7,610 research outputs found
Accurate Estimation of a Coil Magnetic Dipole Moment
In this paper, a technique for accurate estimation of the moment of magnetic
dipole is proposed. The achievable accuracy is investigated, as a function of
measurement noise affecting estimation of magnetic field cartesian components.
The proposed technique is validated both via simulations and experimentally.Comment: Preprin
Removal of electrostatic artifacts in magnetic force microscopy by controlled magnetization of the tip: application to superparamagnetic nanoparticles
Magnetic force microscopy (MFM) has been demonstrated as valuable technique for the
characterization of magnetic nanomaterials. To be analyzed by MFM techniques, nanomaterials
are generally deposited on flat substrates, resulting in an additional contrast in MFM images due to
unavoidable heterogeneous electrostatic tip-sample interactions, which cannot be easily distinguished
from the magnetic one. In order to correctly interpret MFM data, a method to remove the electrostatic
contributions from MFM images is needed. In this work, we propose a new MFM technique, called
controlled magnetization MFM (CM-MFM), based on the in situ control of the probe magnetization
state, which allows the evaluation and the elimination of electrostatic contribution in MFM images. The
effectiveness of the technique is demonstrated through a challenging case study, i.e., the analysis of
superparamagnetic nanoparticles in absence of applied external magnetic field. Our CM-MFM technique
allowed us to acquire magnetic images depurated of the electrostatic contributions, which revealed
that the magnetic field generated by the tip is sufficient to completely orient the superparamagnetic
nanoparticles and that the magnetic tip-sample interaction is describable through simple models once
the electrostatic artifacts are removed
AE-C attitude determination and control prelaunch analysis and operations plan
A description of attitude control support being supplied by the Mission and Data Operations Directorate is presented. Included are descriptions of the computer programs being used to support the missions for attitude determination, prediction, and control. In addition, descriptions of the operating procedures which will be used to accomplish mission objectives are provided
Enhanced real-time pose estimation for closed-loop robotic manipulation of magnetically actuated capsule endoscopes
Pose estimation methods for robotically guided magnetic actuation of capsule endoscopes have recently enabled trajectory following and automation of repetitive endoscopic maneuvers. However, these methods face significant challenges in their path to clinical adoption including the presence of regions of magnetic field singularity, where the accuracy of the system degrades, and the need for accurate initialization of the capsule's pose. In particular, the singularity problem exists for any pose estimation method that utilizes a single source of magnetic field if the method does not rely on the motion of the magnet to obtain multiple measurements from different vantage points. We analyze the workspace of such pose estimation methods with the use of the point-dipole magnetic field model and show that singular regions exist in areas where the capsule is nominally located during magnetic actuation. Since the dipole model can approximate most magnetic field sources, the problem discussed herein pertains to a wider set of pose estimation techniques. We then propose a novel hybrid approach employing static and time-varying magnetic field sources and show that this system has no regions of singularity. The proposed system was experimentally validated for accuracy, workspace size, update rate and performance in regions of magnetic singularity. The system performed as well or better than prior pose estimation methods without requiring accurate initialization and was robust to magnetic singularity. Experimental demonstration of closed-loop control of a tethered magnetic device utilizing the developed pose estimation technique is provided to ascertain its suitability for robotically guided capsule endoscopy. Hence, advances in closed-loop control and intelligent automation of magnetically actuated capsule endoscopes can be further pursued toward clinical realization by employing this pose estimation system
A simplex method for the calibration of a MEG device
MagnetoEncephaloGraphy (MEG) devices are helmet-shaped arrays of sensors that measure the tiny magnetic fields produced by neural currents. As they operate at low temperature, they are typically immersed in liquid helium. However, during the cooling process the sensor position and shape can change, with respect to nominal values, due to thermal stress. This implies that an accurate sensor calibration is required before a MEG device is utilized in either neuroscientific research or clinical workflow. Here we describe a calibration scheme developed for the optimal use of a MEG system recently realized at the "Istituto di Cibernetica e Biofisica" of the Italian CNR. To achieve the calibration goal a dedicated magnetic source is used (calibration device) and the geometric parameters of the sensors are determined through an optimisation procedure, based on the Nelder-Mead algorithm, which maximises the correlation coefficient between the predicted and the recorded magnetic field. Then the sensitivity of the sensors is analytically estimated. The developed calibration procedure is validated with synthetic data mimicking a real scenario
Magnetic sensors and gradiometers for detection of objects
Disertační práce popisuje vývoj nových detekčních zařízení s anizotropními magnetorezistoryThis thesis describes development of innovative sensor systems based on anisotropi
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