Perceval Pondrom

Vibration-based energy harvesting with stacked piezoelectrets

Vibration-based energy harvesters with multi-layer piezoelectrets (ferroelectrets) are presented. Using a simple setup with nine layers and a seismic mass of 8 g, it is possible to generate a power up to 1.3 µW at 140 Hz with an input acceleration of 1g. With better coupling between seismic mass and piezoelectret, and thus reduced damping, the power output of a single-layer system is increased to 5 µW at 700 Hz. Simulations indicate that for such improved setups with 10-layer stacks, utilizing seismic masses of 80 g, power levels of 0.1 to 1 mW can be expected below 100 Hz.

Electret transducer for vibration-based energy harvesting

Vibration-based electret energy harvesters with soft cellular spacer rings are presented. These harvesters are closely related to recently introduced electret accelerometers; however, their development targets are partially differing. Various harvesters with seismic masses from 8 to 23 g and surface potentials in the 500 V regime were built and characterized and powers of up to 8 μW at about 2 kHz and an acceleration of 1 g were measured. An analytical model is presented which, for instance, allows the calculation of the frequency response of the power output into a given load resistance. Finally, experimental and calculated results are compared.

Energy harvesting with single-layer and stacked piezoelectret films

Vibration-based energy harvesting with single- or multiple-layer (stacked) piezoelectret films is discussed. First, a mechanical and an electrical model for this kind of energy harvesting is established and equations for the generated charge, current, voltage, and power are derived. In particular, the case where the electrical corner frequency equals the mechanical resonance frequency of the film stack combined with the seismic mass is of importance since harvesting at this frequency results in maximal generated power. Then, experimental results for harvesters with single layers and with stacks of piezoelectret films are presented. The data confirm the predicted dependence of the generated power on terminating resistance, frequency, seismic mass, acceleration, and number of film layers in the stack. If the stress on the piezoelectret layers, generated by the accelerated seismic mass, is larger than 3 kPa, a nonlinear increase of the generated power with stress is observed. The maximum power harvested with a single-layer piezoelectret is 18 μW for an acceleration of 9.81 m/s2 and for a seismic mass of 40 g. A three-layer harvester yields an increase of the maximum power close to a factor of √3.

Vibration-based energy harvesting with piezoelectrets having high d31 activity

Sandwiched fluoroethylene propylene films with charged, parallel-tunnel voids between the layers, which exhibit high d31 piezoelectric activity, were designed. Stripes of such piezoelectrets were exposed to mechanical stress in length direction by a seismic mass excited to vibrations. Due to the piezoelectricity of the films, a current in a terminating resistor is generated. The harvested power across the resistor amounts to about 0.2 mW for a seismic mass of 2 g and an acceleration of 1 g. In comparison with other piezoelectret or with poly(vinylidene fluoride) harvesters, the generated power referred to equal acceleration and force, is significantly larger.

Detectability and annoyance of warning sounds for electric vehicles

Electric or hybrid vehicles are very quiet at low speeds, which represents a very good opportunity to reduce traffic noise annoyance in cities. On the other hand, this may be very hazardous for vulnerable pedestrians (e.g. visually impaired people). The aim of the eVADER project is to propose solutions in order to add warning sounds to such cars, while fulfilling two contradictory goals : sounds should be detectable but should not contribute to traffic noise annoyance. Different perceptual experiments have been conducted : the first one evaluated the influence of various timbre parameters on sound detectability. It was shown that an electric vehicle equipped with one particular sound was as easily detected as a diesel one, while keeping a very low level. Then the influence of some timbre parameters (pitch and temporal modulation frequency) on the distance and speed as perceived by listeners was measured. Finally, a third experiment was devoted to the consequence on traffic noise annoyance of such warning sounds.

Stacked and folded piezoelectrets for vibration-based energy harvesting

ABSTRACT Vibration-based energy harvesting with piezoelectrets can be significantly improved by using multiple layers of these materials. In particular, folding or stacking of piezoelectrets or a combination of these methods results in increased power output of the energy harvesters. The possibilities of these procedures are explored, together with the effect of seismic mass, resonance frequency, and terminating resistance. It is found that with seismic masses of about 20 g and using radiation-crosslinked polypropylene (IXPP) as a piezoelectret, power outputs of up to 80 µW can be achieved for an acceleration of 1 g. Expected dependencies of generated power on frequency, folding and stacking parameters, in particular number of layers, and on seismic mass, are confirmed.

Compact electret energy harvester with high power output

Compact electret energy harvesters, based on a design recently introduced, are presented. Using electret surface potentials in the 400 V regime and a seismic mass of 10 g, it was possible to generate output power up to 0.6 mW at 36 Hz for an input acceleration of 1 g. Following the presentation of an analytical model allowing for the calculation of the power generated in a load resistance at the resonance frequency of the harvesters, experimental results are shown and compared to theoretical predictions. Finally, the performance of the electret harvesters is assessed using a figure of merit.