15-02-2009, 12:04 PM
This seminars describes an approach to harvesting electrical energy from a mechanically excited piezoelectric element. A vibrating piezoelectric device differs from a typical electrical power source in that it has a capacitive rather than inductive source impedance, and may be driven by mechanical vibrations of varying amplitude.
An analytical expression for the optimal power flow from a rectified piezoelectric device is derived, and an energy harvesting circuit is proposed which can achieve this optimal power flow. The harvesting circuit consists of an ac-dc rectifier with an output capacitor, an electrochemical battery, and a switch-mode dc-dc converter that controls the energy flow into the battery. An adaptive control technique for the dc-dc converter is used to continuously implement the optimal power transfer theory and maximize the power stored by the battery.
Experimental result reveal that the use of the adaptive dc-dc converter increases power transfer by over 400% as compared to when the dc-dc converter is not used...
Piezoelectric materials can be used as a means of transforming ambient vibrations into electrical energy that can 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. However, the energy produced by these materials is in many cases far too small to directly power an electrical device. Therefore, much of the research into power harvesting has focused on methods of accumulating the energy until a sufficient amount is present, allowing the intended electronics to be powered. In a recent study the ability to take the energy generated through the vibration of a piezoelectric material was shown to be capable of recharging a discharged nickel metal hydride battery. piezoelectric devices will be investigated and experimentally tested to determine each of their abilities to transform ambient vibration into electrical energy and their capability to recharge a discharged battery. The three types of piezoelectric devices tested are; the commonly used monolithic piezoceramic material lead zirconate titanate (PZT), the bimorph Quick Pack (QP) actuator and Macro Fiber Composite (MFC). The experimental results estimate the efficiency of the three devices tested and identify the feasibility of their use in real world applications. Various different capacity batteries are recharged using each device, to determine the charge time and maximum capacity battery that can be charged..
The increasing desire for completely self-powered electronics has caused the amount of research into power harvesting devices to become progressively larger over the last decade. With the advances being made in wireless technology and low power electronics, sensor are being developed that can be placed almost anywhere. However, because these sensors are wireless, they require their own power supply which in most cases is the conventional electrochemical battery. Once these finite power supplies are extinguished of their power, the sensor must be obtained and the battery replaced. The task of replacing the battery is tedious and can become very expensive when the sensor is placed in a remote location. These issues can be potentially alleviated through the use of power harvesting devices. The goal of a power harvesting device is to capture the normally lost energy surrounding a system and convert it into usable energy for the electrical device to consume. By utilizing these untapped energy sources electronics that do not depend on finite power supplies, such as the battery, can be developed. One source of typically lost energy is the ambient vibrations present around most machines and biological systems. This source of energy is ideal for the use of piezoelectric materials, which have the ability to convert mechanical strain energy into electrical energy and vice versa.
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