1,017 research outputs found
Electromagnetic Imaging with Atomic Magnetometers: A Novel Approach to Security and Surveillance
We describe our research programme on the use of atomic magnetometers to
detect conductive objects via electromagnetic induction. The extreme
sensitivity of atomic magnetometers at low frequencies, up to seven orders of
magnitude higher than a coil-based system, permits deep penetration through
different media and barriers, and in various operative environments. This
eliminates the limitations usually associated with electromagnetic detection.Comment: 5 pages, 5 figure
Measurement and control systems for an imaging electromagnetic flow meter
Electromagnetic flow metres based on the principles of Faraday's laws of induction have been used successfully in many industries. The conventional electromagnetic flow metre can measure the mean liquid velocity in axisymmetric single phase flows. However, in order to achieve velocity profile measurements in single phase flows with non-uniform velocity profiles, a novel imaging electromagnetic flow metre (IEF) has been developed which is described in this paper. The novel electromagnetic flow metre which is based on the âweight valueâ theory to reconstruct velocity profiles is interfaced with a âMicrorobotics VM1â microcontroller as a stand-alone unit. The work undertaken in the paper demonstrates that an imaging electromagnetic flow metre for liquid velocity profile measurement is an instrument that is highly suited for control via a microcontroller
Forward and inverse problems in fundamental and applied magnetohydrodynamics
This Minireview summarizes the recent efforts to solve forward and inverse
problems as they occur in different branches of fundamental and applied
magnetohydrodynamics. As for the forward problem, the main focus is on the
numerical treatment of induction processes, including self-excitation of
magnetic fields in non-spherical domains and/or under the influence of
non-homogeneous material parameters. As an important application of the
developed numerical schemes, the functioning of the von-K\'{a}rm\'{a}n-sodium
(VKS) dynamo experiment is shown to depend crucially on the presence of
soft-iron impellers. As for the inverse problem, the main focus is on the
mathematical background and some first practical applications of the
Contactless Inductive Flow Tomography (CIFT), in which flow induced magnetic
field perturbations are utilized for the reconstruction of the velocity field.
The promises of CIFT for flow field monitoring in the continuous casting of
steel are substantiated by results obtained at a test rig with a low melting
liquid metal. While CIFT is presently restricted to flows with low magnetic
Reynolds numbers, some selected problems of non-linear inverse dynamo theory,
with possible application to geo- and astrophysics, are also discussed.Comment: 15 pages, 4 figures, accepted for publication in European Physical
Journal Special Topic
Magnetic Induction Imaging with Optical Atomic Magnetometers: Towards Applications to Screening and Surveillance
We propose a new approach, based on optical atomic magnetometers and magnetic induction tomography (MIT), for remote and non-invasive detection of conductive targets. Atomic magnetometers overcome the main limitations of conventional MIT instrumentation, in particular their poor low-frequency sensitivity, their large size and their limited scalability. Moreover, atomic magnetometers have been proven to reach extremely high sensitivities, with an improvement of up to 7 orders of magnitude in the 50 MHz to DC band, with respect to a standard pick-up coil of the same size. In the present scheme, an oscillating magnetic field induces eddy currents in a conductive target and laser-pumped atomic magnetometers, either stand-alone or in an array, detect the response of the objects. A phase-sensitive detection scheme rejects the background, allowing remote detection of the secondary field and, thus, mapping of objects, hidden in cargos, underwater or underground. The potential for extreme sensitivity, miniaturization, dynamic range and array operation paves the way to a new generation of non-invasive, active detectors for surveillance, as well as for real-time cargo screening. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
Electromagnetic Induction Imaging with Atomic Magnetometers
Electromagnetic induction imaging (EMI) is a technique for non-invasively mapping the passive electromagnetic properties of materials. It involves the active probing of samples with a radio-frequency magnetic field and recording the details of the magnetic field produced by the induced eddy current response. The performance of an EMI system is ultimately determined by the choice of magnetic field sensor used in the measurement. The sensorâs sensitivity, range of operation frequency, and sensing volume are all crucial characteristics when considering the imaging platformâs capabilities. Atomic magnetometers (AMs) â based on the coherent precession of a polarised alkali atomic vapour â currently rate amongst the most sensitive devices for magnetic field measurements. Radio-frequency atomic magnetometers (RF-AMs) are ultra-sensitive detectors of oscillating magnetic fields across a broad range of frequencies. As such, they are ideally suited to EMI applications. This work presents the development of EMI systems based on RF-AMs. The imaging performance and a wide range of applications are experimentally demonstrated. The continuous development of a single-channel rubidium RF-AM is described. The final device operates in unshielded environments and near room temperature with a measured sensitivity of 55 fT/âHz, a photon-shot noise limit of 10 fT/âHz, and a linewidth of 36 Hz. Tunability of the device is proven by consistent, narrow-linewidth operation across the kHz â MHz band â operating in magnetic fields significantly greater than previous AM designs. The sensor was developed with a small effective sensor volume, which increases the spatial resolution of the imaging. High-resolution EMI is performed across a broad range of materials. This spans the first EMI images with an RF-AM at 6x107 S/m to low-conductivity, non-metallic samples at 500 S/m. Typically, sample volumes are of a few cm3 and with an imaging resolution around 1 mm. These numbers make EMI with AMs (EMI-AM) suitable for numerous applications. Techniques â including multi-frequency image analysis â are employed to discriminate sample properties. Further work developed novel image reconstruction approaches â based on machine learning â to maximise the amount of information that can be extracted from EMI images. Finally, the potential of biomedical imaging is discussed and its feasibility verified by simulating the application of EMI-AM to imaging the conductivity of the heart
Ultrasensitive 3He magnetometer for measurements of high magnetic fields
We describe a 3He magnetometer capable to measure high magnetic fields (B >
0.1 Tesla) with a relative accuracy of better than 10^-12. Our approach is
based on the measurement of the free induction decay of gaseous, nuclear spin
polarized 3He following a resonant radio frequency pulse excitation. The
measurement sensitivity can be attributed to the long coherent spin precession
time T2* being of order minutes which is achieved for spherical sample cells in
the regime of motional narrowing where the disturbing influence of field
inhomogeneities is strongly suppressed. The 3He gas is spin polarized in-situ
using a new, non-standard variant of the metastability exchange optical
pumping. We show that miniaturization helps to increase T2* further and that
the measurement sensitivity is not significantly affected by temporal field
fluctuations of order 10^-4.Comment: 27 pages, 7 figure
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