웨어러블 에너지 수집, 저장을 위한 첨단유전체/압전체 소재 및 소자개발 = Development of Advanced Dielectric and Piezoelectric Materials and Devices for Wearable Energy Harvesting and Storage

다국어 초록 (Multilingual Abstract)

The realization of energy-autonomous wearable bioelectronic devices represents an important research challenge in contemporary materials science and biomedical engineering. This endeavor demands the efficient collection of mechanical energy generated by the human body, its conversion and storage as electrical energy capable of sustaining continuous operation, and simultaneous integration into skin-conformable flexible platforms through coherent technology frameworks. However, the inherent dependence on electrochemical batteries fundamentally conflicts with the essential requirements of wearable systems, namely mechanical compliance, uninterrupted monitoring, and long-term stability. Moreover, mechanical energy generated during routine bodily activities has yet to be sufficiently exploited as a reliable power source. This study addresses three critical limitations that constrain practical energy autonomy in wearable devices: the low energy conversion efficiency resulting from mechanical impedance mismatch at bio-interfaces, the degraded energy storage and conversion efficiency arising from inherent material limitations of conventional dielectric storage media, and develops an integrated materials and device design strategy encompassing novel energy sources and diverse perspectives on energy harvesting and storage platforms.
First, a bio-inspired hierarchical interface architecture informed by adhesion mechanisms in natural organisms has been designed and implemented. By replicating the micro and nano scale hierarchical structures observed in octopus suckers and gecko toe pads through engineered adhesive layers, simultaneous achievement of high compliance, reversibility, and mechanical stability at the interface between compliant biological tissue and rigid piezoelectric active layers has been demonstrated. This hierarchical interface restructures the strain transfer mechanism at the skin-device boundary, thereby overcoming the limitations in strain transfer efficiency and adhesive durability inherent to conventional flat, tape-based, or hydrogel-based attachment approaches.
Concurrently, advanced dielectric energy storage materials have been developed that surpass the performance limitations of conventional ferroelectric capacitors. Through compositional engineering and microstructural control of lead-free pyrochlore oxide ceramics, relaxor like ferroelectric polarization behavior with suppressed hysteresis losses has been realized. In contrast to conventional ferroelectrics dominated by domain-switching mechanisms, quasi-linear polarization characteristics have been established that are well-suited to the pulsed electrical outputs generated by mechanical energy harvesters, thereby ensuring high efficiency and reproducibility in charge-discharge cycling.
Additionally, β-chitin nanofibrils extracted from deep-sea tubeworms have been investigated to harness their biological structural features, demonstrating the feasibility of exploiting spontaneous polarization and hierarchical architectures formed through evolutionary processes without requiring external poling treatments, thereby enabling electromechanical coupling phenomena.
Collectively, this research establishes a scientific and technological foundation for the paradigm shift from battery dependent wearable devices to energy-autonomous flexible systems compatible with physiological environments. The proposed materials design concepts, interface engineering methodologies, and device integration approaches can be widely applied as design guidelines for next generation wearable bioelectronic devices targeting long term physiological signal monitoring, rehabilitation and assistive technologies, and biointegrated therapeutic systems. Simultaneously, these developments advance fundamental understanding of bio-inspired functional materials, relaxor ferroelectric behavior, and precise bio-electronic device coupling.

목차 (Table of Contents)

• List of Tables xiii
• List of Figures xiv
• ABSTRACT xxx
• Chapter 1. Introduction 1
• 1.1. Bio-inspired interface based wearable energy harvesting 15
• 1.1.1 Evolution of wearable electronics and energy autonomy 15
• 1.1.2. Biomimetic strategies for enhanced material functionality 18
• 1.1.3. Mechanical compliance and interfacial adhesion 22
• 1.1.4. Structural engineering for performance enhancement 26
• 1.1.5. Skin-conformal interface design and energy amplification 31
• 1.1.6. Monolithic integration and system-level considerations 36
• 1.2. Lead‑free pyrochlore dielectric energy storage 39
• 1.2.1. Evolution of dielectric energy storage technologies 39
• 1.2.3 Fundamental structure and crystallography of pyrochlore oxides 42
• 1.2.4. Dielectric behavior and polarization mechanisms in pyrochlore systems 45
• 1.2.5. Compositional engineering and cation substitution strategies 50
• 1.2.6. Microstructural optimization and defect engineering approaches 54
• 1.2.7. Advantages of pyrochlore oxides over conventional dielectrics 58
• 1.2.8. Integration strategies and future perspectives for energy storage devices 61
• 1.3. Electromechanical coupling properties of biomaterials: ferroelectrets 65
• 1.3.1. Fundamentals of ferroelectret materials and energy harvesting mechanisms 65
• 1.3.2. Biological piezoelectric polymers and natural ferroelectret properties 69
• Chapter 2. Conformably skin adherent piezoelectric patch with bio-inspired hierarchically arrayed microsuckers enable physical energy amplification 73
• Experimental and Method 73
• Results and discussion 82
• 2.1. Bio-inspired hierarchical interface architecture design and fabrication 82
• 2.1.1. Conceptual framework of octopus-inspired hierarchical patterns 82
• 2.1.2. Fabrication methodology of hierarchical adhesive interface 85
• 2.1.3. Assembly and integration of flexible piezoelectric energy harvesting patch 89
• 2.2. Structural and chemical characterization 91
• 2.2.1. Morphological analysis via scanning electron microscopy 91
• 2.2.2. Crystal structure analysis by X-ray diffraction 93
• 2.3. Piezoelectric performance characterization 95
• 2.3.1. Dielectric properties and piezoelectric coefficient 95
• 2.3.2. Electrical output performance under mechanical deformation 97
• 2.3.3. Curvature-dependent energy harvesting performance 101
• 2.4. Adhesion Performance Under Diverse Environmental Conditions 104
• 2.4.1. Adhesion Mechanism and Theoretical Modeling 104
• 2.4.2. Quantitative Adhesion Measurements on Rigid and Compliant Substrates 108
• 2.5. Computational modeling of interface mechanics and detachment behavior 110
• 2.6. Demonstration of enhanced energy harvesting via bio-inspired adhesion 113
• 2.6.1. Energy harvesting from wrist flexion under dry conditions 113
• 2.6.2. Waterproof energy harvesting on wet skin 116
• 2.7. Potential applications and future perspectives 119
• Chapter 3. Energy-autonomous and skin-adaptive sensor patch with monolithically nano-interconnected interfaces for spatiotemporal teleoperation 121
• Experimental and Method 121
• Results and discussion 128
• 3.1. Monolithically integrated energy-autonomous sensor patch with bioinspired adhesive interface 128
• 3.1.1. Conceptual design and multilayer architecture 128
• 3.1.2. Synthesis and characterization of lead-free piezoelectric material 133
• 3.1.3. Fabrication methodology of monolithic device architecture 137
• 3.2. Optimization of CNT-embedded electrode for enhanced interfacial stability 146
• 3.2.1. WEC-Based monolithic architecture and CNT embedding characterization 146
• 3.2.2. Electrical conductivity enhancement through CNT embedding 149
• 3.2.3. Interlayer bonding enhancement via CNT interlocking 153
• 3.2.4. Mechanical stability and stretchability performance 159
• 3.3. Bio-inspired adhesive interface engineering for omnidirectional skin attachment 165
• 3.3.1. Hierarchical adhesive architecture design principles 165
• 3.3.2. Wet adhesion mechanism and liquid manipulation 169
• 3.3.3. Multidirectional adhesion and peel resistance 175
• 3.3.4. Reversibility, breathability, and biocompatibility 178
• 3.4. Piezoelectric performance characterization and electrical output analysis 184
• 3.4.1. Piezoelectric signal generation mechanism and operational principles 184
• 3.4.2. Compositional optimization and voltage output performance 187
• 3.4.3. Electrical output under multimodal mechanical deformation 188
• 3.4.4. Cyclic durability and long term electrical stability 193
• 3.4.5. Environmental robustness and wet condition performance 197
• 3.4.6. Underwater operational capability and submerged performance 199
• 3.5. Device application in spatiotemporal teleoperation and virtual reality interfaces 202
• 3.5.1. Biomechanical signal transduction from human movements 202
• 3.5.2. Integration with virtual reality and remote robotic control 206
• 3.5.3. Comparative performance analysis and technological positioning 210
• 3.5.4. Signal quality optimization and noise management 212
• Chapter 4. Yielding optimal dielectric energy storage and breakdown properties of lead-free pyrochlore ceramics by grain refinement strategies 214
• Experimental and Method 214
• Results and discussion 221
• 4.1. Lead-Free pyrochlore dielectric ceramic synthesis and fabrication 221
• 4.1.1. Powder preparation via solid-state reaction method 221
• 4.1.2. Densification through temperature-controlled sintering 225
• 4.1.3. Electrode metallization and sample preparation for electrical characterization 228
• 4.2. Structural and morphological characterization 229
• 4.2.1. Phase evolution and crystallographic analysis via X-ray diffraction 229
• 4.2.2. Microstructural examination via scanning electron microscopy 232
• 4.2.3. Defect chemistry assessment via Raman spectroscopy 235
• 4.3. Dielectric properties and temperature stability 238
• 4.3.1. Temperature-dependent dielectric characteristics 238
• 4.3.2. Frequency-dependent dielectric response 243
• 4.4. Energy storage performance and polarization behavior 245
• 4.4.1. Electric field-dependent polarization characteristics 245
• 4.4.2. Temperature stability of energy storage performance 248
• 4.4.3. Frequency stability and fatigue resistance 251
• 4.5. Breakdown strength and microstructure optimization 254
• 4.5.1. Leakage current and electrical conduction mechanisms 254
• 4.5.2. Weibull statistical analysis of breakdown strength 257
• 4.5.3. Maximum electric field performance before breakdown 259
• 4.5.4. Grain size effect on breakdown field: exponential decay relationship 262
• 4.6. Strategic implications for multilayer ceramic capacitor development 265
• 4.6.1. Trade-Off relationship between polarization and breakdown strength 265
• 4.6.2. Microstructure engineering strategies for enhanced performance 267
• 4.6.3. Implications for multilayer ceramic capacitor design 269
• Chapter 5. Empowering energy storage performance of pyrochlore dielectrics through multicomponent octahedral interactions and nanodomain tuning 271
• Experimental and Method 271
• Results and discussion 276
• 5.1. Lead-Free BZTN pyrochlore dielectric ceramic synthesis and Processing 276
• 5.1.1. Solid-state reaction synthesis of BZTN nanoparticles 276
• 5.1.2. Densification and microstructural control through sintering optimization 278
• 5.1.3. Microstructural evolution and grain size control 282
• 5.1.4. Electrode deposition and sample preparation for electrical characterization 285
• 5.2. Structural and compositional characterization 287
• 5.2.1. Phase evolution and crystallographic analysis via X-ray diffraction 287
• 5.2.3. Local structural probing via Raman spectroscopy 290
• 5.3. Dielectric properties and temperature stability 293
• 5.3.1. Frequency-dependent dielectric response 293
• 5.3.2. Temperature-dependent dielectric characteristics and thermal stability 296
• 5.3.3. Modified Curie-Weiss analysis and domain structure evolution 298
• 5.4. Energy storage performance and polarization behavior 300
• 5.4.1. Polarization-Electric field characteristics and energy density 300
• 5.4.2. PUND measurements and switching solarization analysis 304
• 5.5. Breakdown strength and electrical reliability 309
• 5.5.1. Leakage current characteristics and conduction mechanisms 309
• 5.5.2. Weibull statistical analysis of breakdown strength 312
• 5.5.3. Maximum energy storage performance near breakdown threshold 315
• 5.6. Reliability assessment under operational stresses 317
• 5.6.1. Frequency stability and switching dynamics 317
• 5.6.2. High-temperature energy storage performance 320
• 5.7. Octahedral engineering strategy and design principles 324
• 5.7.1. Role of multicomponent octahedral networks in domain tuning 324
• 5.7.2. Implications for high-entropy oxide design 327
• 5.7.3. Pathways toward commercial implementation 329
• Chapter 6. Biological ferroelectret property based on β-chitin nanofibrils of deep-sea tubeworms 331
• Experimental and Method 331
• Results and discussion 334
• 6.1. Biological ferroelectret material source and biopolymer harvesting 334
• 6.1.1. Morphological characterization of deep-sea tubeworm architecture 334
• 6.1.2. Protein deproteinization and nanostructural purification 337
• 6.2. Structural characterization and crystallographic analysis 340
• 6.2.1. Crystalline phase identification via spectroscopic analysis 340
• 6.2.2. X-Ray diffraction analysis of lattice structure 344
• 6.2.3. Molecular-level organization of polar functional groups 346
• 6.3. Ferroelectret characterization and thickness-dependent performance 348
• 6.3.1. Thickness optimization through controlled delamination 348
• 6.3.2. Mechanical-electrical transduction mechanism 351
• 6.3.3. Thickness-dependent energy harvesting output 353
• 6.4. Frequency-dependent electrical behavior and dielectric characteristics 356
• 6.4.1. Polarization hysteresis and frequency evolution 356
• 6.4.2. Dielectric permittivity and loss characterization 359
• 6.5. Biological ferroelectret versus conventional synthetic systems 362
• 6.5.1. Spontaneous polarization without external poling 362
• 6.5.2. Hierarchical pore architecture enabling optimized dipole distribution 364
• 6.6. Energy harvesting device fabrication and performance metrics 365
• 6.6.1. Electrode integration and electrical interfacing 365
• 6.6.2. Optimized mechanical excitation parameters 366
• 6.6.3. Power output and energy harvesting efficiency 367
• 6.7. Biological energy harvesting applications and future perspectives 368
• 6.7.1. Self-healing and sustainability paradigm 368
• 6.7.2. Wearable biosensor and energy harvesting integration 369
• 6.7.3. Deep-sea and extreme environment biotechnology 370
• 6.7.4. Hybrid bioelectronics and multi-modal sensing 371
• Chapter 7. Conclusion 372
• References 376