Electromagnetic induction imaging with atomic magnetometers: Progress and perspectives

Electromagnetic induction imaging (EMI) allows mapping of the conductivity of target objects and, when combined with appropriate algorithms, the generation of full 3D tomographic images. Despite its tremendous potential, and the wealth of possible applications, the use of EMI has essentially been limited to eddy current testing for monitoring of corrosion and welding in metallic structures. The present work reviews the factors hindering the progress of electromagnetic induction imaging and highlights how the use of atomic magnetometers overcame some of them, opening the path to real world applications of EMI. Perspectives for further developments are discussed

Laser driven self-assembly of shape-controlled potassium nanoparticles in porous glass

We observe growth of shape-controlled potassium nanoparticles inside a random network of glass nanopores, exposed to low-power laser radiation. Visible laser light plays a dual role: it increases the desorption probability of potassium atoms from the inner glass walls and induces the self-assembly of metastable metallic nanoparticles along the nanopores. By probing the sample transparency and the atomic light-induced desorption flux into the vapour phase, the dynamics of both cluster formation/evaporation and atomic photo-desorption processes are characterized. Results indicate that laser light not only increases the number of nanoparticles embedded in the glass matrix but also influences their structural properties. By properly choosing the laser frequency and the illumination time, we demonstrate that it is possible to tailor the nanoparticles'shape distribution. Furthermore, a deep connection between the macroscopic behaviour of atomic desorption and light-assisted cluster formation is observed. Our results suggest new perspectives for the study of atom/surface interaction as well as an effective tool for the light-controlled reversible growth of nanostructures.Comment: 14 pages,6 figures, http://iopscience.iop.org/1612-202X/11/8/085902

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

Optical Magnetic Induction Tomography of the Heart

Atrial Fibrillation (AF) affects a significant fraction of the ageing population, causing a high level of morbidity and mortality. Despite its significance, the causes of AF are still not uniquely identified. This, combined with the lack of precise diagnostic and guiding tools, makes the clinical treatment of AF sub-optimal. We identify magnetic induction tomography as the most promising technique for the investigation of the causes of fibrillation and for its clinical practice. We therefore propose a novel optical instrument based on optical atomic magnetometers, fulfilling the requirements for diagnostic mapping of the heart’s conductivity. The feasibility of the device is here discussed in view of the final application. Thanks to the potential of atomic magnetometers for miniaturisation and extreme sensitivity at room temperature, a new generation of compact and non-invasive diagnostic instrumentation, with both bedside and intra-operative operation capability, is envisioned. Possible scenarios both in clinical practice and biomedical research are then discussed. The flexibility of the system makes it promising also for application in other fields, such as neurology and oncology

Exploring the limits of magnetic field focusing: Simple planar geometries

© 2020 The Authors This work explores the possibility to arbitrarily shape in space low-frequency magnetic fields using a recently introduced synthesization technique (Choi et al., 2016). We investigate the ability to focus a magnetic field on a two-dimensional region using magnetic field sources distributed on a parallel plane. In agreement with the recent work, arbitrarily tight focusing is demonstrated possible. However, our results indicate that this comes at the cost of exponentially large power requirements and also leads to exponentially large fields in the region between the source and target planes. This imposes strict limitations on the application of the technique. In addition, we also demonstrate that arbitrary steering of the magnetic field focus within the target region is possible, without any additional cost in terms of power requirement. In exploring the potential for magnetic field synthesis, our findings highlight limits to be considered for practical applications, as well as promising capabilities not identified before

Through-barrier electromagnetic imaging with an atomic magnetometer

We demonstrate the penetration of thick metallic and ferromagnetic barriers for imaging of conductive targets underneath. Our system is based on an 85Rb radio-frequency atomic magnetometer operating in electromagnetic induction imaging modality in an unshielded environment. Detrimental effects, including unpredictable magnetic signatures from ferromag- netic screens and variations in the magnetic background, are automatically compensated by active compensation coils controlled by servo loops. We exploit the tunability and low-frequency sensitivity of the atomic magnetometer to directly image multiple conductive targets concealed by a 2.5 mm ferromagnetic steel shield and/or a 2.0 mm aluminium shield, in a single scan. The performance of the atomic magnetometer allows imaging without any prior knowledge of the barriers or the targets, and without the need of background subtraction. A dedicated edge detection algorithm allows automatic estimation of the targets’ size within 3.3 mm and of their position within 2.4 mm. Our results prove the feasibility of a compact, sensitive and automated sensing platform for imaging of concealed objects in a range of applications, from security screening to search and rescue

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

Optical atomic magnetometry for magnetic induction imaging of the heart

We report on the use of radio-frequency optical atomic magnetometers for magnetic induction tomography measurements. We demonstrate the imaging of dummy targets of varying conductivities placed in the proximity of the sensor, in an unshielded environment at room-temperature and without background subtraction. The images produced by the system accurately reproduce the characteristics of the actual objects. Furthermore, we perform finite element simulations in order to assess the potential for measuring low-conductivity biological tissues with our system. Our results demonstrate the feasibility of an instrument based on optical atomic magnetometers for magnetic induction tomography imaging of biological samples, in particular for mapping anomalous conductivity in the heart

Machine Learning Based Localization and Classification with Atomic Magnetometers

We demonstrate identification of position, material, orientation, and shape of objects imaged by a ⁸⁵Rb atomic magnetometer performing electromagnetic induction imaging supported by machine learning. Machine learning maximizes the information extracted from the images created by the magnetometer, demonstrating the use of hidden data. Localization 2.6 times better than the spatial resolution of the imaging system and successful classification up to 97% are obtained. This circumvents the need of solving the inverse problem and demonstrates the extension of machine learning to diffusive systems, such as low-frequency electrodynamics in media. Automated collection of task-relevant information from quantum-based electromagnetic imaging will have a relevant impact from biomedicine to security

A radio-frequency Bose–Einstein condensate magnetometer

We report on a radio frequency magnetometer employing a Bose–Einstein condensate of 87Rb atoms held in a dipole trap. An AC sensitivity of [Formula: see text] is achieved at a probing volume of [Formula: see text], leading to a volume-normalized sensitivity of [Formula: see text]. At larger probing volumes with the atoms released from the magnetic trap used in the initial phase of the evaporation sequence, the AC sensitivity is improved to [Formula: see text], allowing a two-mode approach for applications requiring improved sensitivity. Immediate application in high-resolution electromagnetic induction imaging is expected when compared to performance of other induction-based imaging platforms