SQUID detection circuit, sensor, and multi-channel magnetic measurement system

Abstract

The application provides a SQUID detection circuit, a sensor and a multi-channel magnetic measurement system, comprising: a reference resistor and X SQUID detection modules, each SQUID detection module comprising a feedback coil and a SQUID device; the first end of each SQUID device is connected to a common end and is led out, and the second end of each SQUID device is used as a leading-out end; each feedback coil is connected in series, the first end of the feedback coil series structure is connected to the common end, and the second end is used as a leading-out end; one end of the reference resistor is connected to the common end, and the other end is used as a leading-out end. The application has the advantages of small number of leading-out wires, small loss of cryogenic liquid, effective elimination of voltage offset caused by leading-out wire resistance, avoidance of working point drift, reuse of readout circuit, reduction of electronic circuit volume, data acquisition channel number and cost, simple room temperature circuit, low hardware cost, high operation efficiency, no need to move the probe, high accuracy and simple operation.

Description

Technical Field

[0001] This invention relates to the field of magnetic signal detection, and in particular to a SQUID detection circuit, sensor, and multi-channel magnetic measurement system. Background Technology

[0002] Superconducting quantum interference devices (SQUIDs) use sensors that are currently the most sensitive magnetic sensors known. They are widely used in the detection of extremely weak magnetic signals and the study of extremely weak magnetic field anomalies in magnetocardiography, magnetoencephalography, extremely low-field nuclear magnetic resonance imaging, and geophysical magnetic detection.

[0003] like Figure 1 As shown, the existing single-channel SQUID sensor technology solution is as follows: A four-pin SQUID chip 1 is immersed in a cryogenic container 2 containing cryogenic liquid. The SQUID terminals are led out to room temperature via four leads (w1, w2, w3, and w4) and connected to a room temperature readout circuit 3. The room temperature readout circuit 3 injects a feedback current If into the feedback coil L_f. The other ends of the feedback coil L_f and the SQUID device SQ_1 are led out via leads and grounded to GND in the room temperature readout circuit 3. The room temperature readout circuit 3 injects a bias current Ib into the SQUID device SQ_1, while simultaneously reading and amplifying the voltage on the SQUID device SQ_1. Zero-point correction is performed on the amplified voltage, dynamically maintaining the zero-point corrected voltage signal at zero, so that the magnetic flux induced by the SQUID device SQ_1 is proportional to the output voltage Vo.

[0004] For a multi-channel SQUID sensor system, assuming the number of channels is X (X is a natural number greater than 1), there are X SQUID chips 1 operating in a cryogenic container 2, such as... Figure 2 As shown, each SQUID chip 1 requires four leads to connect to a room temperature readout circuit 3, achieving linear flux-to-voltage conversion. An X-channel SQUID sensor system requires 4×X leads to connect to the cryogenic container 2, resulting in significant cryogenic liquid loss and high operating costs. Lead resistance causes the SQUID operating point to change with the cryogenic liquid level, preventing long-term stable operation and leading to operating point drift issues and maintenance difficulties. Furthermore, multi-channel systems require room temperature readout circuits matching the number of channels and a corresponding number of wires, further increasing the cost of multi-channel SQUID sensor systems.

[0005] Therefore, how to achieve rapid setting of the working point, avoid working point drift, and reduce the difficulty and cost of operating and maintaining SQUID sensors has become one of the problems that urgently need to be solved by those skilled in the art.

[0006] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a SQUID detection circuit, sensor and multi-channel magnetic measurement system to solve the problems of high cost, operating point drift and high difficulty in operation and maintenance of existing multi-channel SQUID sensor systems.

[0008] To achieve the above and other related objectives, the present invention provides a SQUID detection circuit, the SQUID detection circuit comprising:

[0009] A reference resistor and X SQUID detection modules, where X is a natural number greater than 1; each SQUID detection module includes a feedback coil and a SQUID device;

[0010] The first end of each SQUID device is connected to the common terminal and led out, and the second end of each SQUID device serves as a lead-out terminal; the feedback coils are connected in series in sequence, and the first end of the series connection structure of the feedback coils is connected to the common terminal, and the second end serves as a lead-out terminal; one end of the reference resistor is connected to the common terminal, and the other end serves as a lead-out terminal.

[0011] Optionally, the SQUID detection circuit further includes X flux conversion modules, each flux conversion module being coupled one-to-one with the SQUID device in each SQUID detection module.

[0012] To achieve the above and other related objectives, the present invention provides a SQUID sensor, the SQUID sensor comprising at least:

[0013] Operating point setting circuit, control circuit, feedback resistor, and the aforementioned SQUID detection circuit;

[0014] The SQUID detection circuit sequentially performs multi-channel detection on the magnetic field to be tested.

[0015] The operating point setting circuit sequentially provides bias current and reference current to the X SQUID detection channels in the SQUID detection circuit, and sets the operating point.

[0016] The control circuit is connected to the output terminal of the operating point setting circuit and generates an output voltage based on the output signal of the operating point setting circuit.

[0017] The feedback resistor provides feedback current to each feedback coil in the SQUID detection circuit. One end of the feedback resistor is connected to the output terminal of the control circuit, and the other end is connected to the second terminal of the series structure of the feedback coil.

[0018] Optionally, the operating point setting circuit includes a bias amplification module, a zero-point setting module, and a gating control module;

[0019] The bias amplification module provides bias current to each SQUID device, provides reference current to the reference resistor, and amplifies and outputs the reference voltage difference between each SQUID device and the reference resistor.

[0020] The zero-point setting module is connected to the output terminal of the bias amplifier module, and amplifies the difference between the output signal of the bias amplifier module and the corresponding DC voltage to set the zero point.

[0021] The gating control module receives the channel selection signal, generates a gating signal based on the channel selection signal, and connects the output terminal to the bias amplification module and the zero-point setting module to select the voltage, reference voltage and DC voltage on the SQUID device corresponding to the same detection channel.

[0022] Alternatively, the bias amplification module includes a first differential amplifier, X bias voltage sources, a first set of bias resistors, a second set of bias resistors, a first set of switches, and a second set of switches, wherein the first set of bias resistors and the second set of bias resistors each include X bias resistors, and the first set of switches and the second set of switches each include X switches.

[0023] In the first group of bias resistors, the first terminal of each bias resistor is connected to the second terminal of each SQUID device, and the second terminal is connected to the first terminal of each bias voltage source. In the second group of bias resistors, the second terminal of each bias resistor is connected to the first terminal of each bias voltage source. The second terminal of each bias voltage source is grounded.

[0024] The first input terminal of the first differential amplifier is connected to the first terminal of each bias resistor in the first group of bias resistors via a first group of switches, and the first input terminal is connected to the first terminal of each bias resistor in the second group of bias resistors via a second group of switches.

[0025] The second input terminal of the first differential amplifier is also connected to the reference resistor.

[0026] Alternatively, the bias resistors in the first set of bias resistors corresponding to the same detection channel have the same resistance value as those in the second set of bias resistors.

[0027] Alternatively, the first input terminal of the first differential amplifier is a non-inverting input terminal, and the second input terminal is an inverting input terminal.

[0028] Alternatively, the zero-point setting module includes a second differential amplifier, X DC voltage sources, and X switches;

[0029] The first input terminal of the second differential amplifier is connected to the first terminal of each DC voltage source via a switch, and the second input terminal is connected to the output terminal of the bias amplifier module; the second terminal of each DC voltage source is grounded.

[0030] Alternatively, the first input terminal of the second differential amplifier is an inverting input terminal, and the second input terminal is a non-inverting input terminal.

[0031] Optionally, the control circuit is a proportional-integral-differential circuit.

[0032] To achieve the above and other related objectives, the present invention provides a multi-channel magnetic measurement system, the multi-channel magnetic measurement system comprising:

[0033] The cryogenic container and M of the above-mentioned SQUID sensors, where M is a natural number greater than or equal to 1;

[0034] The cryogenic container provides a low-temperature operating environment for each SQUID detection module in the SQUID sensor.

[0035] Optionally, when M is greater than or equal to 2 and the magnetic field is measured based on each SQUID detection module, each SQUID detection module is arranged in a two-dimensional array.

[0036] Optionally, when M is greater than or equal to 2 and the magnetic field is measured based on the magnetic flux transformation module coupled one-to-one with each SQUID detection module, the magnetic flux transformation modules are arranged in a two-dimensional array.

[0037] Optionally, the multi-channel magnetic measurement system further includes an M-channel data acquisition unit, which is connected to the output of each SQUID sensor.

[0038] As described above, the SQUID detection circuit, sensor, and multi-channel magnetic measurement system of the present invention have the following beneficial effects:

[0039] 1. The SQUID detection circuit of the present invention only requires X+3 signal lines to realize the signal output of X SQUID channels, with fewer leads and less loss of cryogenic liquid.

[0040] 2. The readout circuit of the SQUID sensor and multi-channel magnetic measurement system of the present invention adopts differential readout, and through the additional reference resistor circuit, it can effectively deduct the voltage offset caused by the change of lead resistance, eliminate the voltage offset caused by the lead resistance, and avoid the operating point drift caused by the change of lead resistance.

[0041] 3. The readout circuit of the SQUID sensor and multi-channel magnetic measurement system of the present invention is multiplexed, which greatly reduces the size of electronic circuits, the number of data acquisition channels and costs.

[0042] 4. The SQUID sensor and multi-channel magnetic measurement system of the present invention have a simple room temperature circuit, low hardware cost, and high operating efficiency.

[0043] 5. The multi-channel magnetic measurement system of the present invention (including at least two SQUID sensors of the present invention) uses electrical scanning to detect the magnetic field at different measurement points without moving the probe, and is highly accurate and easy to operate. Attached Figure Description

[0044] Figure 1 The diagram shows the structure of a single-channel SQUID sensor.

[0045] Figure 2 The diagram shows the structure of a multi-channel SQUID sensor.

[0046] Figure 3 The diagram shown is a structural schematic of the SQUID detection circuit of the present invention.

[0047] Figure 4 The diagram shown is another structural schematic of the SQUID detection circuit of the present invention.

[0048] Figure 5 The diagram shows one implementation of the multi-channel magnetic measurement system of the present invention and a structural schematic of the SQUID sensor.

[0049] Figure 6 The diagram shown is a structural schematic of the operating point setting circuit of the present invention.

[0050] Figure 7 The diagram shown illustrates another implementation of the multi-channel magnetic measurement system of the present invention.

[0051] Figure 8 The diagram shown is a structural schematic of the 4-channel SQUID sensor of the present invention.

[0052] Figure 9 The diagram shows the layout of the 36-channel SQUID detection module of this invention.

[0053] Figure 10 The diagram shown is a structural schematic of the 4-channel operating point setting circuit of the present invention.

[0054] Figure 11 The diagram shows the principle of the multi-channel magnetic measurement system of the present invention reading out the first group of 9 SQUID signals.

[0055] Figure 12The diagram shows the principle of the multi-channel magnetic measurement system of the present invention reading out the second group of 9 SQUID signals.

[0056] Figure 13 The diagram shows the principle of the multi-channel magnetic measurement system of the present invention reading out the third group of 9 SQUID signals.

[0057] Figure 14 The diagram shows the principle of the multi-channel magnetic measurement system of the present invention reading out the fourth group of 9 SQUID signals.

[0058] Figure 15 The diagram shows the structure of a multi-channel magnetic measurement system consisting of 36 single-channel SQUID chips.

[0059] Figure 16 The diagram shows the readout circuit of a multi-channel magnetic measurement system consisting of 36 single-channel SQUID chips.

[0060] Component designation explanation

[0061] 1 SQUID chip

[0062] 2 cryogenic containers

[0063] 3. Room temperature readout circuit

[0064] 4 SQUID detection circuit

[0065] 411, 412, 413, 414~41X First, Second, Third~Xth SQUID Detection Modules

[0066] 421, 422~42X First and Second Magnetic Flux Transformation Modules

[0067] 5 SQUID sensors

[0068] 51 Operating point setting circuit

[0069] 511 Bias Amplifier Module

[0070] 511a Bias Voltage Source

[0071] 511b First set of bias resistors

[0072] 511c Second set of bias resistors

[0073] 511d First group of switches

[0074] 511e Second Group Switch

[0075] 512 Zero Point Setting Module

[0076] 512a DC voltage source

[0077] 512b Third Group Switch

[0078] 513 Gating Control Module

[0079] 52 Control Circuit

[0080] 6. Data Acquisition Unit

[0081] 7 Data Analyzer

[0082] 8. Multiplexed readout circuit

[0083] 9. Readout Circuit

[0084] 91 Bias Amplifier Circuit

[0085] 92 Zero-point setting circuit

[0086] 93 Controller Detailed Implementation

[0087] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0088] Please see Figures 3 to 16 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0089] Example 1

[0090] like Figure 3 As shown, this embodiment provides a SQUID detection circuit 4, which includes:

[0091] The reference resistor Rr and X SQUID detection modules (referred to as the first SQUID detection module 411, the second SQUID detection module 412... the Xth SQUID detection module 41X, respectively), where X is a natural number greater than 1; each SQUID detection module includes a feedback coil (Lf1, Lf2... LfX) and SQUID devices (SQ1, SQ2... SQX).

[0092] Specifically, the first terminal of each SQUID device is connected to a common terminal and led out (through lead w00) to the reference ground of the room temperature circuit. The second terminal of each SQUID device serves as a lead-out terminal (led out through leads w11, w21...wX1). The feedback coils are connected in series, with one end of the series connection connected to the common terminal and the other end serving as a lead-out terminal (led out through lead w02). One end of the reference resistor Rr is connected to the common terminal, and the other end serves as a lead-out terminal (led out through lead w01). All leads of the SQUID detection circuit 4 are led out to the room temperature circuit.

[0093] It should be noted that the first and second terminals of the feedback coil, the SQUID device, and the reference resistor have no polarity definition and can be used interchangeably. Furthermore, the order in which the feedback coils are connected in series is not required; the order can be arbitrarily interchanged, as long as a series circuit with only two terminals is ultimately formed, with one terminal connected to the common terminal and the other terminal led out.

[0094] Specifically, in this embodiment, the SQUID devices in the SQUID detection circuit 4 are used to directly sense the target magnetic field; that is, the SQUID devices (SQUID rings) in each SQUID detection module are directly aligned with the target magnetic field. The SQUID devices couple the magnetic field to generate magnetic flux, which is converted into voltage. The voltage detection completes the measurement of the target magnetic field. At this time, each SQUID detection module can be placed in the designated position according to the requirements of the measurement target. Each SQUID detection module can be implemented in the form of a chip, which will not be described in detail here.

[0095] like Figure 2 and Figure 3 As shown, X SQUID detection modules are also set up. Figure 2 The original system required 4×X cryogenic leads to achieve electrical connections between the device in cryogenic and room temperature environments. However, the SQUID detection circuit 4 of this invention only requires X+3 cryogenic leads, reducing the number of leads. Furthermore, the larger X is, the more leads are saved; for example, X=10. Figure 2 The traditional solution requires 40 leads, while the solution of this invention only requires 13 leads; this can greatly reduce the loss of cryogenic liquid (cryo-cryo liquid is expensive) and the impact of lead resistance on the operating point, thereby reducing operating costs and improving the stability and operating efficiency of the SQUID sensor during long-term operation.

[0096] Example 2

[0097] like Figure 4As shown, this embodiment provides a SQUID detection circuit 4, which differs from the first embodiment in that the SQUID detection circuit 4 further includes X flux transformation modules (referred to as the first flux transformation module 421, the second flux transformation module 422... the Xth flux transformation module 42X, respectively), and each flux transformation module is coupled to the SQUID device in each SQUID detection module in a one-to-one correspondence.

[0098] It should be noted that SQUID is a magnetic flux sensor, where magnetic flux equals magnetic field strength multiplied by area. However, most applications focus more on the magnetic field. When the SQUID detection module is implemented in chip form, due to physical limitations, the ring aperture of the SQUID device is relatively small, resulting in a lower magnetic field resolution for the same magnetic flux resolution. Therefore, in practical magnetic field measurement applications, it can be used in conjunction with a magnetic flux conversion module to achieve indirect measurement.

[0099] Specifically, as an example, each flux conversion module includes a pickup coil 42a and an input coil 42b. One end of the flux conversion module senses the target magnetic field, and the other end is coupled to the SQUID device in the SQUID detection module. The flux conversion module is a pure superconducting ring; the amount of magnetic flux it senses corresponds to the superconducting current generated within the ring. The superconducting ring is wound with superconducting wire, and its area can be set according to the target being detected; the larger the area, the higher the magnetic field sensitivity. The SQUID device in the SQUID detection module only needs to detect the current within the flux conversion module (superconducting ring). The combination of the two can form a magnetic field detection system with various sensitivities.

[0100] Specifically, when using an indirect measurement method, each flux conversion module is set at a specified position according to the requirements of the measurement target, while the position of each SQUID detection module is not limited.

[0101] It should be noted that the other structures of the SQUID detection circuit 4 in this embodiment are the same as those in Embodiment 1, and will not be described in detail here.

[0102] Example 3

[0103] like Figure 5 As shown, this embodiment provides a SQUID sensor 5, which includes:

[0104] Operating point setting circuit 51, control circuit 52, feedback resistor Rf and SQUID detection circuit 4.

[0105] like Figure 5 As shown, the SQUID detection circuit 4 sequentially performs multi-channel detection on the magnetic field to be tested.

[0106] Specifically, the structure of the SQUID detection circuit 4 is described in Embodiment 1 or Embodiment 2. Figure 5(The following description uses the SQUID detection circuit 4 of Embodiment 1 as an example; details will not be elaborated here.) Each SQUID detection module in the SQUID detection circuit 4 corresponds to a detection channel.

[0107] like Figure 5 As shown, the operating point setting circuit 51 sequentially provides bias current and reference current to the X SQUID detection channels in the SQUID detection circuit 4, and sets the operating point. In this embodiment, the operating point setting circuit 51 includes a bias amplification module 511, a zero-point setting module 512, and a gating control module 513.

[0108] Specifically, the bias amplification module 511 provides bias currents (Ib1, Ib2…IbX) to each SQUID device, provides a reference current Ir1 to the reference resistor Rf, and amplifies and outputs the reference voltage difference between each SQUID device and the reference resistor Rf. For example... Figure 6As shown in the figure, as an example, the bias amplification module 511 includes a first differential amplifier A1, a set of bias voltage sources 511a, a first set of bias resistors 511b, a second set of bias resistors 511c, a first set of switches 511d, and a second set of switches 511e. The set of bias voltage sources 511a includes X bias voltage sources, the first set of bias resistors 511b and the second set of bias resistors 511c each include X bias resistors, and the first set of switches 511d and the second set of switches 511e each include X switches. The first terminal of each bias resistor (Rb1…RbX) in the first group of bias resistors 511b is connected to the second terminal of each SQUID device, and the second terminal is connected to the first terminal of each bias voltage source (Vb1…VbX). The second terminal of each bias voltage source is grounded to GND. Thus, each SQUID device, together with its corresponding bias resistor (the resistor in the first group of bias resistors) and bias voltage source, forms an (X-path) bias loop, generating a bias current that is applied to the corresponding SQUID device. One terminal of each switch (S1-2…SX-2) in the first group of switches 511d is connected to the first terminal of each bias resistor (Rb1…RbX) in the first group of bias resistors, and the other terminal is connected to the first input terminal of the first differential amplifier A1. When one of the switches is turned on, the voltage Vs on the corresponding SQUID device is read out (i.e., the corresponding detection channel is selected). The second terminals of each bias resistor (Ra1…RaX) in the second set of bias resistors 511c are connected to the first terminals of each bias voltage source, respectively. One terminal of each switch (S1-1…SX-1) in the second set of switches 511e is connected to the first terminal of each bias resistor (Ra1…RaX) in the second set of bias resistors, and the other terminal is connected to the second input terminal of the first differential amplifier A1 and then connected to the second terminal of the reference resistor Rr in the SQUID detection circuit 4 via a lead. When one of the switches is turned on, a reference current Ir1 is provided to the reference resistor Rr, thereby generating a corresponding reference voltage Vr on the reference resistor Rr. During readout, each SQUID device corresponds to a reference voltage. The first differential amplifier A1 amplifies and outputs the difference between the voltage Vs on the SQUID device corresponding to the selected detection channel and the reference voltage Vr.

[0109] It should be noted that in this embodiment, the bias resistors in the first set of bias resistors 511b and the second set of bias resistors 511c corresponding to the same detection channel have the same resistance value, i.e., Rb1 = Ra1…RbX = RaX. The first input terminal of the first differential amplifier A1 is the non-inverting input terminal, and the second input terminal is the inverting input terminal. In actual use, the polarities of the first and second input terminals of the first differential amplifier A1 can be interchanged, as long as the difference between the two can be obtained.

[0110] Specifically, the zero-point setting module 512 is connected to the output terminal of the bias amplification module 511, amplifying and outputting the difference between the output signal of the bias amplification module 511 and the corresponding DC voltage (Vz1…VzX) to set the operating zero point. Figure 6 As shown in the example, the zero-point setting module 512 includes a second differential amplifier A2, a set of DC voltage sources 512a, and a third set of switches 512b. The DC voltage sources 512a include X DC voltage sources (Vz1…VzX), and the third set of switches 512b includes X switches (S1-3…SX-3). The first input terminal of the second differential amplifier A2 is connected to the first terminal of each DC voltage source via a switch, and the second input terminal is connected to the output terminal of the bias amplifier module 511. This amplifies the difference between the output signal of the bias amplifier module 511 and the corresponding DC voltage, resulting in Vm. The second terminal of each DC voltage source is grounded.

[0111] It should be noted that in this embodiment, the first input terminal of the second differential amplifier A2 is an inverting input terminal, and the second input terminal is a non-inverting input terminal. In actual use, the polarities of the first and second input terminals of the second differential amplifier A2 can be interchanged, as long as the difference between the two is obtained.

[0112] Specifically, the gating control module 513 receives a channel selection signal ch (including but not limited to the channel number), generates a gating signal based on the channel selection signal ch, and connects its output to the bias amplification module 511 and the zero-point setting module 512 to select the voltage Vs, reference voltage Vr, and DC voltage Vz on the SQUID device corresponding to the same detection channel. The gating signal output by the gating control module 513 is used to control the switches in the first group of switches 511d, the second group of switches 511e, and the third group of switches 512b to be turned on or off. In use, only one switch in each group of switches 511d, 511e, and 512b is turned on, while the other switches remain off, and the turned-on switch is in the same detection channel. As an example, when the channel number ch is 0, switches S1-1, S1-2, and S1-3 are closed, and the other switches are open; ... when the channel number ch is X-1, switches SX-1, SX-2, and SX-3 are closed, and the other switches are open.

[0113] like Figure 5 As shown, the control circuit 52 is connected to the output terminal of the operating point setting circuit 51, and generates an output voltage Vo based on the output signal Vm of the operating point setting circuit 51.

[0114] Specifically, the control circuit 52 generates the output voltage Vo and adjusts the voltage on each SQUID device through feedback, so that the difference (i.e., Vm) between the output signal of the bias amplifier module 511 and the corresponding DC voltage is zero. Any circuit that can achieve the above function is applicable to the control circuit 52 of the present invention; in this example, the control circuit 52 is implemented using a proportional-integral-differential circuit, and the output voltage Vo is obtained through proportional, integral, and differential operations.

[0115] like Figure 5 As shown, one end of the feedback resistor Rf is connected to the output terminal of the control circuit 52, and the other end is connected to the second end of the feedback coil series structure.

[0116] like Figure 5 and Figure 6 As shown, the operating point setting circuit 51 of this invention employs a multiplexing method to detect X SQUID signals; at any given time, only the voltage on the SQUID detection module corresponding to channel number ch is amplified and read out. The SQUID detection circuit 4, the operating point setting circuit 51, the control circuit 52, and the feedback resistor constitute a flux-locked loop. The input channel selection signal can perform a linear magnetic field-voltage conversion on the corresponding SQUID detection channel. Taking channel number ch = 0 as an example, the first channel is selected. At this time, the output signal Vm of the operating point setting circuit 51 is the signal after the output voltage of the SQUID device SQ1 is amplified and returned to zero; this signal is sent to the control circuit 52 and generates an output voltage Vo. The output voltage Vo drives X series-connected feedback coils through the feedback resistor Rf. When the feedback magnetic flux generated by the output voltage Vo on the feedback coil Lf1 cancels out the input magnetic flux induced by the SQUID device SQ1, so that the output signal Vm of the operating point setting circuit 51 remains zero, the output voltage Vm is... O The magnetic signal readout for the first channel is proportional to the magnetic flux sensed by the SQUID device SQ1. Similarly, by changing the channel number, the magnetic signals for all SQUID channels can be read out in a time-division manner; details will not be elaborated here.

[0117] Example 4

[0118] like Figure 5 As shown, this embodiment provides a multi-channel magnetic measurement system, which includes:

[0119] The system comprises a cryogenic container 2 and M SQUID sensors 5; in this embodiment, M is set to 1. The cryogenic container 2 provides a cryogenic operating environment for each SQUID detection module in the SQUID sensors 5.

[0120] Specifically, the SQUID sensor used is the SQUID sensor of Embodiment 3, and its specific structure and working principle will not be described in detail here.

[0121] Specifically, in one implementation of the present invention, the cryogenic container 2 uses cryogenic liquid refrigeration, including but not limited to liquid helium (4.2K) and liquid nitrogen (77K). In practical use, different cryogenic liquids at different temperatures can be selected according to the superconducting material used in the SQUID (for example, niobium-based SQUIDs use liquid helium, while high-temperature SQUIDs made of copper-based, iron-based, and other materials use liquid nitrogen refrigeration), which will not be elaborated here. In another implementation of the present invention, the cryogenic container 2 uses a refrigeration mechanism for cooling, and the SQUID detection module (or chip) is placed on the cold head of the refrigeration mechanism (a platform that can remove heat and maintain a low temperature) for operation.

[0122] It should be noted that any cryogenic container 2 that can provide a low-temperature working environment for each SQUID detection module is applicable to the present invention, and is not limited to this embodiment.

[0123] As another implementation of the present invention, the multi-channel magnetic measurement system further includes a data acquisition unit ( Figure 5 (Not shown in the image), the data acquisition device is connected to the output terminal of the SQUID sensor 5. In this embodiment, the data acquisition device is a 1-channel acquisition device.

[0124] The multi-channel magnetic measurement system of this invention is suitable for repeatable sensor systems, including but not limited to magnetocardiography (MCG) and magnetoencephalography (MEG), which will not be elaborated upon here. This embodiment of the multi-channel magnetic measurement system requires only X+3 signal lines to connect the SQUID detection circuit to the room temperature circuit, resulting in fewer leads and less cryogenic liquid loss. Multiplexing one room temperature readout circuit significantly reduces the size of the electronic circuitry and the number of data acquisition channels, thereby reducing costs. (It should be noted that the SQUID device operating at 4.2K is fabricated using a niobium film processing technology, which is mature and has a high chip yield. Like semiconductor chips, mass-produced SQUID chips are inexpensive; therefore, the main cost of the multi-channel SQUID sensor system is not the SQUID chip itself, but rather the room temperature electronic circuitry and data acquisition device.) Furthermore, the multi-channel magnetic measurement system in this embodiment adopts differential readout. By adding a reference resistor circuit, the voltage offset caused by the change in lead resistance is subtracted, thus eliminating the voltage offset caused by the change in lead resistance and avoiding the drift of the operating point caused by the change in lead resistance. Therefore, the sensor of the present invention can operate stably for a long time, and users can quickly set the operating point, reducing maintenance difficulty and maintenance cost.

[0125] Example 5

[0126] like Figure 7As shown, this embodiment provides a multi-channel magnetic measurement system. The difference from Embodiment 4 is that the number M of the SQUID sensors 5 is set to two or more. For example, M is set to 9 and X to 4. In actual use, the values ​​of M and X can be set as needed and are not limited to this embodiment.

[0127] like Figure 7 and Figure 8 As shown, in this example, each SQUID sensor 5 includes 4 channels. The 4-channel SQUID sensor includes 4-channel SQUID detection circuits 4 and 4-channel multiplexing readout circuits 8.

[0128] Specifically, such as Figure 8 As shown, the SQUID detection circuit 4 includes four SQUID detection modules and one reference resistor; the structure, connection relationship, and working principle of each SQUID detection circuit 4 are described in Embodiments 1, 2, and 3, and will not be repeated here. The nine SQUID sensors 5 correspond to nine SQUID detection circuits 4 (numbered a, b, c, d, e, f, g, h, and i respectively); that is, the cryogenic container 2 has a total of 36 SQUID detection modules, such as... Figure 7 As shown. As an example, when directly measuring the magnetic field based on each SQUID detection module, the SQUID detection modules in each SQUID sensor 5 are arranged in a two-dimensional array to facilitate the electrical scanning function; as another example, when indirectly measuring the magnetic field based on a flux conversion module coupled one-to-one with each SQUID detection module, the flux conversion modules are arranged in a two-dimensional array; as... Figure 9 As shown, the nine SQUID detection circuits 4 are arranged in a 3*3 array; the four SQUID detection modules (or four flux conversion modules) in each SQUID detection circuit 4 are arranged in a 2*2 array. In actual use, the arrangement of each SQUID detection module (or each flux conversion module) can be based on needs and is not limited to this embodiment.

[0129] Specifically, such as Figure 8 and Figure 10 As shown, the 4-channel multiplexed readout circuit 9 includes an operating point setting circuit, a control circuit, and a feedback resistor. The 4 SQUID detection signals are read out in a time-division manner. For the specific structure and principle, please refer to Embodiment 3, which will not be elaborated here. The 9 SQUID sensors 5 correspond to 9 4-channel multiplexed readout circuits 8 (numbered A, B, C, D, E, F, G, H, and I respectively), as... Figure 7 As shown.

[0130] like Figure 7As shown, in another implementation of the present invention, the multi-channel magnetic measurement system further includes a data acquisition unit 6, which is connected to the output terminal of each SQUID sensor. In this example, the data acquisition unit includes 9 (i.e., M) channels.

[0131] like Figure 7 As shown, as another implementation of the present invention, the multi-channel magnetic measurement system further includes a data analyzer 7, which is connected to the output of the data acquisition unit 6; as an example, the data analyzer 7 is implemented using a computer.

[0132] In this embodiment of the multi-channel magnetic measurement system, each SQUID sensor 5 selects one SQUID signal for reading, meaning all nine SQUID signals are read out simultaneously as a group, thus achieving the electrical scanning function. Specifically, as follows... Figure 11 As shown, when channel number ch = 0, the first group of 9 SQUID signals is selected (each SQUID sensor selects the corresponding channel with channel number 0 in the 4 SQUID detection channels) for acquisition and measurement. After completing the acquisition of the first group of 9-channel sensors, the data analyzer 7 changes the channel number ch = 1, as shown. Figure 12 As shown, the second group of 9 SQUID signals is selected (each SQUID sensor selects the channel with channel number 1 from the 4 SQUID detection channels) for acquisition and measurement. This process continues in the same manner. Figure 13 and 14 As shown, by sequentially selecting the third group of 9 SQUID signals and the fourth group of 9 SQUID signals, the acquisition of four groups of SQUID signals can be completed, thus completing the acquisition of 36-channel SQUID sensor signals and obtaining the magnetic field information of the space where the 36-channel SQUID device is located. This information can be used for spatial magnetic field analysis of the application system and is suitable for repeatable sensor systems, including but not limited to magnetocardiography (MCG) instruments.

[0133] It should be noted that if a SQUID device is used for direct measurement, then... Figures 11-14 The image shows the location of the SQUID device (chip). If an indirect measurement method using a flux conversion module is used, then... Figures 11-14 The diagram shows the location of each flux conversion module. The location of the SQUID devices coupled to each flux conversion module is not limited, as long as they are used in conjunction with this invention to achieve time-division multiplexing. Figures 11-14 The magnetic field at the described location can be measured.

[0134] like Figure 15As shown, if 36 single-channel SQUID sensors are used for detection, then the parallel data acquisition by these 36 single-channel SQUID sensors requires 36 SQUID chips, 36 readout circuits 9, and a 36-channel data acquisition unit 6. Each readout circuit 9 includes a bias amplifier circuit 91, a zero-point setting circuit 92, a controller 93, and a feedback resistor Rf. This scheme uses 36-channel SQUID chips, each requiring 4 signal lines to connect to the room temperature readout circuit 9, totaling 144 lines. The large number of lines results in significant losses of the cryogenic liquid. This scheme also requires 36 room temperature readout circuits 9 and a subsequent 36-channel data acquisition unit, leading to large electronic circuit size and high cost. Furthermore, single-channel SQUID chips, such as... Figure 1 and Figure 2 As shown, the DC offset voltage of the readout circuit 9 changes with the volume of the cryogenic liquid. This DC offset voltage causes a change in the operating point of the device, resulting in zero-point drift, which in turn leads to a decrease in sensor performance or even failure. Moreover, during long-term operation, the zero-point drift gradually increases due to the drop in the cryogenic liquid level, reducing the reliability of the system. The SQUID sensor system needs to pause operation multiple times to recalibrate the operating point, shortening the continuous operation time of the system, increasing the number of times the system's operating point is calibrated, and reducing the system's operating efficiency.

[0135] The multi-channel magnetic measurement system in this embodiment requires only 63 signal lines, significantly reducing the number of leads and consequently minimizing cryogenic liquid loss. Channel switching allows for magnetic field detection at different measurement points via electrical scanning, eliminating the need to move the probe (SQUID detection module or flux conversion module). Furthermore, the simultaneous reading from nine channels as a group greatly improves efficiency. The use of a four-channel multiplexed readout circuit, with nine data acquisition channels, significantly reduces the size and cost of the electronic circuitry. Differential readout technology and a reference resistor are also employed to suppress zero-point drift, enabling rapid setting of the operating point, meeting the requirements for long-term stable operation, and reducing maintenance costs.

[0136] In summary, this invention provides a SQUID detection circuit, sensor, and multi-channel magnetic measurement system, comprising: a reference resistor and X SQUID detection modules, where X is a natural number greater than 1; each SQUID detection module includes a feedback coil and a SQUID device; the first end of each SQUID device is connected to a common terminal and led out, and the second end of each SQUID device serves as a lead-out terminal; the feedback coils are connected in series, with the first end of the series-connected feedback coil structure connected to the common terminal and the second end serving as a lead-out terminal; one end of the reference resistor is connected to the common terminal, and the other end serves as a lead-out terminal. The SQUID detection circuit of this invention requires only X+3 signal lines to achieve signal output for X SQUID channels, resulting in fewer leads and less cryogenic liquid loss. The readout circuit of the SQUID sensor and multi-channel magnetic measurement system of this invention employs differential readout, and through an additional reference resistor loop, it can effectively deduct voltage offset caused by lead resistance changes, eliminate voltage offset caused by lead resistance, and avoid operating point drift caused by lead resistance changes. The readout circuit is multiplexed, greatly reducing the size of the electronic circuit, the number of data acquisition channels, and cost. The room-temperature circuit is simple, with low hardware cost and high operating efficiency. The multi-channel magnetic measurement system, including at least two SQUID sensors of this invention, uses electrical scanning to detect the magnetic field at different measurement points, eliminating the need to move the probe, resulting in high accuracy and simple operation. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0137] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A SQUID detection circuit, characterized by, The SQUID detection circuit includes: One reference resistor and X SQUID detection modules, where X is a natural number greater than 1; Each SQUID detection module includes a feedback coil and a SQUID device; wherein, the first end of each SQUID device is connected to a common terminal and led out, and the second end of each SQUID device serves as a lead-out terminal; the feedback coils are connected in series in sequence, and the first end of the series connection structure of the feedback coils is connected to the common terminal, and the second end serves as a lead-out terminal; The first end of the reference resistor is connected to the common terminal, and the second end is used as a lead-out terminal. The common terminal, the second terminal of each SQUID device, the second terminal of the feedback coil series structure, and the second terminal of the reference resistor are led out through X+3 leads.

2. The SQUID detection circuit of claim 1, wherein: The SQUID detection circuit also includes X flux conversion modules, each flux conversion module being coupled to a corresponding SQUID device in each SQUID detection module.

3. A SQUID sensor, characterized in that The SQUID sensor includes at least: Operating point setting circuit, control circuit, feedback resistor, and SQUID detection circuit as described in claim 1 or 2; The SQUID detection circuit sequentially performs multi-channel detection on the magnetic field to be tested. The operating point setting circuit provides bias current and reference current to the X SQUID detection channels in the SQUID detection circuit in a time-division multiplexing manner, and sets the operating point accordingly. The control circuit is connected to the output terminal of the operating point setting circuit and generates an output voltage based on the output signal of the operating point setting circuit. The feedback resistor provides feedback current to each feedback coil in the SQUID detection circuit. One end of the feedback resistor is connected to the output terminal of the control circuit, and the other end is connected to the second terminal of the series structure of the feedback coil.

4. The SQUID sensor according to claim 3, characterized in that: The operating point setting circuit includes a bias amplification module, a zero-point setting module, and a gating control module. The bias amplification module provides bias current to each SQUID device, provides reference current to the reference resistor, and amplifies and outputs the reference voltage difference between each SQUID device and the reference resistor. The zero-point setting module is connected to the output terminal of the bias amplifier module, and amplifies the difference between the output signal of the bias amplifier module and the corresponding DC voltage to set the zero point. The gating control module receives the channel selection signal, generates a gating signal based on the channel selection signal, and connects the output terminal to the bias amplification module and the zero-point setting module to select the voltage, reference voltage and DC voltage on the SQUID device corresponding to the same detection channel.

5. The SQUID sensor according to claim 4, characterized in that: The bias amplification module includes a first differential amplifier, X bias voltage sources, a first set of bias resistors, a second set of bias resistors, a first set of switches, and a second set of switches. The first set of bias resistors and the second set of bias resistors each include X bias resistors, and the first set of switches and the second set of switches each include X switches. In the first group of bias resistors, the first terminal of each bias resistor is connected to the second terminal of each SQUID device, and the second terminal is connected to the first terminal of each bias voltage source. In the second group of bias resistors, the second terminal of each bias resistor is connected to the first terminal of each bias voltage source. The second terminal of each bias voltage source is grounded. The first input terminal of the first differential amplifier is connected to the first terminal of each bias resistor in the first group of bias resistors via a first group of switches, and the first input terminal is connected to the first terminal of each bias resistor in the second group of bias resistors via a second group of switches. The second input terminal of the first differential amplifier is also connected to the reference resistor.

6. The SQUID sensor according to claim 5, characterized in that: The bias resistors in the first set of bias resistors corresponding to the same detection channel have the same resistance value as those in the second set of bias resistors.

7. The SQUID sensor according to claim 5 or 6, characterized in that: The first input terminal of the first differential amplifier is the non-inverting input terminal, and the second input terminal is the inverting input terminal.

8. The SQUID sensor according to claim 4, characterized in that: The zero-point setting module includes a second differential amplifier, X DC voltage sources, and X switches; The first input terminal of the second differential amplifier is connected to the first terminal of each DC voltage source via a switch, and the second input terminal is connected to the output terminal of the bias amplifier module; the second terminal of each DC voltage source is grounded.

9. The SQUID sensor according to claim 8, characterized in that: The first input terminal of the second differential amplifier is the inverting input terminal, and the second input terminal is the non-inverting input terminal.

10. The SQUID sensor according to claim 3, characterized in that: The control circuit is a proportional-integral-differential circuit.

11. A multi-channel magnetic measurement system, characterized in that, The multi-channel magnetic measurement system includes: The cryogenic container and M SQUID sensors as described in any one of claims 3-10, where M is a natural number greater than or equal to 1; The cryogenic container provides a low-temperature operating environment for each SQUID detection module in the SQUID sensor.

12. The multi-channel magnetic measurement system according to claim 11, characterized in that: When M is greater than or equal to 2, and the magnetic field is measured based on each SQUID detection module, each SQUID detection module is arranged in a two-dimensional array.

13. The multi-channel magnetic measurement system according to claim 11, characterized in that: When M is greater than or equal to 2, and the magnetic field is measured based on the magnetic flux transformation module coupled to each SQUID detection module, the magnetic flux transformation modules are arranged in a two-dimensional array.

14. The multi-channel magnetic measurement system according to claim 11, characterized in that: The multi-channel magnetic measurement system also includes an M-channel data acquisition unit, which is connected to the output of each SQUID sensor.

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