Biosignals such as electoencephalogram (EEG), electrocorticogram (ECoG), atrial electrogram (AEG) etc. are being recorded from multiple channels simultaneously to improve the spatial resolution of the signals. Conventional multichannel synchronous Analog-to-Digital Converters (ADCs) are used to convert the analog continuous time signals into discrete digital values. Several biosignals have a sparsity in time domain as they have fast-rising peaks in between periods of low activity. Use of conventional synchronous ADCs for conversion of such signals is not an efficient approach as their operation is constant, irrespective
of the activity of the input signals. Asynchronous ADCs such as level-crossing (LC) ADCs exploit the sparsity of biosignals and thus their operation is activity-dependent. However, multichannel configurations of LC ADCs do not yet exist. This problem is investigated in this work and a new ADC architecture is presented that can combine synchronous sampling with level-crossing quantisation method while converting input signals from several channels simultaneously. The synchronous LC ADC presented in this work achieves 3.37 times reduction in quantisation steps and 6 times reduction in number of output bits generated during conversion of AEG signals as compared to conventional synchronous ADCs. The problem in existing LC ADCs of data overhead in adaptive resolution technique is solved through a novel method named split resolution technique which is also presented in this work.

This document describes the design process and implementation of the lighting and casing of a battery free jogger light. This light is meant to increase the safety of joggers in dark environments. The most effective way of increasing the jogger's conspicuity will be researched by considering different light sources and driver circuits to efficiently power the light source in a blinking manner. A casing will be designed to encapsulate the components. Light emitting diodes were chosen as a light source due to their energy efficiency, colour optimisation and small size. Two LEDs are part of a rectifier, while three other LEDs are powered by a driver circuit that uses a clocked decade counter 4017 IC that receives its clock signal from a NAND based oscillator circuit. The casing is designed with 3D modelling software and a prototype is 3D printed. The intended light intensity was not reached, but the brightness in dark environments was deemed suitable for the project's goals. The casing has bigger dimensions than intended; however these can be optimised for mass production.

The deliverable of this project is a light for joggers that does not use a battery and keeps blinking for a short period of time after standing still. This research details the design and implementation of the storage part of a battery free jogger's light. The goal of this storage part is that it stores energy delivered by an energy harvester so that it can power LEDs for at least 30 seconds when there is no energy harvested anymore. The system consists of a full-bridge rectifier, a voltage regulator, a supercapacitor to store the energy and a switch to couple or decouple the load. The main trade-off of this research is between the charging and discharging times of the supercapacitor. Results show that LEDs in the rectifier offer advantages, since there is instant lighting when jogging and which makes the charging time less critical. With this feature the discharging time could be increased up to one minute. The total efficiency of this storage system is calculated to be 67.9\%.

Implantable Medical Devices (IMDs) could fulfill many different functions in the human body. Batteries have always been the main power source of these devices. Batteries have some drawbacks, the biggest one being the replacement of IMDs with fully discharged batteries. In this thesis a wireless power transfer system, with a receiving power conversion system with a maximum volume of 10 mm3, is proposed for IMDs implanted at more than 10 cm deep.
Ultrasonic wireless power transfer to IMDs could enable scaling down the devices to dimensions less than 1 cm. Compared with the electromagnetic far-field and near-field wireless power transfer methods, the power throughput to the IMD is much higher. Piezo-electric elements could be used to perform the acoustic to electric energy conversion. With the Butterworth-Van Dyke modeling technique, the ultrasonic wireless power transfer link could be characterized. Maximum acoustic intensity at the receiving piezo-electric element is assumed because of the high efficiency and the possible methods to focus the waves from the transmitter at a certain point in the human body. An electrical storage element is assumed because of fluctuations both in received and used power.
As the piezo-electric receiver outputs sinusoidal voltage and current waveforms, and the electrical storage element requires DC voltage, the signal requires significant processing for maximum power transfer. A perfect complex conjugate match between the piezo-electric receiver and the power conversion circuit is required for maximum power transfer as well. Two different methods which are used in prior art to achieve maximum power transfer are presented in this thesis, and one new method is developed. The standard method, which is used often in literature, does not include any special processing by means of impedance transformations and is therefore only efficient around one power level operating point. The varying frequency method varies the frequency so as to vary the piezo resistance and match it to the power conversion systems resistance. The piezo inductance varies with the varying piezo resistance, and is canceled out by tunable capacitor banks. A DC boost converter is required for high efficiency to the electric storage element. This method has many drawbacks, among which the continuous communication back to the transmitter to close the loop, which is consuming power and adding delay. The newly proposed method is the AC boost method. The AC voltage of the piezo-electric receiver is transformed into a pulse width modulated square wave voltage, so all power could go through the rectifier and into the storage element. A continuous resistive match is made between the AC boost converter and the piezo-electric element, ensuring maximum power transfer. This new method is validated by performing electric circuit simulations. Circuits are designed for the simulations that are comparable because of using the same piezo-electric element, rectifier, and storage element. The simulations show that it is the most efficient method for a wide load power range of 10 µW to 5 mW. The standard method is as efficient but only at a small range at high power level. The varying frequency method is much more complex and has, therefore, lower power efficiency at high power levels whereas at low power levels it has the same power efficiency.