Radio waves are a type of electromagnetic wave. The wavelength of these waves lies between the electromagnetic spectrum. These waves are emitted by the transmitters and received by antennas, radio receivers. One common question about radio waves that arises is whether radio waves can be polarised or not.
So, In this article, I will answer this question in detail and cover the related topics.
So, Can radio waves be polarized? Yes, radio waves can be polarised because radio waves are a type of electromagnetic wave that consists of electric and magnetic fields traversing perpendicular to each other and also perpendicular to the direction of the motion of wave (up and down or side by side). Therefore, radio waves can be polarised.
The process in which the wave oscillation is made to move in one plane perpendicular to its motion is known as polarisation.
When radio waves are emitted. the electric field denoted by E vector and magnetic field denoted by B vector lie perpendicular to each other. And the direction of motion of radio waves also lies perpendicular to both electric and magnetic fields. Thus, the oscillation of the radio wave is at 90 degrees angle to the motion of the wave.
The prediction of radio waves was done by a British mathematical physicist James Clerk Maxwell. The first practical radio emitter and the receiver were discovered around the year 1894. The frequency of radio waves lies in the region 30 hertz (Hz)-3300 gigahertz (GHz).
Types of polarisation
There are three types of polarisation seen:
Linear polarization: In linear polarization, the electric field oscillates in a linear direction perpendicular to the motion axis of the wave. And the magnetic field also oscillates in a linear direction which is perpendicular to both motion axis and electric field direction.
In linear polarization, the direction of polarisation is taken as the direction of the electric field. This polarisation is also known as horizontal polarization.
Circular polarization: This is the polarization in which the electric field and magnetic field have the same magnitude and the phase difference between both vectors is also multiple of 90 degrees angle.
In circular polarisation, there are two types ie; right circular polarisation and left circular polarisation.
The polarisation is said to be right circular when the superposition vector of the magnetic field and electric field circulates in the clockwise direction. Whereas, when the superposition vector of electric and magnetic field circulates in an anticlockwise direction, the polarization is said to be left circular polarisation.
Elliptical polarisation: This polarisation occurs when the electric field and the magnetic field possess the unequal magnitude and direction. The net superposition seems to circulate in elliptical form.
A wave that has its vibrations in multiple planes is said to be unpolarized. Examples of such waves are the light emitted by the bulb, sunlight coming from the sun. These light waves are created by the electrical charge that vibrates in many directions.
It is possible to covert the unpolarized light into polarized light. Polarized waves have their vibrations only in a single plane. Polarization is a process to convert the unpolarized light into polarized light.
A very common method for polarization is using polaroid filters. It is made up of a material that blocks one of the vibrations of waves leaving only the vibrations occurring in a single plane only. In this way, it filters out half of the vibrations.
On passing unpolarized light through a polaroid, the intensity also reduces to its half value.
How does polarizer work?
A polarizer is prepared in many ways. One of the common polarizers is a polaroid which is made up of polymer containing iodine crystals. The polymer film is stretched that aligns the polymer across polarizer.
It was discovered around the year 1929 by Donald. L brown.
A polarizer lets the light waves of a particular polarization to pass through it and blocks all other polarization light waves. It filters the beam of light of undefined polarization into the beam of well-defined polarization.
Let us understand its working in a better way
Suppose, a linear polarized light beam is incident on a polarizer. Let the angle between the axis of polarizer and polarization of incident light is θ. The electric field passing through the polarizer is the component along the direction of the axis.
Let E and I be the electric field vector and intensity of wave after passing through polarizer and E0 and I0 be the electric field vector and Intensity of the wave before passing through the polarizer.
I =I0 cos 2θ
Properties of radio waves
The radio wave is a classification of electromagnetic waves. If we talk about the speed of radio waves, it can travel with the speed of light as it is an electromagnetic wave.
The wavelength of these waves lies in the electromagnetic spectrum longer than infrared radiation.
The frequency of radio waves lies between the range of 30 hertz (Hz) up to 300 Gigahertz (GHz). The frequency of the radio wave is the number of wavelengths passing through a point in 1 second.
This lowest-frequency portion of radio waves is the lowest frequency among all the waves lying under electromagnetic waves.
The wavelength of radio waves varies between 1 millimeter (mm) to 100 kilometers (Km).
Radio waves are generated by the time-varying electric current like lightening or by means of an astronomical source. Artificial means of producing radio waves are mobiles, satellites, radio towers, etc.
Uses of Radio waves
These radio waves are used to carry signals for commercial radio signals.
Radio waves are further classified in:
AM Radio waves: these radio waves carry commercial radio signals that lie under the frequency range of 540-1600 kHz. The term AM stands for amplitude modulation. These waves carry signals by keeping its frequency constant and varying amplitude.
FM Radio waves: these radio waves also carry commercial radio signals that lie between the frequency range of 88 to 108 MHz. The term FM stands for frequency modulation. These waves keep amplitude constant with varying frequency.
Microwave: the ovens and microwaves used for baking food items also use radio waves; microwaves. These waves use frequency ranging from 300 MHz to 300 GHz.
TV: radio waves are also used for television broadcasting. The TV channels use different ranges of frequency 54 to 88 MHz and 174 to 222 MHz. And some channels that use ultra-high frequency of ranging 470-1000MHz.
Application of Polarization
- It is used for distinguishing the transverse and longitudinal waves.
- They are also majorly used for 3D movies and 3D glasses.
- It has great use in checking the chirality of organic compounds.
- It is also used for sunglasses to filter unwanted light.
Related post: Can sound waves be polarized?