Giant Metrewave Radio Telescope

How galaxies form and how they evolve thus requires measurements of various parameters. Although scientists have successfully studied about stellar masses and formation of stars at different epochs. But still there is little known about the fuel of star formation.   

 A Giant Metrewave Radio Telescope has been set up by NCRA, centre of school of natural sciences of TIFR. It is a versatile instrument which study various astronomical problems such as concerning pulsars, radio galaxies and regarding evolution of universe. It is one of the largest radio telescopes in the world. Galaxies are made up of stars and gas. To understand galaxies, there is need to know about the evolution of gas and stars with time. For this purpose GMRT was built to observe many different astronomical objects.  GMRT consists of 30 fully steerable gigantic parabolic dishes of 45m diameter each spread over distances of upto 25 km.  The number and configuration of the dishes was so selected to have high angular resolution as well as ability to image radio emission from diffuse extended regions. GMRT is being designed to operate in six different frequency bands between 38 and 1420 MHz. All these provides a purpose of dual polarization.

GMRT is an indigenous project. The construction of 30 large dishes at a relatively small cost has been possible due to an important technological breakthrough achieved by Indian Scientists.

Scientists of TIFR and IISER Mohali have used the upgraded GMRT to carry out the distant measurements of atomic hydrogen content of galaxies in the early universe. They found that the star formation efficiency of galaxies appear to have not changed significantly over the last 4 billion years.

Why there was a need to upgrade GMRT?

Scientists answered that most of the atomic gas is in the form of hydrogen, which emits spectral line at the radio length of 21.11cm. This emission is so weak that it is not even detected by powerful telescopes like GMRT. That’s why GMRT has been extended to wide range frequency covering range even of hydrogen spectrum.

The upgraded version of GMRT has made possible to have a direct measurements of gas masses of distant galaxies.

Light electrons- Photoelectric Effect

 

Metals consist of: - positively charged ions called kernals and negatively charged electrons. Kernals are fixed on their positions and does not move whereas electrons are free and they move in between positively charged ions but still they do not allow to leave the metal surface. Now the question arises that is it possible to knock out these free electrons from metal surface? The answer will be YES.

          If we want to eject electrons from the metal surface, it is necessary to give some energy to these free electrons. There are some methods which can cause the ejection of electrons-

First is THERMIONIC EMISSION-

It is the phenomenon of emission of electrons from the metal surface with the help of thermal energy. When we heat the metal surface the free electrons start getting energy and they excited and consequently start ejecting out of the metal surface. More thermal energy will cause more ejection of electrons. Electrons ejected are called thermal electrons.

Second is FIELD EMISSION- It is the phenomenon of ejection of electrons from the surface of metal by applying strong electric field. Battery (denoted by B) connected with metal surface (denoted by A). Positive ions of battery will start attracting electrons from metal surface. First electrons will along battery side of metal and as electric field goes on increasing, it will cause the ejection of electrons out of metal.

Now let’s think- Is it possible to eject electrons from metal surface with the help of light?

Answer will be- YES

This process is named as PHOTOELECTRIC EMISSION

Photoelectric emission is a phenomenon of emission of electrons from the surface of metal when light of suitable frequency falls on it.

When light falls on metals, electrons get energy and get excited after that will ultimately comes out of the metal surface. This phenomenon was explained by Hertz, when he was conducting an experiment related to Maxwell electromagnetic radiation.

HERTZ OBSERVATION - Hertz prepared an apparatus in which he used two plates, one is cathode C and other is anode A. Plate C is photosensitive plate and is given negative potential and plate A is given positive potential. Whole apparatus is evacuated in glass tube. Through a window, light of suitable frequency is made to fall on plate C. Electrons get energy and will start coming out of the plate C and will start attracting towards positive anode A and thus will constitute current. Electrons thus ejected are called photoelectrons and current formed is called photo current.

Supercapacitor vs Battery & Capacitor

In this era of climate change, there is a need to switch from fossil fuels to electric power. Electricity is a versatile form of electricity but it has one problem associated with it. As I had raised same concern in my last post that there is a problem to store electricity for a long time (https://imbibephysics5794.blogspot.com/2020/08/decarbonisation-and-storing-thermal.html). For capacitors and batteries we need to look for two different things, one is amount of charge stored and other is how quickly the energy is delivered. Capacitors deliver energy instantaneously but cannot able to store large amount of charge. Batteries have an ability to store large charge and cannot give energy quickly. So in order to overcome these drawbacks, we need to look for other alternatives. This problem can now be solved by supercapacitors.

SUPERCAPACITORS

Supercapacitor also known as ultracapacitor is an electronic device which is used to store large amount of electric charge. According to following formula, it is cleared that capacitance is directly proportional to surface area and is inversely proportional to distance between the plates.

C = Ɛ_oA/d

How supercapacitors are different from conventional capacitors and batteries?

    Supercapacitors consist of electrodes of large surface area and a thin dielectric plate between electrodes so to have large capacitance. Supercapacitors can store 100 times more charge than a conventional capacitors. Here, electrodes are made up of some porous substance which provides more surface area for storage of charge. In supercapacitors there is no dielectric material between the plates. Both electrodes are soaked in specific electrolyte and are separated by very thin layer of insulator. Plastic, paper or carbon can be used as insulator. That’s why supercapacitors could able to store larger charge because of large surface area of electrodes and lesser distance between them.

    Supercapacitors rely on static charges resting on solid electrodes while batteries rely on the charges which produced through chemical reactions of liquids present in batteries. Batteries have higher energy density while supercapacitors have higher power density. All these factors gave us conclusion that supercapacitors releases energy very quickly as compare to batteries.

Future of supercapacitors

Scientists believe that supercapacitors may replace lithium ion cells as it charges more quickly and can recharge multiple numbers of times.

Scientists are exploring the concept of designing lightweight supercapacitors by designing ECs with graphene which will have high storage capabilities.

Supercapacitors can widely be used in automobiles where regenerative braking is used, in wind turbines, motors and also it been employed in hybrid buses.

By looking its applications it seems that supercapacitors or ultracapacitors are a most promising energy storage device.

Black hole bagged Nobel Prize this time

Black holes, in simple language can be anything but an empty space. But in our universe black hole is super massive monster in which great amount of matter concentrated in a small region. In it, gravitational field is so strong that nothing can escape out of it, not even a light. Black hole forms when massive star collapses at the end of its life cycle. After its formation, it continues to grow by engulfing the matter around it. And in this way it grows in the form of supermassive black hole.

Three scientists share the Nobel Prize in Physics, 2020 for their discoveries about the black holes in universe. Roger Penrose showed that the general theory of relativity leads to the formation of black holes. Albert Einstein who gave general theory of relativity could not able to explain properly the existence of black holes. In 1965, Roger Penrose used various mathematical methods and in his proof tells that black holes are a direct consequence of Einstein’s general theory of relativity. He explains that black hole is a kind of situation in which all the laws of physics ceases. He tells that black hole would be a real and stable astrophysical object. He laid the theoretical foundation which explains the existence of black holes in outer universe.

Reinhard Genzel and Andrea Ghez both led the research that tracked stars at the centre of the Milky Way. Their orbits were bent by what known as supermassive black hole. Their study was mainly focussed on the region called Sagittarius A* at the centre of our galaxy. Both researchers claimed on finding extremely heavy and invisible object that pulls on the closest stars and cause them to orbit around at dizzying speeds. Sagittarius A*, weighs about millions of solar masses and is about 26000 light years away. Genzel and Ghez used world’s largest telescopes and various methods to see through the huge clouds of interstellar dust and gas to the centre of the Milky Way. In their study, they mapped the progress of a single star orbiting around Sagittarius A*. by studying such orbits, they draw out the conclusions of the presence of invisible object. Unique instruments and refined new technologies which reduce distortions and noise has lead us to give most convincing evidences of a supermassive black hole at the centre of our galaxy.

The discoveries of these researchers have open up new doors of the study of supermassive and invisible objects present in our universe. In the end, both these researches provided the strongest evidences of black holes and also lead to the development refined telescope methods and wonderful technologies. But still there are several questions which are still to be answerable by our future researchers.

Decarbonisation and storing thermal energy- Need of an hour

The Paris agreement was signed to slow down climate change. But in order to keep a check on global warming, the need of an hour is to go on a path of decarbonisation. Decarbonisation refers to the reduction of carbon dioxide from the energy resources. And this requires switching to clean renewable energy sources and shifting from fossil fuels to electricity. Studies show that 90% of world’s total energy involves the generation and elimination of heat or thermal energy, which also includes the cooling of food and your rooms. But in order to cope with the problem of climate change there is a strict need to transmit and store thermal energy.

Solar and wind power are very much important part for solving the problem of climate change but will not give efficient energy for running out industrial processes. But still modern renewable technologies are the most inexpensive source of electricity. There is a need to increase its consumption percentage and must decarbonize heat and use this heat and thermal energy to store or convert into electricity.

There is a need to build a technology that could reduce green house emissions by atleast one gigaton. We all are in the hustle to improve our quality of life but on the cost of environment.

One of the major challenge is to store excess solar and wind energy as heat over number of days and then to convert it into electricity when required. Along with this decarbonisation of energy will reduce green house gases emission in environment. But there is need to expand technology because present technology like lithium ion batteries is too expensive to be used to store renewable energy for multiple days. Many heat energy technologies are still in their early development.

  GHG emissions coming out of industries comprise 15% of global emissions and having heat ranging of temperatures 100 to 1000°C. Industrial sector could make steps to decarbonized its emissions by using hydrogen combustors and resistive heaters. Here also R&D work is to build low capacity factor furnaces and cheap high temperature devices.

With the rise of refrigeration and cooling in developing economies, this also comes up a major challenge. Here the goal is to invent refrigerants for air conditioning and food without leakage of hydrofluorocarbons. There is need to develop new refrigerants must which will be non-flammable, non-toxic and affordable.

Also there is a great need to control thermal conductance in building’s shell which could save 10 to 40% of GHG emissions in atmosphere. The new goal is to develop heat equivalent to an electrical power line used for transporting large megawatt of heat to large distance with minimal equipments. Thermal superconductor can be used for this but still lots of discoveries are required in this field.

Decarbonisation and storage of thermal heat will offers the best way for setting a common course for a secure, sustainable and economically successful future on a planet worth living on. 

National Education Policy 2020: Revolution in education sector

Government of India has given its approval for new education policy of the year 2020. This will bring massive changes in education sector and pave its way for key reforms in school and in higher education also. The Ministry of Human Resource and Development has been renamed as Education Ministry. First National Policy on Education came in1968 on the recommendations of Kothari Commission. Then comes National Policy on Education 1986 and now after 34 years we have National Education Policy 2020. This policy is drafted by the panel headed by former ISRO chief K. Kasturirangan.

Key Features:

Its prominent feature is the replacement of 10+2 structure of school curricula with 5+3+3+4 structure.

Existing Academic Structure- in this we have 10years of schooling from class 1-10, after that student has to go for pre university schooling.

New Academic Structure- now the 1986 structure is been replace by 5+3+3+4 structure for transforming educational sector. In this new structure, it has four stages-

1.  Foundational stage (5)- this stage is divided into two compartments. The first 3 years is of pre school belonging to age group of 3-6years. They are made to taught language skills, cognitive skills and is activity and play based learning. Next two years of class 1 and 2.
2. Preparatory stage (3)- belongs to age group of 8-11years and classes 3 to 5. Most of the student will be taught in local language or in mother tongue. This stage is more about discovery, activity and interactive classroom learning.
3. Middle stage (3)- belongs to age group 11-14years and classes 6 to 8. Students will start learning about coding and occasional activities. This will be first time that all the students after 6^th will be taught computer coding.
4. Secondary stage(4)- this stage is multidisciplinary in nature. Greater critical thinking and more flexibility will be given to students. Students would able to select choice of subjects.

Apart from it, teachers are a important factor of educational sector. Now, the govt is emphasising to control pupil-teacher ratio and to hire local and trained teachers.

Multi-disciplinary approach:

Standalone higher education institutes and professional education institutes will be evolved into multidisciplinary approach. The policy drafted multidisciplinary Bachelor’s programme with exit options. Lets consider B.Sc. programme, when student complete his first year and if he want to exit then he will be awarded with the certificate. After finishing 2 years he will be awarded with diploma and after 3 years he will handed over Bachelor’s degree. In case, it is four year degree, then student will enter into research and at end of four year, he will get research certificate as well. In Master’s, student will have to show all these four documents or certificates and we will able to finish his Master’s in one year only. M.Phil. degree would be abolished.

UGC and AICTE will now be replaced by Higher Education Commission of India (HECI) which will carry out all the functions of regulation, funding and learning outcomes in higher education.

Phasing out of all institutions offering single streams: we have IIT’s, they focus on science and technology but now by 2040 IIT’s and other higher education institutes will also focus on arts and commerce related subjects also.

National Educational Technology Forum (NETF): This forum is made to provide the platform for free exchange of ideas and strengthen learning with the use of technology.

Paving the way for foreign universities: but this comes up with criticism also. One is related to higher fees and second is these universities will starts poaching the educators and intellectual minds of country.

SIGNIFICANCE

·As recommended in Kothari Commission, govt. will spend 6% of GDP on education

·Govt will also put a cap on the fees of private institutions to make education affordable for maximum people.

·Learning will become less stressful.

·No rigid separation of subject.

·Govt brings Gender Inclusion Fund as equity measure.

Hall Effect Sensor

Sensors and transducers are used to check the practical behaviour and magnetic behaviour of any electrical equipment. There are so many sensors available in market, but here we would discuss about Hall effect sensors.

What is hall effect?

Hall effect was discovered by Edwin Hall in 1879. This effect is better understood by an experiment: suppose we have thin conductive plate and then set a current through it with the help of battery. The charge carriers would flow through it in a straight line. If we bring magnetic field near it, then the flow of charge carriers would deflect from straight line due to Lorentz force. The electrons would deflect to one side and holes to the other side of plate. This would result in voltage between these charges. This production of voltage difference across conductor is transverse to current and also to magnetic field and this effect is called Hall effect.

Hall effect sensors

Principle of hall effect sensors are totally based on Hall effect. Output voltage of hall effect sensors are quite low, usually of few micro volts. That’s why it is employed with amplifier to increase its sensitivity. The output voltage, called the Hall voltage, (V_H) is directly proportional to the strength of the magnetic field passing through the material (output ∝ H). There are two types of hall effect sensors- analog and digital output sensors.

Analog output Hall effect sensor

Analog output sensors- linear or analog sensors gives a continuous voltage. It increases with strong magnetic field and decreases in weak magnetic field. At a very high magnetic field it attains saturation. These types of sensors are suitable for measuring proximity.

Digital output sensors- it has two output states either ON or OFF. These type of sensors have additional element in their circuit called Schmitt Trigger. When magnetic flux passing through the Hall sensor exceeds a pre-set value the output from the device switches quickly between its “OFF” condition to an “ON” condition without any type of contact bounce. They are often used as limit switches, mostly used in CNC machines, 3D printers and in automation systems.

Digital output hall effect sensor

Physics of Cyclones

         Cyclones are the most violent storms on earth. They are also called hurricanes, typhoons and willy willies depending upon their locations on earth. Geographically these all storms are called tropical cyclones. Tropical regions receive vertically and direct sunrays whereas polar regions receive slanting sunrays. Wind movements are determine by high pressure and low pressure system. Winds always move from high pressure to low pressure areas. The differences in atmospheric pressure create pressure gradient causes the wind to move. Low pressure occurs where land or ocean is warm and high pressure occurs where land or ocean is cool. That’s why winds blow from polar region (cool land) to equator (warm land).

     Another factor which is important in the formation of cyclones is CORIOLIS FORCE. Due to the rotation of earth, a force is generated and it acts perpendicular to the direction of motion and to the axis of rotation. Earth is spherical and it moves from west to east and also, earth is much wider at the equator than at the poles. So, if anything has to be come straight from the poles to the equator it gets deflected towards right in northern hemisphere and towards left in southern hemisphere. Such deflection is caused by coriolis force.

At the centre of every cyclone there is region of low pressure called eye of cyclone. As air moves from high pressure to low pressure which means outer region of cyclone consists of cool air which surrounds low pressure area of cyclone. Warm and moist air rises from the surface of ocean. As it rises, to fill its place cool air rushes to this low pressure region. Now this air becomes warm and moist and this rises too and hence warm air continues to rise. Temperature drops at high altitude, so warm air cools off to form clouds. Now coriolis force comes into factor, as air deflected to right in northern hemisphere but it got attracted to eye of storm (low pressure region) this makes it swirl in anticlockwise direction. Similarly in southern hemisphere due to bending in left side it swirl in clockwise direction.

Cyclones normally occur on the ocean surface due to continuous supply of moisture. When it hits the land, moisture supply cut off and storm dissipates.

Bose Einstein Condensate- our fifth state of matter

We all were well studied about four states of matter - solid, liquid, gas and plasma. There is also fifth state of matter which is much mysterious and is called Bose Einstein Condensate. It is a state of matter in which atoms and subatomic particles are cooled to absolute zero temperature (0K). At such low temperature, they have no free energy to do any random movements. At this point, they clump together and the whole group starts behaving like as though it were a single particle. This form of matter was discovered by Albert Einstein in 1924 on the basis of the formulations derived by the Indian physicist Satyendra Nath Bose.

To make bose Einstein condensate, scientists used atoms of rubidium. Then cooled them with laser, this takes away all their energies by imposing radiative pressure. After that, cooling of atoms starts which was further supported by evaporative cooling. In 1990s Cornell and Wieman succeeded in merging together 2000 individual atoms and called it superatom. Superatom is nothing but a large condensate enough to be viewed by a microscope also.

BEC theory has traced back to 1924, when Bose observed that there are two classes behave differently. Fermions tend to avoid each other and each electron in a group occupies different quantum states. Whereas there are bosons also in which can share number of particles share single quantum state. Einstein extended this work and named such particles as ‘bosonic atoms’ which have even spins and they collapse together to exist in single quantum state at absolute zero temperature. At that time there was no method to attain such low temperature, that’s why we waited so long until 1990s.

BEC is related to two interesting phenomena: superconductivity and superfluidity. Superconductivity- in which electrons move through material with zero electrical resistance and superfluidity- in which helium isotopes forms liquid that offers zero friction.

APPLICATIONS

•  Can be used for the detection of gravitational field intensity.
• It can be combined with atomic lasers to create high precision nano-structures.
• It is used in the study of cosmological phenomena by undergoing various simulations.
• Applications in superconductivity and superfluidity.
• It deepens the knowledge of quantum mechanics.

Quantum Dots - An Introduction to New World

      Could you think that you can control the atoms by your own by controlling their motions, vibrations, shutting them on or off and assigning them different colours? Now, the answer will be YES. This can be made possible by QUANTUM DOTS. These are just artificial atoms. Quantum dots (QDs) are man-made nanoscale semiconductor crystal and are zero dimensional, that can transport electrons and has a ability to convert a spectrum of light into different colours. Each dot emits a different colour depending upon its size.

      Just like atoms, QDs also have quantized energy levels. So, as in atoms when electrons gets excited to higher level, they returned back by emitting light of same energy as they absorbed. In this way, they emit colours also. QDs will give out different colours of light depending upon how big they are. The bigger quantum dots produce longest wavelengths (minimum energies) and smaller quantum dots produce shortest wavelengths (maximum energies). That’s why bigger dot is red in colour and smaller is blue and intermediate sized dot is green in colour. This is because bigger QDs have more closely band gap so will require minimum energy to excite electrons and smaller QDs have bigger energy gap so require more energy to excite electrons.

QDs have wide ranging applications covering various areas of catalysis, electronics, imaging, sensors and photonics.

Applications in field of optics

• QDs have interesting optical properties. A thin filter made of QDs can be fitted on LEDs and convert its light into different shades. QDs can be used instead of dyes and pigments. They produce different colours that are brighter and more controllable than dyes.
• QDs have brought revolution in the field of solar cells. QDs produce more electrons (or holes) for each photon that strikes them, potentially boosting efficiency upto 10 percent over conventional semiconductors.
• QDs can also be used in TV screens and computer display. QDs produce light themselves and do not need any backlight, so are energy efficient. They produce high resolution images. QDs LEDs are more brighter than OLEDs.

Quantum computing

Optical computers could use quantum dots in the same way as modern computers use transistors. In quantum computers, bits are stored in atoms, ions and photons all are linked together and are called qubits. These can store multiple values simultaneously and work on different problems together.

Medicine

QDs can be used effectively in cancer treatment. They can easily target one single organ of body liver, kidney, stomach etc. dots are designed such they accumulate in particular part of body and eject anti cancer drug associated to them.

Applications of neutrinos- ghost like particles

      An invisible and almost massless particle could be the building block for some incredible new technology. It’s called the neutrino. Neutrinos have a potential to do amazing things like speed up global communication, detect the presence of nuclear weapons and confirm the presence of dark matter. To know more about neutrinos, you can check out this post too https://imbibephysics5794.blogspot.com/2020/03/what-is-mystery-of-ghost-like-particles.html

1. A way to monitor nuclear proliferation

Neutrinos are produced from radiation, so it might be possible for the International Atomic Energy Agency to use neutrino detectors to monitor which countries are following the treaty on the Non-Proliferation of nuclear weapons. In most nuclear reactors, uranium decays into plutonium. But to male a nuclear weapon, the reactor has to be shut down, the plutonium removed, and replaced with fresh uranium. Nuclear reactors and nuclear bombs release staggering numbers of neutrinos, so international monitors could rely on neutrinos for surveillance and help prevent proliferation.

2. A way to ‘x ray’ the earth to find cavities of mineral and oil deposits

Some scientists have proposed that intense beams of neutrinos could be used to probe the earth’s crust for mineral or oil deposits.

3.  Faster global communication

These particles can pass through pretty much anything & it would be faster to send the message through it across the earth. It would be easy to communicate in submarines. Scientists had encode a message in neutrinos using binary code.

4. A way to detect dark matter

The presence of dark matter has still not been directly observed by scientists. But neutrinos can help in this matter. The Icelab has built a neutrino detector in Antarctica that has detected extremely high energy neutrinos. The scientists built the detector by actually boring holes into the ice. Scientists observed that some neutrinos come from space and are produced from things like supermassive black holes and violent star deaths. These neutrinos might also come from decaying dark matter in nearby galaxies.

5. Communication with extra terrestrial life

Since, it is possible to encode messages in neutrinos, those encoded neutrinos could be beamed into space. They would act as terrific messengers between advanced civilizations across the galaxy.

6. Finding exploding stars

It has been over four centuries since astronomers have seen a supernova in the Milky way. If a star explodes in the far side of the galaxy, neutrinos would come from it unhindered which can be detected by our detectors.

7. Figure out what keeps the earth’s interior warm

Part of our planet’s heat comes from the decay of radioactive elements -but we don’t know exactly what fraction. Since radioactivity also releases neutrinos, measuring them, we can find how much uranium and thorium are there in earth’s curst and mantle.

Day and night duration- due to refraction or scattering?

Many students have this doubt and they questioned their teachers whether the duration of day and night is due to refraction or scattering of light? And also, there is a big debate among the physics teachers, some of them supported refraction of light and some supported scattering of light. In this post, let’s clarify this question.

        If we look into in this matter, the day and night duration is neither due to refraction nor due to scattering of light. This phenomenon is purely geographical. The duration depends upon rotation of earth about its axis, revolution around sun, inclination of its axis with the plane of the motion of earth and our location on the earth.

Greenland, Norway, Alaska, finland are some countries where nights and days do happen in very long duration. Earth’s rotation causes the period of day and night. The part facing the sun is in daylight and other facing away is in darkness. Earth rotates about its axis (imaginary line). Earth’s axis is not perpendicular. There is an axial tilt of 23.5°. Due to this tilt, the sun shines at different angles on different latitudes. That’s why areas coming under arctic circle experiences 6 month day in northern hemisphere and 6 month night in southern hemisphere. The axial tilt of earth decides the duration of day and night at different locations on earth.

Some people also comments that the refraction and scattering does increases duration of day as compared to night time. But still both these phenomena do not play much role.

Before sun rises, we still see the light of sun, this is due to refraction of sunlight with the atmosphere of earth. When light touches the atmosphere, its bends due to refraction and we able to see the light before the sun rises. Same with the scattering also, particles present in the atmosphere scatters light and we experience light before the sun rises. Both these phenomena add 3 to 4 min in duration of day but doesn’t mean elongation of day than night. This thing explains by geographical concepts.

IR Thermometer- one of the weapons against COVID-19

Coronavirus is a zoonotic disease that allows human to human transmission and raised global health concerns. Common symptoms due to this virus are cough, tiredness, cold and fever. No any particular vaccine is available to prevent this spread. The sudden rise in number of coronavirus cases has caused the nations across the globe to take steps to stop the spread. For this, there has been a need of checking body temperatures regularly. In such cases, mercury thermometers are not used. So, it is advisable to use forehead thermometers known as infrared (IR) thermometers.

Infrared thermometers are used to detect body temperature by not contacting the patient’s body. It checks the human temperature by sensing the infrared energy radiated by the body. Infrared sensor detectors are of two types-

• Photon detector- radiation absorption process directly produces measurable effect i.e. provides reading on screen
• Thermal detector- first convert absorbed incident radiation into heat and then produce measurable effect.

   

   Photon detectors consist of materials which are difficult to grow and fabricate and hence are not much effective. Pyroelectric, bolometer, thermopiles are the sensors belong to the category of thermal detectors. Pyroelectric materials have much higher responsivity and specific detectivity, which is not preferable. Most of the companies manufacture thermopile based thermometers. The sensitivity of this sensor depends upon photosensitive area. Whereas bolometric detectors are independent of photosensitive area, which is its plus point. These detectors show high performance in lower cost. Bolometric materials have large temperature coefficient to resistance ratio (TCR) and low noise equivalent power (NEP) and because of these properties, they are preferred to be used in IR thermometers. 

   Infrared bolometric detectors operated at room temperature offer a large number of competitive advantages in terms of cost, operational convenience, higher reliability, reduced power consumption, small footprint and reduced weight.