VHF Power Delivery Through Tunable Impedance Matching

Abstract

Electromagnetic-based cancer ablation represents an innovative approach to selectively target and destroy cancerous tissues while minimizing damage to healthy cells. One promising mechanism under investigation involves using electric fields to induce localized heating within the targeted tissue. A key challenge in such systems is the ability to deliver energy in a controlled and localized manner, particularly as the electromagnetic properties of the target material vary with frequency and composition. This thesis investigates a tunable matching network and parallel plate structure designed to enable efficient energy transfer to materials under test. This method allows localized electric fields to be induced within the material, facilitating controlled heating. In an effort to maximize energy transfer to a material under test, a tunable impedance matching network design is a key focus of this work. The impedance matching network is characterized by its ability to dynamically adapt to varying complex impedances and frequency-dependent material properties, such as dielectric permittivity, across a frequency range of 20-100 MHz. Commercially available systems are largely limited to fixed-frequency designs, unable to accommodate changing material impedances or optimize energy transfer, making them unsuitable for applications requiring such adaptability. This work addresses these challenges inherent to systems involving changing material properties. This work addresses these limitations by presenting a tunable, system capable of matching to evolving load conditions, thereby enabling efficient energy transfer in scenarios where existing commercially available systems fall short. Complementing the matching network, a set of parallel plates provides the physical structure through which energy can be delivered to a material under test. The parallel plate design builds on those used in previous work, refining the geometry to better contain the electric field between the plates. This refinement aims to reduce radiative losses and improve the efficiency of energy transfer to the material under test, while maintaining continuity with the earlier system's design principles. These improvements align with the broader objective of increasing the specificity of energy delivery while also enhancing non-radiating behavior. Beyond system design, this work uses electromagnetic simulations to investigate the RF interactions of materials like carbon nanotubes (CNTs), which are of particular interest for their potential role in future heating experiments using evolutions of this system. While CNT-based heating is not the primary focus of this thesis, understanding their behavior under RF exposure supports the long-term goal of applying this system to materials with complex electromagnetic properties. Simulations from an electromagnetics perspective provide insights into the RF-induced behaviors of CNTs observed in literature and relevant research. The observed charge distributions and dipole behavior, previously leveraged in other studies to achieve localized heating, help to further contextualize the mechanisms underlying CNT-based RF heating applications. This understanding bridges gaps in existing research, where experimental outcomes have been documented but the mechanisms driving these behaviors remain underexplored. This work proposes and demonstrates a manually tunable, lumped-element matching network integrated with a refined parallel plate structure for controlled RF energy delivery. The system is validated through both simulation and experimental testing, demonstrating the ability to adapt to varying load conditions and maximize energy delivery across a larger frequency range of 20-100 MHz. This system addresses key limitations observed in fixed-frequency commercially-available designs, contributing a practical step towards scalable systems for targeted radiofrequency (RF) energy delivery and localized heating. Lastly, this work highlights practical design challenges and tradeoffs, offering insights and recommendations to guide future implementations and evolutions of this work.