  Low efficiency is the main drawback of many MEMS thermal energy harvesters.
Recently, energy harvesting micro-devices that operate using the pyroelectric
effect gained attention due to their potential superior performance. Operation
of these devices is based on the cyclic motion of a pyroelectric capacitor that
operates between a high temperature and a low temperature reservoirs. In this
paper, we investigate the dynamics of oscillations of a pyroelectric capacitor
self sustained by thermally actuated bimetal micro-cantilevers, a topic which
is so far under investigated. In addition to highlighting key thermodynamic
aspects of the operation, we explore conditions for self-sustained oscillations
and discuss the viability of operation at the mechanical resonance frequency.
The analysis is presented for a new design inspired by the device proposed in
Refs.\cite{2011,2012}, where in contrast, our proposed design boasts the
following features: The pyroelectric capacitor remains parallel to the heat
reservoirs, by virtue of its symmetric support by two bimetallic cantilever
beams; In addition, the cyclic operation of the device does not require
physical contact, thus lowering the risk of mechanical failure; To adjust the
damping force imparted by the surrounding gas, the thermal reservoirs are
equipped with trenches. To study the dynamic operation of the device, we
developed a physically based reduced order, yet accurate, model that accounts
for the heat transfer between and within the different components, and for the
various forces including the gas damping force. The model is embedded within an
optimization algorithm to produce optimal designs over the range 26-38 C of
temperature difference between the two reservoirs. The corresponding range of
harvested power density is 0.4-0.65 mW/cm2.
