New microwave applicators to explore fundamental electromagnetic interactions with cells

Miles, Angharad 2024. New microwave applicators to explore fundamental electromagnetic interactions with cells. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis documents the design and build of two novel microwave applicators, a rectangular waveguide and two 3D coplanar waveguides (CPW), used to explore microwave interactions with biological samples. The devices were utilised to investigate both the thermal and non-thermal mechanisms by which microwaves affect bacterial viability, spore germination, and biofilm integrity. The rectangular waveguide applicator was designed to expose a 96-well plate to 2.45 GHz microwaves, it ensures uniform exposure of multiple biological replicates and facilitates the study of a range of power levels simultaneously. It also allows for both low power, long duration and high power, short duration experiments. The 3D CPW applicators are planar and open structures that create uniform, separated electric and magnetic fields over a three-dimensional space. These novel devices enable precise evaluation of field exposure at the sample location which helps to underpin the mechanism causing microwave effects. Experimental results using the rectangular waveguide revealed significant non-thermal effects of microwaves on the growth dynamics of Staphylococcus aureus bacteria. The results showed increased growth rates after exposure to pulsed 2.45 GHz microwaves. Fluorescent probe analysis revealed microwaves increase low molecular weight thiols within S.aureus, this indicates a change in cellular redox state. The CPW applicators were used to explore the non-thermal effects that both the electric and magnetic components of microwaves have on Bacillus subtilis spore germination. The results showed accelerated spore outgrowth, challenging the current consensus in the literature that spores can be deactivated via non-thermal microwave interactions. S.aureus biofilms were also studied and displayed significant cell death after exposure to 2.45 GHz microwaves in both exposed and unexposed regions of the same biofilm. While this is likely a thermal effect, it confirms the notion that microwaves can effectively disrupt biofilms and could be a useful tool in their management. This research not only expands our understanding of microwave interactions with biological systems through the development of novel applicators but also has practical implications for safer and more effective microwave technologies in medical and industrial settings. This study contributes to a growing body of research suggesting broader applications of microwaves beyond traditional thermal effects. By establishing a set-up for future investigations into both the thermal and non-thermal effects of microwaves on cellular processes, this study highlights the importance of enhancing public health and safety in our increasingly wireless world. i

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1). Microwaves 2). Bacteria 3). High Frequency Design 4). Waveguide 5). 2.45 GHz 6). Thermal Characterisation
Date of First Compliant Deposit:	7 March 2025
Last Modified:	07 Mar 2025 15:42
URI:	https://orca.cardiff.ac.uk/id/eprint/176707

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