Biomedical Engineering Reference
In-Depth Information
photodiode
array
rechargeable
battery
Fig. 1.25.
A near-infrared power supply having a rechargeable battery charged by
a photodiode array
not interfere with surrounding instruments; nor is the transmitter disturbed
by the surroundings.
The principle of near-infrared transcutaneous transmission is simple, as
shown in Fig. 1.20b. For a better signal-to-noise ratio, the light for transmis-
sion is usually modulated in the following way. First, the transmission light is
intensity-modulated in order to produce a carrier wave. Light from LEDs and
LDs can be easily intensity-modulated by changing the current injected to
them. The carrier wave is then frequency- or phase-modulated according to
a baseband signal. Also, pulse modulation such as pulse interval modulation
is made possible by using a pulse wave as a carrier.
Recently, an implantable transmitter driven by near-infrared laser irra-
diation has been proposed. Figure 1.26 shows a schematic diagram of a near-
infrared telemetry system using such a transmitter. The power necessary
for operating the transmitter is sent to the body from outside it, by near-
infrared light transcutaneous power transmission, as shown in Fig. 1.20a.
In addition, a carrier wave is injected by illuminating the transmitter with
intensity-modulated light. A PD in the transmitter receives the intensity-
modulated light and converts it into an electrical carrier signal. The carrier
signal is then phase-modulated by a modulator inside the transmitter. The
