JPH11211804A - Magnetoresistance effect sensor and security system using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fraudulent input imitating input to a sensor from generating by neighboringly arranging the respective elements of two pair or more of magnetoresistance effect (MR) sensors so as to be simultaneously influenced from the magnetic field of an object to be measured, and outputting potential of the connected part between one end of one side element row and one end of the other side element row. SOLUTION: In the (n) channel one output MR sensor 1, a little slender (n) pieces (n is integer of 3 or more) of MR elements R1 -Rn are nearly arranged in parallel, they are connected together in series, and the one side MR element R1 is connected to constant-voltage power source 2 and the other side MR element Rn is earthed. Constant voltage is impressed between the MR elements R1 , Rn, a card magnetically given with inherent physical feature or the like is passed through in the vicinity of the sensor, and the change with the lapse of time of the output voltage is measured. The output voltage is computed by an expression using a factor decided by the magnetic flux density on the position the MR element Rj (1<=j<=n) and the shape of the MR element, because the output voltage is one, even if it is observed and recorded, the magnetic flux density is not obtaind, and the magnetic field can not be imitated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetoresistive sensor (MR sensor: Magneto-R) for detecting a magnetic field.
Efficiency Effect Sensor) and a security system using the same.

[0002]

2. Description of the Related Art As a means for preventing forgery or duplication of an object to be authenticated such as an ID card or a credit card, a physical characteristic inherent to the object to be authenticated is magnetically given and the magnetic characteristic is given to the object. 2. Description of the Related Art There is known a security system using a method of recording data as data and comparing the data with actual magnetic characteristics to determine authenticity.

As a sensor for measuring this magnetic characteristic,
A magnetic field generated by an object to be measured (authentication object) is applied to a magnetoresistive element (MR element: Magneto-Resistance).
An e-effect device) is arranged, and an MR sensor that measures a magnetic field by measuring a change in resistance thereof is used.

FIG. 6 shows a circuit configuration of a typical one-channel one-output MR sensor. MR elements R ₁ and R ₂ are connected in series, and a constant voltage V _const is applied to both ends. And M
The potential between the R element R ₁ and the MR element R ₂ and output V _out. Assuming that the magnetic flux densities at the locations where the _two MR elements R ₁ and R ₂ are located are B ₁ and B ₂ , and the coefficients determined by the shapes of the MR elements R ₁ and R ₂ are G ₁ and G ₂ , respectively, the output voltage V _out is It can be calculated as follows.

[0005]

(Equation 1)

[0006]

The above-mentioned one channel 1
In the case of an output MR sensor, a normal output sequence can be obtained from the sensor, this can be recorded and a corresponding input sequence can be obtained from this sequence, and if there is a technology capable of controlling the magnetic field applied to the sensor, It is possible to improperly generate a magnetic field by imitating a normal input sequence given to the sensor. Therefore, for example, if the security system is applied to a device that becomes operable when a legitimate card is recognized, the device can be illegally operated by imitation that creates the magnetic field, and there is a concern that security may be reduced.

On the other hand, there is an n-channel n-output MR sensor such as a 2-channel 2-output MR sensor. In this case, since the n outputs are compared with the n data, the security is higher than the above. However, a simultaneous equation showing the relationship between the output sequence from each sensor and the magnetic field to be controlled is obtained. If we could stand up, solve it, and control the magnetic field to meet that solution, we could imitate the input to the sensor. Conversely, in the case of an n-channel n-output MR sensor, processing and recording must be performed on n output sequences during normal processing, and high-speed processing is required and the recording area is limited. In some cases, there is a problem that its application is difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and its main purpose is to make it difficult to derive an input sequence from an output sequence, and to make it difficult to imitate an input to a sensor. M that can prevent input
An object of the present invention is to provide an R sensor and a security system using the same.

[0009]

According to the present invention, there is provided a magnetoresistive sensor for detecting a magnetic field of an object to be measured, wherein three or more magnetoresistive elements are electrically connected to each other. The devices are connected so as to affect each other, and the respective devices are arranged at positions simultaneously affected by the magnetic field of one measurement object, and a constant voltage power supply is supplied thereto, and the potential between any two of the devices is set to 1 In a magnetoresistive sensor, or in two or more pairs of magnetoresistive elements, the output is made at a plurality of locations or at a plurality of locations less than the number of the elements, one element of each pair and the other element. Are connected to each other, and one end of the row of the one element and one end of the row of the other element are connected to each other, so that each of the elements is simultaneously affected by the magnetic field of one measurement object. And each element of the pair A constant voltage power supply is connected to the other end of the one element row and the other end of the other element row, and one end of the one element row and one end of the other element row And a magnetoresistive sensor which outputs a potential of a connection portion with the sensor, and a magnetic field of a measurement target that generates a unique magnetic field by these sensors, and the measurement target detects the magnetic field of the measurement target. This is achieved by providing a security system that determines the authenticity of

[0010]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a plan view schematically showing a configuration of an n-channel one-output MR sensor 1 according to a first embodiment to which the present invention is applied.
FIG. 2 is a diagram showing the circuit. As shown in both figures, n slightly elongated (n: 3 or more arbitrarily configurable integers) MR elements R _{1 to} R _n are arranged substantially in parallel, and these are connected in series. Then, plug one MR element R ₁ to the constant voltage power source 2 is grounded and the other MR element R _n. Furthermore, MR elements R _i and the MR element R _{i + 1} output terminal T _o between are provided.

A constant voltage V _const is applied between the MR element R ₁ and the MR element R _n (FIG. 2). Then, not shown inherent physical characteristics magnetically object to be measured such as applied by comprising card brought close to the sensor, for example, is passed through a in the left-right direction in FIG. 1, with time of the output voltage V _out The change, ie the output sequence, is measured. When the n-channel one-output MR sensor 1 is applied to a security system, the authenticity of the object to be measured is determined from this output sequence.

In this case, the output voltage V _out is equal to the MR element R _j
The magnetic flux density at the position of (1 ≦ j ≦ n) is calculated as follows using B _j and a coefficient G _j determined by the shape of the MR element.

[0013]

(Equation 2)

With this configuration, the output voltage V _out (output series)
Therefore, even if this is observed and recorded, B _j cannot be obtained for each magnetic flux density from the above equation, and the magnetic field cannot be imitated.

FIG. 3 is a plan view schematically showing a configuration of an n-channel one-output MR sensor 11 according to a second embodiment to which the present invention is applied, and FIG. 4 is a diagram showing a circuit thereof.
As shown in both figures, n pairs (n:
2 or more layable MR elements R
_1,1 , R _{1,2 to} R _{n, 1} , R _{n, 2} are replaced with one of the MR elements R
_{1,1 to} R _{n, 1} are parallel to each other and the other MR element R
_{1,2 to} Rn _{, 2} are also connected in parallel, and one end of a row of one element is connected to one end of a row of the other element, and each element is affected by the magnetic field of one measurement object. Are arranged at the same time and the elements of each set are close to each other. Then, the other end of the row of one element is connected to the constant voltage power supply 2, and the other end of the row of the other element is grounded. The output terminal T _o to a connection portion between the one end of the column at one end and the other element row of one of the elements described above are provided.

These MR elements R _1,1 , R _{1,2 to} R _{n, 1} , R
_A constant voltage V _const is applied to _{n and 2 from} the constant voltage power supply 2 (FIG. 4). Then, an object to be measured such as a card magnetically provided with a unique physical characteristic (not shown) is brought close to the sensor, and is passed, for example, in the left-right direction in FIG.
The change with time of the output voltage _Vout , that is, the output sequence is measured. When the n-channel one-output MR sensor 11 is applied to a security system, the authenticity of the measurement object is determined from the output sequence.

The output voltage V _{out in} that case is equal to the MR element R
The resistance value of _ij (1 ≦ i ≦ n, j∈ ｛1,2｝) can be calculated as R _ij as follows.

[0018]

(Equation 3)

With this configuration, the output voltage V
_Since there is one _out (output series), even if this is observed and recorded, B _j cannot be obtained for each magnetic flux density from the above equation, and the magnetic field cannot be imitated. Further, in this configuration, since each MR element detects the magnetic flux density in pairs, the locality is smaller than in the first embodiment in which each MR element independently detects the magnetic flux density. It has become strong against noise.

As shown in FIGS. 5A to 5D, there are various variations in making a set of MR elements. For example, FIG. 5A shows rectangular MR elements arranged parallel to each other in a direction orthogonal to the direction in which the measurement object passes, assuming that the measurement object passes in the left-right direction of the drawing. FIG. 5 (b) shows a parallelogram M
The R elements are arranged parallel to each other in a direction inclined with respect to the direction in which the measurement object passes, and FIG.
Are arranged in such a manner that the rectangular MR elements are mutually parallel to and offset from each other in a direction orthogonal to the direction in which the measurement object passes. FIG. 5D shows the measurement of the rectangular MR elements. They are arranged parallel to each other in a direction inclined with respect to the direction in which the object passes. Further, these variations may be arbitrarily combined. For example, it is conceivable to arrange the rectangular MR elements parallel to each other in a direction inclined with respect to the direction in which the measurement object passes and offset from each other. The MR sensor is configured by arbitrarily selecting n of these sets and arranging them in a space or a plane.

When the MR sensor is incorporated in a security system, for example, a reference area magnetically provided with a physical characteristic unique to the card is provided on the surface of a card as an object to be measured, and the card is further provided in a recording area of the card. Data obtained by reading unique physical characteristics is recorded directly or in an encrypted form. Then, by using the MR sensor shown in the first or second embodiment, the magnetic field in the reference area is detected and compared with the data recorded in the recording area to determine the authenticity of the card. At this time, if there is a possibility that this MR sensor will be handed over to an outsider, the number, position, orientation, connection between sensors, etc. of the MR element in the sensor should be molded so that the sensor cannot be checked from the outside. By performing the processing, the analysis becomes more difficult and fraudulent acts by imitation can be more effectively prevented.

Although all the MR elements are connected in series in the first embodiment, they may be connected partially or entirely in parallel. In the second embodiment, one and the other of the pair of MR elements are connected in parallel to each other, and they are connected in series. However, one or more of the pair of MR elements are connected in whole or in part. Alternatively, the other may be connected in the same manner, and one end of both may be connected.

In the case where the MR elements are grouped as in the second embodiment, it is not necessary that the MR elements of each group have the same connection form. There is an advantage of being resistant to local noise.

Further, in each of the above embodiments, one output is used. However, if the number of outputs is set to be smaller than the number of MR elements, output may be performed from another element.

[0025]

As is apparent from the above description, the multi-channel MR sensor according to the present invention has one output M per channel.
Unlike an R sensor or an n-channel n-output MR sensor, the output cannot be obtained by the number of variables of the theoretical equation for obtaining a solution for imitating the input sequence. It becomes extremely difficult unless the number of MR elements inside the sensor, characteristics, position, orientation, connection, etc. of each element are analyzed in detail. In addition, unlike the n-channel n-output MR sensor, the output is small, so that the processing is simple, high-speed processing is possible and the system can be applied to a system with a small storage capacity. -Spatial resources can be saved.

By using this sensor as a sensor of a security system which magnetically imparts a unique physical characteristic to each of the objects to be measured and detects the magnetic characteristic, the output from the sensor can be checked. Improper input by imitating the input can be prevented, and the security is significantly improved.

[Brief description of the drawings]

FIG. 1 shows n in a first embodiment to which the present invention is applied.
FIG. 2 is a plan view schematically showing a configuration of a channel 1 output MR sensor.

FIG. 2 is a diagram illustrating a first embodiment of the present invention;
The figure which shows the circuit of a channel 1 output MR sensor.

FIG. 3 shows n according to a second embodiment to which the present invention is applied.
FIG. 2 is a plan view schematically showing a configuration of a channel 1 output MR sensor.

FIG. 4 shows n according to a second embodiment to which the present invention is applied.
The figure which shows the circuit of a channel 1 output MR sensor.

FIGS. 5A to 5D are diagrams illustrating variations in the shape and arrangement of an MR element.

FIG. 6 is a diagram showing a circuit of a conventional one-channel one-output MR sensor.

[Explanation of symbols]

1, 11 n-channel 1 output MR sensor 2 constant voltage source R ₁ to R _n MR elements _{R 1,1, R 1,2 ~R n,} 1, R n, 2 MR element T _o output terminal

Claims (3)

[Claims] 1. A magnetoresistive sensor for detecting a magnetic field of an object to be measured, wherein three or more magnetoresistive elements are electrically connected to each other, and a magnetic field of one object to be measured. Is placed at a position that is simultaneously affected by the above, and a constant voltage power supply is supplied thereto, and the potential between any two of the above elements is output at one place or at a plurality of places less than the number of the above elements. A magnetoresistive sensor. 2. A magnetoresistive sensor for detecting a magnetic field of an object to be measured which generates a unique magnetic field, wherein at least two pairs of magnetoresistive elements have one element of each pair and the other element. Are connected to each other, and one end of a row of the one element and one end of a row of the other element are connected to each other, so that each of the elements is simultaneously affected by a magnetic field of one measurement object. And arranging the elements of each pair close to each other, connecting a constant voltage power supply to the other end of the row of the one element and the other end of the row of the other element, and connecting one end of the row of the one element And outputting a potential at a connection between the first element and one end of a row of the other element. 3. A security system for detecting a magnetic field of a measurement object that generates a unique magnetic field and determining the authenticity of the measurement object based on the detection result, wherein the magnetic field of the measurement object is determined. A security system, wherein the detection is performed using the magnetoresistive sensor according to claim 2.