Editing SQUID (section)

=== RF SQUID ===
[[File:Squid prototype2.jpg|thumb|A prototype SQUID]]

The RF SQUID was invented in 1967 by Robert Jaklevic, John J. Lambe, Arnold Silver, and [[James Edward Zimmerman]] at Ford.<ref name=clarke/> It is based on the AC Josephson effect and uses only one Josephson junction. It is less sensitive compared to DC SQUID but is cheaper and easier to manufacture in smaller quantities. Most fundamental measurements in [[biomagnetism]], even of extremely small signals, have been made using RF SQUIDS.<ref>{{Cite journal | last1 = Romani | first1 = G. L. | last2 = Williamson | first2 = S. J. | last3 = Kaufman | first3 = L. | doi = 10.1063/1.1136907 | title = Biomagnetic instrumentation | journal = Review of Scientific Instruments | volume = 53 | issue = 12 | pages = 1815–1845 | year = 1982 | pmid =  6760371|bibcode = 1982RScI...53.1815R }}</ref><ref>{{Cite journal | last1 = Sternickel | first1 = K. | last2 = Braginski | first2 = A. I. | doi = 10.1088/0953-2048/19/3/024 | title = Biomagnetism using SQUIDs: Status and perspectives | journal = Superconductor Science and Technology | volume = 19 | issue = 3 | pages = S160 | year = 2006 |bibcode = 2006SuScT..19S.160S | s2cid = 122140082 }}</ref>
The RF SQUID is inductively coupled to a resonant tank circuit.<ref>{{Cite journal|last1=Nisenoff|first1=M.|last2=Wolf|first2=S.|date=1975-09-01|title=Observation of a $cos\ensuremath{\varphi}$ term in the current-phase relation for "Dayem"-type weak link contained in an rf-biased superconducting quantum interference device|journal=Physical Review B|volume=12|issue=5|pages=1712–1714|doi=10.1103/PhysRevB.12.1712}}</ref> Depending on the external magnetic field, as the SQUID operates in the resistive mode, the effective inductance of the tank circuit changes, thus changing the resonant frequency of the tank circuit. These frequency measurements can be easily taken, and thus the losses which appear as the voltage across the load resistor in the circuit are a periodic function of the applied magnetic flux with a period of <math>\Phi_0</math>. For a precise mathematical description refer to the original paper by Erné et al.<ref name=du/><ref>{{cite journal|author1=S.N. Erné |author2=H.-D. Hahlbohm |author3=H. Lübbig |title=Theory of the RF biased Superconducting Quantum Interference Device for the non-hysteretic regime|journal=J. Appl. Phys.|volume=47|pages=5440–5442|year=1976|doi=10.1063/1.322574|bibcode = 1976JAP....47.5440E|issue=12 |doi-access=free}}</ref>