SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements.An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance.By placing seve...SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements.An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance.By placing several magnetometers at different heights along the vertical direction,we could simultaneously obtain the synthetic gradiometers with different baselines.By using the traditional signal-to-noise ratio（SNR） as a performance index,we successfully obtain an optimal baseline for the magnetocardiography（MCG） measurement in a magnetically shielded room（MSR）.Finally,we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR.The SNR about 38 dB is obtained in the recorded MCG signal.展开更多
Fetal magnetocardiography （MCG） is a sophisticated non-invasive technique for the fetal heart diagnosis. We constructed a multichannel fetal MCG system based on a novel superconducting quantum interference device （...Fetal magnetocardiography （MCG） is a sophisticated non-invasive technique for the fetal heart diagnosis. We constructed a multichannel fetal MCG system based on a novel superconducting quantum interference device （SQUID） direct readout scheme called SQUID bootstrap circuit （SBC）. The system incorporates four SBC gradiometers for the signal detection and three SBC magnetometers as the references. The fetal MCG signal at a 28-weeks’ gestation was measured. By the fetal MCG signal separation and average, the P-wave and QRS complex can be clearly identified. These results indicate that the SBC is one of the most promising techniques for the fetal MCG recordings.展开更多
This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K shows that t...This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K shows that the white noise at 200 Hz is about 1×10^-4 φ0/√Hz. The minimal magnetic gradient is measured and the results suggest that the minimal magnetic gradient is 94 pT/m. The planar gradiometer is used in non-destructive evaluation （NDE） experiments to detect the artifacts in conducting aluminium plates by performing eddy current testing in an unshielded environment. The effect of the exciting coil dimension on the NDE results is investigated. By mapping out the induced field distribution, flaws about 10mm below the plate surface can be clearly identified.展开更多
The performance of a superconducting quantum interference device（SQUID） gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the cou...The performance of a superconducting quantum interference device（SQUID） gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the coupled flux threading a magnetometer obtained by Wikswo, we studied how the gradiometer performance parameters, including the current dipole sensitivity, spatial resolution and signal-to-noise ratio（SNR）, are affected by its pick-up coil via Mat Lab simulation.Depending on the simulation results, the optimal pick-up coil design region for a certain gradiometer can be obtained.To verify the simulation results, we designed and fabricated several first-order gradiometers based on the weakly damped SQUID with different pick-up coils by applying superconducting connection. The experimental measurements were conducted on a simple current dipole in a magnetically shielding room. The measurement results are well in coincidence with the simulation ones, indicating that the simulation model is useful in specific pick-up coil design.展开更多
A dual-washer superconducting quantum interference device （SQUID） with a loop inductance of 350 pH and two on- washer integrated input coils is designed according to conventional niobium technology. In order to obta...A dual-washer superconducting quantum interference device （SQUID） with a loop inductance of 350 pH and two on- washer integrated input coils is designed according to conventional niobium technology. In order to obtain a large SQUID flux-to-voltage transfer coefficient, the junction shunt resistance is selected to be 33 Ω. A vertical SQUID gradiometer module with a baseline of 100 mm is constructed by utilizing such a SQUID and a first-order niobium wire-wound antenna. The sensitivity of this module reaches about 0.2 fT/（cm.Hz1/2） in the white noise range using a direct readout scheme, i.e., the SQUID is directly connected to an operational amplifier, in a magnetically shielded room. Some magnetocardiography （MCG） measurements with a sufficiently high signal-to-noise ratio （SNR） are demonstrated.展开更多
Considering the properties of slow change and quasi-periodicity of magnetocardiography （MCG） signal, we use an integrated technique of adaptive and low-pass filtering in dealing with two-channel MCG data measured by...Considering the properties of slow change and quasi-periodicity of magnetocardiography （MCG） signal, we use an integrated technique of adaptive and low-pass filtering in dealing with two-channel MCG data measured by high Tc SQUIDs. The adaptive filter in the time domain is based on a noise feedback normalized least-mean-square （NLMS） algorithm, and the low-pass filter with a cutoff at 100Hz in the frequeucy domain characterized by Caussian functions is combined with a notch at the power line frequency. In this way, both relevant and irrelevant noises in original MCG data are largely eliminated. The method may also be useful for other slowly varying quasi-periodical signals.展开更多
Magnetocardiography(MCG)measurement is important for investigating the cardiac biological activities.Traditionally,the extremely weak MCG signal was detected by using superconducting quantum interference devices(SQUID...Magnetocardiography(MCG)measurement is important for investigating the cardiac biological activities.Traditionally,the extremely weak MCG signal was detected by using superconducting quantum interference devices(SQUIDs).As a room-temperature magnetic-field sensor,optically pumped magnetometer(OPM)has shown to have comparable sensitivity to that of SQUIDs,which is very suitable for biomagnetic measurements.In this paper,a synthetic gradiometer was constructed by using two OPMs under spin-exchange relaxation-free(SERF)conditions within a moderate magnetically shielded room(MSR).The magnetic noise of the OPM was measured to less than 70 fT/Hz1/2.Under a baseline of 100 mm,noise cancellation of about 30 dB was achieved.MCG was successfully measured with a signal to noise ratio(SNR)of about 37 dB.The synthetic gradiometer technique was very effective to suppress the residual environmental fields,demonstrating the OPM gradiometer technique for highly cost-effective biomagnetic measurements.展开更多
金属磁微量能计(Metallic Magnetic Calorimeter,MMC)是一种具有极高能量分辨率的低温光子探测器。它通过顺磁材料磁化率在低温下随温度急剧变化的特性来实现对光子能量的精确测量。金属磁微量能计通常使用超导量子干涉器进行信号读出...金属磁微量能计(Metallic Magnetic Calorimeter,MMC)是一种具有极高能量分辨率的低温光子探测器。它通过顺磁材料磁化率在低温下随温度急剧变化的特性来实现对光子能量的精确测量。金属磁微量能计通常使用超导量子干涉器进行信号读出。研究介绍了一种用于金属磁微量能计信号读出的两级超导量子干涉器电路。初级放大器的设计采用了二阶梯度计构型,测试结果显示该设计方案有效的抑制了环境噪声的干扰。在液氦温度下,两级放大电路在磁通锁定环模式下实现了27400 V/A的跨阻增益,白噪声水平达到11.5 pA/Hz^(1/2)。展开更多
For a magnetocardiography(MCG)system inside a magnetically shielded room(MSR),the residual field should be further suppressed to obtain high-quality MCG signals.In this paper,a compensation system has been developed b...For a magnetocardiography(MCG)system inside a magnetically shielded room(MSR),the residual field should be further suppressed to obtain high-quality MCG signals.In this paper,a compensation system has been developed based on the bi-planar coil and the proportional-integral-derivative(PID)controller.The bi-planar coil,derived from the target-field theory and the Tikhonov regularization method,is utilized to generate magnetic field with high uniformity in the predefined target region.And the PID controller is introduced to provide dynamic compensation current for the coil,according to the residual field change monitored by a reference SQUID magnetometer.The measurement results show that the noise suppression ratio(NSR)can reach above 20 dB in the low-frequency range from 0.1 Hz to 50 Hz.The DC component and the fluctuation of the residual field in time-domain can be respectively suppressed to 0 p T and 4 p T,indicating that this proposed compensation method is useful for the MCG measurement.展开更多
A flip-chip-type gradiometer has been constructed with a 10 mm × 5 mm planar DC-SQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flux transformer made from a YB-CO* /YBCO/CeO2/YSZ multilayer on...A flip-chip-type gradiometer has been constructed with a 10 mm × 5 mm planar DC-SQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flux transformer made from a YB-CO* /YBCO/CeO2/YSZ multilayer on a φ50.8 mm Si wafer. The coupling coefficient between the flux transformer and the planar gradiometer is 0.18. The transformer increases effectively the resolution of the gradiometer. A magnetic field gradient resolution of 73 fT·cm-1·Hz-1/2 in the white region and 596 fT·cm-1Hz-1/2 at 1 Hz has been obtained. High quality magnetocardiogram signals have been successfully measured by using this flip-chip-type gradiometer in an unshielded environment.展开更多
基金supported by the "Strategic Priority Research Program(B)"of the Chinese Academy of Sciences(Grant No.XDB04020200)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KGCX2-EW-105)
文摘SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements.An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance.By placing several magnetometers at different heights along the vertical direction,we could simultaneously obtain the synthetic gradiometers with different baselines.By using the traditional signal-to-noise ratio（SNR） as a performance index,we successfully obtain an optimal baseline for the magnetocardiography（MCG） measurement in a magnetically shielded room（MSR）.Finally,we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR.The SNR about 38 dB is obtained in the recorded MCG signal.
基金Projects supported by the Main Direction Program of Knowledge Innovation of the Chinese Academy of Sciences(Grant No.KGCX2-EW-105)the"100 Tal-ents Project"of the Chinese Academy of Sciences and Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB04020300)
文摘Fetal magnetocardiography （MCG） is a sophisticated non-invasive technique for the fetal heart diagnosis. We constructed a multichannel fetal MCG system based on a novel superconducting quantum interference device （SQUID） direct readout scheme called SQUID bootstrap circuit （SBC）. The system incorporates four SBC gradiometers for the signal detection and three SBC magnetometers as the references. The fetal MCG signal at a 28-weeks’ gestation was measured. By the fetal MCG signal separation and average, the P-wave and QRS complex can be clearly identified. These results indicate that the SBC is one of the most promising techniques for the fetal MCG recordings.
基金Project supported by Ministry of Science and Technology of China （Grant Nos 2006CB601007 and 2002AA306412 ）, National Nature Science Foundation of China （Grant No 10221002） and Chinese Academy of Sciences and National Center for Nanoscience and Technology, China.
文摘This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K shows that the white noise at 200 Hz is about 1×10^-4 φ0/√Hz. The minimal magnetic gradient is measured and the results suggest that the minimal magnetic gradient is 94 pT/m. The planar gradiometer is used in non-destructive evaluation （NDE） experiments to detect the artifacts in conducting aluminium plates by performing eddy current testing in an unshielded environment. The effect of the exciting coil dimension on the NDE results is investigated. By mapping out the induced field distribution, flaws about 10mm below the plate surface can be clearly identified.
基金Project supported by the Key Project of Shanghai Zhangjiang National Innovation Demonstration Zone of the Special Development Fund,China(Grant No.2015-JD-C104-060)the National Natural Science Foundation of China(Grant No.61741122)
文摘The performance of a superconducting quantum interference device（SQUID） gradiometer is always determined by its pick-up coil geometry, such as baseline and radius. In this paper, based on the expressions for the coupled flux threading a magnetometer obtained by Wikswo, we studied how the gradiometer performance parameters, including the current dipole sensitivity, spatial resolution and signal-to-noise ratio（SNR）, are affected by its pick-up coil via Mat Lab simulation.Depending on the simulation results, the optimal pick-up coil design region for a certain gradiometer can be obtained.To verify the simulation results, we designed and fabricated several first-order gradiometers based on the weakly damped SQUID with different pick-up coils by applying superconducting connection. The experimental measurements were conducted on a simple current dipole in a magnetically shielding room. The measurement results are well in coincidence with the simulation ones, indicating that the simulation model is useful in specific pick-up coil design.
基金Project supported by the Main Direction Program of Knowledge Innovation of the Chinese Academy of Sciences(Grant No.KGCX2-EW-105)the "100 Talents Project" of the Chinese Academy of Sciences and Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB04020200)
文摘A dual-washer superconducting quantum interference device （SQUID） with a loop inductance of 350 pH and two on- washer integrated input coils is designed according to conventional niobium technology. In order to obtain a large SQUID flux-to-voltage transfer coefficient, the junction shunt resistance is selected to be 33 Ω. A vertical SQUID gradiometer module with a baseline of 100 mm is constructed by utilizing such a SQUID and a first-order niobium wire-wound antenna. The sensitivity of this module reaches about 0.2 fT/（cm.Hz1/2） in the white noise range using a direct readout scheme, i.e., the SQUID is directly connected to an operational amplifier, in a magnetically shielded room. Some magnetocardiography （MCG） measurements with a sufficiently high signal-to-noise ratio （SNR） are demonstrated.
文摘Considering the properties of slow change and quasi-periodicity of magnetocardiography （MCG） signal, we use an integrated technique of adaptive and low-pass filtering in dealing with two-channel MCG data measured by high Tc SQUIDs. The adaptive filter in the time domain is based on a noise feedback normalized least-mean-square （NLMS） algorithm, and the low-pass filter with a cutoff at 100Hz in the frequeucy domain characterized by Caussian functions is combined with a notch at the power line frequency. In this way, both relevant and irrelevant noises in original MCG data are largely eliminated. The method may also be useful for other slowly varying quasi-periodical signals.
基金Project supported by the National Natural Science Foundation of China(Grant No.61701486)。
文摘Magnetocardiography(MCG)measurement is important for investigating the cardiac biological activities.Traditionally,the extremely weak MCG signal was detected by using superconducting quantum interference devices(SQUIDs).As a room-temperature magnetic-field sensor,optically pumped magnetometer(OPM)has shown to have comparable sensitivity to that of SQUIDs,which is very suitable for biomagnetic measurements.In this paper,a synthetic gradiometer was constructed by using two OPMs under spin-exchange relaxation-free(SERF)conditions within a moderate magnetically shielded room(MSR).The magnetic noise of the OPM was measured to less than 70 fT/Hz1/2.Under a baseline of 100 mm,noise cancellation of about 30 dB was achieved.MCG was successfully measured with a signal to noise ratio(SNR)of about 37 dB.The synthetic gradiometer technique was very effective to suppress the residual environmental fields,demonstrating the OPM gradiometer technique for highly cost-effective biomagnetic measurements.
文摘金属磁微量能计(Metallic Magnetic Calorimeter,MMC)是一种具有极高能量分辨率的低温光子探测器。它通过顺磁材料磁化率在低温下随温度急剧变化的特性来实现对光子能量的精确测量。金属磁微量能计通常使用超导量子干涉器进行信号读出。研究介绍了一种用于金属磁微量能计信号读出的两级超导量子干涉器电路。初级放大器的设计采用了二阶梯度计构型,测试结果显示该设计方案有效的抑制了环境噪声的干扰。在液氦温度下,两级放大电路在磁通锁定环模式下实现了27400 V/A的跨阻增益,白噪声水平达到11.5 pA/Hz^(1/2)。
基金the Open Research Fund of Anhui Key Laboratory of Detection Technology and Energy Saving Devices,Anhui Polytechnic University(Grant No.JCKJ2021A03)the Introduced Talent Research Startup Funds of Anhui Polytechnic University(Grant Nos.2021YQQ006 and 2020YQQ040)the National Natural Science Foundation of China(Grant No.62101004)。
文摘For a magnetocardiography(MCG)system inside a magnetically shielded room(MSR),the residual field should be further suppressed to obtain high-quality MCG signals.In this paper,a compensation system has been developed based on the bi-planar coil and the proportional-integral-derivative(PID)controller.The bi-planar coil,derived from the target-field theory and the Tikhonov regularization method,is utilized to generate magnetic field with high uniformity in the predefined target region.And the PID controller is introduced to provide dynamic compensation current for the coil,according to the residual field change monitored by a reference SQUID magnetometer.The measurement results show that the noise suppression ratio(NSR)can reach above 20 dB in the low-frequency range from 0.1 Hz to 50 Hz.The DC component and the fluctuation of the residual field in time-domain can be respectively suppressed to 0 p T and 4 p T,indicating that this proposed compensation method is useful for the MCG measurement.
文摘A flip-chip-type gradiometer has been constructed with a 10 mm × 5 mm planar DC-SQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flux transformer made from a YB-CO* /YBCO/CeO2/YSZ multilayer on a φ50.8 mm Si wafer. The coupling coefficient between the flux transformer and the planar gradiometer is 0.18. The transformer increases effectively the resolution of the gradiometer. A magnetic field gradient resolution of 73 fT·cm-1·Hz-1/2 in the white region and 596 fT·cm-1Hz-1/2 at 1 Hz has been obtained. High quality magnetocardiogram signals have been successfully measured by using this flip-chip-type gradiometer in an unshielded environment.
