Broad bandwidth vibration energy harvester based on thermally stable wavy fluorinated ethylene propylene electret films with negative charges

Abstract

Wavy fluorinated ethylene propylene (FEP) electret films with negative charges were prepared by a patterning method followed by a corona charging process. The thermal stability of these films was characterized by the surface potential decay with annealing time at elevated temperatures. The results show that thermally stable electret films can be made by corona charging followed by pre-aging treatment. Vibration energy harvesters having a very simple sandwich structure, consisting of a central wavy FEP electret film and two outside metal plates, were designed and their performance, including the resonance frequency, output power, half power bandwidth, and device stability, was investigated. These harvesters show a broad bandwidth as well as high output power. Their performance can be further improved by using a wavy-shaped counter electrode. For an energy harvester with an area of 4 cm2 and a seismic mass of 80 g, the output power referred to 1 g (g is the gravity of the earth), the resonance frequency, and the 3 dB bandwidth are 1.85 mW, 90 Hz, and 24 Hz, respectively. The output power is sufficient to power some electronic devices. Such devices may be embedded in shoe soles, carpets or seat cushions where the flexibility is required and large force is available.

Tuneable resonance frequency vibrational energy harvester with electret‐embedded variable capacitor

“…However, the minimum resonance frequency obtained from a harvester with a smaller capacitance is almost double as high as the theoretically predicted minimum value of 18 Hz, which is partly due to larger initial stress of the film in experiment than assumed. In addition, the electrostatic force between the negatively charged wavy FEP film and the counter arc‐shaped electrode may increase the total stiffness of the harvester, thus causes the increase of measured resonance frequency [35]. Both the ABAQUS finite element analysis and experiment demonstrate that the resonance frequency of the harvester investigated in this study can be adjusted by controlling the stress on the device and the resonance frequencies can be tuned in a relatively broad range.…”

“…Optical images of all three film sample types together with the respective template parameters are shown in Figure 4b. Details of the specific fabrication process of wavy FEP films can be found in [35,36] and are omitted here. Figure 4c shows the optical image of the assembled harvester based on the design shown in Figure 1b upper surface of the wavy films.…”

“…In general, P out is normalized to gravitational acceleration g, and normalized output power P n is given by [35]…”

“…Optical images of all three film sample types together with the respective template parameters are shown in Figure 4b. Details of the specific fabrication process of wavy FEP films can be found in [35,36] and are omitted here.…”

“…In the following, the abbreviation for an “effective” piezoelectric coefficient, d 33,eff , is given by [34]: where σ and denote, respectively, the generated charge density and applied pressure on the harvester. When connecting an optimal load resistance [33], the maximum output power harvested at resonance frequency , can be expressed as [35] …”