COSMA: Coherent Optics Sensors for Medical Application is an European Marie Curie Project running from 2012 to March 2016, with the participation of 10 teams from Armenia, Bulgaria, India, Israel, Italy, Poland, Russia, UK, USA. The main objective was to focus theoretical and experimental research on biomagnetism phenomena, with the specific aim to develop all-optical sensors dedicated to their detection and suitable for applications in clinical diagnostics. The paper presents some of the most recent results obtained during the exchange visits of the involved scientists, after an introduction about the phenomenon which is the pillar of this kind of research and of many other new fields in laser spectroscopy, atomic physics, and quantum optics: the dark resonance.
An electromagnetic induction system, suitable for 2D imaging of metallic samples of different electrical conductivities,
has been developed. The system is based on a parallel LCR circuit comprising a ferrite-cored coil (7.8 mm x 9.5 mm,
L=680 μH at 1 KHz), a variable resistor and capacitor. The working principle of the system is based on eddy current
induction inside a metallic sample when this is introduced into the AC magnetic field created by the coil. The inductance
of the LCR circuit is modified due to the presence of the sample, to an extent that depends on its conductivity. Such
modification is known to increase when the system is operated at its resonant frequency. Characterizing different metals
based on their values of conductivity is therefore possible by utilizing a suitable system operated at resonance. Both
imaging and material characterization were demonstrated by means of the proposed electromagnetic induction technique.
Furthermore, the choice of using a system with an adjustable resonant frequency made it possible to select resonances
that allow magnetic-field penetration through conductive screens. Investigations on the possibility of imaging concealed
metals by penetrating such shields have been carried out. A penetration depth of δ~3 mm through aluminium (Al) was
achieved. This allowed concealed metallic samples- having conductivities ranging from 0.54 to 59.77 MSm<sup>-1</sup> and hidden
behind 1.5-mm-thick Al shields- to be imaged. Our results demonstrate that the presence of the concealed metallic
objects can be revealed. The technique was thus shown to be a promising detection tool for security applications.
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.
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.
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.
A new electromagnetic induction imaging system is presented which is capable of imaging metallic samples of different conductivities. The system is based on a parallel LCR circuit made up of a cylindrical ferrite-cored coil and a capacitor bank. An AC current is applied to the coil, thus generating an AC magnetic field. This field is modified when a conductive sample is placed within the magnetic field, as a consequence of eddy current induction inside the sample. The electrical properties of the LCR circuit, including the coil inductance, are modified due to the presence of this metallic sample. Position-resolved measurements of these modifications should then allow imaging of conductive objects as well as enable their characterization. A proof-of-principle system is presented in this paper. Two imaging techniques based on Q-factor and resonant frequency measurements are presented. Both techniques produced conductivity maps of 14 metallic objects with different geometries and values of conductivity ranging from 0.54х10<sup>6</sup> to 59.77х10<sup>6</sup> S/m. Experimental results highlighted a higher sensitivity for the Q-factor technique compared to the resonant frequency one; the respective measurements were found to vary within the following ranges: ΔQ=[-11,-2]%, Δf=[-0.3,0.7]%. The analysis of the images, conducted using a Canny edge detection algorithm, demonstrated the suitability of the Q-factor technique for accurate edge detection of both magnetic and non-magnetic metallic samples.