We developed a prototype of a mobile, high-resolution, multichannel magnetoencephalography ͑MEG͒ system, called babySQUID, for assessing brain functions in newborns and infants. Unlike electroencephalography, MEG signals are not distorted by the scalp or the fontanels and sutures in the skull. Thus, brain activity can be measured and localized with MEG as if the sensors were above an exposed brain. The babySQUID is housed in a moveable cart small enough to be transported from one room to another. To assess brain functions, one places the baby on the bed of the cart and the head on its headrest with MEG sensors just below. The sensor array consists of 76 first-order axial gradiometers, each with a pickup coil diameter of 6 mm and a baseline of 30 mm, in a high-density array with a spacing of 12-14 mm center-to-center. The pickup coils are 6 ± 1 mm below the outer surface of the headrest. The short gap provides unprecedented sensitivity since the scalp and skull are thin ͑as little as 3 -4 mm altogether͒ in babies. In an electromagnetically unshielded room in a hospital, the field sensitivity at 1 kHz was ϳ17 fT/ ͱ Hz. The noise was reduced from ϳ400 to 200 fT/ ͱ Hz at 1 Hz using a reference cancellation technique and further to ϳ40 fT/ ͱ Hz using a gradient common mode rejection technique. Although the residual environmental magnetic noise interfered with the operation of the babySQUID, the instrument functioned sufficiently well to detect spontaneous brain signals from babies with a signal to noise ratio ͑SNR͒ of as much as 7.6:1. In a magnetically shielded room, the field sensitivity was 17 fT/ ͱ Hz at 20 Hz and 30 fT/ ͱ Hz at 1 Hz without implementation of reference or gradient cancellation. The sensitivity was sufficiently high to detect spontaneous brain activity from a 7 month old baby with a SNR as much as 40:1 and evoked somatosensory responses with a 50 Hz bandwidth after as little as four averages. We expect that both the noise and the sensor gap can be reduced further by approximately half with a gain in SNR of about four. Thus, we conclude from the performance of the prototype that it should be feasible to improve the babySQUID to detect cortical activity in infants in real time with high spatial resolution.

We present results from a mini-array of three iGrav superconducting gravimeters (SGs) at Mount Etna. This is the first network of SGs ever installed on an active volcano. Continuous gravity measurements at active volcanoes are mostly accomplished with spring gravimeters that can be operated even under harsh field conditions. Nevertheless, these instruments do not provide reliable continuous measurements over periods longer than a few days due to the instrumental drift and artifacts driven by ambient parameters. SGs are free from these instrumental effects and thus allow to track even small gravity changes (1-2 μGal) over a wide range of time scales (minutes to months). However, SGs need host facilities with main electricity and a large installation surface, implying that they cannot be deployed in close proximity to the active structures of tall volcanoes. At Mount Etna the three iGrav SGs were installed at distances from the summit active craters ranging between 3.5 and 15 km. Despite the relatively unfavorable position of the installation sites, we show that these instruments can detect meaningful (i.e., volcano-related) changes that would otherwise remain hidden, like, for example, the weak gravity signature (within a few μGal) of gas buildup at intermediate depth in the plumbing system of Etna, during noneruptive intervals. Our results prove that iGrav SGs are powerful tools to monitor and study active volcanoes and can provide unique information on the bulk processes driving volcanic activity.

We have developed a scanning magnetic microscope (SMM) with 25 µm resolution in spatial position for the magnetic features of room temperature objects. The microscope consists of a high-temperature superconductor (HTS) dc SQUID sensor, suspended in vacuum with a self-adjusting standoff, close spaced liquid nitrogen Dewar, X -Y scanning stage and a computer control system. The HTS SQUIDs were optimized for better spatial and field resolutions for operation at liquid nitrogen temperature. Measured inside a magnetic shield, the 10 pT Hz −1/2 typical noise of the SQUIDs is white down to frequencies of about 10 Hz, increasing up to about 20 pT Hz −1/2 at 1 Hz. The microscope is mounted on actively damped platforms, which negate vibrations from the environment as well as damping internal stepper motor noises. A high-resolution video telescope and a 1 µm precision z-axis positioning system allow a close positioning of the sample under the sensor. The ability of the sensors to operate in unshielded environmental conditions with magnetic fields up to about 15 G allowed us to perform 2D mapping of the local ac and dc susceptibility of the objects.

<p>Continuous gravity measurements at active volcanoes are mostly accomplished using spring gravimeters, that can be operated under harsh field conditions. Unfortunately, these instruments do not provide reliable continuous measurements over long time-scales, due to the instrumental drift and artifacts driven by ambient parameters.</p><p>An alternative to spring devices for continuous measurements is given by superconducting gravimeters (SGs), that are free from instrumental effects and thus allow to track even small gravity changes over time-scales from minutes to years. Nevertheless, SGs cannot be deployed in close proximity to the active structures of tall volcanoes, since they need host facilities with main electricity and a large installation surface.</p><p>The mini-array of three SGs that were installed on Etna between 2014 and 2016 makes the first network of SGs ever installed on an active volcano. Here we present results from these instruments and show that, even though they are installed at relatively unfavorable positions (in terms of distances from the summit active craters), SGs can detect volcano-related gravity changes that would otherwise remain hidden, thus providing unique insight into the bulk processes driving volcanic activity.</p>