Innovative Mechanical Metastructures: Design and Material Integration for Sensing and Energy Harvesting

Abstract

본 논문은 기하학적 설계 기반 메커니즘을 통해 센서 및 에너지 하베스터의 기능을 향상시키기 위한 기계적 메타구조의 설계, 제작 및 응용에 대해 다룬다. 본 연구는 재료 대체나 외부 신호처리에 의존하지 않고, 정밀하게 설계된 구조체 자체가 민감도 조절, 변형 분산, 진동 증폭, 자기 보호 등 다양한 기능을 통합적으로 수행할 수 있음을 실험적으로 입증하였다. 이러한 메타구조는 3D 프린팅 기반 조형 기술과 MEMS 미세공정 기술을 통해 다양한 스케일과 플랫폼에 적용 가능하며, 웨어러블 전자기기, 자율 센서, 고신뢰 에너지 소자 등 실제 환경에서 요구되는 핵심 문제들을 해결할 수 있는 실마리를 제공한다. 첫 번째 연구에서는 3D 프린팅된 자이로이드 구조를 활용한 압저항형 압력 센서를 개발하였다. 유닛셀의 기하학적 설계를 조절함으로써 별도의 재료 변경 없이 감지 범위 및 감도를 조정할 수 있었으며, 구조적 강건성 또한 확보하였다. 실제 반복 하중 및 보행 조건에서의 실험을 통해 웨어러블 센서로서의 활용 가능성을 입증하였다. 두 번째 연구에서는 신축성 있는 PDMS 기판에 압저항 및 마찰전기 감지 메커니즘을 결합한 다기능 촉각 센서를 구현하였다. 음의 포아송비를 갖는 기하학적 설계를 통해 기계적 신축성과 균일한 변형 전달이 가능하였고, 배열 형태로 확장하여 복잡한 동적 감지에도 안정적으로 작동함을 실증하였다. 세 번째 연구에서는 두께 구배를 갖는 캔틸레버와 자가제한 메커니즘을 통합한 3D 프린팅 기반 압전 에너지 하베스터를 제안하였다. 두께 구배는 일정한 굽힘 응력을 유지하도록 설계되었으며, 이를 통해 에너지 변환 효율을 향상시켰다. 아울러, 과도한 가속도 조건에서의 소자 파손을 방지하기 위한 수동적인 자기제한 구조를 포함하여 내구성을 확보하였다. 마지막으로, MEMS 기반 압전 에너지 하베스터와 공진 주파수를 일치시키도록 설계된 메타구조 마운트를 제안하였다. 이 구조는 외부 진동을 공진을 통해 증폭하여 MEMS 소자에 전달하며, 추가적인 외부 회로 없이 기계적 입력을 향상시킨다. 실험 결과, 메타구조 마운트를 장착한 MEMS 에너지 하베스터는 5.4배 이상의 전압 증폭을 달성하였다. 본 논문은 메타구조 설계를 통해 센서 및 에너지 하베스터 시스템에 내재된 기능들을 통합할 수 있음을 다각도로 입증하였다. 구조적 형태가 재료나 회로 설계만큼 중요한 기능 설계 변수로 작용할 수 있음을 보여주며, 향후 실용적인 마이크로 시스템 설계와 에너지 자립형 플랫폼 구현에 있어서 새로운 설계 프레임워크를 제시한다. |This thesis investigates the design, fabrication, and application of mechanical metastructures to enhance sensing and energy harvesting functionalities through geometry- driven approaches. Rather than relying on material substitution or external signal processing, this work demonstrates that precisely engineered structures can provide embedded mechanical intelligence, achieving functions such as sensitivity tuning, strain distribution control, vibration amplification, and self-protection within compact and scalable platforms. By utilizing additive manufacturing and MEMS fabrication, the proposed metastructures span multiple length scales and device types, addressing real-world challenges in wearable electronics, autonomous sensors, and robust energy harvesters. The first part of this study explores developing a gyroid-based piezoresistive pressure sensor, wherein a 3D-printed lattice structure acts as both the mechanical support and functional modifier. The sensing range and sensitivity of the device were programmable and adjusted by modifying the unit cell geometry without altering the constituent materials. This approach highlights the potential of volumetric mechanical design in achieving functional reconfigurability. The gyroid lattice also provided excellent stress dispersion, resulting in high structural robustness under repeated loading. The concept was experimentally validated under cyclic pressure and human gait conditions, demonstrating its viability for wearable sensing applications. Building upon the theme of structural programmability, the second study presents a stretchable tactile sensor integrating piezoresistive and triboelectric mechanisms. The sensor leverages an auxetic mechanical design; by embedding an auxetic PDMS substrate beneath the sensing layer, this design enhances stretchability and strain uniformity, thereby addressing common issues in soft sensors such as hysteresis and uneven deformation. The auxetic geometry enabled stable electrical performance under large strain, and the device was successfully demonstrated in a spatially resolved array format, supporting its application in skin-inspired electronics and flexible human-machine interfaces. The third study investigates a 3D-printed piezoelectric energy harvester featuring a gradient-thickness cantilever and a self-limiting metastructured support. The thickness profile of the cantilever was analytically derived to maintain uniform bending stress, which was validated via simulation and experimental tests. A passive self-limiting mechanism was embedded in the supporting structure to constrain displacement under high accelerations, thereby protecting the AlN-based piezoelectric layer from overstrain and fracture. This dual strategy, performance optimization, and structural safety demonstrate how geometry can be used as a physical alternative to electronic regulation in dynamic environments. The final study extends the concept of vibrational enhancement to the MEMS scale by designing a resonance-coupled metastructure mount that integrates with a MEMS piezoelectric energy harvester. The metastructure was designed to match its resonance frequency to that of the MEMS device, thereby amplifying base acceleration through passive dynamic coupling. A self-limiting geometry was also incorporated into the mount to restrict over-displacement and mitigate mechanical failure under high-g excitation. Experimental measurements confirmed a 5.4× increase in RMS output voltage when the MEMS device was mounted on the metastructure, verifying the effectiveness of the geometry-based approach in improving energy conversion efficiency and mechanical durability. These studies establish a unified framework for using mechanical metastructures in electromechanical systems. By embedding functions directly into structural geometry, whether for pressure sensing, tactile feedback, or energy harvesting, this work shows that physical form can serve as a design variable on par with material and electronics. Moreover, the ability to fabricate these architectures using scalable techniques such as FDM 3D printing and standard MEMS processes paves the way for their deployment in a wide range of applications, from wearable systems to autonomous sensing networks. This thesis demonstrates that mechanical metastructure design can be leveraged to realize embedded functionalities in sensing and energy harvesting systems. The presented work provides concrete examples of integrating programmable mechanical behavior into compact platforms, contributing to the field of functional materials by design and informing the development of future sensors and energy solutions. Keywords: Mechanical metastructure, piezoelectric energy harvester, 3D printing, MEMS, tactile sensor, pressure sensor, self-limiting structure, negative Poisson’s ratio, dynamic amplification, geometry-driven design