Biomedical Engineering Reference
In-Depth Information
devices tend to be relatively power hungry, a trade-off between
battery capacity and size has governed the lifespan, dimensions, and capa-
bilities for battery-powered devices. New technologies such as energy
harvesting have the capability to effectively power electronic instruments.
Harnessing energy from sources such as motion, sunlight, and tempera-
ture changes has been employed respectively on electronic self-winding
wristwatches, solar-powered calculators, and thermal-powered wrist-
watches. Therefore, energy harvesting is an alternative to batteries for
energizing electronic devices.
Energy harvesting was the main technology used before the advent
of the internal combustion engine, the power grid, or batteries. For
instance, wind turbine farms and hydroelectric plants are the successors
of windmills and water wheels. Small electrical generators were also
used in radios and flashlights operated by hand cranking in the 1940s.
Other recent examples include the bicycle dynamo (capable of producing
up to 3 W of power) and lever-driven mobile phone chargers (up to 2 W
of power) (Flipsen, 2006; van Donk, 2000). Industrial applications for
recent vibration energy harvesters have been developed to power auton-
omous wireless sensor nodes (Ferro Solutions, Inc.
1
, Perpetuum Ltd.
2
).
Energy scavenging of water flow in oceans and rivers are exploited as
well (Taylor et al., 2001) (similar to an eel swimming, one device uses
the traveling vortices in water to strain piezoelectric polymers). One of
the most well-known examples of energy harvesting from body motion
is the self-winding wristwatch mechanism that evolved from being
entirely mechanical (wind-up) to use a hybrid approach (using a minia-
ture electromagnetic generator to charge a battery).
Wearable microinstruments for environmental monitoring of
humidity, temperature, pressure, and acceleration with data processing
capabilities have been successfully implemented as watch-sized devices
(Mason et al., 1998; Najafi, 2000; Yazdi et al., 2000). Such systems are
commonly powered by batteries, and sometimes the battery is larger
than the entire system. This is normally the case for devices that need
to be functional for long periods of time. For example, batteries for
cardiac pacemakers occupy half the device
'
s volume (Mallela et al.,
2004), while their average lifetime is between 5 and 12 years (Katz and
Akiyama, 2007). Implantable biomedical devices,
such as neural
