Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1999-12-14
2002-03-12
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C324S244000, C331S065000
Reexamination Certificate
active
06356079
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic-field sensor using a magnetic substance and, more particularly, to a magnetic-field sensor of a frequency modulation (variation) type.
A magnetic-field sensor has recently been used in various fields for a resources survey based on geomagnetic anomalies, a car navigation system (e.g., an azimuth sensor type), and biomagnetics instrumentation. Most of magnetic-field sensors were of a flux-gate type and a magnetic multivibrator type employing nonlinear magnetic characteristics of a magnetic substance. Recently, a magnetic impedance effect type utilizing variations in high-frequency resistance of a magnetic substance with an external magnetic field because of skin effects and a high-frequency carrier type for sensing variations in high-frequency magnetic permeability with an external magnetic field, have been developed as magnetic-field sensors using magnetic substances.
A Hall device is a typical magnetic-field sensor using a semiconductor. Further, the application of an superconducting quantum interference device (SQUID) fluxmeter to an magnetoencephalogram (MEG) diagnostic apparatus is proceeding toward commercialization as leading-edge technology in medical diagnosis.
These latest magnetic-field sensors, described above, have been studied and actively announced in the Magnetics Society of Japan, the Institute of Electrical Engineers of Japan, and the Biomagnetics Society of Japan.
The above variety of magnetic-field sensors are appropriately utilized in view of magnetic field detection limits, costs, and specific applied technology matching. In particular, the sensors used for consumer products need to both decrease in cost and size and increase in sensitivity.
In magnetic-field sensors using a magnetic substance, a sensor having nonlinear magnetic characteristics should be constructed such that the magnetic substance itself is excited by a large amplitude at high frequency. Such a sensor has problems of causing an iron copper loss. There were limits to achieving high frequencies. Further, the sensor has a problem that its power consumption is high. Contrastingly, a magnetic-field sensor of a magnetic impedance effect type or a high-frequency carrier type is so designed that its magnetic substance is excited by a small amplitude of high-frequency current flowing therethrough. Therefore, both miniaturization and high sensitivity are compatible with each other and, at the same time, power consumption can be lowered.
However, it is in the mainstream prior art magnetic-field sensor using a magnetic substance that an external magnetic field is converted into a voltage. Even though such a sensor is a magnetic impedance effect type or a high-frequency carrier type, it has drawbacks in which its peripheral analog electronic circuit are increased in size and it is susceptible to an influence of noise on which detection limits of magnetic fields depended.
FIG. 1
schematically shows the arrangement of a prior art magnetic-field sensor (sensor circuit) of a magnetic impedance effect type. This magnetic-field sensor includes an oscillation section
101
, a filter section
102
, a buffer section
103
, a sensor section
104
, a detection section
105
, an amplifier section
106
, and a negative feedback resistor
107
.
Oscillation section
101
is a pulse generation circuit having a complementary metal oxide semiconductor (CMOS) inverter and a quartz oscillator. Filter section
102
is an LC filter for removing a basic-frequency component from repetitive waveforms of pulses generated by oscillation section
101
. Buffer section
103
has a driver amplifier for supplying a sinusoidal high-frequency current, which corresponds to the basic frequency component removed from filter section
102
, to a magnetic-field element MI of sensor section
104
.
Sensor section
104
includes the magnetic-field element MI and a resistance (30 &OHgr;) which is considerably higher than the impedance thereof and is so constructed that the magnetic-field element MI is driven at constant current by the driver amplifier. The magnetic-field element MI generates a voltage, which is proportionate to variations in impedance with the application of external magnetic fields, from both ends thereof. For the magnetic-field element MI, an amorphous magnetic wire is used as a magnetic substance.
In detection section
105
, positive and negative half cycles of a voltage generated from the magnetic-field element MI, whose DC component is cut by a capacitor of sensor section
104
, are detected and smoothed by a diode and converted into a DC voltage.
Amplifier section
106
is constructed of a DC differential amplifier (AMP*25). A DC voltage, which is proportional to the amplitude of the positive half cycle of the voltage generated from the magnetic-field element MI, is applied to one input terminal of the amplifier, while a DC voltage, which is proportional to that of the negative half cycle thereof, is applied to the other input terminal of the amplifier. If, in amplifier section
106
, the output of the differential amplifier is set to zero when an external magnetic field is zero, only one input voltage is varied and a voltage corresponding to the variation is output (OUT).
Negative feedback resistor
107
is a current control element for causing a direct current (coil current) to flow through a coil wound around the magnetic-field element Ml. In this case, the direction of a DC magnetic field generated by the coil current is the same as that of the external magnetic field, and the DC magnetic field is employed as a bias for increasing the linearity and sensitivity of the magnetic field and output voltage.
Since, as described above, the magnetic-field sensor generates an analog voltage, the peripheral analog electronic circuit other than sensor section
104
is increased in size. Actually, in most cases, the magnetic-field sensor is combined with a microprocessor or the like into a system. For example, an output voltage (OUT), which is proportional to the magnetic field, is converted to digital data by an A/D converter and then the digital data is processed by a micro processor. A result of the digital processing is displayed or used for various control operations.
The best way to achieve an analog electronic circuit which is unsusceptible to an influence of noise as a peripheral circuit of the magnetic-field sensor is narrowing the frequency band. It is however difficult to detect a magnetic field varying at high speed.
Considering that the data is finally processed digitally, the analog output (output voltage OUT) of the magnetic-field sensor will include quantization noise as well as noise from the peripheral analog electronic circuit.
As described above, most of magnetic-field sensors, using a magnetic substance, output an analog voltage. Thus, they are easily influenced by noise. Furthermore, these magnetic-field sensors have problems in which the sensor is difficult to miniaturize and manufacture at low cost as an entire system since the peripheral analog electronic circuit is increases in size.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide a magnetic-field sensor which is decreased in size and cost and is capable of containing a peripheral circuit with the fewest possible analog electronic circuits and reducing an influence of noise.
To attain the above object, there is provided a magnetic-field sensor which is constructed by inserting a transmission-line element including a conductor layer, a dielectric layer and a magnetic layer in a feedback circuit of a phase-shift type oscillation circuit.
According to the magnetic-field sensor so constructed, an output of the sensor can be detected as a variation in frequency proportional to the intensity of an external magnetic field. Thus, the entire structure of the sensor including the peripheral circuit can be greatly simplified.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from t
Inoue Tetsuo
Mizoguchi Tetsuhiko
Sato Toshiro
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