To reduce the influence of such environmental noise, biomagnetic measurements have traditionally relied on two kinds of hardware-based solutions: one is magnetically shielded rooms (MSRs) and the other is gradiometer
We used 204 gradiometer
signals among the 306 channels for data analysis because the characteristics of the gradiometer
and magnetometer sensors differ and the signal-to-noise ratio (SNR) of the gradiometers
is better than that of the magnetometers .
Within the same area, sensitive gradiometers
detected magnetic signs of cooking hearths and pot fragments.
Current gravimeters have been used in the air with some success in defining features with a scale of 10 km or greater, but the next generation of airborne gravity instruments will be gradiometers
targeting features 200 to 500 m beneath the ground surface with density contrasts about 300 kg/m3 and smaller than 1 km across.
The pickup coils are configured as second-order gradiometers
. Measuring 1.7 mm in dia., they are arranged in a "plus sign" array.
Using superconductivity, the devices could be built as gradiometers
able to measure magnetic gradients in particular orientations and provide vectors of the magnetic dipoles.
A whole-scalp MEG system (306 channels; 204 planar gradiometers
and 102 magnetometers; Vectorview[TM]; Elekta Oy, Helsinki, Finland) was employed for the recordings.
The MEG system had 102 triple-sensor elements, each comprising two orthogonal planar gradiometers
and one magnetometer.
Methods: Magnetocardiographic mapping is performed with a 36-channel unshielded mapping system, based on DC-SQUID sensors coupled to second-order axial gradiometers
(pick-up coil 19 mm and 55-70 mm baselines; sensitivity of 20 fT/[square root of Hz] in above 1 Hz), as part of the electrophysiologic investigation protocol, tailored to the diagnostic need of each arrhythmic patient.
Researchers around the world are also pursuing the promise of quantum improvements for other instruments, including gyroscopes used in navigation systems, atomic clocks, and gravity-measuring devices, or gradiometers
, that guide oil exploration and geophysical research.
Geoscan Research of Bradford, U.K., is manufacturing three microprocessor-controlled fluxgate gradiometers
having 0.5 m separation of the sensors.
The Navy already uses precision-machined electromechanical gravity gradiometers
to help submarines navigate without noisy sonar.