Electromagnetic Induction Loop
Uses electromagnetic fields of energy
Transmitter-Loop of several wires
Receiver
- T-coil in hearing aid
- desktop receiver
Telephone and other speakers
As small as a neck loop or as large as an auditorium
Notes:
Although electromagnetic induction may be the most difficult to explain, it is one of the easiest systems to use. The induction loop is actually a loop of wires that surround a listening area. The user sits within the loop and switches his or her hearing aid to T. That is all there is to it. (However, if the user does not have a hearing aid with a T-coil, they will need a separate receiver and a coupling device, such as headphones.)
How does it work? The alternating current of an audio signal passing through wire creates an electromagnetic field that radiates away from the wire. When two wires are close, the electromagnetic field of one will induce a current in the other wire (this is where induction comes from). The room loop is one wire, but where is the other wire? The T-coil in a hearing aid is actually a small electromagnetic induction coil.
My analogies fail me here, although there are many every-day objects in our environments that create electromagnetic fields (e.g., telephones, speakers, computer monitors). Are you familiar with the news reports about EMF and power lines? The EMF stands for electromagnetic fields. High voltage power lines give off strong EMF. The farther away you are from the power lines, the weaker the EMF. The news reports were studies of the health impact on persons who were exposed to very high-level EMF over long periods of time, such as people whose houses are built underneath these power lines.
While the electromagnetic induction loop is no where near as strong as that of power lines (and so there is no danger), it may help you remember some of the characteristics of induction loops. First of all, distance makes a difference. The closer you are to the loop of wires (or power line), the stronger the signal (the EMF). In the case of hearing aid use, closer is better. Second, just as EMF travels through walls of houses, so will the signal from induction loop systems.
The symbol shown above is an international symbol indicating ALDs are available. It is also used to indicate an area that is looped.