14 INSTRUMENTATION VIEWPOINT- 17 - WINTER 2014 DESIGN AND CHARACTERIZATION OF AN OSCILLATING ENERGY HARVESTER WITH PLANKED PIEZOELECTRIC FOR OBSERVATORY OBSEA. Daniel M. Toma 7 ; Joaquin del Rio 3 ; Montserrat Carbonell-Ventura 8 ; Ferran Bernet Piquet 9 ; Jaume Miquel Masalles 10 Abstract For the expansion of the OBSEA underwater cable observatory, which is run by the UPC and is located at 4 km away from the coast of Vilanova i la Geltru, new underwater wireless sensors are envisioned. Therefore, a solution is required to generate power to wireless sensors using only sea. In this project we will solve this problem using a prototype based on a Bristol cylinder which can generate electrical voltage using vibration piezoelectric. These vibrations are generated by plectrums impacts which create continuous free vibration in piezoelectric after impacting them. The results give us an acceptable power and it describes a plectrum distribution based on frequency and amplitude of usually OBSEA sea wave behavior. Keywords: Energy Harvesting, Piezoelectric, Bristol cylinder, Prototype, Free vibration. INTRODUCTION In recent years, green energy have been getting more and more important in our world, especially in the feld of engineering. Therefore, the aim of this project is to study how to get enough energy to power underwater wireless sensors installed at 20 meters below sea level using the energy produced by the sea motion in the bottom. To achieve the transformation of mechanical energy to electric energy we use piezoelectric converts installed in a Bristol cylinder. The idea of using a Bristol cylinder to create a pendulum EH with plectra’s impacting the piezoelectrics comes as a result of reading the work presented by S.Crowley, R.Porter and D.V. Evans from the Bristol University [1]. Moreover, from the work presented by P. Pillatsch, E.N. Yeatman and A.S. Holmes from the Imperial College London [2], we could get the expected behavior when the piezoelectrics are vibrating freely. Energy Harvester Prototype To carry out the experiments for the EH prototype, diferent tolls have been used. First, we have made several previous studies done in ORCAFLEX software, which ofers the possibility of dynamic simulations, in order to display data on the behavior of the submerged body, where the pendulum will be hosted on the seabed. All these data obtained from computer simulations have been then used in a testbed simulating the real oscillatory movements using a waveform generator, amplifer, and an oscilloscope for measurements. Most studies have been made for an input frequency of 300 mHz simulating wave periods of 3.3s and an amplitude varying between 50 mV and 450 mV to simulate the rotation of the cylinder produced by waves of 0.5m to 4m which have been obtained from ORCAFLEX simulations as shown in fgure 1. Figure 1 ORCAFLEX simulation results Figure 2 Schematic representation of the proposed underwater energy harvesting systems Figure 3 Illustration of the prototype energy harvesting device mounted on a tube attached to the shake table, showing the pendulum with the plectra’s, the piezoelectric beam, the accelerometer and the gyroscope Observations are based on an initial prototype made from a frst design. In the initial prototype we fnd the base of the pendulum, support for piezoelectric, the piezoelectrics and the plectra’s as described in fgure 2. Once manufactured the prototype, we begun the experiments, which have been divided into two parts, the frst to describe the behavior of plectra’s and the second part to describe the behavior of piezoelectric depending on the electrical connection. In the frst case we had to consider what material to choose by fnding the optimum material to generate the electricity wearing as little as possible the piezoelectric material. Following this study we had to see how it should be designed the plectra for optimal behavior in the planked based vibration generator. Regarding the piezoelectric, we have to obtain the electrical resistance to generate the maximum output power, and what should be the distances between plectra’s to obtain maximum performance. Moreover we have to see what may be the optimal distribution of three piezoelectric installed inside the pendulum system. Finally will be necessary to know what connection should be used between piezoelectric. To carry out this study we use the testbed as described in the fgure 3. Piezoelectric beams Pendulum Shake table Shake table signal generator Plectra Circular motion generator Accelerometer Gyroscope