Date of Award

2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering

Specialization

Biomedical Engineering

Department

Electrical, Computer, and Biomedical Engineering

First Advisor

Kunal Mankodiya

Abstract

Smart Fabric Sensors (SFSs) have recently gained much interest as they are convenient as a long-term wearable as well as for their simplicity, lightweight, low manufacturing cost, high sensitivity, and flexibility. Semiconductive polymer composites SCPCs can be used as smart fabrics to create force or pressure sensors based on the piezoresistive effect, however, their wider application is limited due to their narrow sensing range, hysteresis and output drift issues as well as due to the lack of literature studying their voltage response related errors especially under high impact forces. In this Doctoral research, eight proposed designs of a smart fabric force sensor are introduced for wearable applications within two iterations of improvement. All suggested sensors have been tested and validated to obtain the general characterization of their behavior through many tests and protocols along three stages of testing investigating force-voltage response, linearity, hysteresis, and output drift under various loads from 1 - 50 N. There were three sensors that showed good performance, the 4th design that is mainly composed of Polyurethane PU open-cell foam impregnated with carbon black particles to serve as a resistive sensing element with a combination of other fabrics, the 7th design that is composed of a polyethylene foam with a core of carbon black PU foam RSE layer and the 8th design that is also composed of polyethylene with a core of carbon black polyurethane foam with a compressed RSE of extra 3 mm thickness of PU foam from both sides. Tests were performed through certain procedures and protocols with some modifications based on some available literature in this field. The mathematical representation and calculations were obtained accordingly. The obtained data and results provide a basic characterization for such foam-based sensors that also would be helpful in determining the expected behavior and validation of any similar ones. All obtained results were within the acceptable ranges compared to commercially available sensors. Each sensor could be more convenient than other ones for certain applications but in general, they have a wide sensing range that is giving reputable detection data without reaching the saturation point and without the need for any complicated or special circuitry as the only required circuit is a basic voltage divider circuit without any kind of amplification for the detected signal. Even the unsuccessful designs are not giving correct readings but they all could be improved using labs and technical means especially for mixing and drying materials which was a major limitation in creating those sensors. The three successful designs are precious state-of-art and very promising, that could be appropriate for a very wide range of applications especially in sport and medical fields taking the advantage of using them not only as a sensor but also as means of protection. This Doctoral dissertation has introduced a comprehensive study and development of the mathematical modeling and representation of piezo-resistive SCPCs based pressure sensors that would be immensely helpful for simulating and modeling such types of sensors.

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