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How Virtual Reality (VR) works?

VR Technology :An overview

Working of Virtual reality
Leading VR enabled head mounted display (HMD)

Virtual reality (VR) typically refers to computer technologies that use softwares and hardwares to generate realistic images, sounds and other sensations that replicate a real environment, and simulate a user's physical presence in this environment, by enabling the user to interact with this space and any objects depicted therein using specialized display screens or projectors and other devices. In this article I would like to explore “how Virtual Reality works” and what is the basic principles behind virtual reality.

Nowonly most of us are hearing about VR, but humans have identified Virtual Reality long before. Early versions of VR originated around 1930-40. The first references to the concept of virtual reality came from science fiction. Stanley G. Weinbaum's 1935 short story "Pygmalion's Spectacles" describes a goggle-based virtual reality system with holographic recording of fictional experiences, including smell and touch.After the invention of ‘motion pictures’ ,human’s thrive to experience real world virtually resulted in the invention of various Virtual Reality(VR) equipments. 
For the present generation VR is nothing but google cardboard or Oculus rift head-mounted display or HMD. HMDs typically take the form of head-mounted goggles with a screen in front of the eyes. Some simulations include additional sensory information and provide sounds through speakers or headphones. 

Many of us might have used a VR HMD equipment. How many of us know the simple principle behind this? So, let us have a look at “how does VR work”

Working of a Virtual Reality goggles (head mounted display -HMD)

Virtual reality glasses or goggles are becoming increasingly popular in the gaming and entertainment arena. They are lighter and more comfortable to wear than the standard head mounted display (HMD). Ordinary glasses show a single image but 3D and virtual reality glasses contain polarised lenses which show two images, one per each eye. These images appear to give an illusion of depth of object we see.
The basic principle behind 3D and virtual reality is stereoscopy. Two separate images are shown to each eye, which the brain combines into a single image. We are tricking our brain to perceive two slightly different images as a single image.
VR Video picture frame
Snapshot of a VR Video  frame
Image given above is a snap of 3D VR video. Two images are combined to from a single frame. If you closely observe ,you can see there is slight difference in left and right images. Two slightly different angles of the scene is fed into each eye, simulating depth. This along with other ways to simulate depth like parallax (farther objects to you seem to move slower), shading and techniques create an almost a real world experience. 

360 degree videos

360 videos, also known as immersive videos or 360 degree videos, are videos recording of a real world panorama, where the view in every direction is recorded at the same time, shot using an omnidirectional camera or a collection of cameras. If 360 degree videos are played on your PC screen you can navigate through video using mouse or navigation keys. Using a wearable VR HMD ,You can watch different portions of video as you turn your head around which make it feel more immersive. Your head movement is detected using the gyro sensors on your smart phones. Along with 3D effect, 360 degree view will enhance Virtual Reality effect.
Now,different kinds of wearable VR equipments(HMDs) are available in the market.Google cardboard,Oculs rift,HTC vive and Samsung gear are the major players in the wearable VR HMD market.Google card board is the chepest one,but if you are looking for a real VR experience, go for Oculus rift or HTC vivo.Using a poorly aligned VR product may cause health problems like motion sickness.

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Speciality of IPS LCD displays

IPS LCD Display is one of leading display technology used in smartphones and other handheld devices.

Many Leading Mobile Phones like
iPhone7 use an IPS display
Content Highlights
  • What is LCD and How it works 
  • How LCD panel is wired 
  • Twisted nematic LCD 
  • Different Layers of LCD pannel
  • TFT display and its shortcomings 
  • IPS Display technology 
  • Advantages and Disadvantages of IPS LCD display technology in comparison with TFT,LED etc..



Before going into IPS LCD displays,let us have look at basic operation of LCDs. Liquid crystals (LCs) are matter in a state which has properties between those of conventional liquids and those of solid crystals. For instance, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. When electricity is passed through, this crystals scatter light is different directions. This basic property of Liquid Crystals is exploited in Liquid Crystal Displays.

Basic unit of a LCD display system is a liquid crystal cell consists of a thin layer (about 10 u m) of a liquid crystal sandwiched between two glass sheets with transparent electrodes deposited on their inside faces. With both glass sheets transparent, the cell is known as transmittive type cell. When one glass is transparent and the other has a reflective coating, the cell is called reflective type. The LCD does not produce any light of its own. It depends entirely on light falling on it from an external source for producing viewable light.

Twisted nematic LCD

A nematic liquid crystal is a transparent or translucent liquid that causes the polarization of light waves(focusing of light in a plane) to change as the light pass through it.The extend of polarization depends on the intensity of applied electric field.
Twisted Nematics, a particular nematic substance is twisted naturally. When a known voltage is applied to the substance, it gets untwisted in varying degrees according to our requirement. This in turn is useful in controlling the passage of light. The relatively inexpensive twisted nematic display is the most common consumer display type.

How LCD works
Different Layers of an LCD unit
An LCD unit has two polarized glass pieces(F). The glass which does not have a polarized film on it must be rubbed with a special polymer to form microscopic grooves in the surface(B&E). Grooves are on the same direction as the polarizing film. Nematic crystal layer(D) is sandwiched between electrodes. The grooves will cause the first layer of molecules to align with the filter’s(polarizer) orientation. Two grooved glasses are at right angle to each other. Till the uppermost layer is at a 90-degree angle to the bottom, each successive layer of TN molecules will keep on twisting. The first filter will naturally be polarized as the light strikes it at the beginning. Thus the light passes through each layer and is guided on to the next with the help of molecules. When this happens, the molecules tend to change the plane of vibration of the light to match their own angle. When the light reaches the far side of the liquid crystal substance, it vibrates at the same angle as the final layer of molecules. The light is only allowed an entrance if the second polarized glass filter is same as the final layer. Take a look at the figure given above. Please note two polarizers are at right angle to each other.

The main principle behind liquid crystal molecules is that when an electric field is applied across them, they tend to untwist. This causes a change in the light angle passing through them. This causes a change in the angle of the top polarizing filter with respect to it. So little light is allowed to pass through that particular area of LCD. Thus that area becomes darker comparing to others.

Colour LCDs are those that can display pictures in colours. In addition to above layers, there must be three sub-pixels with red, green and blue colour filters to create each colour pixel.

LCD panel wiring

The liquid crystal displays used in calculators and other devices with similarly simple displays have direct-driven image elements, and therefore a voltage can be easily applied across just one segment of these types of displays without interfering with the other segments.
LCD pannel wiring
Direct driven LCD pannel

This would be impractical for a large display, because it would have a large number of (color) picture elements (pixels), and thus it would require millions of connections, both top and bottom for each one of the three colors (red, green and blue) of every pixel. To avoid this issue, the pixels are addressed in rows and columns, reducing the connection count from millions down to thousands. The column and row wires attach to transistor switches, one for each pixel. The one-way current passing characteristic of the transistor prevents the charge that is being applied to each pixel from being drained between refreshes to a display's image. Each pixel is a small capacitor with a layer of insulating liquid crystal sandwiched between transparent conductive layers.

TFT Displays

TFT Displays uses TN(Twisted nematic technology) The circuit layout process of a TFT-LCD is same as that explained above. However, rather than fabricating the transistors from silicon, that is formed into a silicon wafer, they are made from a thin film of silicon that is deposited on a glass panel. Transistors take up only a small fraction of the area of each pixel and the rest of the silicon film is etched away to allow light to easily pass through it.

Disadvantage of of TFT displays

Since TFT display uses TN technology,it has got disadvantages of TN displays.TN displays suffer from limited viewing angles. Colors will shift when viewed off-perpendicular
Also, most TN panels represent colors using only six bits per RGB color, or 18 bit in total, and are unable to display the 16.7 million color shades (24-bit true-color) that are available from graphics cards. Instead, these panels display interpolated 24-bit color using a method that combines adjacent pixels to simulate the desired shade. This disadvantages lead to the invention of IPS Technology.

IPS Display Technology

IPS (In-Plane Switching) displays provide consistent, accurate color from all viewing angles without blur or grayscale inversion. IPS displays show clear images with stable response time, and no halo effect is produced when touched.

Working of IPS Display
Working of IPS Display
What is an ips display?:Each pixel within an IPS type TFT consists of three sub-pixels (Red, Green and Blue). Each sub-pixel has a pair of electrodes to control the twisting of the Liquid Crystals. Unlike TN type TFTs where the electrodes are on opposing plates, the electrodes in an IPS TFT are on only one of the glass plates (i.e. in the same plane). When voltage is applied to the electrodes, all the Liquid Crystal molecules align in parallel with that plane and allow light to pass through to the polarizers and RGB color filters. In effect, TN displays force the Liquid Crystal molecules perpendicular to the glass which blocks some light from coming out at wide angles, while IPS displays keep the Liquid Crystal molecules in line to allow light through at all angles.
All modern mobiles phones from iPhones,samsung,LG etc.. are using IPS LCD displays.Many varaints of IPS displays are available in market.LG is one of the largest supplier of IPS displays.

Advantages of IPS Display

  • IPS panels display consistent, accurate colour from all viewing angles
  • Unlike TFT- TN LCDs, IPS panels do not lighten or show tailing when touched (halo effect). This is important for touch-screen devices, such as smartphones and tablets 
  • IPS panels offer clear images and stable response time .

Disadvantages of IPS Display

  • IPS panels require up to 15% more power than TN panels.
  • IPS panels are more expensive to produce than TN panels.
  • IPS panels have longer response time than TN panels.
All modern mobiles phones from iPhones,samsung,LG etc.. are using hd ips display.LG is one of the largest supplier of IPS screen displays.Are you planning to buy a IPS display laptop or full HD IPS display smartphone,then do some research ,because many varaints of IPS display monitors are available in market.Choose your product based on the price and affordability.
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Atomic clock -World's most accurate clock-How does it works?

Atomic clock is the most accurate clock:how does an atomic clock work

How does world's most accurate atomic clock works
NIST-F1 would neither gain nor lose one second in about 100 million years
Content Highlights
  • Types of clocks and basic principle behind a clock.
  • What is a atomic clock?
  • Principle behind an atomic clock
  • How does an  Atomic Clock works?
  • NIST-F1 Cesium Fountain Clock
  • Definition of a second
  • Applications of atomic clocks


Before going into the atomic clock, let us see what a clock really is. A clock's job is to measure passage of time. All clocks do this by measuring some sort of resonation of one or another material. Let us have look at some commonly used clocks.
pendulum clock :In a pendulum clock, the resonator is a pendulum and the gears in the clock keep track of time by counting the resonations (swinging) of the pendulum. The pendulum resonates at a frequency of one swing per second.
Digital clock: It either measures oscillations on power line or oscillation provided by an electronics circuit. In US power supply oscillates at 60 cycles per second and in Europe and Asia power supply oscillates at 50 cycles per second.
Quartz clock: In this type of clocks ,on supply of electric current quartz crystal oscillates at a particular frequency. This resonating frequency is converted into measurable form with the help of gears.

What is an atomic clock

NIST Atomic clock
the NIST-F1 in Boulder, Colorado
In an atomic clock an ‘atom’ or a ‘molecule’ is the resonator. In every clock accuracy of resonator determines accuracy of time. An atom resonates at extremely consistent frequency. This ensures the accuracy of an atomic clock. In all other clocks resonator is manufactured, so, there is limitation in accuracy that can be obtained from such resonators.

Basic principle behind an atomic clock

When exposed to certain frequencies of radiation, such as radio waves or microwaves the electrons that orbit an atom's nucleus will "jump" back and forth between energy states. The electrons absorb energy to move to a higher energy level (away from the nucleus), and release energy to move down an energy level (towards the nucleus). This “jumping” happens at extremely consistent frequency .Clocks based on this jumping within atoms can therefore provide an extremely precise way to count seconds.
Commonly used atoms in an atomic clock: Currently caesium (33Cs) is the widely used one,but rubidium (87Rb) and thallium (205Tl) were used earlier.

Working of an Atomic clock.

There are many atomic clocks around the world. Out of which, NIST-F1 Cesium Fountain Clock is one among the most accurate clocks.It is developed by National Institute of Standards and Technology (U.S. Department of commerce) . The uncertainty of NIST-F1 is continually improving. As of January 2013, the uncertainty has been reduced to about 3 x 10-16, which means it would neither gain nor lose a second in more than 100 million years .NIST-F1 is referred to as a fountain clock because it uses a fountain-like movement of atoms to measure frequency and time interval.
Working of atomic clock diagram
Diagrammatic representation of a an atomic clock 
Laser cooling: We know that a moving atom possess higher energy than the stationary one. To restrict the movement of cesium atoms a technique called LASER cooling is used in NIST-F1 clock. First, a gas of cesium atoms is introduced into the clock's vacuum chamber. Six infrared laser beams then are directed at right angles to each other at the center of the chamber. The lasers gently push the cesium atoms together into a ball. In the process of creating this ball, the lasers slow down the movement of the atoms . Laser cooling drops the temperature of the atoms to a few millionths of a degree above absolute zero, and reduces their thermal velocity to a few centimeters per second

working of atomic clock diagram
laser cooling-atoms are stabilized
using six laser beams 

Two vertical lasers are used to gently toss the ball upward (the "fountain" action), and then all of the lasers are turned off. This little push is just enough to loft the ball about a meter high through a microwave-filled cavity. Under the influence of gravity, the ball then falls back down through the microwave cavity.
Working of atomic clock diagram
a ball of atoms tossed up by
laser beams
Working of atomic clock diagram
when laser is turned off ,atoms fall down
due to gravity

The round trip up and down through the microwave cavity lasts for about 1 second. During the trip, the atomic states of the atoms might or might not be altered as they interact with the microwave signal. When their trip is finished, another laser is pointed at the atoms. Those atoms whose atomic state were altered by the microwave signal emit light (a state known as fluorescence). The photons, or the tiny packets of light that they emit, are measured by a detector.
Working princicple of atomic clock diagram
Detection of photons emitted by caesium atoms
This process is repeated many times while the microwave signal in the cavity is tuned to different frequencies. Eventually, a microwave frequency is found that alters the states of most of the cesium atoms and maximizes their fluorescence. This frequency is the natural resonance frequency of the cesium atom (9,192,631,770 Hz), or the frequency used to define the second.
Definition of a second: According to The International System of Units (SI) "The second is the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. This definition refers to a caesium atom at rest at a temperature of 0 K "

Applications of atomic clocks 

What is the need of an atomic clock?..It has got many applications in our life.Some of them are listed below.
1.GPS and similar navigation systems:In GPS our position is calculated based on the time taken by the signal to travel between GPS satellites and receiver. To determine position with high precision even billionths of a second is significant. 
2. Telecommunications systems require synchronization better than 100 billionths of a second .
3. Electrical power companies use synchronized systems to accurately determine the location of faults (for example, lightning damage) when they occur and to control the stability of their distribution systems.
4. In space exploration, radio observations of distant objects in the universe, require exceedingly good atomic reference clocks. And navigation of probes within our solar system depends critically on well-synchronized control stations on earth.
5. The time-related quantity called frequency, basically the rate at which a clock runs, is needed by the radio and television broadcast industry to maintain proper control of transmissions and thus avoid interference between stations.
6.Using the internet every computer can synchronize its time setting with a centralized time server – the atomic clock time server – so that all the computer times all around the world can use standardized settings, even though they are scattered through different time zones. Most operating systems (i.e. Windows, Mac, Linux) have an option to automatically synchronize the system clock periodically using an NTP (network time protocol) server: NIST is offering a network time service to deliver UT1(Universal Time) time.

Still atomic clock researches are going around the globe .And scientists are coming up with more and more accurate atomic clocks.
References:
  1. NIST Cesium Fountains — Current Status and Future Prospects S.R. Jefferts∗ , T.P. Heavner, T.E. Parker and J.H. Shirley http://przyrbwn.icm.edu.pl/APP/PDF/112/a112z506.pdf 
  2.  https://www.nist.gov
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Working of Global Positioning System(GPS)

How does a GPS tracking system work ?-WORKING PRINCIPLE BEHIND GPS IS TRILATERATION

Nowadays GPS is an  inevitable part of our day-today life
Content Highlights
  • · Introduction to GPS and other Navigation   system 
  • · GPS and Trilateration 
  • · 2D and 3D illustration of Trilateration 
  • · How does gps calculate distance 
  • · Types of GPS 
  • · Importance of Atomic clocks in GPS satellites


In this era of smartphones most of us will be familiar with GPS (Global Positioning System).It helps us in position tracking and navigation. But did you ever wonder how GPS works?. GPS was built by the US military and has been fully operational since 1995. Now countries like Russia(GLONASS), China, India(IRNSS-not fully operational) and European union possess their own positioning and navigation systems. GPS uses a lot of complex technologies, but basic concept is simple.

There are three parts for GPS system: A 24 to 32 solar-powered satellites orbiting the earth in orbits at an altitude of approximately 20000 kilometers(24 satellites are operational at a time), a control station and a GPS receivers such as the one in a car or a GPS enabled smartphone.

The Basic principle behind GPS: trilateration

GPS system uses a mathematical principle called trilateration to locate position. The orbits of satellites are designed so that there are always 4-6 satellites in view, from most places on the earth. At least signals from three satellites are needed to carry out trilateration process.

2D illustration of trilateration

Let us assume you are lost some where in Australia. One of your friend in Adelaide told you,you are 650 kms away from him, which means you could be any where on the circle with radius 650 kms and centre Adelaide.

gps working principle and diagram
Fig1
Like that Another friend from Sydney told you, you are 700 kms away from him. Now you know you are on either point p1 or p2 (marked in below figure).
GPS working trilateration 2d illustration
Fig2
If a third friend told you ,you are 1400 kms from Brisbane ,you can locate your position with respect to three cities. Your position will be intersection point of three circles.(Fig3)
GPS working trilateration illustarion
Fig3
This method of locating position is called trilateration. This same concept works in 3 dimension. But , instead of circles you should think in terms of spheres.

Trilateration in 3D space

Assume 3 satellites are visible to your GPS receiver. Name them A,B and C. If you know your distance from A , you could be anywhere on the surface of a huge sphere of that radius.
GPS trilateration 3d illustartion
Fig1
If you know your distance from satellite B you can overlap 1st sphere with 2nd and they intersect in a perfect circle. Now you know you are somewhere on circle.

GPS trilateration 3d illustartion
Fig2
So If you know distance to a third satellite C you got a third sphere which intersects with this circle at to points. And earth acting as fourth sphere ,you can eliminate point in space because you are on earth.
GPS trilateration 3d illustartion
Fig3
If only 3 satellites are available, the GPS receiver can get an approximate position by making the assumption that you are at mean sea level. If you really are at mean sea level, the position will be reasonably accurate. In other words, it requires only 3 satellite to determine latitude and longitude with reasonable accuracy. But calculate altitude you require a fourth satellite. A modern GPS receiver will typically track all of the available satellites simultaneously, but only a selection of them will be used to calculate your position

How GPS receiver determines distance from satellites.

The GPS receiver gets a signal from each GPS satellite. The satellites transmit the exact time the signals are sent. By subtracting the time the signal was transmitted from the time it was received, the GPS can tell how far it is from each satellite. The GPS receiver also knows the exact position in the sky of the satellites, at the moment they sent their signals. So given the travel time of the GPS signals from three satellites and their exact position in the sky, the GPS receiver can determine your position in three dimensions - latitude, longitude and altitude. Distance is calculated by the formula 
D=(tr - ts)C
tr= time at receiver
ts= time signal from satellite
C=Speed of light

Conventional GPS and A-GPS

Conventional GPS :To determine the location of the GPS satellites two types of data are required by the GPS receiver; the almanac and the ephemeris. This data is continuously transmitted by the GPS satellites and your GPS receiver collects and stores this data. The almanac contains information about the status of the satellites and approximate orbital information. The GPS receiver uses the almanac to calculate which satellites are currently visible. Ephemeris gives very precise information about the orbit of each satellite. Your GPS receiver can use the ephemeris data to calculate the location of a satellite precisely.

A-GPS(assisted GPS):GPS receiver in our cell phones are example of a A-GPS. The A-GPS device will use a data connection (internet connection on a cellphone) to contact an assistance server. The server can supply almanac and ephemeris data so the GPS doesn't have to wait to receive them from the satellites. This improves first locking speed considerably.

Atomic clocks

Atomic clocks are high precision clocks used in scientific applications. Since GPS satellites transmits time signal to the receivers it is important to keep precise timing equipment on board . Every single GPS satellite is home to a family of atomic clocks (typically four) that derive their time from cesium or rubidium atoms. In these clocks the energy difference between two specific atomic states is measured. When an atom changes from the high-energy state to the lower energy state, the energy difference is emitted in the form of light. The frequency, or ticking rate, of this light is what we count and how we define time. This energy difference is always the same. These clocks are so precise that it won’t lose a second for 15 billion years.
Though GPS satellites have atomic clocks that keep very precise time, it's not feasible to equip a GPS receiver with an atomic clock. However, if the GPS receiver uses the signal from a fourth satellite it can solve an equation that lets it determine the exact time, without needing an atomic clock.

Real working of GPS system is much more complex.Hope this article  gave you an idea about basic navigation system,GPS satellite and their working principle.
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