A flexible sensing device based on a PVDF/MWCNT composite nanofiber array with an interdigital electrode

•Near-field electrospinning polyvinylidene fluoride nanofibers.•Polyvinylidene fluoride nanofibers mixed with multi-walled-carbon nanotubes.•Piezoelectric nanofiber units in parallel connection.•Nanofiber array on an interdigital electrode for flexible sensing device.

This study reports the electrospinning of polyvinylidene fluoride (PVDF) piezoelectric nanofiber array on an interdigital (IDT) electrode to fabricate a flexible sensing device. This sensing device can convert the mechanical energies of low-frequency ambient vibrations and impacts into electrical signals. A mixed solution of PVDF and multi-wall carbon nanotube (MWCNT) was filled in a metallic needle injector that was connected with a high voltage of 1200 V. When the PVDF droplet in the needle tip was subjected to a high electric field, an extremely fine PVDF fiber can be spun out. The electrospun fibers were collected orderly using an X–Y stage. In the electrospinning process, the fiber was polarized and transformed into the piezoelectric β-crystalline phase. PVDF/MWCNT crystallization as spherical composite structures can enhance the piezoelectric properties of PVDF fibers. Photolithography and etching processes were used to fabricate an IDT electrode with a gap of 100 μm on a flexible polyimide (PI) substrate. The PVDF fiber array was packaged with epoxy/PI film. The packaged PVDF fiber array was repolarized in a high electric field of approximately 7 V/μm to increase d33 mode conversion efficiency. The comparison of the analytical solution of the composite plate equation and the experimental results shows that the device can generate a peak voltage and current of 20.2 mV and 39 nA under 6 Hz vibration. In addition, at an impact testing at 15 Hz, the peak voltage of 24.4 mV with a current of 130 nA can be obtained.