JPH06289110A - Superconductive magnetometer - Google Patents

Abstract

PURPOSE:To provide a superconductive magnetometer which is prevented from the generation of a bump-shaped transient signal, at the time of a reset, to be generated at every variation of magnetic field of fluxoid quantum phi0, and less in the error of measurement. CONSTITUTION:A transient signal preventing circuit 21 which generates a voltage corresponding to fluxoid quantum phi0 or-phi0 according to the increase- decrease signal of an increase-decrease discriminant circuit 17 at the time of reset, and generates a bump-shaped transient signal on the basis of the above voltage to reduce the transient signal from the quantity of precise instrumentation output from a low-pass filter 16A is added for preventing the generation of the bump-shaped transient signal, at the time of reset, to be generated at every variation of magnetic field of phi0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a superconducting quantum interference device (Superconducting Quantum).
(Interference Device: hereinafter referred to as SQUID for short), and relates to a high-sensitivity magnetometer.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing an embodiment of a conventional superconducting magnetometer. In the figure, 1 is SQUID
Elements, 2 is a superconducting ring, 3A and 3B are superconducting rings 2
Josephson device provided inside, 4 is superconducting ring 2
Modulation feedback coil magnetically coupled with 5 is a drive circuit, 6
Is a bias circuit, 7 is a preamplifier, 8 is a multiplier, 9 is a phase shifter, 10 is an oscillator, 11 is an integrator, 12 is a feedback resistor, 13 is an integrator switch, 14 is an integrating capacitor, 1
5 is an amplifier, 16 A is a low-pass filter, 17 is an increase / decrease determination circuit, 18 is an A / D converter, 19 is an increase / decrease counter, 2
Reference numeral 0 is a coarse-fine synthesis circuit, V _K is the output of the drive circuit 5, V _A is the output of the low-pass filter 16A, R and Z are reset signals and increase / decrease signals output from the increase / decrease determination circuit 17, and V _D is The output of the A / D converter 18, N is the count value of the increase / decrease counter 19.

The drive circuit 5 is generally a FLL (Flux).
This is a known circuit called a Locked Loop circuit, and its operation is, for example, Review Of S.
scientific Instrument, 1984
, 55, 952-957.

Next, the operation will be described. Figure 8 is SQU
It shows the Φ-V characteristics of the ID element. However, Φ ₀
Is a magnetic flux quantum and its value is 2.07 × 10 ⁻¹⁵ Wb. When the SQUID element 1 is cooled by immersing it in liquid helium and is transformed into a superconducting state, the SQUID output voltage V changes with a cycle of Φ ₀ with respect to the magnetic flux linking itself. At this time, when the integrator switch 13 of the integrator 11 is opened in the magnetic field to be measured, integration is started from the opened time, and the operating point of the SQUID is the closest at the time when the integrator switch 13 is opened, as shown in FIG. It is fixed at the maximum or minimum position (magnetic flux lock).

After the magnetic flux is locked, the SQUID interlinkage magnetic flux at the time when the integrator switch 13 is opened is set as the origin of the output zero, and the voltage V _K proportional to the relative change amount ΔΦ of the interlinkage magnetic flux from that is output. Each time ΔΦ increases / decreases by Φ _{0, the} increase / decrease circuit 17 determines this and the increase / decrease signal Z corresponding to the increase / decrease.
And reset signal R is output. Next, the increase / decrease counter 1
9, the count value is incremented or decremented by 1 in accordance with the increase / decrease of the increase / decrease signal Z, and at the same time, the integrator switch 13 of the integrator 11 is closed by the reset signal R and the charge accumulated in the integrating capacitor 14 is discharged. Then, the voltage is reset to zero. The relationship between the amount of change ΔΦ and the output voltage V _K is expressed by the following equation.

[0006]

[Equation 1]

However, M _f is a mutual inductance between the feedback modulation coil 4 and the superconducting ring 2, and R _f is a feedback resistor 12.
The resistance value, I _f is the current flowing in the feedback resistor 12.

Next, the operation when the magnetic field to be measured changes by ΔH as in the following equation will be described.

[0009]

[Equation 2]

When the magnetic field to be measured changes by ΔH, the count value of the increase / decrease counter 19 increases by n, and at the same time, the output voltage of the drive circuit 5, that is, the integrator 11 in this circuit is calculated from the equation (2). The voltage shown in the following equation is output.

[0011]

[Equation 3]

Therefore, the output V _K of the drive circuit 5 is set to A / D.
The digital amount is converted by the converter 18, and the A / D
The output V _D of the converter 18 and the count value N of the increase / decrease counter 19 are sent to the coarse-fine synthesis circuit 20. First, the equation (4) is substituted into the equation (1) to calculate ΔΦ _1. Then, the equation (3) is calculated to calculate ΔH. In this way, the SQUID element 1, the drive circuit 5, the increase / decrease determination circuit 1
7, the A / D converter 18, the increase / decrease counter 19, and the coarse / fine synthesis circuit 20, with the measurement resolution of the drive circuit 5, and with the dynamic range of the counter capacity of the increase / decrease counter 19, the amount of change in the magnetic field to be measured. ΔH can be measured. This output is used, for example, to find a magnetic material. The low-pass filter 16A is for removing noise contained in the drive circuit 5.

[0013]

The magnetic field to be measured H of the superconducting magnetometer constructed as described above and the coarse output, fine output, and coarse fine combined output, that is, the count values N and A of the increment / decrement counter 19 are obtained.
Output V _D of the D / D converter 18, output H of the coarse synthesis circuit 20
The relationship with _G is expressed as shown in (a), (b), (c), and (d) of FIG. 9 when the measured magnetic field linearly increases monotonically, for example. However, in the figure, the horizontal axis is associated with the time axis.

As shown in FIG. 9A, the output N of the increase / decrease counter 19 is shown in FIG. 9B each time the measured magnetic field H increases by Φ ₀ .
As described above, the drive circuit 5 outputs a sawtooth wave having an amplitude corresponding to Φ ₀ , but the low pass filter 16A for noise removal provided after the drive circuit 5 causes the sawtooth wave to fall. That is, since a delay occurs when the drive circuit 5 is reset, the output V _D of the A / D converter 18 is as shown in FIG.
It becomes like (c). As a result, the output H _G of the coarse synthesis circuit 20 produces a transient signal on the bump at the joint of Φ ₀ as shown in FIG. 9 (d). When the measured magnetic field H monotonously decreases, the output H _G of the coarse / fine synthesis circuit 20 also has a downward-sloping downward-moving transient signal, which is the reverse of the case of monotonically increasing. The transient signal included in the output H _G of the coarse-fine synthesis circuit 20 sometimes causes a magnetic field measurement error.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to obtain a superconducting magnetometer having a small measurement error by reducing a transient signal generated when the drive circuit 5 is reset. There is.

[0016]

In a superconducting magnetometer according to a first embodiment of the present invention, an SQUID element and the SQUID described above are provided.
A drive circuit that drives the ID element to obtain a desired output, a low-pass filter that removes noise from the drive circuit, and an increase / decrease signal that indicates an increase / decrease in the magnetic field to be measured based on the output of the drive circuit and the drive circuit is reset. An increase / decrease determination circuit that outputs a reset signal, an A / D converter that converts the output of the low-pass filter into a digital amount, and a periodic increase / decrease amount of the magnetic field to be measured based on the increase / decrease signal of the increase / decrease determination circuit. An increase / decrease determination circuit in front of an A / D converter of a conventional superconducting magnetometer equipped with an increase / decrease counter and a coarse / fine synthesis circuit for combining the outputs of the A / D converter and the increase / decrease counter to calculate a magnetic field to be measured. The transient signal prevention circuit for preventing the transient signal at the time of reset by inputting the increase / decrease signal is added.

In the superconducting magnetometer of the second embodiment of the present invention, an SQUID element, a drive circuit that drives the SQUID element to obtain a desired output, a low-pass filter that removes noise of the drive circuit, and the drive circuit. An increase / decrease determination circuit that outputs an increase / decrease signal indicating an increase / decrease in the magnetic field to be measured and a reset signal that resets the drive circuit based on the output of the circuit, and A that converts the output of the low-pass filter into a digital amount.
/ D converter, an increase / decrease counter that measures the periodic increase / decrease amount of the magnetic field to be measured based on the increase / decrease signal of the increase / decrease determination circuit, and the output of the A / D converter and the increase / decrease counter are combined to produce the measured magnetic field. A transient signal canceling circuit is added after the A / D converter of the conventional superconducting magnetometer equipped with a coarse / fine synthesis circuit to calculate It is a thing.

In the superconducting magnetometer of the third embodiment of the present invention, an SQUID element, a drive circuit for driving the SQUID element to obtain a desired output, a low-pass filter for removing noise of the drive circuit, and the drive circuit. An increase / decrease determination circuit that outputs an increase / decrease signal indicating an increase / decrease in the magnetic field to be measured and a reset signal that resets the drive circuit based on the output of the circuit, and A that converts the output of the low-pass filter into a digital amount.
/ D converter, an increase / decrease counter that measures the periodic increase / decrease amount of the magnetic field to be measured based on the increase / decrease signal of the increase / decrease determination circuit, and the output of the A / D converter and the increase / decrease counter are combined to produce the measured magnetic field. The output of the drive circuit and the reset signal of the increase / decrease determination circuit are input instead of the low-pass filter of the conventional superconducting magnetometer equipped with the coarse-fine synthesis circuit for calculating It is provided with a transient signal prevention type low-pass filter for preventing a transient signal.

[0019]

In the superconducting magnetometer according to the first embodiment of the present invention, the transient signal prevention circuit artificially generates a transient signal by the reference voltage generation circuit and the low-pass filter based on the increase / decrease signal of the increase / decrease determination circuit and drives the signal. By subtracting from the output of, the transient signal at the time of reset is prevented.

In the superconducting magnetometer according to the second embodiment of the present invention, the transient signal canceling circuit artificially generates the transient signal reference signal by the transient signal generating circuit, and the signal A By subtracting / adding to the output of the / D converter, a transient signal at the time of reset is prevented.

In the superconducting magnetometer of the third embodiment of the present invention, a switch provided in parallel with a filter resistor forming a low-pass filter is used to short-circuit the filter resistor at the time of resetting by using a reset signal of an increase / decrease discrimination circuit, and a filter capacitor is formed. The transient signal at the time of reset is prevented by rapidly discharging the accumulated charge.

[0022]

【Example】

Embodiment 1 FIG. 1 is a block diagram showing Embodiment 1 of the present invention. In the figure, 1 to 20 are the same as the conventional ones, and 21 is a transient signal prevention circuit for preventing a transient signal at the time of reset.

FIG. 2 is a block diagram showing an example of the configuration of the transient signal prevention circuit 21. In the figure, 16B is the same low-pass filter as the low-pass filter 16A, 22 is a reference voltage generation circuit, 23 is a subtractor, Z is an increase / decrease signal of the increase / decrease determination circuit 17, and _VA is the output of the low-pass filter 16A.

Next, the operation of the superconducting magnetometer according to the first embodiment of the present invention will be described. First, the SQUID element 1 is cooled by immersing it in liquid helium and is transferred to a superconducting state. Then, the integrator switch 13 is opened in the magnetic field to be measured and the magnetic flux is locked. After that, at the time when the integrator switch 13 is opened. The SQUID interlinkage magnetic flux is set as the origin of the output zero, and the relative change amount of the interlinkage magnetic flux from there is set to the drive circuit 5,
The increase / decrease determination circuit 17 and the low-pass filter 16A output the analog value voltage value V _A corresponding to the magnetic field change amount within Φ ₀ as the precise measurement amount, while the increase / decrease determination circuit 17
The increase / decrease counter 19 outputs the magnetic field change amount for each Φ ₀ as the count value N, that is, the rough measurement amount.

Next, the reference voltage generation circuit 22 of the transient signal prevention circuit 21 generates a voltage corresponding to Φ ₀ or -Φ ₀ at the time of resetting according to the increase or decrease of the increase / decrease signal Z of the increase / decrease determination circuit 17, and then this The low-pass filter 16B inputs the voltage to artificially generate a bump-like transient signal that occurs in response to an increase or decrease. Further, by subtracting the transient signal from the precise measurement amount V _A output from the low-pass filter 16A by the subtracter 23, the bump-like transient signal is canceled, and the precise measurement amount that prevents the transient signal at reset is calculated. To do.

Next, this signal is converted into a digital amount by the A / D converter 18, and this and the count value N of the increase / decrease counter 19, that is, the rough measured amount and the fine measured amount obtained by canceling the transient signal are roughly measured. The precise synthesis circuit 20 synthesizes and combines them into one magnetic field measurement amount, and finally the measured magnetic field in which a transient signal at the time of reset is prevented is calculated.

In the above embodiment, the SQUID element 1
Explained an example of a DC-SQUID that includes two Josephson elements in the superconducting ring and drives by applying a DC bias current. However, the superconducting ring contains one Josephson element and is driven by an AC bias current. RF-SQ
UID can also be used.

Second Embodiment FIG. 3 is a block diagram showing a second embodiment of the present invention. In the figure, 1 to 20 are the same as conventional ones, and 24 is a transient signal canceling circuit for preventing transient signals at the time of resetting.

FIG. 4 is a block diagram showing an example of the configuration of the transient signal canceling circuit 24. In the figure, 25 is a transient signal generation circuit, 26 is an addition / subtraction circuit, Z is an increase / decrease signal of the increase / decrease determination circuit 17, and V _D is the output of the A / D converter 18.

Next, the operation of the superconducting magnetometer according to the second embodiment of the present invention will be described. First, the SQUID element 1 is cooled by immersing it in liquid helium and is transferred to a superconducting state. Then, the integrator switch 13 is opened in the magnetic field to be measured and the magnetic flux is locked. After that, at the time when the integrator switch 13 is opened. The SQUID interlinkage magnetic flux is set as the origin of the output zero, and the relative change amount of the interlinkage magnetic flux from there is set to the drive circuit 5,
Increase / decrease determination circuit 17, low-pass filter 16A and A / D
While the converter 18 outputs the voltage value V _D of the digital amount corresponding to the magnetic field change amount within Φ ₀ as the precise measurement amount, the increase / decrease determination circuit 17 and the increase / decrease counter 19 generate Φ.
The magnetic field change amount for each ₀ is output as the count value N, that is, the rough measurement amount.

On the other hand, the transient signal generating circuit 25 of the transient signal canceling circuit 24 stores the waveform of the transient signal on the bump generated at reset as a transient signal reference signal in a memory such as a ROM and receives the increase / decrease signal Z. At the same time, the stored waveform of the transient signal is output to the addition / subtraction circuit 26, and this signal is added / subtracted from the output V _{D of the} A / D converter 18 according to the increase / decrease of the increase / decrease signal Z. Then, the precise measurement amount that cancels the transient signal on the bump is calculated.

Next, the count value N of the increase / decrease counter 19, that is, the coarse measurement amount and the fine measurement amount that cancels the transient signal are combined by the coarse fine combining circuit 20 to be combined into one magnetic field measurement amount, and finally the final measurement result is obtained. Calculate the measured magnetic field that prevents transient signals at reset.

Third Embodiment FIG. 5 is a block diagram showing a third embodiment of the present invention. In the figure, 1 to 20 are the same as conventional ones, and 27 is a transient signal prevention type low-pass filter which removes noise of the drive circuit and prevents a transient signal at the time of reset.

FIG. 6 is a block diagram showing an example of the configuration of the transient signal prevention type low-pass filter 27. 2 in the figure
8 is a filter resistor, 29 is a filter capacitor, 30 is a switch provided in parallel with the filter resistor 29, R is a reset signal output from the increase / decrease determination circuit 17, and V _K is a signal output from the drive circuit 5. .

Next, the operation of the superconducting magnetometer according to the third embodiment of the present invention will be described. First, the SQUID element 1 is cooled by immersing it in liquid helium and is transferred to a superconducting state. Then, the integrator switch 13 is opened in the magnetic field to be measured and the magnetic flux is locked. After that, at the time when the integrator switch 13 is opened. The SQUID interlinkage magnetic flux is set as the origin of the output zero, and the relative change amount of the interlinkage magnetic flux from there is determined by the drive circuit 5 and the increase / decrease determination circuit 17 as a voltage value V of an analog amount corresponding to the magnetic field change amount within Φ _{0. While K} is output as the precise measurement amount, the increase / decrease determination circuit 17 and the increase / decrease counter 19 output the magnetic field change amount for each Φ ₀ as the count value N, that is, the rough measurement amount.

Next, noise contained in this signal is removed by the transient signal prevention type low-pass filter 27, and at the time of reset, the switch 30 is connected by the reset signal output from the increase / decrease determination circuit 17 and the filter resistance is changed. 28 is short-circuited, and the electric charge accumulated in the filter capacitor 29 is rapidly discharged to output a precise measurement amount in which a transient signal at the time of reset is prevented. The subsequent operation is the same as that of the first embodiment.

[0037]

As described above, according to the present invention, the following effects can be obtained.

The present invention is the A / D of the conventional superconducting magnetometer.
Add a transient signal prevention circuit to prevent the transient signal at reset by inputting the increase / decrease signal of the increase / decrease discrimination circuit in front of the converter,
Since the generation of a bump-like transient signal at the time of reset that occurs each time the magnetic field of Φ ₀ changes is prevented, it is possible to obtain a superconducting magnetometer with a small measurement error.

The present invention also relates to the conventional superconducting magnetometer A
A transient signal canceling circuit that inputs the increase / decrease signal of the increase / decrease determination circuit and cancels the transient signal generated at the time of reset is added after the / D converter, and the bump-like transient signal at the time of reset generated for each magnetic field change of Φ ₀ is added. The superconducting magnetometer with less measurement error can be obtained because it is canceled and prevented. further,
Since the prevention of the transient signal can be processed by software such as a microprocessor, there is an advantage that it can be realized more easily and at low cost.

Further, according to the present invention, instead of the low-pass filter of the conventional superconducting magnetometer, the output of the drive circuit and the reset signal of the increase / decrease determination circuit are input to eliminate noise of the drive circuit and a transient signal at the time of reset. It is equipped with a transient signal prevention type low-pass filter to prevent the occurrence of a bump-shaped transient signal at each reset of Φ ₀ magnetic field, so a new circuit is added to the superconducting magnetometer with few measurement errors. You can get it without doing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

2 is a block diagram showing an example of the configuration of a transient signal prevention circuit 21. FIG.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a block diagram showing an example of the configuration of a transient signal cancellation circuit 24.

FIG. 5 is a block diagram showing a third embodiment of the present invention.

FIG. 6 is a block diagram showing an example of the configuration of a transient signal prevention type low-pass filter 27.

FIG. 7 is a block diagram showing an example of a conventional superconducting magnetometer.

FIG. 8 is a diagram showing an operation of the SQUID element.

FIG. 9: Measured magnetic field of superconducting magnetometer and coarse output, fine output,
It is a figure which shows the relationship with a coarse refinement | synthesis output.

[Explanation of symbols]

 1 SQUID element 2 Superconducting ring 3A Josephson element 3B Josephson element 4 Modulation feedback coil 5 Driving circuit 6 Bias circuit 7 Preamplifier 8 Multiplier 9 Phaser 10 Oscillator 11 Integrator 12 Feedback resistor 13 Integrator switch 14 Integrating capacitor 15 Amplifier 16A Low-pass filter 16B Low-pass filter 17 Increase / decrease determination circuit 18 A / D converter 19 Increase / decrease counter 20 Coarse synthesis circuit 21 Transient signal prevention circuit 22 Reference voltage generation circuit 23 Subtractor 24 Transient signal cancellation circuit 25 Transient signal generation circuit 26 Adder / subtractor circuit 27 Transient signal prevention type low-pass filter 28 Filter resistor 29 Filter capacitor 30 Switch

Claims (3)

[Claims] 1. A superconducting quantum interference device, a drive circuit for driving the superconducting quantum interference device to obtain a desired output, a low-pass filter for removing noise of the drive circuit, and an output of the drive circuit. An increase / decrease determination circuit that outputs an increase / decrease signal indicating an increase / decrease of the magnetic field to be measured and a reset signal that resets the drive circuit, an A / D converter that converts the output of the low-pass filter into a digital amount, and an increase / decrease of the increase / decrease determination circuit An increase / decrease counter that measures the cyclic increase / decrease amount of the magnetic field to be measured based on the signal, and a transient signal prevention circuit that inputs the output of the drive circuit and the increase / decrease signal of the increase / decrease determination circuit to cancel the transient signal generated at reset, A superconducting magnetometer, comprising: a transient signal preventing circuit; and a coarse-fine combining circuit that combines outputs of the increase / decrease counter to calculate a magnetic field to be measured. 2. A superconducting quantum interference device, a drive circuit for driving the superconducting quantum interference device to obtain a desired output, a low-pass filter for removing noise of the drive circuit, and an output of the drive circuit. An increase / decrease determination circuit that outputs an increase / decrease signal indicating an increase / decrease of the magnetic field to be measured and a reset signal that resets the drive circuit, an A / D converter that converts the output of the low-pass filter into a digital amount, and an increase / decrease of the increase / decrease determination circuit An increase / decrease counter that measures the periodic increase / decrease amount of the magnetic field to be measured based on the signal, and a transient signal cancellation that cancels the transient signal generated at reset by inputting the output of the A / D converter and the increase / decrease signal of the increase / decrease determination circuit A superconducting magnetometer, comprising: a rectifying circuit; and a coarse synthesizing circuit for synthesizing outputs of the transient signal canceling circuit and the increase / decrease counter to calculate a magnetic field to be measured. 3. A superconducting quantum interference device, a drive circuit for driving the superconducting quantum interference device to obtain a desired output, an increase / decrease signal indicating an increase / decrease of a magnetic field to be measured based on the output of the drive circuit, and the drive. An increase / decrease determination circuit that outputs a reset signal that resets the circuit, and a transient signal prevention that inputs the output of the drive circuit and the reset signal of the increase / decrease determination circuit to remove noise of the drive circuit and prevent a transient signal at the time of reset Type low pass filter, an A / D converter for converting the output of the transient signal prevention type low pass filter into a digital amount, and an increase / decrease for measuring the periodic increase / decrease amount of the magnetic field to be measured based on the increase / decrease signal of the increase / decrease determination circuit. A superconducting magnetometer, comprising: a counter; and a coarse-fine combining circuit that combines the outputs of the transient signal prevention type low-pass filter and the increase / decrease counter to calculate a magnetic field to be measured. .