Year
2022
Degree Name
Doctor of Philosophy
Department
Intelligent Polymer Research Institute
Abstract
A Cochlear implant is a neuro-prosthetic medical device that is surgically placed underneath the skin consisting of a multi-electrode array that stretches into the inner ear or cochlea. The multi-electrode array electrically stimulates the hair cells or nerve cells within the cochlea to produce the sensation of sound. This implant is paired with an external unit that is worn on the ear and resembles a hearing aid. These two units communicate wirelessly with each other through a set of transmitting and receiving antennas over a transcutaneous electromagnetic radio link. The receiving antenna within the Cochlear implant body is the main focus of my work, the project in collaboration with Cochlear Limited, Sydney, under the ARC Industrial Transformation Training Centres (ITTC) hub. Currently, the receiving antennas within the Cochlear implant body are made of a simple multi-stranded platinum wire that is twisted into a circular loop encapsulated in silicone casing. The use of platinum as the core antenna conductor has disadvantages of high impedance at radio frequencies (RF) along with reported long-term cytotoxicity of platinum based electrodes in Cochlear implants. The Cochlear implants including the receiver coil antennas are manufactured through a manual method where each component is hand assembled. The high cost of Cochlear Implants which is between USD 30,000-50,000 stems from the manual hand assembling process. As such, the main idea behind the project is to change the production approach. Within this broad idea and direction from Cochlear Limited, Sydney, the scope of this thesis is limited to examining rapid prototyping and fabrication methods for constructing an electrode layout in the form of a coil antenna for the application of wirelessly powering the implant. The fabrication methods evaluated for the construction of the coil antenna are also suggested to be applied for constructing the multi-electrode array (MEAs) of the cochlear implant, which is made from the same material as the receiving coil antenna. However, unlike the coil antenna, these MEAs are exposed to the biological cells for electrical stimulation and without the silicone casing. These present limitations of the Cochlear implant, including antenna component within the implant, are discussed in detail in chapter 1 with the literature review. This PhD thesis presents the design and fabrication of alternate spiral coil antenna for the Cochlear implants produced through different additive and subtractive manufacturing routes. Suitable conducting materials for fabricating the core conductor of the antenna are identified along with coherent manufacturing strategy for rapid prototyping of the alternate antennas. Chapter 2 presents a general summary of the reagent materials and methods adopted for the fabrication of spiral coil antenna. The coil antenna design including the simulated geometrical dimension and electrical parameters are presented. The chapters following report on the experimentally fabricated spiral coil antennas. In chapter 3, two different additive manufacturing methods of inkjet and extrusion printing are used for the fabrication of gold nanoparticle-based coil antennas on the polydimethylsiloxane (PDMS) substrate. These two methods are compared in terms of ease of fabrication of the coil antenna and thus prepared coil antennas are electrically assessed through impedance measurements. Chapter 4 presents gold-based coil antennas fabricated on flexible PDMS and acrylic Perspex substrates using a laser engraving process. The gold layer is sputter coated onto a chemically treated PDMS surface and acrylic Perspex and through laser engraving process, the gold-coated layer is carved into a functional coil antenna. The coil antennas fabricated using this method are used to evaluate the effect of substrate and deposited conductor compatibility and its subsequent effect on its electrical characteristics. In chapter 5, a laser induced graphene-based coil antenna is constructed on a flexible polyimide (PI) substrate produced through a laser ablation process as an alternative to gold-based coil antennas. Here, the laser light is irradiated on the polymer substrate that locally increases the temperature of the substrate, breaking the chemical bonds to produce graphene. The structural build of all the fabricated coil antennas is assessed through scanning electron microscopy (SEM) and optical microscopy measurements. The printed coil antennas are also used as wireless signal receivers by coupling with a Qi based transmitting module operating at 100-125 KHz frequency for demonstrating its capability as a wireless receiver. This method of producing graphene is also applied for PDMS sheets. The graphene produced on the surface of the PDMS is tested for biocompatibility and assessed as a potential bioelectrode by culturing live cells on it. Finally, chapter 6 discusses the conclusion and future work for the experimental works carried out in the previous chapters and provides future direction.
Recommended Citation
Rajbhandari, Grishmi, Coil Antennas for Cochlear Implants, Doctor of Philosophy thesis, Intelligent Polymer Research Institute, University of Wollongong, 2022. https://ro.uow.edu.au/theses1/1413
FoR codes (2020)
3206 Medical biotechnology, 4003 Biomedical engineering, 4014 Manufacturing engineering, 4099 Other engineering
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.