Bio-Inspired Skin Wearable Hydrophobic Voice Recognition Acoustic Sensor Based On f-MWCNTs-BaTiO₃@PDMS Composite Conductive Network

Skin wearable piezoelectric nanogenerators (WPENGs) have recently drawn significant attention owing to their unique properties, like flexibility, sensitivity, and self-powered nature. Barium Titanate (BaTiO₃) is one of the eco-friendly piezoelectric ceramics. In recent days, BaTiO₃-based piezo-fillers use in WPENGs has attracted broad concern. Herein, bio-inspired microcracks, skin wearable, cost-effective, highly sensitive, and flexible PENGs were developed using functionalized multi-walled carbon nanotubes (<i>f</i>-MWCNTs) doped barium titanate (BaTiO₃)/poly(dimethylsiloxane) (PDMS) film. <i>f</i>-MWCNTs/BaTiO₃@PDMS was prepared by mixing of <i>f</i>-MWCNTs/BaTiO₃ and PDMS polymer solution by the overnight vacuum drying process. The sensor film was prepared by sandwiching <i>f</i>-MWCNTs/BaTiO₃@PDMS film between two PDMS films, followed by making electrical connections with two copper wires to form the WPENG. The as-prepared composite and PENG film were characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The composite PXRD data revealed the degree of crystallinity is 63%. FE-SEM and TEM results clearly showed that BaTiO₃in-situ coupled with <i>f</i>-MWCNTs with the addition of BaTiO₃with <i>f</i>-MWCNTs. The real-time application of the developed sensor was carried out by attaching the sensor to the throat to detect the minute oscillations produced during speaking. Monosyllabic, disyllabic, and polysyllabic words were spoken by the reader and their corresponding waveforms are recorded to show the ability of the sensor to clearly differentiate between these words. The sensor is also equally sensitive to male and female voices. A disyllabic word was spoken by a male and a female, and the recorded waveforms have a similar trend with different amplitudes. These results indicate the potential of the fabricated sensor to detect the human vocal cord vibrations efficiently, and paving a path to design a system for a wider range of applications in the next generation of noise detection and skin wearable sensors.