Bengt Hagström

Energy harvesting textiles for a rainy day: woven piezoelectrics based on melt-spun PVDF microfibres with a conducting core

Recent advances in ubiquitous low-power electronics call for the development of light-weight and flexible energy sources. The textile format is highly attractive for unobtrusive harvesting of energy from e.g., biomechanical movements. Here, we report the manufacture and characterisation of fully textile piezoelectric generators that can operate under wet conditions. We use a weaving loom to realise textile bands with yarns of melt-spun piezoelectric microfibres, that consist of a conducting core surrounded by β-phase poly(vinylidene fluoride) (PVDF), in the warp direction. The core-sheath constitution of the piezoelectric microfibres results in a—for electronic textiles—unique architecture. The inner electrode is fully shielded from the outer electrode (made up of conducting yarns that are integrated in the weft direction) which prevents shorting under wet conditions. As a result, and in contrast to other energy harvesting textiles, we are able to demonstrate piezoelectric fabrics that do not only continue to function when in contact with water, but show enhanced performance. The piezoelectric bands generate an output of several volts at strains below one percent. We show that integration into the shoulder strap of a laptop case permits the continuous generation of four microwatts of power during a brisk walk. This promising performance, combined with the fact that our solution uses scalable materials and well-established industrial manufacturing methods, opens up the possibility to develop wearable electronics that are powered by piezoelectric textiles.Wearable electronics: textile piezoelectric generators made washableCore-sheath design shielding the inner electrodes brings the washable function and boosts the performance of the piezoelectric generators.A collaborative team led by Christian Müller from Chalmers University of Technology, Sweden presents piezoelectric generator based on textiles made of core-sheath structured polymer microfibers. The black carbon/polyethylene based hidden electrodes are coated with piezoelectric polymer PVDF by a melt spinning process and then woven into textile bands with PA silver conducting yarns as the outer electrodes. Such a design guarantees the water proof function and even improves the performance with water due to reduced resistance. As a result, a 2.5 cm × 20 cm textile delivers an output pulse voltage of up to 8 V under wet conditions and continuous output power of 4 µW in a brisk walk.