Amplifier MMICs for Electrosurgical Devices and Microwave Therapeutic Systems

  • Abdul Moiz Ahmed Pirkani

Student thesis: Phd

Abstract

Advancement in semiconductor technologies and fabrication processes has enabled the development of advanced microwave circuits having the capability to generate high enough levels of microwave power at an affordable cost. These circuits that were once used in the communications sector have found applications in electrosurgical devices and microwave therapeutic systems during the past decades, due to the non-ionising nature of microwave energy and its interaction with the human body that can be defined in terms of electrical properties. Electrosurgical devices and therapeutic systems are being widely used for the treatment of various medical conditions like tumours, cancer, ablation, coagulation, atrial-fibrillation, wound sterilisation, enhanced liposuction, keratoconus, endoscopic, laparoscopic and open surgeries; with RF cutting, coagulation and ablation being the most popular biomedical modalities. However, many challenges need to be overcome, a few of which include focused power delivery and tissue dissection with small depth of effect, smart and integrated high efficiency power sources, localised generation of microwave power close to the treatment site to reduce transmission losses and distributed tissue heating, and large size of microwave power generators that are difficult to employ beyond specialised medical facilities, especially in portable electrosurgical devices. Research work presented in this thesis targets above mentioned limitations of microwave power sources by exploiting recent advances in high efficiency power amplifier and oscillator circuits; especially class AB, class J, class F, class F-1 power amplifiers and class E switching mode oscillators, that can be developed using discrete or Monolithic Microwave Integrated Circuit (MMIC) fabrication technologies. High efficiency discrete power amplifiers operating at 5.8 GHz ISM (Industrial Scientific and Medical) band frequencies developed during the scope of this PhD research include: class AB amplifier that provides 13 W continuous wave (CW) output power with 62.1 % power added efficiency (PAE), class F amplifier that provides 15.2 W CW power with 55.2 % PAE, and multistage amplifier with class AB and class F amplifiers in gain and power stages, respectively that provides 21.9 W CW output power with 65.4 % DC to RF efficiency. The amplifiers were tested and validated to effectively cause coagulation on liver bench test model with controlled depth of effect. An application envisioned for discrete amplifiers is portable field haemostasis. High efficiency class E oscillator and class AB amplifier were developed using WINPP10-15 GaAs MMIC process from WIN Semiconductors foundry. Class AB amplifier provides 17.43 dBm output power with 49 % PAE at 30 GHz, while class E oscillator provides 24 dBm output power with 40 % DC to RF efficiency at 14.5 GHz. These results are based on large signal simulations with EM simulated circuit elements. Initial small signal on-wafer measurements of class AB MMIC die showed similar trends; however, comparison between simulated and measured results indicated inaccuracies in MMIC process design kit models. On-wafer measurements of class E oscillator were performed at reduced bias conditions due to limited power handling capability of the bias tees at the measurement facility. Clean oscillations with 16.4 dBm output power and 27.9 % DC to RF efficiency at 10.7 GHz were obtained. Further tests will be performed after packaging the MMIC dies followed by mounting on a custom designed PCB evaluation board. Class E oscillator and class AB amplifier MMICs are envisaged for application within an endoscopic channel for localised power generation close to the treatment site, and an on-chip diagnostic and neutralisation system, for medulloblastoma and glioblastoma highly malignant grade IV cancerous cells, respectively.
Date of Award1 Aug 2020
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRobin Sloan (Supervisor) & Emad Alsusa (Supervisor)

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