Sound and Oscillation

# Antenna

In this globalized world, information circulates much faster thanks to a device that captures and emits electromagnetic waves, the antenna.

How are electromagnetic waves produced? They are produced by moving electrical charges, that is, electrical charges are the sources of electromagnetic fields. As sources vary with time, electromagnetic waves propagate away from the sources. So, we can say that there was the emission of electromagnetic waves. This process of emission of electromagnetic waves can be carried out by structures called antennas. Although any structure can emit electromagnetic waves, antennas emit more efficiently.

An antenna radiates its electromagnetic signal in all directions in space

Antennas can be used both to emit and to receive electromagnetic signals. But how does this process take place?

An alternating electric current is produced in the transmitter and this type of current has its intensity varying as a function of time, according to the sine trigonometric function, to this variation we associate a quantity called frequency, which is measured in hertz. The current then oscillates along a conductor and this oscillation will produce an electromagnetic field, that is, it will produce electromagnetic waves. The electromagnetic waves produced are emitted and travel through space in all directions, as space is full of electromagnetic waves coming from different sources, and as they are waves, they have frequency and wavelength. It is exactly these two quantities that will differentiate one from the other.

Each wave has its own frequency, the higher the frequency value, the shorter the wavelength. Therefore, the longer the wavelength, the lower the frequency of the wave. These waves reach a multitude of receiving antennas scattered throughout the cities, but each antenna will only capture waves that are in the programmed frequency band. Upon reaching the receiving antenna, the wave will induce an alternating current that will oscillate with a frequency equal to its frequency. Although this current is much weaker than the current that generated the wave in the transmitting antenna, it can be amplified in the receiving device.

Thus, the two electrical currents, the low frequency and the high frequency, combine, and the high frequency current becomes a kind of transport of the low frequency current – which is the speaker’s voice. This new current then arrives at the station’s transmitting antenna and it emits electromagnetic waves in all directions of space, that is, it propagates information. This information in the form of electromagnetic waves is picked up by the receiving antenna of a radio device.