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Vibrational energy harvesters of air-spaced cantilever design, utilizing ferroelectrets as the electroactive element, are a very recent concept. Such systems, based on the d₃₁ piezoelectric effect are further studied with harvesters of improved design, partially implemented by additive manufacturing. The focus of the present work is on the dependence of frequency response, resonance frequency, and generated power on the distance of the ferroelectret from the cantilever beam and on the pre-stressing of the ferroelectret. Experimental data are compared with both analytical and numerical evaluations. It is found that the power generated can be increased by one to two orders of magnitude by proper choice of distance. A suitable pre-stress yields another increase of power by a factor of 2 to 10 and linearizes the response.Thus, normalized output powers more than 1000μW referred to an acceleration of 9.81 ms² and a seismic mass of 3.5 g, can be achieved, which significantly exceeds previous results of cantilever-based energy harvesters.

Keywords: air-spaced cantilever, energy harvesting, ferroelectret, piezoelectret, piezoelectric polymers