A supply of electrical power is naturally a critical
requirement for wireless sensor nodes, and because
batteries have limited energy capacity, these frequently dominate the size and weight of such
nodes. They also impose a maintenance burden of
recharging or replacement if a long sensor lifetime
is required. For this reason, devices that extract
energy from their surroundings in some way (so
calledenergy harvestingorenergy scavengingdevices)
have attracted attention from many researchers [1,2].
Ambient light, and temperature differences, are
useful potential power sources in some applications,
but there will be many instances where neither is sufficiently available. Mechanical motion is another
energy source that has attracted considerable
interest. Such motion sources generally fall into two