Biomedical Engineering Reference
In-Depth Information
Figure 8-3.
Williams Sound WIr rX22-4 Ir receiver.
Image courtesy of Williams Sound.
of sight there could be some loss of the
transmitted signal. Finally, recall that
direct sunlight can cause interference
with IR transmissions. Other technolo-
gies not affected by sunlight (e.g., FM
and induction) would be advised over IR
in those applications. Having stated these
limitations, there is anecdotal evidence
that at least the direct-line-of-sight dis-
advantage may not be strictly true. For
example, Steve Boone (personal com-
munication, 2014) cited situations at
conferences that individuals wearing IR
receivers with their backs to the speaker
could hear the speech perfectly well. This
situation occurred because the IR waves,
much like sound waves, reflected off the
walls in that room and were picked up by
the receiver.
There are a number of advantages to
IR systems as assistive technology. First,
two IR systems can be used in adjacent
rooms simultaneously without interfer-
ence from each other because the signal
(i.e., light) cannot travel through walls.
Although the development of multiple
channel assistive listening devices may
make that lack of interference less impor-
tant today than it was in earlier decades,
it is still an important consideration
for commercial uses. Second, IR can be
used in rooms of almost any size because
