Wednesday, February 16, 2011

SQUID

Superconducting Quantum Interference Device also known as squid is a mechanism used to measure extremely weak signals as well as weak magnetic fields. The device consist of tiny loops of superconductors which employ the Josephson junction to achieve superposition. (each electron moves simultaneously in both directions). Josephson effect is defined as: the phenomenon of electric current across two weakly coupled superconductors, separated by a very thin insulating barrier.
With this in mind, there are two types of squid: direct current (DC) and radio frequency (RF). DC was invented in 1964 and contains two Josephson junctions which are parallel in a superconducting loop. RF was invented in 1965 and is based on the AC Josephson effect and uses only one Josephson junction. However, radio frequency is less sensitive, cheaper, and easier to manufacture in smaller  quantities.
Traditional superconducting materials for squid are pure niobium or a lead alloy with ten percent gold or indium. Sure pure lead is unstable when it's temperature is repeatedly changed to maintain superconductivity, the entire device needs to operate within a few degrees of absolute zero cooled with liquid helium. The most common uses for this device is in studies for biology. They are used in magnetic marker monitoring method, which is used to trace the path of orally applied drugs. However, in the clinical environment they are used in cardiology for magnetic field imaging which helps detect the magnetic field of the heart for diagnosis and risk stratification.


(Picture of SQUID)


References:
1. SQUID Magnetometer Sensitivity. February 13, 2011.
<http://hyperphysics.phy-astr.gsu.edu/hbase/solids/squid2.html>.
2. SQUID. Wikipedia Encyclopedia. February 13, 2011. <http://en.wikipedia.org/wiki/SQUID>.
3. Superconducting Quantum Interference Device. February 13, 2011.
<http://searchciomidmarket.techtarget.com/sDefinition/0,,sid183 gci816722,00.thml>.
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2 comments:

  1. Don FlowersFebruary 20, 2011 at 12:07 PM

    Overall this is a good and informative blog. When you say squid is used for measuring extremely weak signals, what kind of signals are you talking about? Other than that confusion, you did a good job explaining how squid works. I felt that it would have been good to expand more on squids capabilities (what other information it gives if any). Some other things that I thought would be good to include would be what the restrictions of squid are (are there any compounds that squid cannot be used on? or is it more effective when used on certain types of compounds versus others?).

    -The High School Chemist

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  2. AnonymousFebruary 27, 2011 at 2:01 PM

    I thought your post was very successful in introducing the technique of SQUID and its uses. I found that SQUID is now becoming used in predicting natural disasters such as earthquakes and exploration of minerals and oil. Also, it is being used in surveying geothermal energy. Overall, very nice blog.

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