Analysis of a Small Loop Antenna With Inductive Coupling to Nearby Loops

This paper analyzes the inductive coupling that occurs when a loop antenna is near other conductive objects that form complete loops and are excited by incident low-frequency magnetic fields. The currents developed on the closed loops from the time changing magnetic fields generate their own magnetic fields that alter the voltage received by nearby open loop antennas. We will demonstrate how inductance theory can be used to model the system of loops. Using this theory, time domain circuit models are developed to find the open circuit voltage of a loop near one closed loop and for the open circuit voltage of one loop near two closed loops. We will show that the model is in good agreement with measurements that have been made in a TEM cell. One important application of this work is for electroexplosive device safety. It is necessary to ensure that if lightning strikes a facility that the electromagnetic fields generated inside do not have strong enough coupling to a detonator cable to cause initiation of explosives. We will show how the model can be used to analyze magnetic field coupling into a detonator cable attached to explosives in one typical type of work stand.