Swarup Kumar Neogi, Author at Adamas University

#EnergyNext: Looking for an efficient alternative in the domain of Renewable Energy: the Solar-energy and Solar-cells

Introduction:

Discovery of electricity brought a revolution to human society. Since then the demand of electricity is escalating day by day. In 2004, the total world energy consumption was found roughly 14.5 terawatts (TW) per-day. This huge consumption of energy was first highlighted by Professor Richard E. Smalley as terawatts challenge (December 2004, Materials Research Society Fall Meeting in Boston). The Energy Information Administration (EIA) of United States regularly published survey reports on total world energy consumptions. According to EIA reports, the consumption was 104,426 TWh in 2012, increased to 113,009 TWh in 2017 (wikipedia.org/wiki/World energy consumption). The energy consumption is typically measured per year basis and it includes all possible energy harnessed from all possible energy resources; such as fossil fuels, hydrothermal power, nuclear power, and others (solar, wind, geothermal, biomass, known as renewable energy sources). To meet-up this ever-increasing energy needs, we need to develop and deploy technology to use renewable resources available to us alongwith the improvement of electrical grid and energy storage devices.

Electricity Generation:

Electricity generated from different energy resources is given in the figure here (provided by International Energy Agency, 2019). We can see even today the electricity generation mostly (~70 %) depend on fossil fuels. Nearly 20 % is coming from hydrothermal power-plant and only 7 % is coming from solar energy and wind power. Hydropower is an excellent renewable energy source but it requires reserved water in reservoirs at high altitudes, therefore not suitable for every place in earth. Another choice is off-course geothermal energy. It can provide almost what we need at present but generation and extraction of electricity from geothermal-source into usable from is very difficult. Solar energy and wind power are very promising renewable energy resources. Future of electricity generation and supply will possibly depend on these two. I highlight the importance of solar energy as a renewable source and development of solar cells in the following sections.

Why do we need solar energy?

The main concern is that we need huge amount of energy per-day (roughly 15 TW). At the moment most of the energy is coming from fossil fuels (coal, petroleum, natural-gases), non-renewable resources. These fossil fuels take millions of years to reform and if we consumed at the present rate then the available amount of reserved oil, natural gases and coal will end up soon. So, we need to reduce our dependence on fossil fuels and look for alternatives. In addition, burning of fossil fuels generates CO₂/CO gases causing environmental pollution. We are looking for some alternatives that are more environment friendly.

The Sun is a massive source of energy. Nuclear fusion reactions always go on inside the Sun, in which hydrogen atoms fused into helium atoms, realising energy into space in the form of radiation. Our Earth receives energy from the Sun in two forms : heat and light. Direct radiation from the Sun reaches almost every corners of earth. Total energy received by earth from Sun is roughly 1.75×10¹⁷ Watts. Here we need to consider loss of radiation due to atmospheric scattering and absorption of radiation in the upper atmosphere. Almost 30% of the incoming radiation is reflected back into space and rest portion is absorbed by clouds, oceans and land-masses (wikipedia.org/wiki/solar-energy). We consider the energy absorbed by the land-mass only, termed as technical potential of direct radiation; it is P_technical = 26,000 TW. We see that P_technical is several times larger than total energy consumption per day. It is really remarkable and makes solar energy a captivating source for generation of electricity. What we need is to develop an efficient device (solar cells) to produce electricity directly from sunlight. Solar technology it is quite expensive initially but in the last 5 to 10 year development in photovoltaics is promising and prices are coming down very fast. The following sections I will focus more about solar-cells and the three generations of solar-cells.

History of Solar cells:

The photovoltaic effect was discovered in 1839, by Alexandre Edmond Becquerel and with this the journey of solar cells began. In 1983, selenium solar cell with efficiency roughly 1% (fraction of incident power converted to electricity) was developed. However next significant breakthrough in this field came in 1954, with the discovery of modern silicon solar cells in Bell Laboratory, efficiency of 6%. After that in 1959, Hoffman Electronics manufactured commercial solar cells of 10 % efficiency. Initially solar devices were quite expensive and were used in space-applications mainly. As it is not possible to carry huge batteries into space, solar cells proved to be a good alternative although it is expensive. The silicon solar module was first installed in satellite Vanguard-1, in 1958. Thereafter solar cells have been regularly used as main power source for satellites.

Figure 1: Use of solar cells in space applications; Vanguard-1, Explorer 6 and Telstar (source: wikipedia.org/wiki/Vanguard 1, Explorer 6, Telstar)

Since 1990, solar technology has been shifted slowly from silicon to gallium arsenide (GaAs) based technology. Subsequently thin film solar-cells, polymer solar-cells, multi-junction devices are developed. In this long journey, since 1839 to 2020 several milestones have been reached. Different Companies in collaboration with International Labs have participated in the race of developing solar technology; in this way efficiency and stability of the solar devices are improving day by day.

Three Generations of Solar cells:

First generation: Silicon solar-cells belong to this group, are really dominating in the market at present. Either mono-crystalline or polycrystalline silicon are used to fabricate solar cells. Generally silicon cells are thick so materials cost is huge, they are efficient and stable with reasonably high energy payback time; it means more energy/cost has been spent in manufacturing the solar-cell than electricity gained from it.

Second generation: Thin films solar cells belong to this group. Main 3 candidates are copper-indium-gallium-selenide (CIGS), cadmium-telluride (CdTe) and amorphous silicon solar cells. Materials used here are direct band-gap semiconductors and thickness of the absorbing layer varies from few nano-meters to micro-meters. The main advantages are; much thinner than silicon cells so material cost is minimized, can be prepared on flexible substrates and have much lower energy payback time. The main drawback is they are less efficient than conventional solar cells.

Figure 2: 2^nd generation Photovoltaic solar-cells (wikipedia.org/wiki/Thin-film solar cell)

Third generation: Actually various different types belong to this third generation. It includes polymers solar cells, dye-sensitized solar cells, multi-junction solar cells, quantum-dot solar cells, and perovskite solar cells (wikipedia.org/wiki/Third-generation photovoltaic cell).

Polymers cells come under organic solar-cells. Polymers cells can prepared directly from solutions, they can be printed or coated over a flexible substrate. The production time is less hence they have really low energy payback time.
Multi-junction cells consist of multiple p-n They are GaAs based solar-cells, are really very efficient and expansive, mainly used for space applications.
Quantum dot cells are basically nano-crystals of semiconducting materials like; cadmium sulphide (CdS), cadmium selenide (CdSe), lead sulphide (PbS). Main advantage here is one can tune the band-gap of these semiconductors by changing the size of nano-crystals.
Perovskites solar cells are very new and fastest developing technology. In 2009 the recorded efficiency was 3.8% and it increases to 22% in 2016. They can be made like polymer solar-cells but stability is the main challenge that is to be improved.

Conclusion:

Solar cells are capable of generating electricity from Sun light. They are environment friendly as they do not emit any greenhouse gases like fossil fuels or toxic wastes like nuclear energy. The main drawback is their efficiency and high cost. Lots of research is going on in this direction and we believe that in future many efficient and cost-effective photovoltaic devices will be available for us and would resolve our energy need.

#PositiveCorona: Impact of COVID-19 on evolution of Online Teaching-Learning

Introduction:

Coronavirus disease (COVID-19) caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) was first detected in China in 2019 in Wuhan of Hubei Province. Since then coronavirus has become a new threat to humanity and many countries across the world have implemented forced lockdown to tackle the spread of COVID-19.

In our country, we are also facing the coronavirus threat since March 2020. Following the declaration by World Health Organization (WHO) that COVID-19 is a pandemic, the Central and State Governments have announced lock down with immediate effect and havealso taken several possible safety measures like closure of all academic and educational institutions, imposing strict restriction in public gatherings, shutdown of shopping malls, play grounds, hotels and restaurants, cinema halls, etc. to prevent the spread of coronavirus.

Pandemic make changes in the delivery model of education. Manyacademic institutions havedecided to move their courses online and have chosen different online platforms (Google-Meet, Skype, Team, Zoom) to impart education.Concept of online teaching learning evolves as a promising alternative to regular classroom teaching.It bridges the gap between students and teachers and makesthem feel as if they are sitting in a classroom.In this brief note, I am going to highlight some advantages and some key challenges in this field.

The Impact of COVID-19 on Education Sectors:

Coronavirus has imposed a serious challenge to the academic sector. It has caused disruption of education for nearly 290 million students globally (Reported by UNESCO). Closure of academic institutions was indeed necessary to save life from coronavirus threat. The three key words of life now are ‘stay at home, stay safe and social distancing’. Learning-online is the mostacceptable option for students and academician until a vaccine becomes available. Digital tools and platforms can play a vital role during this COVID-19 created crisis.So with the help of technology, we can re-think and then re-orient our teaching learning pedagogy based on the needs of the students.

Approach towards Online Teaching:

Many of us still believe that face-to-face model of teaching-learning-evaluation is the best option as compared to teaching online. But it is the right time to look for alternatives. If students aren’t able to come to the classroom then the only option left is to bring the classroom into their house.

Thisonline remote learningincludes computer based learning, web-based learning, online virtual classes offered by various academic institutions. However the immediate move towards online education is not easy. It requires lot of planning at the ground level. In this context preparation of resources (lecturer materials, lecturer video) are very important. Institutions should take initiatives to create a technology-enabled environment for maintaining contacts with students and guardians and to teach them online. Professors and teachers from Colleges and Universities can use several communicating platforms like Zoom, Team, or Skypeto reach the students to impart education. The mode of communication includes:

Conduction of online classes.
Sharing and uploading of lecturer materials (pre-recorded lecturers, PDFs, power-point presentations) through emails, Institution’s website.
Sending regular assignments and taking online tests.

If someone misses a particular online class due to interruption in internet connection, he/she can later see the recorded version of the same in his/her suitable time. Only appropriate link has to be shared among the learners. In addition, students can also avail several online educational platforms like Coursera, FutureLearn, Simplilearn and continue their education by watching video lectures, listening to audio and downloading reading materials. Learners can learn according to his/her preferences and interest through these online educational-platforms. However, the present model of online education is just web based learning. Installation of any package-software is not required. A laptop/desktop orsmart phone with internet connection and web-browsers, that’s all we need to starttransferring knowledge and skills. It is rightly described as ‘emergency remote teaching’.

Does Pandemic reforms our Education:

At present we are going through the phase of Unlock 2 and have observed a sudden abrupt enhancement in the number of reported confirmed cases in India. We have the highest reported confirmed cases in Asia and also it is the third highest in the world after Untied States of America and Brazil (https://en.wikipedia.org/wiki/COVID-19 pandemic in India). If problems caused by COVID-19 pandemic stay in same intensity for next couple of months, then normal interactive classroom teaching will be very difficult even in next semester.

Can these digital platforms be a suitable replacement of a physical classroom? At this point we don’t actually know how long the academic institutions will remain closed. Teaching online requires communication, delivery, distribution of class materials and assessments; hence a meaningful integration of education with technology is the necessity.All academic institutionsare now slowly incorporate online education into their strategic planning to impart education at the state of emergency. It is not that we are looking for a drastic change in the conventional way of teaching and learning; rather we are trying to re-orient the conventional way to continue teaching-learning process even in this present scenario.Quality online education requires both rich content and scope for interaction among student-content, student-student and student-teacher. Integration of content with scope for interaction in a meaningful way could enhance the learning outcomes. Followings are some key advantages of remote teaching:

Advantages ofOnline learning:

The interface between learners and trainers is user friendly and above all students feel a classroom experience by sitting safely at his/her home.
One can easily share study materials in all formats (PDFs, PPTs, and lecturer videos) either through emails or can upload it in website and conduct online live classes.
Flexible in time, teachers can upload the lecture materials before the class hours, andclassroom time could then be more productive and interactive.
One can easily note down the participation of students in online classes and online exams, based on the performance extra tutorials can be conducted.
Presently most of the competitive exams are being conducted in online mode. Participation in online tests, quizzes can improve competitive mind of students.
One can also conduct webinars,communications between renowned subject experts and students is made possible through these online webinars.

India is a vast country. Indian Universities and colleges are gradually developing their online teaching-learning programmes. Quality online learning programmes require lot of planning, preparation and investments. It is equally true that participation in online education requires computers/smart phones and internet connectivity. Problem comes when a student do not have access to those digital devices and internet connection. In the long run success of online learning requires Govt. should provide free broad-band connection and suitable devices to every leanersand digital equity in education has to be ensured.

Conclusions:

At present, whole world is fighting against the COVID-19 pandemic. In spite of some challenges, teaching online covers a lot of ground in academics in this crisis situation. In future India will do well on online education and will create far better opportunity for learners. Recently IIT-Bombay has introduced a self-paced online course (https://sites.google.com/view/iitb-teachonline) for instructors.It is a continuous process, more such courses are needed to be prepared and also on regional languages and shared among the learners and experts, that willincrease awareness of online education.As rightly said every cloud has a silver lining. Lock down gave us short but some effective time to introduce online teaching and learning into mainstream education. Once we will return to normal life, realize that digital technology and online classes are companion to the face-to-face teaching and learning. On top of that, the resource materialsprepared for online courses will be an asset for academician and institution. In this crisis moment parents and teachers can join hands to motivate students to be fully involved in online teaching-learning process.

Spintronics: A Journey from Physics Laboratory to Industry; a Prospective field for Engineers and Scientists

Introduction:

Spintronics or spin transport electronics has emerged with a promise that we can now simultaneously use both charge and spin of electrons in a device.

Operation of conventional electronic device such as; transistors, OPAMPs Integrated Circuits (ICs) solely depends on the transport of the charge carriers (electrons/holes) and spin is ignored totally. In contrast, a spintronic device measures the difference in transport of “spin up” and “spin down” electrons in the circuit. During last 30 years the idea of spintronics technology has flourished and has created huge job openings for engineers and scientists. The journey was started following the discovery of giant magneto resistance (GMR) in 1988. At present, GMR based sensors are used in hard drives, in robotics, electric vehicles, MRAMs, Industrial motors, magnetic sensing and in navigation.

What is Spin and how it can be used in a Device??

An electron has 3 fundamental properties; charge (e = -1.602×10^-19 C), mass (9.1×10^-19kg) and spin. In addition an electron has two kinds of angular momentum that describes it’s orbital motion and spin motion separately. All particles in our world are classified according to their spins. Some of them have integer spin are called bosons and others have half integer spin called fermions. According to quantum mechanics an electron have spin either (+1/2) or (-1/2).

Motion of electrons inside a conductor is described by electrical current (I) is defined as: I = q/t (in units of Ampere). Spin is another fundamental quantity like charge could be detected by measuring magnetic moment (in units of Bohr magneton of an electron). All kinds of magnetic ordering and interaction inside a solid are now explained through spin of electrons.

Spin of an electron can have two stable states; “spin up” and “spin down” in presence of magnetic field. The spin up and down states of an electron can be used to represent the two binary logic states: 0 and 1. The idea behind spintronic technology is to encode information in these two spin states.

Figure 1: Description of spin angular momentum of spins ½ particles (Reference: Wikipedia.Org).

Importance of Spin electronics …

Movement of spins like flow of charges can also carry information in a device.
Spin transport requires less amount of energy than that of charge transport in electronic circuits.
Once spin state (up or down) is created for an electron it would stay in that state unless we change it by applying field.
Spin states can be flipped quickly (up to down) and easily by switching the external magnetic field.

Applications: (i) Magnetic sensors (ii) Non-volatile RAM (iii) Quantum computing.

Developments of Spintronic Devices in Laboratory:

The first breakthrough in this field came in 1988, with the discovery of giant magneto resistance (GMR) by Albert Fert in France and Peter Gruenberg in Germany. After that several milestones has been reached and now we can broadly categorized all spin electronic devices into four groups

Spin valves based on magnetic nonmagnetic layered structure.
Magnetic tunnel junctions

Ferromagnetic-semiconductor hybrid structure

Organic devices

Spin Valves: A schematic of layered ferromagnetic (FM)/nonmagnetic (NM) “spin valve” structure is represented in Figure 2. Spin orientation in a given layer could be changed by external field.

GMR Device: A thin NM metallic layer is sandwiched between two magnetic layers; presented in Figure 2. The conduction electrons became spin polarised while passing through the FM layer. The resistance is minimum (R_min) if spins of the neighbouring magnetic layers are aligning parallel. If magnetic layers have opposite spin configuration then resistance is maximum (R_max) and GRM ratio is defined as

Figure 2: Schematic of layered FM/NM structure (Source: https://www.physicscentral.com)

Magnetic tunnel junctions (MTJ): The structure is similar as described above; the only difference is that NM metallic layer is replaced ultra-thin insulating oxide (Al₂O₃/MgO) layer. Electrons can tunnel through one magnetic layer to other easily when both them have same spin configuration otherwise resistance is high. The spin dependent tunnelling current in MTJs depends on the structure and morphology at the interface with the FM layer. Like GMR, MTJs are used for fabrication of spin valves.
Ferromagnetic/semiconductor hybrid structure: Different types like; Schottky Diode, Spin FET, Spin LED, Spin transistors belong to this category. There is another type; known as “Diluted magnetic semiconductors” have been studied extensively in last two decades. The idea was to introduce magnetic elements; such as Mn (transition metals: d block element) as dopants in semiconductors such as; GaN, GaAs to produce a magnetic semiconductors. They are fascinating because within a single device we could see amplification of electrical signals in addition spin polarized carriers could be used for storing information.
Organic Devices: Recently organic materials (grapheme, carbon nanotubes) have been used as NM media to store and carry spin polarized carriers (electrons/holes). A new research field “molecular electronics” has evolved recently which aims to build electronic devices from single molecules.

A Journey from Laboratory to Industry:

Scientist came up with idea, technologist converts it into devices and industry came up with the final product, if it is profitable. The journey began when IBM industry first implemented GMR “spin-valve” into hard drives. This “spin-valve” technology ensures better storage capacity in magnetic hard drives. IBM research scientist, Dr. Stuart Parkin with his colleagues had taken initiatives to commercialize this “spin-valve” technology. The first spin valve sensor “Deskstar 16 GP Titan” (capacity 16.8 GB) released into market in 1997, within 10 years of the discovery of GMR. In September 2007 “The New York times” reports that the huge increase of digital storage capacity by virtue of “spin-valve” technology made possible consumer audio and video iPods, and Google style giant data centres in reality. Latter Hitachi (2013 onwards) had launch model: 7K 1000 with 1 TB capacity and model: 7K 3000 with 3 TB of storage capacity. We could never find such a rapid development in any other scientific field.

Over the last two decades physicist and technologist around the world had work hard on TMR spin valves (MTJs). These MTJs could be used in magnetic random access memory (MRAM) cell, perhaps the best commercially useful spintronic product. Several companies; Everspin-technologies, Freescale, IBM-corporation, Inter-corporation, Hitachi, Micron, and startup groups in collaboration with research institutes are involved now in MRAM technology. The larger storage space and faster data transfer speed of MRAMs make it more useful and it might replace the other memory chips such as; SRAM, DRAM, Flash-memory in future. In addition MRAM is non-volatile means no information is lost when powered off. It consumes less power and is more robust hence suitable for extreme condition to work such as; at high temperature or in high level of radiation.

Figure 3: Major breakthroughs in spintronic field. Red cross symbol represents commercialize technology and green cross represents the scientific idea. (Reference: https://doi.org/10.1038/s43246-020-0022-5).

Conclusion and Future Prospect:

Spin-electronics involve active control and manipulation of electron’s spin in solid state devices. However this novel idea could be realized only if the 3 requirements; (i) Efficient spin injection (ii) Slow spin relaxation and (iii) reliable spin detection are satisfied. At present hard drives and MRAMs holds the market for spintronics however it is difficult to predict in which direction it will move in future. Faster data transfer speed with high storage capacity requires nanoscale fabrication of these devices to enhance the areal density in hard drives. But it causes enhancement in energy consumption. It is possible that spintronics successfully used in quantum computation in future. On-going research and development in this field during last 30 years is very promising, so in my opinion it will enhance the job opportunities and may controls the economic growth of several countries.

Superconductivity: A Mysterious State of Matter that controls the future of Medical diagnostics and Research

Introduction:

In 20-th century a major breakthrough in science came with the discovery of new state of matter, called the superconducting state. Generally materials are divided into three different classes based on their ability to conduct current. They are metals, insulators and semiconductors. Metals (Example: Copper, silver, gold) are good conductors, electrons are moving freely and carry electrical charge inside a conductor. Insulators (Example: rubber, glass, plastics) are bad conductors. Semiconductors are those whose conductivity lies in between metals and insulators. Superconductor are not belongs to any three above categories.

Metallic wires conduct current offer resistance to the flow of electrons. Inside conductor electrons suffer scattering from lattice defects, vibration of atoms in the crystals, and free paths of those electrons become truncated. This is what is called resistance of a wire and it depends on the metal itself. Due to this resistance we see heating effect in wires and energy loss. If one can make a zero resistance coil then we can forget about this heating effect. This dream came into reality in 1911 with the discovery of superconductivity. Professor Kamerlingh Onnes observed that on cooling mercury below 4.2 K its electrical resistance suddenly drops down to zero. The zero resistance state is named as superconducting state. The temperature at which the transition from normal state to superconducting state took place is called critical temperature Tc.

History behind the discovery of superconductors:

Professor Kamerlingh Onnes in his laboratory at University of Leiden had developed technology to liquefy gases like; oxygen, hydrogen to produce low temperature. He wants to study how conductivity of elements like mercury, lead would behave at this extreme low temperature. Finally in 1908 he succeeded in liquefying helium at temperature of 4.2 K, the lowest among all other gases. Discovery of liquid helium promotes the discovery of superconductivity in mercury in 1911. Even today many of us could not imagine how much cold 4.2 K is. In the beginning of 20-th century Professor Onnes made his laboratory equipped with unique cryogenic facility to investigate properties of matter at such extreme condition. He received the Nobel Prize in 1913 for his striking discovery.

Why should we learn Superconductivity?

Discovery of superconductors creates revolutions in science. It changes our understanding behind the microscopic source of electrical resistance in materials below T_C. So many unexpected observations associated with superconductivity create tremendous research interest in this field. Here I am mentioning few of them.

In 1914, Professor Onnes discovered once current induced in a superconducting ring persists for long time never degrading or dissipating.
Superconductivity observed in many metals, in alloys, in ceramics, allotropes of carbon etc., but it has not been observed in some good normal conductors like; cooper, silver, gold except at high pressure.
Superconductivity can be destroyed by application of strong magnetic field, called the critical field H_Ceven if the temperature of the sample is less than T
External magnetic field can never penetrate inside a superconductor. This is Meissner effect, discovered in 1933. Flux exclusion was also seen when a material first cooled to T_C and then the field is switched on.
When two superconductors are joined by a very thin insulating layer, tunnelling of superconducting electron pairs across the thin layer happens. This is called Josephson Effect, discovered in 1962.
Levitation is the magneto-mechanical phenomenon. Being a perfect diamagnet bulk of the superconductor is shielded from external magnetic field by appropriate surface current that causes a counter reacting magnetic field and superconductors are found to be levitate over a strong magnet.

Superconductors are neither conductors nor insulators. It is a unique state of a material. Zero electrical resistance and perfect diamagnetism defines the superconducting state.Theoretical understanding of superconducting phase has been reached after several years from the discovery. Meissner Effect describes that magnetic flux cannot penetrate inside the bulk of specimen was explained by two British Physicists; H. London and F. London in 1935. London equation described that magnetic flux lines does not abruptly stops at the surface rather enters into superconductor and exponentially die out within 50 nm to 500 nm. Finally quantum mechanical description of superconductivity came in 1957 by Barden, Cooper and Schrieffer. This is so called the BCS theory of superconductivity. BCS theory describes that supercurrent is not carried by a single electron rather by pair of electrons with opposite spin and momentum, called cooper pairs.

Applications of superconductors

Science from the discovery in 1911 thousands of material found as superconductors. Zero electrical resistance, perfect diamagnetism, persistent current are some of the key features that make them suitable for application in science and technology. Superconducting electromagnet can produce stable high magnetic field, used in particle accelerators, magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) machine. Josephson Junctions are used in sensitive magnetometers based on SQUID (superconducting quantum interference device). But perhaps MRI is the best successful commercial application of superconductors in 20-th century.

Magnetic Resonance Imaging (MRI)

Application of superconductor in medical science was started around 1970 in Great Britain and United States of America. Once current is stored in superconducting coli it stays for ever and produces a steady strong magnetic field used in MRI machines. The MRI body scanner became an essential diagnosis tool for the doctors across the world.

How does it work???

Inside human body soft tissues, blood vessels, fat molecules contains a large percentage of water molecules that contains protons behaving as tiny magnet or like a compass needle. When a person is placed inside a MRI scanner those protons orient them in the direction of magnetic field. The typical field strength needed is 1 Tesla or more. However some of those protons going out of alignment by absorbing energy from radio waves at just right frequency generated by MRI machine. Radio frequency field is composed of short pulses. At the end of a short pulse those protons gradually realign with the static constant field. You may consider this as deflection in compass needle occurs every time when a weak magnet passes nearby. As proton in various parts of the body realign at different rates, different structure of the tissues can be identified and captured. In addition MRI can produce cross sectional view therefore various tissues and their associated disordered could be identified.

Advantages and Disadvantages of MRI Scanner:

MRI can take images of every parts of the body. It is less harm full because human cells are not exposed to any kind of ionizing radiation.
Perhaps the best possible technique to look inside our body without having any cut or open. There are other techniques also like; CT scans but MRI produces better image quality than others, hence most widely used for medical diagnostic.
MRI usually takes longer time for imaging. If a patient have pacemaker in his body then MRI scan is not advisable. Strong magnetic field and powerful radio frequency source causes some harmful effects in this case.

Future Prospects:

The initial problems of cryostat design were overcome and MRI technology is quite mature now. Long solenoid type magnets with uniform winding density are used to produce strong field. The strength of the magnetic field could be found from Ampere’s Law. Most of the high resolution MRI scanners are operated at field strength of 1.5 Tesla. Although 3 Tesla MRI are regularly used for diagnosis and 7 Tesla systems are mainly used for medical research. High field MRI scanner gives better signal to noise ratio and better resolution. With the advancement of superconducting technology we expect that more functionality could be incorporated and cost of the system could be reduced to make it more accessible for us.