Definition

Noun: - Extremely Low Frequency (ELF): A band of radio frequencies from 3 Hz to 3,000 Hz (3 kHz), situated below the very low frequency (VLF) band. It is used primarily for submarine communications and studying the Earth's ionosphere and magnetosphere.

Usage

• As a technical term: The term is used as a singular noun phrase to describe a specific range of the electromagnetic spectrum.
  • Submarines use extremely low frequency for one-way communication due to its ability to penetrate seawater.
  • Research into natural atmospheric phenomena often involves monitoring extremely low frequency signals.

Advanced Usage

• "ELF waves": A common compound where "ELF" acts as an adjective modifying "waves," referring to electromagnetic waves within this frequency range.
  • The propagation characteristics of ELF waves are unique.

Variants and Related Words

• ELF: The standard acronym for "extremely low frequency."
  • The ELF band is crucial for certain military applications.
• Extremely Low Frequency (ELF) radiation: A compound term specifying the type of energy emission.
  • The study focused on the sources of natural ELF radiation.

Synonyms

• ELF band: A near-synonymous term emphasizing the range of frequencies.
• Sub-3 kHz frequencies: A descriptive synonym referencing the upper limit of the band.

Related Phrases

• ELF communication: A compound phrase describing the application of these frequencies.
  • ELF communication systems are complex and require large antennas.

Noun

1. below 3 kilohertz