JP2005308573A - Method for detecting electrical signal accompanying magnetic field change due magnetic substance and detecting device used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detecting method for detecting an electric signal accompanying magnetic field change due to a magnetic substance in a simple circuit configuration, and to provide a detecting device used for the detecting method. <P>SOLUTION: The detecting device 20 for evaluating the magnetic substance includes a magnetic field generating device 22. The magnetic field generating device 22 includes a Helmholtz coil composed of two exciting coils 22a and 22b, and generates a uniform alternating magnetic field by a drive device 24. Two sensors 26a and 26b are arranged in the uniform alternating magnetic field. A magnetism sensitive detected body 30 is put at the side of one sensor 26a, and the magnetic field change accompanying change of a magnetic state is output from the sensors 26a and 26b. The electric signals due to the uniform alternating magnetic field are canceled by detecting the difference between outputs of the electric signals and the electric signals corresponding to the magnetic field change due to the change of the magnetic state of the magnetism sensitive detected body 20 are detected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for detecting an electric signal accompanying a magnetic field change by a magnetic material and a detection device used therefor, and more particularly, for example, using a magnetic material for evaluating a ferromagnetic material for a magnetic tag used in an electronic article monitoring system. The present invention relates to a method for detecting an electric signal accompanying a change in a magnetic field and a detection device used therefor.

  In recent years, there has been a rapid increase in the damage caused by unauthorized removal of goods at department stores, supermarkets, retail stores, libraries, exhibition halls, and the like. In order to prevent such unauthorized removal or theft of the article, a magnetic tag having a linear or belt-like magnetic sensing object is attached to the article, and when the article passes through the detection area, 2. Description of the Related Art An electronic article monitoring system that detects a magnetic field change caused by a magnetic sensing object and issues an alarm is employed.

  As shown in FIG. 5, the magnetic tag 1 includes a sheet-like base material 2. An overcoat layer 3 is formed on one surface of the substrate 2, and a magnetically sensitive object 4 is held in the overcoat layer 3. Examples of the magnetic sensing object 4 used here include high magnetic permeability materials such as permalloy and sendust, Co-B, Co-Fe-B, Co-Fe-Ni-B, and Fe-Ni-Mo-. Amorphous metal materials such as B, Fe-Ni-PB, Fe-Ni-B, Fe-B, Fe-Mo-B, and Co-Fe-Mo-B-Si -Various so-called soft magnetic materials whose magnetization state changes due to changes in a relatively weak external magnetic field, such as metal materials exhibiting large Barkhausen jumps such as Si-based and Ni-Fe-based materials, and oxide materials such as soft ferrite. Can be used. An adhesive layer 5 is formed on the local surface of the substrate 2, and a release paper 6 is temporarily attached on the adhesive layer 5. When the magnetic tag 1 is used, the release paper 6 is peeled from the adhesive layer 5 and the magnetic tag 1 is attached to the article.

  When an article to which such a magnetic tag 1 is attached passes through the detection region, an alarm must be reliably issued by the magnetic sensor to be detected 4, so that the magnetic sensor to be detected 4 or the produced magnetic tag is used. An evaluation of 1 is performed. Although there are few literatures on evaluation devices for performing such evaluation, it is conceivable to apply a monitoring device used in an electronic article monitoring system to the evaluation of the magnetic tag 1. As such a monitoring device, for example, as shown in FIG. 6, a monitoring device including a transmission antenna 7 and a reception antenna 8 is disclosed. The monitoring device includes a transmission control circuit 9, and an interrogation signal waveform is formed in the transmission control circuit 9. This interrogation signal waveform is amplified by the output amplifier 10 to form an antenna drive signal. Then, when the antenna drive signal is input to the transmission antenna 7, an alternating magnetic field as an interrogation signal is generated.

  In the receiving antenna 8, the change in the magnetic field due to the interrogation signal from the transmitting antenna 7 is output as an AC signal. Here, when the magnetic tag 1 is inserted between the transmitting antenna 7 and the receiving antenna 8, a change occurs in the magnetic field due to the interrogation signal from the transmitting antenna 7 due to a change in the magnetization state of the magnetically sensitive object 4. An electric signal corresponding to a change in the magnetic field is output from the receiving antenna 8. The electric signal output from the receiving antenna 8 is separated in the receiving circuit 11 into an electric signal corresponding to the call signal and an electric signal corresponding to a change in the magnetic field by the magnetically sensitive object 4. Then, the presence of the magnetic tag 1 is detected by detecting an electric signal corresponding to a change in the magnetic field by the magnetically sensitive body 4. In such a monitoring device, it has been shown that the presence of the magnetic tag 1 can be reliably detected by making the interrogation signal a pulsed AC signal (see, for example, Patent Document 1).

JP-A-10-62530

  In such a monitoring apparatus, as shown in FIG. 7, an AC signal A corresponding to the interrogation signal is output from the receiving antenna. Then, for example, when a magnetic tag having a magnetic sensing object having a very small coercive force is inserted into the magnetic field, the AC magnetic field as an interrogation signal becomes zero (more precisely, the AC magnetic field has become zero). Thereafter, the magnetic sensing object undergoes magnetization reversal at the time when the value of the opposite sign close to 0 occurs), and an electric signal B corresponding to the magnetization reversal is output from the receiving antenna. In order to extract the electric signal B corresponding to this magnetization reversal, filtering is required to separate the electric signal A corresponding to the interrogation signal and the electric signal B corresponding to the magnetization reversal. Even when the pulse-like interrogation signal as described above is employed, filtering is indispensable because an electric signal corresponding to the interrogation signal is output from the receiving antenna. For such filtering, it is necessary to provide a filtering circuit in the receiving circuit, resulting in a complicated circuit configuration.

  SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide a detection method capable of detecting an electric signal accompanying a magnetic field change caused by a magnetic material with a simple circuit configuration, and a detection device used in such a detection method. .

The present invention includes a step of applying a substantially equal AC magnetic field to two sensors for outputting a change in magnetic field as an electric signal, and a step of inserting a magnetic material by shifting to one side of the two sensors in the AC magnetic field. And a method for detecting an electric signal accompanying a magnetic field change by the magnetic material, including a step of detecting a difference in output of the electric signal from the two sensors accompanying the change of the magnetic field by the magnetic material in the alternating magnetic field.
Within a substantially equal alternating magnetic field, the change in the magnetic field is output as an electric signal by two sensors, and the output of the electric signal from these sensors is taken to output an electric signal by the substantially equal alternating magnetic field. Are canceled out, and the output becomes nearly zero. In this state, when the magnetic material is inserted (placed) on one side of the two sensors, a change occurs in the magnetization state of the magnetic material due to the alternating magnetic field, and the output accompanying the change in the magnetic field due to the change in the magnetization state of the magnetic material. A signal is superimposed on the output from the alternating magnetic field and output from the two sensors. At this time, since the magnetic body is shifted toward one side of the two sensors, a large output is obtained from a sensor close to the magnetic body, and a small output is obtained from a sensor far from the magnetic body. Therefore, even if the difference between the outputs from the two sensors is taken, the output accompanying the change in the magnetic field due to the change in the magnetization state of the magnetic material does not become zero. In this way, by measuring the difference between the outputs from the two sensors, it is possible to cancel out the output caused by substantially the same AC magnetic field, and to detect the electrical signal accompanying the change in the magnetic field due to the change in the magnetization state of the magnetic material. .

The present invention also includes a magnetic field generator for generating a uniform alternating magnetic field and two magnetic fields that are placed in an alternating magnetic field generated by the magnetic field generator and output changes in the alternating magnetic field as electrical signals. An apparatus for detecting an electrical signal that accompanies a change in a magnetic field caused by a magnetic body, including a sensor and a detection device for detecting a difference in output of electrical signals from the two sensors.
By generating a uniform alternating magnetic field by the magnetic field generator and detecting the difference in the output of the electrical signals from the two sensors placed in the alternating magnetic field, the electrical signal due to the uniform alternating magnetic field is canceled out. Then, by inserting the magnetic material toward one side of the two sensors, an electric signal accompanying a change in the magnetic field due to a change in the magnetization state of the magnetic material can be detected by the detection device by the method described above.
In such a detection device, a Helmholtz coil capable of generating a uniform magnetic field can be used as the magnetic field generation device.
In addition, detection coils having the same characteristics can be used as the two sensors, and two detection coils are connected by connecting the two detection coils so that the electrical signals output from these detection coils are in opposite phases. The difference in the output of the electrical signal from the coil can be detected by the detection device.

According to the present invention, by taking the difference between the outputs of the electric signals from the two sensors, the electric signals appearing by the substantially equal AC magnetic field can be canceled, so that the substantially equal AC output from the sensors can be obtained. There is no need to separate an electric signal due to a magnetic field and an electric signal that appears due to a magnetic field change due to a change in the magnetization state of the magnetic material. Therefore, it is not necessary to provide a circuit for filtering in the detection device for detecting the output of the sensor, and a simple circuit configuration can be obtained.
In addition, since this detection device can detect a magnetic field change due to a change in the magnetization state of a magnetic material inserted in a substantially equal alternating magnetic field, evaluation of a magnetically sensitive object used in an electronic article monitoring system. In addition, for example, the present invention can be used as an electronic article monitoring system of a type in which a magnetic tag is brought close to the sensor of this apparatus, or a metal detector for detecting a blade hidden in a container.

  The above object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

  FIG. 1 is an illustrative view showing one example of a detection apparatus used in a method for detecting an output accompanying a magnetic field change by a magnetic body of the present invention. The detection device 20 includes a magnetic field generation device 22 that can generate a uniform alternating magnetic field. As such a magnetic field generator 22, a Helmholtz coil etc. can be used, for example. The Helmholtz coil has two circular coils of radius a placed in parallel and coaxially, and a distance equal to a, and is used to obtain a uniform magnetic field. In order to obtain such a Helmholtz coil, the magnetic field generator 22 has two exciting coils 22a and 22b arranged in parallel and coaxially.

  In order to generate a uniform alternating magnetic field by the magnetic field generator 22, a driving device 24 is connected to the exciting coils 22a and 22b. The driving device 24 includes an oscillation circuit and an amplification circuit. In the oscillation circuit, for example, a uniform AC signal such as a sine wave is oscillated, and the AC signal is amplified in the amplifier circuit to obtain a drive signal. The obtained drive signal is applied to the exciting coils 22 a and 22 b, and a uniform alternating magnetic field is formed in the magnetic field generator 22. The drive signal formed by the drive device 24 is not limited to a sine wave signal, and may be a triangular wave signal, a sawtooth wave signal, or the like.

  Two sensors 26a and 26b are arranged between the two exciting coils 22a and 22b. These sensors 26a and 26b output electrical signals corresponding to changes in the magnetic field in the magnetic field generator 22. As the sensors 26a and 26b, for example, detection coils having the same characteristics are used. And the difference of the output of the electric signal obtained from the sensors 26a and 26b can be obtained by connecting so that the polarities of the two detection coils are reversed. The difference in the output of the electrical signals of the sensors 26a and 26b is detected by the detection device 28. Thus, since the difference in the output of the electrical signals of the sensors 26a and 26b is input to the detection device 28, the detection device 28 does not require an addition circuit or a subtraction circuit.

  In the detection device 20, uniform AC signals are output from the two sensors 26 a and 26 b by the uniform AC magnetic field generated by the magnetic field generator 22. Here, since detection coils having the same characteristics are used as the sensors 26a and 26b, electrical signals having the same output can be obtained from the sensors 26a and 26b. And since the difference of the output of sensor 26a, 26b is input into the detection apparatus 28 by connecting so that the polarity of two detection coils may be reversed, the electrical signal detected by the detection apparatus 28 is substantially. 0.

  Here, as shown in FIG. 2, for example, when the magnetic sensing object 30 is inserted on the one sensor 26 a side, the magnetization state of the magnetic sensing object 30 changes due to the AC magnetic field generated by the magnetic field generator 22. . For example, when the magnetically sensitive body 30 is a magnetic body having a coercive force close to 0, as shown in FIG. 3, the reverse sign close to 0 is obtained after the AC magnetic field in the magnetic field generator 22 becomes 0. At that time, the magnetic sensing object 30 is reversed in magnetization. When the magnetic sensing object 30 undergoes magnetization reversal, the magnetic field in the vicinity thereof changes, and electrical signals are output from the sensors 26a and 26b in response to the magnetic field change.

  Since the magnetic sensing object 30 is inserted on the one sensor 26a side, the magnetic field change due to the magnetization reversal of the magnetic sensing object 30 in the vicinity of the sensor 26a is large, and the magnetic field change in the vicinity of the other sensor 26b is small. . Therefore, a large electrical signal is output from one sensor 26a and a small electrical signal is output from the other sensor 26b along with the magnetization reversal of the magnetic sensing object 30 (in the case of FIG. 2, the electrical signal of the sensor 26b). Is close to 0). Therefore, by taking the difference in the output of the electrical signals of the sensors 26a and 26b, the detection device 28 can detect the output as an electrical signal accompanying the magnetization reversal of the magnetically sensitive body 30.

  FIG. 4 is a waveform diagram showing an electrical signal (voltage) detected by the detection device 28. In FIG. 4, a sine wave signal A is detected as a difference between the outputs of the electrical signals output from the sensors 26 a and 26 b by the uniform alternating magnetic field generated by the magnetic field generator 22. Nearly zero. When the magnetic sensing object 30 is inserted on the one sensor 26a side, the magnetic sensing object 30 undergoes magnetization reversal when the alternating magnetic field becomes zero and becomes a reverse sign value close to zero. The change in the magnetic field is output as an electrical signal from the sensors 26a and 26b. In the detection device 28, the difference in the output of the electric signals from the sensors 26a and 26b is detected. However, since the magnetically sensitive object 20 is inserted on the one sensor 26a side, the electric signals of the sensors 26a and 26b are detected. The detection device 28 detects an electrical signal B that is much larger than the electrical signal A generated by an alternating magnetic field.

  As described above, in this detection device 20, almost no electrical signal due to the alternating magnetic field generated by the magnetic field generation device 22 is input to the detection device 28, and only the electrical signal associated with the magnetic field change due to the magnetization reversal of the magnetic sensing object 30. Input to the detector 28. Therefore, it is not necessary to provide a filtering circuit for separating the electric signal due to the alternating magnetic field and the electric signal due to the magnetic field change due to the magnetization reversal of the magnetic sensing object 30 in the detection device 28, and a simple circuit configuration. can do. Further, since the electric signal generated by the AC magnetic field generated by the magnetic field generator 22 is hardly detected, the electric signal associated with the magnetic field change due to the magnetization reversal of the magnetically sensitive object 30 can be accurately detected. It is possible to accurately evaluate a magnetic tag using the same. Further, by evaluating the output of an electric signal from the magnetic material used for the magnetically sensitive object using this detection device 20, it is possible to determine whether the lot of the magnetic material for the magnetically sensitive object is good or bad.

  By using this detection device 20, it is possible to accurately evaluate the magnetic sensing object 30 and the magnetic tag using the same, so that the electronic article monitoring system reliably detects illegal take-out of articles. The magnetic tag which can be obtained can be obtained. Further, the detection device 20 can be used as an electronic article monitoring system of a type in which a magnetic tag having a magnetically sensitive object 30 is close to the sensor 26a or 26b.

  The detection device 20 can detect an electrical signal accompanying a change in the magnetic field due to a change in the magnetization state of the magnetic material. However, as described above, it is limited to a change in the magnetic field due to a change in the magnetization state such as magnetization reversal of the magnetic material. It is not something that can be done. For example, by inserting a magnetic material in a uniform alternating magnetic field, an eddy current is generated in the magnetic material, and even a magnetic field change caused by this eddy current can be detected by the detection device 20.

  Therefore, for example, a small blade or the like entering the container can be found, and it is possible to prevent the blade from being brought into an area in which such blade is restricted. In addition, the presence of a metal object in the envelope can be confirmed without opening the envelope of the mail. Thus, this detection device 20 can also be used as a small metal detector.

  Thus, the magnetic field accompanying the change in the magnetization state of the magnetic material due to the alternating magnetic field is superimposed on the uniform alternating magnetic field, and the magnetic field around the magnetic material changes. And by detecting the electric signal due to the magnetic field change by the two sensors 26a and 26b by the differential method, it is possible to detect a minute magnetic field change due to the magnetic material, and to easily detect the magnetic field change. The detection device 20 can be downsized. Note that the magnetic body can be detected if it is inserted offset to one of the two sensors 26a and 26b, and it is not necessary to strictly specify the insertion position.

  Further, the sensors 26a and 26b are not limited to the detection coils. For example, a change in magnetic field may be converted into an electric signal using a Hall element or the like, and the output may be detected by the detection device 28 through a differential circuit. Thus, any sensor that can convert a magnetic field change into an electrical signal can be used as the sensors 26a and 26b.

It is an illustration figure which shows an example of the detection apparatus of this invention. FIG. 2 is an illustrative view showing a state in which a magnetically sensitive object is inserted into the detection device shown in FIG. 1. It is a characteristic view which shows the BH curve of the magnetic sensing body inserted in the detection apparatus shown in FIG. It is a wave form diagram which shows the electric signal (voltage) detected with the detection apparatus of a detection apparatus, when a magnetic sensitive body is inserted in the detection apparatus shown in FIG. It is sectional drawing which shows an example of the magnetic tag used for an electronic article monitoring system. It is an illustration figure which shows the conventional monitoring apparatus used for an electronic article monitoring system. It is a wave form diagram which shows the electrical signal detected when the articles | goods which stuck the magnetic tag pass a monitoring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Detection apparatus 22 Magnetic field generator 22a, 22b Excitation coil 24 Drive apparatus 26a, 26b Sensor 28 Detection apparatus 30 Magnetic sensing object

Claims (4)

Applying substantially equal alternating magnetic fields to the two sensors for outputting changes in the magnetic field as electrical signals;
A step of inserting a magnetic material to one side of the two sensors in the alternating magnetic field, and a difference in output of electric signals from the two sensors due to a change in the magnetic field by the magnetic material in the alternating magnetic field. A method for detecting an electric signal accompanying a magnetic field change by a magnetic material, comprising a step of detecting. A magnetic field generator for generating a uniform alternating magnetic field,
Two sensors placed in an alternating magnetic field generated by the magnetic field generator for outputting a change in the magnetic field in the alternating magnetic field as an electrical signal, and a difference in output of electrical signals from the two sensors is detected The detection apparatus of the electric signal accompanying the magnetic field change by a magnetic body is included including the detection apparatus for.   The detection device according to claim 2, wherein a Helmholtz coil is used as the magnetic field generation device.   The two sensors are detection coils having the same characteristics, and the two detection coils are connected by connecting the two detection coils so that electrical signals output from the two detection coils are in opposite phases. The detection device according to claim 2, wherein a difference in output of electrical signals from is detected by the detection device.

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