SUPER CONDUCTORS-EXPLAINED

        Now we will learn about new concept called 'SuperConductors'.We will start from beginning,metals are classified into 3 types conductors,semiconductors and insulators.when voltage is applied to conductors or semiconductors,electron flow(current) occurs, and this flow is restricted by resistance which is the property of conductors.This resistance is resulted due to impurities,defects and vibrations of materials in the crystal lattice.This phenomena is called resistivity which depends upon length and area of the conductor.

        Inverse of resistivity is conductivity.conductivity of conductor lot depends on temperature.Normal conductors conduct below 30k.Scientists worked a lot to increase the conductivity of a conductor.They have varied the temperature but couldn't get much from conductors,because the conductors already have free electrons and increase in temperature will further add energy to this free electrons which makes them to move in less organised patterns making less conductivity at higher temperature.This is not the case with semiconductors,when temperature is increased,the energy is added and in turn helps to free a electron,so at high temperatures more electrons are freed which increases the conductivity.This kind of transition from normal conductivity to super conductivity which will occur when we go from room temperature to high temperature is called Superconducting state and the metals are called Super conductors.The phenomena of exactly zero electrical resistance occurring in certain metals when they are at high temperature is called Superconductivity.

What causes superconductivity?
        We had seen that certain metals suddenly become superconductors,when they are kept at critically high temperature.Reason is, at this temperature electrons inside them will join with each other which are called copper pairs.At this temperature electrons will move more freely without being scattered.High temperature will result more free electrons thus increasing the conductivity of semiconductors at high temperature.At present scientists are working hard to have this feature at room temperature.

        Another interesting thing that need to pay attention with superconductors is Meissner Effect.Normally materials allow magnetic fields to flow through them,but when semiconductors were at high temperature,they increasingly expel these fields.This effect is called Meissner effect and the principle is used in maglev trains.

        Technological applications of superconductors are adopted in Maglev trains,MRI(Magnetic Resonance Imaging) and NMR(Nuclear Magnetic Resonance) as they require strong electromagnetic fields. 

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Brain Computer Interface-The Next Generation User Interface

Brain-computer interface (BCI) is a fast-growing emergent technology, in which researchers aim to build a direct channel between the human brain and the computer.

These are linguistic independent and can be used anywhere across the world .

Types of BCI:

1.    Invasive 2. Non-Invasive 3. Semi Invasive

Invasive: Invasive BCIs are implanted directly into the grey matter of the brain during neurosurgery. As they rest in the grey matter, invasive devices produce the highest quality signals but are prone to scare tissues.

Non-Invasive: In this process the user wears a wearable cap which is studded with electrodes.It has no complication of surgery but signals are weak as they are placed above the thick skull.

Semi Invasive: Semi-Invasive BCI devices are implanted inside the skull but rest outside the brain rather than amidst the grey matter.

Applications:

• Provide disabled people with communication, movement restoration.

• Provide enhanced control of devices such as wheel chairs, vehicles, or assistance robots for people with disabilities.

• Provide additional channel of control in computer games.

• Monitor attention in long-distance drivers or aircraft pilots, send out alert and warning for aircraft pilots.

• Develop intelligent relaxation devices.

• Control robots that function in dangerous or inhospitable situations (e.g., underwater or in extreme heat or cold).

• Bionics/Cybernetics

• Dream Capture

• “Google Search” through brain

BCI research is an interdisciplinary endeavour involving neuroscience,engineering,signal processing,rehabilitation and lies at the intersection of emerging technologies such as Machine learning and artificial intelligence among others.

BCI is considered as a new frontier in science and technology.

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Difference between Normal diode and LASER,LED Diode's

 Hi friends, every one who knows about electronics devices will be familiar with diode and optical sources like LASER and LED. The optical sources are also diodes. By knowing this every one may think that why a normal diode could not emit light where as a LASER and LED does?

The answer to this question lies in developing of these normal and optical diodes.

The major differences between normal and LASER and LED type of diodes is

“Semiconductor materials used for making”

Due to this we have variation in formation of junction between P and N region and differences in band gap energies also plays a role to not emit light(radiate) in case of normal diode

*As we know that Normal diode is made from semiconductor materials of group 4 like Si and Ge. These are doped with either group 3 or group 5 elements to form  P and N type materials respectively and when this doping is done on single semiconductor material, a diode is formed.

*In this case we will see a non heterojunction formed between P and N regions of a diode, this is called depletion layer(or)region  which is increased or decreased  by biasing.

*We have used single semiconductor material for making, so indirect band gap exists between conduction and valence band. On baising  electrons  and holes recombine across the band gap and third particle generated in this process will conserve the momentum which is the reason for normal diode to not emit the light.

 *LASER and LED diode cant be developed with single semiconductor element, as these need direct band gap materials. These are made from compounds of a group 3(Al,Ga,In) and group 5(P,As,Sb). These are suitable for developing optical sources like LASER and LED.

*In case of laser and led diodes hetrojunction is formed between two adjoining materials with different band gap energies.

*In direct band gap semiconductor, electrons and holes can recombine directly across the band gap without needing a third particle to conserve momentum. In this radiative recombination is sufficiently high to produce an adequate level of optical emission.

Why Si and Ge are widely used as semiconductor materials?

It is known that inert gases like Ne(10),Ar(18),Kr(36) contain stable electronic configuration. These atoms have no tendency to combine with other atoms as they have stable electronic configuration. Elements like fluorine(9) and chlorine(17) are very reactive as they are one short of stable electronic configuration. Electronic configuration is defined as systematic arrangement of electrons in the atomic orbits. The maximum number of electrons present in each orbit is generally given by 2(n*n),where n=number of orbit.

1^st orbit =2,2^nd orbit=8,3rd orbit=18….Electrons present in the last orbit of an atom is called "valence electrons".

Si,Ge belong to group 4 of periodic table and they have 4 valence electrons at T>0k,neither have  stable electronic configuration nor they are too far to attain stable electronic configuration like nonmetals. This is reason why group 4 is treated as semiconductor metals. In this we also have carbon which is non metal so we will not consider it, remaining are Sn,Pb,Fl which are post transistion metals (poor metals) and these have lower melting and boiling points which make them to not consider as semiconductor metals. So Si and Ge are widely used as semiconductor metals.

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Introduction to RADAR Systems.

RADAR is abbreviated as Radio detection and ranging. Radar is an electromagnetic system, which generates EM signals to detect and to find the distance from system to objects (or) targets near to it.

How it can detect?

As said earlier radar transmits the EM signal from an antenna, these signals spread out in space and when they hit any object they come back to receiver, present in the same antenna. Returned signal is called ECHO signal and the direction it came from provides the direction of object with respect to radar system.

How it determines the Range (distance)?

Radar system is capable of determining the distance from system to object. we know that distance(R) = speed(c) * time(t).

R=(CTr)/2--->eq.1; where c=velocity of signal

                             Tr=pulse repetition time period.

In the denominator 2 is placed, as we calculated the time for to and fro motion.

This range equation does not provide the correct distance from system to object, so many factors have to be included like radar cross section, aperture gain, gain of antenna(G), the power transmitted from the antenna(Pt),minimum power detectable signal(Smin),by this radar equation is developed.Even this is not perfect.

Many other factors like noise need to be included,as noise is the chief facor limiting receiver sensitivity,it needs to be described.Even if you operate in noise free region,then also noise is entered which is due to thermal motion of conduction electrons in the ohmic portions of reciever,this is called johnson noise or thermal noise.So the total noise power at the output of receiver is equal to thermal noise power multiplied by noise figure(Fn).The minimum power Smin will become as

Smin=KToBnFn(So/No),replacing in the above equation will give you the better range valve.

*If a signal is transmitted from radar,it may strike the object at multiple locations, due to this many pulses are usually returned from a object on each scan and can be used to improve detection.The process of summing  all the radar echo pulses to improve the detection is called integration of radar pulses.The integration activity can be performed before the second detector(in the radar block diagram) and after the second detector.The integration performed before is called predetection or coherent detection and after is called postdetection or noncoherent detection.Predetection is mostly  adopted as it is capable of storing the phase information for further purpose like finding the range in CW radar,but postdetection is not entertained as it destroys the phase informaion for further access.

The integration effeciancy is Ei(n)=((S/N)1/n(S/N)n)

                             Where n=no of pulses integrated

                                      (S/N)1 =signal to noise ratio of a single pulse required to produce given probability of detection(n=1)

(S/N)1 =signal to noise ratio per  pulse required to produce same  probability of detection when n pulses are integrated.

Placing the above one in the radar equation we get better results.

*The transmitted power Pt in the radar equation is called peak power.This is not the instantaneous power of a radar wave.The average radar power Pav is ratio of average transmitter power over pulse repetition period.

                                      Pav=(Ptt/Tp)           Tp=pulse repetition period

Replacing the above one in radar equation will give better results.

                             

*Even in the final equation,we havent considered the losses take place in the system,these reduce the signal to noise ratio at the receiver output.These losses are classified depending upon whether they are predictable or not.The losses that are predictable are antenna beam shape losses,plumbing losses,collapsing losses and the losses that aren't predictable are operator losses,integration of radar pulses,the losses due to field degradation.

Plumbing losses are the losses that are experienced in the transmission.

Antenna beam shape losses include the pulses that are returned from target are received correctly or not by aperture of receiver antenna.

Collapsing losses occur in radar that is capable of integrating additional noises samples along with the wanted signal,the additional noise results in a degradation.

*Now we look on another type of radar called CW radar.The difference between the CW radar and the pulse type of radar what we have discussed is,suppose if strong signal has to be separated from weak echo(normally 10-18 times that of transmitted power) then it is better to use continuous wave rather than pulse wave as carrier.

Upto now we had considered that the object(target) is in rest.Now if the target is in motion then relative velocity exists between radar and the target,an apparent shift in frequency will result,this is doppler effect and is basis of CW radar.the doppler frequency is given by

                             Fd=2VrF0/c ------->eq.2         where c=velocity of light

                                                                   Vr=relative velocity

                                                                   F0=Transmitted frequency.

So the frequency that is received at the receiver will be F0 +(or)- Fd.

When the object is approaching towards radar system we have F0+Fd and when the object is moving away from radar system then we have F0-Fd.By this we will know Fd as we know F0(transmitted frequency), and if it is placed in the above equation(eq.2),we get the relative velocity(Vr) existed between radar system and target.

*The major disadvantage with the CW radar is that it cannot measure the range,this can be overcome by modulating the CW carrier.The inability of simple CW radar to measure is related to the relatively narrow spectrum of its transmitted waveform and a widely used technique to broaden the spectrum of CW radar is to frequency modulate the carrier.This type of radar is called FMCW(frequency modulated continuous wave) radar.

In this type of radar the transmitter frequency is changed as a function of time in a known manner which is transmitted and echo is received after time T=2R/c(from eq.1).This echo signal frequency,along with transmitter signal frequency is fed to mixer and the output is beat frequency Fb. suppose if there is no doppler frequency shift i.e no relative motion existed between radar and target,the beat frequency is equal to range frequency Fr=(df0/dt)*T

                                                                   Fr=2Fm*(2R/c)----->eq.3 

We know the returned frequency at the receiver Fr,modulating frequency Fm,velocity of light c,placing all these we get the Range(R).

We calculated the range when the target is in rest,for suppose if target is in motion,then we get two Fb(up)=Fr+Fd

                                                                                                     Fb(down)=Fr-Fd   

Above two equations are added to get the Fr,which is placed in the above equation(eq.3) to get the range(R).       

If suppose multiple frequencies are resulted from the target,then narrow band pass filters are used at the receiver to separate individual frequencies.

*Now we look on another type of radar called “MTI(moving target indicator) radar”,major differences between CW and MTI radar is CW radar operates with continuous wave and the MTI radar operates with pulse wave,so MTI radar is also called as pulse doppler radar.The principle remains the same but there is slight differences between MTI and pulse radar.MTI radar operates with ambiguous doppler measurements but with inambiguous range measurements,whereas the pulse doppler radar operates exactly opposite.

The moving targets produce,with time ,a “butterfly” effect on the A-scope,but for the display on the PPI(plane position indicator),we need delay line canceller,which acts as a filter to eliminate the dc component of fixed targets and to pass as components of moving targets.

*Another type of radar we have to know is “Tracking radar” which measures the coordinates of target and provides data about the position of target in future.

Appliations of Radar:

We have many applications of radar as it can see through those conditions impervious to normal human,such as darkness,dnow,fog and rain.

In ATC(Air Traffic Control),radar is employed for purpose of safely controlling air traffic en route and in the vicinity of airports.

In Aircraft navigation to avoid terror attacks.

In ship safety also radar is employed.In titanic movie the ship hit the iceberg and collapsed because the human was visualising as the human eye cannot see through snow he couldn’t inform it before.now in the ships radar is employed to  signal the operator before he founds it.

In space also radar is employed to detect the asteriods and smash it when found it is approaching towards earth.

In military also radar is employed to detect the enemy moves.

In highways police use it to detect the speed of the vehicles.

In sports like cricket it is used to measure the cricket ball speed.

There are many,these are only few.                 

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SMART CARD-EXPLAINED

In simple words smart card is a credit card with a microprocessor.

*This is the microprocessor that is embedded in smart card. Vcc is power supply,Rst is used to reset the card communication,clk is used to provide card with a clock signal,Vpp is programming voltage,Gnd is to provide ground,I/O is serial interface as smart card uses it and C4,C8 are AUX1,AUX2 respectively and are used for USB interfaces.

*Before knowing more about smart cards let us have a look on credit cards as these smart cards are evolved to overcome the disadvantages in credit cards.

*Credit cards store information on magnetic strip line, which is easily breakable. Magnetic strip technology remains in wide use in US, however the data on stripe can easily be read, write or even can modified as stripe is not the best place to store information, we need an alternative and confidential place to store it.
*To protect the customer business in US, smart cards are introduced which will overcome the above said disadvantage.
*Smart card usually contain an embedded microprocessor, which is under gold plated contact pads and performs mathematical encryption calculations used in security function and also store additional card holder account data.
*In Europe, health insurance and banking industries use smart card extensively.
*A smart card has 8kb of RAM,346kb of ROM,256 kb of PROM and a 16 bit microprocessor

*Smart card uses a serial interface and receive power from external sources like card reader.

How it works?

*When a smart card is inserted in smartcard holder, transaction is similar to that of an ATM, but in here power goes from smart card reader(machine) to chip and switches it ON, once it is ON, it is able to conduct, an electron conversation  with chip reader. When the reader is online, the chip uses the reader to communicate to card issuer,during this time security procedure is activated that authenticates the card. A fake card would not be able to duplicate the security procedures and would be detected invalid.

*Magnetic strip information on credit card can be copied and put on fake card,  which looks exactly as valid card. The technology required to copy data  from smart card to a fake card is beyond capability of criminals, and the information sent online to authenticate the card is different for every transaction ,also to attempt to physically remove the chip from smart card would cause the chip to blow and chip cannot be used again.

*Smart card is of two types

1.       Contact smart card:

Contact area of smart card is approx. 1 sqcm,comprising of several gold plated contact pads, these pads provide electrical connectivity when inserted into reader, which is used as communication between smartcard and host(PC),these do not have batteries, power is supplied by card reader

2.       Contactless smart card

In this type of smartcard, card communication with Is powered by reader through RF induction.

Problems in using smart card:

1.The plastic card in which chip is embedded is fully flexible, so hard to maintain it.

2.As I said before, smart card is inserted into smart card holder, if the holder contains malware then it tries to know the information which makes the card  to turn invalid.

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Working of WI-VI(WIRELESS VISION)

Hi friends,this time came up with new technology "WI-VI(Wireless Vision)".This technology uses  "WI-FI"(Wireless Fidilety) to allow user to look into the walls.This technology analyses the reflected WI-FI signals to estimate an object in a particular room,even if it is in motion we can able to detect the exact location of object.
Here in this case,the user has two antennas which generate WI-FI signals continuously with 180 degree phase difference and a single receiver.Generally a portion of WI-FI signal can penetrate in to wall.When two antennas radiate,due to 180 degree change in phase they cancel out each other without reaching at receiver when they hit any stationary objects,but when these signals hit any moving object there generates a change which will appear at the receiver,by analyzing the received signal we estimate perfect location of object.

Actually this concept is similar to RADAR(Radio detection and ranging),in which 'radio' signals are transmitted in to space to 'detect' the presence of object and 'ranging' involves knowing the exact location of object from the system,how?range or distance is speed over time,we know the speed of transmitting signal and the time taken for signal to strike the object from system(user),by this range is detected.
WI-VI systems are capable of tracking the person in a closed room.Assume that a WI-VI device is fixed outside the room,initially room is empty,when a person enters into it based on the movement of person the device is capable of showing variations i.e when he moves towards the WI-VI, signal may be in one format and when he moves away from it we can see the signal in another format.A small variations can also be grabbed by WI-VI device.

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Introduction to Zener diode

Hi friends,this time we wanna discuss about zener diode which is heavily doped diode and is specially fabricated to with stand high power dissipation.
Main application of zener diode is, it can act as a voltage regulator.

Forward characteristics of zener diode:

when high potential is applied at anode compared to cathode,then the characteristics of 

zener diode are

Negative characteristics of zener diode:

when lower potential is applied at anode compared to cathode,then the characteristics of 

zener diode are

Major concern related to zener diode is determining the state in which the zener diode is residing,there are various steps that to be followed in this process,

1. Replace zener diode by an open circuit
2. Find terminal voltage across the diode from N to P side,say vt
3. If vt>vz,  zener is reverse ON  and replace it with vz
4. If vt<vz,  zener is OFF and hence open circuit.

Consider a circuit ,

now the circuit becomes 

Terminal voltage Vt=(8*1.2)/(1+1.2)=4.3v and since Vt<Vz zener is OFF hence open circuit.

If  RL=3.6k then terminal voltage Vt=(8*3.6)/(1+3.6)=6.26v. Here Vt>Vz hence zener is reverse ON and replace zener diode with Vz=6v.

Now the question is how to place a terminal voltage,the answer is conventional direction of zener voltage is considered to be opposite to the direction of normal PN diode,because  PN diode is used in forward biased and zener diode is used in reverse biased.

For RL=3.6,the circuit becomes 

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TRANSISTOR Disadvantages-MOSFET Advantages

Hi friends,this time i wanna talk about basic electronic devices, they are transistor and mosfet with their disadvantages and advantages respectively. Major disadvantages that i would consider for transistor are,
1.Input impedence
2.Stability
I would also explain how these two are advantages for mosfet.
1.Input impedence : 
For transistor:Any small input at the base terminal will turn transistor active and make it work (i.e as a amplifier or as a switch),which is not required at particular small input. Transistor should respond only to a reasonable input .This indicates the input impedence(Ri) of a transistor is low.Actually for CC based transistor configuration,the input impendence is upto 500k ohms,which is enough, but if transistor is biased then due to R1 and R2 the net input impedence will decrease(R1||R2||Ri).
For mosfet:Mosfet abbreviates metal oxide semiconductor field effect transistor,as the name itself indicates presence of oxide(SiO2) an insulator,which  prevents mosfet not to respond for small inputs
2.Stabilty
For transistor:We desire a fixed operating point that to in active region with Ib,Ic,Vce.The flow of small current(due to low input impedence) into BJT results in dissipation of electrical energy inform of heat.This results in rise of tempoerature which inturn increases Ic0 but Ic=(alpha)IE+Ic0,so Ic also increases.With this operating point is disturbed.It is referred as bias instability.To overcome bias instability,we have bias circuits which will stabilise the Q pont even change occured in Ic0 and temparature.Ic0 increases by 2 times for every 10 degree rise in temperature.
For mosfet:Bais instability is occured in BJT due to low input impedence,but as i said mosfet has high input impedence(due to SiO2) compared to transistor,so chances of instability is less in case of mosfet.

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Circuit which indicates the charging level of battery

Hi friends ,As the need for rechargeable devices are increasing it is necessary to maintain the life of electronic devices which runs with  battery.Life of any rechargeable device depends upon the usage of charging capacity it has.Overcharging leads to reduce the life of device.Now a days due to overcharging many of the devices are out of work field.So if we know proper charging level of battery at every instant of time,it would help us to know whether to charge the battery or to use it.My circuit provides this features i.e when the battery is fully charged we can see a LED light glowing by this one will come to know that the battery is fully charged and has to unplug it.If not it need to be charged. Today i wanna show a circuit which will indicates the charging level of a DC storage battery.

Circuit description:

Input is an alternating voltage signal of 220v and 50hz supply,given to capacitor which is used to block DC,Stepdown transformer to reduce the signal level ,a rectifier to convert AC to DC,inverting and non inverting amplifiers,LED,1 v DC source and the battery whose charging level is to be detected.

Working:

Initially AC signal is passed through 'C' to block DC,which is fed to step down transformer to reduce the voltage signal from 220v to 13v.Now this is given to rectifier circuit for conversion process i.e from AC to DC.This constant 13V is given to non inverting terminal of opamp-1,inverting terminal is given with battery positive terminal for same opamp.Output of opamp-1 is given to inverting terminal of opamp-2 and its non inverting terminal is grounded.Output of opamp-2 is fed to LED which has -1v supply.

Operation:

case:1 Assume initially the battery has 2v in it ,V+>V-,therefore V01 is 13-2=11v,V02=-11v,since the potential at anode is much less than potential at cathode the LED doesnot glow.It means that battery is not yet fully charged.

case:2 Assume now the battery is fully charged i.e upto 13v,V+=V-,therefore V01=0,V02=0 and now the potential at anode(0v) is greater than potential at cathode(-1v),LED glows and indicates us that battery is fully charged and need to be unplugged.

*Since the ouput of rectifer is given to battery,it charges the battery when it is discharged by the user.

*Here two opamp are used,but the same work can be done with single opamp.For better explanation i has shown two.

,

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DISPLAY DEVICES-EXPLAINED

HI friends in this post we are going to learn about the various types of DISPLAY DEVICES which we had been known.In this the foremost one is 

1.CRT(Cathode ray tube):Experiments to discover more on smallest  particle "atom"(on that time)by J.J thomson, landed him to know about electron.In his experiment he noticed that a ray of particles called electrons(named by G.J stoney) were travelling from cathode to anode,he made this electrons to fall on fluorescent screen when this electrons hit the screen bright spot is produced.On their way from electron gun to screen their is chance of deflection, due to surrounding fields(as electrons are negative),to overcome this he placed horizontal and vertical deflection plates in between the space.So based upon the electrons, which hit the screen display is produced.now a days we can observe CRT's in CRO(cathode ray oscilloscope) .Next to this is 
2.LCD(liquid crystal display):Display by liquid crystals.Normally we know crystals in solid form like rochelle salt,quartz etc unlike here it is liquid crystals,means crystals which are in liquid form or in which the  molecules tend to orientate easily.Actually liquid crystals state is in between solids and liquids.As we know that even on slight increase of temperature will turn this liquid into real liquid so liquid crystal  are effected easily by electric current.Based upon this feature, applied electric current results molecules change their orientation with which display is produced.Next to this
3.LED(light emitting diodes):The diodes which emit light when they are forward biased are LED's.when we look at aluminum-gallium-arsenide(AlGaAs), in this type of semiconductor made diodes the interaction between electrons and holes is interesting , which is responsible to emit light.we knew in previous post "introduction to pn junction diode" about diode condition when no external bias is applied i.e  depletion layer is formed(electrons recombine with holes due to diffusion) on recombination electrons jump from lower orbital to higher orbital and vice versa .Electrons lose(release) energy when they jump from higher to lower orbital and needs(gains) energy to move from lower to higher orbital.The energy released in this process is in form of photons which are basic particles of light,these photons have speed and momentum but have no mass.
you can ask me, why this emission of light doesn't occur in normal Si, Ge diode,the reason is that atoms in normal diode are arranged in a manner that energy drop is relatively short which is invisible to normal eye.By release of photons in led's display is produced.Next to this
4.OLED(organic light emitting diodes):The main differences between led and Oled is the presence of organic layer present between anode and cathode of a diode.The organic layers in Oled are organic layer,conducting layer,emissive layers,the main purpose of this layers are to transport much holes from anode and much electrons from cathode, this will increases the recombination rate which in turn increases the emission of photon which are basic particles of light,this is how display is produced in Oled.

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TRANSMISSION MEDIA

Now a days communication is necessary in every field and to communicate a transmission media is needed. Transmission media is classified into two types.

·         Wire communication (a connection between transmitter and receiver.)

·         Wireless communication (no connection between transmitter and receiver.)

1.                                                          In case of wire line communication, nonelectrical signals are converted into electrical signals                         at the entry and these electrical signals(voltage,current) are transmitted with the help of                                   conductor.The device which transforms it is called the “Transducer”

There are 3 major and well known types of wire communication

·         COAXIAL CABLE:

*It is kind of copper cable mostly used by cable tv companies between communicating antenna and user home tv set and is applied by telephone companies from their offices to poles.

*This cable has three layers enclosed in it, inner layer is conducting copper wire and  two outer layers are used to protect the conducting(cu wire) path from outer damages.

*Major disadvantage regarding this cable is electromagnetic induction

HOW? Here it is said that electrical signals are transmitted by inner cu layer ,it means we have electric field and as these electrons are flowing(current) we have magnetic field around the conductor.so both fields exists. whenever another conductor is brought near to it, we may have collision and there is chance of loss of information.

·         TWISTED PAIR:

*To overcome the loss of information in the coaxial cable Twisted pair cable was introduced as name itself indicates pair of wires are twisted one, to collapse electromagnetic interference.

*It is ordinary wire that connects home and many business computers. To reduce  cross talk and electromagnetic induction between pairs of  wires ,two insulated cu wires are twisted. These are sometime enclosed in single cable this acts as a shield for twisted pair cable.

*For secure information this shield acts as ground and is called as shield twisted pair cable and for home transmit information this shield acts as unshielded and is called unshielded twisted pair cable.

*Major advantage is twisted pair is cheaper than coaxial cable and it overcomes EM induction.

*Disadvantage is slow transfer of information.

·         OPTICAL FIBER:

Up to this security is enough and every one needed the speed and thought of using the light as source to transmit the information as we knew that the speed of light is 3*108m/sec. Based on this technique optical fibre was designed. Similar to coaxial cable it also has 3 layers, outer one is buffer or sheath,middle one is cladding and the inner one where the light is gonna transmit is core. For proper transmission refractive index of core must be slightly greater than cladding. To know how light transmits in the core one should know about the critical angle and total internal reflection.

      *critical angle: When a wave is transmitting from one medium to another medium of different refractive indices and if wave incident angle is greater than 90 degrees this angle is referred as critical angle

      *Total internal reflection: When angle of incident is equal to critical angle then no reflection occurs only refraction into medium.

*By using these light parameters transmission is done in optical fiber. *Major advantages is Optical fiber carries much more information than normal cu wire and is not subjected to EM interference, so most telephone companies long distances lines are made of optical fibers by use of Repeaters at regular distances.
 2.     In case of wireless communication no wired media is present between transmitter and receiver. Here communication is by EM waves HOW? As I said before around a conductor both fields exists and these EM waves are necessary for communication.

The first wireless transmission went on air in early 20^th century using morse code. Later by modulation it made possible for transmitting voices and music via wireless.

Modes:

Wireless communication can be via,

·         Radio communication(Radio frequency)

·         Microwave communication(high frequency)

·         Infrared communication

·         Ultrasonic communication.are made of optical fibers by use of Repeaters at regular distances.

1.                                    

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Li-Fi(Light Fidelity) future wireless communication

In future it is suspected that every light bulb will be replaced by LED's the reason is LI-FI .Li-Fi  is acronym for light fidelity.The word fidelity means the ability of the receiver to reproduce all the signals.Light fidelity indicates transmission of data or information through light or illumination. The inventor defines it simply if LED is ON you transmit a digital '1' and if it is OFF you transmit a digital '0'.Li-Fi is the  next version to Wi-Fi(wireless fidelity) as it overcomes some of the limitations of Wi-Fi like speed,application areas like medical and in aircraft,outreach in remote areas etc.
NEED FOR LI-FI:
When you are using mobile phone or pc connected to wireless internet we have to compete for bandwidth and sometimes we get frustrated with slow speeds when more than one devices are connected. To solve this problem german scientist Herald Hass found an alternative way and he calls it with "data through illumination".He conveys that in future communication is done through Light in a room.
HOW IT GONNA WORK?
Li-Fi is transmission of data through illumination by taking fiber out of fiber optics by sending data through LED(light emitting diodes) light bulb that varies its intensity faster than human eye can follow.As said before  if LED is ON you transmit a digital '1' and if it is OFF you transmit a digital '0.As the reaction time of LED's to respond to the changes is very fast the transmission of data will also be fast. Theoretical calculations had proven that the rate of data transmission would be 224 giga bits per second.
*The requirements to adopt this technology are some LED's and controller that code data into those LED's
*Since it just uses light ,it can be used safely in aircraft and in hospitals that are prone to interference from radio waves.
*Simply radio waves are replaced by light waves in new method called Li-Fi.
*This method of using rapid waves of light to transmit information wirelessly is referred as Visible Light Communication(VLC) the transmitting frequency in VLC is around is 400Thz to 800Thz.
MAJOR APPLICATION AREAS OF LIFI:
1.IN FIELD OF MEDICAL:
Most hospitals donot allow Wi-Fi to enter into operating rooms due to radiation concerns and even it is lagged by some other cellphones or ipods, but communication is necessary in operation theaters  to treat patients.
LI-FI overcomes it.I think many of we know about the properties of light like inteference,diffraction ,polarization etc.Diffraction means bending up of light around the edges or obstacles.This property helps LI-FI to increase its efficiency.
2.AIRLINES: Where radio waves are not much efficient.
3.OUTREACH IN REMOTE AREAS:As the equipment for Wi-Fi is necessary, it is not possible to lay plant anywhere but since here in LI-FI it is through light we just need LED's and a controller.
4.UNDERSEAS:As it is difficult to lay optical fibers beneath water, it is better to communicate with help of light and as salt water is good conductor of electricity it is easy to work with LI-FI
5.FAST TRANSFER OF INFORMATION:As LED's ON and OFF very quickly which gives nice opportunities for fast transmitting the data.  

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chemistry concepts

                           Universe is composed of  matter,during vedic period in india ,maharshi kanada proposed that matter is composed of smallest particles such as "anu" and "paramanu". later a greek philospher proposed that matter consists of smallest particles called "Atoms" meaning indivisible , Atoms combine to form "compound atoms",which later on called as molecules. According to modern theories Atoms contain positive charged nucleus and negatively charged electrons. Nucleus further contain protons which are positively charged and neutrons which are neutral, combinely both protons and neutrons are called Nucleons. Mass of electron is negligable while mass of proton is 1837 times of electrons. J.J Thomson is the person who discovered the cathode rays(electrons which are travelling from cathode to anode and these are invisible.G.J Stoney named these cathode rays as "electrons".

  Two types of forces are present in atom a)force of attraction between the electrons and protons(Attractive force).This force pulls the electrons towards the nuclues. second type of force is b)the revolving electrons experience a centrifugal force directed away from the moving path of electrons.This force pulls away the electrons from nucleus ,since these two forces are equal and opposite ATOM is stable.

IF THESE ATOMS ARE STABLE WHY THEY COMBINE?

It is known that inert gases like Ne(10),Ar(18),Kr(36) have stable electronic configuration and have no tendency to combine with other atoms.Elements like fluorine(9),chlorine(17) are very reactive as they are short of one or two.Similarly atoms of Alkali metals like Li(3),Na(11),K(19) are very reactive and form numerous compounds.

WHY SOME ARE REACTIVE AND SOME OTHER NOT?

In the above paragraph i used the word "electronic configuration",it is defined as systematic arrangement of electrons in the atomic orbits.The maximum number of electrons present in each orbit is generally given by 2nsquare.(n=number of orbit) i.e 1st orbit -2,2nd orbit-8,3rd orbit-18...

*Electrons present in the outer most orbit of an atom are known as valence electrons and based on these atoms are said to be reactive or not.Now observe electronic configuration of inert gases they have 8 electrons in their outermost orbit except helium(2) all are stable in inert gases.

*Halogens have 7 electrons in outermost orbit.Normally every atom has tendency to attain nearest noble gas configuration and become stable,As they are 1 electron short they combine with another atom to have 8 electrons which provides them with much stability.

This is perfect reason for "chemical bonding".Atoms combine to form molecules so "molecules are much stable than atoms".

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Basics in Electronics

1.Purpose of Tank circuit.
      To amplify a selective range of frequency this circuit is used.Output impedence(Rc) is replaced by tank circuit

Operation:When initially C is charged,it finds path to discharge through L it stores the energy in form of magnetic field.Now according to lenz law,magnetic field start collapsing and this in turn charges the capacitor in opposite direction.After some time capacitor fully charges.Here magnetic energy is converted back to eletrostatic energy.Now the capacitor again starts discharging through inductor L .This capacitor produces alternating current in tank circuit.

By selecting the L and C and placing it in f=1/(2pi root(LC)),We can fix the frequency and at a specified frequency we can amplify the signals.

2.Why in P-type semiconductor majority charge carries are holes and in N-type semiconductor majority charge carries are electrons

Semiconductors like silicon and germanium belong to 4th group of periodic table.To form a P-type semiconductor silicon(4 valence electrons)  is doped with 3rd group elements like berillium(3 valence electrons) so one electron is short.so in P-type majority charge carries are holes(positive charge).In the same manner

To form N-type semiconductor silicon(4 valence electrons) is doped with 5th group elements like phosphorus(5 valence electrons) so one electron is more.so in N-type majority charge carries are electrons(negative charge)

3.why cant capacitor stores only DC but not AC

AC signal is which varies accordingly with time, and has amplitude in both positive and negative levels like a sine wave.Capacitor also does charging for the positive cycle of AC and discharges for negative cycle of AC so net is zero. 

4.Transistors disadvantages

a.Input impedence : Rb for the transistor is low.Actually the input impedence of CC configuration is around 500kohms which is sufficient.But since we place R1,R2 for biasing purpose(to place the transistor to act as an amplifier)the net impedence decreases(R2//R1//Ri).To overcome this situation we have 2 techniques they are Darlington connection and Bootstrap emitter follower.But since we cant adopt this type of situations we consider this as a disadvantage because a week signal should not drive the transistor.

b.Stability:This is also one of the reason to implement the FET(field effect transistor).We desire a fixed operating point that to in active region with Ib,Ic,Vce. The flow of I2 into BJT results in dissipation of electrical energy in form of heat . That results in rise of temperature which in turn increases Ic0 but Ic depends upon Ic0. so Ic also increases and operating point is disturbed, it is referred as Bias Instability.

5.Why in BJT conduction is from Emitter to Collector and not viceversa.

First off all one should remember that BJT is not a symmetrical device (Emitter and Collector regions are not interchangable).As we know BJT provides two configurations i.e NPN and PNP.In any of these  Base(middle region) is lightly doped to have small recombination ,Emitter is heavily doped  and collector is moderately doped.So normally when base current is applied,conduction is carried from higher region to a lower region(process known as Diffusion) since emitter is heavily doped and collector is moderately doped,conduction is from Emitter to Collector.This is reason behind why in  BJT conduction is from Emitter to Collector and not viceversa.

6.Why P mos is ON for logic 0 , OFF for logic 1 and N mos is ON for logic 1,OFF for logic 0

When Vgs is positive there is force of attraction between gate(positive) terminal and N majority charge carriers electrons(negative) so no channel is formed between two highly doped N regions.By this we can say that P mos will be in OFF state when logic 1(high) is applied.

When Vgs is 0 or negative due to force of repulsion between gate(negative)and N majority carriers electrons(negative) and channel formation takes place which leads to conduction from source to drain.So P mos conducts when logic 0 is applied.

Similar action is followed in N mos

 When Vgs is positive there is force of repulsion between gate(positive) terminal and P majority charge carriers holes(positive) so  channel is formed between two highly doped P regions.By this we can say that N mos will be in ON state when logic 1(high) is applied.

When Vgs is 0 or negative due to force of attraction between gate(negative)and P majority carriers holes(positive) and no channel formation takes place between two highly doped P regions.So N mos doesn't conducts when logic 0 is applied.

7.Why P mos connected in pull up network where as N mos connected in pull down network

or

source of P mos is connected to Vdd and source of N mos connected to Vss

As i said before P mos will be in ON state when logic 0 is applied i.e Vgs is negative this happens when gate terminal is negative and source is positive,So in P mos source is always connected to Vdd which is positive.Coming to N mos it will be in ON  state when logic 1 is applied i.e Vgs is positive this happens when gate terminal is positive and source is negative,So in N mos source is always connected to Vss which is negative.This is reason why P mos is connected in pull up network and N mos is connected in pull down network.

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TRANSISTOR

Transistor:
Transistor is an electronic device that can be used as an amplifier or as a switch.Transistor is the next version to diode.Diode can simply pass through current in uni direction and can act as switch,but transistor can also amplify.They can control a large current flowing through 2 regions of semiconductor like si to a small current applied to a middle region.There are many kinds of transistors typical is bipolar transistor. Transistor has 3 layers. Transistor is designed by appending another region on diode(PN-diode) either left or right,so the transistor configurations are PNP,NPN . The layers are Emitter,Collector and Base.In transistor current flow from Emitter to Collector and that flow is controlled by current applied to middle terminal called Base.

Demonstration:  
When current is applied to Emitter electrons cross over to P-type base filling the electrons holes ,when holes are filled resulting negative charges so repell further electrons to come from Emitter and transistor doesnt conduct.But a small amount of current is applied to base that will produce additional holes ,this will further invite much electrons from Emitter to pass through base to collector because Emitter to Collector flow is several 100 times more than Emitter to Base thus making transistor a power amplifier.
As base current is controlling the amplification process transistor is a current controlled voltage source.
Transistor is also called Bipolar junction transistor.since both holes and electrons are operating this is a bipolar device and since junction is present between PN and NP.This is referred as bipolar junction transistor.

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Machine - Motor

As already we discussed about the generator now we see the action of motor.Actually motor is a electronic device which converts electrical energy into mechanical energy.

HOW DOES IT ACTUALLY WORK?

When ever a current carrying conductor is wounded around a cock and is placed between the magnets,electric field(due to flow of electrons in the conductor) and magnetic field(due to the magnets) interact with each other resulting in the motion of the cock.The direction can be known by Fleming left hand rule and can be changed by changing the direction of current(flow of electrons) . This is how the electrical energy is converted into mechanical energy.

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Machine-Generator

Generator is a great invention.Normally machine can be a machine or a motor. In this section we will learn about a generator. Actually a generator is a electronic device which is used to convert mechanical energy into  electrical energy.

How does it actually do?

The answer to the question is when a conductor is placed between a strong magnetic fields and when it is rotating (i.e when applied mechanical force ),the conductor cuts the flux lines(magnetic lines of force between two poles) an EMF(electro motive force or simply voltage)will be induced into the conductor. With this the electrons travel causing an electric current.In this way mechanical energy is converted into electrical energy 

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RECTIFIER

In the last article we studied about a P N junction diode,how it works ,whats it nature in forward and reverse bias condition and one application that is as a switch. Today we learn about an another application that is a diode can act as a "RECTIFIER".

         In this section we observe how a diode act as a rectifier.
RECTIFIER  :   It  is a device which is used to convert AC(continuous variable with time) into a DC(constant with time).

NEED TO CONVERT AC TO DC:

1. We cannot store an AC signal as it is continuously varying with time.But we can store a DC signal like in batteries etc.
2. Our all electronic goods require DC because a continuous change in signal will affect the device.
3. Our renewable energy sources like hydro electric ,wind turbine generate AC so there is a need to convert to DC.

There are 3 types of rectifiers using diode.

• half wave rectifier
• full wave rectifier
• bridge rectifier

1. Half wave rectifier:

In this half wave rectifier only half of the input AC signal into DC signal.

OPERATION:

                      Here when the input AC is in positive state, diode becomes ON and allows for rectification but for negative input of AC diode will be in OFF state so open circuit(no output will be resulted). 

Efficiency is around 40.6%.

Transformer is to allow only AC and reject DC.

output resistance is used to measure the output DC signal.

2. Full wave rectifier:

In the full wave rectifier both positive and negative cycles of input AC is converted in DC.

OPERATION:

                      Here for the positive input cycle, diode D1 becomes ON so the output DC is resulted and for the negative input cycle diode D2 becomes ON so same process continues and DC signal is resulted.

*Hence in the full wave rectifier, input AC signal is completely converted into DC signal.

*Efficiency is around 81.2%(double of half wave rectifier).

3. Bridge rectifier:

                        similar to the full wave rectifier bridge rectifier also converts AC into DC,it is one of the design process using 4 diodes.

OPERATION:

If we name the diodes as D1,D2,D3,D4 respectively in clockwise direction from right top then for positive AC signal D1 & D3 will be in ON condition remaining will be in OFF state where as for negative AC signal D2 & D4 will be ON and remaining will be in OFF state.

*This is how AC signal is completely converted into DC signal.

*Efficiency is also the same.

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