In the present work we explore some aspects of energy harvesting from unsteady, turbulent fluid flow using piezoelectric generators. Turbulent flows exhibit a large degree of coherence in their spatial and temporal scales, which provides a unique opportunity for energy harvesting. The voltage generated by short, flexible piezoelectric cantilever beams placed inside turbulent boundary layers and wakes of circular cylinders at high Reynolds numbers is investigated. Matching the fluid flow’s predominant frequency with the natural frequency of the piezoelectric generator appears to maximize the piezoelectric output voltage. This voltage is also dependent on the generator’s location inside the flow field. A three-way coupled interaction simulation that takes into account the aerodynamics, structural vibration, and electrical response of the piezoelectric generator has been developed. The simulation results agree reasonably well with the experimental data paving the way of using such a tool to estimate the performance of different energy harvesting devices within unsteady flow fields.

The available power in a flowing fluid is proportional to the cube of its velocity, and this feature indicates the potential for generating substantial electrical energy by exploiting the direct piezoelectric effect. The present work is an experimental investigation of a self-excited piezoelectric energy harvester subjected to a uniform and steady flow. The harvester consists of a cylinder attached to the free end of a cantilevered beam, which is partially covered by piezoelectric patches. Due to fluid–structure interaction phenomena, the cylinder is subjected to oscillatory forces, and the beam is deflected accordingly, causing the piezoelectric elements to strain and thus develop electric charge. The harvester was tested in a wind tunnel and it produced approximately 0.1 mW of non-rectified electrical power at a flow speed of 1.192 m s−1. The aeroelectromechanical efficiency at resonance was calculated to be 0.72%, while the power per device volume was 23.6 mW m−3 and the power per piezoelectric volume was 233 W m−3. Strain measurements were obtained during the tests and were used to predict the voltage output by employing a distributed parameter model. The effect of non-rigid bonding on strain transfer was also investigated. While the rigid bonding assumption caused a significant (>60%) overestimation of the measured power, a non-rigid bonding model gave a better agreement (<10% error).

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Wireless sensors and sensor networks are beginning to be used to monitor structures. In general, the longevity, and hence the efficacy, of these sensors are severely limited by their stored power. The ability to convert abundant ambient energy into electric power would eliminate the problem of drained electrical supply, and would allow indefinite monitoring. This paper focuses on vibration in civil engineering structures as a source of ambient energy; the key question is can sufficient energy be produced from vibrations? Earthquake, wind and traffic loads are used as realistic sources of vibration. The theoretical maximum energy levels that can be extracted from these dynamic loads are computed. The same dynamic loads are applied to a piezoelectric generator; the energy is measured experimentally and computed using a mathematical model. The collected energy levels are compared to the energy requirements of various electronic subsystems in a wireless sensor. For a 5 cm 3 sensor node (the volume of a typical concrete stone), it is found that only extreme events such as earthquakes can provide sufficient energy to power wireless sensors consisting of modern electronic chips. The results show that the optimal generated electrical power increases approximately linearly with increasing sensor mass. With current technology, it would be possible to self-power a sensor node with a mass between 100 and 1000 g for a bridge under traffic load. Lowering the energy consumption of electronic components is an ongoing research effort. It is likely that, as electronics becomes more efficient in the future, it will be possible to power a wireless sensor node by harvesting vibrations from a volume generator smaller than 5 cm 3 .

This article presents an equivalent circuit model for a piezoelectric generator which can include any number of vibrational modes. First the electromechanical equations are formulated using an assumed mode (for example, the Rayleigh-Ritz method), the mechanical equations are then decoupled by the standard eigenvector approach. A set of single degree of freedom equations are thus produced. The electromechanical coupling terms are modeled in the equivalent circuit using an ideal transformer, or a set of current-and voltage-dependent sources. To validate the equivalent circuit model, the results show excellent agreement with published analytical solutions for the first three vibration modes of a cantilever unimorph generator. The main advantage of the new method is that it can be used to simulate any circuit topology, for which there is no analytical solution, using a standard electronic simulation program. To demonstrate this, the analysis and design of a more complicated diode bridge circuit is presented.