Wireless Signals and Electromagnetic (EM) Waves
- [Saitama Prefecture, Japan - Civil Engineering Discoveries]
- Electromagnetic Waves
Electricity can be static, like what holds a balloon to the wall or makes your hair stand on end. Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves - electromagnetic waves.
Electromagnetic waves are formed when an electric field couples with a magnetic field. Magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave. James Clerk Maxwell and Heinrich Hertz are two scientists who studied how electromagnetic waves are formed and how fast they travel.
- Wave Characteristics: Frequency, Wavelength, Amplitude and Wave Speed
Waves cause a disturbance of the medium through which they travel, which allows them to carry energy. The quantity of energy carried relates to the amplitude of the wave.
The amplitude of a wave is the distance from the centre line (or the still position) to the top of a crest or to the bottom of a trough (i.e., the distance between the top and the bottom of a wave). Amplitude is measured in metres. The greater the amplitude of a wave then the more energy it is carrying. The frequency of a wave is the number of waves passing a point in a certain time. We normally use a time of one second, so this gives frequency the unit hertz, since one hertz is equal to one wave per second.
Wave speed is measured in metres per second. All the electromagnetic waves travel at 300,000,000 metres per second. Sound travels at about 340 metres per second.
- Radio Waves and Electromagnetic Spectrum
Radio waves are measured by wavelength or frequency, with wavelength being the distance between two identical points in a waveform signal, and frequency referring to the number of waves that passes a given point per second. The sweet spot for most modern data communication is between 300 megahertz (MHz) and 6 gigahertz (GHz) frequency.
Most IoT systems link networks of sensors via radio waves, which transmit data from one place to another. Radio waves, which are primarily used in communication technologies, are a type of electromagnetic radiation (a form of energy); they make up a small part of what is called the electromagnetic (EM) spectrum, which is divided up into sections called frequency bands.
The EM spectrum is a limited resource - there are only so many radio frequencies in existence. But too much activity on particular radio frequency bands would create interference to the point where nothing would be discernible. Like other countries, the U.S. has tasked a government organization, the Federal Communications Commission (FCC), to allocate the spectrum so it’s used effectively.
- Wireless Transmission and Radio Waves
All wireless transmission is accomplished through waves. In the case of Wi-Fi, the waves are produced on the electromagnetic spectrum. The electromagnetic spectrum consists of many different types of waves that make up the spectrum. The smallest type of waves is the gamma-ray, followed by X-rays. Further down the spectrum is the visible spectrum of light. Further, still are micro-waves. Finally, the largest waves found at the other end of the spectrum are radio waves. Radio waves are the waves upon which data are transmitted.
All types of waves can be measured by their amplitude and frequency. The amplitude of a wave measures how tall a wave is from its midpoint to its top or bottom. The frequency of a wave measures how fast a wave is traveling. This also translates into how compressed the wave is or how many crests and troughs can be found per unit of distance. Radio waves can be naturally generated through electric pulses. Both the amplitude and the frequency of a wave can be modulated.
The transmission of data wirelessly is made possible by the manipulation of radio waves. These waves are generated naturally by generating pulses of electricity. These radio waves can then be modified by their amplitude or frequency in order to transmit sound or data. This process can also be improved in order to increase the amount of data transmitted as well as the speed by which the data can be transmitted.
- Wireless Signals and Electromagnetic (EM) Waves
Wireless signals are important because they can transfer information - audio, video, our voices, data - without the use of wires, and that makes them very useful. Wireless signals are electromagnetic (EM) waves travelling through the air.
Electromagnetic (EM) radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays and gamma rays. Sunlight is also a form of EM energy, but visible light is only a small portion of the EM spectrum, which contains a broad range of electromagnetic wavelengths.
Signal processing is a subfield of mathematics, information and electrical engineering that concerns the analysis, synthesis, and modification of signals, which are broadly defined as functions conveying "information about the behavior or attributes of some phenomenon", such as sound, images, and biological measurements. For example, signal processing techniques are used to improve signal transmission fidelity, storage efficiency, and subjective quality, and to emphasize or detect components of interest in a measured signal.
- Electromagnetic Spectrum
Electromagnetic energy travels in waves and spans a broad spectrum from very long radio waves to very short gamma rays. The human eye can only detect only a small portion of this spectrum called visible light. A radio detects a different portion of the spectrum, and an x-ray machine uses yet another portion. All together, electromagnetic waves make up what is called the electromagnetic spectrum. Radio waves are used for wireless transmission of sound messages, or for passing information.
Electromagnetic radiation travels in waves that "vibrate" at different frequencies. Radio waves are in the range of about 10 kHz (or ten thousand waves per second) to 100 GHz (which is one hundred million vibrations per second). Electromagnetic radiation is used for communications and transmission of information. The waves that are used in this way are radio waves, microwaves, infrared radiation and light. Radio waves - are used to transmit television and radio programs. Microwaves - are used to transmit satellite television and for mobile phones. Infrared - is used to transmit information from remote controls.
- Wave Communication
Today we use codes to send signals using electromagnetic radiation. There are two types of signal, analogue and digital. An analogue signal changes in frequency and amplitude all the time in a way that matches the changes in the voice or music being transmitted. A digital signal has just two values – which we can represent as 0 and 1. An analogue signal varies in frequency and amplitude. A digital signal has two values, 0 and 1 (or ‘on’ and ‘off’).
The signal (voice, music or data) is converted into a code using only the values 0 and 1. The signal becomes a stream of 0 and 1 values. These pulses are added to the electromagnetic wave and transmitted. The signal is received and then decoded to recover the original signal. Both analogue and digital signals can pick up unwanted signals that distort the original signal. These unwanted signals are called noise. Digital signals can be cleaned up in a process known as regeneration because each pulse must be a 0 or a 1, so other values can be removed. Analogue signals can be amplified, but the noise is amplified too. This is why digital signals give a better-quality reception.
Digital signals give a better-quality reception because noise on digital signals is more easily removed.
- Demand For Spectrum Is Exploding
Spectrum = electromagnetic energy. It is all around us. Radio spectrum is broken up into what we call frequency “bands” (distinct parts of spectrum based on how often their energy waves oscillate) to transmit and receive signals. A familiar example may be FM radio. That band, as the numbers on the dial will indicate, goes from 88 megahertz to 108 megahertz - a slice of this large range of spectrum is available for transmitting information.
How Does the FCC License Spectrum Use? To prevent chaos over the air. Spectrum is mostly licensed by both frequency bands and by geographic area. Generally, commercial licenses are awarded via competitive auction. Spectrum is a way to transmit and receive radio signals (like in your car). Some signals power mobile telephones and broadband. The FCC awards exclusive licenses to entities for much of the spectrum associated with the provision of radio, basic mobile phone, and advanced wireless services. Generally, in order to get mobile phone coverage, an entity that holds an exclusive license with the FCC for spectrum must be deploying service. Because the demand for spectrum has grown so quickly, particularly for mobile telecommunications, the FCC is reallocating spectrum historically available for broadcast TV stations to wireless telecommunications providers.
[More to come ...]
