Biomedical Engineering Reference
In-Depth Information
CHAPTER
2
Power Sources
2.1 ACTUAL POWER SOURCES
As most devices are being powered by batteries,
Table 2.1
presents the
energy content of several sources to keep them in perspective. It is
interesting to see the energy content of 1 L of gasoline is comparable
in order of magnitude as the average daily calorie intake. Combustion
engines are without doubt the kings because they provide energy at
several orders of magnitude over batteries. Although actual technology
has evolved at a fast pace, battery technology is still lagging behind,
but nanotechnology promises new developments.
Zinc/mercuric oxide batteries were the first type of battery used for
the first cardiac pacemaker implanted in 1960, but they lasted between
2 and 3 years (zinc/mercuric oxide or mercury cells are no longer man-
ufactured because of the mercury content). However, it wasn
'
t until
the use of lithium batteries in the 1970s that equipment with longevity
over 10 years was a possibility (Holmes, 2001). After successful imple-
mentation of the pacemaker, similar techniques were employed to treat
other conditions. Implanted defibrillators and neurostimulators took
advantage of this. While pacemakers are low current drain devices, neuro-
stimulators operate with medium rate currents (1
5 mA) and defibrilla-
tors with high pulse power (Drews et al., 2001). Implantable biomedical
devices are powered by batteries or by inductive links. Inductive link is
radio frequency using coupling coils where an implanted coil receives
power and communication when coupled with an external coil. As
Table 2.1 Summary of Energy Sources
Source
Energy (J)
10
3
Button cell battery
B
B
10
4
AA battery, cellphone battery
B
10
5
Laptop battery
10
6
Lead acid battery
B
B
10
7
Liter of gasoline
10
7
Average human diet (per day)
B
