Near Field Communication (NFC)

Near Field Communication(NFC) is a new short range wireless transmission technology which enables exchange of data between devices held close to each other max 10cm . NFC can be defined as an extension of existing technologies radio frequency identification (RFID) or proximity card standard , It also complies with the Smart card technology for contact based systems. NFC and is therefore compatible with modern day

NFC in Action
(using mobile phone for transaction)

 contactless infrastructure used for payment of Bills and making receipt. NFC technology is mainly developed primarily aimed at usage in mobile phones. it won't be long when your local vegetable vendor would gonna make you a receipt or the bus conductor making your ticket using his mobile phone attached or kept close to a small handy printing machine which pops your Receipt/Bill in no time . Its extremely cheap and reliable and is quite a very important Add-on to the mobile phone especially to the people engaged in small business(especially those in rural areas) . who couldn't afford expensive Billing machine yet need to make a transaction/Billing record (which will get saved in phone's internal memory). NFC devices can also be used to read RFID tags.

The Google Nexus S, a full-featured smartphone
 has NFC support built in

In todays modern technical world fast and secured wireless communication is one of the prime necessity . Wireless technologies have brought revolutionary changes not only in our gadgets but also in the way we carry out different task . Through radio and cellular communications we can send data to our destination over a thousand kilometer away and  for short distances we use the most popular and most favorite of all "BLUETOOTH" , with the Bluetooth feature enabled in almost all present day mobile phones , laptop it has never been so easy to transfer data (eBooks, songs , video clip or other documents) to others fast without taking any trouble with connecting a cable to maintain a link .
       But the most biggest disadvantage with Bluetooth is its security , Once the Bluetooth is activated in a device it can be easily traced by other Bluetooth devices. Even though security can be increased. But Hackers are gearing up too. And are still not that secured to transmit sensitive data like personal identification number (PIN) of credit card or debit card payment . Where the need for NFC appears NFC operates in a frequency of 13.56MHz  allowing data to be transferred at speeds up to 424 Kbits/second within a distance of only 10 cm hence making it fast, reliable,secured. and cheap

There are two modes by which NFC devices communicate :

• Passive Communication Mode: The transmitting device provides a carrier field and the target device answers by modulating the existing field. In this mode, the Target device may draw its operating power from the Transmitter provided electromagnetic field, thus making the Target device a transponder(Transmitter-responder ).
• Active Communication Mode: Both Transmitting and Receiving device communicate by alternately generating their own fields. A device deactivates its RF field while it is waiting for data. In this mode, both devices typically have power supplies.

NFC devices could attain a peer-to -peer (P2P) mode to continually  communicating together and exchanging information.


Mobile phone manufacturers – namely Nokia and Apple – have recently vowed to integrate the technology into their future handsets, Nokia  along with NXP and Sony opened the NFC forum to promote NFC technology. 

E - Waste

E-waste stands for electronic waste , With more and more sophisticated gadgets getting in the market everyday taking in as much functions as possible to made it handy for almost anywhere you go , Ever wondered what happens to those old electronic stuff you had which you throw away to make place for new ones.

Dumped Old computers
via:Treehugger

          
 About approx 4000 computers (on an average) are thrown away in India daily , Electronic waste or E-waste is the most rapidly growing waste problem in the world. Releasing about a thousand toxic waste in the environment – such  as the lead, beryllium, mercury, cadmium, and  zinc sulphide.like for example CRT monitor contains more than 6% lead which if inhaled can cause harm to kidney, nervous system and impair mental condition especially of unborn baby. that's why the most complex treatment is that of CRT(Cathode ray tube) only the front glass can be reused and the rest is send away for recycling where dismantling is done in a vacuum chamber so that the toxic elements inside doesn't escape out.

         SOME OF THE COMMONLY FOUND HARMFUL CHEMICALS IN E-WASTE

SUBSTANCE	FOUND IN	EFFECTS
Lithium	CRT tubes and Lithum batteries	Develops explosive gases (hydrogen)
Zinc sulphide	Interior of a CRT screen	Toxic , Hazardous in case of skin contact (irritant, permeator), of eye contact (irritant), of ingestion, of inhalation.
Chips and other gold plated components	Printed Circuit Board (PCB)	- Acid contact with eyes, skin may result in permanent injury - Inhalation of mists and fumes of acids, chlorine and sulphur dioxide gases can cause respiratory irritation to severe effects including  circulatory failure, and death.
Mercury	Mercury batteries	Very poisonous and a long-term perspective injurious to health
Lead	CRT screens , Batteries,PCB	Damages nervous system, kidneys, cause learning disabilities in childrens
Plastics	Keyboard , mouse , printer etc	Causes Cancer
Cadmium	Rechargable batteries,printer inks	Very poisonous

 A large number of electronic waste are recycled and reused in various industry.Electronic waste can be very valuable sometimes if it is processed using techniques which won't harm the environment. There are many e-waste processing plant , e-waste processing plant are firms who take up the e-waste recycling into a business (or trade) they have logistics in place to pick it all up from a coverage area. most of the electronic waste like broken or old CD drive , hard disk , television, graphics card , motherboard lands up in here , If of course you sell your old e-stuff and now an e-waste into the right scrap dealers in the computer hardware market . if you throw off your electronic stuff  to your general waste collector or scrap dealer who buys stuff by weight , you are just slowly killing your mother nature ,  A tremendous amount of imported E-waste material and
process residues are not recycled but simply dumped in open fields, along riverbanks, ponds, wetlands, in rivers.

                                                              
WHATS GOING WRONG ??


The awareness about e-waste have gone far and wide , especially among the environmental activist . As E-waste are formed from general household electronic items (consumer electronics) ,with such a large population and there dependency on electronic stuff like MP3 players, television , computers , e-waste can grow by several hundred times and e-waste are far more dangerous than other domestic waste because of the presence of toxic elements in it.
          And the worst of them all is small scrap dealers especially in south asian country like India , These dealers try to reuse the expensive metals in the PCB(Printed Circuit Board ) of every electronic items by extracting the metal from pcb . Valuable metals present in PCBs are Palladium,gold , silver , tin, copper and aluminium.  Although illegal ,These kinds of activity is often practised in rural areas using methods although cheap but extremely dangerous and hazardous methods and many a times employing child labor which is biggest of all the crime . After removing the ICs from the pcb , It is done usually by these procedure :

An E-waste scrap dealer
via:Greenpeace

•  Utilizing nitric acid on the circuit boards to remove gold and platinum.
• The PCBs are burnt in the open by roadside recyclers using blowtorches  to retrieve the rest of the solder and copper.  After burning, the ashes are floated in water to remove lighter ash.

Both the methods being dangerous to both lives and environment , There are no facility in India to extract valuable metals from PCBs , they are usually send abroad for disposal . Hazardous substance and other non - reusable materials are landfilled on government approved sites . efforts have been made, by NGOs and the Government, to make the process of recycling of e-waste safer and more eco-friendly .Other e-waste scrap yards have been found in Meerut, Ferozabad, Chennai, Bangalore and Mumbai.

p-n diode

A P-N diode

The most frequently encountered  semiconductor electronic device  is the diode. It is a two terminal device consisting of a P-N junction formed either in germanium or silicon crystal. P-N junction is also sometimes called as crystal diode as the P-N junction is directly grown out of a crystal . A diode is a unidirectional device  it permits a easy flow to the current passing from one side only and offers a high resistance when the direction of the current is opposite.

  It is because , on the formation of the p-n junction some of the holes from the P-type material tend to diffuse across the boundary into N-type material and some of the free electrons similarly diffuse into the P-type material as shown  where blue circles are the holes and green circles are the free electron


this happens because of the concentration of holes is higher on P-type than on N-type and theconcentration of free electrons is higher on N-type than at P type . this process is called diffusion , the region across the junction is completely immobilized which leads to the formation of a depletion layer , transition layer or potential barrier.

The thickness of the depletion region is of the order of 1 micron (millionth of a meter ,10^(-6) meters )  .

• Forward biasing- When a positive voltage is applied across the P-type semiconductor and negative terminal connected to the N-type semiconductor , then the diode is said to be in forward bias . the holes of P-type being positive charge repel away from the supplied positive charge and move towards the junction and similarly the free electrons from N-type also are driven towards the junction , In other words the forward potential establishes an electric field opposite to the potential barrier and hence the width of the depletion layer is reduced , and current could pass through it(diode) easily.

• Reverse biasing - When the negative terminal is connected to the P-type semiconductor and the positive terminal to the N-type , the diode is in reverse bias . Because the applied reverse voltage establishes a electric field which acts in the same direction as that of potential barrier , thus making the depletion layer wider and offering high resistance to the current flowing through it .

Diodes are mainly used in rectifiers(AC to DC converters), clippers and as a safety device (to block the flow of current in reverse order), 

Semiconductor

Almost every electronics devices (mostly active components) ranging from transistor to ICs are all made of semiconductor. Semiconductor is one of the most important Electronics engineering material ever, which revolutionized  the modern world of Electronics. semiconductor devices have found wide application because of their compactness,reliability, power efficiency and low cost . They are also used in power devices ,optical sensors , light emitters(LED) and even solid state lasers.
        Resistivity of metals like iron and copper is 0.1 x  10^-6 Ω·m and  1.7 x   10^-8 Ω·m . The resistivity of  insulators like glass is 9 x 10^-11 Ω·m , whereas the resistivity of semiconductor substance  are between 10^-4   to 0.5  Ω·m . Thus those substance which have resistivity lower than insulators and higher than conductors are the semiconductors. 

Pure silicon crystal
(source : www.images-of-elements.com)

      Anyway, Resistivity is not the only factor which decide whether the substance is a semiconductor or not . There are other factors(properties) too which make a semiconductor crystal unique and quite useful in the field of electronics . like ...

• The resistivity of the semiconductor decreases with temperature an vice versa (semiconductor materials behaves as insulator at absolute zero (zero Fahrenheit))
• The second and the most important property is that if  suitable impurity are added (doped) to a semiconductor block like arsenic,gallium , phosphorous the current conducting property increases , giving rise to a new improved semiconductor block with high conductivity  "Extrinsic semiconductor "  

Extrinsic semiconductor are mainly of two kinds "the P-type" and the "the N-type" . The P-type semiconductor are created by doping impurities with valency 3 (trivalent) like boron,aluminium etc and N- type semiconductors are created by doping impurities with valency 5 (pentavalent) impurity like arsenic and phosphorous .
                       like in a silicon crystal with valency 4 when a trivalent impurity (impurity for p-type semiconductor) is doped  the 3 outer electron (valence electron) of silicon crystal form a covalent bond with the 3 electron of the trivalent impurity . But in the fourth covalent bond only silicon atom contributes one valence electron and there is a deficiency of electron which is called a hole .Holes are positively charged and are the prime charge carrier in P-type semiconductor.
                               Whereas when a pentavalent(valency 5) impurity are doped the four atoms of silicon forms a covalent bond with the 4 valence electron of impurity leaving behind one free electron . These free  Electrons are the prime charge carrier of N-type semiconductor.


N-type semiconductor is more preferred then P-type as the mobility (drift velocity to applied electric field across material) of electrons ( prime charge carrier of N-type) is greater than that of holes (charge carrier of P-type).  

Introduction to Electonics

The world Electronics means "electron mechanics" , It is a science which deals with the motion of electrons under the influence of electric or magnetic field , The ability to control electron flow is usually applied to information handling or device control ,thus giving rise to two field of engineering disciple Electronics & Telecommunication engineering.

All electronic circuits however complicated contains a large number of some basic electronics components
these components are either brought individually and are assembled together on a circuit board using soldering or through the process of micro-miniaturisation (reduction in size) are reduced to  extremely small dimension to make an integrated circuit (IC) , IC  revolutionized the world of electronics today .As many circuits which once used to be impossible to make once (late in 1948s) as it contains many thousands of components, can be made(fabricated) today on a single semiconductor chip. 
Electronics components are mainly divided into two parts Active components and passive components 

• Active components - those devices which are capable of amplifying or processing an electrical signal .    eg Transistor, silicon controlled rectifier (SCR)
• Passive components - Those devices which have neither of the feature of active components and are generally incapable of power gain , But can dissipate or store energy. eg Resistor , capacitor , inductor