Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1999-08-04
2002-10-29
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C360S110000
Reexamination Certificate
active
06472868
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic-sensor, and more particularly to a magnetic impedance sensor which is a high-sensitive magnetic sensor.
2. Description of the Related Art
As information devices and measuring and control devices are being rapidly developed in recent years, demand of magnetic sensors which are low in size and costs and high in sensitivity and response speed have increased more and more. For example, in a hard disc device of an external memory device for a computer, a high performance has been advanced such that an induction type magnetic head of the bulk type has been changed to a thin-film magnetic head or a magnetic resistance effect (MR) head. Since in a rotary encoder which is a rotary sensor for use in a motor, a magnetic ring having a high magnetic density has been demanded, there has been required a magnetic sensor which is capable of detecting a fine surface magnetic flux with a high sensitivity instead of the conventional magnetic resistance effect (MR) sensor used. Also, demand of high-sensitive sensor which can be used for a non-destructive investigation or a bill investigation has increased more and more.
As representative magnetic detecting elements which are now being used, there are an induction type reproduction magnetic head, a magnetic resistance effect (MR) element, a flax gate sensor, a hall element and so on. Also, in recent years, there have been proposed magnetic sensors high in sensitivity using the magnetic impedance effect of an amorphous wire (refer to Japanese Patent Laid-open Publication No. Hei 6-176930, Japanese Patent Laid-open Publication No. Hei 7-181239, Japanese Patent Laid-open Publication No. Hei 7-333305) or the magnetic impedance effect of a magnetic thin-film (refer to Japanese Patent Laid-open Publication No. Hei 8-75835, Japanese Applied Magnetic Institute Journal, vol. 20,553 (1996)).
The induction type reproduction magnetic head suffers from such problems that a magnetic head per se becomes large-sized because a coil winding is required, to the contrary, that the sensitivity of detection is remarkably deteriorated in case the number of turns of coil is reduced for the purpose of making the magnetic head small. On the other hand, the magnetic resistance effect (MR) element using a ferromagnetic film is being employed. The MR element is so designed as to detect not a temporal variation in magnetic flux but the magnetic flux per se, to thereby advance the miniaturizing of the magnetic head. However, even in the existing MR element, for example, the MR element using a spin valve element, the rate of change in the electric resistance is small to the degree of 6% or less at the maximum, and the external magnetic field necessary for obtaining the resistance change of several % is large to the degree of 1.6 kA/m or more. Therefore, the magnetic resistance sensitivity is low to the degree of 0.001%/(A/m) or less. Also, in recent years, there has been found a giant magnetic resistance effect (GMR) due to an artificial lattice in which the rate of change in the magnetic resistance is several tens %. However, in order to obtain the resistance change of several tens %, the external magnetic field of several tens A/m is necessary, and therefore the practical use of the magnetic resistance element as a magnetic sensor has not been realized.
The flux gate sensor which is the conventional high-sensitivity magnetic sensor is so designed as to measure the magnetism by using the phenomenon in which the symmetric B-H characteristic of a high permeability magnetic core such as a permalloy is changed according to the external magnetic field, and has the high resolution and the high directivity of 1. However, the above flux gate sensor suffers from such problems that a large-sized magnetic core is required in order to enhance the sensitivity of detection, that it is difficult to reduce the dimensions of the entire sensor and that the power consumption is large.
The magnetic sensor using a hall element is a sensor using a phenomenon in which when a magnetic field is applied perpendicularly to a surface of the sensor into which a current flows, an electric field is developed in a direction perpendicular to both of the current flowing direction and the magnetic field applying direction, to thereby induce an electromotive force in the hall element. The hall element is advantageous in the costs but has such defects that the sensitivity of the magnetic field detection is low and that the temperature characteristic of the magnetic field sensitivity is low because the mobility of electrons or positive holes is changed by diffusion of lattices within the semiconductor due to thermal vibrations to a change of temperature since the hall element is made of semiconductor such as Si or GaAs.
Japanese Patent Laid-open Publication No. Hei 6-176930, Japanese Patent Laid-open Publication No. Hei 7-181239 and Japanese Patent Laid-open Publication No. Hei 7-333305 have proposed therein magnetic impedance elements by which a great improvement in the magnetic field sensitivity has been realized. The magnetic impedance element is a magnetic impedance element that has a basic principle in which only a voltage caused when a circumferential magnetic flux changes as a time elapses, which is produced when a current which varies as a time elapses is supplied to a magnetic line is detected as a change caused by the externally applied magnetic field.
FIG. 16
shows an example of the magnetic impedance element. In the magnetic impedance element
1
of
FIG. 16
, an amorphous wire (a wire which has been tension-annealed after having been drawn) which is made of FeCoSiB or the like and about 30 &mgr;m in the diameter of exciting distortion is employed as a magnetic line
2
.
FIG. 17
is a graph showing the applied magnetic field dependency of the wire (for example, the magnetic line
2
in
FIG. 16
) with respect to the impedance change. Even in a wire having a small dimension of about 1 mm in length, when a high-frequency current of about 1 MHz is supplied to the wire, the amplitude of a voltage across the wire changes with the high sensitivity of about 0.1% /(A/m) which is 100 times or more of the MR element.
As the magnetic sensor, there has been demanded a high-sensitive magnetic sensor which is small in size, low in the costs and excellent in the linearity and the temperature characteristic of an output to the detected magnetic field. The magnetic sensor using the magnetic impedance effect of the amorphous wire exhibits the magnetic field detection characteristic of a high sensitivity. Also, Japanese Patent Laid-open Publication No. Hei 6-176930 and Japanese Patent Laid-open Publication No. Hei 6-347489 disclose that the application of a bias magnetic field allows the linearity of the dependency of the applied magnetic field on the impedance change to be improved; and that a negative feedback coil is wound on the amorphous wire, and a current proportional to a voltage between both ends of the amorphous wire is supplied to the coil to conduct negative feedback, thereby being capable of providing a sensor (high-sensitive magnetic impedance element) which is excellent in linearity and uniform in the magnetic field detection sensitivity with respect to the temperature change of the sensor section.
However, because the high-sensitive magnetic impedance element is formed of the amorphous wire the diameter of which is about 30 &mgr;m, it is not proper for fine machining, thereby making it difficult to provide a super-miniaturized magnetic detecting element. Also, since both of the bias coil and the negative feedback coil must be prepared by winding a thin copper wire, there is a limit of miniaturizing the high-sensitive magnetic impedance element, and there also arises a problem from the viewpoint of productivity such that the soldering property of the electrode is low since an oxide film is formed on the surface of the wire.
In addition, if the length of the element is lengthened in order to increase the impe
Goto Akira
Kato Hideki
Takayama Akio
Umehara Tamio
Yuguchi Akiyo
Aurora Reena
Lefkowitz Edward
Minebea Co. Ltd.
Oliff & Berridg,e PLC
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