MRI with an atomic magnetometer suitable for practical imaging applications

Conventionally implemented MRI is performed in a strong magnetic field, typically >1 T. The high fields, however, can lead to many limitations. To overcome these limitations, ultra-low field (ULF) [or microtesla] MRI systems have been proposed and implemented. To-date such systems rely on low-Tc Superconducting Quantum Interference Devices (SQUIDs) leading to the requirement of cryogens. In this letter, we report ULF–MRI obtained with a non-cryogenic atomic magnetometer. This demonstration creates opportunities for developing inexpensive and widely applicable MRI scanners.     

基于滚动时域估计的飞行器姿态估计及三轴磁强计在线校正

针对飞行器姿态估计以及三轴磁强计在线校正问题, 提出了一种实时滚动时域估计算法. 首先, 为了解决在卡尔曼滤波框架下系统约束不能显式求解的问题, 设计了滚动时域估计滤波算法. 该算法将飞行器姿态估计问题转化为优化问题, 显式求解四元数归一化性质, 缩小搜索空间的同时提高了搜索效率和精度. 其次, 滤波时域窗内应用高斯-牛顿迭代法求解最优状态估计值, 满足了实时性要求. 最后, 在没有增加系统状态维数的情况下, 在线求解了三轴磁强计校正参数, 保证了磁强计量测值以矢量形式输入系统. 仿真结果表明, 由于合理地利用了历史信息, 该方法精度较高, 且对初始误差、系统误差均不敏感, 具有一定鲁棒性.     

Characterization of magnetic core-shell nanoparticles by fluxgate magnetorelaxometry, ac susceptibility, transmission electron microscopy and photon correlation spectroscopy—A comparative study

We have compared the structure parameters of magnetic core-shell nanoparticles determined from fluxgate magnetorelaxometry measurements applying the moment superposition model with the results from other methods. For the characterization of the magnetic cores, the nanoparticles are immobilized by freeze-drying. The core size distribution estimated for superparamagnetic Fe₃O₄ magnetic nanoparticles (MNPs) with polyacrylic acid shell agrees well with that from transmission electron microscopy measurements. The distribution of hydrodynamic diameters of nanoparticle suspensions estimated from magnetorelaxometry measurements is in good agreement with that obtained from ac susceptibility and photon correlation spectroscopy measurements. Advantages of magnetorelaxometry compared to the other two integral techniques are that it is fast and the signal is less dominated by larger particles.     

圆锥运动下磁场辅助角速度测量方法与实验

利用磁场传感器可辅助载体进行角速度测量.在用于飞行载体时,由于载体通常伴随有圆锥运动,并且载体自身会对内部磁场产生干扰,使磁场传感器输出产生畸变,从而导致利用磁场辅助测量的载体角速度的误差较大.针对这个问题,提出了一种基于实时误差补偿的在圆锥运动及磁场干扰影响条件下利用磁场辅助进行角速度测量的方法.该方法利用载体过去1周旋转的数据,实时对圆锥运动与磁场干扰进行补偿,然后根据补偿结果计算当前载体的角速度.当载体角速度越大时,精度越高.通过飞行实验对该方法进行了验证,实验结果表明,在角速度大于300 (°)/s时,角速度误差小于1(°)/s.     

用于近代物理实验教学的振动样品磁强计

简述了振动样品磁强计的工作原理,采用电磁驱动方式自制了振动样品磁强计.利用该仪器测试了各向同性永磁钡铁氧体的永磁特性,与商业振动样品磁强计的测量结果相比,测量误差小于1%,可用于近代物理实验教学.     

静电加速度计悬浮质量块质心偏移量在轨标定

高精度静电加速度计已广泛地应用于航天任务中,用于测量作用于航天器的非引力加速度。如果静电加速度计悬浮质量块的质心与航天器的质心安装有偏差时,重力梯度力、姿态耦合产生的干扰加速度,静电加速度计控制系统引入的干扰加速度等干扰力会夹杂在测量数据中。针对这一问题,研究了航天器小质量特性变化情况下,当静电加速度计处于动态设计良好并进入稳态后,利用静电加速度计、陀螺仪和磁强计作为敏感元件,基于非线性卡尔曼滤波理论的静电加速度计悬浮质量块质心偏移量的在轨标定。仿真结果表明,该方案的精度J向可以达到0．1mm,Y和Z向能达到0．04mm。     

Structural and magnetic properties of CoxZn1−xFe2O4 nanocrystals synthesized by microwave method

Microwave assisted combustion method was used to produce nanocrystalline cobalt doped zinc ferrite, Co_xZn_1−xFe₂O₄, from stoichiometric mixture of (Co(NO₃)₂·6H₂O), (Fe(NO₃)₃·9H₂O), (Zn(NO₃)₂·6H₂O), and urea (CO(NH₂)₂) as a fuel. The structural, morphological and magnetic properties of the products were determined by X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) respectively. The average crystallite sizes obtained from XRD were between 35 and 39 nm. Magnetization measurements indicate that samples with less Co content have superparamagnetic behavior at room temperature. When the Co substitution increases the saturation magnetization due to the magnetic character of the Co cations substituting the non-magnetic Zn and coercivity also increase due to anisotropic nature of cobalt. The Co_xZn_1−xFe₂O₄ nanocrystals exhibit typical features of an assembly of magnetic particles with a distribution of blocking temperatures and indicate the spin-glass behavior.     

抽运-检测型原子磁力仪对电流源噪声的测量

用于在宽量程范围内标定原子磁力仪的灵敏度的复现磁场通常由精密电流源和标准线圈产生,电流源噪声将直接影响原子磁力仪在宽量程范围内标定的灵敏度.本文基于抽运-检测型原子磁力仪首先提出抑制复现磁场漂移的磁补偿方法,其次开展宽量程范围内电流源的噪声和原子磁力仪的灵敏度之间依赖关系的研究.研究结果表明,抽运-检测型原子磁力仪的灵敏度主要由电流源噪声决定,因此可用特定磁场下的灵敏度估算电流源在对应输出电流条件下的电流噪声.本文研究对弱磁传感器灵敏度指标的标定、高精度电流源的研制、磁感应强度计量和电流计量的协同发展都具有参考价值.