4 Finally, the prototype of the free-standing structure is characterised and maximised so
that the devices would be able to operate at low level of ambient vibration and able to generate electrical energy which meet the minimum requirement for powering a
microsystem.
1.3 The Book Structure
This book is divided into three main parts. Chapter 2 and 3 form the first part of the discussion about the technology, which includes a literature review of piezoelectricity,
thick-film technology application and fabrication methods, and the design of free- standing energy harvesting device. The second part of the book is discussed in Chapter
4, about the fabrication techniques and the improvement method for fabricating robust thick-film free-standing cantilever. The final part of the book is presented in Chapters 5
– 8, dealing with the characterisation of the free-standing structures, optimisation of electrical output and developing a multi-frequency structure for wider bandwidth
operation.
Chapter 2 introduces the background of piezoelectricity and its applications particularly in energy harvesting. The enabling technology for fabricating piezoelectric energy
harvesters based on thick-film technology is also discussed. Thick-film technology, from the evolution to the standard processing technique is briefly introduced in this
chapter, this follows by discussing the advantages of free-standing structures and the possibility of fabrication process.
Chapter 3 addresses the issues of energy harvesting design. Beam theory is used to estimate the natural frequency of the structure. The influence of the distance from the
centroid of the piezoelectric material to the neutral axis of the structure in stress, deflection and electrical output is also discussed. Simulation results of finite element
analysis with ANSYS are compared with analytical calculation results.
Chapter 4 explains the fabrication process, which combines conventional thick-film and sacrificial layer techniques in fabricating a free-standing structure. The process flow for
fabrication is listed in this chapter. Fabrication steps that were taken to enhance free- standing structures are explained.
5 Chapter 5 presents the experimental results of piezoelectric materials characterisation
using Berlincourt direct and resonant measurement method for determining the properties of the PZT materials. Comparison is made between a clamped and
unclamped sample to verify the analytical model developed by other researchers.
Chapter 6 discusses the results of testing a unimorph free-standing structure under harmonic base excitation. The mechanical and electrical properties of the piezoelectric
cantilever having different lengths are characterised with and without a proof mass attached to the end of the structure. The efficiency of energy conversion is compared
between cantilevers with different lengths and proof masses.
Chapter 7 describes multimorph cantilever structures. These structures are an extension of the unimorph structure arranged in a multi-layer fashion. Experimental results reveal
an improved performance compared to the unimorph structure. Two polarisation modes are studied; series and parallel. The electrical outputs from both of these configurations
are measured and discussed in the chapter.
Chapter 8 considers an alternative approach for wide-bandwidth operations. An array of multi-cantilevers is designed to operate in multi-frequency environments, with the
intention to harvest energy in a broader frequency spectrum. Experiment results of multi-frequency response are presented and discussed in this chapter.
