JPH04204278A - Multi-channel squid magnetic meter - Google Patents

Abstract

PURPOSE:To eliminate the problem of response for input magnetic flux and lessen a quantity of consumption of a freezing mixture such as liquid helium of SQUID by always operating a plurality of SQUID magnetic flux sensors and lessening the number of output lines by the use of a multiplexer. CONSTITUTION:An oscillator 2 supplies bias current (a) of a lower frequency to each of a plurality of magnetic flux sensor 1 respectively. Next, pulse outputs (b1-bN) from each of the magnetic flux sensors 1 (1-N) are completely changed over to a multiplexer 4 during a half cycle of the bias current (a) by the use of a control signal (d) of a control circuit 3 to convert into serial data(d). Thereafter the serial data(d) are transmitted to a multiplexer 5 provided at the side of room temperature through an output cable. The multiplexer 5 is changed over by the use of a signal (c') of a control circuit 3 synchronized with the control signal of the multiplexer 4 to convert the serial data into parallel data so as to transmit into a signal processing circuits 6 corresponding to each magnetic flux sensor 1.

Description

[Detailed description of the invention] 〔overview〕 Uses multiple magnetic flux sensors using SQUID.

- Relating to a multi-channel SQUID magnetometer that detects magnetic fields from many different regions at once.

The purpose is to accurately respond to each channel even if the bias frequency is low.

Bias means for supplying bias current to the plurality of magnetic flux sensors; and first conversion means for converting the output of each of the plurality of magnetic flux sensors into serial data.

a signal processing means that is provided corresponding to each of the plurality of magnetic flux sensors and outputs the magnetic flux signal; and a signal processing means that converts the serial data into parallel data.

a second conversion means for supplying each of the bias currents to a corresponding one of the signal processing means, and a control means for supplying a signal synchronized with the bias current to the first and second conversion means,
While each of the magnetic flux sensors outputs a pulse due to the bias current from the bias means, the first conversion means converts the pulse into the serial data according to a signal from the control means.

[Industrial application field]

The present invention relates to a multi-channel SQUID magnetometer that uses a plurality of SQUID magnetic flux sensors to detect magnetic fields from a large number of different regions at once.

In recent years, SQ has been used to measure minute magnetic fields generated from living organisms, etc.
U I D (Superconducting Qu
antum Interference Device
: A highly sensitive magnetometer using a superconducting quantum interference device) is being used. In particular, by measuring the magnetic field distribution in the brain and heart, it is possible to estimate the current source that generates the magnetic field, which provides extremely meaningful information for diagnosis as well as elucidating neural activity within the body. It has been pointed out that it is useful. Such measurement of magnetic field distribution is possible by using a one-channel SQUID magnetometer and sequentially measuring time-series data for each site. but,
This method has problems, such as the time it takes to measure and fatigue of the subject, and the inability to estimate the current source with high accuracy because magnetic fields at different locations cannot be measured simultaneously. Therefore, a multi-channel SQUID magnetometer is required that can arrange a plurality of magnetic flux sensors and simultaneously measure the magnetic field at each location.

[Prior art] As a conventional multi-channel SQUID magnetometer, 1
Compatible with the channel's magnetic flux sensor.

A processing circuit for converting the obtained detection signal into a magnetic field signal is also provided for one channel, and a multi-channel system has been proposed (H, E, Hoenig et al., +
Biomagnetic ＋＊ultichannel
5yste+w with integrated
SQUIDs and first order gr
adiometers operating in a
5 shielded room + cryogenics
, vol, 29°＾gust, pp809-813.
(1989), each 5QtJID is driven at a different frequency and multiplexed to connect multiple SQUID output lines into one.
A method to simplify the system by writing a book has also been proposed (Furukawa et al., Japan
nese Journal of Apply Phy
sics.

vol, 2B, No, 3. Marcb, 1989, 1L
456-L45B), these methods use SQUID
All three use SQUIDs with analog operation in which the SQUID output is a minute analog signal. On the other hand, as a digital SQUID that can obtain a pulse output, a SQUID consisting of a two-junction quantum interference device is biased with AC and outputs a pulse (Japanese Patent Laid-Open No. 63-290
No. 979) is known. analog operated dc
Adding the voltage output of the SQUID to a 1-bit conduction comparator or 1-bit A/D converter to obtain a pulse output (D. Drung, Cryogenics, vo.
1, 26+pp623-627.1986) is known. Digital SQUID has the characteristic of being able to have a high output S/N ratio.

A multi-channel method using digital SQUID is related to the application filed by the present applicant.

Output of digital SQUID of each channel.

A method in which the signals are switched at fixed intervals using a multiplexer and converted into a magnetic flux signal using a single processing circuit (Patent Application No. 1-17).
No. 8851), and also uses a one-way conduction feedper/seven circuit, which is also related to the applicant's application.

One-chip SQUID (N, Fuji) that integrates all functions necessary for converting magnetic flux into electrical signals on one chip.
imaki et al, -A Single-Ch
ip SQUID Magnetometer”, IH
EE Trans, Electron Device,
vol, 35°No, 12 pp2412-2418.
There is a method (Japanese Patent Application No. 1-340964) in which a plurality of one-chip SQUIDs are switched over by a selection circuit at regular intervals using a method (Japanese Patent Application No. 1988) to obtain a magnetic flux signal.However, in both of these methods, only one SQUID is selected. The SQUID has stopped operating (not outputting pulses), therefore,
If a channel is selected again after all channels have been scanned, it will need time to catch up with the new flux signal. Let me explain this specifically.

It will look like this:

For example, what is the frequency band required for biomagnetic measurement?

Considering the previous examples, it is several hundred Hz. Therefore, if we try to provide a frequency band of 3 (11) Hz, from the sampling theorem, all channels must be scanned every 1/6 (11) Hz, that is, every 1.7 S.

If the number of channels is 1 (11) channels, the time allocated per channel is 1.7ss/1
(11) -17 μs. Meanwhile, to obtain the magnetic flux signal.

When performing feedback operation on a digital SQUID, the magnetometer has a transfer function in the same form as a first-order low-pass filter for minute signals such as biomagnetism (Fujima
ki et al, +J, ^pp1. Phys, ,
65(4), pp1626-1630.1989),
Cutoff frequency ω. is given by the following equation.

ω. =2f,・ΔΦ・d P/dΦ f, ... Bias frequency given to SQUID °ΔΦ・
・Feedback amount P per pulse ・Switch probability Φ ・Signal magnetic flux ゛If the bias frequency is IMH2 and ΔΦ is 1×104
Φ. , dP/dΦ is 1(11)/Φ. Then, f.

is approximately 320Hz. However, within the allocated time of 17 μs per channel, it catches up with the input magnetic flux (to
At least a band of 20KHz (90%) or more is required, and therefore the bias frequency must be increased by two orders of magnitude or more.Also, to increase the sensitivity of the magnetometer,
In order to avoid the influence of quantization noise, ΔΦ must be made small, but then it is necessary to further increase the bias frequency to compensate for this.

By the way, one of the important things when creating multi-channels is how to reduce the number of signal lines to and from the SQUID.
This can be mentioned. this is.

Normally, SQUID sensors are placed in a low-temperature environment such as liquid helium, so as the number of channels increases, the number of cables connecting them to the room-temperature circuit increases, which also increases the consumption of expensive cryogens such as liquid helium. It is. In the conventional analog-operated SQUID, as mentioned above, the SQUID
Since a processing circuit (room temperature) is provided for each QUID sensor.

Output lines and feedback lines for the number of channels are required. Also, in the single frequency multiplexing method, although there is only one output line, feedback lines are required for the number of channels.

[Problem to be solved by the invention]

Multi-channel SQUI with more than 1 (11) channels
When realizing a D magnetometer, as described above.

Operation at a bias frequency of several hundred MHz or higher is required. However, the operation in such frequency domain.

In the case of multi-channels, a problem arises in that crosstalk between channels is more likely to occur. Also,
In the conventional multi-channel 5QUI'D magnetometer, the more the number of channels increases.

Problems arise, such as increased consumption of cryogens such as liquid helium.

The present invention provides a multi-channel SQU that can accurately respond to each channel even if the bias frequency is low.
The purpose is to provide an ID magnetometer.

Another object of the present invention is to provide a multi-channel SQUID II PL fluxmeter that consumes less SQUID cryogen such as liquid helium even if the number of channels increases.

Furthermore, according to the present invention, the response of each channel is accurate.

Multi-channel SQUI with low cryogen consumption
The purpose is to provide a D magnetometer.

[Means to solve the problem]

FIG. 1 is a diagram illustrating the principle of the present invention and shows a multi-channel SQUID magnetometer according to the present invention.

1 is a magnetic flux sensor using SQUID, which converts a magnetic field from a living body into an electrical signal.

There are multiple locations. 2 is an oscillator, SQUID
3 is a control circuit that supplies a signal to multiplexers 4 and 5 to switch their switches; 4 is a multiplexer, and each A device that converts the outputs of multiple magnetic flux sensors 1 into serial data by switching the output of magnetic flux sensor 1. 5 is also a multiplexer, which converts serial data into parallel data, and is called a demultiplexer due to its function. Sometimes. A signal processing circuit 6 extracts a magnetic flux signal from an electric signal (detection signal), and is provided corresponding to each of the plurality of magnetic flux sensors 1.

(Operation) FIG. 2 is an explanatory diagram of the operation of the present invention, and shows the time sequence in the multi-channel SQUID [bundle meter] shown in FIG.

The oscillator 2 supplies each of the plurality of magnetic flux sensors 1 with a bias current (a) at a relatively low frequency (for example I MHz). Pulse outputs (bl to bN) from each magnetic flux sensor 1 (1-N) corresponding to each part of the magnetic field measurement region of the living body
) are all switched by the multiplexer 4 during a half cycle (actually 174 cycles) of the bias current (a) by the control signal (C) of the control circuit 3, and converted into serial data (d). After that, serial data (d) is obtained using one output cable.

The signal is transferred to the multiplexer 5 provided on the room temperature side. By switching the multiplexer 5 using the signal (C') of the control circuit 3 synchronized with the control signal of the 1 multiplexer 4, the serial data (d) is converted to parallel data, and the signal corresponding to each magnetic flux sensor 1 is converted to parallel data. It is sent to the processing circuit 6. While applying this bias current,
If you do it repeatedly.

Since time series data for each magnetic flux sensor 1 is obtained in each signal processing circuit, it can be converted into m flux signals, and data of magnetic flux signals 1 to N corresponding to the measurement site can be obtained.

In the present invention, as described above, each magnetic flux sensor l operates continuously while the bias current (a) is applied (the on-off measurement of the pulse signal is performed every half cycle T/2 of the bias current m(a)). 7 equivalently, each magnetic flux sensor 1 operates in one channel. Therefore, there is no problem regarding the response of the SQUID, and since the multiplexers 4 and 5 are used to combine the output lines into one line, it is possible to reduce the amount of SQUID cryogen such as liquid helium consumed.

〔Example〕

FIG. 3 is a configuration diagram of an embodiment of the present invention.

In this embodiment, the bias current (a) is supplied to a plurality of magnetic flux sensors l at the same timing, and the magnetic flux sensor l
This is an example in which a superconducting feedback circuit is built into each.

In this embodiment, the magnetic flux sensor 1 and the multiplexer 4 are provided in a cryostat 7 and cooled with a cryogen such as liquid helium. This point also applies to other embodiments described later.

In addition, in this embodiment, in order to operate the magnetic flux sensor l continuously during measurement according to the present invention, the bias l@(a) is continuously supplied during measurement, and the feedback input is disconnected by a selection circuit or the like. 1
The output of the bundle sensor l is always supplied to the multiplexer 4. This point also applies to other embodiments described later.

Regarding the cable extending from the low temperature chamber to the room temperature side, since the multiplexer 4 is provided, there is only one output line 8 for signal output. Regarding the bias current (a), there is only one bias line 9 because the supply timing is set to one (common). Regarding the control signal (C) line 10 from the control circuit 3, the number of lines is log N, where N is the number of fli bundle sensors 1. Regarding feedback input, it has a built-in feedback circuit.

The number is 0. This allows the consumption of liquid helium to be reduced.

Hereinafter, the magnetic flux sensor 1 and multiplexer 4 provided on the low temperature side will be explained first.

In order to incorporate the feedback circuit, the magnetic flux sensor 1 has one of the configurations shown in FIGS. 4A to 4C. That is, the magnetic flux sensor l includes a sensor part using SQUID (hereinafter referred to as SQUID sensor) 21 and a superconducting feedback circuit 22 integrated into one chip.
It consists of

FIG. 4A shows the configuration of a one-chip magnetic flux sensor.
In figure A, 31a and 31b are superconducting loops, and a pair of pickup coils take out the magnetic flux interlinking within the loop in order to big-amplify the magnetic flux to be measured (magnetic flux to be measured), and 32 is an input coil, which is a pink-up coil 31.
A and 31b constitute a superconducting loop 33. The input coil 32 constitutes a part of the SQUID sensor 21 and applies magnetic flux generated in the superconducting loop 33 to the SQUID sensor 21.

The SQUID sensor 21 uses a two-junction quantum interference device with alternating current bias, and includes a superconducting loop 34 including Josephson junctions J, , J, and a superconducting inductance 35. Signal magnetic flux Φ3 (coupling coefficient is M) and feedback magnetic flux Φ2. This is pulsed by an alternating current bias current (a), and a current pulse corresponding to the input magnetic flux (Φ, -Φ1.) is output to the feedback circuit 22.

One feedback circuit 22 includes 9, for example, a superconducting loop 37, a Josephson junction J, , J, and a first inductance 38, and a second inductance that is magnetically coupled to the first inductance 38 (coupling coefficient is Mz). A superconducting storage loop consisting of a write gate 40 which has an inductance 39 and converts the pulses sent from the SQUID sensor 21 into magnetic flux quanta, and a superconducting inductor 41 which converts the pulses that have passed through the write gate 40 into magnetic flux quanta and stores them. 4
2 is used. Further, the magnetic flux quantum of the superconducting inductor 41 is returned to the input side of the SQUID sensor 210 as a feedback magnetic flux through a feedback loop 43 that is magnetically coupled.

Therefore, the feedback circuit 22 measures the pulses output from the SQUID sensor 21 and feeds back magnetic flux quanta according to the measurement results to the input side of the SQUID sensor 21 through magnetic field coupling by the feedback loop 43.

In the above configuration, the SQUID sensor 21 generates a pulse train depending on the applied magnetic flux, which pulse train is respectively sent to the multiplexer 4.

The output of the SQUID sensor 21 is sent to a feedback circuit 22. The output pulses of the SQUID sensor 21 are counted by the feedback circuit 22, and a magnetic flux proportional to the result is fed back to the SQUID sensor 21. therefore.

The feedback loop 43 is the pickup coil 31a
, 31b always operate to cancel the measured magnetic flux picked up by the feedback magnetic flux, and looking at the amount of feedback,
The magnitude of the magnetic flux to be measured can be determined.

Next, FIG. 4B shows an example in which the analog output of a conventional dc-SQUID sensor is input to a superconducting comparator to obtain a pulse.

Components common to the example shown in FIG. 4A are given the same reference numerals. A dc-SQUID is used for the SQUID sensor 51, and the SQUID sensor 51 includes a superconducting loop 34, a Josephson junction JxJt, a resistor 52, 53, and a superconducting inductance 35, and receives the measured signal magnetic flux applied from the input coil 32. It receives the difference between Φ, (coupling coefficient is M) and feedback magnetic flux ゛Φ,1, converts it into a voltage output using a DC bias 54, and sends it to a superconducting comparator 56 via a resistor 55. The superconducting comparator 56 includes a Josephson junction Js, Jh and a first inductance 58 in a superconducting loop 57.

First inductance 58 and magnetic field coupling (coupling coefficient is Ms
) has a second inductance 59.

The output of the SQUID sensor 51 is compared in response to the AC bias current (a), and a digital current pulse is output to the superconducting digital feedback circuit 61. The superconducting digital feedback circuit 61 is the superconducting comparator 5
6, and feeds the magnetic flux quantum according to the measurement result to the input side of the SQUID sensor 51 through magnetic field coupling by a feedback loop 62. and a D/A converter, and may further include a circuit such as a filter if necessary.

FIG. 4C shows an example in which a superconducting digital feedback circuit 61 similar to that described above is attached to the SQUID sensor 21 which operates in pulses.

Although the superconducting digital feedback circuit 61 may be placed at room temperature, the superconducting digital feedback circuit 6
1, the number of feedback lines can be reduced.

Figure 5 shows SQUID sensor (digital SQU+D) 2
FIG. 1 is an explanatory diagram of the operation of FIG.

This figure shows the SQUID for the input magnetic flux Φ of the SQUID.
The characteristics (threshold characteristics) of the magnetic field current i of D are shown. Φ. teeth,
'&! The one-bundle quantum is 2.07
D is a superconducting state. In addition, in the sI region outside the SQUID, the SQUID is in a voltage state and outputs a pulse.

Here, the magnitude of the bias current (a) is the input magnetic flux Φ,
It is made equal to the magnitude of the critical current i in the case of = 0. Due to such bias conditions.

A positive pulse and a negative pulse are output depending on whether the input magnetic flux is positive or negative. Also, since the dark value characteristics are said to be asymmetric,
bias within one period T of the flow.

Outputs one positive or negative pulse.

Note that the magnitude of the input magnetic flux Φ is 4. For example, in Fig. 7,
- It is as shown by the dotted chain line. Further, the pulse width of the output pulse depends on the magnitude of the human force magnetic flux Φ, but has a pulse width of at least T/4 or more.

The multiplexer 4 is constructed using a Josephson logic circuit for operation in a coolant such as liquid helium.

6A to 6C show the configuration of one multiplexer 4. FIG.

As shown in FIG. 6A, the output bl of a plurality of magnetic flux sensors l
. . . are input into five parallel Josephson AND gates 71, respectively. Also, the AND gate 71 has 1
A selection signal from the selection circuit 70 is input. This results in output.

are selectively output from the AND gate 71 in this order,
The multiplexer output consists of serial data.

Here, the details of the 2 selection circuit 70 are as follows: The 0 selection circuit 70 shown in FIG. 6B has 256 selection gates Q, ~Q!
2. and each selection gate Ql to Q□. A1 for
An 8-bit signal consisting of ~A is input, and these 8
Control signals 1 to n (logical product of A and A1) from which 256 bit signals can be selected are generated from the bit signals A1 to A.

As an example, the configuration of one selection gate Q1 is shown in FIG. 6C, and one selection gate Q1 receives 4-bit signals A1 to
A. (It is originally 8 bits.

(only 4 bits shown) are received by Josephson OR gates 72 to 75, respectively, and internally there are Josephson OR gates 79 to 8 and Josephson AND gates 76 to 78. ...and A+
A control signal consisting of the AND of ~A is generated. This control signal is supplied to AND gate 71 shown in FIG. 6A.

The multiplexer 4 may also have the configuration shown in FIG. 7A or 7Bl.

In FIG. 7A, multiplexer 4 has three-phase clocks Φ1. It consists of a shift register driven by Φ and Φ. When both the load signal and the shift signal S are set to "1", the logic sum of Φ1 drive (OR gate) 82, 83 and the AND gate 84 output "1". The sum gate 85 shifts the signal, the 3J OR gate 86 outputs "1", and the 3J OR gate 87 outputs the signal b1.Furthermore, Φ, the driving AND gate 88 outputs "1". , the signal b1 is output to the 0UTPUT terminal, and the OR gate 89 driven by Φ shifts the signal to the next stage (second stage).Here.

When the soft signal S is input, the same operation is performed and the signal b8 is output. Further, the 3J OR gate converts the page pulse from the SQUID into a positive pulse of positive polarity to facilitate subsequent processing means.

In FIG. 7B, the input of the shift signal S in FIG. 7A is omitted and the load signal is shifted in synchronization with the clocks Φ1 to Φ, so that the output pulse train
... shows a shift register that obtains b and l.

Figure 7C shows the stage before the first stage (hereinafter referred to as
(referred to as stage 0), each has a three-phase clock Φ1. An example is shown in which three OR gates driven by Φ2 and Φ3 are connected in series. in this case.

Prior to the output pulse b1, an output pulse of “1” (
Hereinafter, a MARK signal) is obtained. Therefore.

Timing can be easily determined by extracting the MARK signal at the multiplexer 5 or at a stage preceding it and using this to trigger the control signal C'. As a result, in response to the time delay caused by the serial data d being sent via the cable, the control signal C'
can be easily delayed.

Note that the circuit corresponding to the 0th stage (including the output resistor) does not necessarily need to be provided at the stage before the 1st stage. That is, 11 or more may be provided in a predetermined stage between the first stage and the Nth stage.

By including one or more "1" high level bits in the output pulse train, the operation timing of the control signal C' of the multiplexer 5 can be determined based on the information of these bits. Alternatively, a plurality of circuits corresponding to the 0th stage may be provided, and the AND of each of their outputs may be calculated and this may be used as a trigger. Further by taking the conjunction.

The reliability of the operation of the multiplexer 5 can be improved in terms of timing determination.

With the above, the magnetic flux sensor l installed on the low temperature side in FIG.
And that concludes the explanation of multiplexer 4.

Next, each circuit provided on the room temperature side will be explained. In addition, in the following description, FIG. 8 will be referred to. FIG. 8 includes the magnetic flux sensor 1 and the multiplexer 4. This is a time sequence showing the operation of each circuit.

The oscillator 2 supplies a bias current a of a sinusoidal wave with a frequency of 1, for example, OT, and also supplies a synchronization pulse e in phase with this to the 90'' phase shifter 12.

The bias current does not necessarily have to be a sine wave, but may have a waveform that allows the output pulses of all the magnetic flux sensors 1 to be sustained due to the input magnetic flux Φ while being switched by the multiplexer 4.

The 90° phase shifter 12 shifts the phase of the synchronization pulse e to 90°.
to form a 90° synchronization pulse f. This pulse f is supplied to the control circuit 3 and the positive/negative discrimination circuit 14.

The control circuit 3 supplies multiplexers 4 and 5 in synchronization with a bias current a using a pulse r.

Multiplexer control signal C consisting of signals A to A1, etc.
and C'. The timing of the signal C' is later than that of the signal C by a transmission delay time τ in a cable or the like.

Here, the operation timing of multiplexer 4 is as follows.

The timing is always delayed by 90° with respect to the bias current a. That is, multiplexer 4.

From the moment when all magnetic flux sensors have finished outputting pulses,
The operation is started. This allows multiplexer 4
Even if the machine is operated in a high-speed swinging motion.

This can prevent the SQUID from malfunctioning due to crosstalk or the like.

On the other hand, the output pulses of the magnetic flux sensor 1 are as follows. That is, this pulse is 1/of the bias current a.
The output pulses b1 to b1 of the total magnetic flux sensor 1 are sampled at high speed by the multiplexer 4 within the period of this pulse width, which has a pulse width of four cycles or more.

As a result, serial data d is obtained. This sampling is started using a 90° synchronization pulse r as a trigger,
It ends within T/4 period.

The norial data d is amplified by the preamplifier 13 and sent to the multiplexer 5. Due to this.

The S/N ratio can be improved.

The multiplexer 5 forms parallel data g to gs from the serial data d in response to the control signal C', and inputs the parallel data g to the corresponding signal processing circuit 6. This parallel data g
+ to g8 are a mixture of positive and negative pulse outputs. Note that the control signal C' is as follows.

It may be of the same timing as signal C.

Also, instead of obtaining the serial data d from the control circuit 3,
The synchronization clock of the pulse train of P L L (Phase
Locked Loop) or the like may be used to extract the signal and use this as the signal C'.

The signal processing circuit 6 includes a positive/negative discrimination circuit 14 and an up/down counter 15.

The positive/negative determining circuit 14 determines whether the corresponding parallel data g is positive or negative using the 90° synchronization pulse f. That is, the data g during the period when the 90° synchronization pulse f is “1” is taken as a positive pulse P′, and the data g during the period when the 90° synchronization pulse f is “0” is taken as the negative pulse P−.
shall be. The positive pulse P' and the negative pulse P- are used as the amplifier input and down input of the 1 up/down counter 15, respectively. As described above, the magnetic flux signal of each magnetic flux sensor 1 can be obtained as digital data. That is.

Since the pulse outputs b+ to b1 are pulses obtained as a result of being fed back within the magnetic flux sensor 1, digital data of the magnetic flux signal can be immediately obtained by counting them.

In addition, the positive/negative discrimination circuit 14 and the knob down counter 15
It goes without saying that an analog integrator may be used instead of the up/down counter 15, and analog data can be directly obtained by using a D/A converter after the up/down counter 15.

FIG. 9 is a block diagram of another embodiment of the present invention.

FIG. 10 is a time sequence showing the operation.

In this embodiment, a plurality of (2N) magnetic flux sensors 1 are divided into two sets, and bias currents a and d at different timings are applied to each set.
This is an example of supplying

The same number (N) of magnetic flux sensors 1' as the magnetic flux sensor 1 are prepared. That is, magnetic flux sensors l and 1' are.

Both are a set consisting of N magnetic flux sensors. A bias current a is supplied to the magnetic flux sensor 1, as in the previous embodiment. The magnetic flux sensor 1' has a bias current a of 90
Bias currents d whose phases differ by .degree. are supplied. For this purpose, a 90° phase shifter 12' is newly provided.

Due to the bias currents a and d, the outputs S to b8 and b'1 to b'8 of the magnetic flux sensors 1 and 1' become as shown in FIG. 1O.

The control circuit 3 is supplied with a signal "f" obtained by inverting the synchronization pulse "e" in addition to the signal "f" similar to that in the above-described embodiment.
results in a 90° synchronization pulse corresponding to the bias current d. The control circuit 3 uses the signal f to form a control signal for sampling the output pulses b to b8, and uses the signal ``to form a control signal for sampling the output pulses b'1 to br8.

Therefore, the multiplexer 4 operates even during the half period in which it was not operating in the previous embodiment.

As a result, serial data d shown in FIG. 10 is obtained.

In the positive/negative discrimination circuit 14' corresponding to the magnetic flux sensor 1'.

A signal ``is supplied and used to determine whether it is positive or negative.

In this embodiment, the control circuit 3 does not supply a control signal to the multiplexer 5, but extracts a synchronous clock from the serial data d using a PLL or the like and uses this.

According to the above, even if there is a limit to the operating frequency of the multiplexer 4, the frequency cannot be increased.

The number of magnetic flux sensors 1 can be doubled. That is, the multiplexer 4 can be operated efficiently, and the output 1i8 can remain one.

FIG. 11 is a block diagram of still another embodiment of the present invention, and FIG. 12A is a time sequence showing its operation.

In this embodiment, each of a plurality of (N) magnetic flux sensors 1 has two
Bias current a to a at different timings in time series
This is an example of supplying 8.

The bias currents a to aN are supplied in this order with timings shifted as shown in Figure 1, and the repetition period is T.
(Equivalent to the circumference '#J4T of the previous embodiment). Each of the bias currents a to aS is:

This is a sine wave of one period with a pulse width t. Therefore.

The number of operable magnetic flux sensors 1 is T/l.

The output of one magnetic flux sensor 1 has a pulse width within
Positive and negative outputs are obtained continuously. To detect this, the synchronization pulse e is applied to bias currents a1 to aM
(not shown), and the 90' synchronization pulse f is a pulse that rises and falls in synchronization with the positive and negative peaks of each of the bias currents a to aS. The multiplexer 4 selectively outputs the output b1, for example, in synchronization with the rising edge of the 90° synchronizing pulse f, and selectively outputs the output b1 again in synchronization with the falling edge of the 90° synchronizing pulse. Note that a delay corresponding to the operating time of the control circuit 3 and multiplexer 4 is taken into consideration.

Here, the bias current may be as shown in FIG. 12B. That is, in the first T/2 period, only positive pulses with a pulse width of t/2 are sequentially supplied to each magnetic flux sensor,
In the later T/2 period.

Similarly, a negative pulse is supplied. In other words, in one period T, one positive pulse and one negative pulse may be applied to each magnetic flux sensor 1 with one time phase shifted.

FIG. 13 is a block diagram of still another embodiment of the present invention.

This embodiment is an example in which the feedback circuit is provided on the room temperature side.

The digital output of the up/down counter 15 is.

The signal is input to the corresponding D/A converter 11 and converted into an analog signal. This signal is connected to the feedback resistor 90
is input to the corresponding magnetic flux sensor l via.

The magnetic flux sensor 1 is the 14th Ay! J or the configuration shown in FIG. 15B. The magnetic flux sensor 1 shown in FIGS. 14A and 14B has the same configuration as the SQUID sensor 21 shown in FIG. 4A and the SQUID sensor 51 shown in FIG. 4B, respectively. In addition, the first
As shown in FIG. 4A, a feedback coil 91 is added for inputting the feedback signal FB. 14th B
Also for illustrations.

Although not shown, □ is similar.

According to this embodiment, the number of feedback lines 92 (N
The number of wires connecting the cooling side and the room temperature side increases by the number of wires connected to the cooling side and the room temperature side. However, the amount of feedback is determined by the feedback resistance 9
It can be easily changed to 0. Also, the dynamic range of the entire magnetometer.

Since it is determined by the dynamic range of the up/down counter 15 and the D/A converter 11, it is easy to change.

Although the present invention has been described above using examples, the present invention is not limited to these examples, and various modifications can be made within the scope of the spirit thereof.

For example, as shown in FIG. 15, in any embodiment, between the magnetic flux sensor 1 and other circuits.

The ground (ground potential or ground potential wiring) may be separated for the following reasons. Usually, the multiplexer 4 is composed of a digital sensor circuit.

A bias current several tens of times larger than that of 5QUID flows. This bias current corresponds to a direct current in so-called TTL, and is an alternating current in the Fuson circuit. Now, assume that the ground of the SQUID is common to the ground of other circuits. In this case, it is inevitable that the ground 5 has impedance, so its potential fluctuates due to the return current of the bias current. Here, as mentioned above.

Since the bias current of multiplexer 4 is larger than that of the SQUID, the ground level variation due to this is:
This has a large impact on the operation of the SQUID and cannot be ignored. In particular, when noise is added to the bias current, the current value becomes large, which poses a big problem. Therefore, in order to eliminate such influence, it is preferable to separate the ground.

That is, in FIG. 15, a transformer T by magnetic field coupling is provided between each of the magnetic flux sensors 1 and the multiplexer 4, and their grounds are separated from each other. Note that different ground symbols are used to indicate that the ground is separated by one in each figure. The same applies between the 111 bundle sensor 1 and the bias line 9 (ie, the oscillator 2). By doing this, the bias current of other circuits becomes S
It is possible to prevent noise from affecting the ground of the QUID, and the reliability of the operation of the magnetic flux sensor 1 can be improved.

Furthermore, the bias current does not necessarily have to be a sine wave, but rather provides a positive and negative bias for a predetermined period (i.e., while the multiplexer 4 is sampling).
Any device that can maintain the output of the magnetic flux sensor l may be used.

Further, the control circuit 3 can also be provided on the cooling side.

In this case, the number of cables extending from the cooling side can be further reduced.

Moreover, it is possible to use a combination of the above-mentioned embodiments. That is, in the embodiment of FIG. 13, a bias current like that of the embodiment of FIG. 9 or FIG. 10 may be supplied. In each of the embodiments of FIGS. 3, 9 and 11, a portion (for example, half) of the N magnetic flux sensors 1
may be configured as in the embodiment shown in FIG. In this case, by providing the feedback circuit on the room temperature side.

The amount of feedback can be changed as appropriate. Furthermore, a plurality of sets of the embodiments shown in FIGS. 3, 9, and 11 and the embodiment shown in FIG. 13 may be provided in parallel. For example, N magnetic flux sensors 1 according to the embodiment of FIG. 3 and N magnetic flux sensors 1 according to the embodiment of FIG. 13 may be used together. Furthermore, a plurality of sets of the embodiment shown in FIG. 3 may be provided in parallel;
The same applies to the embodiments shown in FIG. 13 and FIG. in this case.

While it is no longer necessary to consider the limitation on the number of magnetic flux sensors l due to the operating frequency of the multiplexer 4, the advantages of each embodiment are not lost.

[Effects of the Invention] According to the present invention as described above, in a multi-channel SQUID magnetometer, a plurality of SQUID flux sensors are always in operation.

Since we use a multiplexer to reduce the number of output lines,
There is no problem of response to input magnetic flux, and it is possible to reduce the consumption of SQUID cryogen such as liquid helium.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of the present invention. FIG. 2 is a diagram illustrating the operation of the present invention. FIG. 3 is a configuration diagram of one embodiment. FIG. 4 is a configuration diagram of a magnetic flux sensor. FIG. 5 is an explanatory diagram of the operation. FIG. 6 is a multiplexer configuration diagram. FIG. 7 is another configuration diagram of the multiplexer. FIG. 8 shows a time sequence. FIG. 9 is a configuration diagram of another embodiment. FIG. 10 is a diagram showing a time sequence. FIG. 11 is a configuration diagram of still another embodiment. FIG. 12 is a diagram showing a time sequence. FIG. 13 is a configuration diagram of still another embodiment. FIG. 14 is a configuration diagram of a magnetic flux sensor. Figure 15 is an explanatory diagram of magnetic flux sensor separation, in which 1: magnetic flux sensor, 2: oscillator, 3: control circuit, 4
．． 5: Multiplexer, 6: Signal processing circuit. 11: D/A converter, 12: Phase shifter, 13
: Preamplifier, 14; Positive/negative discrimination circuit, 15 Near-tub down counter. Patent applicant Fujitsu Ltd. Company representative patent attorney Hiroshi Mori (2 others)? (J Komano V 12″9 wafu \su (Manzuzu Figure 6A Ma) V Chiarekbu ShojL floor plan 1 0 OtJTPUT Multi-γRekbu conversion: Class m to n7 Rhinoceros 7B time sequence〉S Σ construction drawing Figure 8 Thai melon sequence〉Sεshow] 12A diagram

Claims (15)

[Claims] (1) In a multi-channel SQUID magnetometer that detects magnetic flux signals by arranging a plurality of magnetic flux sensors (1) made of digital SQUIDs that can obtain pulse output, bias means (1) for supplying bias current to the plurality of magnetic flux sensors (1) 2), a first conversion means (4) that converts the output of each of the plurality of magnetic flux sensors (1) into serial data, and a first conversion means (4) that is provided corresponding to each of the plurality of magnetic flux sensors (1) and converts the output of the magnetic flux signal into serial data. a signal processing means (6) that outputs the serial data and converts the serial data into parallel data;
control means (3) for supplying signals synchronized with the bias current to the signal processing means (6) and the first and second conversion means (4, 5), respectively; While each of the magnetic flux sensors (1) outputs a pulse due to the bias current, the first conversion means (4) converts the pulse into the serial data according to a signal from the control means (3). A multi-channel SQUID magnetometer featuring: (2) The plurality of magnetic flux sensors (1) and other means (2, 4)
2. The multi-channel SQUID magnetometer according to claim 1, wherein their grounds are separated between the two. (3) A transformer by magnetic field coupling is provided between the plurality of magnetic flux sensors (1) and the first converting means (4) and between the plurality of magnetic flux sensors (1) and the biasing means (2). 3. The multi-channel SQUID magnetometer according to claim 2, wherein a plurality of SQUID magnetometers are inserted, and their grounds are separated. (4) The plurality of magnetic flux sensors (1), bias means (2)
), control means (3), first and second conversion means (4, 5)
The multi-channel SQUID magnetometer according to claim 1, characterized in that a plurality of sets of the signal processing means (6) and the signal processing means (6) are provided. (5) The bias current is applied from the bias means (2) to the plurality of magnetic flux sensors (1) at the same timing, and the pulses that the individual magnetic flux sensors simultaneously output are
3. The multi-channel SQUID magnetometer according to claim 1, wherein the first conversion means (4) performs high-speed switching and converts the data into serial data within the output period. (6) From the bias means (2) to the magnetic flux sensor (1)
), a pulse is sequentially applied to each of the magnetic flux sensors (1) in chronological order, and in synchronization with the pulse, the output of the corresponding magnetic flux sensor (1) is sampled by the first conversion means (4) and converted into serial data. Claim (1) or (2)
) Multi-channel SQUID magnetometer. (7) Divide the plurality of magnetic flux sensors (1) into two groups, shift the phase of the bias current applied to each group by 90 degrees, and output pulses that are output at timings that differ by 90 degrees for each group. The multi-channel SQUID magnetometer according to claim 1, wherein the multi-channel SQUID magnetometer is converted into serial data by the first converting means (4) within a period of time. (8) The multi-channel SQUID magnetometer according to any one of claims (1) to (5), wherein the bias means (2) is an oscillator. (9) The multi-channel SQUID magnetometer according to any one of claims (1) to (5), wherein the first conversion means (4) is a multiplexer. (10) The multiplexer (4) outputs one or more high-level bits, and the second conversion means (5) uses the high-level bits as a trigger for the conversion. (9) The multichannel SQUID magnetometer described. (11) A multi-channel SQUID magnetometer according to claim 7, characterized in that said multiplexer (4) comprises a Josephson integrated circuit and operates in a superconducting state. (12) The multi-channel SQUID magnetometer according to claim 11, wherein the multiplexer (4) is a shift register made of a Josephson integrated circuit. (13) The multi-channel SQUID magnetometer according to any one of claims (1) to (5), wherein each of the plurality of magnetic flux sensors (1) includes a feedback circuit configured of a superconducting circuit. . (14) The superconducting feedback circuit comprises a superconducting inductance and a superconducting gate that stores magnetic flux quanta therein, and the signal processing means (6) comprises a counter (15). Multichannel SQUID magnetometer as described. (15) Each of the signal processing means (6) has a counter (1
5) and a D/A converter (11), the output of which is applied to each of the corresponding magnetic flux sensors (1) in a direction that cancels the input magnetic flux. The multichannel SQUID magnetometer described in .