Theoretical Basis of Biomimetic Flexible Piezoelectric Acoustic Sensors for Future Customized Auditory Systems

Flexible piezoelectric sensors have been spotlighted as an essential human–machine interface (HMI) by obtaining high-quality data from omnipresent biomechanical inputs. Because human voice is the most intuitive bio-signal among them, flexible piezoelectric acoustic sensors (f-PAS) have a potential to shift the paradigm of HMI technologies. Despite the reported outstanding performance such as high sensitivity and speaker recognition accuracy, the theoretical investigation of f-PAS has been insufficient to realize future customized development, because sensing principles are fundamentally different from commercialized microphones. Here, a theoretical framework of self-powered f-PAS by using mechanical and electrical physics is introduced. First of all, the basic theory of f-PAS is compared with the auditory system of human cochlear. Based on the biomimetic trapezoidal shape, the resonant frequencies are analyzed with various structural and material conditions. In addition, the piezoelectricity of f-PAS is derived to predict the sensitivity and SNR prior to experiments. To investigate sensor properties under the medium condition that is similar to human ear, the acoustic responses depending on the states of matter are theoretically compared. Finally, the distance limit of f-PAS is studied with the correlations between piezoelectricity and sound pressure, which would provide novel strategies of functional material design for future applications of f-PAS.