EM Waves: The Beginning of Wireless Communication PDF

THE BEGINNING OF WIRELESS COMMUNICATION Heinrich Hertz, a German physicist, applied Maxwell's theories to the production and. reception of radio waves. The unit of frequency of a radio wave -- one cycle per second -- is named the hertz, in honor of Heinrich Hertz. Hertz proved the existe...

THE BEGINNING OF WIRELESS COMMUNICATION Heinrich Hertz, a German physicist, applied Maxwell's theories to the production and. reception of radio waves. The unit of frequency of a radio wave -- one cycle per second -- is named the hertz, in honor of Heinrich Hertz. Hertz proved the existence of radio waves in the late 1880s. He used two rods to serve as a receiver and a spark gap as the receiving antennae. Where the waves were picked up, a spark would jump. Hertz showed in his experiments that these signals possessed all of the properties of electromagnetic waves. With this oscillator, Hertz solved two problems. First, timing Maxwell's waves. He had demonstrated, in the concrete, what Maxwell had only theorized - that the velocity of radio waves was equal to the velocity of light! (This proved that radio waves were a form of light!) Second, Hertz found out how to make the electric and magnetic fields detach themselves from wires and go free as Maxwell's waves. His setup consisted of two circuits. The first circuit(1) had a gap. He connected it to a high voltage source. When the voltage had built up in the gap, sparks jumped back and forth. The second circuit (2) consisted of a simple conductor bent into a circle with a small gap between its ends. Hertz observed that whenever sparks produced at circuit 1, sparks were also observed at circuit 2, even when the circuit 2 was about 2 m away from circuit 1. Somehow, energy from the first spark was being propagated through air and received by the second circuit. The energy was carried by what are called ELECTROMAGNETIC WAVE.  ELECTROMAGNETIC WAVE  About 150 years ago, James Clerk Maxwell, an English scientist, developed a scientific theory to explain electromagnetic waves. He noticed that electrical fields and magnetic fields can couple together to form electromagnetic waves. Neither an electrical field (like the static which forms when you rub your feet on a carpet), nor a magnetic field (like the one that holds a magnet onto your refrigerator) will go anywhere by themselves. But, Maxwell discovered that a CHANGING magnetic field will induce a CHANGING electric field and vice-versa. Maxwell hypothesized that electromagnetic induction also happens in space even when there is no actual conductor present. He based his hypothesis on the findings of: A.OERSTED – current-carrying wires produce a magnetic field B. Faraday – changing magnetic field induces current in a conductor. Imagine a loop in space. As a bar magnet approaches the loop, the magnetic field B inside the loop changes. The changing B is accompanied by the production of an induced electric field E along the loop. Maxwell suggested that the symmetrical effect also occurs. When an oscillating charge is inside the loop, E changes inside and produce B alongside it. With this observation, Maxwell showed that E and B can propagate together in space. Therefore, A. a changing electric field E induces a magnetic field B B. A changing B induces E C. A changing E induces a changing B and a changing B induces a changing E and so on. The changing electric and magnetic fields that propagate in space what Maxwell called EM waves. Changing electric and magnetic fields themselves constitute these waves. Maxwell imagined the magnetic field to be at right angles to the electric field as they moved out in space.  ELECTROMAGNETIC WAVES Accelerating electrons produce electromagnetic waves. These waves are a combination of electric and magnetic fields. A changing magnetic field produces an electric field and a changing electric field produces a magnetic field.  Differences between EM wave and Mechanical Wave *Mechanical Wave Characteristics It requires a medium (matter) to travel. How they move: Longitudinal wave Compressional wave Transverse wave Example: Sound waves, Seismic waves, water waves, ropes and springs Electromagnetic waves Characteristics: Can travel through the vacuum of empty space. How they move: Transverse wave Example: Light RADIATION is the term used to describe the transfer of energy in the form of EM wave. For mechanical wave to travel, it must need a medium as it moves. This makes use some of the waves’ energy. In the end, it makes them transfer all energy to the medium. As for EM waves, they can travel through empty space or vacuum so they do not give up their energy. This enables EM waves to cross great distances such as that from the sun to the Earth without losing much energy. In vacuum, EM waves travel at a constant speed of 3x108 m/s. The wave speed, frequency, and wavelength are related to the equation: Speed = wavelength x frequency Example: What is the frequency of radio waves with wavelength of 20 m? f=speed/wavelength  = 3x108 m/s/ 20 m  = 1.5 x 107 Hz  ELECTROMAGNETIC SPECTRUM Is a continuum of electromagnetic waves arranged according to frequency and wavelength. It is a gradual progression from the waves of highest frequencies. The different types of EM waves are defined by the amount of energy carried/possessed by photons. Photons are bundles of wave energy. The energy of a photon is given by the equation: E = hf h= Planck’s constant (6.63 x 10-34 Joules per second)