Magnetoencephalography (MEG) is a powerful technique for functional neuroimaging, offering a non-invasive window on brain electrophysiology. MEG systems have traditionally been based on cryogenic sensors which detect the small extracranial magnetic fields generated by synchronised current in neuronal assemblies, however, such systems have fundamental limitations. In recent years, non-cryogenic quantum-enabled sensors, called optically-pumped magnetometers (OPMs), in combination with novel techniques for accurate background magnetic field control, have promised to lift those restrictions offering an adaptable, motion-robust MEG system, with improved data quality, at reduced cost. However, OPM-MEG remains a nascent technology, and whilst viable systems exist, most employ small numbers of sensors sited above targeted brain regions. Here, building on previous work, we construct a wearable OPM-MEG system with ‘whole-head’ coverage based upon commercially available OPMs, and test its capabilities to measure alpha, beta and gamma oscillations. We design two methods for OPM mounting; a flexible (EEG-like) cap and rigid (additively-manufactured) helmet. Whilst both designs allow for high quality data to be collected, we argue that the rigid helmet offers a more robust option with significant advantages for reconstruction of field data into 3D images of changes in neuronal current. Using repeat measurements in two participants, we show signal detection for our device to be highly robust. Moreover, via application of source-space modelling, we show that, despite having 5 times fewer sensors, our system exhibits comparable performance to an established cryogenic MEG device. While significant challenges still remain, these developments provide further evidence that OPM-MEG is likely to facilitate a step change for functional neuroimaging.
Part I of this study covered ballistic tests, in which both solid (steel) and fragmenting (ice) spherical projectiles were fired at specimens of carbon-fibre-reinforced polymer (CFRP) composite. The velocity of impacts varied from 70 to 90 m/s for the solid projectiles and from 300 to 500 m/s for the fragmenting projectiles, resulting in three consistent and comparable levels of structural damage for both types of projectiles. The observed dynamic deformation behaviour and resultant damage were examined using a combination of non-invasive analysis techniques. The focus of this Part II is on the development of a mesoscale modelling strategy for CFRP employing a phenomenological continuum-damage approach. The developed model was validated against the data from original ballistic-impact experiments, demonstrating accurate predictions of both deformation behaviour and observed resultant damage of tested specimens for the various experimental loading conditions without modification of the modelling parameters.
Magnetoencephalography (MEG) is a powerful technique for functional neuroimaging, offering a noninvasive window on brain electrophysiology. MEG systems have traditionally been based on cryogenic sensors which detect the small extracranial magnetic fields generated by synchronised current in neuronal assemblies, however such systems have fundamental limitations. In recent years quantum-enabled devices, called opticallypumped magnetometers (OPMs), have promised to lift those restrictions, offering an adaptable, motion-robust MEG device, with improved data quality, at reduced cost. However, OPM-MEG remains a nascent technology, and whilst viable systems exist, most employ small numbers of sensors sited above targeted brain regions. Here, building on previous work, we construct a wearable OPM-MEG system with 'whole-head' coverage based upon commercially available OPMs, and test its capabilities to measure alpha, beta and gamma oscillations. We design two methods for OPM mounting; a flexible (EEG-like) cap and rigid (additively-manufactured) helmet.Whilst both designs allow for high quality data to be collected, we argue that the rigid helmet offers a more robust option with significant advantages for reconstruction of field data into 3D images of changes in neuronal current. Using repeat measurements in two participants, we show signal detection for our device to be highly robust. Moreover, via application of source-space modelling, we show that, despite having 5 times fewer sensors, our system exhibits comparable performance to an established cryogenic MEG device. While significant challenges still remain, these developments provide further evidence that OPM-MEG is likely to facilitate a step change for functional neuroimaging. HIGHLIGHTS A 49-channel whole-head OPM-MEG system is constructed System evaluated via repeat measurements of alpha, beta and gamma oscillations Two OPM-helmet designs are contrasted, a flexible (EEG-like) cap and a rigid helmet The rigid helmet offers significant advantages for a viable OPM-MEG device 49-channel OPM-MEG offers performance comparable to established cryogenic devices
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