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Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/923580

Title
Implantable microelectronics for biological signals
Author/Creator
Laskovski, Anthony Nikola
Institution
University of Newcastle. Faculty of Engineering and Built Environment, School of Electrical Engineering and Computer Science
Description
Research Doctorate - Doctor of Philosophy (PhD)
Description
Ageing populations in the developed world are perhaps one of the greatest concerns for providing quality healthcare in the future. Medical professionals are dependent on non-biological technology in order to understand how the human body works. Electronics has been a relatively recent area of science, and it has seen an escalating rate of sophistication. The body’s nervous system operates by using electrical signals, and from an engineering perspective the bodys organs behave as sensors and transducers. The ability to monitor vital health indicators such as the electrocardiogram (ECG), body temperature and blood pressure information via medical telemetry may offer adequate tools to view the logged or real time data of vulnerable patients, especially the elderly. Miniaturising this technology will also open new opportunities to access more biological information. Growing telecommunications infrastructure with increasing sophistication is opening the possibilities with regards to medical telemetry, making it theoretically possible for patients to carry out their daily tasks while being remotely monitored by doctors. Implantable electronics have become a topic of considerable research, with the implementation of the Cochlear implant and more recently Retinal prosthesis, in addition to telemetry devices. Implantable telemetry is also used in biomedical research to identify the physiological activity of animal subjects in confined laboratory environments. This dissertation presents new techniques in data and power transfer applied to implantable devices in the body. In particular it studies high frequency inductive links to reduce the size of implantable devices. It introduces the concept of Class-E oscillators, which combines Class-E amplifiers commonly used in inductive power transfer links, with oscillators, increasing the overall efficiency of the wireless power transmitter. A multi-array technique is implemented in power-transmitting coils to provide continuous wireless power to implants despite movements by laboratory animals in an enclosed environment. At the implant site, this thesis presents stacking techniques for power-receiving coils in order to increase the efficiency and reduce the physical size of the implanted power coil. An antenna has been implemented to transmit data from the implant to a site external to the body while the implant is loaded in tissue. A unique type of implant architecture is also proposed which generates harmonic signals, one harmonic of which forms the data carrier frequency thus avoiding the need for an oscillator block in the implant. The supply of power to implants may not always be conducted with a battery, and much effort has been committed to investigate ways of transmitting power wirelessly, mainly with inductive links. Switching power amplifiers, in particular Class-E amplifiers, are known for operating efficiently at high frequencies. This thesis will offer a simple way to analyse and design Class-E amplifiers using second order principles in the Laplace domain. Further investigation of Class-E amplifiers also leads to the concept of Class-E self oscillation for wireless power delivery to implants. Power amplifiers and oscillators are considered as two separate blocks in wireless power transmission. By combining these topologies into a self-oscillating power transmitter, greater efficiency has been achieved. Various topologies of Class-E oscillators as inductive power transmitters are compared with measured hardware results, determining that a crystal feedback network provides both accuracy and high output power. The thesis includes modeling, a design process and the hardware implementation of an ISM-band 27MHz Class-E oscillator as a power transmitter to an implant through biological tissue. A power of 27.5dBm was transmitted through 2cm of beef and 20.6dBm was received on the power-receiving implanted coil. The transmission of power occurs more efficiently at lower frequencies, however this requires transmitting and receiving coils with larger dimensions. Space restrictions in the implantable environment naturally leads to a need to transmit power at higher frequencies. This dissertation presents an inductive power transmission coil for biosensor-based telemetric implants. Using stacked spirals reduces the consumed space and also the self-resonant frequency (SRF) of the spiral, in addition to the required power transmission frequency for the implanted device. A four-layer 15mm x 15mm spiral coil of seven turns is simulated in CST Microwave Studio (TM), constructed and tested in hardware with comparable results. Measurements also include the receipt of power inductively from an energised array of spirals powered by a Class-E transmitter at 27MHz, and rectified to 1V, which is sufficient to drive an implant. This dissertation also investigates the design procedures of the Class-E amplifier as a data-transmitter for biotelemetry systems using different modulation techniques. A Class-E data-transmitter circuit that produces On-Off Keying (OOK), Frequency Shift Keying (FSK) and Phase Shift Keying (PSK) modulated signals has been designed, optimised and analysed in terms of a second order system for general implantable electronics. This development will provide flexibility and offer increased performance for implantable devices. It is generally preferred that the power and data signals for telemetric implants are supplied by two different frequency levels due to different tissue absorption levels at various frequencies. An implant’s data carrier frequency is traditionally generated by an oscillator block within the implant. At higher frequencies such as the Medical Implant Communication Service band (MICS: 401-406MHz) this can potentially require a significant amount of power. This thesis presents a harmonics based telemetry system for implantable devices. The outlined system generates harmonics from the power signal within the implant to create a carrier frequency for data transmission at the fifteenth harmonic within the MICS band, 405MHz. The prototype is capable of operating in a multi-user system using available frequency bands for medical use.
Relation
University of Newcastle Research Higher Degree Thesis
Date
2011
Keyword(s)
implants;  telemetry;  biomedical engineering;  analogue circuits;  RF;  radio frequency;  wireless power
Resource Type
thesis
Rights
Copyright 2011 Anthony Nikola Laskovski
Identifier
http://hdl.handle.net/1959.13/923580
Language
eng
 
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"Implantable microelectronics for biological signals"
 
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