SQUID Magnetometer |
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| The superconducting quantum interference device (SQUID) consists of two superconductors separated by thin insulating layers to form two parallel Josephson junctions. The device may be configured as a magnetometer to detect incredibly small magnetic fields -- small enough to measure the magnetic fields in living organisms. Squids have been used to measure the magnetic fields in mouse brains to test whether there might be enough magnetism to attribute their navigational ability to an internal compass. | ||||
Threshold for
SQUID: 10-14 T |
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| The great sensitivity of the SQUID
devices is associated with measuring changes in magnetic
field associated with one flux quantum. One of the
discoveries associated with Josephson junctions was tha
flux is quantized in units If a constant biasing current is maintained in the SQUID device, the measured voltage oscillates with the changes in phase at the two junctions, which depends upon the change in the magnetic flux. Counting the oscillations allows you to evaluate the flux change which has occurred. |
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| Devices based upon the
characteristics of a Josephson junction are valuable in
high speed circuits. Josephson junctions can be designed
to switch in times of a few picoseconds. Their low power
dissipation makes them useful in high-density computer
circuits where resistive heating limits the applicability
of conventional switches. Parallel Josephson junctions are used in SQUID devices for the detection of minute magnetic fields. |
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http://hyperphysics.phy-astr.gsu.edu/hbase/solids/squid.html |
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