SQUID…Ever Heard of it??

Background

SQUID is an acronym for Superconducting Quantum Interference Device[1][2][4]. It is a very sensitive magnetometer which measures small/weak magnetic fields very accurately[2].

Fig 1. Quantum Design MPMS XL SQUID[8]

The sensitivity of the SQUID is linked to measuring the changes in the magnetic field corresponding to one flux quantum[7].

Principle of Working

The principle behind SQUID was discovered by a theoretical physicist, Brian Josephson in 1962 at the University of Cambridge while pursuing his Ph.D.[12].

In a SQUID, two superconductors are separated by thin insulating layers. At the junction, a current will flow without any voltage drop. If there is a voltage drop, the current will oscillate at a frequency in sync to the voltage and this is linked to the magnetic field.

This superconductor junction is called as Josephson junction & effect is called a Josephson effect[2][7].

SQUID Device.JPG

Fig 2. SQUID working concept[2][7]

Now as the current density through a weak electric contact between the two superconductors depends on the phase difference ‘Δφ’ of the two superconducting wave functions – the time derivative of Δφ is correlated with the voltage and is used for sensing via electronic circuitry as shown below.

Fig 3. SQUID Flux-Voltage Conversion[4][5][6]

The following video gives a better idea regarding SQUID along with the sample loading & movement along the pickup coil which disrupts the magnetic field of the Josephson junction.

Realizing SQUID

  • The materials used to realize SQUID’s are normally made from pure niobium or a lead alloy with 10% gold or indium[5][8][14]
  • High-temperature SQUID’s are realized using YBCO. In this case, Liquid Nitrogen is used as a coolant instead of helium[5][8][14]

Types of SQUID

Radio frequency (RF) SQUID
  • Consists of only one Josephson junction
  • Cheaper
  • Less Sensitive
Direct Current  (DC) SQUID
  • Two or more Josephson junction
  • Expensive
  • Sensitive

Applications

  • SPMR for cancer detection[13]
  • Voltameter for voltage detection
  • Magnetic Tanks in biological labs and food industry
  • Quantum Information Processing[11]
  • Defect Detection
  • Gradiometer for surveying and mineral exploration[10]
  • Defense application like a submarine and mine detection

 

If you want to share your opinion kindly do so in the comments section or email me at u2d2tech@gmail.com.


References

  1. https://en.wikipedia.org/wiki/SQUID
  2. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/Squid.html
  3. https://www.qdusa.com/products/laboratory-squids.html
  4. http://squid.iitd.ernet.in/Basic_Literature.htm
  5. http://www.cmp.liv.ac.uk/frink/thesis/thesis/node48.html
  6. https://www.nobelprize.org/nobel_prizes/physics/laureates/1973/josephson-facts.html
  7. http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/T.J_Barry/applications.html
  8. https://www.iitr.ac.in/hi/centers/IIC/pages/Organisation+SQUID.html
  9. https://www.slideshare.net/dlinkdiangeorgiev/squids-26824489
  10. http://www.gemsys.ca/mineral-exploration-applications/
  11. http://www.npl.co.uk/science-technology/quantum-detection/research/nanomagnetism/nanosquids-for-single-particle-detection
  12. https://en.wikipedia.org/wiki/Brian_Josephson
  13. A. Matlashov et.al.,”SQUID instrumentation for early cancer diagnostics”, IEEE 14th International Superconductive Electronics Conference (ISEC), 2013 
  14. https://en.wikipedia.org/wiki/SQUID
  15. https://www.nature.com/news/superconductivity-record-sparks-wave-of-follow-up-physics-1.18191
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