Most triaxial-vectorial magnetic field measurements with spin-exchange relaxation free(SERF)atomic magnetometer(AM)are based on the quasi-steady-state solution of the Bloch equation.However,the responding speed of the...Most triaxial-vectorial magnetic field measurements with spin-exchange relaxation free(SERF)atomic magnetometer(AM)are based on the quasi-steady-state solution of the Bloch equation.However,the responding speed of these methods is greatly limited because the frequency of the modulation signal should be slow enough to ensure the validity of the quasi-steady-state solution.In this work,a new model to describe the response of the three-axis sensitive SERF AM with high modulation frequency is presented and verified.The response of alkali-atomic spin to high-frequency modulation field is further investigated by solving the Bloch equation in a modulation-frequency-dependence manner.This solution is well verified by our experiments and can offer a reference for selection of modulation frequencies.The result shows a potential to achieve a SERF AM operating in a geomagnetic field without heavy aluminum shielding when the modulation frequencies are selected properly.展开更多
The Macao Science Satellite-1(known as MSS-1)is the first scientific exploration satellite that was designed to measure the Earth's low latitude magnetic field at high resolution and with high precision by collect...The Macao Science Satellite-1(known as MSS-1)is the first scientific exploration satellite that was designed to measure the Earth's low latitude magnetic field at high resolution and with high precision by collecting data in a near-equatorial orbit.Magnetic field data from MSS-1's onboard Vector Fluxgate Magnetometer(VFM),collected at a sample rate of 50 Hz,allows us to detect and investigate sources of magnetic data contamination,from DC to relevant Nyquist frequency.Here we report two types of artificial disturbances in the VFM data.One is V-shaped events concentrated at night,with frequencies sweeping from the Nyquist frequency down to zero and back up.The other is 5-Hz events(ones that exhibit a distinct 5 Hz spectrum peak);these events are always accompanied by intervals of spiky signals,and are clearly related to the attitude control of the satellite.Our analyses show that VFM noise levels in daytime are systematically lower than in nighttime.The daily average noise levels exhibit a period of about 52 days.The V-shaped events are strongly correlated with higher VFM noise levels.展开更多
High-precision magnetic field measurements are crucial for understanding Earth’s internal structure,space environment,and dynamic geomagnetic variations.Data from the Fluxgate Magnetometer (FGM) on the Macao Science ...High-precision magnetic field measurements are crucial for understanding Earth’s internal structure,space environment,and dynamic geomagnetic variations.Data from the Fluxgate Magnetometer (FGM) on the Macao Science Satellite-1A (MSS-1A),added to data from other space-based magnetometers,should increase significantly the ability of scientists to observe changes in Earth’s magnetic field over time and space.Additionally,the MSS-1A’s FGM is intended to help identify magnetic disturbances affecting the spacecraft itself.This report focuses on the in-flight calibration of the MSS-1 FGM.A scalar calibration,independent of geomagnetic field models,was performed to correct offsets,sensitivities,and misalignment angles of the FGM.Using seven months of data,we find that the in-flight calibration parameters show good stability.We determined Euler angles describing the rotational relationship between the FGM and the Advanced Stellar Compass (ASC) coordinate system using two approaches:calibration with the CHAOS-7 geomagnetic field model,and simultaneous estimation of Euler angles and Gaussian spherical harmonic coefficients through self-consistent modeling.The accuracy of Euler angles describing the rotation was better than 18 arcsec.The calibrated FGM data exhibit good agreement with the calibrated data of the Vector Field Magnetometer (VFM),which is the primary vector magnetometer of the satellite.These calibration efforts have significantly improved the accuracy of the FGM measurements,which are now providing reliable data for geomagnetic field studies that promise to advance our understanding of the Earth’s magnetic environment.展开更多
The flying-wing aircraft has excellent aerodynamic efficiency and stealth performance.However,due to the lack of tails,the flying-wing aircraft has a serious attitude control problem.In this paper,the effective flow c...The flying-wing aircraft has excellent aerodynamic efficiency and stealth performance.However,due to the lack of tails,the flying-wing aircraft has a serious attitude control problem.In this paper,the effective flow control strategy of three-axis control is proposed by using continuous jets for a flapless flying-wing aircraft.The wind tunnel test of two kinds of flying-wing models,namely one flow control model and one mechanical control model,is conducted,and the control effect is analyzed and compared.By simultaneous blowing of the circulation control actuators inboard and differential blowing of the circulation control actuators outboard,the pitch and roll controls are achieved,respectively.It also has an effective control effect at very large angles of attack where the conventional control surface fails.A linear relationship is found between the increment of the controlled aerodynamic force/moment coefficient and the momentum coefficient for circulation control actuators.Moreover,to resolve the difficulty in yaw control,a novel wingtip jet is proposed based on the concept of the all-moving tip and compared with apex jet and circulation control jet.It is found that the wingtip jet is the most efficient actuator,followed by the simultaneous-blowing circulation control jet.Therefore,based on the research above,two optimized fluidic control configurations are proposed.One employs circulation control jet and wingtip jet,and the other is completely dependent on circulation control jet.Finally,the flow control mechanism of circulation control is discussed.Circulation control significantly accelerates the flow on the upper surface of the airfoil in attached flow and reduces the flow separation region in separated flow,leading to aerodynamic performance improvement.These results provide an important theoretic basis for the flapless flight control of flying-wing aircraft.展开更多
Zero-and ultralow-field nuclear magnetic resonance(ZULF NMR)has experienced rapid development and provides an excellent tool for diverse research fields ranging from materials science and quantum information processin...Zero-and ultralow-field nuclear magnetic resonance(ZULF NMR)has experienced rapid development and provides an excellent tool for diverse research fields ranging from materials science and quantum information processing to fundamental physics.The detection of ZULF NMR signals in samples with natural abundance remains a challenging endeavor,due to the limited sensitivity of NMR detectors and thermal polarization.In this work,we demonstrate a femtotesla(fT)Potassium spin-exchange relaxation-free(SERF)magnetometer designed for ZULF NMR detection.A Potassium vapor cell with high buffer gas pressure and high atomic number density is used in the magnetometer.With absorption spectroscopy and SERF effect,the key parameters of the vapor cell are characterized and applied to optimize the magnetometer sensitivity.To combine our SERF magnetometer and ZULF NMR detection,a custom-made vacuum chamber is employed to keep NMR sample close to the magnetometer cell and protect the sample from undesired heating effects.Gradiometric measurement is performed to greatly reduce the magnetic noise.With the phase calibration applied,the gradiometric measurement achieves 7-fold enhancement in magnetic-field sensitivity compared to the single channel and has a magnetic noise floor of 1.2 fT/Hz^(1/2).Our SERF magnetometer exhibits high sensitivity and is promising to realize ZULF NMR detection of samples with natural abundance.展开更多
A miniature quad-channel optically pumped atomic magnetometer(OPM) has been developed based on the spinexchange relaxation-free(SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated...A miniature quad-channel optically pumped atomic magnetometer(OPM) has been developed based on the spinexchange relaxation-free(SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated four SERF magnetometer channels, which provides sufficient spatial resolution for magnetoencephalography(MEG). The four channels share the same laser beam for the best cancellation of common mode noise due to laser fluctuations. With gradient measurement, the sensitivities of the four sensors are better than 6 fT/Hz^(1/2), which is also good enough for MEG measurement. The vapor cell is heated to 160℃ by a novel nonmagnetic current-heating structure. Our sensor with high spatial resolution and compact size is particularly suitable for MEG systems.展开更多
This article presents a near-Earth satellite orbit estimation method for pico-satellite applications with light-weight and low-power requirements. The method provides orbit information autonomously from magnetometer a...This article presents a near-Earth satellite orbit estimation method for pico-satellite applications with light-weight and low-power requirements. The method provides orbit information autonomously from magnetometer and sun sensor, with an extended Kalman filter （EKF）. Real-time position/velocity parameters are estimated with attitude independently from two quantities： the measured magnitude of the Earth’s magnetic field, and the measured dot product of the magnetic field vector and the sun vector. To guarantee the filter’s effectiveness, it is recommended that the sun sensor should at least have the same level of accuracy as magnetometer. Furthermore, to reduce filter’s computation expense, simplification methods in EKF’s Jacobian calculations are introduced and testified, and a polynomial model for fast magnetic field calculation is developed. With these methods, 50% of the computation expense in dynamic model propagation and 80% of the computation burden in measurement model calculation can be reduced. Tested with simulation data and compared with original magnetometer-only methods, filter achieves faster convergence and higher accuracy by 75% and 30% respectively, and the suggested simplification methods are proved to be harmless to filter’s estimation performance.展开更多
For the vector attitude determination, the traditional optimal algorithms which are based on quaternion estimator（QUEST） measurement noise model are complicated for just two observations. In our application, the mag...For the vector attitude determination, the traditional optimal algorithms which are based on quaternion estimator（QUEST） measurement noise model are complicated for just two observations. In our application, the magnetometer and accelerometer are not two comparable kinds of sensors and both are not small field-of-view sensors as well. So in this paper a new unit measurement model is derived. According to the Wahba problem, the optimal weights for each measurement are obtained by the error variance researches. Then an improved quaternion Gauss–Newton method is presented and adopted to acquire attitude. Eventually, simulation results and experimental validation employed to test the proposed method demonstrate the usefulness of the improved algorithm.展开更多
We observed the steady-state visually evoked potential(SSVEP) from a healthy subject using a compact quad-channel potassium spin exchange relaxation-free(SERF) optically pumped magnetometer(OPM). To this end, 30 s of ...We observed the steady-state visually evoked potential(SSVEP) from a healthy subject using a compact quad-channel potassium spin exchange relaxation-free(SERF) optically pumped magnetometer(OPM). To this end, 30 s of data were collected, and SSVEP-related magnetic responses with signal intensity ranging from 150 fT to 300 f T were observed for all four channels. The corresponding signal to noise ratio(SNR) was in the range of 3.5–5.5. We then used different channels to operate the sensor as a gradiometer. In the specific case of detecting SSVEP, we noticed that the short channel separation distance led to a strongly diminished gradiometer signal. Although not optimal for the case of SSVEP detection, this set-up can prove to be highly useful for other magnetoencephalography(MEG) paradigms that require good noise cancellation.Considering its compactness, low cost, and good performance, the K-SERF sensor has great potential for biomagnetic field measurements and brain-computer interfaces(BCI).展开更多
Satellite attitude information is essential for pico-satellite applications requiring light-weight,low-power,and fast-computation characteristics.The objective of this study is to provide a magnetometer-only attitude ...Satellite attitude information is essential for pico-satellite applications requiring light-weight,low-power,and fast-computation characteristics.The objective of this study is to provide a magnetometer-only attitude estimation method for a low-altitude Earth orbit,bias momentum pico-satellite.Based on two assumptions,the spacecraft spherical symmetry and damping of body rates,a linear kinematics model of a bias momentum satellite's pitch axis is derived,and the linear estimation algorithm is developed.The algorithm combines the linear Kalman filter(KF) with the classic three-axis attitude determination method(TRIAD).KF is used to estimate satellite's pitch axis orientation,while TRIAD is used to obtain information concerning the satellite's three-axis attitude.Simulation tests confirmed that the algorithm is suited to the time-varying model errors resulting from both assumptions.The estimate result keeps tracking satellite attitude motion during all damping,stable,and free rotating control stages.Compared with nonlinear algorithms,such as extended Kalman filer(EKF) and square root unscented Kalman filer(SRUKF),the algorithm presented here has an almost equal performance in terms of convergence time and estimation accuracy,while the consumption of computing resources is much lower.展开更多
Four levels of the data from the search coil magnetometer(SCM) onboard the China Seismo-Electromagnetic Satellite(CSES)are defined and described. The data in different levels all contain three components of the wavefo...Four levels of the data from the search coil magnetometer(SCM) onboard the China Seismo-Electromagnetic Satellite(CSES)are defined and described. The data in different levels all contain three components of the waveform and/or spectrum of the induced magnetic field around the orbit in the frequency range of 10 Hz to 20 kHz; these are divided into an ultra-low-frequency band(ULF,10–200 Hz), an extremely low frequency band(ELF, 200–2200 Hz), and a very low frequency band(VLF, 1.8–20 kHz). Examples of data products for Level-2, Level-3, and Level-4 are presented. The initial results obtained in the commission test phase demonstrated that the SCM was in a normal operational status and that the data are of high enough quality to reliably capture most space weather events related to low-frequency geomagnetic disturbances.展开更多
In a pico-satellite with small volume, measurements from on-board three-axis magnetometer （TAM） are not accurate, as it can be easily disturbed by other electronic systems. To improve its accuracy, a scheme of compe...In a pico-satellite with small volume, measurements from on-board three-axis magnetometer （TAM） are not accurate, as it can be easily disturbed by other electronic systems. To improve its accuracy, a scheme of compensation methods is introduced in this article. The scheme is based on an improved meast, rement model of pico-satellite TAM, and it mainly consists of three steps. First, in satellite design stage, several techniques are recommended to simplify the afterwards compensations. Then after satellite assembly, TAM ground tests and pre-launch calibration with least-square batch filter are introduced to improve magnetometer performance. At the end, a post-launch calibration with unscented Kalman filter （UKF） is implemented with in-orbit data. The compensation scheme is used in the development of Chinese pico-satellite ZDPS-1A made by Zhejiang University. Results show that with the introduced compensation scheme, the maximum error of ZDPS-1A TAM can be reduced from 80 mG to 6 naG （1 G=10^-4T）.展开更多
The laser-pumped potassium spin-exchange relaxation free （SERF） magnetometer is the most sensitive detector of magnetic field and has many important applications. We present the experimental results of our potassium...The laser-pumped potassium spin-exchange relaxation free （SERF） magnetometer is the most sensitive detector of magnetic field and has many important applications. We present the experimental results of our potassium SERF magne- tometer. A pump-probe approach is used to identify the unique spin dynamics of the atomic ensemble in the SERF regime. A single channel sensitivity of 8 f.THz-1/2 is achieved with our SERF magnetometer.展开更多
A transverse relaxation determination of spin-exchange relaxation free （SERF） magnetometer based on polarization modulation technique is proposed. Compared with the radio-frequency （RF） excitation and light intens...A transverse relaxation determination of spin-exchange relaxation free （SERF） magnetometer based on polarization modulation technique is proposed. Compared with the radio-frequency （RF） excitation and light intensity excitation meth- ods used in SERF magnetometer, the light polarization modulation method has a high stability in low-frequency range, which indicates a more accurate transverse relaxation measurement.展开更多
As one of the seven scientific payloads on board the Tianwen-1 orbiter,the Mars Orbiter Magnetometer(MOMAG)will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction wi...As one of the seven scientific payloads on board the Tianwen-1 orbiter,the Mars Orbiter Magnetometer(MOMAG)will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction with the solar wind.The instrument consists of two identical triaxial fluxgate magnetometer sensors,mounted on a 3.19 meter-long boom with a seperation of about 90 cm.The dual-magnetometers configuration will help eliminate the magnetic field interference generated by the spacecraft platform and payloads.The sensors are controlled by an electric box mounted inside the orbiter.Each magnetometer measures the ambient vector magnetic field over a wide dynamic range(to 10,000 nT per axis)with a resolution of 1.19 pT.Both magnetometers sample the ambient magnetic field at an intrinsic frequency of 128 Hz,but will operate in a model with alternating frequency between 1 and 32 Hz to meet telemetry allocations.展开更多
A Chinese Antarctic Magnetometer （CAM） chain from Zhongshan Station （ZHS） to Dome-A （DMA） has been established since February 2009. A regular magnetometer is operated at ZHS, and four low power magnetometers are...A Chinese Antarctic Magnetometer （CAM） chain from Zhongshan Station （ZHS） to Dome-A （DMA） has been established since February 2009. A regular magnetometer is operated at ZHS, and four low power magnetometers are operated along the interior route from ZHS to DMA in the cusp latitude, extending over a distance of 1260 km. These stations fill an important void in the Antarctic magnetometer network. Furthermore, the CAM chain is magnetically conjugated with the Arctic region reaching from the Svalbard archipelago to Daneborg, on the east coast of Greenland. Conjugate measurements using the Arctic and Antarctic magnetometers provide excellent opportunities to investigate phenomena related to the coupling of the solar wind to the magnetosphere and ionosphere, such as magnetic impulse events, flux transfer events, traveling convection vortices and ultra-low frequency waves.展开更多
We present an experimental and theoretical investigation of the coherent population trapping （CPT） resonance excited on the D1 line of 87Rb atoms by bichromatic linearly polarized laser light. The experimental resul...We present an experimental and theoretical investigation of the coherent population trapping （CPT） resonance excited on the D1 line of 87Rb atoms by bichromatic linearly polarized laser light. The experimental results show that a lin｜｜lin tran- sition scheme is a promising alternative to the conventional circular-circular transition scheme for an atomic magnetometer. Compared with the circular light transition scheme, linear light accounts for high-contrast transmission resonances, which makes this excitation scheme promising for high-sensitivity magnetometers. We also use linear light and circular light to detect changes of a standard magnetic field, separately.展开更多
We constructed a 36-channel magnetocardiography（MCG） system based on low-Tc direct current（DC） superconducting quantum interference device（SQUID） magnetometers operated inside a magnetically shielded room（MSR）...We constructed a 36-channel magnetocardiography（MCG） system based on low-Tc direct current（DC） superconducting quantum interference device（SQUID） magnetometers operated inside a magnetically shielded room（MSR）. Weakly damped SQUID magnetometers with large Steward–Mc Cumber parameter βc（βc≈ 5）, which could directly connect to the operational amplifier without any additional feedback circuit, were used to simplify the readout electronics. With a flux-to-voltage transfer coefficient V / Φ larger than 420 μV/Φ0, the SQUID magnetometers had a white noise level of about 5.5 f T·Hz-1/2when operated in MSR. 36 sensing magnetometers and 15 reference magnetometers were employed to realize software gradiometer configurations. The coverage area of the 36 sensing magnetometers is 210×210 mm2. MCG measurements with a high signal-to-noise ratio of 40 d B were done successfully using the developed system.展开更多
This Inertial Navigation System (INS), Global Positioning System (GPS) and fluxgate magnetometer technologies have been widely used in a variety of positioning and navigation applications. In this paper, a low cost so...This Inertial Navigation System (INS), Global Positioning System (GPS) and fluxgate magnetometer technologies have been widely used in a variety of positioning and navigation applications. In this paper, a low cost solid state INS/GPS/Magnetometer integrated navigation system has been developed that incorporates measurements from an Inertial Navigation System (INS), Global Positioning System (GPS) and fluxgate magnetometer (Mag.) to provide a reliable complete navigation solution at a high output rate. The body attitude estimates, especially the heading angle, are fundamental challenges in a navigation system. Therefore targeting accurate attitude estimation is considered a significant contribution to the overall navigation error. A better estimation of the body attitude estimates leads to more accurate position and velocity estimation. For that end, the aim of this research is to exploit the magnetometer and accelerometer data in the attitude estimation technique. In this paper, a Scaled Unscented Kalman Filter (SUKF) based on the quaternion concept is designed for the INS/GPS/Mag integrated navigation system under large attitude error conditions. Simulation and experimental results indicate a satisfactory performance of the newly developed model.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.42074216).
文摘Most triaxial-vectorial magnetic field measurements with spin-exchange relaxation free(SERF)atomic magnetometer(AM)are based on the quasi-steady-state solution of the Bloch equation.However,the responding speed of these methods is greatly limited because the frequency of the modulation signal should be slow enough to ensure the validity of the quasi-steady-state solution.In this work,a new model to describe the response of the three-axis sensitive SERF AM with high modulation frequency is presented and verified.The response of alkali-atomic spin to high-frequency modulation field is further investigated by solving the Bloch equation in a modulation-frequency-dependence manner.This solution is well verified by our experiments and can offer a reference for selection of modulation frequencies.The result shows a potential to achieve a SERF AM operating in a geomagnetic field without heavy aluminum shielding when the modulation frequencies are selected properly.
基金supported by the National Key R&D Program of China(Grant2022YFF0503700)the National Natural Science Foundation of China(42474200 and 42174186)。
文摘The Macao Science Satellite-1(known as MSS-1)is the first scientific exploration satellite that was designed to measure the Earth's low latitude magnetic field at high resolution and with high precision by collecting data in a near-equatorial orbit.Magnetic field data from MSS-1's onboard Vector Fluxgate Magnetometer(VFM),collected at a sample rate of 50 Hz,allows us to detect and investigate sources of magnetic data contamination,from DC to relevant Nyquist frequency.Here we report two types of artificial disturbances in the VFM data.One is V-shaped events concentrated at night,with frequencies sweeping from the Nyquist frequency down to zero and back up.The other is 5-Hz events(ones that exhibit a distinct 5 Hz spectrum peak);these events are always accompanied by intervals of spiky signals,and are clearly related to the attitude control of the satellite.Our analyses show that VFM noise levels in daytime are systematically lower than in nighttime.The daily average noise levels exhibit a period of about 52 days.The V-shaped events are strongly correlated with higher VFM noise levels.
文摘High-precision magnetic field measurements are crucial for understanding Earth’s internal structure,space environment,and dynamic geomagnetic variations.Data from the Fluxgate Magnetometer (FGM) on the Macao Science Satellite-1A (MSS-1A),added to data from other space-based magnetometers,should increase significantly the ability of scientists to observe changes in Earth’s magnetic field over time and space.Additionally,the MSS-1A’s FGM is intended to help identify magnetic disturbances affecting the spacecraft itself.This report focuses on the in-flight calibration of the MSS-1 FGM.A scalar calibration,independent of geomagnetic field models,was performed to correct offsets,sensitivities,and misalignment angles of the FGM.Using seven months of data,we find that the in-flight calibration parameters show good stability.We determined Euler angles describing the rotational relationship between the FGM and the Advanced Stellar Compass (ASC) coordinate system using two approaches:calibration with the CHAOS-7 geomagnetic field model,and simultaneous estimation of Euler angles and Gaussian spherical harmonic coefficients through self-consistent modeling.The accuracy of Euler angles describing the rotation was better than 18 arcsec.The calibrated FGM data exhibit good agreement with the calibrated data of the Vector Field Magnetometer (VFM),which is the primary vector magnetometer of the satellite.These calibration efforts have significantly improved the accuracy of the FGM measurements,which are now providing reliable data for geomagnetic field studies that promise to advance our understanding of the Earth’s magnetic environment.
文摘The flying-wing aircraft has excellent aerodynamic efficiency and stealth performance.However,due to the lack of tails,the flying-wing aircraft has a serious attitude control problem.In this paper,the effective flow control strategy of three-axis control is proposed by using continuous jets for a flapless flying-wing aircraft.The wind tunnel test of two kinds of flying-wing models,namely one flow control model and one mechanical control model,is conducted,and the control effect is analyzed and compared.By simultaneous blowing of the circulation control actuators inboard and differential blowing of the circulation control actuators outboard,the pitch and roll controls are achieved,respectively.It also has an effective control effect at very large angles of attack where the conventional control surface fails.A linear relationship is found between the increment of the controlled aerodynamic force/moment coefficient and the momentum coefficient for circulation control actuators.Moreover,to resolve the difficulty in yaw control,a novel wingtip jet is proposed based on the concept of the all-moving tip and compared with apex jet and circulation control jet.It is found that the wingtip jet is the most efficient actuator,followed by the simultaneous-blowing circulation control jet.Therefore,based on the research above,two optimized fluidic control configurations are proposed.One employs circulation control jet and wingtip jet,and the other is completely dependent on circulation control jet.Finally,the flow control mechanism of circulation control is discussed.Circulation control significantly accelerates the flow on the upper surface of the airfoil in attached flow and reduces the flow separation region in separated flow,leading to aerodynamic performance improvement.These results provide an important theoretic basis for the flapless flight control of flying-wing aircraft.
基金supported by National Science Foundation of China(Grant Nos.T2388102,11927811,92476204,12150014,12205296,12274395,and 12261160569)Innovation Program for Quantum Science and Technology(Grant No.2021ZD0303205)+1 种基金Youth Innovation Promotion Association(Grant No.2023474)Chinese Academy of Sciences Magnetic Resonance Technology Alliance Research Instrument and Equipment Development/Functional Development(Grant No.2022GZL003).
文摘Zero-and ultralow-field nuclear magnetic resonance(ZULF NMR)has experienced rapid development and provides an excellent tool for diverse research fields ranging from materials science and quantum information processing to fundamental physics.The detection of ZULF NMR signals in samples with natural abundance remains a challenging endeavor,due to the limited sensitivity of NMR detectors and thermal polarization.In this work,we demonstrate a femtotesla(fT)Potassium spin-exchange relaxation-free(SERF)magnetometer designed for ZULF NMR detection.A Potassium vapor cell with high buffer gas pressure and high atomic number density is used in the magnetometer.With absorption spectroscopy and SERF effect,the key parameters of the vapor cell are characterized and applied to optimize the magnetometer sensitivity.To combine our SERF magnetometer and ZULF NMR detection,a custom-made vacuum chamber is employed to keep NMR sample close to the magnetometer cell and protect the sample from undesired heating effects.Gradiometric measurement is performed to greatly reduce the magnetic noise.With the phase calibration applied,the gradiometric measurement achieves 7-fold enhancement in magnetic-field sensitivity compared to the single channel and has a magnetic noise floor of 1.2 fT/Hz^(1/2).Our SERF magnetometer exhibits high sensitivity and is promising to realize ZULF NMR detection of samples with natural abundance.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2016YFA0300600 and 2016YFA0301500)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB07030000)the National Natural Science Foundation of China(Grant No.11474347)
文摘A miniature quad-channel optically pumped atomic magnetometer(OPM) has been developed based on the spinexchange relaxation-free(SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated four SERF magnetometer channels, which provides sufficient spatial resolution for magnetoencephalography(MEG). The four channels share the same laser beam for the best cancellation of common mode noise due to laser fluctuations. With gradient measurement, the sensitivities of the four sensors are better than 6 fT/Hz^(1/2), which is also good enough for MEG measurement. The vapor cell is heated to 160℃ by a novel nonmagnetic current-heating structure. Our sensor with high spatial resolution and compact size is particularly suitable for MEG systems.
基金New Century Program for Excellent Talents of Minis-try of Education of China (NCET-06-0514)China Postdoctoral Science Foundation (20081458, 20080431306)
文摘This article presents a near-Earth satellite orbit estimation method for pico-satellite applications with light-weight and low-power requirements. The method provides orbit information autonomously from magnetometer and sun sensor, with an extended Kalman filter （EKF）. Real-time position/velocity parameters are estimated with attitude independently from two quantities： the measured magnitude of the Earth’s magnetic field, and the measured dot product of the magnetic field vector and the sun vector. To guarantee the filter’s effectiveness, it is recommended that the sun sensor should at least have the same level of accuracy as magnetometer. Furthermore, to reduce filter’s computation expense, simplification methods in EKF’s Jacobian calculations are introduced and testified, and a polynomial model for fast magnetic field calculation is developed. With these methods, 50% of the computation expense in dynamic model propagation and 80% of the computation burden in measurement model calculation can be reduced. Tested with simulation data and compared with original magnetometer-only methods, filter achieves faster convergence and higher accuracy by 75% and 30% respectively, and the suggested simplification methods are proved to be harmless to filter’s estimation performance.
文摘For the vector attitude determination, the traditional optimal algorithms which are based on quaternion estimator（QUEST） measurement noise model are complicated for just two observations. In our application, the magnetometer and accelerometer are not two comparable kinds of sensors and both are not small field-of-view sensors as well. So in this paper a new unit measurement model is derived. According to the Wahba problem, the optimal weights for each measurement are obtained by the error variance researches. Then an improved quaternion Gauss–Newton method is presented and adopted to acquire attitude. Eventually, simulation results and experimental validation employed to test the proposed method demonstrate the usefulness of the improved algorithm.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2016YFA0300600 and 2016YFA0301500)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB07030000 and XDBS32000000)+1 种基金the National Natural Science Foundation of China(Grant Nos.11474347 and 31730039)the Fund from the Ministry of Science and Technology of China(Grant No.2015CB351701)
文摘We observed the steady-state visually evoked potential(SSVEP) from a healthy subject using a compact quad-channel potassium spin exchange relaxation-free(SERF) optically pumped magnetometer(OPM). To this end, 30 s of data were collected, and SSVEP-related magnetic responses with signal intensity ranging from 150 fT to 300 f T were observed for all four channels. The corresponding signal to noise ratio(SNR) was in the range of 3.5–5.5. We then used different channels to operate the sensor as a gradiometer. In the specific case of detecting SSVEP, we noticed that the short channel separation distance led to a strongly diminished gradiometer signal. Although not optimal for the case of SSVEP detection, this set-up can prove to be highly useful for other magnetoencephalography(MEG) paradigms that require good noise cancellation.Considering its compactness, low cost, and good performance, the K-SERF sensor has great potential for biomagnetic field measurements and brain-computer interfaces(BCI).
基金supported by the Program for New Century Excellent Talents in University (No. NCET-06-0514),Chinathe Postdoctoral Science Foundation of China (Nos. 20081458 and 20080431306)
文摘Satellite attitude information is essential for pico-satellite applications requiring light-weight,low-power,and fast-computation characteristics.The objective of this study is to provide a magnetometer-only attitude estimation method for a low-altitude Earth orbit,bias momentum pico-satellite.Based on two assumptions,the spacecraft spherical symmetry and damping of body rates,a linear kinematics model of a bias momentum satellite's pitch axis is derived,and the linear estimation algorithm is developed.The algorithm combines the linear Kalman filter(KF) with the classic three-axis attitude determination method(TRIAD).KF is used to estimate satellite's pitch axis orientation,while TRIAD is used to obtain information concerning the satellite's three-axis attitude.Simulation tests confirmed that the algorithm is suited to the time-varying model errors resulting from both assumptions.The estimate result keeps tracking satellite attitude motion during all damping,stable,and free rotating control stages.Compared with nonlinear algorithms,such as extended Kalman filer(EKF) and square root unscented Kalman filer(SRUKF),the algorithm presented here has an almost equal performance in terms of convergence time and estimation accuracy,while the consumption of computing resources is much lower.
基金supported by the State Key R&D Project (Grant No. 2016YFE0122200)the Civil Aerospace Scientific Research Project “Data calibration and validation for CSES, ”the Central-Level Public Welfare Research Projects of the Institute of Crustal Dynamics Institute, China Earthquake Administration (Grant No. ZDJ2017-21)
文摘Four levels of the data from the search coil magnetometer(SCM) onboard the China Seismo-Electromagnetic Satellite(CSES)are defined and described. The data in different levels all contain three components of the waveform and/or spectrum of the induced magnetic field around the orbit in the frequency range of 10 Hz to 20 kHz; these are divided into an ultra-low-frequency band(ULF,10–200 Hz), an extremely low frequency band(ELF, 200–2200 Hz), and a very low frequency band(VLF, 1.8–20 kHz). Examples of data products for Level-2, Level-3, and Level-4 are presented. The initial results obtained in the commission test phase demonstrated that the SCM was in a normal operational status and that the data are of high enough quality to reliably capture most space weather events related to low-frequency geomagnetic disturbances.
基金Program for New Century Excellent Talents in University (NCET-06-0514)China Postdoctoral Science Foundation (20081458, 20080431306)
文摘In a pico-satellite with small volume, measurements from on-board three-axis magnetometer （TAM） are not accurate, as it can be easily disturbed by other electronic systems. To improve its accuracy, a scheme of compensation methods is introduced in this article. The scheme is based on an improved meast, rement model of pico-satellite TAM, and it mainly consists of three steps. First, in satellite design stage, several techniques are recommended to simplify the afterwards compensations. Then after satellite assembly, TAM ground tests and pre-launch calibration with least-square batch filter are introduced to improve magnetometer performance. At the end, a post-launch calibration with unscented Kalman filter （UKF） is implemented with in-orbit data. The compensation scheme is used in the development of Chinese pico-satellite ZDPS-1A made by Zhejiang University. Results show that with the introduced compensation scheme, the maximum error of ZDPS-1A TAM can be reduced from 80 mG to 6 naG （1 G=10^-4T）.
基金supported by the National Natural Science Foundation of China(Grant No.61227902)
文摘The laser-pumped potassium spin-exchange relaxation free （SERF） magnetometer is the most sensitive detector of magnetic field and has many important applications. We present the experimental results of our potassium SERF magne- tometer. A pump-probe approach is used to identify the unique spin dynamics of the atomic ensemble in the SERF regime. A single channel sensitivity of 8 f.THz-1/2 is achieved with our SERF magnetometer.
基金Project supported by the National Natural Science Foundation of China(Grant No.61227902)the National Key R&D Program of China(Grant No.2017YFB0503100)the Natural Science Foundation of Beijing Municipality,China(Grant No.4162038)
文摘A transverse relaxation determination of spin-exchange relaxation free （SERF） magnetometer based on polarization modulation technique is proposed. Compared with the radio-frequency （RF） excitation and light intensity excitation meth- ods used in SERF magnetometer, the light polarization modulation method has a high stability in low-frequency range, which indicates a more accurate transverse relaxation measurement.
基金supported by the Chinese National Space Administration,and the science team of MOMAG is supported by the Strategic Priority Program(Grant No.XDB41000000)the key Research Program of Frontier Sciences(No.QYZDB-SSW-DQC015)of the Chinese Academy of Sciences.
文摘As one of the seven scientific payloads on board the Tianwen-1 orbiter,the Mars Orbiter Magnetometer(MOMAG)will measure the magnetic fields of and surrounding Mars to study its space environment and the interaction with the solar wind.The instrument consists of two identical triaxial fluxgate magnetometer sensors,mounted on a 3.19 meter-long boom with a seperation of about 90 cm.The dual-magnetometers configuration will help eliminate the magnetic field interference generated by the spacecraft platform and payloads.The sensors are controlled by an electric box mounted inside the orbiter.Each magnetometer measures the ambient vector magnetic field over a wide dynamic range(to 10,000 nT per axis)with a resolution of 1.19 pT.Both magnetometers sample the ambient magnetic field at an intrinsic frequency of 128 Hz,but will operate in a model with alternating frequency between 1 and 32 Hz to meet telemetry allocations.
基金supported by the CNSF project(Grant nos.41574164,41431072)the International Cooperation Project(Grant no.IC201509)of the Chinese Arctic and Antarctic Administration,State Oceanic Administration
文摘A Chinese Antarctic Magnetometer （CAM） chain from Zhongshan Station （ZHS） to Dome-A （DMA） has been established since February 2009. A regular magnetometer is operated at ZHS, and four low power magnetometers are operated along the interior route from ZHS to DMA in the cusp latitude, extending over a distance of 1260 km. These stations fill an important void in the Antarctic magnetometer network. Furthermore, the CAM chain is magnetically conjugated with the Arctic region reaching from the Svalbard archipelago to Daneborg, on the east coast of Greenland. Conjugate measurements using the Arctic and Antarctic magnetometers provide excellent opportunities to investigate phenomena related to the coupling of the solar wind to the magnetosphere and ionosphere, such as magnetic impulse events, flux transfer events, traveling convection vortices and ultra-low frequency waves.
基金Project supported by the National Basic Research Program of China (Grant No.2013CB329501)the National Natural Science Foundation of China (Grant Nos.60925022 and 11125863)the Fundamental Research Funds for the Central Universities (Grant No.2012FZA3001)
文摘We present an experimental and theoretical investigation of the coherent population trapping （CPT） resonance excited on the D1 line of 87Rb atoms by bichromatic linearly polarized laser light. The experimental results show that a lin｜｜lin tran- sition scheme is a promising alternative to the conventional circular-circular transition scheme for an atomic magnetometer. Compared with the circular light transition scheme, linear light accounts for high-contrast transmission resonances, which makes this excitation scheme promising for high-sensitivity magnetometers. We also use linear light and circular light to detect changes of a standard magnetic field, separately.
基金Project supported by"One Hundred Persons Project"of the Chinese Academy of Sciences and the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB04020200)
文摘We constructed a 36-channel magnetocardiography（MCG） system based on low-Tc direct current（DC） superconducting quantum interference device（SQUID） magnetometers operated inside a magnetically shielded room（MSR）. Weakly damped SQUID magnetometers with large Steward–Mc Cumber parameter βc（βc≈ 5）, which could directly connect to the operational amplifier without any additional feedback circuit, were used to simplify the readout electronics. With a flux-to-voltage transfer coefficient V / Φ larger than 420 μV/Φ0, the SQUID magnetometers had a white noise level of about 5.5 f T·Hz-1/2when operated in MSR. 36 sensing magnetometers and 15 reference magnetometers were employed to realize software gradiometer configurations. The coverage area of the 36 sensing magnetometers is 210×210 mm2. MCG measurements with a high signal-to-noise ratio of 40 d B were done successfully using the developed system.
文摘This Inertial Navigation System (INS), Global Positioning System (GPS) and fluxgate magnetometer technologies have been widely used in a variety of positioning and navigation applications. In this paper, a low cost solid state INS/GPS/Magnetometer integrated navigation system has been developed that incorporates measurements from an Inertial Navigation System (INS), Global Positioning System (GPS) and fluxgate magnetometer (Mag.) to provide a reliable complete navigation solution at a high output rate. The body attitude estimates, especially the heading angle, are fundamental challenges in a navigation system. Therefore targeting accurate attitude estimation is considered a significant contribution to the overall navigation error. A better estimation of the body attitude estimates leads to more accurate position and velocity estimation. For that end, the aim of this research is to exploit the magnetometer and accelerometer data in the attitude estimation technique. In this paper, a Scaled Unscented Kalman Filter (SUKF) based on the quaternion concept is designed for the INS/GPS/Mag integrated navigation system under large attitude error conditions. Simulation and experimental results indicate a satisfactory performance of the newly developed model.
