Transpiration as a mechanism for mechanical and electrical energy conversion

Devices that scavenge power by utilizing energy present in their environment are of interest to researchers for powering sensors in areas where hard-wired connections are not feasible and battery maintenance is costly. Researchers have made of use vibrations, temperature, and other environmental stimuli.;In this thesis, transpiration is researched as a mechanism for mechanical and electrical energy conversion. Two energy scavenging devices inspired by the transpiration mechanism in plants were developed and tested. The first is a class of mechanical actuators that operate via the evaporation of water to generate forces per unit length of 5.75 - 67.75 mN/m, angular rotations of 330° and tip deflections of 3.5 mm. The actuators were also studied as a way to achieve bottom-up self assembly by programming deflection profiles into materials using geometric parameters. These actuators can be used in applications for an evaporation-powered and controlled self-assembly of micro components. The experimental work is coupled with the development of an accurate theoretical model based on the principle of virtual work.;The second type of devices developed in this thesis use an evaporation-induced flow within leaf-like microvasculature networks to drive the movement of gas bubbles through capacitor plates. This motion allows the charge pumping of an energy conversion circuit. Evaporation-driven flow was enhanced by using porous materials at the fluidic channel outlets to achieve a maximum flow velocity of 1.5 cm/s. Changes in capacitance measured at 1 MHz were between 8 - 10 pF and greater than 30 pF at lower frequencies for each bubble. Current generated by capacitance change was measured to reach up to 1 nA. Using the conversion circuit, voltage outputs up to 5 muV were measured for each water to air interface. A theoretical bound of the scavenged power density was calculated as a function of the size of the storage capacitor. Theoretical analysis and simulation results are presented to describe how the circuit can be modified to suit the energy harvesting application.;The primary contribution of this thesis is the demonstration that the transpiration mechanism of plants can be mimicked in microscale devices to provide mechanical and electrical energy.