Near field sequentially electrospun three-dimensional piezoelectric fibers arrays for self-powered sensors of human gesture recognition

Near-field electrospinning (NFES) is a newly-established technique by electrically charged a polymer solution to produce the site addressable one-dimensional (1D) fibers or two-dimensional (2D) aligned fibrous meshes. Nevertheless, the direct electrospinning of fibers into controllable is still a nascent technology. In this paper, a new integration of paper-based self-powered sensors (PSS) and three-dimensional (3D) architectures of NFES electrospun polyvinylidene fluoride (PVDF) micro/nano fibers (MNFs) is demonstrated in a direct-write and in-situ poled manner. Owing to the principle of piezoelectricity, the uni-poled dipole moment will be accumulated across the electrospun fibers and the output voltage and current could reach to 4 V and 100 nA respectively. Such charge transfer grounds the locally deposited fibers and renders them the preferential sites for the deposition of subsequent fibers. We apply NFES to directly write arbitrarily shaped 3D structures through consistent and spatially controlled fiber-by-fiber stacking of PVDF fibers. An element central to the success of this 3D electrospinning is the use of a printing paper placed on the grounded conductive plate and acting as a fiber collector. Once deposited on the paper, residual solvents from near-field electrospun fibers can infiltrate the paper substrate, enhancing the charge transfer between the deposited fibers and the ground plate via the fibrous network within the paper. Such charge transfer grounds the deposited fibers and turns them into locally fabricated electrical poles, which attract subsequent in-flight fibers to deposit in a self-aligned manner on top of each other. Finger striking and pushing motions are validated the open-circuit voltage and short-circuit current can be harvested during one finger striking motion is measured as similar to 1.2 V/60 nA. The proposed technique has the potential to advance the existing electrospinning technologies in constructing 3D structures for biomedical and wearable electronics.