Exploiting the properties of electromagnetism has enabled transmission and communication of energy and information without dependence on physical mediums using conductive materials. This is the reason why the types and modes of wireless transmission and communication are always based on electromagnetic radiation.
For starters, electromagnetism is a phenomenon associated with the interactions between the electric and magnetic fields and the resulting electric charges and currents. On the other hand, electromagnetic radiation is a form of energy produced by oscillating electric and magnetic disturbance. It also corresponds to the waves of an electromagnetic field that propagate and travel through free space while carrying radian energy.
Note that there are different forms of electromagnetic radiation and they collectively form the electromagnetic spectrum. To understand further, the electromagnetic spectrum is divided into seven regions in order of decreasing wavelength and increasing energy and frequency: gamma rays, x radiation or x-ray, ultraviolet light, the visible light, infrared radiation, microwaves, and radio waves. These seven correspond to the form of electromagnetic radiation.
The fact that the forms of electromagnetic radiation travel through space while carrying radiant energy independent of a physical medium makes them appropriate for transmitting and/or communicating power and/or information without wires. Below are the types modes and types of wireless transmission and communication:
1. Radio-based transmission and communication systems
Most modern transmission and communication systems rely on wireless connectivity to mediate problems with distance and other physical limitations. Manipulating the properties of radio waves is at the heart of the most common types of wireless transmission and communication.
Within the electromagnetic spectrum, radio waves have wavelengths that range from 100 kilometer and 1 meter and frequencies ranging from as low as 3 KHz to as high 300 MHz. Some reference materials classify electromagnetic radiations with frequencies ranging from above 300 MHz to 300 GHz as radio waves although they should be specifically classified as microwaves.
Nonetheless, the theory of electromagnetism first proposed in 1865 by James Clerk Maxwell, the first artificial generation of radio waves by Heinrich Hertz in 1887, and the invention of radio transmitters and radio receivers by Gugliemo Marconi during the 1890s to demonstrate the first wireless long distance communication were critical turning points in the history of radio-based transmission and communication systems.
Radio waves are the most common mode of wireless transmission and communication nowadays. The specific types of wireless transmission and communication systems using radio waves include mobile telephony systems that are integrated in the general telecommunication systems and broadcast communication for radio and television. Other types and applications include navigation systems and radar systems that also include other technologies to include satellite communications and microwave transmissions, among others. Short-range communication systems such as wireless local area network and Wi-Fi networks that use at least the 2.5 GHz ultra high frequency band, Bluetooth technology that uses standardized frequencies around 2.4 GHz, and Radio-Frequency Identification or RFID and Near-Field Communication or NFC protocols that use radio waves with a frequency of around 13 MHz.
2. Transmission and communication using microwaves
Microwaves are electromagnetic radiation with wavelengths between 1 meter and 1 millimeter and frequencies ranging from 300 MHz ultra high frequency band to 300 GHz extremely high frequency band. They are situated between radio waves and infrared radiation within the electromagnetic spectrum nonetheless, microwaves rest between.
The discovery of microwaves paralleled with the scientific history of electromagnetic radiation and radio waves. However, their first practical applications in wireless transmission and communication emerged during the 1930s with the first microwave line-of-sight systems and further in late 1940s and early 1950s with large-scale transcontinental microwave transmission systems. Progress emerged further during the 1960s and the 1970s with improvements in line-of-sight microwave communication systems.
Notable applications of microwaves as a mode of wireless transmission and communication supplement existing radio-based systems such as broadcast communication, telecommunications, and navigation systems. This is because they have two key advantages over radio waves. First is that they can pass through the ionosphere unlike radio waves. Second is that their higher frequencies allow them to carry larger information. These properties make them suitable for long-distance and/or satellite-based wireless transmission and communication involving large amount of information.
Specific types of wireless communication using microwaves center on point-to-point communications rather than one-to-many communication. Examples include broadcast relays, the implementation of 3G to LTE standards in telecommunications, and Global Positioning Systems or GPS. Other WLAN and Bluetooth communication applications use higher frequencies within the microwave band although most of these practices are unregulated or reserved for industrial uses.
Wireless energy transfer is another application of microwaves. Falling the under the general far-field or radiative power transfer technology, the specific microwave power transfer or MPT involves using microwaves to transmit energy between earth and the outer space, particularly from orbiting satellites that harvest solar energy to the earth or from the earth to power manned or unmanned spacecraft.
3. Optical wireless transmission and communication
Infrared radiation, the visible light, and ultraviolet radiation are the forms of electromagnetic radiation exploited under optical wireless transmission and communication technologies. Otherwise known as free-space optics, these technologies are direct alternatives to wired optical communication systems such as optical fiber cable systems.
The use of infrared is one of the earliest and most common modes of free-space optics. Home appliances such as televisions with remote controls are notable demonstration of this technology. These remotes are equipped with low-powered infrared transmitters to establish a single-point one-to-one communication with the receivers equipped in the appliances.
Infrared networking is another application in which wireless connectivity that is similar with radio-based wireless local area networking are established with two or more devices equipped with infrared transmitters and receivers. Although this system is very limited than radio-based systems because infrared depends on line-of-sight and cannot pass through walls, they offer more security against listening devices.
Using visible light and ultraviolet radiation as modes of wireless transmission and communication have also been proposed and tested. For example, a networked visible light communication system called Li-Fi has been positioned as a modern alternative to Wi-Fi. Proposed iterations to the Li-Fi technology include the use of infrared and ultraviolet. Once developed, the technology can supplement or replace existing Wi-Fi systems.
It is worth mentioning that free-space optics have been explored and demonstrated since World War I but further development has been stagnant over the decades due to the progresses in radio-based mode of wireless communication and transmission. Prospects are emerging once again because of advantages over radio-based systems such as higher and faster transfer rates and less legal restrictions. Take note that frequency authorization and a special license controlled by government regulatory agencies are required in wireless transmission and communication systems and applications using radio waves and microwaves.
Beyond communication systems, infrared and the visible light have also been proposed to transmit power in free space. The working theory centers on converting infrared or light back to electricity the same way electricity is used to generate these forms of electromagnetic radiation. Because these forms can travel in free space without any medium, they are suitable candidate for novel modes of wireless power transmission.
REFERENCES AND FURTHER READINGS:
- Bertoni, H. L. 1999. Radio propagation: For modern wireless systems. London: Pearson Education
- Bouchet, O., Sizun, H., Boisrobert, C., de Fornel, F., & Favenecc, P. N. 2006. Free-space optics: Propagation and communication. London: ISTE Ltd.
- Massa, A., Oliveri, G., Viani, F., & Rocca, P. 2013. “Array designs for long-distance wireless power transmission: State-of-the-art and innovative solutions.” Proceedings of the IEEE. 101(6): 1464-1481. DOI: 10.1109/JPROC.2013.2245491
- Maxwell, J. C. 1865. “A dynamical theory of the electromagnetic field.” Philosophical Transactions of the Royal Society of London. 155, pp. 459-512. DOI: 10.1098/rstl.1865.0008