CN101923153B - Calibration method for multichannel SQUID (Superconducting Quantum Interference Device) biological magnetic system - Google Patents
Calibration method for multichannel SQUID (Superconducting Quantum Interference Device) biological magnetic system Download PDFInfo
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- CN101923153B CN101923153B CN 201010212981 CN201010212981A CN101923153B CN 101923153 B CN101923153 B CN 101923153B CN 201010212981 CN201010212981 CN 201010212981 CN 201010212981 A CN201010212981 A CN 201010212981A CN 101923153 B CN101923153 B CN 101923153B
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Abstract
The invention discloses a calibration method for a multichannel SQUID (Superconducting Quantum Interference Device) biological magnetic system, which is a calibration method in which room temperature and low temperature are united. The equivalent error area of a gradiometer is determined by room temperature calibration, and the voltage coefficient of a system magnetic field is calibrated by using the uniform magnetic field generated by a Helmholtz coil, corresponding voltage signal output by the system and measured error area at low temperature. The invention comprises the following steps of: (1) calibrating room temperature for equivalent error area of the gradiometer; (2) installing an SQUID biological magnetic system; and (3) calibrating low temperature by the Helmholtz coil. The invention is characterized by calibrating the system by means of the consistency of the room temperature and low temperature equivalent error areas and has the advantages of avoidance of spatial positioning precision and calculation caused by the single low temperature coil, simple operation, simultaneous calibration of multichannel and good consistency.
Description
Technical field
The present invention relates to the scaling method of the biological magnetic system of a kind of hyperchannel SQUID.
Background technology
(Superconducting Quantum Interference Device is present the sensitiveest known magnetic flux transducer SQUID) to superconducting quantum interference device, and the magnetic field sensitivity of typical low-temperature superconducting SQUID is 3-5fT/sqrt (Hz).An important applied field as SQUID proves through clinical research, and biological magnetic system has unique application potential [V.Pizzela et al, Supercond.Sci.Technol.14 (2001) R79-R114] at aspects such as medical diagnosis on disease, functional studies.
SQUID has realized the conversion of magnetic flux to voltage, and biological magnetic system has recorded human life activity's magnetic information with the form of voltage.Because the otherness between SQUID device, detecting coil and the supporting electronic system, there is certain deviation in each passage magnetic flux of system to a certain extent to the transmission coefficient of voltage.For signal being carried out aftertreatments such as imaging, location, need demarcate multi-channel system.The demarcation of multi-channel system is in order to draw magnetic field to the transmission coefficient of voltage, and according to the field signal of the voltage signal inverting reality of measuring, the magnetic field here is that the magnetic flux equivalence of measuring is obtained to receiving coil.
At present, system calibrating is mainly based on cryogenic system, and adopting maximum is small coil and big coil method [P.H.Ornelas et al, Supercond.Sci.Technol.16 (2003) 427-431].The small coil method can only be demarcated one by one to each passage, seeks a certain channel voltage output maximal value by the position of mobile small coil and locatees, and the magnetic flux at compute gradient meter place and record output voltage are realized demarcating on this basis.The small coil standardization implements simple relatively, but it is subjected to spacial influence big, needs accurately location and calculating, and can only demarcate one by one, and efficient is low.The diameter of small coil is increased, usually to two of gradiometer coil diameter more than the order of magnitude, demarcate with this type of coil and to be called big coil method [P.C.Ribeiro et al, IEEE Trans.Biomed.Eng.35 (1988) 551-560].Big coil is because its size is big, and planar central zone perpendicular to axial direction can be approximately uniform magnetic field, can demarcate simultaneously a plurality of passages thus.Big coil standardization is subjected to spacial influence less relatively, demarcates the efficient height, high conformity, but its size is big, is difficult for installing and operation.
Above scaling method respectively has excellent lack, and seeks high-level efficiency, easy-operating scaling method has great importance.
Summary of the invention
The object of the present invention is to provide the scaling method of the biological magnetic system of a kind of hyperchannel SQUID, this method is characterised in that it is based on room temperature and low temperature two cover systems, at first, determine the equivalent uneven area of gradiometer by room temperature calibration, based on cryogenic system, adopt the Helmholtz coil to produce uniform magnetic field, realize demarcating by calculating magnetic flux and measurement voltage signal.
The step of room temperature low temperature combined calibrating method of the present invention is:
(1) gradiometer equivalent error area room temperature calibration
Select the required gradiometer of biological magnetic system, as the uniform magnetic field source, because the existence of gradiometer area of error can produce induction electromotive force in uniform magnetic field, utilize lock-in amplifier record gradiometer induction electromotive force with solenoid, calculate the equivalent error area.The gradiometer induction electromotive force can be expressed as
ε＝ω·μ
0nI·ΔS
Wherein ω feeds power frequency in the solenoid, μ
0Be the magnetic permeability in the vacuum, n is the solenoidal number of turn of unit length, and I is the electric current in the solenoid, and Δ S is gradiometer equivalent error area.
Feed the electric current of a certain frequencies omega of solenoid, the voltage signal ε of record input current I and output, many groups are carried out linear fit, calculate equivalent error area Δ S.
(2) the biological magnetic system of SQUID is installed
The SQUID system comprises no magnetic Dewar, gradiometer, SQUID sensor, sensing circuit, control enclosure, adapter, data collecting card and computing machine.Gradiometer and SQUID input coil are formed superconducting transmission line, by the mutual inductance between input coil and the SQUID external flux transfer in SQUID, SQUID sensor and gradient coil work in liquid helium temperature 4.2K.By control enclosure and sensing circuit, realize the adjusting of SQUID parameter and the linearity output of magnetic flux voltage conversion.Adapter, data collecting card and computing machine have been formed collection and the processing of system data.
(3) Helmholtz coil low temperature is demarcated
Utilize the Helmholtz coil as the uniform magnetic field source, the gradiometer in system's Dewar is placed the uniform magnetic field zone of hub of a spool part.Feed the current signal of certain frequency in the Helmholtz coil, system log (SYSLOG) corresponding frequencies voltage of signals output V
S
Wherein σ is the magnetic field voltage transmission coefficient, and BH is the Helmholtz uniform magnetic field, and Δ S is gradiometer equivalent error area, and S is the receiving coil area.Can get the magnetic field voltage transmission coefficient thus
In (1) and (2), the gradiometer coil encapsulates with paraffin, guarantees the consistance of room temperature and cryogenic conditions lower coil.In the SQUID system installation process, gradiometer is numbered the output voltage of corresponding corresponding SQUID, the unified demarcation.
This method is compared with prior art, has adopted room temperature gradiometer calibration technique, carries out low temperature on this basis and demarcates.The Helmholtz calibration coil is of moderate size, and is less demanding to coil location, and operation and calculating are simple, can once demarcate total system.
In sum, the invention discloses a kind of calibration method for multichannel SQUID (Superconducting Quantum Interference Device) biological magnetic system, is a kind of room temperature and low temperature scaling method linked together.Determine the equivalent error area of gradiometer to use the Helmholtz coil to produce uniform magnetic field at low temperatures by room temperature calibration, utilize the corresponding voltage signal of system's output and the area of error of measurement, carry out the demarcation of system magnetic field voltage coefficient.The present invention includes following steps: (1) gradiometer equivalent error area room temperature calibration; (2) the biological magnetic system of SQUID is installed; (3) Helmholtz coil low temperature is demarcated.The characteristics of this method are to utilize the consistance of room temperature and low temperature equivalent error area to carry out the demarcation of system, and its advantage is to have avoided single cryogen to demarcate spatial positioning accuracy and the computational problem of bringing, and simple to operate, hyperchannel is demarcated simultaneously, high conformity.
Description of drawings
Fig. 1 is SQUID receiving coil synoptic diagram: 1 is magnetometer; 2 is the single order gradiometer; 3 is the second order gradiometer.
Fig. 2 is the calibration experiment system schematic: 4 are signal generator; 5 is the constant pressure source driving circuit; 6 is solenoid; 7 is gradiometer; 8 is oscillograph; 9 is lock-in amplifier.
Fig. 3 is the biological magnetic system synoptic diagram of hyperchannel SQUID: 10 are no magnetic Dewar; 11 is SQUID; 12 is sensing circuit; 13 is control enclosure; 14 is adapter; 15 is data collecting card; 16 is computing machine.
Fig. 4 is the system calibrating synoptic diagram: 17 are the Helmholtz coil.
Embodiment
1, utilize solenoid 6 as the uniform magnetic field source, feed the electric current I of certain frequency ω, oscillograph 8 detects the electric current I that flows through in the solenoid, utilizes lock-in amplifier 9 to measure the induction electromotive force ε of gradiometer 7, and equivalent area of error Δ S is demarcated.
As shown in Figure 2, signal generator 4 is connected with constant pressure source driving circuit 5, and the output terminal of constant pressure source driving circuit is connected with oscillograph 8 with solenoid 6 respectively again.The position of gradiometer 7 places the axial centre position of solenoid 6, to guarantee the axial direction unanimity of gradiometer 7 and solenoid 6.The voltage signal of signal generator 4 input certain frequency ω drives the uniform magnetic field that solenoid 6 produces corresponding frequencies to constant pressure source driving circuit 5, with oscillograph 8 monitoring solenoid branch road reference resistance R
mVoltage V
mBe the reference signal of lock-in amplifier 9 with signal generator 4 output signals, adopt lock-in amplifier 9 to detect the induced voltage signal V of gradiometers 7
LIn the measuring process, under certain frequency, change the voltage of signal generator, measure one group of monitoring voltage V
mAnd phase-locked magnitude of voltage V
LUse single order gradiometer or second order gradiometer among gradiometer such as Fig. 1.Gradiometer places solenoidal axial centre position in demarcating test macro, make the axial direction of solenoid and gradiometer consistent, signal generator is connected with the constant pressure source driving circuit, the constant pressure source driving circuit is connected with oscillograph with solenoid respectively again and is connected, the voltage signal of input certain frequency ω drives solenoid and produces corresponding uniform magnetic field in the constant pressure source driving circuit; Oscillograph monitoring solenoid branch road reference resistance R
mVoltage V
mBe the reference signal of lock-in amplifier with the signal generator output signal, adopt lock-in amplifier to detect the induced voltage signal V of gradiometer
LIn the measuring process, under certain frequency, change the voltage of signal generator, measure one group of monitoring voltage V
mAnd phase-locked magnitude of voltage V
L
2, gradiometer 7 inserts the input coil interface of SQUID11, places cooled cryostat 10, works in liquid helium temperature 4.2K.Sensing circuit 12 connects the output of SQUID11, utilizes control enclosure 13 to regulate the parameter of sensing circuit 12, makes output signal maximum under the unlock state, and is benchmark intensity symmetry up and down with the zero point.Locking sensing circuit 12, SQUID11 and sensing circuit 12 have been realized the linear transformation of magnetic flux to voltage.The voltage signal interface of system's output is connected to data collecting card 15 by adapter 14, carries out data acquisition and processing (DAP) with computing machine 16.
3, the electric current of given certain frequency, general 80Hz utilizes Helmholtz coil 17 about length of side 2m as the uniform magnetic field source, and no magnetic Dewar 10 interior gradiometers 7 are placed Helmholtz coil 17 central areas, and measuring system is to the response of uniform magnetic field.The theoretical uniform magnetic field B that calculates in the Helmholtz coil 17
H, associating gradiometer receiving coil area S, the voltage V of equivalent error area Δ S and measurement
S, calibration system magnetic field is to the transmission coefficient σ of voltage.
Claims (5)
1. the scaling method of the biological magnetic system of a hyperchannel SQUID, it is characterized in that described scaling method is the scaling method that a kind of room temperature and low temperature combine, determine the equivalent error area of gradiometer by room temperature calibration, use the Helmholtz coil to produce uniform magnetic field at low temperatures, utilize the corresponding voltage signal of system's output and the area of error of measurement, carry out the demarcation of system magnetic field voltage coefficient;
Described scaling method comprises following 3 steps: (1) gradiometer equivalent error area room temperature calibration; (2) the biological magnetic system of SQUID is installed; (3) Helmholtz coil low temperature is demarcated;
Wherein, in step 1, select the required gradiometer of biological magnetic system, as the uniform magnetic field source, in uniform magnetic field, produce induction electromotive force with solenoid, utilize lock-in amplifier record gradiometer induction electromotive force, calculate the equivalent error area; The gradiometer induction electromotive force is
ε＝ω·μ
0nI·ΔS
Wherein feed power frequency in the ω solenoid, μ
0Be the magnetic permeability in the vacuum, n is the solenoidal number of turn of unit length, and I is the electric current in the solenoid, and Δ S is gradiometer equivalent error area;
Feed the electric current of a certain frequencies omega of solenoid, the voltage signal ε of record input current I and output, many groups are carried out linear fit, calculate equivalent error area Δ S;
In step 2, the biological magnetic system of hyperchannel SQUID comprises no magnetic cooled cryostat, gradiometer, SQUID sensor, sensing circuit, control enclosure, adapter, data collecting card and computing machine; Gradiometer and SQUID input coil are formed superconducting transmission line, by the mutual inductance between input coil and the SQUID external flux transfer in SQUID, SQUID sensor and gradiometer coil working are under liquid helium temperature; By control enclosure and sensing circuit, realize the adjusting of SQUID parameter and the linearity output of magnetic flux voltage conversion; Adapter, data collecting card and computing machine have been formed collection and the processing of system data;
In step 3, utilize the Helmholtz coil as the uniform magnetic field source, gradiometer in the no magnetic cooled cryostat in the biological magnetic system of step 2 hyperchannel SQUID is placed the uniform magnetic field zone of hub of a spool part, in the Helmholtz coil, feed the current signal of certain frequency, system log (SYSLOG) corresponding frequencies voltage of signals output V
s
Wherein σ is the magnetic field voltage transmission coefficient, B
HBe Helmholtz uniform magnetic field field intensity, Δ S is gradiometer equivalent error area, and S is the receiving coil area; Can get the magnetic field voltage transmission coefficient thus
Gradiometer inserts the input coil interface of SQUID in the biological magnetic system of the SQUID of hyperchannel described in the step 2, place the no magnetic cooled cryostat that works under the liquid helium temperature, sensing circuit connects the output of SQUID, utilize control enclosure to regulate the parameter of sensing circuit, make output signal maximum under the unlock state, and be benchmark intensity symmetry up and down with the zero point, the locking sensing circuit makes SQUID and sensing circuit realize the linear transformation of magnetic flux to voltage; The voltage signal interface of system's output is connected to data collecting card by adapter, carries out data acquisition and processing (DAP) with computing machine.
2. by the described scaling method of claim 1, it is characterized in that utilizing lock-in amplifier record gradiometer induction electromotive force, equivalent area of error Δ S is demarcated.
3. by the described scaling method of claim 1, it is characterized in that the coil of gradiometer described in step 1 and the step 2 encapsulates with paraffin.
4. by the described scaling method of claim 1, the current signal that it is characterized in that the frequency described in the step 3 is 80Hz.
5. by the described scaling method of claim 1, the length of side that it is characterized in that the Helmholtz coil is 2m.
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| CN104569884B (en) * | 2013-10-18 | 2017-10-27 | 中国科学院上海微系统与信息技术研究所 | The caliberating device and method of a kind of SPUID three axis magnetometer |
| CN105842636A (en) * | 2016-03-22 | 2016-08-10 | 中国科学院上海微系统与信息技术研究所 | Room temperature calibration-based gradiometer equivalent error area correction method and system |
| CN108896946B (en) * | 2018-07-04 | 2020-05-19 | 中国原子能科学研究院 | Calibration method for calibrating area of induction coil probe |
| CN114002634A (en) * | 2021-11-15 | 2022-02-01 | 安徽工程大学 | Calibration device and method for magnetic field-voltage coefficient of multi-channel magnetocardiogram detection system |
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Effective date of registration: 20180928 Address after: Room 801, block B, 1455 Ping Cheng Road, Jiading District, Shanghai. Patentee after: Man Di medical instruments (Shanghai) Co., Ltd. Address before: 200050 No. 865, Changning Road, Shanghai, Changning District Patentee before: Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences |
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