Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2001-12-31
2003-05-20
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S260000
Reexamination Certificate
active
06566872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic sensor device which detects a change in magnetic properties of a magnetic material caused by an external magnetic field by using an imaginary part of complex magnetic permeability of the magnetic material, that is, characteristics of a frequency range in which the magnetic material loses its own properties. More particularly, the present invention relates to a magnetic sensor device which is used to detect a magnetic pattern stored through magnetization, such as a magnetic head of a hard disk drive or the like, a rotary encoder for use in a motor or the like, or a magnetic head of a barcode reader, and which is used for a signal transmitter which transmits a signal through a magnetic field excited by an electric signal in a digital household electrical appliance such as a mobile telephone, a DVD (a digital versatile disc) or a digital television, or the like.
2. Description of the Prior Art
Recent advances in microelectronics and digital signal processing technology yield rapid progress in size reduction and performance improvement of a mobile telephone, AV equipment, a personal computer and the like. The performance of the above-mentioned digital information equipment is determined by the capability of processing a digital signal, namely, the number of bits of a signal which can be processed per unit second. Consequently, possible advances in the digital equipment continue requiring a higher processing speed of all components to be used in the equipment.
A magnetic sensor has played an important part in the above-mentioned equipments. For example, the magnetic sensor is used for various applications such as the reading of information stored in a magnetic storage medium and a rotary encoder for use in a motor of the storage medium. However, the prior arts have reached the limit of the capability to keep and develop the part of the magnetic sensor in the future, and therefore the technology of speeding up processing requires the development of a magnetic sensor device based on a new principle capable of speeding up processing.
As a magnetic sensor using a magnetic material, an MR sensor (a magneto-resistance effect sensor) and a GMR sensor (a giant magneto-resistance effect sensor) have been heretofore developed, and a new sensor called an MI device (a magneto-impedance device) has been recently developed. However, none of the sensors can yet meet a request to the magnetic sensor, such as the speedup of processing incident to the processing of a rapidly increasing amount of information.
Both the MR sensor and the GMR sensor are sensors which function in the following manner: that is, a change in a spin direction in a magnetic material is caused by an external magnetic field, consequently this change causes a change in electrical resistance of the magnetic material, and thus each sensor detects the amount of change in electrical resistance as the amount of external magnetic field. An advantage of these sensors is that the sensors can directly detect DC resistance of the magnetic material without the need for a specifically designed circuit without the passage of an alternating current, as distinct from the MI device. However, the nonuse of a change in magnetic properties caused by the alternating current causes a threshold detectable frequency to lie in low frequencies. The reason is as follows.
FIG. 1
shows a magnetic field to be detected by a GMR sensor and output characteristics of a resistance change (an output change) of the GMR sensor. From a plot shown in
FIG. 1
, it can be seen that the output change of the GMR sensor has hysteretic resistance output relative to positive and negative magnetic fields to be detected. This means that a magnetic material remains partly magnetized by the magnetic field to be detected. In other words, the following phenomenon emerges: that is, when a positive or negative magnetic field to be detected is applied to the GMR sensor, the GMR sensor does not keep up with a change in the magnetic field and is thus not restored to its original state. This shows that the GMR sensor is a sensor disadvantageous for detection of a change in high frequencies of the magnetic field to be detected.
Causes of output hysteresis include hysteresis of magnetic properties (a B-H curve) of a magnetic material, and magnetic aftereffect. Because of these magnetic loss phenomena, there is a threshold frequency which does not change with an external magnetic field and cannot be detected.
That is, the GMR sensor is a sensor which is used in a frequency band in which magnetic properties such as magnetic permeability of a magnetic material that is little affected by threshold and lower frequencies at which a loss such as the magnetic aftereffect increases have uniform properties, and the GMR sensor has usable frequencies which are generally as low as about one-tenth of the threshold frequency at which the loss increases.
Next, the description is given with regard to a problem of the MI device. The MI device is a magnetic sensor which is driven by the passage of an alternating current and can thus perform detection with far higher sensitivity than the GMR sensor without causing output hysteresis that is a problem of the GMR sensor.
The MI device is a sensor which functions in the following manner: that is, the passage of an alternating current causes a change in a magnetic field to be detected, thus the change in the magnetic field causes a change in effective magnetic permeability of a magnetic material acting on the current, and thus the change in the magnetic permeability causes a change in reactance acting on the current and also causes a change in resistance by a skin effect, so that the magnetic field to be detected causes a change in AC impedance of two components, i.e., the reactance and the resistance.
In other words, the principle of the MI device is that the MI device is a sensor which utilizes a change in the effective magnetic permeability of the magnetic material, namely, a change in a real part of complex magnetic permeability of the magnetic material, and thus a threshold detectable frequency of the MI device depends on a threshold value of the effective magnetic permeability of the magnetic material (i.e., the real part of the complex magnetic permeability thereof). Similarly to the MR and GMR sensors, the MI device must be therefore used in a band of relatively low frequencies in which the effective magnetic permeability is little affected by an increase in an imaginary part of the complex magnetic permeability and is thus uniform, not near the threshold frequency at which the imaginary part of the complex magnetic permeability increases sharply.
There are two general, typical phenomena of magnetic properties which occur when an external magnetic field is applied to the sensor. One phenomenon is a change in the effective magnetic permeability which is caused by a change in the spin direction for use in the conventional magnetic sensors such as the MR and GMR sensors and the MI device. The other phenomenon is a change in a frequency range in which the real part that is an effective component of the complex magnetic permeability decreases sharply and the imaginary part that is a loss component of the complex magnetic permeability increases sharply, in other words, a threshold frequency range in which the magnetic material loses its own properties.
SUMMARY OF THE INVENTION
The present invention provides a magnetic sensor device which uses a change in a threshold frequency caused by an external magnetic field as means for detecting the external magnetic field. More specifically, a new detecting method that does not require a uniform effective magnetic permeability is envisaged to overcome the problems of conventional detecting methods that require the uniform effective magnetic permeability, and thus the magnetic sensor device is designed so that the device can increase a response frequency to high frequencies about 10 times the threshold frequency even if th
Armstrong Westerman & Hattori, LLP
Lefkowitz Edward
Xenosensors, Inc.
Zaveri Subhash
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