Large‐area low‐noise seven‐channel dc SQUID magnetometer for brain research
作者:
Jukka Knuutila,
Seppo Ahlfors,
Antti Ahonen,
Jari Ha¨llstro¨m,
Matti Kajola,
Olli V. Lounasmaa,
Visa Vilkman,
Claudia Tesche,
期刊:
Review of Scientific Instruments
(AIP Available online 1987)
卷期:
Volume 58,
issue 11
页码: 2145-2156
ISSN:0034-6748
年代: 1987
DOI:10.1063/1.1139478
出版商: AIP
数据来源: AIP
摘要:
The design, construction, and performance of a new high‐sensitivity dc SQUID magnetometer, covering a circular area of 93‐mm diameter, is described. The device, now used routinely in our brain research, comprises seven asymmetric first‐order gradiometers, located on a spherical surface of 125‐mm radius and with the symmetry axis tilted 30° with respect to the vertical. The pickup coil diameter is 20 mm, and the channels are separated by 36.5 mm from each other in a hexagonal array. The overall field sensitivity of the system, measured inside our magnetically shielded room, is 5 fT/(Hz)1/2, mainly limited by the thermal noise in the radiation shields of the Dewar. The optimization of the coil configuration and the measurement system is discussed in detail, and a system to determine automatically the position and orientation of the Dewar with respect to certain fixed points on the subject’s head is described. Finally, some examples of measurements carried out with the new device are given.
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