A simple perimetric loop emits widely around it in all three dimensions, up to a distance of up to three to four times its width. If this is not a problem in most cases, this is not permissible if other loops exist in the neighborhood (interference) or if there is need for confidentiality.
Choosing the amplifier for a single loop
With an equal area, depending on the ratio width / length of the loop, the characteristics of the amplifier may be substantially different. Regardless of this, the larger the loop, the greater the difference in altitude, and the more powerful the amplifier will be in order to compensate for the losses due to the distance.
Given the type of operation of a BIM, the amplifier must for each case be able to provide a proper amperage and voltage. The characteristics of the amplifier must be related to the minimum resistance and the maximum impedance of the loop (so as to remain within the linear range of operation of the amplifier). In case of the boucle d’induction magnétique this is important.
Single perimeter loops cannot be used in the following cases:
- the surfaces to be covered are too large,
- metal losses are no longer negligible,
- there are other loops likely to interfere in the neighborhood,
- there is need for confidentiality.
In these cases, “8” loops, or low or ultra-low overhead pin-nets, usually placed on the ground, may be used.
Loop in “8”
Like single perimetric loops, “8” loops emit largely around them in all three dimensions.
Networks of hairpin loops make it possible to compensate for metal losses and to circumscribe the magnetic field in all three dimensions. It is thus possible to operate juxtaposed and totally independent systems, each network having its distinct amplifier, without interference and to respect confidentiality needs.
We understand that the implementation of a BIM requires a preliminary study of the premises and must be performed by a professional installer. On the other hand it is important that the proper functioning of the BIM is evaluated periodically, (tests, field measurements). Its use is simple yet it is necessary that the technical staff has a user manual understandable!
The interest of the magnetic loop for hearing-impaired people was discovered in 1947 by Samuel Lybarger, engineer at the “Radio Ear Hearing Aid Company” (radio and hearing aid company). Today this simple, inexpensive system is still as efficient.
Why use a magnetic induction loop?
The magnetic induction loop allows you to hear a sound source while avoiding distance (theaters), ambient noise (public places), echo phenomena or sound reverberations (churches, bare walls) , deformations made by headphones (phones, MP3) or speakers (television, radio, cinema).
Can anyone with hearing loss benefit from magnetic induction listening?
To benefit from magnetic induction listening, the hearing impaired person must be paired. The majority of earloops and implants have a magnetic induction listening program, called the “T” position (from the English telecoil).