JPH1114722A - Magnetism detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetism detecting device capable of correctly detecting a fine local magnetic pattern recorded on a magnetic card, a bank bill. SOLUTION: A first and a second wire-like magnetic impedance elements 11, 12 are provided in line in the lengthwise direction, the lengthwise direction is arranged so as to be perpendicular to a bank bill 14, and magnetic flux is acted only on the first magnetic impedance element 11. After detecting the output signals of the first and second magnetic impedance elements 11, 12 by respective wave detecting circuits 15, 16, they are supplied to the positive and negative input terminals of a differential amplifier 17. Because the external noise magnetic flux similarly acts on both magnetic impedance elements 11, 12, and by taking differential it can be cancelledly removed, the fine local magnetic flux can be correctly detected without being influenced from noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic detection device for detecting a magnetic flux emitted from a test object such as a magnetic card or a bill using a magnetic impedance element.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional magnetic detecting device using a magnetic impedance element. The magneto-impedance element 1 is arranged to sense a magnetic flux emitted from the test object 2, and the magneto-impedance element is driven by a signal output from the oscillation circuit 3. Since the impedance of the magnetic impedance element 1 changes due to the action of the magnetic flux emitted from the test object 2 such as a magnetic card or a bill, the amplitude of the signal obtained from the magnetic impedance element changes accordingly. Therefore, the output signal of the magnetic impedance element 1 is
Amplification circuit 5 amplifies the obtained detection output, whereby a detection signal corresponding to the magnetic flux emitted from the object to be detected is obtained at output terminal 6. By processing this detection signal, the object to be detected is processed. The upper magnetic pattern can be detected.

[0003]

In the above-described conventional magnetic detecting apparatus, the external magnetic flux other than the magnetic flux emitted from the test object 2, that is, the magnetic flux which is greatly affected by the noise magnetic flux and accurately emits the magnetic flux emitted from the test object 2 can be obtained. There is a problem that can not be detected. For example, when a banknote is to be inspected, the magnetic flux emitted from the portion printed with magnetic ink is very small, and the surrounding environment is not always suitable for magnetic detection. And the magnetic pattern recorded on the bill with magnetic ink cannot be accurately detected. In particular, in such a magnetic detection of bills, since the authenticity of the bill is determined based on the detection result,
False detection leads to erroneous determination of the authenticity, which is a serious problem. Further, although the magnetic flux emitted from a magnetic card such as a prepaid card is larger than that of a bill, the detection environment is still often not good, and erroneous detection due to noise magnetic flux often poses a problem. Erroneous detection also has a significant effect on such a magnetic card.

When detecting the magnetic flux emitted from the above-mentioned banknote, the magnetic flux emitted from the magnetic ink is not only minute, but the resolution of the magnetic detection is required to detect the magnetic pattern printed with the magnetic ink. Need to be higher. That is, it is necessary to accurately detect a local magnetic flux. Further, in magnetic cards, as the amount of magnetically recorded information increases, magnetic detection with high resolution is required. As described above, it is very difficult to detect a minute and local magnetic pattern with a conventional magnetic detection device using a magnetic impedance element.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic detection device which can reduce the above-mentioned drawbacks of the prior art and can accurately detect minute and local magnetic fluxes without being affected by surrounding noise magnetic fluxes. It is something to offer.

[0006]

According to the magnetic detecting device of the present invention, the first and second magneto-impedance elements having substantially the same characteristics can be obtained by applying the magnetism generated from the test object to only one of the magneto-impedance elements. The first and second magneto-impedance elements are connected to the positive and negative input terminals of a differential amplifier via first and second detection circuits, respectively, and the output side of the differential amplifier And outputting a magnetic detection signal.

In a preferred embodiment of the magnetic detecting device according to the present invention, the first and second magneto-impedance elements are arranged on a common substrate, and the substrate is mounted on the magneto-impedance element. Are arranged so that the alignment directions of the are substantially perpendicular to the test object. With this arrangement, one of the magneto-impedance elements is arranged close to the test object, and the other magneto-impedance element moves away from the test object. As soon as it acts on the elements, the external magnetic flux acts on both magneto-impedance elements in the same way. Also, in this case,
It is preferable that the first and second magneto-impedance elements are formed in a wire shape, and that these magneto-impedance element wires are aligned in the longitudinal direction and adhered to the substrate. Is detected at the end face of the magneto-impedance element wire, so that the local magnetic flux can be detected extremely efficiently.

[0008]

2 to 4 show an embodiment of the magnetic detection device according to the present invention. As shown in FIG.
First and second magnetic impedance elements 11 and 12 are provided, and these magnetic impedance elements are driven by a pulse supplied from a pulse oscillation circuit 13. In this example, the oscillation circuit 13 is configured with a pulse oscillator.
The pulse frequency is 300 KHz. The first and second magnetic impedance elements 11 and 12 are arranged so that the magnetic flux emitted from the test object 14 acts mainly only on the first magnetic impedance element 11 as described later. These first and second magneto-impedance elements 11
And 12 are detected by detector circuits 15 and 16, respectively, and the output signals of these detector circuits are differentially amplified.
By supplying the positive and negative input terminals of 17, a magnetic detection signal is output to an output terminal 18.

FIG. 3 is a circuit diagram of the magnetic detection device of the present embodiment. The first and second detection circuits 15 and 16 include:
They are composed of diodes 21 and 22, capacitors 23 and 24 and resistors 25 and 26, respectively, and the common connection point of the capacitors and the common connection point of the resistors are both grounded.

FIG. 4 is a perspective view showing the structure of the first and second magneto-impedance elements 11 and 12 in detail.
In this example, the first and second magnetic impedance elements 11
Numerals 12 and 12 are each formed of a wire having a diameter of 30 μm and a length of 2 mm, and these wire-shaped magneto-impedance elements are fixed to a common substrate 31 made of glass epoxy resin with epoxy resin. As shown in the drawing, the first
And the second magneto-impedance elements 11 and 12 are aligned in the longitudinal direction, and the distance between them is 2 mm.

In order to apply a magnetic bias to the first and second magneto-impedance elements 11 and 12, these elements are each surrounded by a coil having a winding diameter of 0.3 mm. Although fixed to the substrate 31 by resin, these magnetic bias coils are not shown in FIG. As described above, the first and second magneto-impedance elements 11 arranged on the common substrate 31 so that the longitudinal directions thereof are aligned, and
12 is arranged so that its longitudinal direction is at right angles to the test object 14, for example, a bill.

Next, the operation of reading a magnetic pattern recorded on the banknote 14 with magnetic ink by the magnetic detection device of this embodiment will be described. In FIG. 4, the banknote 14 is moved at a constant speed with respect to the magneto-impedance elements 11 and 12 as shown by arrows. Thus, the desired position of the bill 14 can be scanned by the magnetic detection device. In this case, the first
Since the end surface of the magneto-impedance element 11 is very close to the banknote 14, the magnetic flux generated from the magnetic ink of the banknote can be effectively captured. However, since the second magneto-impedance element 12 is far away from the bill 14,
The magnetic flux from the magnetic ink is hardly sensed. On the other hand, the external noise flux is generated by the first and second magnetic impedance elements.
Since they act on both 11 and 12, they are sensed almost identically in these magneto-impedance elements.

Therefore, the output signal of the first magneto-impedance element 11 is a signal obtained by detecting the superposition of the magnetic flux from the magnetic ink on the banknote 14 and the noise magnetic flux. The signal is obtained by detecting almost only the noise magnetic flux. Therefore, by taking the difference between the signals detected from the output signals of the first and second magnetic impedance elements 11 and 12 in the differential amplifier 17, the influence of the external noise magnetic flux is eliminated and the magnetic flux of the bill 14 is reduced. A magnetic detection signal representing only the magnetic flux from the ink is obtained at the output terminal 18.

As described above, in the magnetic detection device of this embodiment, the first and second wire-shaped magnetic impedance elements 11 and 12 having a diameter of 30 μm are aligned in the longitudinal direction, and the first magnetic impedance element Object to be inspected 14
Since it is disposed so as to face, the minute and local magnetic pattern recorded on the test object 14 can be detected with very high resolution without being affected by external noise. By processing the magnetic detection signal obtained from the output terminal 18 in this way, it is possible to accurately read the magnetic pattern recorded on the banknote 14 with magnetic ink, and to accurately determine whether the banknote is authentic based on that. Can do it.

The present invention is not limited only to the above-described embodiment, and many modifications and variations are possible. For example, in the above-described embodiment, the first and second magneto-impedance elements are formed in a wire shape, but may be formed in another shape such as a strip shape. In the above-described embodiment, the pulse oscillation circuit is used to drive the magneto-impedance element. However, another driving circuit can be used.

[0016]

As described above, according to the magnetic detection device of the present invention, the magnetic flux from the object to be tested acts on one of the first and second magnetic impedance elements, and the external magnetic flux acts on both. With such a configuration, the output signals of these magnetic impedance elements are differentially detected, so that a minute magnetic flux can be accurately detected without being affected by external noise. Further, a local magnetic flux can be detected by arranging the magneto-impedance element in the form of a small-diameter wire and arranging the end face of the element so as to face the test object. Therefore, it is possible to effectively detect even a fine magnetic pattern that is printed on a banknote with magnetic ink.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a magnetic detection device using a conventional magnetic impedance element.

FIG. 2 is a block diagram showing a configuration of one embodiment of a magnetic detection device according to the present invention.

FIG. 3 is a circuit diagram of the same.

FIG. 4 is a perspective view showing a state in which a magneto-impedance element is arranged on a common substrate.

[Description of Signs] 11, 12 First and second magneto-impedance elements 13 Oscillation circuit 14 DUT 15, 16 First and second detection circuit 17 Differential amplifier 31 Substrate

Claims (3)

[Claims] A first and a second magneto-impedance element having substantially the same characteristics are arranged so that magnetism generated from a test object acts on only one of the first and second magneto-impedance elements. Are connected to the positive and negative input terminals of a differential amplifier via first and second detection circuits, respectively, and a magnetic detection signal is output from the output side of the differential amplifier. A magnetic detection device characterized by the above-mentioned. 2. The method according to claim 1, wherein the first and second magneto-impedance elements are arranged on a common substrate so that the orientation of the magneto-impedance elements is substantially perpendicular to a test object. The magnetic detection device according to claim 1, wherein the magnetic detection device is disposed at a position where the magnetic field is detected. 3. The device according to claim 2, wherein the first and second magneto-impedance elements are formed in a wire shape, and these magneto-impedance element wires are aligned and adhered on a substrate in a longitudinal direction. Magnetic detection device.