Ingenious Engineering

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How is sunlight turned into electricity?

Solar or photovoltaic (photo = light, voltaic = voltage or electricity) cells are created from special materials such as Silicon (Si) mixed with other elements, which when exposed to sunlight will generate an electrical current. Basically sunlight is absorbed into the photovoltaic material, which in turn knocks electrons within the material loose. This allows the electrons to flow freely within the material structure, creating an electrical current.

Why use Silicon?

Silicon is a common choice for solar cells because of its inherent physical qualities. Silicon has 4 outer shell electrons from a possible 8 ‘holes’. It will always try to fill the other 4 ‘holes’, and does this by sharing electrons with neighbouring silicon atoms. This creates a lattice type structure, where every atom in the structure bonds with four other atoms in the structure.



When energy is added to the silicon, in the form of sunlight, it can knock electrons free of the lattice structure, but this requires a lot of energy and generates very few free electrons. With few free electrons, there is very little current flow, so impurities are added to the silicon to increase its current carrying properties. This process is called ‘doping’.

The silicon is ‘doped’ with atoms which contain more electrons to create negatively charged silicon or with atoms which contain less electrons to create positively charged silicon. These compounds are referred to as n-type and p-type respectively.

When energy is added to n-type silicon there are a lot more free electrons present within the structure. This n-type silicon is placed next to the p-type silicon, causing the free electrons in the n-type silicon to rush towards the holes in the p-type silicon, which creates a current flow.

In today’s field of modern engineering technology and science thyristors form an extremely important device and is almost universally employed these days for all high power controlled gadgets.

It all started in the year 1950 when Sir William Shockley of the BELL LABs proposed a model fabricated on a silicon-based semiconductor similar to a silicon controlled rectifier, which later went on to be named as a thyristor. Its first prototype was introduced by GEC(USA) in the year 1957, and since then there has been a lot of research and development on the device and its industrial application, which led to the evolution of a whole family of semiconductor devices with identical properties, like the diac, triac, silicon-controlled switch, PTU ( programmable uni junction transistor ), etc. to be employed for different purposes as per the requirement. This entire family of semiconductors is named as thyristors, as it has the same basic principal of operation, with a few variations here and there.

One of the most primitive yet most widely used member of the thyristor family is known as an SCR or a silicon controlled rectifier. The SCR has been so widely used in the present era of engineering applications, that it has become almost synonymous to a thyristor, unlike the other members of the same family. Now to get into all these silicon fabricated devices in details, its important that we are well versed with the basic constructional details and the functionalities of the thyristor.
Thyristor basics and construction.

Thyristors are essentially, four layer, three junction p-n-p-n semiconductor switching device. It basically consists of four heavily doped semiconductor layers, namely the:

i) Outer p layer.

ii) Inner n layer.

iii) Inner p layer.

iv) And outer n layer.

These four layers are cascaded together to form the three junctions J1,J2 and J3 respectively as has been explained in the schematic diagram of the thyristor below.
construction of thyristor

Construction of Thyristor

Here the terminal connected to the outer p region is known as the anode or the positive terminal. Similarly the outer n region is connected to the negative terminal known as cathode. And most importantly there is this inner p region that is known as the gate terminal, which results in the main distinguishing feature between the diodes and thyristors, as the thyristor can be switched on by means of gate triggering voltage, which will be taken up later in details in a separate article to understand its overall functionality.

HOW DOES A TOUCH SCREEN WORKS,,,,,,?

Capacitive Touch Screen

The capacitive touch screen has been around the longest. The very first one was invented way back in 1965 in the UK by the Royal Radar Establishment. The capacitive touchscreen works on the principal that since the human body is an electrical conductor, then movement of a finger against a screen will cause a distortion to the electrostatic field. The current from this distortion is broadcast to the corners of the screen on the mobile device, and a controller processes that information to know where the point of contact is. There can be more than one point of contact on a capacitive touch screen, which allows for multi-touch capabilities like pinching or zooming in our out of an image. The material used for these types of screens are insulators such as glass, and are then coated with a transparent conductor such as indium tin oxide. Since this technology uses the distortion of the electrostatic field caused by contact of the human body, any shielding of that body part, like putting on a glove, will negate the effects of the screen. Many of mobile devices out today use this type of technology including the iPhone and the HTC Hero. Incidentally, the Blackberry Storm also used this type of touch screen, but the guys over at RIM just didn’t do a great job with the application of it on the device.

WORLDS FIRST LAPTOP,,,,,,,,

I was born in 1985 and I wouldn’t lay my hands on a PC until 10 years later. In that same 1985 though, the first mass market consumer laptop was released by Toshiba and it was called the T1100. Now you may think that it was a piece of crap and to today’s standards it most certainly is but it can still have a sense of humor:

Ah, you can’t read German? It asks to “be patient, because it isn’t that young anymore”. The specs on this beauty?

256KB of RAM and a 4.77 MHz Intel Processor made your computing dreams come to life and just like the Macbook Air of today it didn’t have a regular Hard Drive. Instead it supported floppy disks and weighed in at a whopping 4.1 Kilograms. Pricing was set at $1899,- not bad if you ask me, it could have made me the coolest newborn around the block.

ohm's laws formulas