Skin-Attachable Capacitive Vibration Sensor Array with Non-Contact Piezoelectric Diaphragm and Novel Star-Shaped Structure

Skin-attachable vibration sensors have garnered significant interest due to their vast potential in noninvasive mobile continuous healthcare, advanced communication, and human-robot interactive tools. However, existing wearable vibration sensors fall short of their potential due to unsatisfactory sensing performance, such as non-flat frequency response and low signal-to-noise ratio (SNR), and their susceptibility to external environmental factors, particularly physical contact and humidity. Herein, we present a new concept of employing a piezoelectric poly(vinylidene fluoride trifluoroethylene) (PVDF-TrFE) diaphragm as a non-contact power source for a capacitive vibration sensor. Additionally, we implement a unique spacer design that simultaneously allows for (i) in-plane air ventilation and (ii) maximizing the number of sensors in an array. The piezoelectric diaphragm successfully supplies operating power by generating deformation-induced charges; this creates an electric field between the two capacitive electrodes, allowing the capacitive sensor to operate effectively with a good linear dynamic range (0.1-2 g). Furthermore, our novel star-shaped spacer design enables extremely efficient, facile in-plane air ventilation and the arrangement of 64 sensors in an array. This enhances overall sensing performance by suppressing air damping and increasing the effective capacitive area. The latter is achieved by maximizing the number of sensors in the array and eliminating the need to perforate the diaphragm or backplate for through-hole air ventilation. Overall, our vibration sensor exhibits outstanding sensitivity (380 mV g^-1), excellent flat frequency response (80-5000 Hz), and an exceptional SNR of 45 dBA (A-weighted). Its substantial potential as a next-generation auditory electronic skin is demonstrated by its ability to recognize important voice and physiological information when attached to human skin.