Biomedical Engineering Reference
In-Depth Information
Researchers have also investigated commercial wristwatch genera-
tors to determine if it is possible to use them for implantable biomedical
applications. For example, Goto et al. (1998, 1999) exploited the
Seiko
'
s generator for powering a circuit to pace the heart of a dog.
The generator, when placed for a 30 min period on the right ventricu-
lar wall of a dog
s heart beating at 200 bpm, was able to store 80 mJ
of energy in a capacitor. Another test using a charged capacitor was
capable of pacing a dog
'
s heart at 140 bpm for 60 min consuming
420 mJ. The actual energy requirement of 210 mJ for 30 min was high-
er than the energy produced in the same amount of time, 80 mJ. The
13
'
J of energy produced was compared against a cardiac pacemaker
requiring only 5
μ
load). This showed the
feasibility of generating the power needed for the stimulation. No
long-term studies were presented considering the possible effects of the
generator on the heart wall. Later work from Gorge et al. (2001) tried
to determine how much power could be generated using the Seiko
'
s
generator taped to the chest of individuals working in an office envi-
ronment. It was concluded that, over a period of 8 h, the power gener-
ated varied from 0.2 to 2.1
μ
J (2.5 V, 0.4 ms, and 500
Ω
μ
W, with a mean value of 0.5
μ
W. This
power level was considered to be 10
100 times less than required for
charging a cardiac pacemaker battery.
Further studies employing the Seiko generator have also been
undertaken. The analysis performed by Sasaki et al. (2005) found that
if the right conditions are given to keep the rotations, this generator
can produce up to 10 times more energy than from swinging motion
alone. A swinging motion at 1 Hz was found to produce 15
μ
W, while
self-excited rotations were able to produce up to 170
W at 2 Hz. The
conditions to maintain these rotations were described as
μ
jθj
t
5
0
.
ω
(3.1)
2c
Amaω
,
1
(3.2)
where
is the angular speed,
c
is the electro-
magnetic damping,
A
is the amplitude of the external oscillation,
m
is
the pendulum mass, and
a
is the distance between the center of gravity
and the axis of rotation. Another promising linear generator was also
presented by this group. It was composed of a permanent magnet mass
suspended by springs and surrounded by a 400-turn coil. Although the
linear generator had an overall volume of 500 cm
3
, it was reported
θ
is the rotation angle,
ω
