C. T. Pan National Sun Yat-Sen University, Taiwan

Y. M. Hwang National Sun Yat-Sen University, Taiwan

Liwei Lin University of California, Berkeley, USA

Ying-Chung Chen National Sun Yat-Sen University, Taiwan

Preface xiii

Acknowledgments xv

1 Introduction 1

1.1 Background 1

1.2 Energy Harvesters 2

1.2.1 Piezoelectric ZnO Energy Harvester 3

1.2.2 Vibrational Electromagnetic Generators 3

1.2.3 Rotary Electromagnetic Generators 4

1.2.4 NFES Piezoelectric PVDF Energy Harvester 4

1.3 Overview 5

2 Design and Fabrication of Flexible Piezoelectric Generators Based on ZnO Thin Films 7

2.1 Introduction 7

2.2 Characterization and Theoretical Analysis of Flexible ZnO-Based Piezoelectric Harvesters 10

2.2.1 Vibration Energy Conversion Model of Film-Based Flexible Piezoelectric Energy Harvester 10

2.2.2 Piezoelectricity and Polarity Test of Piezoelectric ZnO Thin Film 12

2.2.3 Optimal Thickness of PET Substrate 15

2.2.4 Model Solution of Cantilever Plate Equation 15

2.2.5 Vibration-Induced Electric Potential and Electric Power 18

2.2.6 Static Analysis to Calculate the Optimal Thickness of the PET Substrate 19

2.2.7 Model Analysis and Harmonic Analysis 21

2.2.8 Results of Model Analysis and Harmonic Analysis 23

2.3 The Fabrication of Flexible Piezoelectric ZnO Harvesters on PET Substrates 27

2.3.1 Bonding Process to Fabricate UV-Curable Resin Lump Structures on PET Substrates 27

2.3.2 Near-Field Electro-Spinning with Stereolithography Technique to Directly Write 3D UV-Curable Resin Patterns on PET Substrates 29

2.3.3 Sputtering of Al and ITO Conductive Thin Films on PET Substrates 29

2.3.4 Deposition of Piezoelectric ZnO Thin Films by Using RF Magnetron Sputtering 31

2.3.5 Testing a Single Energy Harvester under Resonant and Non-Resonant Conditions 34

2.3.6 Application of ZnO/PET-Based Generator to Flash Signal LED Module 39

2.3.7 Design and Performance of a Broad Bandwidth Energy Harvesting System 40

2.4 Fabrication and Performance of Flexible ZnO/SUS304-Based Piezoelectric Generators 48

2.4.1 Deposition of Piezoelectric ZnO Thin Films on Stainless Steel Substrates 48

2.4.2 Single-Sided ZnO/SUS304-Based Flexible Piezoelectric Generator 50

2.4.3 Double-Sided ZnO/SUS304-Based Flexible Piezoelectric Generator 51

2.4.4 Characterization of ZnO/SUS304-Based Flexible Piezoelectric Generators 52

2.4.5 Structural and Morphological Properties of Piezoelectric ZnO Thin Films on Stainless Steel Substrates 54

2.4.6 Analysis of Adhesion of ZnO Thin Films on Stainless Steel Substrates 56

2.4.7 Electrical Properties of Single-Sided ZnO/SUS304-Based Flexible Piezoelectric Generator 59

2.4.8 Characterization of Double-Sided ZnO/SUS304-Based Flexible Piezoelectric Generator: Analysis and Modification of Back Surface of SUS304 61

2.4.9 Electrical Properties of Double-Sided ZnO/SUS304-Based Piezoelectric Generator 63

2.5 Summary 66

References 67

3 Design and Fabrication of Vibration-Induced Electromagnetic Microgenerators 71

3.1 Introduction 71

3.2 Comparisons between MCTG and SMTG 74

3.2.1 Magnetic Core-Type Generator (MCTG) 74

3.2.2 Sided Magnet-Type Generator (SMTG) 76

3.3 Analysis of Electromagnetic Vibration-Induced Microgenerators 76

3.3.1 Design of Electromagnetic Vibration-Induced Microgenerators 77

3.3.2 Analysis Mode of the Microvibration Structure 78

3.3.3 Analysis Mode of Magnetic Field 81

3.3.4 Evaluation of Various Parameters of Power Output 84

3.4 Analytical Results and Discussion 88

3.4.1 Analysis of Bending Stress within the Supporting Beam of the Spiral Microspring 90

3.4.2 Finite Element Models for Magnetic Density Distribution 93

3.4.3 Power Output Evaluation 97

3.5 Fabrication of Microcoil for Microgenerator 103

3.5.1 Microspring and Induction Coil 103

3.5.2 Microspring and Magnet 105

3.6 Tests and Experiments 106

3.6.1 Measurement System 106

3.6.2 Measurement Results and Discussion 107

3.6.3 Comparison between Measured Results and Analytical Values 110

3.7 Conclusions 112

3.7.1 Analysis of Microgenerators and Vibration Mode and Simulation of the Magnetic Field 112

3.7.2 Fabrication of LTCC Microsensor 112

3.7.3 Measurement and Analysis Results 113

3.8 Summary 113

References 114

4 Design and Fabrication of Rotary Electromagnetic Microgenerator 117

4.1 Introduction 117

4.1.1 Piezoelectric, Thermoelectric, and Electrostatic Generators 119

4.1.2 Vibrational Electromagnetic Generators 119

4.1.3 Rotary Electromagnetic Generators 120

4.1.4 Generator Processes 121

4.1.5 Lithographie Galvanoformung Abformung Process 122

4.1.6 Winding Processes 123

4.1.7 LTCC 123

4.1.8 Printed Circuit Board Processes 124

4.1.9 Finite-Element Simulation and Analytical Solutions 126

4.2 Case 1: Winding Generator 126

4.2.1 Design 127

4.2.2 Analytical Formulation 132

4.2.3 Simulation 134

4.2.4 Fabrication Process 138

4.2.5 Results and Discussion (1) 139

4.2.6 Results and Discussion (2) 142

4.3 Case 2: LTCC Generator 146

4.3.1 Simulation 147

4.3.2 Analytical Theorem of Microgenerator Electromagnetism 148

4.3.3 Simplification 152

4.3.4 Analysis of Vector Magnetic Potential 153

4.3.5 Analytical Solutions for Power Generation 154

4.4 Fabrication 157

4.4.1 LTCC Process 157

4.4.2 Magnet Process 159

4.4.3 Measurement Set-up 160

4.5 Results and Discussion 162

4.5.1 Design 162

4.5.2 Analytical Solutions 168

4.5.3 Fabrication 170

References 178

5 Design and Fabrication of Electrospun PVDF Piezo-Energy Harvesters 183

5.1 Introduction 183

5.2 Fundamentals of Electrospinning Technology 187

5.2.1 Introduction to Electrospinning 187

5.2.2 Alignment and Assembly of Nanofibers 190

5.3 Near-Field Electrospinning 191

5.3.1 Introduction and Background 191

5.3.2 Principles of Operation 194

5.3.3 Process and Experiment 196

5.3.4 Summary 202

5.4 Continuous NFES 202

5.4.1 Introduction and Background 202

5.4.2 Principles of Operation 202

5.4.3 Controllability and Continuity 205

5.4.4 Process Characterization 208

5.4.5 Summary 211

5.5 Direct-Write Piezoelectric Nanogenerator 211

5.5.1 Introduction and Background 211

5.5.2 Polyvinylidene Fluoride 212

5.5.3 Theoretical Studies for Realization of Electrospun PVDF Nanofibers 213

5.5.4 Electrospinning of PVDF Nanofibers 216

5.5.5 Detailed Discussion of Process Parameters 219

5.5.6 Experimental Realization of PVDF Nanogenerator 223

5.5.7 Summary 241

5.6 Materials, Structure, and Operation of Nanogenerator with Future Prospects 241

5.6.1 Material and Structural Characteristics 241

5.6.2 Operation of Nanogenerator 243

5.6.3 Summary and Future Prospects 248

5.7 Case Study: Large-Array Electrospun PVDF Nanogenerators on a Flexible Substrate 248

5.7.1 Introduction and Background 248

5.7.2 Working Principle 249

5.7.3 Device Fabrication 249

5.7.4 Experimental Results 251

5.7.5 Summary 252

5.8 Conclusion 253

5.8.1 Near-Field Electrospinning 253

5.8.2 Continuous Near-Field Electrospinning 254

5.8.3 Direct-Write Piezoelectric PVDF 254

5.9 Future Directions 255

5.9.1 NFES Integrated Nanofiber Sensors 255

5.9.2 NFES One-Dimensional Sub-Wavelength Waveguide 256

5.9.3 NFES Biological Applications 257

5.9.4 Direct-Write Piezoelectric PVDF Nanogenerators 258

References 258

Index 265

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