[en] Pyroelectric materials have recently received attention for harvesting waste heat owing to their potential to convert temperature fluctuations into useful electrical energy. One of the main challenges in designing pyroelectric energy harvesters is to provide a means to induce a temporal heat variation in a pyroelectric material autonomously from a steady heat source. To address this issue, we propose a new form of wind-driven pyroelectric energy harvester, in which a propeller is set in rotational motion by an incoming wind stream. The speed of the propeller’s shaft is reduced by a gearbox to drive a slider-crank mechanism, in which a pyroelectric material is placed on the slider. Thermal cycling is obtained as the reciprocating slider moves the pyroelectric material across alternative hot and cold zones created by a stationary heat lamp and ambient temperature, respectively. The open-circuit voltage and closed-circuit current are investigated in the time domain at various wind speeds. The device was experimentally tested under wind speeds ranging from 1.1 to 1.6 m s⁻¹ and charged an external 100 nF capacitor through a signal conditioning circuit to demonstrate its effectiveness for energy harvesting. Unlike conventional wind turbines, the energy harvested by the pyroelectric material is decoupled from the wind flow and no mechanical power is drawn from the transmission; hence the system can operate at low wind speeds (<2 m s⁻¹). (paper)

[en] Highlights: • Theoretical and an experimental investigation of a novel inertial triboelectric sensor. • Electromechanical model to study dynamic behaviour. • Design optimization model using particle swarm optimization to find the optimum parameters. This paper aims to provide a better understanding of how the triboelectric effect could be utilized in the context of an inertial motion sensor. The device consists of a base-excited fixed-fixed beam carrying a middle mass that is brought into cyclic contact/separation with a dielectric mounted on the base. A theoretical model was developed encompassing both the electrical and mechanical phenomena. A low-cost device was designed and fabricated to experimentally validate the model. A parametric study was performed to distinguish the effects of the various device parameters. A hybrid Particle Swarm Optimization (PSO) and direct search technique was utilized for device improvement on some of the physical device parameters. The device was experimentally tested at input accelerations ranging from 0.4 g to 1.2 g and an objective function was formulated in terms of the output voltage density, i.e. peak output voltage per unit volume at different excitation frequencies for various design parameters. The usefulness and validity of the optimization techniques utilized was proved highlighting their possible usage in other applications based on the triboelectric effect.

[en] Highlights: • Manufacture methods and the pore characteristics were discussed. • Properties in terms of mechanical, electrical and harvesting performance were described and compared. • Modelling approaches for microstructural design or predicting vibrational and frequency dependent response were examined. • Perspectives for future application on pyroelectric energy harvester were provided. -- Abstract: This paper provides an overview of ferroelectret materials for energy harvesting applications. These materials take the form of a cellular compliant polymer with polarised pores that provide a piezoelectric response to generate electrical energy as a result of an applied strain or surrounding vibration. The manufacturing processes used to create ferroelectret polymer structures for energy harvesting are discussed, along with the range of microstructural features and pore sizes that are formed. Their important mechanical, electrical and harvesting performance are then described and compared. Modelling approaches for microstructural design or for predicting the vibrational and frequency dependent response are examined. Finally, conclusions and future perspectives for ferroelectret materials for energy harvesting applications are provided.