JPH0799390B2 - Magnetic detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic detection device capable of measuring a weak magnetic field due to biomagnetism, earth magnetism, etc. by using a magnetoresistive element made of a superconducting material.

<Prior Art> Conventionally, such a magnetic detection device is shown in FIG. This magnetic detection device is provided on both ends of the magnetoresistive element 51 made of a superconducting material manufactured by silk screen or spray on a non-magnetic insulating substrate (not shown) such as an alumina plate. A current on the order of milliamperes is applied from the microampere through the current electrodes 52a, 52b, and the voltage electrodes 53a, 53b are measured by measuring the voltage between the voltage electrodes 53a, 53b provided inside the current electrodes 52a, 52b. The resistance R of the magnetoresistive element 51 between them is measured.

The resistance R changes depending on the magnetic field B acting on the magnetoresistive element 51, and the change of the resistance R with respect to the magnetic field B when the current is constant is as shown in FIG. Therefore, the magnetic field can be measured by measuring the resistance R.

<Problems to be Solved by the Invention> By the way, there is a magnetic gap in the direction perpendicular to the substrate of the magnetoresistive element 51, and the magnetic field B acting on the magnetoresistive element 51 by the magnetic gap is shown in FIG. 7 (A). When the resistance R changes with time, the resistance R becomes as shown in FIG. Next, under the same condition, the resistance R when the magnetic field B as shown in FIG. 7 (B) acts is also as shown in FIG. 7 (C). That is, in the above conventional magnetic detection device,
Even if magnetic fields having different polarities as shown in FIGS. 7A and 7B act on the magnetoresistive element 51, the resistance values are as shown in FIG. 7C, and the difference in the polarities of the magnetic fields is detected. There is a problem that you cannot do it. This poses a serious problem, for example, when performing medical diagnosis based on a weak magnetic field such as a magnetocardiogram.

Therefore, an object of the present invention is to provide a magnetic detection device capable of detecting a difference in polarity of a weak magnetic field by using a magnetoresistive element made of a superconducting material.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the present invention provides a magnetic detection device having a magnetoresistive element made of a superconducting material and a detector for detecting the resistance of the magnetoresistive element. In the device, an AC power supply that generates a voltage having a frequency higher than the frequency of the magnetic field to be measured, and that is connected to the AC power supply and that causes an AC magnetic field having the same frequency as the frequency of the AC power supply to act on the magnetoresistive element. A loop circuit, a first differentiating circuit for differentiating the detection signal detected by the detecting section when the magnetic field to be measured and the alternating magnetic field generated by the loop circuit act on the magnetoresistive element at the same time, and the alternating current power supply is generated. Of the second differentiating circuit, a second differentiating circuit that differentiates the generated voltage signal, a first binarizing circuit that receives the output of the first differentiating circuit, and binarizes the zero voltage as a slice voltage. The second binarization circuit that receives the output and binarizes it with zero volt as the slice voltage, and the output of the first binarization circuit and the output of the second binarization circuit, so that both outputs are the same A discriminating circuit for discriminating whether or not it has a polarity, and when the discriminating circuit discriminates that the both outputs have the same polarity, it outputs the detection value detected by the detecting section as it is, and the discriminating circuit When it is determined that the both outputs do not have the same polarity, the selection inversion circuit that inverts the detection value detected by the detection unit and outputs the inverted detection value, and the detection value output by the selection inversion circuit A low-pass filter for removing a component having the same frequency as the frequency of the AC magnetic field is provided.

<Operation> The AC power supply generates a voltage having a frequency sufficiently higher than the frequency of the magnetic field to be measured, and the loop circuit connected to the AC power supply applies an AC magnetic field having the same frequency as the frequency of the AC power supply to the magnetoresistive element. Occurs to let you. The detection signal detected by the detection unit when the magnetic field to be measured and the AC magnetic field generated by the loop circuit simultaneously act on the magnetoresistive element is differentiated by the first differentiating circuit, and further zero volts by the first binarizing circuit. Is binarized as a slice voltage. On the other hand, the voltage signal generated by the AC power supply is differentiated by the second differentiating circuit and further binarized by the second binarizing circuit with zero volt as the slice voltage. And
The discriminating circuit receives the output of the first binarizing circuit and the output of the second binarizing circuit and discriminates whether or not both outputs have the same polarity. When it is determined that the both outputs have the same polarity, the detection value detected by the detection unit is directly output, and when the determination circuit determines that the both outputs do not have the same polarity, The detection value detected by the detection unit is inverted and output. Next, the low-pass filter removes the component of the same frequency as the frequency of the alternating magnetic field from the detection value output by the selective inverting circuit.

In this way, the polarity of the increase / decrease of the detection value detected by the detection unit when the magnetic field to be measured and the AC magnetic field simultaneously act on the magnetoresistive element and the polarity of the increase / decrease of the voltage for generating the AC magnetic field are determined. When the polarities are the same, the detected value is output as it is, and when the polarities are different, the detected value is output by inverting the positive and negative values. You can get the value.

<Example> Hereinafter, the present invention will be described in detail with reference to illustrated examples.

FIG. 1 is a schematic configuration diagram of a main part in one embodiment of the present invention.

In FIG. 1, 1 is a non-magnetic insulating substrate, 2 is a magnetoresistive element made of a film-shaped ceramic superconductor formed on the substrate 1, and 3 is the magnetoresistive element 2 on the substrate 1 by a printing technique. Loop wires 4 formed as an integral structure are excitation power supplies for passing a current through the loop wires to generate a magnetic field.

FIG. 2 shows an example of a measuring circuit of a magnetic detection device in which the exciting power source 4 is an AC power source, an AC magnetic field is generated in the loop wire 3, and the magnetic field to be measured is measured together with its polarity. FIG. 3 shows the waveform of the magnetic field and the waveform in each part of the circuit for explaining the operation of the circuit.

FIG. 3A shows the waveform of the magnetic field to be measured. This magnetic field to be measured has a different polarity depending on time, as in the magnetic field to be measured shown in FIG. 7 (B) in the conventional example. Further, FIG. 3 (B) shows an AC magnetic field generated by the loop line 3. This AC magnetic field is drawn lower than the actual frequency in the figure for easy understanding,
This is a sinusoidal minute reference magnetic field having a frequency sufficiently larger than the frequency of the magnetic field to be measured shown in FIG. 3 (A). The instantaneous value of this AC magnetic field is expressed as S = Sm sin ωt, where Sm is the amplitude and ω is the angular frequency. Here, the magnitude of the amplitude Sm may be equal to or smaller than the amplitude of the magnetic field to be measured. Further, the angular frequency ω needs to be made sufficiently larger than the angular frequency of the magnetic field to be measured, but it is not preferable to unnecessarily increase it because of the processing of the signal later. In the case of biomagnetic field, it is of the order of KHz.

When the AC magnetic field shown in FIG. 3 (B) is added to the magnetic field to be measured shown in FIG. 3 (A), the magnetic field having the waveform shown in FIG. 3 (C) is obtained. Then, a change in resistance of the magnetoresistive element 2 when the combined magnetic field acts on the magnetoresistive element 2 shown in FIG. 1 is detected by a detection unit (not shown) connected to the magnetoresistive element 2. Since the characteristic of the magnetoresistive element 2 is as shown in FIG. 6, the detection value of the detecting section becomes a signal voltage as shown in FIG. 3 (D). That is, when the measured magnetic field (A) is in the positive region between the times t ₀ and t ₁ ,
It has the same characteristics as the synthetic magnetic field shown in FIG. 6C, but shows the characteristics like full-wave rectification as shown in the figure between time t ₁ and t ₂ in the region where the magnetic field to be measured (A) is zero. time t ₂ after that shows a reversal characteristics with respect to the composite magnetic field of FIG. 3 (c). Here, the waveform of FIG. 3 (B) is compared with the waveform of FIG. 3 (D), and in the area where the increasing and decreasing directions of both waveforms are the same, the value (V ₁ ) Is left as it is, and the polarity of V ₁ is reversed in the region where the increase / decrease direction is different, the measured value of the same characteristic as the characteristic shown in FIG. 3 (C) is obtained.

Therefore, the voltage for generating the reference magnetic field shown in FIG. 3 (B) is differentiated by the differentiating circuit 21 shown in FIG.
The detected value shown in Fig. 2 is the high-pass filter (HPF) 2 shown in Fig. 2.
The low frequency component is removed in 2 and then differentiated in the differentiating circuit 23.
The output of the differentiating circuit 21 is shown in FIG.
The output of 23 is shown in FIG. The HPF22 is not always necessary when the magnetic field to be measured changes little with time. Next, the output (G) of the differentiation circuit 21 and the differentiation circuit 23
The output (E) is binarized by the binarization circuits 24 and 25, with the positive part being "High" and the negative part being "Low".
The outputs shown in FIGS. 3 (H) and 3 (F) are obtained. Two
The outputs (H) and (F) of the binarization circuits 24 and 25 are confirmed to be in agreement by the comparison circuit 26, and the signal shown in FIG. 3 (I) is obtained.
The comparison circuit 26 is an exclusive OR gate which is usually used, and outputs "High" when the binarized outputs (F) and (H) match each other, and outputs "High" when they do not match each other. It outputs "Low".

The output (I) of the comparison circuit 26 is input to the selective inversion circuit 27. The selective inversion circuit 27 receives this output (I) and the detection value (D), and when the output (I) is "High", outputs the detection value (D) as it is, and the output (I) is " In the case of "Low", the detection value (D) is inverted in polarity and output. Therefore, the output waveform of the selective inverting circuit 27 is as shown in FIG. 3 (J), and this waveform is the same as the waveform of the composite magnetic field shown in FIG. 3 (C). This output (J) is a low-pass filter (LP
When F) 28 is passed, an output having the same waveform as the magnetic field to be measured shown in FIG. 3 (A) is obtained.

FIG. 4 illustrates the operation of the magnetic detection device in which the exciting power source 4 shown in FIG. 1 is used as a DC power source and a DC magnetic field is generated in the loop wire 3.

The magnetic detection device generates a DC bias magnetic field B ₀ to the loop line 3, the operating point by the measured magnetic field as shown in FIG. 3 (A) is shifted by ₀ minutes the bias magnetic field B, the magnetic resistance element 2 The resistance value is set to be higher than the lowest resistance point. By subtracting the DC magnetic field component from the measured value thus obtained, a measured value corresponding to the polarity of the magnetic field to be measured can be obtained.

This magnetic detection device is simpler than the above-described magnetic detection device for generating an alternating magnetic field, but has a narrow operating range and slightly reduced reality, but is highly applicable to a practical machine.

As described above, by applying an alternating current or a direct current to the loop wire and applying the alternating magnetic field or the direct current magnetic field to the magnetoresistive element 2 in addition to the measured magnetic field, the measured value corresponding to the polarity of the measured magnetic field can be obtained. it can.

In the above embodiment, the loop line is formed on the substrate by the printing technique, but it may be a loop line made of a wire, or the loop line may be formed on another substrate, and the substrate may be the substrate 1
You may leave it close to.

In addition to the applications described above, a reference current may be passed through the loop line to check the operation of the magnetoresistive element or the entire device and make corrections. Further, it is arranged so that the angle with respect to the magnetoresistive element is variable, and is used for confirming the direction of the magnetic field to be measured. It is also possible to confirm the direction of the magnetic field to be measured by arranging a plurality of loop lines at different angles and supplying a reference current having a phase difference to each loop line.

<Effects of the Invention> As is clear from the above, the magnetic detection device of the present invention is
While the detection signal when the alternating magnetic field by the loop circuit is applied to the magnetoresistive element is differentiated by the first differentiating circuit, the alternating voltage signal to the loop circuit is differentiated by the second differentiating circuit, and the polarities of both differential signals are Since the polarities of the detection signals are reversed when they are different, it is possible to obtain a measured value according to the polarities of the magnetic field to be measured even when the polarities of the magnetic field to be measured change.

Further, by differentiating the detection signal by the first differentiating circuit, even a weak magnetic field at the time of medical diagnosis or the like can be detected.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a main part in one embodiment of the present invention, FIG. 2 is a measurement circuit diagram for generating an alternating magnetic field in a loop line in the above embodiment to measure the magnetic field, and FIG. FIG. 4 is a waveform diagram for explaining the operation of the measuring circuit, FIG. 4 is an operation explanatory diagram when a DC magnetic field is generated in the loop line in the above embodiment, and FIG. Is a diagram showing general characteristics of a magnetoresistive element made of a superconducting material, and FIG. 7 is a diagram showing an example of a magnetic field acting on the magnetoresistive element and measured values. 1 ... Substrate, 2 ... Magnetic resistance element, 3 ... Loop line, 4 ... Excitation power supply, 21,23 ... Differentiation circuit, 26 ... Comparison circuit, 27 ... Selection inversion circuit, 28 ... Low pass filter .

Claims (1)

[Claims] 1. A magnetic detection device having a magnetoresistive element made of a superconducting material and a detection section for detecting the resistance of the magnetoresistive element, for measuring a magnetic field, wherein a voltage having a frequency higher than a frequency of a magnetic field to be measured is applied. A generated AC power supply, a loop circuit that is connected to the AC power supply and that causes an AC magnetic field having the same frequency as the AC power supply to act on the magnetoresistive element, and a magnetic field to be measured and the loop circuit generated. A first differentiating circuit for differentiating a detection signal detected by the detecting unit when an alternating magnetic field acts on the magnetoresistive element at the same time; a second differentiating circuit for differentiating a voltage signal generated by the alternating current power supply; A first binarization circuit which receives the output of the differentiating circuit and binarizes 0 volt as a slice voltage, and a binary signal which receives the output of the second differentiating circuit and binarizes 0 volt as a slice voltage. A second binarization circuit, and a discrimination circuit which receives the output of the first binarization circuit and the output of the second binarization circuit to determine whether or not both outputs have the same polarity, When the determination circuit determines that the both outputs have the same polarity, the detection value detected by the detection unit is output as it is, and the determination circuit determines that the both outputs do not have the same polarity. At this time, a selective inversion circuit that outputs the detection value detected by the detection unit by inverting its positive and negative values, and a low-pass filter that removes a component of the same frequency as the frequency of the alternating magnetic field from the detection value output by the selective inversion circuit. And a magnetic detection device.