Electromagnetic waves below the frequency of radio waves refer to the lower frequency range of the electromagnetic spectrum, which includes extremely low frequency (ELF), very low frequency (VLF), and low frequency (LF) waves. These waves have some distinct characteristics and applications that set them apart from higher-frequency radio waves. Here are a few notable features:
Penetration through obstacles: Electromagnetic waves at lower frequencies tend to have better penetration capabilities compared to higher-frequency waves. They can pass through obstacles like buildings, soil, and water more effectively. This property makes them suitable for long-range communication with submarines, underground facilities, and other environments that impede the passage of higher-frequency waves.
Wave propagation: Lower-frequency waves experience less attenuation (weakening) and absorption in the Earth's atmosphere. They can propagate for longer distances without significant loss of signal strength, making them useful for long-range communications.
Natural resonance: The Earth-ionosphere cavity acts as a natural resonator for extremely low frequency (ELF) and very low frequency (VLF) waves. The waves in these frequency bands can circulate within this resonator, resulting in global coverage. ELF and VLF waves can be used for submarine communication, as well as for transmitting time signals and monitoring natural phenomena like lightning activity.
Research applications: Lower-frequency electromagnetic waves are employed in various scientific research fields. For example, ELF waves are utilized for studying the Earth's magnetosphere, investigating the ionosphere, and examining the effects of solar activity on the Earth's environment.
Power transmission: Due to their better penetration capabilities, lower-frequency waves are sometimes used for power transmission. High-voltage power lines, for instance, can use ELF or VLF waves to carry power over long distances.
It's important to note that while lower-frequency electromagnetic waves have unique properties, they also have limitations. They generally have lower data-carrying capacity compared to higher-frequency waves, which makes them less suitable for high-speed data communication. Additionally, the allocation of frequency bands and regulations regarding their usage may vary across different regions and countries.