We developed tunnel magneto-resistive (TMR) sensors based on magnetic tunnel junctions (MTJs) that are able to detect a weak, sub-pT, magnetic field at a low frequency. Small detectivities of 0.94 pT/Hz1/2 at 1 Hz and 0.05 pT/Hz1/2 at 1 kHz were achieved by lowering the resistance of MTJs and enhancement of the signal using a thick CoFeSiB layer and magnetic flux concentrators. We demonstrated real-time measurement of magnetocardiography (MCG) and nuclear magnetic resonance (NMR) of protons using developed sensors. This result shows that both MCG and NMR can be measured by the same measurement system with ultra-sensitive TMR sensors.

SynopsisBubble dispersion and mass transfer between gas and liquid in a gasstirred system have been studied experimentally and theoretically.Nitrogen gas was injected into water through a nozzle located at the bottom center of a cylindrical vessel. Local gas-holdup distributions were measured by an electrical resistivity probe . The volumetric coefficient in the bubble-dispersion zone for the absorption of C02-water system was measured. Experimental conditions were as follows: gas-flow rate (qG) =(16.7-167) X 10-6 m3/s, radius of vessel (r1)=O.055-.'0.50m, height of water (z1) = 0.1-0.4 m and diameter of nozzle = 6 mm.A mathematical model based on the boundary-layer theory is proposed. The model consists of equation of flow with uniform effective kinematic viscosity ve and equations of bubble and solute diffusion with uniform effective d fusivities, De ,B and Dens, respectively. Equations were solved numerically assuming ve=De ,B=Dens, and the theoretical distribution of local gas holdup, axial velocity, and solute concentration were obtained. By comparing the theoretical distributions of local gas holdup with the measured ones, values of ye could be obtained for various qG, rl and z1. The values of ve were correlated with qG on the basis of dimensional analysis. This correlation was consistent with related data available in the literature. Volumetric coefficients, calculated by the present model, were in agreement with the observed ones.

Non-invasive human brain functional imaging with millisecond resolution can be achieved only with magnetoencephalography (MEG) and electroencephalography (EEG). MEG has better spatial resolution than EEG because signal distortion due to inhomogeneous head conductivity is negligible in MEG but serious in EEG. However, this advantage has been practically limited by the necessary setback distances between the sensors and scalp, because the Dewar vessel containing liquid helium for superconducting quantum interference devices (SQUIDs) requires a thick vacuum wall. Latest developments of high critical temperature (high-Tc) SQUIDs or optically pumped magnetometers have allowed closer placement of MEG sensors to the scalp. Here we introduce the use of tunnel magneto-resistive (TMR) sensors for scalp-attached MEG. Improvement of TMR sensitivity with magnetic flux concentrators enabled scalp-tangential MEG at 2.6 mm above the scalp, to target the largest signal component produced by the neural current below. In a healthy subject, our single-channel TMR-MEG system clearly demonstrated the N20m, the initial cortical component of the somatosensory evoked response after median nerve stimulation. Multisite measurement confirmed a spatially and temporally steep peak of N20m, immediately above the source at a latency around 20 ms, indicating a new approach to non-invasive functional brain imaging with millimeter and millisecond resolutions.