Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    High-k dielectric screen-printed inks for mechanical energy harvesting devices
    ( 2022)
    Leese, H.S.
    ;
    Tejkl, M.
    ;
    Vilar, L.
    ;
    Georgi, L.
    ;
    Yau, H.C.
    ;
    Rubio, N.
    ;
    Reixach, E.
    ;
    Buk, J.
    ;
    Jiang, Q.
    ;
    Bismarck, A.
    ;
    Hahn, Robert
    ;
    Shaffer, M.S.P.
    There are a range of promising applications for devices that can convert mechanical energy from their local environment into useful electrical energy. Here, mechanical energy harvesting devices have been developed to scavenge low-frequency energy from regular biomotion such as joint movement and heel strike. Specifically, these harvesters exploit novel printed nanocomposite dielectric inks in combination with commercially available conductive elastomers to develop a low cost, high performance embodiment of a variable capacitance mechanism device. The filler of the nanocomposite dielectric ink, consists of high-k dielectric nanoparticles (barium titanate and strontium doped barium titanate) functionalised with poly(methyl methacrylate) to improve the interface with the epoxy matrix. Characterisation by thermogravimetric analysis coupled to mass spectrometry and X-ray photoelectron spectroscopy confirmed the successful covalent grafting of up to ca. 16 wt% poly(methyl methacrylate) onto the dielectric nanoparticle surfaces, with a thickness of approximately 14 nm, measured by transmission electron microscopy. The dielectric inks were screen printed onto copper-polyimide foils, resulting in large area and flexible five to twenty-micron thick films with dielectric constants up to 45. Nanoparticle polymer functionalisation improved the homogeneity and stability of the inks. Using these screen-printed dielectrics with the commercial conductive elastomer, the mechanical energy harvester prototype demonstrated high mechanical cycling stability and low leakage current. It provided a promising power density of 160 μW cm-3, at low frequency (0.5 Hz), over a 1000 cycles, making the device suitable for wearable applications. This type of harvester has two advantages over the state of the art: it is mechanically flexible for integration into wearables and can be produced at low cost with printing methods. This journal is