Showing papers on "Energy harvesting published in 2002"

Adaptive piezoelectric energy harvesting circuit for wireless remote power supply

Abstract: This paper 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 results reveal that use of the adaptive DC-DC converter increases power transfer by over 400% as compared to when the DC-DC converter is not used.

Optimized piezoelectric energy harvesting circuit using step-down converter in discontinuous conduction mode

Abstract: An optimized method of harvesting vibrational energy with a piezoelectric element using a step-down DC-DC converter is presented. In this configuration, the converter regulates the power flow from the piezoelectric element to the desired electronic load. Analysis of the converter in discontinuous current conduction mode results in an expression for the duty cycle-power relationship. Using parameters of the mechanical system, the piezoelectric element, and the converter an optimal duty cycle can be determined where the harvested power is maximized for a given frequency of mechanical excitation. It is shown that, as the magnitude of the excitation increases, the optimal duty cycle becomes essentially constant, greatly simplifying the control of the step-down converter. The expression is validated with experimental data showing that the optimal duty cycle can be accurately determined and maximum energy harvesting attained. A circuit is proposed which implements this relationship, and experimental results show that the converter increases the harvested power by approximately 325%.

Micro-Electrostatic Vibration-to-Electricity Converters

Abstract: Advances in low power VLSI design, along with the potentially low duty cycle of wireless sensor nodes open up the possibility of powering small wireless computing devices from scavenged ambient power. Low level vibrations occurring in typical household, office, and manufacturing environments are considered as a possible power source for wireless sensor nodes. This work focuses on the design of electrostatic vibration-to-electricity converters using MEMS fabrications technology. Detailed models of three different design concepts are developed. The three design concepts are evaluated and compared based on simulations and practical considerations. A formal optimization of the preferred design concept is performed, and a final design is produced using the optimal design parameters. Simulations of the optimized design show that an output power density of 116 µW/cm

Low Power Energy Harvesting with Piezoelectric Generator

Abstract: Energy harvesting using piezoelectric material is not a new concept, but its generation capability has not been attractive for mass energy generation. For this reason, little research has been done on the topic. Recently, concepts such as wearable computers, as well as small portable electrical devices have re-ignited the study of piezoelectric energy harvesting. The theory behind cantilever type piezoelectric elements is well known, but transverse moving diaphragm elements, which can be used in pressure type energy generation have not been yet fully developed. Power generation in a diaphragm depends on several factors. Among them, the thickness of each layer, the poling direction, and stress distribution are most important. In this thesis, unimorph and triple-morph diaphragm structures with various poling configurations were considered. Their energy generation was calculated with varying thickness ratios and poling directions at various locations using piezoelectric constitutive equations. The results of this analysis are presented, along with experimental results that indicate that an optimal electrode pattern will result in maximum electrical energy generation.

Piezoelectric Eels For Energy Harvesting In the Ocean

Abstract: To perform long endurance military missions, small, unattended sensor packages must generate and harvest power from their surroundings. The experiments described extend our previous studies on the possibility of using piezoelectric polymers as power generation devices. Thin flexible piezoelectric membranes, or “eels,” are mounted aft of a rectangular bluff body and are excited by vortex shedding in the wake of the body. This flapping motion generates strain energy in the material that can be converted to electric power and stored in a battery to power small sensors and an acoustic modem. Here we report new experiments on the behavior of multiple eels, stacked vertically behind a single bluff body. Experiments show a range of flow regimes, ranging from poorly coupled motions, where three-dimensionality in the vortex shedding is important, to an optimally coupled state, where the membranes oscillate at the natural frequency of the undisturbed wake. The effects of membrane length are also studied. Figure 1: Vortex shedding from a leading bluff body causes deformation in a flexible membrane. The motion of the membrane is “locked in” when it is flapping at the shedding frequency of the leading body.

Ultra low-energy transceivers for wireless sensor networks

Abstract: Summary form only given. An untapped opportunity in the realm of wireless data lies in low data-rate (<10 kbit/sec) low-cost wireless transceivers, assembled into distributed networks of sensor and actuator nodes. This enables applications such as smart buildings and highways, environment monitoring, user interfaces, entertainment, factory automation, and robotics. While the aggregate system processes large amounts of data, individual nodes participate in a small fraction only (typical data rates <1 kbit/sec). These ubiquitous networks require that the individual nodes are tiny, easily integratable into the environment, and have negligible cost. Most importantly, the nodes must be self-contained in terms of energy via a one-time battery charge or a replenishable supply of energy scavenged from the environment. With the proposed size limitations, battery power alone does not suffice to ensure self-containment. Energy scavenging approaches can deliver up to 100 /spl mu/W. Achieving such ultra-low power-dissipation level requires reductions from the system architecture down to the circuit technology. The presentation presents a number of techniques to accomplish this, and outlines avenues for further research.