Technology World

Routh Hurwitz criterion in MATLAB

2012-04-11T22:37:00.002+05:00


The Routh-Hurwitz stability criterion is a necessary method to establish the stability of linear time invariant (LTI) control system. More generally, given a polynomial, some calculations using only the coefficients of that polynomial can lead us to the conclusion that it is not stable.

In this program you give your system coefficents and the Routh-Hurwitz table would be shown

clc
clear
r=input('input vector of your system coefficents: ');
m=length(r);
n=round(m/2);
q=1;
k=0;
for p = 1:length(r) 
    if rem(p,2)==0
        c_even(k)=r(p); 
    else
        c_odd(q)=r(p); 

        k=k+1;
        q=q+1;
    end
end
a=zeros(m,n); 

if m/2 ~= round(m/2)
    c_even(n)=0;
end
a(1,:)=c_odd;
a(2,:)=c_even;
if a(2,1)==0
    a(2,1)=0.01;
end
for i=3:m
    for j=1:n-1
        x=a(i-1,1);
        if x==0
            x=0.01;
        end

        a(i,j)=((a(i-1,1)*a(i-2,j+1))-(a(i-2,1)*a(i-1,j+1)))/x;

    end
    if a(i,:)==0
        order=(m-i+1);
        c=0;
        d=1;
        for j=1:n-1
            a(i,j)=(order-c)*(a(i-1,d));
            d=d+1;
            c=c+2;
        end
    end
    if a(i,1)==0
        a(i,1)=0.01;
    end
end
Right_poles=0;
for i=1:m-1
    if sign(a(i,1))*sign(a(i+1,1))==-1
        Right_poles=Right_poles+1;
    end
end
fprintf('\n Routh-Hurwitz Table:\n')
a
fprintf('\n Number Of Right Poles =%2.0f\n',Right_poles)

reply = input('Do You Need Roots of System? Y/N ', 's');
if reply=='y'||reply=='Y'
    ROOTS=roots(r);
    fprintf('\n Given Polynomials Coefficents Roots :\n')
    ROOTS
else
end

Samsung Exynos: The Best Processor for tablet PC’s

2011-12-17T13:01:00.000+05:00

Advancement in Computer Technologies:

Since the introduction of the first computers the Computer technology has advanced at a very fast pace. Every single day a new innovation, a new concept is being introduced in the computer technology. The pace in the computer technology is so fast that if a person says about a task that it is impossible, a person in another part of the world is already working on it. These advancements have encouraged different companies to come up with their ideas and compete with the pioneers of the computer market.

Tablet PC’s: The latest and the best:

Tablet PC’s are the latest and the best form of computers. Users have found them and liked them a lot. A tablet PC provides in the true sense the portability and ease that the miniaturised computers have promised. Tablet PC’s, since their origin, have been made better and faster. A few companies have come up with some lightening fast and attractive tablet PC’s. These include Apples, Samsung, Amazon, LG and many others. All of them have tried to make the tablet PC’s faster and better. But if you are talking about the best in this field then there is no doubt only one and that is Samsung.

Samsung and Tablet PC’s:

Samsung has been the pioneers in producing Tablet PC’s. Samsung has always tried to give its customers the best. That is why latest processors and sleek stylish designs have been seen in Samsung’s Products. The latest in this field is the Samsung Exynos 5250 Chip. This 2 GHz Cortex A15 Exynos 5250 Chip is the latest and the fastest processor chip that has been yet made for the tabs. This dual core processor provides better speed and enhanced performance in the tablet PC. This design is better adaptive to 3D technology and provides a new maximum resolution of 2506x1600. Samsung says that this processor will be available in the market by the end of 2012.

SONY TABLET S

2011-12-17T11:42:00.000+05:00

For Sony it was almost two years hard work to enter in to the Tablet market.

To launch a new product of already growing tablet market, where it has so many competitors like the obvious iPad, the Samsung galaxy tablets, Motorola and Acer.

The Sony Tablet S has therefore a different design and look. It has a very different look like it has been folded back from a single textured plastic. It is thicker from one end and very thin sleek surface at the other end.

The Tablet also weighs just 600g so it is very easy to carry compared to the iPad 2. The back is also textured so that it is very easy to carry.

There's a dual-core Tegra 2 processor clocked at 1GHz, 1GB of memory, capacitive touchscreen, and an SD expansion slot.

The Company has strived hard to make it as much versatile as it can from its competitors.

There are front and rear cameras, 1080p video capture and playback, PlayStation certification, which enables users to access a range of exclusive titles, and a host of Sony created apps, including a universal remote for controlling other Sony products.

It has a Beautiful screen quality, Excellent software keyboard, Excellent music application.

With access to the Android Market, you can browse through thousands of useful, time-saving and entertaining apps. There's also instant access to Google™ mobile services and applications including 3D maps and easy web search with Google Voice Search. Download what you want and make your tablet truly yours.

apple iCam concept camera

2011-12-13T23:07:00.000+05:00

Apple iCam is a concept that is given by the Italian designer Antonio DeRosa. And it is likely to be a part of new iPhone 5.

The camera will be having interchangeable lenses, as well as it is going to be operated via your iPhone. So that now we have a huge screen, high processing power, connectivity to various applications and the internet.

The camera also has a rear panel to which the iPhone can be easily connected. It features a 10.1-megapixel sensor and supports video recording with high resolution Full HD at 60 fps.

The iCams two front cameras bring 3D technology to palm of your hand. Which means you can share, edit, record, take pictures all in 3D

Dell stops the production of its Android Tablet

2011-12-13T15:09:00.000+05:00

Dell 7-inch Streak tablet has been taken out of market, according to their website the company has stopped the production of this android tablet and it is no more available for sale on their website.

As the company has informed that it didn’t meet their market expectations of the previous year and it also failed to generate any significant interest.

The company now will launch their windows 8 tablet when the operating system will be launched next year.

According to the CEO of Dell the product has been stopped because it did not meet their market demand; however the Dell 10-inch tablet is still in production.

It appears that Dell has to look into their tablet production and have to take better contracts to make their tablets the talk of 2012.

AUDIO STEGANOGRAPHY

2011-12-12T19:43:00.000+05:00

Ever LISTENED to a text message ???

No!!!

Well this project will make you do so.

Surprised ???

Don’t be because AUDIO STEGANOGRAPHY is the method in which we can encode our secret messages on an audio signal ensuring their safety. In this way we can decrypt a message on an audio signal without its detection.

Lsb coding:-

The type of coding used in this project is the LSB or the Least Significant Coding.

Least significant bit (LSB) coding is the simplest way to embed information in a digital audio file. By substituting the least significant bit of each sampling point with a binary message, LSB coding allows for a large amount of data to be encoded.

Working:-

In this project we first read a wav file using the MATLAB wavread command. Then we input a message from the user. This message is then converted into its ASCII coded signal which then bit by bit replaces the LSB of the wav file. In this way we convert our message into audio form and transmit it.

At the receiver end when the signal is received or the audio file is received, we just take out the last bit of the audio signal. This now is our ASCII coded message we just convert it back into our message signal.

The program is also generating a graphical user interface, from which you can easily hide the message and can then extract it later. All the related codes as well as the audio files can be downloaded here.

VOIP working-- cutting of long distance rates

2011-12-11T18:52:00.001+05:00

VOIP stands for voice over internet protocol. VOIP is getting popular nowadays in audio communication around the globe. It is providing the people with less rates long distance calls. VOIP is basically digital form of transmission compared to the older telephone system that uses analog transmissions.

The analog systems consume more resources, like even if the signal is not traversing on the channel the channel still remains dedicated to that particular session.

Whereas VOIP, as compared to that, utilize the resources efficiently. The information is sent in the form of packets that take any path that is readily available; also the resources are allocated on demand. These packets are than reassemble at the destination.

This compression of information and utilization of different routes made it possible for the information to be sent is less expensive form. With VOIP you have no set up fee, no per minute charges or you don’t have to wait for specific days or places to call from. You can call from anywhere in the world all you need is an internet connection. VOIP is also particularly famous for the conference call service.

Different types of VoIP calling are available

The most common is calling from one computer to another. This service needs an internet connection, microphones and sound card installed in the computer. Also there would be software that provides you the option of VOIP based calls.
IP phones are also available if a person is use to the traditional telephone sets. All the routing and forwarding options are available within that phone.
Analog telephone adaptors (ATA) enable you to connect a standard telephone to your computer Internet connection in order to take advantage of VoIP options. ATA converts analog signals to digital so that it can be transmitted properly via the Internet.
The newest option is the Wi-Fi phone, which uses short-distance Internet transmission of VoIP to replace cell phones calls. Wi-Fi broadcasts over the radio spectrum to cover short range areas for users in certain areas.

Science Explains Why Breaking Up Is Hard to Do

2011-12-11T12:34:00.001+05:00

The studies related to love and affection has always been the main attraction for so long, but it is hardly ever given any thought that what happens when relationships break up. What brain activities are involved in such a scenario? Why it is always been so hard to break up? And does time really heals?

Well now we have some answers to these questions as reported by a scientist name Helen Fisher at New Jersey. Helen has already studied a lot about the love and knows everything regarding this most romantic and beautiful relationships of on the mother earth. But now she thought about studying the other side of picture.

She and her colleagues carried out the experiments on the people who had recent broken relationships but were still in love. All the patient’s brain activities were observed through MRI. It showed that they had the activity in their brain reward system in the same way as the normal lovers do. But the neural pathways were activated due to craving and addiction.

Rejected lovers had an increased response in the controlling emotion areas of brain. As they were considering the fact that what happened. How should they react and what should they do next?

And as the time moves on they showed little and little activity in the attachment linked region of brain. And as we say LOVE HURTS BUT TIME HEALS.

AUDIO COMPRESSION IN MATLAB

2011-12-09T20:49:00.001+05:00

Audio compression is data compression designed to reduce the transmission bandwidth requirement of digital audio streams and the storage size of audio files. Broadly compression techniques are classified into two types:

Lossless compression algorithms usually exploit statistical redundancy in such a way as to represent the sender's data more concisely without error. Lossless compression schemes are reversible so that the original data can be reconstructed
Lossy schemes accept some loss of data in order to achieve higher compression.

In both lossy and lossless compression, information redundancy is reduced, using methods such as coding, pattern recognition and linear prediction to reduce the amount of information used to represent the uncompressed data.

There are numerous methods of compressing audio files. The Discrete Cosine Transform is a lossy technique that removes certain frequencies from the audio data such that the size is reduced with reasonable quality.

The Discrete Cosine Transform is a first-level approximation to mpeg audio compression, which are more sophisticated forms of the basic principle used in DCT.

This discrete cosine Transform Audio Compression is performed in MATLAB.

It takes a wave file as input, compress it to different levels and assess the output that is each compressed wave file. The difference in their frequency spectra will be viewed to assess how different levels of compression affect the audio signals.

PROGRAM WORKING:-

An audio waveform is a continuous sequence of data in one long vector. In that sense, an audio data structure is different from an image data structure. We will need to apportion the vector manually into several pieces, and cannot rely on existing rows or columns.

Read the audio file
Determine a value for the number of samples that will undergo a DCT at once. In other words, the audio vector will be divided into pieces of this length.
Again, we examine at different compression rates:

50%

75%

87.5%

Resulting compressed-and-uncompressed audio waves

For simplicity, we iterate over the vector, window-by-window, but we discard whatever remainder exists:

Now we plot the time domain signals

However, closer inspection does reveal qualitative differences in the densely packed regions (high frequencies).

A look at the spectrogram reveals a clear idea of the loss of high frequencies.

The qualitative difference is clearly apparent when listening to the audio files

Saving the files and viewing the difference in size

CODE

%read a file and convert it to a vector

%chosing a block size

%changing compression percentages

%initializing compressed matrice

%actual compression

%plotting audio signals

%expanded view of audio signals

%spectrogram of audio signals

%playing files

The MATLAB code and related files can be downloaded here:-

3-bit Microprocessor using 89C51

2011-12-09T00:35:00.001+05:00

A 3 bit microprocessor can be designed using a 89C51 micro controller. This code for the program is written in the C language. The code is then loaded into the "Keil uVision 2" Software and a hex file is made through the software. The Hex File is then burned on to the micro controller using a micro controller burner. The circuit diagram is shown below and "Proteus" was used to simulate the software. The Hex file can be directly loaded into the Micro controller using the Proteus Software.

Working of the Project:

Setting numbers as Input:

The project makes use of the basic programming techniques using the C language. First of all basic programs are made as functions like addition function, subtraction function, multiplication function and so on. Then the number is input through the Port 0 of the micro controller. The input is always a binary number.

Selecting an Operation:

After the two inputs are set onto the switches then the operation switch is turned on. Operations are defined on the Port 1 of the micro controller. As it is a 3 bit microprocessor so the total number of operations would be 2³=8. So the whole Port 1 is for operations. The operations include the basic mathematical and logical operations. Selection of two operations at the same time will generate an error and the error bit (Port 2 Pin 7) will turn on indicating the error.

Displaying an Output:

The output is displayed in the output registers. As it is a 3 bit microprocessor so all the registers will be of 3 bits, so when the output of addition is increases than 7 or can’t be displayed in the three bits the overflow bit (Port 2 Pin 0) is turned on indicating the overflow.

In case of multiplication, if the input goes higher than 3 bits then the second register is used to display the remaining bits of the solution. In this way the basic architecture of the computer is followed in the microprocessor.

Flag Register:

Flag register is again of three bits. It contains 3 flag indicators that are zero flag, overflow flag and the sign flag. The zero flag turns on to indicate a result equal to zero. The overflow flag turn to indicate the overflow of the 1^st output register. The sign flag indicates a negative result.

Error Bit:

Error bit is used to indicate an error either in the input port or the operations port. In case of two operations being turned on at the same time, the error bit turns on. Similarly when there is division by zero, the error bit indicates the error.

Note:

This project was implemented and is found fully working. The hex file and the C file are attached for the help. Furthermore the Proteus design is also attached along with the files.

Audio Mixer in ADS

2011-12-08T11:48:00.001+05:00

Mixer is a non-linear circuit that combines two signals in such a way to produce the sum and difference of the two input frequencies at the output.

COMPONENTS:-

C1 = 0.1uF

C2 = 0.1uF

C3 = 0.1uF

R1 = R2 = 10kOhm

R3 = R4 = 100kOhm

R5 = 6.8kOhm

The design and simulation was carried out in ADS software. And the circuit is like this:-

The mixer is implemented by an NPN transistor 2N3904.

The circuit used was basically for audio mixing, it had an input from the triangular wave generator and the noise generator. And it is passsed through the audio mixer to form the wave.

The practical waveform was like dis:-

While the waveform from simulation in ADS was like this:-

Samsung 20nm class DDR3 and SSD

2011-12-06T00:54:00.001+05:00

Samsung’s all new 20nm class DDR3 and SSD is not just great news for the processors but also for the planet. As Samsung is going all green with this new mass production.

This semiconductor chip is more speed and less energy device, not only consumes 38% less energy but is 3.5x faster than other memories in use. It has a really high potential of reducing the waste of energy.

At server level this chip can reduce the power level up to 45W. Even more! The Samsung 20nm DDR3 can reduce the temperatures of the server by almost 21° Celsius. And by this the server fan noise will also be reduced due to low heat generation.

This performance was shown not just for the new processors but also worked the same with the older ones.

The company expects it market level to rise and the chip would be made the part of every technological environment.

The company is also planning to make 4GB memory chips very soon and then moving on to the 8GB, 16GB and so on.

Line Follower Robot

2011-12-05T23:43:00.001+05:00

The robot project works with two motors for driving the rear wheels while the front wheels are free.

It uses 4 infra red sensors for detecting the line that it has to follow. It can be either a black line on white background or a white line on black background.

AT89C2051 microcontroller is used in the project for instructing the robot to move according to the sensors input. The motor driving circuit is made with L293D, which is an H-bridge IC. It can control the two motors simultaneously.

The code is written in C and is a fully functional code.

Care must be taken while choosing the motors. It should be a high torque motor so that it can take the weight of your robot. Otherwise the wheels would work fine while in the air but would not move once the robot is set down.

The sensor circuits as well as the control circuit is given below and the C code can be downloaded as a word file.

Control circuit:-

Sensors circuit:-

These sensor circuits need to be attatched at the points labeled as sensors in the main figure.

Position of Sensors:-

C code:-

Paper Wasp Develops The Same Face Learning Ability As Humans

2011-12-04T23:56:00.001+05:00

Although the brain of a paper wasp is somewhat a millionth in size to that of human brain still they have developed this strange ability of distinguishing faces.

A study has been carried out in Michigan University, in which the biologists reveal that the paper wasps have face-learning ability analogous to the humans.

It’s the very first time that an insect has developed such an intelligent activity. The paper wasps can recognize the individuals of other species by the difference in the face markings. And are more aggressive to those of unfamiliar species.

Some years earlier the biologists had published a paper regarding the long term memory exhibited by these paper wasps. And interestingly their behavior towards other individuals is based on previous interactions.

The biologist carried out the tests by teaching the wasps to distinguish between two separate images. It was seen in the trials that the wasps can pick out the differences between the original pictures more quickly than those that has been edited. Similarly they can figure out the differences between complicated shapes more readily than the geometric shapes.

The face recognizing ability may have been developed due to the reason that these wasps live under colonies in which multiple queens raise the offsprings together.

It appears that they treat the face learning as a different thing from that of other images or objects. Several tests among other species were also carried out but they showed no meaningful result.

The biologist was assisted by a research student and the whole project was funded by the Michigan University and the student was given a full scholarship for this purpose.

This evolutionary behavior shows that certain that specialized cognition may result in to complex behavioral tasks over the time.

Alaska Airlines: Promoting Environment Friendly Airplanes

2011-12-04T23:45:00.000+05:00

Evolution of Air Planes:

Airlines and airplanes have a very brief yet very interesting history. Airplanes were first introduced commercially in 1914 and since then airplanes have gone through a very fast revolution. Due to this revolution we have seen some extra ordinary and state of the art airplanes. Airplanes have become the primary source of travel. Users find it easy and time saving to travel by air, so airlines have developed themselves such that they provide the users with best airline services and make the journey of users a memorable one.

Best Airline Services:

Some of the best airline services include Emirates, Thai Air, Qatar Airways and Singapore Airlines. The competition is very tough in the airline industry and so every airline is trying to produce something unique in their services so that users are attracted towards the airlines and choose the airline every time for their journey.

Environmental Friendly Airline Services: The Alaska Airlines:

In this regard Alaska Airline has introduced a very environmental friendly technique in their airplanes. According to this method the airplanes of Alaska airlines are now flown using bio-fuel. The blend used to fly the airplanes consisted of 80% Petroleum Fuel and 20% Bio Fuel. The Bio Fuel was made up from cooking oil. Yeah Alaska Airlines is running the airplanes using cooking oil.

Cooking oil for Airplanes:

This technique has made the airplanes to release less polluted gas from the exhausts and run as an environmental friendly airline. This technique will damage the environment less and will create an understanding in the other airlines to use such environment friendly techniques in their airlines as well. The bio fuel not only is user friendly but also energy efficient. The use of this technique in all the Alaska airline’s airplanes would decrease the energy consumption equivalent to 28,000 homes or 64,000 cars per annum.

Surface Technology launching in Pakistan

2011-12-04T01:21:00.001+05:00

Microsoft is going to launch state of the art technology very soon in Pakistan. More precisely on dec 11, 2011. As promised by their platform manager while addressing a seminar. The surface technology will be a multi touch product that will allow its users to communicate via the gestures. The communication would involve motion of hands or the physical objects.

Microsoft has launched a portal for one million students and 41000 teaching staff from where they can download educational stuff, books etc free of cost.

Air Cleaning Machine for Asthmatics

2011-12-04T00:57:00.001+05:00

Asthma is a disorder that is caused by the inflammation in the airways of lungs. It occurs when the muscles surrounding the air passage way are swollen and hence constricting the air passage way leading to difficult breathing. The common causes are dust, pollen, chemicals, or other agents in the air that are inhaled by the person.

Statistics shows that over 300 million people around the world are suffering from asthma. Out of which 250,000 die annually due to this cause.

Recently a new air cleaning machine has been developed called Protexo. Protexo basically works in a way that it removes the toxic agents surrounding the breathing area of a person. And generates a slightly cooler air around them, it is operated during sleep.

This prevents the person from inhaling irritants and dust particles present in air that triggers the asthma attacks during his sleep time.

People from different countries were observed for almost a year using Protexo during the sleeping time. A major reduction in the nitric oxide, which is an inflammatory agent, was seen among those patients. A better lifestyle was observed.

Despite all this advances the condition among those that are severely suffering is getting worse.

The machine is not yet available for private purchase. And costs around 2000 pounds for six months use.

FINGER PRINT RECOGNITION IN MATLAB

2011-12-03T00:39:00.001+05:00

Finger print recognition algorithm is used extensively in security related areas. For accessing any database, authenticating to any special services in your company or any other form of security service that use to ask about your ID cards or stuff like that previously.
Here we have provided the MATLAB code of the Finger Print Recognition Algorithm.
That takes the finger print as an image. The 'add to database' option lets you enrol your fingerprint into the database for future queries.
The 'match option then lets you match the finger print image with the database its going to have.
A user friendly GUI is also developed for this purpose with easily monitored buttons.
The attached file also have some fingerprint images for the testing purpose.

Downloads:

DOOR PHONE

2011-12-03T00:15:00.001+05:00

CIRCUIT OPERATION

The basic operation of the circuit is based on impedance matching and then amplifying the signal to give it to the output. Two normal speakers can be used both as the input and the output devices. The first stage which is at BC109C receives the signal in the common base configuration. It gives a good voltage gain and low input impedance which is used for impedance matching with the 8ohms speaker.
Self DC bias is used allowing variations in the transistor’s current gain.
The signal is then filtered for any DC part that may be present, through the capacitor. Thus a pure AC audio signal is sent to the 2nd part of the circuit which is the audio amplifier booster.
A constant Vcc is provided to this circuit, the two diodes check the backward flow of current. The signal is amplified on the 2nd stage through 2 transistors in cascade and later the signal is purified through a capacitor and sent to the output speaker. The basic function of the amplifier is to boost the voltage gain of the circuit and than provide it to the output speaker.

The double pole double throw switch, reverses the loudspeaker positions, so that one is used to talk while the other to listen.
The circuit i used instead of LM386 is:-

OUTPUT ANALYSIS
The output analysis of the circuit tells that its providing 2 watts gain to the speaker so that the voice is audible. If the gain of the amplifier exceed s above the limit than the output signal is clipped off.

QUASI OPTICAL OPEN RESONATOR

2011-12-02T23:32:00.001+05:00

An optical cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric oscillators and some interferometers. Light confined in the cavity reflect multiple times producing standing waves for certain resonance frequencies. The standing wave patterns produced are called modes; longitudinal modes differ only in frequency while transverse modes differ for different frequencies and have different intensity patterns across the cross section of the beam.[1]

Different resonator types are distinguished by the focal lengths of the two mirrors and the distance between them. (Flat mirrors are not often used because of the difficulty of aligning them to the needed precision.) The geometry (resonator type) must be chosen so that the beam remains stable (that the size of the beam does not continually grow with multiple reflections. Resonator types are also designed to meet other criteria such as minimum beam waist or having no focal point (and therefore intense light at that point) inside the cavity.[2]

IMPORTANCE OF A RESONATOR:
Certain devices when excited through a gunn oscillator doesnot produce satisfactory oscillations. There are certain jitters in whole range of frequencies. For this we use a resonator in which the beam of just a particular frequency is choosen to be reflected multiple times in order to produce oscillations. All the other frequencies are not reflected and hence no oscillations are generated at those frequencies. The advantage of the open cavity is that it is non reflecting hence the beam of frequencies which are not focussed at the mirrors move out of the cavity.
We have constructive interference at resonance and a destructive interference at all others. So a sharp peak is detected.[1]

Resonator modes:
Light confined in a resonator will reflect multiple times from the mirrors, and due to the effects of interference, only certain patterns and frequencies of radiation will be sustained by the resonator, with the others being suppressed by destructive interference. In general, radiation patterns which are reproduced on every round-trip of the light through the resonator are the most stable, and these are the eigenmodes, known as the modes, of the resonator.
Resonator modes can be divided into two types: longitudinal modes, which differ in frequency from each other; and transverse modes, which may differ in both frequency and the intensity pattern of the light. The basic, or fundamental transverse mode of a resonator is a Gaussian beam.

Resonator types:
For a resonator with two mirrors with radii of curvature R1 and R2, there are a number of common cavity configurations. If the two curvatures are equal to half the cavity length (R1 = R2 = L / 2), a concentric or spherical resonator results. This type of cavity produces a diffraction-limited beam waist in the centre of the cavity, with large beam diameters at the mirrors, filling the whole mirror aperture. Similar to this is the hemispherical cavity, with one plane mirror and one mirror of curvature equal to the cavity length.

WORKING PRINCIPLE
• It works on the principle of optics and probability(statistics).
• 2 walls are made reflecting to an extent that they behave as mirrors.
• Only 2 walls are contributing to receive the dominant mode at the coupling hole at resonance.

CALCULATIONS:
a=22.86 mm b=10.16 mm
Formulas used to calculate d:

k=2πf/c
d=(l π)/[k²-(π/a)]^0.5
d=16.99021661 mm

RADIATION PATTERNS

REFLECTION COEFFICIENT:
• Hemispherical resonator
• Resonant frequency(theoretical)=11 GHz
• Resonant frequency(practical)=11.5 GHz
• Length of the resonator=d=16.99021661 mm
• Height of the resonator=2a=45.72 mm
• Mode used: TE₁₀₁

Q FACTOR:

OUTPUT POWER:

FEATURES:-
1. STABILITY:
Only certain ranges of values for R1, R2, and L produce stable resonators in which periodic refocussing of the intracavity beam is produced. If the cavity is unstable, the beam size will grow without limit, eventually growing larger than the size of the cavity mirrors and being lost. By using methods it is possible to calculate a stability criterion:
0 ≤ ≤ 1.
Values which satisfy the inequality correspond to stable resonators.
The stability can be shown graphically by defining a stability parameter, g for each mirror:
,
and plotting g1 against g2 as shown. Areas bounded by the line g1 g2 = 1 and the axes are stable. Cavities at points exactly on the line are marginally stable; small variations in cavity length can cause the resonator to become unstable, and so lasers using these cavities are in practice often operated just inside the stability line.
A simple geometric statement describes the regions of stability: A cavity is stable if the line segments between the mirrors and their centers of curvature overlap, but one does not lie entirely within the other.

IS OUR RESONATOR STABLE?
Putting our values into the inequality we get:
0.515
(since our R1=35mm>L=16.99021661mm and R2= ∞)
Thereby proving that our resonator is stable!

2. Q FACTOR:
The Q factor (quality factor) of a resonator is a measure of the strength of the damping of its oscillations, or for the relative linewidth.
• Definition via resonance bandwidth: the Q factor is the ratio of the resonance frequency ν0 and the full width at half-maximum (FWHM) bandwidth δν of the resonance:

Loaded and unloaded Q factors are important characteristics of a resonator used in high-power mm-wave sources[3]
The resonator is composed of parallel curved-plate waveguide sections [4], shorted at the end, with entrance and exit holes for transporting an electron beam through the resonator. In order to study the resonator’s characteristics, it is excited from an external source, such as a network analyzer. The polarizing grid coupler is illuminated by a free-space Gaussian beam, formed by means of a mode exciter and a mirror, as described in [5]

Q Factor of an Optical Resonator
The Q factor of a resonator depends on the optical frequency ν0, the fractional power loss l per round trip, and the round-trip time Trt:

(assuming that l << 1). For a resonator consisting of two mirrors with air (or vacuum) in between, the Q factor rises as the resonator length is increased, because this decreases the energy loss per optical cycle. However, extremely high Q values (see below) are often achieved not by using very long resonators, but rather by strongly reducing the losses per round trip.

High-Q Resonators
One possibility for achieving very high Q values is to use super mirrors with extremely low losses, suitable for ultra-high Q factors of the order of 1011. Also, there are toroidal silica microcavities with dimensions of the order of 100 μm and Q factors well above 108, and silica microspheres with whispering gallery resonator modes exhibiting Q factors around 1010.
High-Q optical resonators have various applications in fundamental research (e.g. in quantum optics) and also in telecommunications (e.g. as optical filters for separating WDM channels). Also, high-Q reference cavities are used in frequency metrology, e.g. for optical frequency standards. The Q factor then influences the precision with which the optical frequency of a laser can be stabilized to a cavity resonance. [6]

3. Phase Noise Reduction
Q (unloaded) = 1097
Bandwidth (practical) = 300Mhz
Q (loaded) = 38.33
1/QL = 1/Qext + 1/Qo
Qe = 39.71
PNR=20 log (1+ Qo/Qext)
PNR= 28.82 dB

4. FREQUENCY STABILTY
BW=300MHz
Narrow bandwidth given that input is in GHz
A load with high Q factor will improve it even further.

REFERENCES:
[1] www.wikipedia.com/opticalcavity
[2] A STUDY OF INTER-INJECTION-LOCKED PHASED ARRAYS Final Report by Karl D. Stephan October 10, 1989 Department of Electrical and Computer Engineering University of Massachusetts.
[3] Paschotta, Rüdiger. "Q Factor". Encyclopedia of Laser Physics and Technology. RP Photonics. http://www.rp-photonics.com/q_factor.html.
[4] M.E. Hill, W.R. Fowlex, X.E. Lin, and D.H. Whittum, Beam-cavity interaction circuit at W-band, IEEE Trans MTT 49 (2001), 998–1000.

[5] M.A. Shapiro and S.N. Vlasov, Study of a combined millimeter-wave resonator, IEEE Trans MTT 45 (1997), 1000–1002.

[6] "Quasioptical microwave and millimeter-wave power combining," by K.D. Stephan
and S.L. Young, SPIE (vol. 947) Conf. on Interconnection of High Speed and High Frequency Devices and Systems, Newport Beach, CA, March "1988.

Windows 8: The Next in Line

2011-12-02T22:42:00.001+05:00

Computer Technology:

Computer Technology has advanced a lot in the past few decades. We have seen some extremely eye catching and awesome computers being made available in the market. Computers with awesome specification and attractive body have made the use of computers easier and simple. To drive these computers different companies have produced different operating systems. Some in the line are Windows OS, Macintosh OS, Ubuntu, Linux, UNIX and many others.

Operating Systems:

Operating Systems have been made better and better as the years have passed. The best company and the one which is ruling on the computer world is the Microsoft Corporation. Microsoft has given some extra ordinary and user friendly OS to the computer users. Some of them being Windows 95, Windows 98, Windows NT, Windows ME, Windows XP, Windows Vista, and the latest in this line is Windows 7. Windows 7 is considered to be the best and the most user friendly OS in the line.

Improvement in the Windows OS:

Microsoft has always been of the view point that the consumers be provided with the best computer solutions. That is why the Microsoft team is constantly in process to create such a product that is both safe, secure and extremely user friendly. So to raise the bar even more a further enhancement in the Windows 7 OS has been done and a new OS is going to be introduced in the market by the Microsoft Corporation.

Windows 8: Safer, Securer and Better:

Windows 7 was a huge success for sure, and to make the things better Microsoft has come up with the latest OS, named as Windows 8. Windows 8 is being interpreted as much better and secure than its predecessor. The actual release date of Windows 8 is still unknown, but some sources say that Windows 8 Beta version will be released in February in the next year. Users are anxiously waiting for the release of Windows 8 and are hoping that it is better than Windows 7 (fingers crossed).

Triangular Wave Generator

2011-12-02T00:56:00.001+05:00

Circuit Diagram:

Components:

· 2x LM 741 IC’s

· 20kΩ Resistor

· 5kΩ Resistor

· 10kΩ Resistor

· 1.1uF Capacitor

Working:

Assemble the components as shown in the circuit diagram above. In the above diagram the capacitor C1 acts as a integrator and integrates the square input into a triangular wave. In this way a triangular wave is generated.

Results:

Result of the above circuit diagram is a perfect triangular wave.

OPERATIONAL AMPLIFIERS Noise Theory

2011-12-02T00:33:00.001+05:00

Abstract
This paper begins with background information. First, introductory
Topics on the basic principles of amplifiers are presented, including
the ideal op amp model, next the design, layout, simulation and noise theory of Operational Amplifier (Op-Amp) structures. Emphasis has been placed on the noise properties of the Op-Amp performance. The OP-Amp noise types and characteristics. Our results show that Experimental testing needs to be carried out for further evaluations.

History:
1941: First (vacuum tube) op-amp
Let's go back in time a bit and see how this device was developed. The term "operational amplifier" goes all the way back to about 1943 where this name was mentioned in a paper written by John R. Ragazzinni with the title "Analysis of Problems in Dynamics" and also covered the work of technical aid George A. Philbrick.
Today, and since that month in 1976, the types of op amps have increased almost daily. An op-amp, defined as a general-purpose, DC-coupled, high gain, inverting feedback amplifier, was first found in US Patent 2,401,779 "Summing Amplifier" filed by Karl D. Swartzel Jr. of Bell labs in 1941. This design used three vacuum tubes to achieve a gain of 90dB (decibells) and operated on voltage rails of ±350V. It had a single inverting input rather than differential inverting and non-inverting inputs, as are common in today's op-amps.

INTRODUCTION
What exactly is an OPerational AMPlifier? Let's define what that component is and look at the parameters of this amazing device. An operational amplifier IC is a solidstate integrated circuit that uses external feedback to control its functions. It is one of the most versatile devices in all of electronics. The term 'op-amp' was originally used to describe a chain of high performance DC amplifiers that was used as a basis for the analog type computers of long ago. The very high gain op-amp IC's our days uses external feedback networks to control responses. The op-amp without any external devices is called 'open-loop' mode, refering actually to the so-called 'ideal' operational amplifier with infinite open-loop gain, input resistance, bandwidth and a zero output resistance. However, in practice no op-amp can meet these ideal characteristics.

EXPLANATION
An operational amplifier is a differential input, single-ended output amplifier, as shown symbolically in Figure 1-1. This device is an amplifier intended for use with external feedback elements, where these elements determine the resultant function, or operation. This gives rise to the name “operational amplifier,” denoting an amplifier that, by virtue of different feedback hookups, can perform a variety of operations.
We now enjoy a variety of op amps that will provide the user essentially with anything s/he needs, such as high common-mode rejection, low-input current frequency compensation, CMOS, and short-circuit protection. All a designer has to do is expressing his needs and is then supplied with the correct type. Op-Amps are continually being improved, especially in the low noise areas.

Ideal Op Amp Attributes
An ideal op amp has infinite gain for differential input signals. In practice, real devices will have quite high gain (also called open-loop gain) but this gain may not necessarily be precisely known. In terms of specifications, gain is measured in terms of VOUT/VIN, and is given in V/V, the dimensionless numeric gain. More often, however, gain is expressed in decibel terms (dB), which is mathematically dB = 20 log (numeric gain).
Also, an ideal op amp has zero gain for signals common to both inputs, that is, common-mode (CM) signals.
Or, stated in terms of the rejection for these common-mode signals, an ideal op amp has infinite CM rejection (CMR). In practice, real op amps can have CMR specifications of up to 130 dB for precision devices, or as low as 60 dB–70 dB for some high speed devices.
The ideal op amp also has zero offset voltage (VOS = 0), and draws zero bias current (IB = 0) at both inputs. Within real devices, actual offset voltages can be as low as 1 pV or less, or as high as several mV. Bias currents can be as low as a few fA, or as high as several ìA. This extremely wide range of specifications reflects the different input structures used within various devices.

The Noninverting Op Amp Stage
The op amp non-inverting gain stage, also known as a voltage follower with gain, or simply voltage follower,
Transfer expression of the network is defined as seen from the top of RF to the output across RG as β. This usage is a general feedback network transfer term, not to be confused with bipolar transistor forward gain. β can be expressed mathematically.
So, the feedback network returns a fraction of Vout to the op amp (–) input. Considering the ideal principles of zero offset and infinite gain, this allows some deductions on gain to be made. The voltage at the (–) input is forced by the op amp’s feedback action to be equal to that seen at the (+) input, Vin. Given this relationship, it is relatively easy to work out the ideal gain of this stage, which in fact turns out to be simply the inverse of β. This is apparent from a comparison of Equations.
The Inverting Op Amp Stage
The op amp inverting gain stage, also known simply as the inverter, is shown in Figure 1-4. As can be noted by comparison of Figures 1-3 and 1-4, the inverter can be viewed as similar to a follower, but with a transposition of the input voltage Vin. In the inverter, the signal is applied to RG of the feedback network and the op amp (+) input is grounded.
For clarity, these expressions are again included in the figure. The major difference between this stage and the non-inverting counterpart is the input-to-output sign reversal, denoted by the minus sign in Eq. 1-5. Like the follower stage, applying ideal op amp principles and some basic algebra can derive the gain expression of Eq. 1-5.
The inverting configuration is also one of the more useful op amp stages. Unlike a non-inverting stage, however, the inverter presents a relatively low impedance input for Vin, i.e., the value of RG. This factor provides a finite load to the source. While the stage gain can in theory be adjusted over a wide range via RF and RG, there is a practical limitation imposed at high gain, when RG becomes relatively low. If RF is zero, the gain becomes zero. RF can also be made variable, in which case the gain is linearly variable over the dynamic range of the element used for RF. As with the follower gain stage, the gain is ratio dependent, and is relatively insensitive to the exact RF and RG values.
The inverter’s gain behavior, due to the principles of infinite op amp gain, zero input offset, and zero bias current, gives rise to an effective node of zero voltage at the (−) input. The input and feedback currents sum at this point, which logically results in the term summing point. It is also called a virtual ground, because of the fact it will be at the same potential as the grounded reference input.
A special gain case for the inverter occurs when RF = RG, which is also called a unity gain inverter. This form of inverter is commonly used for generating complementary VOUT signals, i.e., VOUT = −VIN. In such cases it is usually desirable to match RF to RG accurately, which can readily be done by using a wellspecified matched resistor pair.
A variation of the inverter is the inverting summer, a case similar to Figure 1-4, but with input resistors RG2, RG3, etc (not shown). For a summer individual input resistors are connected to additional sources VIN2, VIN3, and so forth, with their common node connected to the summing point. This confi guration, called a summing amplifier, allows linear input current summation in RF.3 VOUT is proportional to an inverse sum of input currents.

Noise Gain (NG)
The first aid to analyzing op amps circuits is to differentiate between noise gain and signal gain. We have already discussed the differences between noninverting and inverting stages as to their signal gains, which are summarized in Eqs. 1-2 and 1-4, respectively. But, as can be noticed from Figure 1-6, the difference between an inverting and noninverting stage can be as simple as where the reference ground is placed. For a ground at point G1, the stage is an inverter; conversely, if the ground is placed at point G2 (with no G1) the stage is noninverting.
Note, however, that in terms of the feedback path, there are no real differences. To make things more general, the resistive feedback components previously shown are replaced here with the more general symbols ZF and ZG, otherwise they function as before. The feedback attenuation, â, is the same for both the inverting and noninverting stages:

Noise gain can now be simply defined as: The inverse of the net feedback attenuation from the amplifier output to the feedback input. In other words, the inverse of the â network transfer function. This can ultimately be extended to include frequency dependence (covered later in this chapter). Noise gain can be abbreviated as NG.
As noted, the inverse of â is the ideal noninverting op amp stage gain. Including the effects of fi nite op amp gain, a modifi ed gain expression for the noninverting stage is:

Open-Loop Gain:
Lets have a look how the 'ideal' amplifier would look like in Fig. 5-1. The search for an ideal amplifier is, of course, a futile exercise. The characteristics of the operational amplifier are good enough, however, to allow us to treat it as ideal. Below are some amplifier properties that make this so. (Please realize that these ratings are next to impossible to achieve).

Op Amp Noise Theory and Applications
The purpose of op amp circuitry is the manipulation of the input signal in some fashion.
Unfortunately in the real world, the input signal has unwanted noise superimposed on it.
Noise is not something most designers get excited about. In fact, they probably wish the
whole topic would go away. It can, however, be a fascinating study by itself. A good understanding of the underlying principles can, in some cases, be used to reduce noise in the
design.
Noise is a purely random signal, the instantaneous value and/or phase of the waveform
cannot be predicted at any time. Noise can either be generated internally in the op amp,
from its associated passive components, or superimposed on the circuit by external sources.

Noise Floor
When all input sources are turned off and the output is properly terminated, there is a level
of noise called the noise floor that determines the smallest signal for which the circuit is
useful. The objective for the designer is to place the signals that the circuit processes
above the noise floor, but below the level where the signals will clip.

Signal-to-Noise Ratio
it is a ratio of signal voltage to noise voltage (hence the name signal-tonoise
ratio).

Types of Noise
There are five types of noise in op amps and associated circuitry:
1) Shot noise
2) Thermal noise
3) Flicker noise
4) Burst noise
5) Avalanche noise

Some or all of these noises may be present in a design, presenting a noise spectrum
unique to the system. It is not possible in most cases to separate the effects, but knowing
general causes may help the designer optimize the design, minimizing noise in a particular
bandwidth of interest. Proper design for low noise may involve a “balancing act” between
these sources of noise and external noise sources.

Noise Colors
While the noise types are interesting, real op amp noise will appear as the summation of
some or all of them. The various noise types themselves will be difficult to separate. Fortunately,
there is an alternative way to describe noise, which is called color. The colors of noise come from rough analogies to light, and refer to the frequency content. Many colors are used to describe noise, some of them having a relationship to the real world, and some of them more attuned to the field of psycho-acoustics.
White noise is in the middle of a spectrum that runs from purple to blue to white to pink
and red/brown. These colors correspond to powers of the frequency to which their spectrum
is proportional.

AMPLIFIER NOISE
Amplification of low level audio or RF signals is always accompanied by noise generated within the amplifier itself. The following article discusses the generation of this noise and some of the methods of assessing noise performance.

INTRODUCTION
One of the factors which governs the performance of any amplifier system is the noise in the system. Noise might be defined as signals in the system which are unwanted and which degrade the desired signal content in the system.
As far as the amplifier system is concerned, noise can be divided into noise it receives at its input and noise it generates itself. A good system is one in which the noise generated by the amplifier itself is small compared to noise from the incoming source. In a HF receiver, for example, atmospheric noise is high and it is not difficult to achieve this requirement. At VHF and UHF frequencies, atmospheric noise is low and performance is limited by the noise generated in the first stages of the radio receiver.

An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation. High input impedance at the input terminals (ideally infinite) and low output impedance (ideally zero) are important typical characteristics.
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities. Op-amps sometimes come in the form of macroscopic components (see photo), or as integrated circuit 'cells' or patterns that can be reprinted several times on one chip that is more complex, such as for a cell phone.
Modern designs are electronically more rugged than earlier implementations and some can sustain direct short circuits on their outputs without damage.
The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but which works fine with common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network).

World’s Fastest Computer

2011-12-01T21:32:00.001+05:00

Evolution of Computers:

Computers have become an integral part of life nowadays. People all around the world use computers in some way. Calculators, Tablets, Netbooks, PC, Laptops, PDAs and many other gadgets are some examples in which we interact with computers. The evolution of computers started since the first computer was invented in 1946. The first computer was just like a simple calculator like in nowadays and but it covered an area of a whole large hall. Since then the evolution started and both the speed and miniaturization were made better and better. And it is due to that evolution that we see laptops and Netbooks and the fastest computers in the world, “The Super Computers”.

Supercomputers:

Super computers are the fastest computers in the world. They are huge in size as well as calculations. Super computers are used for highly intensive calculations like weather forecasting, quantum physics, molecular modeling and many others.

Speeds of Supercomputers:

Super computers are extremely fast in doing these calculations and have a capacity of calculating at very high rates. Speed of super computers is measured in FLOPS (FLoating Point Operations Per Second) with SI-Prefixes like Tera-FLOPS or TFLOPS (Tera is 10¹²), and Peta-FLOPS or PFLOPS (Peta is 10¹⁵).

Fastest Supercomputer in the World:

China has left America behind in the technology world that has made the fastest Supercomputer of the world. Chinese named this computer Tianhe-1A. This supercomputer has a speed of 2.507 PFLOPS. In other words it can perform 2,507 trillion FLOPS in the blink of an eye. This Chinese computer will take the spot of America’s Cray XT5 aka ‘Jaguar’ which had the speed of 1.759 PFLOPS.

The Tianhe-1A was designed by the National University of Defense Technology and will be constantly used for intense and large scientific calculations.

SOLID STATE RELAYS

2011-12-01T14:45:00.000+05:00

Abstract—the paper discusses that Solid-state relays (SSR) are able to perform many of the same tasks as electromechanical relay (EMRs). The main difference is that SSRs have no moving mechanical parts within it. SSRs use a control circuit and a separate circuit for switching the load. The relay is energized by a light-emitting diode. The types of SSR are photo-coupled SSR, transformer-coupled SSR, and hybrid SSR.

I-INTRODUCTION: Solid State Relays (SSRs) are switching devices consisting of electronic components. The term "Solid State" means that these relays do not incorporate any moving parts in the load switching circuit. Often, solid state relays are used where the circuit under control must be protected from the introduction of electrical noises. [1]

II-DEFINITION: A solid state relay (SSR) is an electronic switch, which contains no moving parts. Essentially, it is an electronic device that relies on the electrical, magnetic, and optical properties of semiconductors and electrical components to achieve its isolation and relay switching function [2].The SSR requires relatively low control circuit energy to switch the output state from OFF to ON, or vice versa. Since this control energy is very much lower than the output power controllable by the relay at full load, "power gain" in an SSR is substantial--frequently much higher. Being solid-state devices, there are no moving parts to wear out, and they are able to switch on and off much faster than any mechanical relay armature can move. There is no sparking between contacts, and no problems with contact corrosion. [3]

III-PRINCIPLE OF OPERATION: These active semiconductor devices use light instead of magnetism to actuate a switch. The light comes from an LED, or light emitting diode. When control power is applied to the device’s output, the light is turned on and shines across an open space. On the load side of this space, a part of the device senses the presence of the light, and triggers a solid state switch that either opens or closes the circuit under control. [4]

IV-TRIACS: A triac is an electronic component approximately equivalent to two silicon-controlled rectifiers joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together. This results in a bidirectional electronic switch that can conduct current in either direction. The triac is ideal for switching resistive AC loads. [5]
SSRs use a control circuit and a separate circuit for switching the load. The output device (SCR, TRIAC, or transistor) is optically-coupled to an LED light source inside the relay. The relay is turned on by energizing this LED, usually with low-voltage DC power. When voltage is applied to the input of the SSR, the relay is energized by a light-emitting diode. The light from the diode is beamed into a light-sensitive semiconductor that, in the case of zero-voltage crossover relays, conditions the control circuit to turn on the output solid-state switch at the next zero-voltage crossover. In the case of nonzero-voltage crossover relays, the output solid-state switch is turned on at the precise voltage occurring at the time. Removal of the input power disables the control circuit and the solid-state switch is turned off when the load current passes through the zero point of its cycle. [6]

V-ADVANTAGES:
• When applied properly, Solid State Relays (SSRs) will last millions of cycles due to the fact that no mechanical devices are included in the load switching circuit. The user will experience no arcing problems, and operation will be trouble free, even in polluted environments (dust, gasses, etc.) SSRs are a faster alternative to electromechanical relays because their switching time is dependent on the time required to power the LED on and off - approximately 1 ms and 0.5 ms respectively. Because there are no mechanical parts, their life expectancy is higher than an electromechanical relay.
• One significant advantage of a solid-state SCR or TRIAC relay over an electromechanical device is its natural tendency to open the AC circuit only at a point of zero load current. Because SCR's and TRIAC's are thyristors, their inherent hysteresis maintains circuit continuity after the LED is de-energized until the AC current falls below a threshold value (the holding current). In practical terms what this means is the circuit will never be interrupted in the middle of a sine wave peak. Such untimely interruptions in a circuit containing substantial inductance would normally produce large voltage spikes due to the sudden magnetic field collapse around the inductance. This will not happen in a circuit broken by an SCR or TRIAC. This feature is called zero-crossover switching. [7]
• Additionally, SSRs are completely silent in their operation given their purely electronic nature.
• Increased lifetime due to the fact that there are no moving parts, and thus no wear
• Clean, bounce less operation
• Decreased electrical noise when switching
• Can be used in explosive environments where a spark must not be generated during turn-on
• Totally silent operation
• Smaller than a corresponding mechanical relay.
• Can continue to operate while subjected to severe vibration.

VI-DISADVANTAGES:
• One disadvantage of solid state relays is their tendency to fail "shorted" on their outputs, while electromechanical relay contacts tend to fail "open." In either case, it is possible for a relay to fail in the other mode, but these are the most common failures. Because a "fail-open" state is generally considered safer than a "fail-closed" state, electromechanical relays are still favored over their solid-state counterparts in many applications. [8]
• Fail short more easily than electro-mechanical relays
• Increased electrical noise when conducting
• Higher impedance when closed (-> heat production)
• Lower impedance when open
• Reverse leakage current when open (µA range)
• Possibility of false switching due to voltage transients
• Isolated bias supply required for gate charge circuit
• Higher Transient Reverse Recovery time (Trr) due to the presence of Body diode.

VII-TYPES OF SRR’s: It is convenient to classify SSR's by the nature of the input circuit, with particular reference to the means by which input-output isolation is achieved. Three major categories are recognized:
A-Reed-Relay-Coupled SSR’s in which the control signal is applied (directly, or through a preamplifier) to the coil of a reed relay. The closure of the reed switch then activates appropriate circuitry that triggers the thyristor switch. Clearly, the input-output isolation achieved is that of the reed relay, which is usually excellent.
B-Transformer-Coupled SSR’s in which the control signal is applied (through a DC-AC converter, if it is DC, or directly, if It is AC) to the primary of a small, low-power transformer, and the secondary voltage that results from the primary excitation is used (with or without rectification, amplification, or other modification) to trigger the thyristor switch. In this type, the degree of input-output isolation depends on the design of the transformer.
C-Photo-coupled SSR’s in which the control signal is applied to a light or infrared source (usually, a light-emitting diode, or LED), and the radiation from that source is detected in a photosensitive semi-conductor (i.e., a photosensitive diode, a photo-sensitive transistor, or a photo-sensitive thyristor). The output of the photo-sensitive device is then used to trigger (gate) the TRIAC or the SCR's that switch the load current. Clearly, the only significant “coupling path” between input and output is the beam of light or infrared radiation, and electrical isolation is excellent. These SSR's are also referred to as “optically coupled” or “photo-isolated. [9]

IX-Thermal considerations: one of the major considerations when using an SSR is properly managing the heat that is generated when switching currents higher than about 5 amperes (A). In this case, the base plate of the SSR should be mounted onto a good heat conductor, like aluminum, and used with a good thermal transfer medium like thermal grease or a heat transfer pad. Using this technique, the SSR case to heat sink thermal resistance is reduced to a negligible value of 0.1°C/W.

X-Load considerations: a leading cause of application issues with SSRs is improper heat sinking. Problems can also arise from operating conditions that specific loads impose upon an SSR. The surge characteristics of the load should be carefully considered when designing in a SSR as a switching solution.

XI-Resistive loads: Loads of constant values of resistance are the simplest application of SSRs. Proper thermal consideration, along with attention to the steady state current ratings, will result in trouble-free operation.

XII-DC loads: this type of load should be considered inductive, and a diode should be placed across the load to absorb any surges during turn-off.

XIII-Lamp loads: Incandescent lamp loads, though basically resistive, can present some challenges. Because the resistance of the cold filament is about 5 to 10 percent of the heated value, a large inrush current can occur. It is essential to verify that this inrush current is within the surge specifications of the SSR. One must also check that the lamp rating of the SSR is not exceeded. Due to the unusually low filament resistance at the time of turn-on, a zero-voltage turn-on characteristic is particularly desirable with incandescent lamps.

XIV-Capacitive loads: these types of loads can prove to be problematic because of their initial appearance as short circuits. High surge currents can occur while charging, limited only by circuit resistance. Caution must be used with low-impedance capacitive loads to verify that the di/dt capabilities are not exceeded. Zero-voltage turn-on is a particularly valuable means of limiting di/dt with capacitive loads.

XV-Motors and solenoids: Motor and solenoid loads can create challenges for reliable SSR functionality. Solenoids have high initial surge currents because their stationary impedance is very low. Motors also frequently have severe inrush currents during starting and can impose unusually high voltages during turn-off. As a motor’s rotor rotates, it creates a back EMF that reduces the flow of current. This back EMF can add to the applied line voltage and create an overvoltage condition during turn-off. Likewise, the inrush currents associated with mechanical loads having high starting torque or inertia, such as fans and flywheels, should be carefully considered to verify that they are within the surge capabilities of the SSR. A current shunt and oscilloscope should be used to examine the duration of the inrush current. [10]

XVI-APPLICATIONS: The SSR is usually used in applications where there is a need to separate high voltage circuits from the low voltage or low power circuits. By using SSR, circuits can exchange signals, and at the same time, they are galvanically isolated. The SSR allows for a safe interface between the high voltage and low voltage circuits. It breaks the ground loop to eliminate cross talk and interference between the high voltage and low voltage circuit.
The SSR has been extensively used in the telephone set, modems, fax machine, PBX or central office equipments. In telephone applications, it is always necessary to isolate the telephone equipments from the incoming telephone lines. Isolation is important to protect the electronic equipments from harmful voltages or current caused by lightning. SSR, with high input-output transient rejection specifications, can provide good isolation and surge protection.
Since its introduction, the SSR has gained acceptance in many areas that had previously been the sole domain of the EMR or the contactor. The SSR is increasingly employed in industrial process control applications, particularly temperature control, motors, lamps, solenoids, valves and transformers. The list of specific applications for the SSR is broad. [11]
Typical examples of SSR applications include:
• Industrial automation
• Electronic appliances
• Industrial appliances
• Packaging machines
• Tooling machines
• Manufacturing equipment
• Food equipment
• Security systems
• Industrial lighting
• Fire and security systems
• Dispensing machines
• Production equipment
• On-board power control
• Traffic control
• Instrumentation systems
• Vending machines
• Test systems
• Office machines
• Medical equipment
• Display lighting
• Elevator control
• Metrology equipment
• Entertainment lighting[12]
XVII-CONCLUSIONS: DC output solid state relays give designers a great deal of flexibility in the relative connections of control and load voltages. Care must be taken when a solid state relay is used to control and inductive load, to ensure that at turn off, the voltage rating of the solid sate relay is not exceeded. SSRs are highly susceptible to surge currents and damage when used at signal levels above their rating. Although there are no metal contacts to weld, damage to the MOSFET can render the relay unusable. SSRs are a nice alternative to mechanical relays but have higher path resistances and are not fully isolated between the contacts.

REFERENCES
[1] Technical letters, National Plastic heater sensor and control Inc.
[2] By TJ Landrum, Product Manager, Eaton, Research book.
[3] Tony R. Kuphaldt, Lessons in Electric Circuits, Volume IV – Digital, ch 5 pg 142
[4] Anthony Bishop, Solid-state relay handbook with applications‎ - 224 page
[5] By TJ Landrum, Product Manager, Eaton, Research book.
[6] By TJ Landrum, Product Manager, Eaton, Research book.
[7] Tony R. Kuphaldt, Lessons In Electric Circuits, Volume IV – Digital, ch 5 pg 142
[8] Tony R. Kuphaldt, Lessons in Electric Circuits, Volume IV – Digital, ch 5 pg 143
[9] Research book, Relays defined and described by Crydom Corporation
[10] By TJ Landrum, Product Manager, Eaton, Research book.
[12] By TJ Landrum, Product Manager, Eaton, Research book.