Design and Fabrication of Piezoelectric Energy Harvesting System for IoT Sensors

Abstract

스마트 도로 및 스마트 홈에 대한 관심이 높아지면서, 사물인터넷 센서 구동을 위한 독립전원 관련 연구가 활발하게 이루어지고 있다. 이러한 연구는 기존 신재생 에너지 기술을 넘어 ‘에너지 하베스팅’ 기술까지 영역이 확대되고 있다. 특히 압전 에너지 하베스팅 기술은 기계적 에너지를 전기적 에너지로 바꾸는 효과적인 기술로 각광을 받고 있다. 압전 에너지 하베스팅 기술 관련 연구가 집중적으로 진행되고 있음에도 불구하고 실제 환경에 적용한 연구는 드문 실정이다. 이는 압전 에너지 하베스팅 기술을 실제 환경에 성공적으로 적용하기 위해서는 재료•기계•전기 공학 기술의 융합 연구가 필수적이기 때문이다. 본 논문에서는 압전 에너지 하베스팅 기술을 활용하여 사물 인터넷 센서들을 구동하기 위한 재료, 기계, 전기의 융합연구가 수행되었다. 그 결과, 실제 도로에 적용된 압전 에너지 하베스팅 시스템을 이용한 도로 노면 온도 모니터링 모델을 구현하였다. 제안된 도로 온도 모니터링 모델을 통해 운전자는 도로 노면 결빙 상태를 파악하고 사고 위험을 피할 수 있다. 이를 위해, 다음의 융합 연구가 수행되었다. 첫 번째로, 도로 실증을 위한 압전 에너지 하베스터 설계 및 제작 연구가 수행되었다. 총 3번의 개발 과업이 수행되었으며, 3 종류의 압전 에너지 하베스터가 설계 및 제작되었다. 결과적으로 압축형 하베스터가 도로 실증용 하베스터로 선정되었다.

두 번째로, 실제 도로에 압전 에너지 하베스터를 실증하고 무선 온도 센서를 구동하는 과업을 수행하였다. 경기도 여주시에 위치한 시험고속도로에 개발된 압전 에너지 하베스터가 설치되었으며, 도로 노면 온도 모니터링 모델을 위한 전력변환 회로가 설계 및 제작 되었다. 세 번째로, 압전 소자 대량 생산을 위한 제조 공정 최적화 연구가 수행되었다. 먼저, 볼밀링 조건 최적화를 위해 최적의 볼 직경과 볼밀링 공정 수행 시간이 선정되었다. 다음으로, 테이프캐스팅 조건 최적화를 위해 최적의 탈포 공정 수행 시간과 comma blade의 높이가 선정되었다. 마지막으로, 분극 공정 최적화를 위해 최적의 분극 세기와 분극 공정 수행 시간이 선정되었다. 이 연구는 압전 에너지 하베스팅 기술을 실제 환경에 적용하고 사물 인터넷 센서를 구동하는 것을 목표로 하였다. 결과적으로 압전 에너지 하베스팅 기술을 실제 도로에 적용하고, 이를 활용한 도로 노면 온도 모니터링 모델을 구현하였다. 이를 통해, 사물 인터넷의 독립전원으로서 압전 에너지 하베스팅 기술의 활용성을 보여준다.|Due to concerns about smart highways and smart homes, the needs for energy technology about independent energy source for wireless sensors for sensors increase worldwide. The research field extends not only to traditional renewable energy technologies such as solar, wind, hydropower and geothermal energy, but also to technologies such as piezoelectric energy harvesting. Piezoelectric energy harvesting techniques have attracted numerous research attentions because of its effectiveness of converting mechanical energy into electrical energy with various energy sources. However, the demonstration of the piezoelectric energy harvesting technology to practical applications has been seldom studied, because the fusion of technologies which are, the mechanical engineering technology to develop the optimized energy harvester, the electrical engineering technology to design power management circuit for the energy harvester, and the material engineering technology to manufacture piezoelectric device for the energy harvester, is essentially required to fully adapt the piezoelectric energy harvesting technology to practical applications. In this thesis, the fusion research about design and fabrication of piezoelectric energy harvesting system for IoT sensor was discussed. We developed the optimized structure of the piezoelectric energy harvester for real road application. The designed harvester was fabricated and installed to the Korea expressway (Yeoju-si, Gyeonggi-do). As a results, operating wireless temperature sensor (eZ430-RF2500, Texas Instruments, USA) using the installed piezoelectric energy harvester was conducted. In addition, the researches about optimizing manufacturing process were conducted for mass production of the piezoelectric device. First, the design and fabrication of the three harvester were conducted. Three cycles of development process have been conducted for application to real road. Finally, the press type harvester was selected as an optimized harvester structure for application to real road. Second, the demonstration of the pressing type energy harvester was conducted. The fabricated harvester was installed to real road and analyzed. The power generation amount of piezoelectric road energy harvesters was measured and high-quality harvesters were supplied. The waterproofing, heat-resistance, and axial load-carrying performance of each harvester were validated to evaluate their durability. In addition, accompanying circuits were designed and built to prevent any disruption in the operation of harvesters during emergency. In addition, the road temperature monitoring system using piezoelectric energy harvester and wireless temperature sensor was proposed to prevent the car accident due to the road surface freezing section. DC/DC converter circuit was designed and fabricated to convert the power generated from piezoelectric energy harvesters into the voltage level needed for electrical load. Among the commercial energy-harvesting DC/DC converter circuits, TPS62125 was selected because of the threshold and hysteresis specifications, allowing the storage level and output voltage of the power generated from harvesters to be adjusted according to the electrical load. Using the selected circuit of TPS62125, a power converter circuit was built by modifying and designing the surrounding circuits to meet the electrical load conditions. The transmitter and receiver of the wireless temperature sensor can communicate more than 25 seconds by one car pass. The transmitted temperature data was displayed by the monitoring system. Third, the research about optimization of piezoelectric material manufacturing process for mass production was conducted. In order to increase the piezoelectric properties, ball milling process, tape-casting process, and the poling process were optimized. For ball milling process, the 48 hour milling time with 10 mm diameter zirconium balls are the optimal conditions for increasing the energy density of a 0.69Pb(Zr0.47Ti0.53)O3–0.31Pb[(Zn0.4Ni0.6)1/3Nb2/3]O3 [0.69PZT–0.31PZNN] thick film fabricated by tape casting. These conditions produce not only the highest d × g value of 13,819 × 10-15 m2/N when sintered at 1100 °C, which is 145.2% higher than has previously been achieved with this material, but also the highest d value (251 pC/N) and g value (55.08 × 10-3 Vm/N) of the various conditions tested. As the slurry viscosity increases, the thickness of each laminated layer increases, which leads to an increased density. Degassing the slurry increased its viscosity, which increased the piezoelectric green-sheet thickness. This, in turn, minimized the number of layers that could be laminated, thereby increasing the ceramic’s density and the dielectric constant of the piezoelectric ceramic. The optimal PZT-PZNN green-sheet thickness was 70 µm. For poling process, the magnitude of applied field and poling process time were optimized as 10 kV/mm and 60 min. The optimized d33 × g33 value increased 179% from the previously obtained reference value.