Electromagnetic Waves

Electromagnetic wave: definition

An electromagnetic wave is a propagating disturbance of electric and magnetic fields. It carries energy and can carry information between points without a physical medium. Sunlight warming your face, the Wi-Fi signal connecting your laptop, and the radio broadcast heard in a car are examples of electromagnetic waves. These waves form the basis of wireless communication.

Core properties: wavelength and frequency

The basic quantities used to describe an electromagnetic wave include wavelength, frequency, and propagation speed. Wavelength and frequency are related to the wave speed:

• Wavelength ($λ$): This is the distance between two consecutive points on a wave that have the same phase, such as neighboring peaks. It is typically measured in meters, centimeters, or nanometers.
• Frequency ($f$): This is the number of full wave cycles passing a given point in one second. It is measured in Hertz (Hz).
• Wave speed ($v$): This is the propagation speed of the wave. It equals wavelength ($λ$) multiplied by frequency ($f$): $v = \lambda \cdot f$. In a vacuum, the speed of an electromagnetic wave equals the speed of light ($c$).

The electromagnetic spectrum

The electromagnetic spectrum is the continuous range of electromagnetic waves organized by frequency. Visible light occupies a small part of this range. The bands below are ordered from lowest to highest frequency:

• ELF and SLF fields and waves: The extremely low-frequency (ELF) band spans 3 to 30 Hz. Power-line fields at 50/60 Hz belong to the super-low-frequency (SLF) band.
• Radio waves: A broad range used for AM/FM radio, television broadcasts, Wi-Fi, Bluetooth, and various two-way radio systems. Many wireless communication systems use this range.
• Microwaves: Higher frequency radio waves used for satellite communication, mobile phones (cellular networks), radar, and microwave ovens.
• Infrared (IR): Used in remote controls, thermal imaging cameras, and night vision. Fiber-optic communication uses near-infrared wavelengths.
• Visible light: The small range of frequencies our eyes can detect, from red to violet. This is also used in fiber optics and emerging technologies like Li-Fi.
• Ultraviolet (UV): Higher energy than visible light, it can cause sunburn and is used for sterilization.
• X-rays: High-energy waves used in medical imaging to see through soft tissues.
• Gamma rays: The highest energy and frequency waves, originating from nuclear reactions and cosmic events.

Frequency ranges used in telecommunications

Telecommunication systems primarily operate within the radio, microwave, infrared, and visible-light bands. Frequency selection is an engineering decision because it affects the main properties of the communication system:

• Antenna size: The typical electrical dimension of an antenna is related to wavelength. A higher frequency means a shorter wavelength and can allow a smaller, practical antenna.
• Range and penetration: In many conditions, lower frequencies travel farther and penetrate obstacles such as walls more easily (e.g., AM radio). Higher frequencies can have a shorter range and be blocked more easily (e.g., 5 GHz Wi-Fi).
• Bandwidth availability: Higher frequency bands can provide wider channels. Available bandwidth depends on spectrum allocation, regulation, and system design, while a wider channel can increase the data transmission rate.