“Bluetooth” wireless technology
Deepak Bagai
large amount of data is carried over wired networks. Even cordless and mobile telephones rely on wired ‘landline’ telephone systems to carry and route calls between endpoints. The rat’s nest of cables behind the computer is going to be the thing of past now.

New products & discoveries

  • Stunning view of Saturn

  • New types of transistors

  • Farthest known galaxy


Building tips



“Bluetooth” wireless technology
Deepak Bagai

A large amount of data is carried over wired networks. Even cordless and mobile telephones rely on wired ‘landline’ telephone systems to carry and route calls between endpoints. The rat’s nest of cables behind the computer is going to be the thing of past now. “Bluetooth” is an economical radio technology that enables computers, cellphones, laptops and other devices to talk to one another wirelessly within a 30-foot radius. Till date the most apparent application of Bluetooth devices has been in mobile phones. Headsets with Bluetooth chips enable hands-free access to the latest phone models. Very soon, digital cameras, laptops, computers and PDAs shall access Internet wirelessly via Bluetooth enabled 3G mobile phones. Prior to the Bluetooth, wireless computer link was enabled through infrared light waves. Infrared has limitation of use within line of sight.

Bluetooth technology has originated from an organisation called the Bluetooth Special Interest Group (SIG). There are numerous stories behind the emergence of the name Bluetooth. Hanary Blatand was king of Denmark who united Denmark and Norway and brought Christianity to Scandinavia. “Blatand” actually translates to “Bluetooth”. Bluetooth wireless communication makes use of radio frequency technology to communicate through the air. RF incorporates high power transmitters and receivers tuned to a particular frequency range for a long-range transmission in TV. Short-range communication requires less power and thereby batteries can suffice the power requirements. RF waves can penetrate the obstacles and there is no requirement of Line of Sight here. FM radio broadcast operates in 88 MHz to 108 MHz range, cordless phones work in 900 MHz spectrum and the Bluetooth technology operates in 2.4 gigahertz spectrum. Through an international agreement, the 2.4-gigahertz Bluetooth spectrum does not require a license to operate.

The Bluetooth spectrum is divided into 79 channels and the Bandwidth is limited to 1MHz per channel. The concept of frequency hopping spread spectrum communication is deployed here. There are other applications also which make use of this spectrum. Microwave ovens work in this frequency range. Some cordless phones also use the 2.4 GHz spectrum. This fact is attributed to the unlicensed 2.4 GHz range and the interferences have to be taken care of by proper design. Spread spectrum divides the existing spectrum according to frequency, time, coding scheme or some other method. Bluetooth wireless communication makes use of the technique of frequency division spread spectrum i.e. frequency hopping. Here the spectrum is divided into different frequencies or channels. One packet of the message is transmitted on a particular channel and then the next packet is transmitted on a new channel, and the process continues.

Bluetooth link between two devices consists of a master and a slave. Any Bluetooth radio can assume any role and the master only controls the synchronisation and frequency pattern of FHSS. A piconet consists of a single master and all slaves in close proximity. A Bluetooth device in the connection state is in the Active mode, Hold, Sniff or Park mode. In the Active mode the Bluetooth device actively participates on the channel. The master coordinates the transmission based on traffic demands to and from the slaves. In the Sniff mode, a slave device listens to the piconet at reduced rate and this interval is programmable. The Hold mode refers to the power saving mode i.e the data transmission and reception restarts when units come out of the Hold mode. In the Park mode the device is synchronised to the Piconet but does not participate in transmission and reception.

Bluetooth Technology has been implemented successfully in many applications. There are Bluetooth enabled cars, which unlock automatically as the owner approaches the vehicle. The location of the vehicle as per the area is also indicated. The driver receives a new message on the route via the speakerphone of the car. Bluetooth enabled office will ensure that the PDA automatically synchronises with the desktop PC of the office and transfers files emails. Long queues at the public places like hospitals, theatres, hotels, railway stations and airports can be minimised. A person can use his PDA to wirelessly confirm and pay for the tickets. Bluetooth has become an important building block of wireless technology. It has been predicted that there will be more than 700 million Bluetooth enabled devices worldwide by year 2005.

The writer is Asst. Professor Dept. of Electronics, Punjab Engineering College, Chandigarh.


New products & discoveries

Stunning view of Saturn

Four months before its scheduled arrival at Saturn, the Cassini-Huygens spacecraft sent its best colour postcard back to Earth of the ringed world. The spacecraft is expected to send weekly postcards, as it gets closer to the ringed giant.

The view from Cassini shows Saturn growing larger and more defined as the spacecraft nears a July 1, 2004, arrival date. On February 9, Cassini’s narrow angle camera, one of two cameras onboard the spacecraft, took a series of exposures through different filters, which were combined to form the colour image released.

“We very much want everyone to enjoy Cassini’s tour of this magnificent planetary system,” said Dr. Carolyn Porco, leader of the Cassini imaging science team at the Space Science Institute in Boulder, Colo. “And I can say right now the views out the window will be stunning.”

New types of transistors

Hungry for details, dozens of microcircuit specialists surrounded Tahir Ghani after his talk last December at an annual microelectronics conference in Washington, D.C. Ghani, a senior-level engineer with the chip giant Intel in Hillsboro, Ore., had sketchily revealed two new types of transistors that his company was getting ready to use in its Pentium microprocessors and Centrino chips. After his talk, Ghani remained cagey. After all, his inquisitors were from IBM, Taiwan Semiconduc-tor Manufacturing Com-pany, NEC, and other rival chip makers. All these companies are confronted by the same daunting challenge: to maintain the swift pace of miniaturisation even while their mainstay manufacturing methods are reaching their limits.

For decades, chip manufacturers have made transistors faster by making them smaller. Lately, however, this approach has begun to unravel.

Farthest known galaxy

Using the ISAAC near-infrared instrument on ESO’s Very Large Telescope, and the magnification effect of a gravitational lens, a team of French and Swiss astronomers (2) has found several faint galaxies believed to be the most remote known.

Further spectroscopic studies of one of these candidates has provided a strong case for what is now the new record holder - and by far - of the most distant galaxy known in the universe.

Named Abell 1835 IR1916, the newly discovered galaxy has a redshift of 10 [3] and is located about 13,230 million light-years away. It is therefore seen at a time when the universe was merely 470 million years young, that is, barely 3 per cent of its current age.

This primeval galaxy appears to be ten thousand times less massive than our Galaxy, the Milky Way. It might well be among the first class of objects which put an end to the Dark Ages of the universe.



Prof Yash PalIn Norway sun is seen throughout the day for weeks. How is this happening?

You know that our earth revolves around the sun. The seasons are caused by the fact that the axis of the earth rotation is not perpendicular to the plane in which the earth revolves – it is tilted by an angle of 23.5 degrees. Day and night on the earth result from the rotation of the earth around its axis. On June 21, during the summer solstice of the Northern hemisphere, the North Pole and the region around it that lies within the Polar circle is illuminated by the sun for full 24 hours of the day.

There is no night. Geographic location of Norway is such that parts of it lie with the Polar circle. That is the reason for the phenomenon that has baffled you. After 6 months the same regions live through 24 hours of darkness because the polar region does not come into the view of the sun.

Why do all surgeons wear only green clothes in an operation theatre?

I can only guess the answer. Surgeons have to have some clean apparel while they are close to a patient being opened up. It could be white but you do not want any doctor in white cutting you up. Perhaps surgeons want to show off that they are different. What are the choices of colour? Red is clearly out - too bloody. Of the rest green is a good compromise because there is good reason to believe that it is a soothing colour, particularly for patients who are filled with anxiety. Perhaps someone could suggest that saffron might have a preference over green!

I cannot find a good argument against or in favour of such a change. I have a suspicion that someone started a convention in favour of the green and it caught up. Maybe a big hospital chain where it began also had an interest in a factory with large stocks of green fabric!

I have heard that most fundamental forces between particles are understood as exchange forces. What is exchanged and what does it mean?

I will try answering this question without using too much jargon, avoiding technicalities as much as I can. A charged particle like a proton has an electric field around it. This field represents its sphere of influence.

The electric field extends to infinity though its intensity decreases inversely as square of the distance. In modern physics the electric field can be considered as an assemblage of virtual photons and its effect on another charge as being mediated through exchange of these photons. Theory of electrons developed on this basis by Dirac has been exceedingly successful. This theory was based on quantum mechanics, recognising the fact that light cannot travel faster than a certain speed. One could say that in some sense the theory was based on the reality of exchange interaction.

But protons do not interact only through electromagnetic interaction. They have other interactions in addition. Strong interaction is the one that keeps atomic nuclei together. Nuclear force is much stronger and has a different character. Specifically its range is very short. It was postulated that there should exist particles of mass over 200 times the electron mass that might act as mediators of strong force through exchange reaction between strongly interacting particles. Quantum mechanical wavelength of these particles would be short. The success of this idea has been demonstrated through discovery of such particles. It is to be realised that though such gluing particles might be virtual when causing the exchange interaction they can also be concretely produced when enough energy is available to create them.

These glue particles are sprinkled out in abundance in interaction of particles at high energies. Incidentally photons that are the virtual glue of electromagnetic interaction are also produced in abundance in electron interactions at high energy. This way of thinking has been successfully employed to understand another category of interactions called weak interactions. The mediating particles with right properties have been discovered as predicted. Proceeding further the nucleons (namely protons and neutrons) have been postulated to be composed of various types of quarks which are again combined with the help of gluons of right properties. Searches are on to detect these gluon particles.

Many features of the universe we live in have been understood successfully through universalising a certain way of thinking. One might say that this has resulted in a significant success in achieving the unification of three out of four forces of nature we know of. Considering that they pertain to such different regimes of strength and properties it seems amazing that this has happened. One could almost say that one has got some insight into the mind of Nature, including the tricks it likes to use. Gravity has not yet been caught in this web. No one can say that he has found the graviton. The hunt is on. If and when that happens it will be a big day for science.

What is the principle of a telescope? Can we make a telescope with PVC pipes?

I do not want to go into a detailed discussion of telescopes, but mention only the essential features. A telescope has to be able to detect distant sources from which very little light comes to us. The diameter of our eye pupil is about a millimetre. So we can collect only that much light as falls on the small entrance area of our eye.

Some of the modern telescopes have lenses of diameters that are in the range of several metres. Also unlike the eye the telescope detectors can accumulate the signal for a long time. Combined with the fact that the light collection area goes as the square of the diameter, these telescopes can detect sources that are weaker by many orders of magnitude. So we can see far.

Building tips

Throughout the construction of a building, one aspect that must be kept in view is Curing, commonly known as tarai. This single item brings best strength at minimum cost. All RCC work should be given special attention. Keep the water standing over the roof slab for at least 7 days and preferably for 15 days. Sprinkle water on brick work and plastered work at regular intervals round the clock for the first 7 days. Wrap gunny bags around door lintels as these will retain the moisture for longer periods. Never forget to cover freshly laid concrete with plastic sheet or gunny bags immediately after its laying. Keep sprinkling water on the roof for the first day after its laying and thereafter make arrangement for standing water over it.

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Soak bricks in water before using them in masonry work. Just sprinkling of water on the stacks is of no use. If the bricks are soaked in water, these will not draw water from the cement mortar and cement will have more moisture available to gain full strength. Prefer to create a lined tank full of water and place bricks into it. Soaking is very important for at least one hour before use of bricks. Avoid placing soaked bricks on ground or mud. Place them on the platform near the mason's position.

— Jagvir Goyal