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 S m −1 level is still missing. In this Letter, we use an 87 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 S m −1 . We measure a signal-to-noise ratio of 2.7 at 2 MHz for 0.9 S m −1 , 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.Recent years have seen a vast increase in the applications of quantum technologies and, in particular, atomic magnetometers 1 to the biomedical field.Notable examples include magnetocardiography 2-5 and magnetoencephalography 4,6,7 . Applications for monitoring the reactivity of the nervous system have been also reported 8 . In all cases, the superior performance of the atomic magnetometers pushes existing technologies and diagnostic methods towards their fundamental limits.However, mapping the electric conductivity of biological tissues -and in particular of the human heart -is still an open issue. To date, no diagnostic tool is capable of non-invasively mapping the conductivity of cardiac tissue 9 . Current investigations require the invasive recording of activation potentials via surgically introduced electrodes. This does not allow direct mapping of conductivity, and presents issues due to the inconsistent adhesion of electrodes to the inner surface of the beating heart 10 .Electromagnetic induction imaging -often referred to as magnetic induction tomography 11 to highlight its tomographic capabilities -has been proposed as a diagnostic tool for various conditions characterized by a variation or an anomaly in electric conduction [12][13][14][15] . With this technique, eddy currents are excited in the specimen under investigation by an AC magnetic field (primary field). The response, containing information about the electric conductivity, electric permittivity, and magnetic permeability of the specimen, is detected via the magnetic field generated by the eddy currents (secondary field). One of the main limitations of this approach is the limited sensitivity of the magnetic field sensors in use. Therefore, until recently, detection and imaging were limited to relatively large samples 16 , in most cases well above usea) Electronic mail: l.marmugi@ucl.ac.uk ful volumes for medical applications. This issue was potentially solved by the demonstration of electromagnetic induction imaging with atomic magnetometers [17][18][19] . The higher sensitivity of the core sensor paved the path ...
We demonstrate imaging of ferromagnetic carbon steel samples and we detect the thinning of their profile with a sensitivity of 0.1 mm using a Cs radio-frequency atomic magnetometer. Images are obtained at room temperature, in magnetically unscreened environments. By using a dedicated arrangement of the setup and active compensation of background fields, the magnetic disturbance created by the samples' magnetization is compensated. Proof-of-concept demonstrations of non-destructive structural evaluation in the presence of concealing conductive barriers are also provided. Relevant impact for steelwork inspection and health and usage monitoring without disruption of operation is envisaged, with direct benefit for industry, from welding in construction, to pipelines inspection and corrosion under insulation in the energy sector.
We demonstrate the penetration of thick metallic and ferromagnetic barriers for imaging of conductive targets underneath. Our system is based on an Rb radio-frequency atomic magnetometer operating in electromagnetic induction imaging modality in an unshielded environment. Detrimental effects, including unpredictable magnetic signatures from ferromagnetic 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.
We report on a single-channel rubidium radio-frequency atomic magnetometer operating in unshielded environments and near room temperature with a measured sensitivity of 130 fT/ . We demonstrate consistent, narrow-bandwidth operation across the kHz-MHz band, corresponding to three orders of magnitude of the 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 in the 50 Hz noise contribution by an order of magnitude. The small effective sensor volume, 57 mm, 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.
Current-injection quantum-entangled-pair emitter using droplet epitaxial quantum dots on GaAs(111)A
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