“Adrishya Alok”: The Scintillating Legacy Of Electromagnetic Waves

It was in 1672 that Isaac Newton experimentally segregated a beam of light into its seven component colours and established the fact that what we consider light is actually a combination of multiple waves having different frequencies and wavelengths. Therefore, it came to light that our perception of colours can be attributed to the reflection of a light wave by an object corresponding to its perceived colour while absorbing all the other components.

However, it was much later, in the nineteenth century, that mankind began to understand that there is more than what meets the eye, literally.

In 1800, astronomer William Herschel, while conducting an experiment to note the temperatures corresponding to different colours of light refracted by a prism, abruptly placed a thermometer on the farther side of the visible red light and, surprisingly, observed that the temperature recorded by this thermometer was the highest. The invisible light rays heating up that thermometer eventually came to be known as infrared rays.

Similarly, the next year, Johann Wilhelm Ritter established the existence of ultraviolet rays by observing that invisible rays beyond the violet end of the spectrum reacted rapidly with a silver chloride solution (a precursor to photography).

In the 1860s, a scientist called James Clerk Maxwell revolutionised the world by upgrading the perception of these visible and invisible light waves to carriers of electromagnetic radiation associated with time-varying and codependent electric and magnetic fields.

Twenty-five years later, Maxwell's theory was verified by Heinrich Hertz using an instrument called the "spark-gap generator" to create and discharge electromagnetic waves having a shorter frequency than visible light (radio waves) and using an open-loop circular detector placed nearby to detect them through the spark they created.

In 1895, Indian scientist Jagdish Chandra Bose discovered waves having frequency as high as 60 GHz (millimetre waves) and demonstrated their presence by igniting gunpowder and using what he termed as "Adrishya Alok" in his Bengali essay, to ring a bell beyond the wall. While Bose got the formal recognition for his contribution around 120 years too late (by the Institute of Electrical and Electronics Engineers), it is this discovery of millimetre waves that forms the backbone of 5G technology as the world swoons over high-speed internet today.

Further, building on the works of Lodge, Bose, and Tesla, Italian engineer Guglielmo Marconi laid the foundation for wireless communication in 1899 by sending radio waves across the English Channel.

While all these discoveries pertained to waves on the infrared side of the spectrum, the beginning of the twentieth century saw the discovery of high-energy waves from the farther side of the violet end of the spectrum.

In 1896, German physicist Wilhelm Conrad Röntgen came across some invisible rays that had the property of showing the interiors of the human body when passed through it. Calling these mysterious rays “x-rays,” he immediately envisaged the medical uses of his discovery while presenting the skeletal image of his wife's hand taken on a photographic plate.

This, followed by the discovery of radioactivity by Marie Curie and experiments by Ernest Rutherford, led to the discovery of similar waves called alpha, beta, and gamma rays.

Electromagnetic Waves Revolutionised The World

After the potential of x-rays and gamma rays (high frequency means high energy and low wavelength) was recognised, they were immediately embraced by the medical world for applications like radiotherapy to cure tumours, sterilisation of medical equipment, as medical tracers, and so on.

Similarly, micro and radio waves captured the human imagination for (wireless) transfer of data over large distances. It was possible using an instrument called antenna, which could:

● Translate the applied electric signals to electromagnetic waves and radiate them in the atmosphere (transmitter), and

● Detect and capture electromagnetic radiation and convert it back to electric signals at the receiving end.

Despite the constant upgrades and improvisation in technology over time, this simple framework formed the basis of many communication, navigation, and surveillance aids.

Radar Technology

Radar works on a simple principle: ground-based machinery transmitting a radio wave and receiving its reflected component after it hits a moving or stationary object (target), and thus using this time difference and the speed of the emitted wave to calculate the distance to the target.

While radar was invented during the Second World War, mainly for military purposes, it eventually became a common instrument used for maritime and aircraft navigation, meteorological applications, and for surveillance of commercial aircraft by air traffic controllers (ATCs).

Today, the aviation world uses a more sophisticated set of radars whereby, on receiving the "interrogatory pulse" by ground-based equipment, transponders aboard the aircraft "reply" with the pertinent pre-fed information apprising the ATCs of necessary information regarding their flight plan.

These “reply waves” are captured by the receiver antenna of the ground radar and translated into electrical signals, which are then converted into a displayable format and relayed to the monitor screen of the ATCs.

While dispatching and maintaining a satellite in Earth orbit requires meticulous knowledge and compliance with Kepler and Newton’s laws, using them for telecommunication, radio and TV broadcasting (DTH service), and data communication uses the same principle: the use of electromagnetic waves to transmit data from one location on the ground to a space-based satellite and then back to Earth as a broadcast and available at multiple places with the use of receiving antennas.

Avionics

Just like many birds have an ability called “homing,” which is to find their way over long distances, airborne aircraft make use of homing devices to find their way from one place to another.

For example, a device called a non-directional beacon (popularly known as radio compass) sends out long radio waves, which the airborne aircraft can receive and 'home in' to find its way. Every airport has such navigational aids with a uniquely assigned frequency. The pilot of the aircraft can look into her charts and tune into the frequency of the desired airport.

Bigger airports like Mumbai and Chennai use high-power navigational aids that can provide homing signals for long distances, as much as 900 km, to facilitate navigation over long-haul routes like Bangkok to Chennai.

Similarly, guidance systems like the instrument landing system help the pilot or autopilot to land the plane by giving them electronic signals along the extended centre-line of the runway and ideal angle of descent. Following these signals is particularly helpful for a pilot to accomplish a safe landing during low- or no-visibility conditions.

With regards to ATC-pilot communication, VHF bands between 108-137 MHz are used. A pilot tunes into the frequency of the ATC unit whose jurisdiction it is traversing to obtain the required instructions and clearances.

The speech signals corresponding to their interaction are converted to electric signals, which are radiated in the form of VHF signals following line-of-sight propagation. However, suppose an aircraft is flying over the Arabian Sea somewhere between Mumbai and the Middle East. At such a long distance, line-of-sight communication isn't possible owing to Earth's curvature and, thus, communication is carried out using the sky-wave propagation technique where the transmitted HF waves are reflected by the ionosphere and received by the intended station.

Mobile Communication And Internet

Whatever content we are partaking on the internet (including this article) is contained in a huge repository of a computer called a server, located at some 'data centre'. While one way of summoning this data to our device is through satellite technology, it is inefficient owing to the huge distance and associated delay and latency.

Therefore, service providers rely on laying down a humongous network of optical fibre cables (traversing deep into the oceans and high across mountains) connecting these data centres across the world.

Every website and internet-enabled device bears a unique address. Typing the name of the intended website (or clicking on the corresponding link) triggers the request signal to the corresponding server and is meted out by the flow of data signals through this huge cable network to the intended Wi-Fi router or to the nearest cell tower (in case of use of cellular data), from where it is received by our device-antenna as an electromagnetic wave.

Glimpse Into The Future: Internet Of Things

At present, we perceive the term "internet" as a source of unlimited information at our disposal. But, soon, it would mean a network of physical objects interacting with each other using pertinent sensors, software, and an ability to process data and exchange information.

A simplest example of such a future is a device like the Amazon Echo Dot, which enables us to operate a light bulb through a simple voice command. The future brags of doing away with electrical switching altogether and an array of such home appliances operating over the internet.

Imagine sitting in a self-driving vehicle taking you to your intended destination via the best-possible route while interacting with the other traffic on the road and making self-adjustments accordingly.

Better still, imagine a scenario where a doctor is operating on a patient located miles away. How? While the doctor is moving his fingers visualising the body parts of the patient as seen on his monitor screen, the robotic arms located at the patient's end are sensing and mimicking the movements of his fingers in real time.

Obviously, such applications require impeccable internet speed with zero tolerance for latency. And, thus, despite the advent of high-speed 5G and 6G technologies, there is a long way to go before they are applicable in a full-fledged manner.

But, remember, even telecommunication was once a fantasy.

This article has been published as part of Swasti 22, the Swarajya Science and Technology Initiative 2022. Read other Swasti 22 submissions.

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