A novel method for noise removal from the rotating accelerometer gravity gradiometer(MAGG)is presented.It introduces a head-to-tail data expansion technique based on the zero-phase filtering principle.A scheme for det...A novel method for noise removal from the rotating accelerometer gravity gradiometer(MAGG)is presented.It introduces a head-to-tail data expansion technique based on the zero-phase filtering principle.A scheme for determining band-pass filter parameters based on signal-to-noise ratio gain,smoothness index,and cross-correlation coefficient is designed using the Chebyshev optimal consistent approximation theory.Additionally,a wavelet denoising evaluation function is constructed,with the dmey wavelet basis function identified as most effective for processing gravity gradient data.The results of hard-in-the-loop simulation and prototype experiments show that the proposed processing method has shown a 14%improvement in the measurement variance of gravity gradient signals,and the measurement accuracy has reached within 4E,compared to other commonly used methods,which verifies that the proposed method effectively removes noise from the gradient signals,improved gravity gradiometry accuracy,and has certain technical insights for high-precision airborne gravity gradiometry.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
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
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
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 coupled f...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
Newton＇s gravitational constant G is the least known fundamental constant of nature. Since Cavendish made the first measurement of G with a torsion balance over two hundred years ago, the best results of G have been ...Newton＇s gravitational constant G is the least known fundamental constant of nature. Since Cavendish made the first measurement of G with a torsion balance over two hundred years ago, the best results of G have been obtained by using torsion balances. However, the uncorrected anelasticity of torsion fibers makes the results questionable. We present a new method of G measurement by using a superconducting gravity gradiometer constructed with levitated test masses, which is free from the irregularities of mechanical suspension. The superconducting gravity gradiometer is rotated to generate a centrifugal acceleration that nulls the gravity field of the source mass, forming an artificial planetary system. This experiment has a potential accuracy of G better than 10 ppm.展开更多
The next-generation gravity satellite mission equipped with the Cold Atom Interferometry(CAI)gradiometer has great potential for the Earth's gravity field estimation.Deploying a CAI gradiometer on the Chinese Tian...The next-generation gravity satellite mission equipped with the Cold Atom Interferometry(CAI)gradiometer has great potential for the Earth's gravity field estimation.Deploying a CAI gradiometer on the Chinese Tiangong Space Station launched for long-term Earth science research not only reduces the cost compared to a dual-satellite constellation but also enhances interdisciplinary collaboration in the Earth's gravity field detection.In this study,we conducted gravity gradient-based simulations to assess the contribution of deploying a CAI gradiometer on the Tiangong Space Station to collaboratively observe the Earth's gravity field with a polar-orbit gravity satellite.The simulation results demonstrate that whether utilizing V_(yy) component,three diagonal components or full components,the derived gravity field models show significant improvements within 100 degree and above 200 degree after incorporating Tiangong Space Station.In particular,the gravity field solution recovered from three diagonal components achieves the best accuracy.In the case of using diagonal components,the collaboration observation scheme effectively reduced the cumulative geoid height error by approximately 5.3 cm(300 d/o).In the spatial domain,the incorporation of the Tiangong Space Station primarily impacts the estimated gravity field within the orbital coverage area of the space station,and this effect is particularly pronounced when just employing V_(yy) component.However,due to the limitation of angular velocity observation inaccuracy associated with the CAI gradiometer in nadir mode,there is no substantial accuracy improvement observed above 200 degree when adding gradient components.展开更多
A flip-chip-type gradiometer has been constructed with a 10 mm × 5 mm planar DCSQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flux transformer made from a YBCO*/YBCO/CeO2/YSZ multilayer on ?50...A flip-chip-type gradiometer has been constructed with a 10 mm × 5 mm planar DCSQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flux transformer made from a YBCO*/YBCO/CeO2/YSZ multilayer on ?50.8 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?1Hz?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
The full magnetic gradient tensor （MGT） refers to the spatial change rate of the three field components of the geomagnetic field vector along three mutually orthogonal axes. The tensor is of use to geological mappin...The full magnetic gradient tensor （MGT） refers to the spatial change rate of the three field components of the geomagnetic field vector along three mutually orthogonal axes. The tensor is of use to geological mapping, resources exploration, magnetic navigation, and others. However, it is very difficult to measure the full magnetic tensor gradient using existing engineering technology. We present a method to use triaxial aeromagnetic gradient measurements for deriving the full MGT. The method uses the triaxial gradient data and makes full use of the variation of the magnetic anomaly modulus in three dimensions to obtain a self-consistent magnetic tensor gradient. Numerical simulations show that the full MGT data obtained with the proposed method are of high precision and satisfy the requirements of data processing. We selected triaxial aeromagnetic gradient data from the Hebei Province for calculating the full MGT. Data processing shows that using triaxial tensor gradient data allows to take advantage of the spatial rate of change of the total field in three dimensions and suppresses part of the independent noise in the aeromagnetic gradient. The calculated tensor components have improved resolution, and the transformed full tensor gradient satisfies the requirement of geological mapping and interpretation.展开更多
Although satellite gravity gradient data plays a great role in determining short-wavelength part of static gravity field model,accuracy of the long-wavelength part of gravity field model recovered by them are poor,whi...Although satellite gravity gradient data plays a great role in determining short-wavelength part of static gravity field model,accuracy of the long-wavelength part of gravity field model recovered by them are poor,which leads to only a few applications in time-variable gravity investigation.The reason is that some factors limit the accuracy of the gravity field recovered using gradient data,including accuracy of the gravity gradient observations,measurement bandwidth(MBW)of gradiometer,satellite inclination,etc.This paper aims at analyzing the influence of these limitations on gravity field recovery and discusses the possibility of time-variable gravity field detection by using gravity gradient observations.Firstly,for arbitrary satellite orbit inclination,we give the frequency distributions of all the components of gravity gradients(i.e.Txx;Tyy;Tzz;Txy;Txz and Tyz,).The results show that the maximum frequency of each component of the gravity gradients is the same,i.e.l=Ts(l is degree of the gravity field model,Ts is the orbital periods),and it is not influenced by the inclination of the satellite orbits.Secondly,the paper gives a theory proof to explain why only the low orders of the coefficients are influenced by polar gaps.Big polar gaps are experimented by a numerical test with inclination of 45°.Finally,considering that the measurement bandwidth can be expanded and accuracy of gradient observations can be improved by superconducting gravity gradiometer(SGG)compared to gradiometer used in Gravity field and steadystate Ocean Circulation Explorer(GOCE),the possibility of detecting time-variable gravity using gravity gradient observations is discussed.The results show that the SGG creates errors in MBW with magnitude of 0.014 m E,which is smaller than the magnitude of the time-variable gravity gradient signals(i.e.,0.02 m E)derived from Gravity Recovery and Climate Experiment(GRACE)gravity field models.This indicates the potential of SGG in time-variable gravity detection.展开更多
Background Compared with traditional biomagnetic field detection devices,such as superconducting quantum interference devices(SQUIDs)and atomic magnetometers,only giant magneto impedance(GMI)sensors can be applied for...Background Compared with traditional biomagnetic field detection devices,such as superconducting quantum interference devices(SQUIDs)and atomic magnetometers,only giant magneto impedance(GMI)sensors can be applied for unshielded human brain biomagnetic detection,and they have the potential for application in next-generation wearable equipment for brain-computer interfaces(BCIs).Achieving a better GMI sensor without magnetic shielding requires the stimulation of the GMI effect to be maximized and environmental noise interference to be minimized.Moreover,the GMI effect stimulated in an amorphous filament is closely related to its working point,which is sensitive to both the external magnetic field and the drive current of the filament.Methods In this paper,we propose a new noise reducing GMI gradiometer with a dual-loop self-adapting structure.Noise reduction is realized by a direction-flexible differential probe,and the dual-loop structure optimizes and stabilizes the working point by automatically controlling the external magnetic field and drive current.This dual-loop structure is fully program controlled by a micro control unit(MCU),which not only simplifies the traditional constant parameter sensor circuit,saving the time required to adjust the circuit component parameters,but also improves the sensor performance and environmental adaptation.Results In the performance test,within 2 min of self-adaptation,our sensor showed a better sensitivity and signal-to-noise ratio(SNR)than those of the traditional designs and achieved a background noise of 12 pT/√Hz at 10 Hz and 7pT/√Hz at 200 Hz.Conclusion To the best of our knowledge,our sensor is the first to realize self-adaptation of both the external magnetic field and the drive current.展开更多
This paper reports on a study of the methodology of external calibration of GOCE data,using regional terrestrial-gravity data.Three regions around the world are selected in the numerical experiments.The result indicat...This paper reports on a study of the methodology of external calibration of GOCE data,using regional terrestrial-gravity data.Three regions around the world are selected in the numerical experiments.The result indicates that this calibration method is feasible.The effect is best with an accuracy of scale factor at 10-2 level,in Australia,where the area is smooth and the gravity data points are dense.The accuracy is one order of magnitude lower in both Canada,where the area is smooth but the data points are sparse,and Norway,where the area is rather tough and the data points are sparse.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
The sensing organs are exponentially better than any of analogous artificial ones. That is why using them in full scale is a perspective trend to the efficient (advanced) machine perception. On the other hand, limitat...The sensing organs are exponentially better than any of analogous artificial ones. That is why using them in full scale is a perspective trend to the efficient (advanced) machine perception. On the other hand, limitations of sensing organs could be replaced by the perfect artificial ones with the subsequent training the nervous system on their output signals. An attempt to lay down the foundations of biosensing by natural sensors and in addition to them by the artificial transducers of physical quantities, also with their expansion into space arrays and external/implantable functioning in relation to the nervous system is performed. The advances in nanotechnology are opening the way to achieving direct electrical contact of nanoelectronic structures with electrically and electrochemically active neurocellular structures. The transmission of the sensors' signals to a processing unit has been maintaining by an electromagnetic transistor/memristor (externally) and superconducting transducer of ionic currents (implantable). The arrays of the advanced sensors give us information about the space and direction dynamics of the signals' spreading.The measuring method and necessary performance data of the sensor for the robot's orientation in the ambient magnetic field with living being-machine interaction in order to obtain input and output signals from brain and motor nerves to the measurement system and vice versa are introduced. The range of applied sensors differs from an induction sensor to superconducting induction magnetometer. The analytical expressions for arrangements of the head sensors in differential and vector (3D) relative positions are deduced. Sensitivity of the perception method makes it possible to recognize the linear translation of 10?2 m and disposal in space of 10?3 m3. Interaction between living beings and robotic equipment is given analytical treatment.展开更多
The paper presents a morphological study of real time magnetocardiograms(MCGs) of a normal subject.The MCGs were measured by using a 3 D second order gradiometer connected to three rf SQUIDs in a prefabricated magneti...The paper presents a morphological study of real time magnetocardiograms(MCGs) of a normal subject.The MCGs were measured by using a 3 D second order gradiometer connected to three rf SQUIDs in a prefabricated magnetically shielded room.The base line of the detecting coil for Bz is 2.8 cm and that of the coil for Bx and By is 1.4 cm.The magnetic field components perpendicular to the chest (Bz component )and tangential to the chest (Bx,By components) were studied.From isofield contour maps and arrow maps of the QRS wave of the MCG,when multiple sources exist simulataneously,we can infer the locations and positions of different sources by combining the Bz component with the Bx and By components.The analyzed results showed that a method using a 3 D second order gradiometer that we developed is useful for discriminating the directions and locations of multiple sources.展开更多
文摘A novel method for noise removal from the rotating accelerometer gravity gradiometer(MAGG)is presented.It introduces a head-to-tail data expansion technique based on the zero-phase filtering principle.A scheme for determining band-pass filter parameters based on signal-to-noise ratio gain,smoothness index,and cross-correlation coefficient is designed using the Chebyshev optimal consistent approximation theory.Additionally,a wavelet denoising evaluation function is constructed,with the dmey wavelet basis function identified as most effective for processing gravity gradient data.The results of hard-in-the-loop simulation and prototype experiments show that the proposed processing method has shown a 14%improvement in the measurement variance of gravity gradient signals,and the measurement accuracy has reached within 4E,compared to other commonly used methods,which verifies that the proposed method effectively removes noise from the gradient signals,improved gravity gradiometry accuracy,and has certain technical insights for high-precision airborne gravity gradiometry.
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.
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.
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.
文摘Newton＇s gravitational constant G is the least known fundamental constant of nature. Since Cavendish made the first measurement of G with a torsion balance over two hundred years ago, the best results of G have been obtained by using torsion balances. However, the uncorrected anelasticity of torsion fibers makes the results questionable. We present a new method of G measurement by using a superconducting gravity gradiometer constructed with levitated test masses, which is free from the irregularities of mechanical suspension. The superconducting gravity gradiometer is rotated to generate a centrifugal acceleration that nulls the gravity field of the source mass, forming an artificial planetary system. This experiment has a potential accuracy of G better than 10 ppm.
基金National Key R&D Program of China(2021YFB3900101)the National Natural Science Foundation of China(42174099 and 42192532)It is also partly supported by the Fundamental Research Funds for the Central Universities.
文摘The next-generation gravity satellite mission equipped with the Cold Atom Interferometry(CAI)gradiometer has great potential for the Earth's gravity field estimation.Deploying a CAI gradiometer on the Chinese Tiangong Space Station launched for long-term Earth science research not only reduces the cost compared to a dual-satellite constellation but also enhances interdisciplinary collaboration in the Earth's gravity field detection.In this study,we conducted gravity gradient-based simulations to assess the contribution of deploying a CAI gradiometer on the Tiangong Space Station to collaboratively observe the Earth's gravity field with a polar-orbit gravity satellite.The simulation results demonstrate that whether utilizing V_(yy) component,three diagonal components or full components,the derived gravity field models show significant improvements within 100 degree and above 200 degree after incorporating Tiangong Space Station.In particular,the gravity field solution recovered from three diagonal components achieves the best accuracy.In the case of using diagonal components,the collaboration observation scheme effectively reduced the cumulative geoid height error by approximately 5.3 cm(300 d/o).In the spatial domain,the incorporation of the Tiangong Space Station primarily impacts the estimated gravity field within the orbital coverage area of the space station,and this effect is particularly pronounced when just employing V_(yy) component.However,due to the limitation of angular velocity observation inaccuracy associated with the CAI gradiometer in nadir mode,there is no substantial accuracy improvement observed above 200 degree when adding gradient components.
文摘A flip-chip-type gradiometer has been constructed with a 10 mm × 5 mm planar DCSQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flux transformer made from a YBCO*/YBCO/CeO2/YSZ multilayer on ?50.8 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?1Hz?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.
基金supported by the National High Technology Research and Development Program of China(863 Program)(No.2013AA063901 and No.2006AA06A201)
文摘The full magnetic gradient tensor （MGT） refers to the spatial change rate of the three field components of the geomagnetic field vector along three mutually orthogonal axes. The tensor is of use to geological mapping, resources exploration, magnetic navigation, and others. However, it is very difficult to measure the full magnetic tensor gradient using existing engineering technology. We present a method to use triaxial aeromagnetic gradient measurements for deriving the full MGT. The method uses the triaxial gradient data and makes full use of the variation of the magnetic anomaly modulus in three dimensions to obtain a self-consistent magnetic tensor gradient. Numerical simulations show that the full MGT data obtained with the proposed method are of high precision and satisfy the requirements of data processing. We selected triaxial aeromagnetic gradient data from the Hebei Province for calculating the full MGT. Data processing shows that using triaxial tensor gradient data allows to take advantage of the spatial rate of change of the total field in three dimensions and suppresses part of the independent noise in the aeromagnetic gradient. The calculated tensor components have improved resolution, and the transformed full tensor gradient satisfies the requirement of geological mapping and interpretation.
基金funded by National Natural Science Foundation of China(No.41674026,41404019,41774089)Fundamental Research Funds for the Central University(No.2652018027)+2 种基金China Geological Survey(DD20191006)Open Research Fund of Qian Xuesen Laboratory of Space Technology,CAST(No.GZZKFJJ2020006)Open Research Fund of Key Laboratory of Space Utilization,Chinese Academy of Sciences(LSU-KFJJ201902)
文摘Although satellite gravity gradient data plays a great role in determining short-wavelength part of static gravity field model,accuracy of the long-wavelength part of gravity field model recovered by them are poor,which leads to only a few applications in time-variable gravity investigation.The reason is that some factors limit the accuracy of the gravity field recovered using gradient data,including accuracy of the gravity gradient observations,measurement bandwidth(MBW)of gradiometer,satellite inclination,etc.This paper aims at analyzing the influence of these limitations on gravity field recovery and discusses the possibility of time-variable gravity field detection by using gravity gradient observations.Firstly,for arbitrary satellite orbit inclination,we give the frequency distributions of all the components of gravity gradients(i.e.Txx;Tyy;Tzz;Txy;Txz and Tyz,).The results show that the maximum frequency of each component of the gravity gradients is the same,i.e.l=Ts(l is degree of the gravity field model,Ts is the orbital periods),and it is not influenced by the inclination of the satellite orbits.Secondly,the paper gives a theory proof to explain why only the low orders of the coefficients are influenced by polar gaps.Big polar gaps are experimented by a numerical test with inclination of 45°.Finally,considering that the measurement bandwidth can be expanded and accuracy of gradient observations can be improved by superconducting gravity gradiometer(SGG)compared to gradiometer used in Gravity field and steadystate Ocean Circulation Explorer(GOCE),the possibility of detecting time-variable gravity using gravity gradient observations is discussed.The results show that the SGG creates errors in MBW with magnitude of 0.014 m E,which is smaller than the magnitude of the time-variable gravity gradient signals(i.e.,0.02 m E)derived from Gravity Recovery and Climate Experiment(GRACE)gravity field models.This indicates the potential of SGG in time-variable gravity detection.
基金Supported by the China Postdoctoral Science Foundation(4139ZRL)the National Natural Science Foundation of China(U19A2083).
文摘Background Compared with traditional biomagnetic field detection devices,such as superconducting quantum interference devices(SQUIDs)and atomic magnetometers,only giant magneto impedance(GMI)sensors can be applied for unshielded human brain biomagnetic detection,and they have the potential for application in next-generation wearable equipment for brain-computer interfaces(BCIs).Achieving a better GMI sensor without magnetic shielding requires the stimulation of the GMI effect to be maximized and environmental noise interference to be minimized.Moreover,the GMI effect stimulated in an amorphous filament is closely related to its working point,which is sensitive to both the external magnetic field and the drive current of the filament.Methods In this paper,we propose a new noise reducing GMI gradiometer with a dual-loop self-adapting structure.Noise reduction is realized by a direction-flexible differential probe,and the dual-loop structure optimizes and stabilizes the working point by automatically controlling the external magnetic field and drive current.This dual-loop structure is fully program controlled by a micro control unit(MCU),which not only simplifies the traditional constant parameter sensor circuit,saving the time required to adjust the circuit component parameters,but also improves the sensor performance and environmental adaptation.Results In the performance test,within 2 min of self-adaptation,our sensor showed a better sensitivity and signal-to-noise ratio(SNR)than those of the traditional designs and achieved a background noise of 12 pT/√Hz at 10 Hz and 7pT/√Hz at 200 Hz.Conclusion To the best of our knowledge,our sensor is the first to realize self-adaptation of both the external magnetic field and the drive current.
基金supported by the Director Foundation of the Institute of Seismology,China Earthquake Administration(IS201126025)The Basis Research Foundation of Key laboratory of Geospace Environment&Geodesy Ministry of Education,China(10-01-09)
文摘This paper reports on a study of the methodology of external calibration of GOCE data,using regional terrestrial-gravity data.Three regions around the world are selected in the numerical experiments.The result indicates that this calibration method is feasible.The effect is best with an accuracy of scale factor at 10-2 level,in Australia,where the area is smooth and the gravity data points are dense.The accuracy is one order of magnitude lower in both Canada,where the area is smooth but the data points are sparse,and Norway,where the area is rather tough and the data points are sparse.
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.
文摘The sensing organs are exponentially better than any of analogous artificial ones. That is why using them in full scale is a perspective trend to the efficient (advanced) machine perception. On the other hand, limitations of sensing organs could be replaced by the perfect artificial ones with the subsequent training the nervous system on their output signals. An attempt to lay down the foundations of biosensing by natural sensors and in addition to them by the artificial transducers of physical quantities, also with their expansion into space arrays and external/implantable functioning in relation to the nervous system is performed. The advances in nanotechnology are opening the way to achieving direct electrical contact of nanoelectronic structures with electrically and electrochemically active neurocellular structures. The transmission of the sensors' signals to a processing unit has been maintaining by an electromagnetic transistor/memristor (externally) and superconducting transducer of ionic currents (implantable). The arrays of the advanced sensors give us information about the space and direction dynamics of the signals' spreading.The measuring method and necessary performance data of the sensor for the robot's orientation in the ambient magnetic field with living being-machine interaction in order to obtain input and output signals from brain and motor nerves to the measurement system and vice versa are introduced. The range of applied sensors differs from an induction sensor to superconducting induction magnetometer. The analytical expressions for arrangements of the head sensors in differential and vector (3D) relative positions are deduced. Sensitivity of the perception method makes it possible to recognize the linear translation of 10?2 m and disposal in space of 10?3 m3. Interaction between living beings and robotic equipment is given analytical treatment.
文摘The paper presents a morphological study of real time magnetocardiograms(MCGs) of a normal subject.The MCGs were measured by using a 3 D second order gradiometer connected to three rf SQUIDs in a prefabricated magnetically shielded room.The base line of the detecting coil for Bz is 2.8 cm and that of the coil for Bx and By is 1.4 cm.The magnetic field components perpendicular to the chest (Bz component )and tangential to the chest (Bx,By components) were studied.From isofield contour maps and arrow maps of the QRS wave of the MCG,when multiple sources exist simulataneously,we can infer the locations and positions of different sources by combining the Bz component with the Bx and By components.The analyzed results showed that a method using a 3 D second order gradiometer that we developed is useful for discriminating the directions and locations of multiple sources.
