76 research outputs found
Sub-picotesla widely tunable atomic magnetometer operating at room-temperature in unshielded environments
We report on a single-channel rubidium radio-frequency atomic magnetometer
operating in un-shielded environments and near room temperature with a measured
sensitivity of 130 fT/\sqrt{Hz}. We demonstrate consistent, narrow-bandwidth
operation across the kHz - MHz band, corresponding to three orders of magnitude
of magnetic field amplitude. A compensation coil system controlled by a
feedback loop actively and automatically stabilizes the magnetic field around
the sensor. We measure a reduction of the 50 Hz noise contribution by an order
of magnitude. The small effective sensor volume, 57 mm^3, increases the spatial
resolution of the measurements. Low temperature operation, without any magnetic
shielding, coupled with the broad tunability, and low beam power, dramatically
extends the range of potential field applications for our device.Comment: Main text: 6 pages, 9 figures. Supplementary material: 3 pages, 3
figures. Published version can be found at
https://aip.scitation.org/doi/full/10.1063/1.5026769 . V2: Added journal
layout, minor typos fixed. Content unchange
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 sensor’s sensitivity, range of operation frequency, and sensing volume are all crucial characteristics when considering the imaging platform’s capabilities. Atomic magnetometers (AMs) – based on the coherent precession of a polarised alkali atomic vapour – 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/√Hz, a photon-shot noise limit of 10 fT/√Hz, and a linewidth of 36 Hz. Tunability of the device is proven by consistent, narrow-linewidth operation across the kHz – MHz band – 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 – including multi-frequency image analysis – are employed to discriminate sample properties. Further work developed novel image reconstruction approaches – based on machine learning – 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
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
Electromagnetic induction imaging with a radio-frequency atomic magnetometer
We report on a compact, tunable, and scalable to large arrays imaging device,
based on a radio-frequency optically pumped atomic magnetometer operating in
magnetic induction tomography modality. Imaging of conductive objects is
performed at room temperature, in an unshielded environment and without
background subtraction. Conductivity maps of target objects exhibit not only
excellent performance in terms of shape reconstruction but also demonstrate
detection of sub-millimetric cracks and penetration of conductive barriers. The
results presented here demonstrate the potential of a future generation of
imaging instruments, which combine magnetic induction tomography and the
unmatched performance of atomic magnetometers.Comment: 5 pages, 5 figure
Sub-Sm electromagnetic induction imaging with an unshielded atomic magnetometer
Progress in electromagnetic induction imaging with atomic magnetometers has
brought its domain to the edge of the regime useful for biomedical imaging.
However, a demonstration of imaging below the required 1 Sm level is
still missing. In this Letter, we use an Rb radio-frequency atomic
magnetometer operating near room temperature in an unshielded environment to
image calibrated solutions mimicking the electric conductivity of live tissues.
By combining the recently introduced near-resonant imaging technique with a
dual radio-frequency coil excitation scheme, we image 5 mL of solutions down to
0.9 Sm. We measure a signal-to-noise ratio of 2.7 at 2 MHz for 0.9
Sm, increased up to 7.2 with offline averaging. Our work is an
improvement of 50 times on previous imaging results, and demonstrates the
sensitivity and stability in unshielded environments required for imaging
biological tissues, in particular for the human heart.Comment: 5 pages, 5 figures. V2: minor additions, typos fixed. Physics and
results unchanged. Published version can be found at
https://aip.scitation.org/doi/10.1063/5.000214
Active Underwater Detection with an Array of Atomic Magnetometers
We report on a 2x2 array of radio-frequency atomic magnetometers in magnetic
induction tomography configuration. Active detection, localization, and
real-time tracking of conductive, non-magnetic targets are demonstrated in air
and saline water. Penetration in different media and detection are achieved
thanks to the sensitivity and tunability of the sensors, and to the active
nature of magnetic induction probing. We obtained a 100% success rate for
automatic detection and 93% success rate for automatic localization in air and
water, up to 190 mm away from the sensors' plane (100 mm underwater). We
anticipate magnetic induction tomography with arrays of atomic magnetometers
finding applications in civil engineering and maintenance, oil&gas industry,
geological surveys, marine science, archeology, search and rescue, and security
and surveillance.Comment: 6 pages, 7 figures. Published version can be found at
https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-10-234
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