International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol:19 No:04 7 190604-3737-IJMME-IJENS © August 2019 IJENS I J E N S Piezo-electric Energy Harvesting from Human Motion based on 2-DOF Vibration Absorber Mode: Design Methodology and Experimental Validation Maurine N. Andanje *1 Bernard W. Ikua *2 and Ahmed M.R. Fath Elbab *3 1Maurine N. Andanje, Pan African University Institute For Basic Sciences, Technology and Innovation (PAUSTI) . 2Bernard W. Ikua, Department of Mechatronic Engineering, Jomo Kenyatta University of Agriculture and Technology (JKUAT) . 3Ahmed M.R. Fath Elbab, Department of Mechatronics and Robotics , Egypt-Japan University of Science and Technology (EJUST ), on leave from Mechanical Engineering Department, Faculty of Engineering, Assiut University. *Maurine N. Andanje – Email: Maureen.andanje@jkuat.ac.ke Abstract-- This paper presents the design and experimental testing of an energy harvesting (EH) device that can harvest human motion energy at low frequency and wide bandwidth using the vibration absorber mode. Based on the concept of the 2-DOF vibration system, the parameters namely; the proof masses and spring constants for maximizing the power output, are selected to harvest energy at low frequency (1-10 Hz) and wide bandwidth (± 20% of the mean frequency), which matches the human motion. The piezoelectric layer used is polyvinylidene fluoride (PVDF) which portrays favorable characteristics. A finite element model is developed in COMSOL to investigate the system performance with the selected parameters. Experimental work is then carried out to validate the design with the selected parameters and investigate the system performance. The designed energy harvester prototype is expected to generate low power in the order of micro-watts to milli-watt in a range of frequencies between the system’s two resonant frequencies. This amount of power is sufficient enough to provide additional power for wearable devices and medical implants. Index Term-- Energy Harvesting (EH), Two Degree of freedom (2-DOF), Piezoelectricity, Polyvinylidene fluoride (PVDF) INTRODUCTION Energy harvesters are devices used to collect and convert energy available in the environment into useful electrical power to satisfy the power requirements of autonomous systems. With the development of low power electronics and energy harvesting technology, self-powered systems have become a research hotspot over the last decade. The main advantage of self-powered systems is that they require minimum maintenance which makes them to be deployed in large scale or previously inaccessible locations. Therefore, the target of energy harvesting is to power autonomous fit and forget electronic systems over their lifetime [1]. Among the many energy sources, mechanical energy can be found in instances where thermal or photonic energy is not suitable, which makes extracting energy from mechanical energy an attractive approach for powering electronic systems. The source of mechanical energy can be a vibrating structure, a moving human body or air/water flow induced vibration. The frequency of the mechanical excitation depends on the source: less than 10Hz for human movements and typically over 30Hz for machinery vibrations [1]. The kinetic energy is transferred to a proof mass of the energy harvester, where various transduction techniques can be used to transform it to electrical energy such as piezoelectric, electromagnetic and electrostatic [2]. Energy harvesting devices are designed to match their natural resonant frequency with that of the energy source in order to maximize the power output. The possibility of using body motion to convert the kinetic energy to electrical energy is a solution that can be used to power wearable or implantable systems. An energy harvester has normally three main components: the micro-generator which converts ambient environment energy into electrical energy, the voltage booster which pumps up and regulates the generated voltage and the storage element [2]. Fig. 1. Block diagram of an energy harvester [2] A key challenge for vibration-based EH device is that it obtains the optimal power within a narrow frequency bandwidth near its resonant frequency. Away from the resonant frequency, the power generation drops dramatically and may be too low to be utilized [3]. In fact, the frequencies of environmental vibration sources are relatively low (normally less than 200 Hz) and vary in a certain frequency range. As a result, energy harvesting mechanisms which can respond to low-frequency vibrations with wide-band operation range or tunable resonant frequency are considered to be promising solutions. Piezoelectric energy harvesters convert mechanical strain into voltage output, i.e., electric field across the piezoelectric layer, based on the piezoelectric effect. They have received much attention because of the advantages of simple