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Chapter 2 Background: Energy, Sensing, and Wireless Communication
(a) Device
(b) Performance
Figure 2.14: Bosch Hydropower generator used with the MPWiNodeX (reproduced
from [45]).
(a)
(b)
(c)
Figure 2.15: Wind-powered generators used by wireless sensor nodes: (a) is a prototype vertical unit used by Morais et al. and (b) is its performance at a range of
wind speeds (reproduced from [45]) (c) is an off-the-shelf turbine used by Park et al.
(reproduced from [46]).
2.3.6
Human power
Human power may be categorised as being either active or passive. An actively powered device requires the user to do a form of work that would not otherwise be done,
specifically in order to power the device. Conversely, a passively powered device harvests energy from the user’s normal bodily motion and properties, not requiring any
additional work. Among the earliest human-powered wearable devices have been wristwatches; for example, the Seiko Kinetic range harvests power from arm movement, while
Seiko’s Thermic technology can power the wristwatch from the temperature difference
between the skin and the surrounding air, by means of the thermoelectric technology
discussed in Section 2.3.4. The ability to harness thermal energy at any point on the
body adds an element of flexibility, in that a device need not be located at a point of
maximum movement. There are drawbacks, however, in that the skin may naturally
act to restrict blood flow to areas in contact with cold objects which obviously causes
the skin temperature, and hence the magnitude of the heat gradient, to decrease and