Date of Award

Fall 11-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Dr. Adarsh Radadia

Abstract

The primary aim of this study is to contribute to the field of additives that would enable the fabrication of electrical sensors and actuators completely via Material Extrusion based Additive Manufacturing (MEAM). The second aim of the study is to provide the necessary characterization to facilitate the development of applications that predicts electrical part performance. The electrical characterization of two conductive poly-lactic acid (PLA) filaments, namely, c-PLA with carbon black and graphene PLA was performed to study the temperature coefficient of the resistance. Resistivity of carbon black filament was compared to a printed single layer and with that of a cube. The raw and printed c-PLA showed a positive temperature coefficient of resistance (α) ranging from ~0.03-0.01 ℃-1 while its counterpart in the study, graphene PLA, did not exhibit significant (α). Parts from graphene PLA with multilayer MEAM exhibited a negative α to a certain temperature before exhibiting positive α. The resistivity of the printed parts was 300 times higher for c-PLA and 1500 times for graphene PLA. However, no microstructural or chemical compositional changes were observed between the raw filaments and the printed parts. Due to the high α of the c-PLA, it was deemed as the better material for constructing electro thermal sensors and actuators using MEAM.

First, c-PLA was used to fabricate and package a completely 3D printed flow meter that operates on the principle of Joule heating and hotwire anemometry. When the designed flowmeter was simulated using a finite element package, a flow sensitivity of -2.33 Ω sccm-1 and a relative change in resistivity of 0.036 sccm-1 was expected. For an operating voltage of 12-15 V, the experimental results showed a flow sensitivity within the range of 0.014-0.032 sccm-1 and the relative change in resistivity ranged from 0.039 – 0.065 sccm-1. Thus, a completely 3D printed flowmeter was demonstrated. Second, using the same principle of Joule heating, an actuator inspired from MEMS chevron grippers was designed, simulated, and fabricated. Simulation showed the feasibility of the structure and further predicted a displacement of a few hundred microns with a potential as low as 3 V with a cooling time as little less than 120 seconds. Experimentally, a displacement of 120.04, 97.05, and 88.96 μm were achieved in 15, 10, and 5 seconds with actuation potentials of 12.7, 13.8, and 17.9 V, respectively. As predicted by the simulation results, it took longer for the gripper to cool (close to 180 seconds) when compared to actuation times.

During the above studies, we discovered the printing parameters altered the part resistance. Our final study examined how extrusion temperature and printing speed affects the impedance of the MEAM printed parts. Further, anisotropy in the impedance was observed and the influence of the interface to it was examined. From the experimental results, the anisotropy was quantified with a Z/F ratio and was found to be nearly constant, ~2.15±0.23. Impedance scaling with the number of interfaces was measured and showed conclusively that the interlayer bonding was the sole source for the observed Z/F ratio. Scanning electron microscope images shows the absence of air gaps at the interface, and energy dispersion spectroscopy shows the absence of oxidation at the interface. By investigating the role of print parameters and scaling of impedance with interfaces, a framework to model and predict electrical behavior of electro thermal sensors and actuators made via MEAM can be realized.

Download

Share

COinS