plotting MI characteristics of said MI element made of thin film magnetic material.
These characteristics indicate a relationship between the external magnetic field Hex and the element's voltage varying coefficient &Dgr;Ew/Ewo (%) under a condition of high frequency current Iac=10 mA and frequency f=40 MHz.
As will be understood from
FIG. 8
, the MI element
10
exhibits symmetrical MI characteristics in response to positive side and negative side of the external magnetic field Hex. A point Hp of the external magnetic field magnitude at which the impedance reaches the maximum value is approximately |12.0| (Oe).
In this graphic diagram, a characteristic curve in solid line indicates MI characteristics obtained when the external magnetic field Hex varies from its negative side to its positive side and a characteristic curve in dotted line indicates MI characteristics obtained when the external magnetic field Hex varies from its positive side to its negative side.
When a linear magnetic field sensor is constructed from said well known MI element
10
made of thin film magnetic material, a pair of MI elements are used. One of these two MI elements is supplied with high frequency current superposed with positive DC current while the other MI element is supplied with high frequency current superposed with negative DC current and both of them are applied with a bias magnetic field.
As will be apparent from
FIG. 9
, said one MI element exhibits asymmetrical MI characteristics
10
A that this MI element has the maximum impedance on positive side of the external magnetic field and the other MI element exhibits asymmetrical MI characteristics
10
B that this MI element has the maximum impedance on negative side of the external magnetic field.
A differential output voltage of these two MI elements applied with the bias magnetic field, respectively, may be determined to detect the external magnetic field Hex with linear sensor characteristics.
FIG. 10
plots such sensor characteristics.
FIG. 11
is a perspective view partially showing another example of well known MI element
20
made of laminated thin film magnetic material.
This MI element
20
is laminate type and comprises a glass substrate
21
, first magnetic material
22
laid as thin film on a surface of said glass substrate
21
, a conductive material laid as thin film on a surface of said first magnetic material
22
and second magnetic material
24
laid as thin film on a surface of said conductive material
23
.
The conductive material
23
is patterned with a width smaller than said first and second magnetic materials so that this conductive material
23
is wrapped by the second magnetic material
24
.
Of this MI element
20
, the first and second magnetic materials
22
,
24
have, their axes of easy magnetization Jm extending at right angles (transversely of the respective magnetic materials
22
,
24
) with respect to a direction corresponding to a path of the high frequency current Iac (i.e., the longitudinal direction of the conductive material
23
).
With this MI element
20
, similarly to the case of the previously described MI element
10
, magnetic permeabilities of these first and second magnetic materials vary depending on the external magnetic field Hex when said conductive material
23
is supplied with high frequency current Iac so far as said external magnetic field Hex is being applied to the MI element
20
longitudinally thereof. Upon variation of said magnetic permeabilities, an impedance of said conductive material
23
remarkably varies. Based on this variation of the impedance, a magnitude of the external magnetic field Hex can be detected.
With the well known MI elements as have been described hereinabove, the symmetrical MI characteristics are exhibited in response to the directions, i.e., positive and negative sides of the externally applied magnetic field. To construct a linear magnetic field sensor using such MI elements, it is necessary apply the sensor with bias magnetic field by a fixed magnet or a coil.
Particularly, the level of the external magnetic field's magnitude at which the impedance reaches the maximum value is undesirably high. This is for the reason that the coil for application of said bias magnetic field must be supplied with correspondingly large bias current which inevitably increases an energy co
Mouri Kaneo
Ueno Kazuhiko
Hogan & Hartson LLP
Snow Walter E.
Stanley Electric Corporation
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