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| {{Use dmy dates|date=August 2013}}
| | Hi there Our name is Jonas Fricke and that I think whenever you say it it looks rather great What he enjoys doing will be to do cryptography although it isn't a typical thing and he's been doing it for quite a while Application establishing is what I do and that I'll be marketed quickly Time ago she made a decision to reside in Illinois and he or she will never proceed<br><br>[https://medium.com/@SecretShopping/ medium.com] |
| {{other uses|Squid (disambiguation)}}
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| [[File:SQUID by Zureks.jpg|thumb|Sensing element of the SQUID]]
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| A '''SQUID''' (for '''superconducting quantum interference device''') is a very sensitive [[magnetometer]] used to measure extremely subtle [[magnetic field]]s, based on superconducting loops containing [[Josephson junction]]s.
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| SQUIDs are sensitive enough to measure [[magnetic flux units|fields]] as low as 5 [[atto-|a]][[Tesla (unit)|T]] (5×10<sup>−18</sup> T) within a few days of averaged measurements.<ref name=Ran04>{{cite book |url=http://einstein.stanford.edu/content/education/GP-B_T-Guide4-2008.pdf |last=Ran |first=Shannon K’doah |title=Gravity Probe B: Exploring Einstein's Universe with Gyroscopes |format=[[PDF]] |page=26 |year=2004 |publisher=[[NASA]]}}</ref> Their noise levels are as low as 3 [[femto-|f]]T·[[Hertz|Hz]]<sup>-½</sup>.<ref>{{cite journal|url=http://ib.ptb.de/de/org/7/75/751/SQUID_Stromsensoren/Drung_ASC06_Preprint.pdf|title=Highly sensitive and easy-to-use SQUID sensors|author=D. Drung, C. Assmann, J. Beyer, A. Kirste, M. Peters, F. Ruede, and Th. Schurig|journal=IEEE Transactions on Applied Superconductivity|year=2007|volume=17|issue=2|page= 699|doi=10.1109/TASC.2007.897403|bibcode = 2007ITAS...17..699D }}</ref> For comparison, a typical [[refrigerator magnet]] produces 0.01 teslas (10<sup>−2</sup> T), and some processes in animals produce very small magnetic fields between 10<sup>−9</sup> T and 10<sup>−6</sup> T. Recently invented [[SERF]] atomic magnetometers are potentially more sensitive and do not require [[cryogenic]] [[refrigeration]] but are orders of magnitude larger in size (~1 cm<sup>3</sup>) and must be operated in a near-zero magnetic field.
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| == History and design ==
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| There are two main types of SQUID: [[direct current]] (DC) and [[radio frequency]] (RF). RF SQUIDs can work with only one [[Josephson junction]], which might make them cheaper to produce, but are less sensitive.
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| === DC SQUID ===
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| [[File:DC SQUID.svg|thumb|200px|Diagram of a DC SQUID. The current <math>I</math> enters and splits into the two paths, each with currents <math>I_a</math> and <math>I_b</math>. The thin barriers on each path are Josephson junctions, which together separate the two superconducting regions. <math>\Phi</math> represents the magnetic flux threading the DC SQUID loop.]]
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| [[File:SQUID IV.jpg|thumb|Electrical schematic of a SQUID where I<sub>b</sub> is the bias current, I<sub>0</sub> is the critical current of the SQUID, <math>\Phi</math> is the flux threading the SQUID and <math>V</math> is the voltage response to that flux. The X-symbols represent [[Josephson junction]]s.]]
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| [[File:IV curve.jpg|thumb|Left: Plot of current vs. voltage for a SQUID. Upper and lower curves correspond to nΦ<sub>0</sub> and (n+1/2)Φ<sub>0</sub> respectively. Right: Periodic voltage response due to flux through a SQUID. The periodicity is equal to one flux quantum, Φ<sub>0</sub>]]
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| The DC SQUID was invented in 1964 by Robert Jaklevic, John J. Lambe, James Mercereau, and Arnold Silver of Ford Research Labs<ref name=Jaklevic64>{{cite journal|author=R. C. Jaklevic, J. Lambe, A. H. Silver, and J. E. Mercereau|title=Quantum Interference Effects in Josephson Tunneling|journal=Phys. Rev. Letters|volume=12|pages=159–160|year=1964|doi=10.1103/PhysRevLett.12.159|bibcode=1964PhRvL..12..159J|issue=7}}</ref> after [[Brian David Josephson]] postulated the [[Josephson effect]] in 1962, and the first Josephson junction was made by John Rowell and [[Philip Warren Anderson|Philip Anderson]] at [[Bell Labs]] in 1963.<ref>{{cite doi|10.1103/PhysRevLett.10.230}}</ref> It has two Josephson junctions in parallel in a superconducting loop. It is based on the DC Josephson effect. In the absence of any external magnetic field, the input current <math>I</math> splits into the two branches equally. If a small external magnetic field is applied to the superconducting loop, a screening current, <math>I_s</math>, begins circulating in the loop that generates a magnetic field canceling the applied external flux. The induced current is in the same direction as <math>I</math> in one of the branches of the superconducting loop, and is opposite to <math>I</math> in the other branch; the total current becomes <math>I/2 + I_s</math> in one branch and <math>I/2 - I_s</math> in the other. As soon as the current in either branch exceeds the critical current, <math>I_c</math>, of the [[Josephson junction]], a voltage appears across the junction.
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| Now suppose the external flux is further increased until it exceeds <math>\Phi_0/2</math>, half the [[magnetic flux quantum]]. Since the flux enclosed by the superconducting loop must be an integral number of flux quanta, instead of screening the flux the SQUID now energetically prefers to increase it to <math>\Phi_0</math>. The screening current now flows in the opposite direction. Thus the screening current changes direction every time the flux increases by half integer multiples of <math>\Phi_0</math>. Thus the critical current oscillates as a function of the applied flux. If the input current is more than <math>I_c</math>, then the SQUID always operates in the resistive mode. The voltage in this case is thus a function of the applied magnetic field and the period equal to <math>\Phi_0</math>. Since the current-voltage characteristics of the DC SQUID is hysteretic, a shunt resistance, <math>R</math> is connected across the junction to eliminate the hysteresis (in the case of copper oxide based high-temperature superconductors the junction's own intrinsic resistance is usually sufficient). The screening current is the applied flux divided by the self-inductance of the ring. Thus <math>\Delta \Phi</math> can be estimated as the function of <math>\Delta V</math> (flux to voltage converter)<ref name=du>{{cite book|author=E. du Trémolet de Lacheisserie, D. Gignoux, and M. Schlenker (editors)|title=Magnetism: Materials and Applications|volume=2|publisher=Springer|year=2005}}</ref><ref name=clarke>{{cite book|author=J. Clarke and A. I. Braginski (Eds.)|title=The SQUID handbook|volume=1|publisher=Wiley-Vch|year=2004}}</ref> as follows:
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| :∆''V'' = ''R'' ∆''I''
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| :2''I'' = 2 ∆''Φ''/''L'', where ''L'' is the self inductance of the superconducting ring
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| :∆''V'' = (''R''/''L'') ∆''Φ''
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| The discussion in this Section assumed perfect flux quantization in the loop. However, this is only true for big loops with a large self-inductance. According to the relations, given above, this implies also small current and voltage variations. In practice the self-inductance ''L'' of the loop is not so large. The general case can be evaluated by introducing a parameter
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| :<math>\lambda = \frac{i_cL}{\Phi_0}</math>
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| with ''i''<sub>c</sub> the critical current of the SQUID. Usually ''λ'' is of order one.<ref>{{cite journal|author=A.TH.A.M. de Waele and R. de Bruyn Ouboter|title=Quantum-interference phenomena in point contacts between two superconductors|journal=Physica|volume= 41|year=1969|pages=225–254|doi=10.1016/0031-8914(69)90116-5|issue=2|bibcode = 1969Phy....41..225D }}</ref>
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| === RF SQUID ===
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| [[File:Squid prototype2.jpg|thumb|A prototype SQUID]]
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| The RF SQUID was invented in 1965 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 doi|10.1063/1.1136907}}</ref><ref>{{cite doi|10.1088/0953-2048/19/3/024}}</ref>
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| The RF SQUID is inductively coupled to a resonant tank circuit. 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 ''Φ''<sub>0</sub>. For a precise mathematical description refer to the original paper by Erné et al.<ref name=du/><ref>{{cite journal|author=S.N. Erné, H.-D. Hahlbohm, 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 }}</ref>
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| === Materials Used ===
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| The traditional [[superconducting]] materials for SQUIDs are pure [[niobium]] or a lead [[alloy]] with 10% gold or [[indium]], as pure lead is unstable when its temperature is repeatedly changed. To maintain superconductivity, the entire device needs to operate within a few degrees of [[absolute zero]], cooled with [[liquid helium]].{{Citation needed|date=May 2012}}
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| "High-temperature" SQUID sensors are more recent; they are made of [[High-temperature superconductivity|high-temperature superconductors]], particularly [[yttrium barium copper oxide|YBCO]], and are cooled by [[liquid nitrogen]] which is cheaper and more easily handled than liquid helium. They are less sensitive than conventional "low temperature" SQUIDs but good enough for many applications.{{Citation needed|date=May 2012}}
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| == Uses ==
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| [[File:Squid prototype.jpg|thumb|The inner workings of an early SQUID]]
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| The extreme sensitivity of SQUIDs makes them ideal for studies in biology. [[Magnetoencephalography]] (MEG), for example, uses measurements from an array of SQUIDs to make inferences about [[neuron|neural]] activity inside brains. Because SQUIDs can operate at acquisition rates much higher than the highest temporal frequency of interest in the signals emitted by the brain (kHz), MEG achieves good temporal resolution. Another area where SQUIDs are used is [[magnetogastrography]], which is concerned with recording the weak magnetic fields of the stomach. A novel application of SQUIDs is the [[magnetic marker monitoring]] method, which is used to trace the path of orally applied drugs. In the clinical environment SQUIDs are used in [[cardiology]] for [[magnetic field imaging]] (MFI), which detects the magnetic field of the heart for diagnosis and risk stratification.
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| Probably the most common commercial use of SQUIDs is in magnetic property measurement systems (MPMS). These are [[Turnkey |turn-key]] systems, made by several manufacturers, that measure the magnetic properties of a material sample. This is typically done over a temperature range from that of 300 mK to roughly 400 K.<ref>{{cite doi|10.1109/JPROC.2004.833655}}</ref>
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| For example, SQUIDs are being used as detectors to perform [[magnetic resonance imaging]] (MRI). While high-field MRI uses precession fields of one to several teslas, SQUID-detected MRI uses measurement fields that lie in the microtesla range. In a conventional MRI system, the signal scales as the square of the measurement frequency (and hence precession field): one power of frequency comes from the thermal polarization of the spins at ambient temperature, while the second power of field comes from the fact that the induced voltage in the pickup coil is proportional to the frequency of the precessing magnetization. In the case of untuned SQUID detection of prepolarized spins, however, the NMR signal strength is independent of precession field, allowing MRI signal detection in extremely weak fields, of order the Earth's field. SQUID-detected MRI has advantages over high-field MRI systems, such as the low cost required to build such a system, and its compactness. The principle has been demonstrated by imaging human extremities, and its future application may include tumor screening.<ref>{{cite book
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| |last1=Clarke
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| |first1=J.
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| |last2=Lee
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| |first2=A.T.
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| |last3=Mück
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| |first3=M.
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| |last4=Richards
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| |first4=P.L.
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| |chapter=Chapter 8.3: Nuclear Magnetic and Quadrupole Resonance and Magnetic Resonance Imaging
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| |pages=56–81
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| }} in {{harvnb|Clarke|Braginski|2006}}</ref>
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| Another application is the [[scanning SQUID microscope]], which uses a SQUID immersed in liquid [[helium]] as the probe. The use of SQUIDs in [[Petroleum|oil]] [[prospecting]], [[mineral exploration]], earthquake prediction and [[geothermal energy]] surveying is becoming more widespread as superconductor technology develops; they are also used as precision movement sensors in a variety of scientific applications, such as the detection of [[gravitational wave]]s.<ref>{{cite book
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| |last=Paik
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| |first=Ho J.
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| |chapter=Chapter 15.2: Superconducting Transducer for Gravitational-Wave Detectors
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| |pages=548–554
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| }} in {{harvnb|Clarke|Braginski|2006}}</ref>
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| A SQUID is the sensor in each of the four gyroscopes employed on [[Gravity Probe B]] in order to test the limits of the theory of [[general relativity]].<ref name=Ran04/>
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| A modified RF SQUID was used to observe the [[Casimir effect#Dynamical Casimir effect|dynamical Casimir effect]] for the first time.<ref>{{cite news|url=http://www.technologyreview.com/blog/arxiv/26813/|title=First Observation of the Dynamical Casimir Effect|publisher=Technology Review}}</ref><ref>{{cite journal|last1=Wilson|first1=C. M.|title=Observation of the Dynamical Casimir Effect in a Superconducting Circuit|journal=Nature|volume=479|pages=376–379|year=2011|doi=10.1038/nature10561|arxiv = 1105.4714 |bibcode = 2011Natur.479..376W }}</ref>
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| It has also been suggested that they might be implemented in a [[quantum computer]].<ref>[http://iopscience.iop.org/1402-4896/1998/T76/024 Quantum coherence with a single Cooper pair], V Bouchiat, D Vion, P Joyez, D Esteve, M H Devoret, 1998 Phys. Scr. 1998 165</ref> These are the only macroscopic devices that have been cited as possible [[qubits]] in this context.
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| A potential military application exists for use in [[anti-submarine warfare]] as a [[magnetic anomaly detector]] (MAD) fitted to [[maritime patrol aircraft]].<ref>{{cite web|url=http://www.aip.org/tip/INPHFA/vol-4/iss-2/p20.pdf|title=SQUID Sensors Penetrate New Markets|first=Jennifer|last=Ouellette|page=22|publisher=The Industrial Physicist}}</ref>
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| == See also ==
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| * [[Macroscopic quantum phenomena]]
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| * [[Geophysics]]
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| * [[Electromagnetism]]
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| * [[Magnetometer]]
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| * [[Superconducting tunnel junction]]
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| * [[Aharonov-Bohm effect]]
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| == Notes ==
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| {{reflist|2}}
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| == References ==
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| *{{cite book
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| |ref=harv
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| |volume=2
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| |title=Applications of SQUIDs and SQUID Systems
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| |editor1-first=John |editor1-last=Clarke
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| |editor2-first=Alex I. |editor2-last=Braginski
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| |isbn=978-3-527-40408-7
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| |publisher=Wiley-VCH
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| |year=2006 }}
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| {{DEFAULTSORT:Squid}}
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| [[Category:American inventions]]
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| [[Category:Measuring instruments]]
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| [[Category:Superconductivity]]
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| [[Category:Josephson effect]]
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| [[Category:Magnetometers]]
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Hi there Our name is Jonas Fricke and that I think whenever you say it it looks rather great What he enjoys doing will be to do cryptography although it isn't a typical thing and he's been doing it for quite a while Application establishing is what I do and that I'll be marketed quickly Time ago she made a decision to reside in Illinois and he or she will never proceed
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