Page 503 - Handbook of Biomechatronics

Bioinspired and Biomimetic Micro-Robotics for Therapeutic Applications 497

can find detailed information in the given reference, but, it is noted that this
approach is inherently stochastic rather than depending on formulae perti-
nent to pure Newtonian mechanics, and dimensions can be much smaller
than the limit of continuity assumption.
One of the sought after power supply techniques in MEMS is “energy
scavenging” from the environment which usually contains stray mechanical,
EM or electrostatic, and thermal energy in abundance (Cook-Chennault
et al., 2008; Khaligh et al., 2010; Nielsen et al., 2003). Mechanical energy
scavenging depends on sensing and capitalizing on mechanical vibrations via
piezoelectric materials. Piezoelectric cantilevers of different lengths, thus
with different natural frequencies, could be used in an array to detect a fre-
quency band. However, the downside is that a power-regulation circuit is
required to achieve continuous supply with the conditioned current. EM
and electrostatic energy scavenging depends on a similar approach: The
oscillation in the field could be used to generate current on coils by induc-
tance or creating an alternating potential difference on capacitor plates
owing to electrostatic forces. On top of these, the field vibrations could
be detected by capacitor plates or magnetic particles attached to piezoelectric
cantilever beams hanging freely thus generating electrical energy by piezo-
electric effect invoked by the resultant structural vibrations. It is obvious that
piezo materials can be used for both actuation, for example, consuming
energy to generate wave propagation (Ko ´sa et al., 2007) as presented in
Fig. 13, and for transforming stray energy to electrical power to sustain that
wave propagation.
Another scavenging method proposed to power MEMS devices is heat
scavenging. This method is based on “thermo-photovoltaic” effect, which is
very similar to field emission electron gun technology. Heat energy can be
used to create photon emissions from a silicon-based source, and those
photons could be collected by a photovoltaic cell on the collector side
(Nielsen et al., 2003) which in turn may be used to harvest heat energy in
the organism as the primary or an auxiliary means of the power generation.

Fig. 13 COMSOL Multiphysics FEM simulation of piezoelectric-effect and linear struc-
tural deformation. Each shear-mode PZT laminate is driven by a in-phase electric field
thus the convoluted local deformation results in planar wave propagation in a certain
direction.