JPH03248895A - Magnetic medium - Google Patents

Abstract

PURPOSE:To prevent a judging or decoding error by providing substantially constant magnetic flux to a magnetic material in a predetermined range of a magnetic field excepting a magnetic saturation state. CONSTITUTION:The magnetic material of a magnetic medium has substantially constant magnetic flux in a predetermined range of a magnetic field excepting a magnetic saturation state. For example, as magnetic bars, three kinds of magnetic materials are used and, with respect to the B (magnetic flux density) : H (magnetism) characteristics of magnetic materials, high and low coercive force magnetic materials (1), (2) and a magnetic material (3) having intermediate coercive force and almost becoming zero in magnetic flux density B between applied magnetic fields -HC3H, -HC3L are used. The magnetic material (3) is obtained by laminating or mixing two kinds of the magnetic materials (1), (2) different in coercive force. When the coercive forces of the magnetic materials (1), (2) are HC1, HC2, HC1 is made almost same to or more than HC3H and HC2 is made almost same to or less than HC3L. As a result, when the magnetic field within the predetermined range is applied, the magnetic materials can be set to a constant magnetized state (e.g. demagnetized state) and possibility such that a proper magnetic medium is judged by mistake is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to magnetic materials (and non-magnetic materials) having different coercive forces.
This invention relates to a magnetic medium that retains unique fixed information through a combination of

[Prior Art] Magnetic media that magnetically record unique signals on magnetic materials include bank cards, ID cards, and various prepaid cards. With such magnetic media, if there is any unauthorized use such as forgery, alteration, alteration, or plagiarism, it may cause great damage, so it is extremely important to have a function that can prevent such unauthorized use. In particular, when personal data, such as a PIN code, is simply magnetically recorded on the magnetic stripe, it can be easily read and copied with a simple device, but cannot be read or copied with a simple device. A means is desired.

To prevent unauthorized use such as forgery and alteration, firstly, magnetically recorded information cannot be easily deciphered, and secondly, even if it can be deciphered, it is impossible to produce the same thing or there are economical or technological issues. It only needs to be extremely difficult to manufacture.

For example, in some prepaid cards, a bar-shaped magnetic material is coated like a printed bar code, and the residual magnetic flux distribution pattern of the bar-shaped magnetic material is deciphered to determine its authenticity and the type of card. using configuration. However, with this configuration, the residual magnetic flux distribution of the bar-shaped magnetic material can be easily determined using a magnet viewer, and it is also extremely easy to form a magnetic card having the same magnetic material distribution as the real card. Therefore, such a method has a poor ability to prevent unauthorized use.

In contrast, the present applicant has filed patent application No. 789 of 1988.
No. 10 (Publication of Patent Application No. 244401 of 1988) proposed a configuration in which magnetic materials having different coercive forces are distributed and each magnetic medium retains unique information based on the coercive force distribution pattern. That is, in the invention related to this patent application, all magnetic materials are once magnetized in one direction, and then,
A magnetic field in a reverse direction intermediate to the coercivity of each magnetic material is applied to sequentially reverse the magnetization direction, and the distribution pattern of the coercive force is determined from the reversal of the magnetization direction.

The magnetic medium disclosed in this patent application uses a magnet.
Even if you look at the distribution of residual magnetic flux with a viewer, you can only know the pattern distribution of the presence or absence of magnetic material, but you cannot know the distribution pattern of coercive force, which is the original information. In other words, they do not know the principle of encoding based on differences in coercive force. However, it is known that the reading method (confirmation method) disclosed in the patent application No. 1 retains information based on the magnitude of coercive force. However, there is a problem in that it is easily forged or altered. That is, for example, in the case of a magnetic medium that uses two types of magnetic materials, one with high coercive force and the other with low coercive force, it is sufficient to prepare magnetic materials with similar coercive forces and distribute them in the same way as the genuine one. Such a task is not impossible or extremely difficult.

In contrast, in another patent application filed at the same time, the present applicant has determined that the magnitude of the coercive force itself can be measured by detecting the magnetization state of a magnetic material with a predetermined coercive force in a demagnetized state. We proposed a method to determine and confirm authenticity. According to this confirmation method, even if a magnetic material with an appropriate coercive force is used, unless the coercive forces are substantially the same, it will be judged as a counterfeit, and a counterfeit or altered magnetic medium will be judged as a fake. can be definitely eliminated.

However, even if the same direct current is applied to the magnetizing magnetic head, the target magnetic material may not be completely demagnetized. This is because the distance between the magnetic head and the magnetic medium changes due to wear of the magnetic head and wear of the surface protective layer of the magnetic medium.
Due to dust intervening in the gap between the magnetic head and the magnetic medium,
This is because it is not the same for each magnetic medium and for each read operation. On the other hand, the B (magnetic flux density) vs. H (magnetic) characteristic of a magnetic material is a hysteresis characteristic, as is well known, and when a reverse magnetic field equivalent to a coercive force is applied, the magnetic flux changes greatly depending on the magnitude of the applied magnetic field. Therefore, when trying to measure the coercive force itself of the magnetic material used, as in the concurrently filed patent application, errors in judgment are likely to occur unless the magnitude of the applied magnetic field is controlled quite strictly.

Therefore, an object of the present invention is to propose a magnetic medium that does not cause such judgment or decoding errors.

[Means for Solving the Problems] A magnetic medium according to the present invention is a magnetic medium that retains fixed information using a magnetic material, in which the magnetic material substantially remains in a magnetic field in a predetermined range except in a state of magnetic saturation. It is characterized by being a magnetic material with a constant magnetic flux.

The magnetic medium according to the present invention is also a magnetic medium that retains fixed information by using at least two types of magnetic materials or a non-magnetic material and at least one type of magnetic material with different coercive forces, and which retains fixed information except in a state of magnetic saturation. The method uses a magnetic material that has a substantially constant magnetic flux over a range of magnetic fields.

[Operation] If a magnetic field within the predetermined range is applied by the above means,
Regardless of various variations, the magnetic material can be kept in a constant magnetized state (eg, demagnetized state). Therefore, the possibility of erroneously determining a legitimate magnetic medium as an unauthorized one can be reduced by the method of decoding the fixed information by bringing the magnetic material into a constant magnetization state.

In addition, it is extremely difficult to know these magnetic properties through analysis and prepare magnetic materials with the same properties.
It is also resistant to counterfeiting and alteration.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a front view of a magnetic card 10, which is a magnetic medium according to an embodiment of the present invention. The surface of the magnetic card 10 is coated with bar-shaped magnetic materials (hereinafter referred to as magnetic bars) having different coercive forces.

) and bars made of non-magnetic material (hereinafter referred to as non-magnetic bars).
A magnetic barcode 12 that retains unique fixed information by combining and distributing it like a printed barcode.
It is printed. Of course, the magnetic barcode 12 is protected by a protective layer (not shown).

In this example, three types of magnetic materials are used as the magnetic bar, and their B-H characteristics are illustrated in FIG. Figure 2 (1) shows a magnetic material with high coercive force such as barium ferrite, (2) shows a magnetic material with low coercive force such as gamma ferrite, and (3) shows the magnetic material of (1). It is a magnetic material that has a coercive force intermediate to that of the magnetic material (2) and whose magnetic flux density B becomes almost zero between applied magnetic fields -HcsH and -Hc8L. Specifically, Figure 2 (
The magnetic material with the characteristics shown in 3) is obtained by laminating two types of magnetic materials with different coercive forces (for example, the magnetic material shown in Figure 2 (1) and the magnetic material shown in Figure 2 (2)) or by laminating them at an appropriate mixing ratio. It is a mixture of

Regarding the magnetic materials having the characteristics shown in FIG. 2(3), instead of mixing two types of magnetic materials with different coercive forces, they may be laminated in layers. FIG. 3 (1) is a cross-sectional view of a configuration realized by mixing and dispersing the magnetic materials shown in FIG. 2 (3).
FIG. 3(2) shows a cross-sectional view of a structure realized by laminating a high coercive force layer and a low coercive force layer. 20 is a base material, 22 is a mixed layer in which two types of magnetic materials with different coercive forces are mixed and dispersed, and 24
2 is a base material, 26 is a high coercive force layer, and 28 is a low coercive force layer.

In the case of stacking, the high coercive force layer 26 is placed on the low coercive force layer 28.
It is better to place

In addition, the coercive force of the magnetic material in Figure 2 (1) is expressed by HCI and HCI (
If the coercive force of the magnetic material in 2) is H62, and the magnetic material in (3) is H68111, the higher magnetic field in the magnetic field region where the magnetic flux density B is almost zero, and Heat the lower magnetic field, then H
CI is the same as or higher than H68H, HO2 is H68
It is set to the same level as L or lower. In addition, in this example, a magnetic material with B r I ” B r Q is used, but in order to improve confidentiality, the following steps (1), (2), and (3) in Figure 2 are The residual magnetic flux density B rll B rL B rll of the magnetic material is preferably set to the same or different values as appropriate so that the residual magnetic flux distribution appears to indicate some information.
This can be achieved by adjusting the mixing ratio of magnetic powders in the magnetic ink.

Even with the same magnetic material, there are differences in coercive force depending on the manufacturing method and particle shape. Therefore, legitimate manufacturers of magnetic media can create magnetic materials with the characteristics shown in Figure 2 (3) by using appropriate combinations and mixing ratios. It is relatively easy to obtain. On the other hand,
To counterfeit or alter a magnetic medium as described above, analyze an existing magnetic medium, obtain magnetic materials that compose the magnetic material shown in Figure 2 (3), mix them so that they have the same magnetic properties,
It needs to be applied in place. Analytical work and composition identification require fairly expensive analytical equipment when the amount to be tested is small, and it is quite difficult to obtain composition materials with the same magnetic properties unless they are obtained in large quantities. Therefore,
Forgery and alteration will be extremely difficult.

10 - FIG. 4 shows a block diagram of a circuit example for decoding (and determining authenticity) the magnetic barcode F12 of FIG. 1. Reference numeral 10 designates the magnetic card shown in FIG. 1, and the magnetic card 10 is carried in the horizontal direction by rollers 13 and motor-driven rollers 14. 15 is a motor drive circuit that drives the motor of the motor drive roller 14. 16 is a magnetizing magnetic head for applying a direct current magnetic field, and 18 is a direct current generating circuit that generates a direct current for causing the magnetizing magnetic head 16 to generate a desired direct current magnetic field.

20 is magnetized (including demagnetized) by the magnetizing magnetic head 16.

22 is an amplifier that amplifies the output of the read magnetic head 20, 24 is a rectifier circuit that rectifies the output of the amplifier 22, and 26 is the rectifier circuit 24. This is a waveform shaping circuit that shapes the waveform of the output.

28 is an arithmetic circuit that performs an operation to determine the authenticity of the magnetic card 10 from the pulse train signal from the shaping circuit 26; 30 is a memory circuit that stores data such as the pulse train signal data from the shaping circuit 26 for use in the arithmetic operation of the arithmetic circuit 28; 32 is a control circuit that controls the DC current level generated by the DC current generation circuit 18, controls the rotation direction of the motor drive roller 14 via the motor drive circuit 15, and further controls the calculation sequence of the calculation circuit 28. . In reality, the arithmetic circuit 28 and the control circuit 32 are realized by one microprocessor or microcomputer.

A clock generation circuit 34 generates a clock serving as a reference for the entire operation, and its output clock is supplied to the motor drive circuit 15, waveform shaping circuit 26, arithmetic circuit 28, and control circuit 32.

The basic operation shown in FIG. 1 will be explained. First, the magnetic card 10 is moved by the roller 13, the motor drive roller 14, and the motor drive circuit 15 so that the magnetization magnetic head 16 and the reproduction magnetic head 20 scan the magnetic barcode 36. At this time, the DC current generation circuit 18 generates a DC current that magnetically saturates all the magnetic bars of the magnetic barcode 36, and the magnetizing magnetic head 16 magnetically saturates the magnetic barcode 36. Then, the reproducing head 20 detects the residual magnetic flux distribution of the magnetically saturated magnetic barcode 36. The reproduction output of the reproduction head 20 is amplified by an amplifier 22, rectified by a rectifier circuit 24, and then sent to a waveform shaping circuit 26.
The signal is waveform-shaped and input to the arithmetic circuit 28, and is stored in the memory circuit 30 as a binary signal.

Next, the motor drive circuit 15 causes the motor drive roller 14 to
is rotated in the reverse direction to return the magnetic card 10 to its initial position, and the motor drive roller 14 is rotated in the normal direction again. At this time, the output current of the DC current generating circuit 18 is controlled, and a non-DC magnetic field corresponding to the coercive force of the magnetic material to be demagnetized is applied to the magnetizing magnetic head 16.
to demagnetize a portion of the magnetic material of the magnetic barcode 36.

A magnetic material with a coercive force smaller than that of the magnetic material being demagnetized will be magnetized in the opposite direction. The residual magnetic flux distribution of the demagnetized (and reverse magnetized) magnetic barcode is detected by the reproducing head 20, and the detection result is stored as a binary signal in the memory circuit 30 as before.

3 - The arithmetic circuit 28 performs a logical operation on the binary signal of the residual magnetic flux distribution stored in the memory circuit 30 to decode the magnetic barcode. The actual logical operation process will be described later with reference to a pulse waveform diagram, but by this logical operation process, it is possible to know in which position the magnetic bar with the desired coercive force exists. If a magnetic barcode is read simply based on the magnitude distribution of coercive force, it will be determined to be valid if the relative relationship with the coercive force of other magnetic materials used at the same time is satisfied. However, according to this embodiment, the value of coercive force itself is tested, and the authenticity of the magnetic card can be confirmed more reliably.

The operation of the arithmetic circuit 28 will be explained using the magnetic barcode 66 shown in FIG. 5 as an example. The magnetic barcode 66 is a high coercive force magnetic bar 60. having the characteristics shown in FIG. 2(1). Figure 2 (
It consists of a combination of a medium coercive force magnetic bar 62 having the characteristics shown in (3) and a low coercive force magnetic bar 64 having the characteristics shown in FIG. 2 (2).

In FIG. 5, AI and A2 are timing pulses 14-pulses φ1. It is φ2. The reproducing head 2 after the magnetic barcode 66 has been saturated magnetized by the magnetizing magnetic head 16
The output waveform of 0 is as shown in FIG. 5B, and the corresponding output waveform of the waveform shaping circuit 26 is a pulse train as shown in FIG. 5C.

Here, a reverse magnetic field equivalent to the coercive force of the medium-coercive magnetic bar 62 is applied to the magnetic barcode 66 by the magnetizing magnetic head 16 . As shown in FIG. 2(3), the magnetic bar 62 is -
Since the reverse magnetic field in the range from Hcao to -Hc3L can almost demagnetize the magnetic bar 62, the magnetic bar 62 can be reliably demagnetized regardless of variations in individual magnetic medium reading devices or the distance between the magnetic head 16 and the magnetic barcode 66. can. As a result, the medium coercive force magnetic bar 62 appears to the reproducing head 20 as if it were a non-magnetic bar, and the low coercive force magnetic bar 64 is magnetized in the opposite direction.

Therefore, the output waveform of the reproducing head 20 becomes as shown in FIG. 5, and the corresponding output waveform of the waveform shaping circuit 26 becomes as shown in FIG. 5E.

FIG. 5E shows the position of the magnetic bar 60 with a high coercive force and the position of the magnetic bar 64 with a low coercive force (however, the phase is shifted by 180°). By ANDing the pulse train shown in FIG. 5E and the timing pulse φ1 (FIG. 5 Al), a pulse train indicating the location of the high coercive force magnetic bar 60 can be extracted, which is shown in FIG. 5F. . In addition, the pulse train and timing pulse φ2 (
By logical product with Fig. 5 A2), the magnetic bar 6 with low coercive force
A pulse train indicating the location of 4 can be extracted, and this is shown in FIG. 5G.

The pulse train in FIG. 5G is caused by the low coercive force magnetic bar 64 magnetized in the opposite direction, and is therefore 180° out of phase. Therefore, the pulse train of FIG. 5F is delayed by 180° as shown in FIG. 5H, the pulse train of FIG. 5C is delayed by 180'' as shown in FIG. 5I, and the phase of FIG. 5G is The pulse train shown in FIG. 5I shows the positions of all the magnetic bars 64 of high, medium and low coercive force, and FIG. 5G shows the position of the magnetic bar 64 of low coercive force, Since FIG. 5H shows the position of the high coercive force magnetic bar 60, by exclusive ORing the pulse train of FIG. 51 and the pulse train of FIG. By removing the magnetic bar 64 and exclusive ORing the resulting pulse train with the pulse train of FIG.
Remove 0. The results show the position of the magnetic bar 62 with medium coercive force, and the pulse train is shown in FIG. 5J.

In the manner described above, the presence or absence of a magnetic material with a specific coercive force and its location can be determined. The DC current for demagnetizing the magnetic bar 62 with medium coercive force is 1 (from C8H to -Hc).
By setting the current value to produce a reverse magnetic field in the range of at, variations in individual magnetic reading devices and the magnetization magnetic head 16 can be avoided.
Even if there are some uncertain factors such as variations in the distance between the magnetic bar code 66 and the magnetic bar code 66, the medium coercive force magnetic bar 62 can be reliably demagnetized. It can be prevented.

In this way, if there is a wide range in the strength of the reverse magnetic field for demagnetization, it seems that it becomes vulnerable to counterfeiting and alteration, but as explained earlier, it is possible to use magnetic materials with the same or similar magnetic properties. It is extremely difficult to prepare magnetic materials, and counterfeiting and
Alteration becomes more difficult. Furthermore, if by chance a normal magnetic material with a coercive force equivalent to the inverse magnetic field for demagnetization is used, it may be determined to be legitimate; If we investigate whether or not it is demagnetized by multiple reverse magnetic fields that almost bring it into a demagnetized state,
It can be definitely eliminated.

Examples of magnetic materials include barium ferrite or strontium ferrite metal, which have a higher coercive force, and cobalt-coated ferrite or chromium oxide, which have a lower coercive force. Small examples include gamma ferrite or triiron tetroxide. Of course, other magnetic materials can be used.

In the above embodiment, one medium-coercive force magnetic material with a wide range of reverse magnetic fields that can be brought into a demagnetized state is provided, but the present invention is of course not limited to this. A plurality of magnetic materials may be provided, and a magnetic material with a high coercive force or a low coercive force may be used.
18- The reverse magnetic field that can be made into a substantially demagnetized state may have a wide range. Alternatively, a combination of non-magnetic materials may be used for fixed information.

[Effects of the Invention] As can be easily understood from the above description, the present invention eliminates the possibility of erroneously determining that legitimate magnetic materials are forged or altered. Furthermore, knowing the magnetic material used and its composition requires expensive analysis equipment, and it is also difficult to prepare magnetic materials with the same characteristics, making counterfeiting and falsification extremely difficult. effective.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the structure of the magnetic material of the front holder of a magnetic card according to an embodiment of the present invention, FIG. 4 is a block diagram of the structure of the decoding circuit, and FIG. 5 is a timing diagram of the magnetic barcode reading operation. . 10: Magnetic card 12: Magnetic barcode 13: Roller 14: Motor drive roller 15: Motor drive circuit
16: Magnetizing magnetic head 18: DC current generation circuit 2
0: Reproducing magnetic head 22: Amplifier 24: Rectifier circuit
26 Two-waveform shaping circuit 28: 28: Arithmetic circuit 30
: Memory circuit 32: Control circuit 34: Clock generation circuit 60: High coercive force magnetic bar 62: Medium coercive force magnetic bar 64: Low coercive force magnetic bar 66 = Magnetic bar code

Claims (6)

[Claims] (1) A magnetic medium that retains fixed information using a magnetic material, characterized in that the magnetic material is a magnetic material that has a substantially constant magnetic flux in a magnetic field within a predetermined range except in a magnetic saturation state. magnetic medium. (2) The magnetic medium according to claim (1), wherein the magnetic material is a mixture of a plurality of magnetic materials having different coercive forces. (3) The magnetic material is a lamination of a plurality of layers made of magnetic materials having different coercive forces.
) Magnetic media described in paragraph 1. (4) A first magnetic material that has magnetic properties such that the magnetic flux is approximately constant in a predetermined range with respect to changes in the magnetic field in a predetermined range of magnetic fields, excluding magnetic saturation, and the first magnetic material has magnetic properties. A magnetic medium that retains unique fixed information using at least one of a second magnetic material and a non-magnetic material having different values. (5) The magnetic medium according to claim (4), wherein the first magnetic material is a mixture of a plurality of magnetic materials having different coercive forces. (6) The magnetic medium according to claim (4), wherein the first magnetic material is a stack of a plurality of layers made of magnetic materials having different coercive forces.