Improvement of Piezoelectric Energy Harvesting System for Smart Road utilizing Material??Mechanical??Electrical Approach

Interest in eco-friendly energy technology is increasing worldwide due to energy depletion and environmental problems. Area of interest is not only limited to conventional renewable energy technologies such as solar, wind, hydraulic and geothermal, but also expands to other energy harvesting technologies such as piezoelectric, thermoelectric and triboelectric. Among these technologies, Piezoelectric Energy Harvesting (PEH) technology which converts mechanical energy into electrical energy has relatively high energy density and an advantage of versatility because it can be used with various energy sources. Research on manufacture of PEH device is widely conducted with focus on such processes as ceramic thick film, bulk, and polymer. Also, various designs for effective energy harvesting from vibration or direct contact are being researched. Furthermore, more research has been conducted to make PEH for variety of energy sources such as hydraulic power, wind, human motion, pavement, and train vibration. To enable PEH device adaptable with diverse energy sources, there is a need to increase its output power. In order to achieve this goal, multidisciplinary research is essential. Improvement of certain properties of PEH materials has to be done ground up. Energy harvest system with mechanisms that relay power from the energy source to PEH device should be designed. Finally, research on electric circuit technology that can store electric energy effectively is also needed. In this thesis, the manufacturing process of piezoelectric thick film was investigated to increase its material properties, and a new type of PEH module was proposed and its electrical properties were analyzed. A road piezoelectric energy harvester was designed as a new PEH module and was applied to an actual road. First, the manufacturing process of ceramic piezoelectric thick film was investigated. To optimize the thickness for the material sintering temperature, PZT-PZNN powder was produced and consecutively ceramic piezoelectric green sheets with thickness of 70 ??m were fabricated by tape casting process. When the thick film was stacked four sheets high and then sintered at 1000oC, it exhibited most favorable piezoelectric properties. The poling condition was also optimized by adjusting the polarization intensity and the total polarization time. Second, a PEH module which can adjust the displacement of the cantilever free end to control the strain was proposed. While the conventional vibration module is unable to maintain the constant strain as vibration frequency changes, the proposed module can adjust the strain regardless of the vibration frequency. The result showed that the output voltage was influenced by the strain greatly more than the vibration frequency. For maximum power transfer, impedance matching is required. At high vibration frequency, the resistive impedance matching load is lower because of the small internal impedance. At the constant strain condition, with a high vibration frequency, a small resistive load was matched and more output power could be generated. Third, the relation between current and impedance was investigated. Improvement of the controllable strain PEH module by using the vibration exciter for higher frequencies was conducted for higher current. The current and the impedance change according to the strain showed that the internal impedance was almost constant and the output current and voltage increased only in proportion to each other, despite varying the strain. It was also found that the output current increased by the decrease of the composite impedance when piezoelectric devices were connected in the parallel. Particularly in the case of parallel connection, impedance matching was done without impedance-converting circuit because of the dependency of the impedance with the vibration frequency decreased. Finally, a controllable strain PEH module was applied to PEH road system which can harvest electrical energy from traffic. PEH road system was first designed as a pushing free end type, but it was improved to a pushing center type where it can apply more stress to the piezoelectric device under the road pavement when displacement condition is restricted to 2 mm. UTM, MMLS3 and APT tests were conducted, and the output power was 29.58 W/m2 when it was installed on a real road. Experimental results showed that PEH road system can supply power to adjacent infrastructure and it can be a part of developing autonomous driving car technology.Docto