Inductive loop communication system for classroom for deaf pupils - has small coplanar loop to cancel magnetic field of main loop

摘要

The inductive communications system, for classrooms used in teaching the hard-of-hearing, has a horizontal induction loop to transmit signals to receivers lying in the plane of the loop inside the classroom. A compensation loop reduces the strength of the main loop magnetic field outside the classroom. The comparatively small compensating loop (14) is located in the plane of the main loop (15) between it and the wall (12) delineating the area needing magnetic screening. The current in the compensating loop flows in the opposite direction to that in the main loop and the turns/current product of both loops is roughly the same.