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Flexible stretchable electronics for sport and wellbeing applications

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thesis
posted on 2019-07-16, 08:24 authored by Jonny Flowers
Wearable electronics are becoming increasingly widespread in modern society. Though these devices are intended to be worn, integrated into clothing and other everyday objects, the technologies and processes used to manufacture them is no different than those that manufacture laptops and mobile phones. Many of these devices are intended to monitor the user’s health, activity and general wellbeing, within clinical, recreational and assistive environments. Consequently, the inherent incompatibility of these rigid devices with the soft, elastic structure of the human body can in some cases can be uncomfortable and inconvenient for everyday life. For devices to take the step from a ‘wearable’ to an ‘invisible’, a drastic rethinking of electronics manufacturing is required.
The fundamental aim of this research is to establish parameters of usefulness and an array of materials with complimentary processes that would assist in transitioning devices to long term almost invisible items that can assist in improving the health of the wearer. In order to approach this problem, a novel architecture was devised that utilised PDMS as a substrate and microfluid channels of Galinstan liquid alloy for interconnects. CO2 laser machining was investigated as a means of creating channels and vias on PDMS substrates. Trace speeds and laser power outputs were investigated in order to find an optimal combination. The results displayed upper limits for power densities; where surpassing this limit resulted in poor repeatability and surface finish. It was found that there was an optimal set of trace speeds that ranged from approximately 120mm/s to 190mm/s that resulted in the most reliable and repeatable performance. Due to the complex nature of a materials variable energy absorption properties, it is not possible to quantify a single optimal parameter set.
To understand the performance of these devices in situ, finite element analysis was employed to model deformations that such a device could experience. The aims here were to investigate the bond strength required to prevent delamination, between the silicon-PDMS and PDMS-PDMS bonds, in addition to the stress applied to the silicone die during these deformations. Based upon the applied loads the required bond strengths would need to be at least ~65kPa to maintain PDMS-PDMS adhesion during these tests, while stress on the silicone-PDMS adhesion required an expected v higher ~160kPa, both of which are within the reach of existing bonding techniques that are capable of withstanding a pressure of ~600kPa before failure occurs. Stress on the silicon die did not exceed ~7.8 MPa during simulation, which is well below the fracture stress.
By developing knowledge about how various components of such a system will respond during use and under stress, it allows future engineers to make informed design decisions and develop better more resilient products.

History

School

  • Mechanical, Electrical and Manufacturing Engineering

Publisher

Loughborough University

Rights holder

© Jonathan Flowers

Publication date

2019

Notes

This dissertation is submitted in partial fulfilment of the requirements for the award of Master of Philosophy [at Loughborough University]

Language

  • en

Supervisor(s)

Sean Mitchell ; Dale Esliger

Qualification name

  • MPhil

Qualification level

  • Masters

This submission includes a signed certificate in addition to the thesis file(s)

  • I have submitted a signed certificate

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