Open-Source System and New Methods of Characterisation for Novel Piezoelectric Materials and Harvesters

Abstract

Electronic devices capable of converting ambient vibration energy into useful electrical power are highly desirable for next generation of self-powered, wireless, and wearable devices. It enables them to work independently and with no need of replacement and management of batteries. Piezoelectric materials are of prime interest among researchers as successful candidate to act as the harvesting source for such devices. However, several challenges in the characterisation and energy extraction from ambient vibrations need to be addressed to enable successful commercial application. One of the key problems is a lack of dedicated measurement tools for complex characterisation of the electrical output when harvesting from structures that incorporate piezoelectric transducers. In addition, due to a complex mechanical-electrical form of operation of energy harvesters, their performance testing during operation is challenging as the functioning
of the device depends on environmental parameters such as temperature, humidity, frequency, and excitation amplitude.

To open up research on piezoelectric energy harvesters to a broader audience, the main issues and challenges are discussed, and potential solutions with respect to new measurement techniques, experimental setups and method for characterisation of harvesting devices are proposed in this thesis. This is realised via the development of a novel, adjustable measurement system capable of complex characterisation of energy harvesting devices at room temperature and at elevated temperatures as encountered in real life applications. Additionally, a new method for evaluation of piezoelectric energy
harvester during its operation allowing for estimation of device core parameters and simple, yet effective performance characterisation is also proposed.

In line with current world research in the field, significant improvements in the area of piezoelectric ceramics, piezoelectric composites and mechanical structures are also proposed. This is realised with a study on freeze-cast piezoelectric composites where complex porous structures were found to have enhanced energy harvesting figures of merit and increased piezoelectric coefficients, demonstrating improved effectiveness in energy harvesting system. Finally, a novel cantilever beam structure operating in bend-twisting mode for broadening of the available frequency bandwidth and increased power density of piezoelectric energy harvester is proposed.

The work presented in this thesis further expands on the potential applications of freeze-cast porous piezoelectric materials, mechanical twist bending modes, and shows new opportunities for manufacturing of future electronic self-powered devices.

Date of Award	18 Nov 2020
Original language	English
Awarding Institution	University of Bath
Supervisor	Chris Bowen (Supervisor) & Peter Wilson (Supervisor)