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The use of optical techniques in biomedical monitoring and diagnosis is becoming increasingly widespread, primarily because of the non-invasive nature of optically derived measurements. Physiological analysis is usually achieved by characterisation of the spectral or temporal properties of the interaction between light and the anatomy. Although some optical measurements require complex instrumentation and protocols, recent technological advances have resulted in robust and compact equipment that is now used routinely in a multitude of clinical contexts. Unfortunately, these measurements are inherently sensitive to corruption from dynamic physical conditions or external sources of light, inducing signal artefact. Artefact is the primary restriction in the applicability of many optical measurements, especially for ambulatory monitoring and tele-medicine. The most widely used optical measurement is photoplethysmography, a technique that registers dynamic changes in blood volume throughout the peripheral vasculature and can be used to screen for a number of venous disorders, as well as monitoring the cardio-vascular pulse wave. Although photoplethysmographic devices are now incorporated into many patient-monitoring systems, the prevalent application is a measurement known as pulse oximetry, which utilises spectral analysis of the peripheral blood to estimate the arterial haernoglobin oxygen saturation. Pulse oximetry is well established as an early warning for hypoxia and is now mandatory under anaesthesia in many countries. The problem of artefact is prominent in these continuous monitoring techniques, where it is often impossible to control the physical conditions during use. This thesis investigates the possibility of reducing artefact corruption of photoplethysmographic signals in real time, using an electronic processing methodology that is based upon inversion of a physical artefact model. The consequences of this non-linear artefact reduction technique for subsequent signal analysis are discussed, culminating in a modified formulation for pulse oximetry that not only has reduced sensitivity to artefact but also possesses increased generality. The design and construction of a practical electronic system is then used to explore both the implementation issues and the scope of this technique. The performance of artefact reduction obtained is then quantified under realistic experimental conditions, demonstrating that this methodology is successful in removing or reducing a large proportion of artefact encountered in clinically relevant situations. It is concluded that non-linear artefact reduction can be applied to any photoplethysmographic technology, reducing interpretation inaccuracies that would otherwise be induced by signal artefact. It is also speculated that this technology could enable the use of photoplethysmographic systems in applications that are currently precluded by the inherent severity of artefact.

The objective of this research is to introduce two state-of-the-art wireless biomedical systems: (1) a multiband transcutaneous communication system for implantable microelectronic devices (IMDs) and (2) a new wireless power delivery system, called the “EnerCage,” for experiments involving freely-behaving animals. The wireless multiband link for IMDs achieves power transmission via a pair of coils designed for maximum coupling efficiency. The data link is able to handle large communication bandwidth with minimum interference from the power-carrier thanks to its optimized geometry. Wireless data and power links have promising prospects for use in biomedical devices such as biosensors, neural recording, and neural stimulation devices. The EnerCage system includes a stationary unit with an array of coils for inductive power transmission and three-dimensional magnetic sensors for non-line-of-sight tracking of animal subjects. It aims to energize novel biological data-acquisition and stimulation instruments for long-term experiments, without interruption, on freely behaving small animal subjects in large experimental arenas. The EnerCage system has been tested in one-hour in vivo experiment for wireless power and data communication, and the results show the feasibility of this system. The contributions from this research work are summarized as follows: 1. Development of an inductive link model. 2. Development of an accurate PSC models, with parasitic effects for implantable devices. 3. Proposing the design procedure for the inductive link with optimal physical geometry to maximize the PTE. 4. Design of novel antenna and coil geometry for wireless multiband link: power carrier, forward data link, and back telemetry. 5. Development of a model of overlapping PSCs, which can create a homogenous magnetic in a large experimental area for wireless power transmission at a certain coupling distance. 6. Design and optimization for multi-coil link, which can provide optimal load matching for maximum PTE. 7. Design of the wireless power and data communication system for long-term animal experiments, without interruption, on freely behaving small animal subjects in any shape of experimental arenas.