International Journal of Advanced Science and Engineering Research
Volume: 1, Issue: 1, june 2016
www.ijaser.in
ISSN: 2455-9288
SUPERCONDUCTING MATERIALS AND ITS APPLICATIONS
IN ENGINEERING
Y.Devakumari
Department of Physics, Al-Ameen Engineering College, Erode-638002, Tamil Nadu, India.
*Correspondence email: devakumariy@gmail.com
Abstract: A short account is given of the characteristic properties of superconductors and the reasons for the
importance of superconductivity in science and technology. The occurrence of the phenomenon in metals, alloys and
chemical compounds is briefly discussed, with particular reference to those materials having the highest critical
temperatures. The major part of the article is concerned with the applications of superconductivity in engineering,
and attention is particularly devoted to materials for magnet construction, the various uses of superconducting
magnets, and the other applications of superconductors such as power transmission cables, and transformers.
Superconductors and superconducting materials are metals, ceramics, organic materials, or heavily doped
semiconductors that conduct electricity without resistance. Superconducting materials can transport electrons with
no resistance, and hence release no heat, sound, or other energy forms. Superconductivity occurs at a specific
material's critical temperature (Tc). As temperature decreases, a superconducting material's resistance gradually
decreases until it reaches critical temperature.
I. INTRODUCTION
Superconductivity is one of the most exciting phenomena in physics. It is an interesting and
unusual property of the solids and it has immense potential of prospective applications. Superconducting
materials have extraordinary electrical and magnetic characteristics. Several hundreds of superconductors
have been discovered and studied so far. Superconductivity appears to be the biggest revolution that
occurred recently in physical and material sciences since the invention of transistor.
1.1 Principle
Superconductor principle can be explained by examining various formulas. First, lack of
resistance in a current-carrying superconductor can be illustrated by Ohm's law, R=V/I, where R is
resistance, V is voltage, and I is current. Since superconducting materials carry current with no applied
voltage, R=0. Superconductivity also does not involve power loss, since power is defined as P=I2R; since
R is zero in a superconducting material, power loss is zero.
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Fig.1.1 Superconductor principle
1.2 Types of Superconductor
Superconductors are classified into Type I and Type II materials.
Type I Superconductor
These materials show at least some conductivity at ambient temperature and include mostly pure
metals and metalloids. They have low critical temperatures, typically between 0 and 10 K (-273°C and 263°C respectively). As discussed above, this type experiences a sudden decrease in resistance as well as
the complete expulsion of magnetic fields (perfectly diamagnetic) at critical temperature.
Type I metals achieve superconductivity through slowing down molecular activity via low
temperatures. According to BCS theory, this creates an environment conducive to Cooper pairing so that
electron pairs are able to overcome molecular obstacles, leading to free electron flow without applied
voltage.
Copper, silver, and gold are three of the best metallic conductors but are not superconductive. This is
due to their face-centered cubic (FCC) unit cells lattice structures, which are so tightly packed that the
low-temperature lattice vibrations essential to superconductivity fail to coerce free electrons into Cooper
pairs. While some FCC metals such as lead are capable of superconductivity, this is due to outside factors
such as lead's low modulus of elasticity.
Type II Superconductor
Type II materials are metallic compounds or alloys, although elemental vanadium, technetium,
and niobium also fall within this group. They are capable of superconductivity at much higher critical
temperatures. For example, the 2015 testing of Sn8SbTe4Ba2MnCu14O28+ yielded a Tc of 400 K
(+129°C), over 100°C above ambient temperature, although more common Type II materials have critical
temperatures within the 10-130 K range. As of 2015 there is no scientific consensus as to the reason for
these higher critical temperatures.
Type II materials also take on a mixed state, which contrasts with plunging resistance at Tc for Type I
materials, when approaching their critical temperature. Mixed states are caused by the fact that Type II
superconductors never completely expel magnetic fields, so that microscopic superconducting "stripes"
can be seen on the material.
Other Classifications
Classification according to the types above is theoretically done by magnetic field behavior.
Type I materials have a single critical field temperature above which superconductivity ceases
completely, while Type II materials have two critical field points between which a mixed state may exist.
Another method for classifying superconductors is by temperature, with "low-temperature" materials
falling below liquid-nitrogen-cooled superconductivity and "high-temperature" ones falling above it.
Low-temperature materials may be cooled using liquid gases such as neon, hydrogen, and helium.
A comprehensive list of critical temperatures for superconductive materials can be found here for Type
I and here for Type II.
The graph below illustrates this distinction, as well as a timeline showing the history of critical
temperature discoveries. Materials with critical temperatures falling above the boiling point of liquid
nitrogen (around 77 K) are known as high-temperature materials. The dramatic increase in Tc seen in the
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ISSN: 2455-9288
middle of the graph is the result of the discovery of superconductive cuprates and perovskites with high
Tc in 1986 and 1987.
Fig 1.2. Tc of various materials
1.3 Product Form Factors
Suppliers of superconductors and superconducting materials offer products in various different
forms, some of which are listed below. Raw superconducting materials include chemical compounds in
the form of powders or crystals. Superconducting powder is incorporated into the manufacture of more
efficient fuel cells, gas separation membranes, and lithium-ion batteries.
Superconductor manufacturers may specialize in the advancement of a certain superconducting
compound, such as niobium-based formulas or magnesium diboride (mgb2).
II.APPLICATIONS OF SUPERCONDUCTORS
2.1. Industrial application
Superconductors are already used in many fields: electricity, medical applications, electronics and
even trains. They are used in laboratories, especially in particle accelerators, in astrophysics with the use
of bolometer, in ultrasensitive magnetic detectors called squids, and in superconducting coils to produce
very strong magnetic fields.
2.1.1 MAGLEV Train
When a Superconductive magnets to practically eliminate friction between the train and the tracks.
The use of conventional electromagnets would waste vast quantities of energy via heat loss and
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necessitate the use of an unwieldy magnet, whereas superconductors result in superior efficiency and
smaller magnets.
How MAGLEV Train Works
Maglev is short for Magnetic Levitation in which trains float on a guide way using the principle of
magnetic repulsion. Each magnet has two poles. Now if you play with two magnets, you'll realize that
opposite poles attract, whereas similar poles repel. This repulsive property of magnets is used in Maglev
trains.
However, instead of using permanent magnets, the principle of electromagnetism is used to create
strong and large temporary magnets. When an electric current is passed through a coil of wire, magnetic
field is generated around the coil according to Faraday's laws.
Fig.2.1 Maglev Track
Magnetized coils run along the track called a guide way. These repel the large magnets on the train's
undercarriage, allowing the train to levitate between 0.39 and 3.93 inches (1 to 10 cm) above the guide
way. Once the train is levitated, power is supplied to the coils within the guide way walls to create a
unique system of magnetic fields that pull and push the train along the guide way. The electric current
supplied to the coils in the guide way walls is constantly alternating to change the polarity of the
magnetized coils. This change in polarity causes the magnetic field in front of the train to pull the vehicle
forward, while the magnetic field behind the train adds more forward thrust.
Maglev trains float on a cushion of air, eliminating friction. This lack of friction and the trains'
aerodynamic designs allow these trains to reach unprecedented ground transportation speeds of more
than 310 mph (500 kph). Developers say that maglev trains will eventually link cities that are up to 1,000
miles (1,609 km) apart. At 310 mph, you could travel from Paris to Rome in just over two hours.
2.1.2. Electric Generators
Electric generators built with superconductive wire have achieved 99% efficiency ratings in
experimental tests but have yet to be built commercially.
2.1.3 Electric Power Generation
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ISSN: 2455-9288
Electric power generation using superconductive cables and transformers has been experimentally
tested and demonstrated.
2.1.4 SQUID
A superconducting quantum interference device (SQUID) is a mechanism used to measure
extremely weak signals, such as subtle changes in the human body's electromagnetic energy field. Using a
device called a Josephson junction, a SQUID can detect a change of energy as much as 100 billion times
weaker than the electromagnetic energy that moves a compass needle. A Josephson junction is made up
of two superconductors, separated by an insulating layer so thin that electrons can pass through.
A SQUID consists of tiny loops of superconductors employing Josephson junctions to
achieve superposition: each electron moves simultaneously in both directions. Because the current is
moving in two opposite directions, the electrons have the ability to perform as quits (that theoretically
could be used to enable quantum computing). SQUIDs have been used for a variety of testing purposes
that demand extreme sensitivity, including engineering, medical, and geological equipment. Because they
measure changes in a magnetic field with such sensitivity, they do not have to come in contact with a
system that they are testing.
Fig.2.1.4 SQUID
2.1.5 Accelerators
Particle accelerators were invented at the beginning of the 20th century. These super-microscopes
enable to probe matter on a subatomic scale and have an effect on beams of charged particles (electrons,
protons, ions) thanks to electromagnetic fields. Since then, other uses of these devices have appeared,
especially in medicine or as a source of light. The electric field that accelerates the particles is produced
by radio-frequency (RF) resonant cavities, whereas the magnetic field that guides and focuses them is
produced by electromagnets. Superconductivity gives access to stronger fields and reduces the energy loss
in RF cavities and magnets: it enables to build more powerful and compact accelerators that are cheaper
to use. Thus, the large hadrons’ collider (LHC) of the CERN in Geneva uses several
thousand superconducting magnets spread on the 27-km circumference, producing a magnetic field four
times higher than classical electromagnets, with an electric intake ten times smaller (considering the
power consumed by the cryogenic cooling device).
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2.1.6 Superconducting coils
Magnets produce magnetic fields that can be strong but that strongly weaken when moving
away. In order to get a strong field on a big volume, electromagnets are required, i.e. a metal wire coil in
which flows an electric current. The current that flows in circle creates a magnetic field perpendicular to
the section of the coil and in all its volume.
To get a strong field, a high electric current is required. But when there is a current, there is resistance,
and where there is resistance, there is heating, because of the Joule effect. If the current is too strong, the
coil will melt. To avoid this problem, we can either cool the wire with water (very expensive and not very
convenient) or use a superconducting wire, because the latter does not resist and hence does not heat.
Magnetic fields of several teslas (1 tesla is equal to about 10 000 times the earth magnetic field) can be
obtained; using coils with several thousands turns of superconducting wires plunged in liquid helium.
These wires are often made from niobium and titanium alloys (NbTi) or niobium and tin (Nb3Sn). These
coils are often called “superconducting magnets” by misuse of language.
2.1.7 Bolometer (Super-thermometers)
Superconductors are often used in radiation sensors called bolometers. These sensors work at a
very low temperature and are very sensitive tools to study extremely weak radiations, such as the fossil
radiation of the Universe at 3 K, for instance. Bolometers are used in many astrophysics and astroparticle
physics experiments. Among the experiments that use thermometers made of superconductors, there are
experiments that are conducted in order to try and find dark matter (CDMS)and CRESST.
The sensitivity of these sensors is so powerful that today, they are strongly developing and many projects
will use them soon. For instance, we are thinking about equipping satellites with bolometers in order to
detect the universe radiation and to measure the cosmic microwave background radiation byBSD. These
superconducting bolometers could also be used to detect planets outside our solar system by XO
telescopes.
Fig2.1.7 Bolometers (the superconducting thermometer is in the centre of the squares)
2.2 Applications in Medical Imaging Diagnostics
2.2.1 Magnetic Resonance Imaging (MRI)
Magnetic resonance (MR) technology and its applications that involve dynamic magnetic
resonance imaging (MRI). Among the hardware systems of an MRI device, the magnet, radio-frequency
(RF), and gradient systems deserve particular R&D attention. For example, the development of suitable
high-temperature superconductors (HTSs) and their integration into MRI magnets represents one
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potentially fruitful area of interaction between solid-state physicists, materials scientists, and the
biomedical imaging research community. High-speed imaging pulse sequences, with particular focus on
functional imaging, are discussed in this chapter, as are algorithms for image reconstruction; both are
promising fields of research. Significant attention is given also to two applications for which MRI has
unique potential: blood flow imaging and quantification, and functional neuroimaging based on exploiting
dynamic changes in the magnetic susceptibility. Finally, this chapter highlights recent technological
advances toward real-time monitoring of interventional and therapeutic procedures.
MRI technology has undergone amazing strides over the last two decades, much of it due to advances
from the mathematical sciences and physics. For example, Figure 4.1 demonstrates a tremendous
improvement in resolution over that period. There is every reason to believe exciting progress still lies
ahead.
Magnetic resonance imaging (MRI) uses superconductor-generated magnetic fields to interact with
hydrogen atoms and fat molecules within the human body. These atoms and molecules then release
energy that is detected and formed into a graphic image. MRI is a widely used radiographic method for
medical diagnosis or staging of diseases such as cancer.
2.2.2 Ultra-Low Field Magnetic Resonance Imaging (ULF-MRI)
Conventional Magnetic Resonance Imaging, discussed above, created a revolution in noninvasive imaging procedures, and the technique is used worldwide for many diagnoses. MRI is enabled
by the high magnetic fields that only superconducting magnets can produce. Incremental improvements in
the performance and cost of this established technology continue, but today researchers are also
developing a complementary technique, Ultra-Low-Field MRI. In this new approach, instead of a high
magnetic field from a superconducting magnet, a very low field - 10,000 times lower - is used. This low
magnetic field is produced by simple, low cost magnets made with room temperature copper wire. To
compensate for the loss of the high magnetic field, the extreme sensitivity of a superconducting detector
is required. This detector, a “SQUID” (Superconducting Quantum Interference Device), enables the
following benefits at low field:
Significantly lower system cost, which could enable the new system to be much more widely available.
Recent measurements on ex vivo prostate tissue demonstrate a significantly higher contrast between
healthy and malignant tissue than at high fields. It is essential, however, to carry out studies to confirm
that tumor imaging is viable in vivo. If ULF-MRI is successful in imaging cancer, it has a number of
potential applications: diagnosing the severity of prostate cancer prior to biopsy, imaging of prostate
cancer to guide biopsy, monitoring cancer progression during active surveillance or radiation therapy and
imaging of other types of cancer, for example, brain and breast tumors.
These two benefits combine to make ULF-MRI an important advance geared towards reducing the cost of
healthcare on the one hand and enhancing the diagnostic ability of certain conditions on the other. The
effort is slowly advancing from research to in vivo imaging; it holds also the promise of combining ULFMRI with Magnetoencephalography (MEG). ULF-MRI is viewed by some as “greener” than high-field
MRI in that it consumes vastly less electrical power, though helium usage is not as efficient.
2.3 Specific R&D needed for Industry to Adopt HTS Materials
Below are some of the research and development areas the UK can do to enable wide use of
HTS devices and commercialization of HTS applications.
HTS materials
 Uniform critical current along full length of wires and tapes
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Cheap and competitive conductor • 2G today, ~ 400 $/kAm for long lengths [9]
1G today, ~ 180 $/kAm for long lengths [10]
Desirable target for future applications ~ 20 $/ kAm
Conductor must have low AC losses in applications.
Superconducting coils
Coils must be able to cope (mechanically & thermally)
With over–currents and fault–currents
Without excessive AC loss in routine operation
Without excessive AC during over–current operation
Without excessive AC loss during the fault.
Device development and engineering
Terminations (demonstrate & standardize)
Robustness - duration of faults
System Integration - in harmony with network.
III. CONCLUSIONS AND RECOMMENDATIONS
The deployment of more superconducting devices will increase the reliability, availability and quality of
power for customers sensitive to these parameters and will provide size, capacity, environmental and
efficiency benefits. The table below summarizes some of the HTS contribution to key performance
improvements required by the energy sector In order for the benefits of HTS to be realized, the following
activities need to be addressed:
1. improving the performance of HTS wire over longer lengths while reducing manufacturing costs
2. Conducting fundamental studies necessary to support wire and systems development
3. Demonstrating the applicability and the potential benefits of superconductivity in electric power
systems
4. Strategic research on supporting fundamental research activities to better understand relationships
between the microstructure of HTS materials and their ability to carry large electric currents over long
lengths
5. Support research and development activities to design superconducting materials 6. Increased funding
should be available to train more engineers and scientists in superconducting applications.
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