Biomedical Engineering Reference
In-Depth Information
serial ID at 310 MHz every 3
6 steps up to a 20 m distance. Later
work described a power output of 1.3 mW for the PVDF stack and
8.4 mW for two back-to-back unimorphs (Shenck and Paradiso, 2001).
Similar work from this group used push buttons with piezoelectric
materials. These push buttons (commercial piezoelectric strikers con-
nected to amorphous-core transformers) produced 0.5 mJ of energy at
3 V for transmitting 12-bit ID code over 30 m several times (Paradiso
and Feldmeier, 2001).
Heartbeats have been ideated as well for devising generators using
piezoelectric materials. A patent granted in 1969 to Wen H. Ko
described one of the first attempts to harness heart motion for electric
generation. This generator described by Professor Ko was a piezoelec-
tric rectangular-shaped cantilever beam with an added weight at its
free end. The structure when vibrating at a suitable frequency pro-
duced a signal rectified by a voltage doubler. This design was intended
to power an electrical implant such as a cardiac pacemaker. This pie-
zoelectric device was tested on a dog
'
s heart beating at 80 bpm produc-
ing a 4 V output voltage on a 105
W of power.
Edward A. Schroeppel
'
s patent (1987) described a different approach
when trying to harness the heart motion to power a cardiac pacemaker
circuit. This patent described a piezoelectric strip inside a catheter for
human heart insertion. When the heart is beating, it bends the catheter
which stresses the piezoelectric strip generating an output signal.
Ω
load for 160
μ
The first commercial oscillating rotational generators originated
from wristwatch companies. The Japanese company Seiko presented
the Automatic Generating System (AGS) in 1986. This self-winding
mechanism was used on wristwatches under the Kinetic brand name.
The design consisted of a rotating pendulum mass, a gear box train
(ratio 1:100), and a small permanent magnet generator. Due to wrist
position changes, one oscillation from the pendulum mass produced
100 rotations on the generator. According to Paradiso and Starner
(2005), 5
W of power was estimated to be produced when worn
and 1 mW could be obtained when forcibly shaken. Swiss company
ETA later introduced the Autoquartz with a different approach. The
pendulum mass wound a spring connected to a small generator using a
gear box train. Once the spring was fully wound, it unwound making
the generator rotate at 5
10
μ
15 krpm for a short time (50 ms), generating
more than 15 V and 6 mA (90 mW) (Paradiso and Starner, 2005).
