Multi turn loops Antenna are often
used as low frequency receiving antennas. Applications such as
geophysical research, oil exploration and survivable
communications require maximum sensitivity of receiving loop
antennas. The loop sensitivity decreases as frequency decreases,
becoming a formidable problem below 1 Hz. Basic electromagnetic
theory is developed here as it relates to electrically small
multi-turn loops at low frequencies. Simple algebraic
expressions are produced describing the sensitivity of loops in
simple geometries. The concept of antenna factor (effective
aperture) is introduced, which allows comparison of different
loops, and conversion of observations to common magnetic units
of measure. It is hoped this work will be a useful reference to
geophysical researchers, and to anyone designing loops for low
frequencies.
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