Sensing element of the SQUID

Superconducting Quantum Interference Devices (SQUID) are very sensitive magnetometers used to measure extremely small magnetic fields, based on superconducting loops containing Josephson junctions. Superconductivity is a phenomenon occurring in certain Materials generally at very low Temperatures characterized by exactly zero electrical resistance Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern A magnetometer is a scientific instrument used to measure the strength and/or direction of the Magnetic field in the vicinity of the instrument In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges The Josephson effect is the phenomenon of current flow across two weakly coupled Superconductors, separated by a very thin insulating barrier They are sensitive enough to measure fields as low as 5 aT within a few days of averaged measurements. ^[1] Their noise levels are as low as 3 fT·Hz^-½. For comparison, a typical refrigerator magnet produces 0. A refrigerator (often called a " fridge " for short is a cooling appliance comprising a thermally insulated compartment and a Heat pump - A magnet (from Greek grc μαγνήτης λίθος " Magnesian stone" is a material or object that produces a Magnetic field. 01 tesla (10^-2 T), and some processes in animals produce very small magnetic fields between 10^-9 T and 10^-6 T. Recently invented SERF atomic magnetometers are potentially more sensitive and do not require cryogenic refrigeration but must be operated near zero field. A spin-exchange relaxation-free (SERF Magnetometer achieves very high magnetic field sensitivity by monitoring a high density vapor of Alkali metal atoms precessing in a near-zero Cryogenics is often used incorrectly to refer to Cryonics, cryopreserving humans or animals Refrigeration is the process of removing Heat from an enclosed space or from a substance and moving it to a place where it is unobjectionable

History and design

The DC SQUID was invented in 1964 by Arnold Silver, Robert Jaklevic, John Lambe, and James Mercereau of Ford Research Labs after B. D. Josephson postulated the Josephson effect in 1962 and the first Josephson Junction was made by John Rowell and Philip Anderson at Bell Labs in 1963. Year 1964 ( MCMLXIV) was a Leap year starting on Wednesday (link will display full calendar of the 1964 Gregorian calendar. Brian David Josephson (born 4 January, 1940; Cardiff, Wales) is a Welsh physicist, professor and became a Nobel Prize The Josephson effect is the phenomenon of current flow across two weakly coupled Superconductors, separated by a very thin insulating barrier Year 1962 ( MCMLXII) was a Common year starting on Monday (the link is to a full 1962 calendar of the Gregorian calendar. Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization Year 1963 ( MCMLXIII) was a Common year starting on Tuesday (link will display full calendar of the Gregorian calendar. The RF SQUID was invented in 1965 by James Edward Zimmerman and Arnold Silver at Ford. James Edward Zimmerman ( February 19, 1923 &ndash August 4, 1999) was born in Lantry South Dakota.

There are two main types of SQUID: DC and RF. Direct current ( DC) is the unidirectional flow of Electric charge. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz RF SQUIDs can work with only one Josephson junction, which might make them cheaper to produce, but are less sensitive. The Josephson effect is the phenomenon of current flow across two weakly coupled Superconductors, separated by a very thin insulating barrier

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. Superconductivity is a phenomenon occurring in certain Materials generally at very low Temperatures characterized by exactly zero electrical resistance Niobium (naɪˈoʊbiəm or columbium (/kəˈlʌmbiəm/ is a Chemical element that has the symbol Nb and Atomic number 41 Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Indium (ˈɪndiəm is a Chemical element with chemical symbol In and Atomic number 49 To maintain superconductivity, the entire device needs to operate within a few degrees of absolute zero, cooled with liquid helium. Absolute zero is the point at which molecules do not move (relative to the rest of the body more than they are required to by a quantum mechanical effect called Zero-point Helium exists in Liquid form only at very low Temperatures The Boiling point and critical point depend on the Isotope

"High temperature" SQUID sensors are more recent; they are made of high temperature superconductors, particularly YBCO, and are cooled by liquid nitrogen which is cheaper and more easily handled than liquid helium. High-temperature superconductors (abbreviated high Tc or HTS) are a family of superconducting Ceramic materials largely Yttrium barium copper oxide, often abbreviated YBCO is a Chemical compound with the formula Y[[Barium Ba]]2 Cu 3 O 7 Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of They are less sensitive than conventional "low temperature" SQUIDs but good enough for many applications.

A prototype of a Semiconductor Superconducting Quantum Interference Device (SQUID).

Uses for SQUIDs

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 neural activity inside brains. Magnetoencephalography ( MEG) is an imaging technique used to measure the Magnetic fields produced by electrical activity in the Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain 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. Magnetogastrography is the science of recording magnetogastrograms (MGGs A novel application of SQUIDs is the magnetic marker monitoring method, which is used to trace the path of orally applied drugs. Magnetic marker monitoring is a method to monitor the passage of an orally applied Drug ( Tablet, capsule, etc A drug, broadly speaking is any chemical substance that when absorbed into the body

Probably the most common use of SQUIDs is in magnetic property measurement systems. These are 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 liquid helium (~4K), to a couple of hundred degrees above room temperature.

For example, SQUIDs are being used as detectors to perform Magnetic Resonance Imaging. While high field MRI uses precession fields of one to several tesla, SQUID-detected MRI uses measurement fields that lie in the microtesla regime. Since the NMR signal drops off as the square of the magnetic field, a SQUID is used as the detector because of its extreme sensitivity. The SQUID coupled to a second-order gradiometer and input circuit, along with the application of gradients are the fundamental entities which allows his research group to retrieve noninvasive images. 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 proven by imaging human extremities, and its future application may involve tumor screening.

Another application is the scanning SQUID microscope, which uses a SQUID immersed in liquid helium as the probe. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical The use of SQUIDs in 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 waves. Petroleum ( L petroleum, from Greek πετρέλαιον, lit Prospecting is the physical search for Minerals Fossils precious metals or mineral specimens and is also known as Fossicking. Mineral exploration is the process undertaken by companies partnerships or corporations in the endeavour of finding Ore (commercially viable concentrations of minerals to An earthquake is the result of a sudden release of energy in the Earth 's crust that creates Seismic waves Earthquakes are recorded with a Seismometer Geothermal power (from the Greek roots geo, meaning earth and therme, meaning heat is energy generated by heat stored in the earth or the collection In Physics, a gravitational wave is a Fluctuation in the Curvature of Spacetime which propagates as a wave, traveling outward from Four SQUIDs were employed on Gravity Probe B in order to test the limits of the theory of general relativity. Gravity Probe B ( GP-B) is a Satellite -based mission which launched in 2004 General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916

The inner workings of an early Superconducting Quantum Interference Device (SQUID).

SQUIDs in fiction

• The science fiction writer William Gibson made reference to SQUIDs in his 1981 story Johnny Mnemonic, where a genetically engineered ex-military dolphin uses a SQUID implant to read a memory device in the title character's brain. William Ford Gibson (born March 17 1948 is an American - Canadian writer who has been called the "noir prophet" of the Cyberpunk subgenre
• In the film Strange Days, SQUIDs are used to record and play back human memories, some of which are exchanged on the black market. Strange Days is the title of a 1995 Science fiction Film directed by Kathryn Bigelow and produced and co-written by James Cameron
• In Michael Crichton's 1999 novel Timeline, SQUIDs are mentioned as a part of the Quantum Teleportation device developed by ITC. John Michael Crichton, ˈkraɪtən, (born October 23 1942 is an American author Film producer, Film director, Medical doctor, and Television producer Timeline is a Science fiction novel by Michael Crichton that was published in November 1999. Quantum teleportation, or entanglement-assisted teleportation, is a technique used to transfer information on a Quantum level usually from one Particle
• Jon Courtenay Grimwood's novel redRobe makes reference to SQUID probes being used to read memories and thoughts as part of a particularly invasive interrogation. Jon Courtenay Grimwood is a British Science fiction Author. He was born in Valletta, Malta, grew up in Britain Southeast redRobe is a 2000 Novel by Jon Courtenay Grimwood. Details in the text suggest that it is set in the same world as that of his earlier
• SQUIDs are used as part of a polygraph machine in Neal Stephenson's novel Snow Crash. Neal Town Stephenson (born October 31, 1959) is an American writer known primarily for his Science fiction works in the Postcyberpunk genre Snow Crash is Neal Stephenson 's third Novel, published in 1992

See also

• Josephson Effect
• Spallation Neutron Source Superconducting RF Cavities
• Mineral exploration
• Geophysics
• Electromagnetics

References

External links