Mechanism Used To Measure Extremely Weak Signals Biology Essay

superconducting quantum intervention device is a mechanism used to mensurate highly weak signals, such as elusive alterations in the human organic structure ‘s electromagnetic energy field. Using a device called a Josephon junction, a SQUID can observe a alteration of energy every bit much as 100 billion times weaker than that of the electromagnetic energy which moves a compass acerate leaf. SQUIDs have been used for a assortment of proving intents which require utmost sensitiveness, including technology, medical, and geological equipment. Since SQUIDS step alterations in a magnetic field with really high sensitiveness so that they do non hold to come in contact with a system that they are proving.


A SQUID ( superconducting quantum intervention device ) is a really sensitive gaussmeter used to mensurate highly weak magnetic Fieldss based on superconducting cringles incorporating Josephson junctions..SQUIDs are sensitive plenty to mensurate Fieldss every bit low as 5 astatine ( 5A-10a?’18 T ) within a few yearss of averaged measurings Their noise degrees are every bit low as 3 fTA·Hz A? . For comparing, a typical icebox magnet produces 0.01 tesla ( 10a?’2 T ) , and some procedures in animate beings produce really little magnetic Fieldss between 10a?’9 T and 10a?’6 T. Recently invented SERF atomic gaussmeters are potentially more sensitive and do non necessitate cryogenic infrigidation but are orders of magnitude larger in size ( ~1A cm3 ) and must be operated in a near-zero magnetic field.

Superconductors are the best known for their ability to carry on current without developing a corresponding electromotive force. Possibly a more cardinal belongings is the coupling of conductivity negatrons. The belongings of the microscopic charges bearers leads to the macroscopic phenomenon associated with superconductivity. It besides led to the innovation of the most sensitive sensors of magnetic flux known, the superconducting quantum intervention device, or SQUID. SQUIDs are used to mensurate highly bantam magnetic Fieldss ; they are presently the most sensitive such devices known, with noise degrees every bit low as 3 fT/sqrt ( Hz ) . Discovery of High Temperature superconductivity in 1986 by Karl Muller and Johannes Bednorz and YBCO in 1987 by Paul Chu and his pupils changed the prospective of SQUID uses and superconductors. The SQUID is, to the applied scientist, a magnetic flux to voltage transducer of alone sensitiveness. It arguably the most sensitive sensor of any sort, with an tantamount energy sensitiveness that approaches the quantum bound.The rule of operation, the methods of industry, and the application of SQUIDs are each discussed in bend.

A superconducting quantum intervention device ( SQUID ) is a mechanism used to mensurate highly weak signals, such as elusive alterations in the human organic structure ‘s electromagnetic energy field. Using a device called a Josephson junction, a SQUID can observe a alteration of energy every bit much as 100 billion times weaker than the electromagnetic energy that moves a compass acerate leaf. A Josephson junction is made up of two superconductors, separated by an insulating bed so thin that negatrons can go through through. A SQUID consists of bantam cringles of superconductors using Josephson junctions to accomplish superposition each negatron moves at the same time in both waies. Because the current is traveling in two opposite waies, the negatrons have the ability to execute as qubits ( that theoretically could be used to enable quantum calculating ) . SQUIDs have been used for a assortment of proving intents that demand utmost sensitiveness, including technology, medical, and geological equipment. Because they measure alterations in a magnetic field with such sensitiveness, they do non hold to come in contact with a system that they are proving. SQUIDs are normally made of either a lead metal ( with 10 % gold or In ) and/or Nb, frequently dwelling of the tunnel barrier sandwiched between a basal electrode of Nb and the top electrode of lead metal. A wireless frequence ( RF ) SQUID is made up of one Josephson junction, which is mounted on a superconducting ring. An oscillatory current is applied to an external circuit, whose electromotive force alterations as an consequence of the interaction between it and the ring. The magnetic flux is so measured. A direct current ( DC ) SQUID, which is much more sensitive, consists of two Josephson junctions employed in analogues so that negatrons burrowing through the junctions demonstrate quantum intervention, dependent upon the strength of the magnetic field within a cringle. DC SQUIDs demonstrate opposition in response to even bantam fluctuations in a magnetic field, which is the capacity that enables sensing of such minute alterations.


Superconductivity is a phenomenon sometimes occurs in particular types of stuffs, when they are kept below a certain temperature. In superconductors the resistanceless current is carried by braces of negatrons, known as Cooper Pairs which is the brace of negatrons. Each negatron has a quantal wavelength. With a Cooper brace each negatrons wave twosomes with its opposite figure over a big distances. This phenomenon is a consequence of the really low temperatures at which many stuffs will superconduct.

( conventional representation of the sprinkling of negatrons as they pass through a vibrating lattice )

The stuff of a superconductor is designed to hold really little quivers, these quivers are lessened even more by chilling the stuff to highly low temperatures. With no quivers there is no sprinkling of the negatrons and this allows the stuff to superconduct. The beginning of a Cooper brace is that as the negatron passes through a crystal lattice at superconducting temperatures it negative charge pulls on the positive charge of the karyon in the lattice through coulombic interactions bring forthing a rippling. An negatron going in the opposite way is attracted by this rippling. This is the beginning of the yoke in a Cooper brace.

( conventional representation of the Cu brace matching theoretical account )

This consequence has two most of import features: perfectly zero electrical electric resistance and exclusion of the interior magnetic field, latter one is known as Meissner consequence. The electrical electric resistance of a metallic music director has a additive relation with temperature ; it decreases bit by bit while the temperature is lowered. However, in ordinary music directors such as Cu and Ag, drosss and other defects impose a lower bound. On the contrary, the opposition of a superconductor drops dramatically to zero when the stuff is cooled below a temperature called “ critical temperature ” ( calculate 1 ) . It has been found that an electric current, fluxing in a cringle of superconducting wire can prevail indefinitely with no external power beginning. Superconductivity is a quantum mechanical phenomenon. It can non be understood merely as the idealisation of “ perfect conduction ” in classical natural philosophies.

Since the find of superconductive stuffs in 1911 by Heike Kamerlingh Onnes and colleagues, their magnetic belongingss attracted considerable attending. A discovery came in 1933 when Meissner and Ochsenfeld showed that in magnetic Fieldss below a certain threshold value the flux inside the superconductor was expelled. They concluded that this belongings defined a new thermodynamic province and is non a effect of infinite conduction.


Operation – Josephson consequence

The Josephson consequence occurs when an electric current ( Cooper braces ) flows between two superconductors separated by a thin non super carry oning layer through quantum tunnelling. Junction is called a Josephson junction.

Josephson junction can merely back up a certain upper limit ( critical ) current in a superconducting province.

Operation – Superconducting cringle

a-?A SQUID consists of a cringle of superconductor with one or more Josephson junctions, called

Weak links.

a-? Inner diameter of cringle ~ 100 mm..

a-? Generally made from either an metal of lead and

gold or In, or pure Nb.

a-? Ceramic superconductors such as yttrium- , Ba, copper-oxide besides possible, but hard to fabricate.

Types of Squid:

There are two chief types of SQUID, DC and RF ( or AC ) . RF SQUIDs have merely one Josephson junction whereas DC SQUIDs have two or more junctions.This makes DC SQUIDs more hard and expensive to bring forth, but DC SQUIDs are much more sensitive


2. RF ( or AC ) SQUIDs

Operation – DC SQUID

a-? Current made to flux around the cringle through

both Josephson junctions.

a-? Electrons tunnel through

the junctions, interfere.

a-? Magnetic field through the cringle causes a stage

difference between

negatrons, affects current

through the cringle.

Operation – RF SQUID

a-? Besides called AC SQUID

a-? Merely one Josephson junction.

a-? Radio frequence hovering current

a-? Measure interactions between the

superconducting ring and an external resonant LC


– External inductance induces current in SQUID ring, and

when the Josephson junction enters the resistive province

it damps the LC circuit

Weak Links and Josephson Effectss:

Two superconductors which are coupled together in such a manner that the critical current in the contact part is much lower than that of the single components, set up a ‘weak nexus ‘ . Josephson in 1962 predicted that such a junction should be able to prolong a supercurrent without application of a electromotive force. He besides mentioned that if such a junction was driven by an external current beginning to transcend its critical current, radiation of high frequence electromagnetic moving ridges would look.

Several constellation of a weak nexus are illustrated in figure 3. The method which is showed in ( figure 3-c ) is a late developed method, in which the weak nexus is achieved by lodging a high-Tc movie across a of course happening grain boundary in a substrate like SrTiO3. Such contacts are normally referred to as grain boundary junctions or bicrystal junctions. Along the length of the grain boundary, it forces the superconductor to develop a concatenation of defects. Above the grain boundary, hence, there is a weak nexus between the two parts of the superconductor movie.

The weak nexus creates a junction which is called Josephson junction. An interesting fact about this junction relates to its critical current: All superconductors cease to be resistanceless every bit shortly as the current carrying through them exceeds a maximal value called the critical current ; but the critical current of a weak nexus is much smaller than a superconductor itself. Sing Ic as the critical current of a Josephson junction, the current base on ballss through a weak nexus can be determined by:

Where are the stages of moving ridge map. This equation is called the District of Columbia Josephson Effect.


( Typical SQUID, V-I feature )

The critical current of the SQUID is shown as a level topographic point in the center of the curve. In this part, there is current fluxing with no electromotive force which is a supercurrent.

Since the critical current is dependent on the flux, the I-V feature will alter with the flux every bit good, which means the electromotive force will besides depend on and hover with the flux and have a minimal value for a integer Numberss of flux quantum and upper limit for half an whole numbers.The high sensitiveness of SQUID electromotive force to the applied magnetic field caused this device be highly used as flux to voltage convertor or in better words, as a magnetic flux detector.

( Typical electromotive force created by applied flux in a SQUID )

Superconducting quantum intervention device ( SQUID )

A superconducting quantum intervention device ( SQUID ) uses the belongingss of electron-pair moving ridge coherency and Josephson Junctions to observe really little magnetic Fieldss. The cardinal component of a SQUID is a ring of superconducting stuff with one or more weak links called Josephesons Junctions. An illustration is shown in the below. With weak-links at points Wand X whose critical current, Ic, is much less than the critical current of the chief ring. This produces a really low current denseness doing the impulse of the electron-pairs little. The wavelength of the electron-pairs is therefore really long taking to small difference in stage between any parts of the ring.

( superconducting quantum intervention device ( SQUID ) as a simple gaussmeter )

If a magnetic field, B is applied perpendicular to the plane of the ring ( Figure 9 ) , a stage difference is produced in the electron-pair moving ridge along the way XYW and WZX. One of the characteristics of a superconducting cringle is that the magnetic flux ( o ) , go throughing through it which is the merchandise of the magnetic field and the country of the cringle and is quantized in units of, where H is Planck ‘s changeless, 2e is the charge of the Cooper brace of negatrons, and has a value of 2 A- tesla. If there are no obstructions in the cringle, so the superconducting current will counterbalance for the presence of an arbitrary magnetic field so that the entire flux through the cringle ( due to the external field plus the field generated by the current ) is a multiple of.

( conventional representation of a SQUID placed in a magnetic field )

Josephson predicted that a superconducting current can be sustained in the cringle, even if its way is interrupted by an insulating barrier or a normal metal. The SQUID has two such barriers or ‘Josephson junctions ‘ . Both junctions introduce the same stage difference when the magnetic flux through the cringle is 0, and so on, which consequences in constructive intervention, and they introduce opposite stage difference when the flux is and so on, which leads to destructive intervention. This intervention causes the critical current denseness, which is the maximal current that the device can transport without dissipation, to change. The critical current is so sensitive to the magnetic flux through the superconducting cringle that even tiny magnetic minutes can be measured. The critical current is normally obtained by mensurating the electromotive force bead across the junction as a map of the entire current through the device. Commercial SQUIDs transform the transition in the critical current to a electromotive force transition, which is much easier to mensurate. An applied magnetic field produces a stage alteration around a ring, which in this instance is equal

where oa is the flux produced in the ring by the applied magnetic field. The magnitude of the critical measurement current is dependent upon the critical current of the weak-links and the bound of the stage alteration around the ring being an built-in multiple of 2. For the whole ring to be superconducting the undermentioned status must be met

where I± and I? are the stage alterations produced by currents across the weak-links and 2 oa/oo is the stage alteration due to the applied magnetic field. When the measurement current is applied I± and I? are no longer equal, although their amount must stay changeless. The stage alterations can be written as

whereis related to the mensurating current I. Using the relation between current and stage from the above Eqn. and rearranging to extinguish I we obtain an look for I,

As sincannot be greater than integrity we can obtain the critical measurement current, Ic from the above

which gives a periodic dependance on the magnitude of the magnetic field, with a upper limit when this field is an integer figure of fluxons and a lower limit at half whole number values as shown in the below figure.

( critical measurement current Ic as a map of applied magnetic field )


The Korean Superconductivity Group within KRISS has carried biomagnetic engineering a measure further with the development of a double-relaxation oscillation SQUID ( Superconducting QUantum Interference Device ) for usage in Magnetoencephalography. SQUID ‘s are capable of feeling a alteration in a magnetic field over a billion times weaker than the force that moves the acerate leaf on a compass ( compass: 5e-5T, SQUID: e-14T. ) . With this engineering, the organic structure can be probed to certain deepnesss without the demand for the strong magnetic Fieldss associated with MRI ‘s.

Magnetic-levitation is an application where superconductors perform highly good. Transport vehicles such as trains can be made to “ drift ” on strong superconducting magnets, virtually extinguishing clash between the train and its paths. Not merely would conventional electromagnets waste much of the electrical energy as heat, they would hold to be physically much larger than superconducting magnets. A landmark for the commercial usage of MAGLEV engineering occurred in 1990 when it gained the position of a nationally-funded undertaking in Japan. The Minister of Transport authorized building of the Yamanashi Maglev Test Line which opened on April 3, 1997. In December 2003, the MLX01 trial vehicle ( shown supra ) attained an unbelievable velocity of 361 miles per hour ( 581 kilometers per hour ) .


I )

hypertext transfer protocol: //, ,sid183_gci816722,00.html

two )


three )

hypertext transfer protocol: //