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Report on the Piezoelectric Energy Harvesting Methods

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Energy harvesting is one of the major and an important part of our day-to-day activities. There are various methods for energy harvesting but there is high demand for the generation of clean energy so as to protect environment for future generation. Piezoelectric materials are those which generate electric charge when mechanical stress is applied, this is one of the best way to implement for the micro energy harvesting. Piezoelectric film can generate good amount of electrical energy which can be stored in rechargeable batteries. In this work, we have presented the electricity generation by piezoelectric transducers. The simulation is carried out for a single transducer under stationary load using Comsol Multiphysics and comparison of the voltage in different type of connections like series, parallel and series–parallel. The practical values are in good comparison with the theoretical calculations and simulation.

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The recent fluctuations on the price of petroleum product have affected the economy of the country. The disruptions in the weather condition have also affected the renewable energy sources through which the generation of electricity takes place. Some of the ways for generation of electricity are nuclear power plants, tidal power generators, hydroelectric power generators etc. However these require larger space and huge financial capacity for the setup. Due to the advancements in the technology of components consuming less power supply there is a need for fulfilling the micro energy requirements which can be satisfied by this work.

Energy harvesting, or energy scavenging, is the process of re-collecting small amounts of energy that would be lost as heat, light, sound, vibration or movement. Also it uses this captured energy to improvise the efficiency and to enable new technologies like wireless sensor networks etc. Energy harvesting also has the potential to replace batteries for small, low power electronic devices Energy harvesting has a great application in a wide range of electronic sensors that consume less energy like portable devices, military applications etc. Piezoelectric transducers are constituted by piezoelectric materials. This material has the ability to directly convert applied strain into electrical charge. It happens because when a load is applied in the material it causes the molecular structure deformation that in turn causes a separation of the positive and negative centers, resulting in the macroscopic polarization of the material. One of the unique characteristics of the piezoelectric effect is that it is reversible, meaning that materials exhibiting the direct piezoelectric effect (the generation of electricity when stress is applied) also exhibit the converse piezoelectric effect (the generation of stress when an electric field is applied).

Piezoelectric materials can be used as a means of transforming ambient vibrations into electrical energy that can then be stored and used to power other devices. With the recent surge of micro scale devices, piezoelectric power generation can provide a convenient alternative to traditional power sources used to operate certain types of sensors/actuators, telemetry, and MEMS devices. Piezoelectric sensors are used in a variety of applications to convert mechanical energy to electrical energy such as pressure-sensing applications, detecting imbalances of rotating machine parts, flow rate measurement, sound transmitters (buzzers), sound receivers (microphones) etc

The systematic way of building circuit using piezoelectric transducers plays an important role in energy harvesting, A piezoelectric energy harvesting circuit can be built in three different ways viz series connection, parallel connection and Series-Parallel connections. The method in which the circuit is built matters for the amount of voltage and current generated from the circuit. The study is done on all these three types of the circuit connections for different known loads and conclusion is derived for the maximum instantaneous output voltage.

Theoretical Calculations

The voltage obtained from the single piezoelectric transducers is calculated using the relation for a piezoelectric disk of a given thickness of t, the voltage V generated across the electrode disk when subjected to a stress T is given by V=gtT Where g is piezoelectric voltage coefficient (For PZT type 5H g33 is 19×〖10〗

(-3)) For 0.2Kg static load condition, F=0.2×9.81 T=F/A V=24×〖10〗

(-6)×0.25×7710.172 V=0.036V Where F is the Force, A is the area of the PZT transducer

Simulation

The single PZT piezoelectric transducer was simulated using COMSOL multiphysics software with static load condition. The Voltage v/s diameter plot was obtained which shows the increase in voltage along the diameter of the transducer. The voltage obtained from the simulation is 0.032V. The simulated model of Piezoelectric transducer is shown in the Fig.4 and the plot of Voltage v/s diameter is shown in the Fig.5

Experimental Procedure

The Piezoelectric transducers are connected to Digital storage oscilloscope (DSO) to check the individual voltages and the values for the peak voltage which is noted and verified with the manufacturer data sheet. Then the circuit is built for series, parallel and series-parallel connections using individual sensors on a flexible sheet. They are built in layers where two layers consist of the six sensors with respective circuit arrangements. The layers of particular circuit arrangements are placed opposite to each other with a separation in between them so that voltages on both compression and decompression upon the applied load can be obtained. The circuit arrangements are tested with DSO for variation in the peak voltages upon known applied load conditions, Each Circuit arrangements is tested with 0.20Kg, 0.25Kg and 0.30Kg mass which is applied from a fixed vertical distance 0.05m and the waveforms are obtained. Fig.5 shows the piezoelectric transducer with PZT core and Fig.6 shows the experimental setup with circuit connections.

Results and Discussions

Single Piezoelectric transducer: The single piezoelectric transducer was simulated on COMSOL multiphysics software and also theoretical calculations was performed to check the outout voltage under stationary load condition. The output voltage obtained in both simulation and theoretical calculations was in the range of 0.032V-0.036V.

Series connection: The circuit arrangement for series is tested by applying three different loads with fixed impact distance and the amount of voltage obtained is noted. It was observed that output voltage increased as the mass of the load applied increased. The circuit arrangement for series is shown in the fig.7 and the variation in the waveforms for all the three load conditions are shown in the fig.8,9,10. The output voltage for series connection was in the range of 132V-270V.

Parallel Connection: In the parallel connection the output voltage increased as the mass of the load applied increased and the voltage was in the range of 8.2V-22V. The circuit arrangement for parallel is shown in the Fig.11, and the variation in the waveforms for all the three load conditions are shown in the Fig.12, 13, 14. It was observed that the amount of output voltage received from the parallel connection was less compared to that of series connection.

Series-parallel connection: In series-parallel connection the output voltage increased as the mass of the load applied increased and the voltage was in the range of 114V-174V. The circuit arrangement for parallel is shown in the Fig.15, and the variation in the waveforms for all the three load conditions are shown in the Fig.15,16,17 . It was observed that the amount of output voltage received from the series-parallel connection was less compared to that of series connection and slightly high compared to that of parallel connection.

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