Molecular Ferroelectrics for Highly Sensitive Detection Toward Low-Frequency Sound Recognition

Human hearing cannot sensitively detect sounds below 100 Hz, which can affect the physical well-being and lead to dizziness, headaches, and nausea. Piezoelectric acoustic sensors still lack sensitivity to low-frequency sounds owing to the low piezoelectric coefficient or high elastic modulus of materials. The low elastic modulus and substantial piezoelectric coefficient of molecular ferroelectric materials make them excellent candidates for acoustic sensors. In this study, the molecular ferroelectric, [(CH₃)₃NCH₂Cl]CdCl₃, is used as a piezoelectric active layer in the construction of a piezoelectric acoustic sensor for low-frequency sound detection. The sensor exhibits high sensitivity (47.43 mV Pa^-1 cm^-2) at 87 Hz, with an excellent level of frequency resolution (up to 0.1 Hz). This facilitates the accurate discrimination and detection of low-frequency sounds, which is suitable for noise detection applications. The sensor differentiates between various musical instruments and heartbeats, and recognizes audio signals. This study highlights the potential of molecular ferroelectric materials in piezoelectric acoustic device applications, including noise detection, health monitoring, and human-computer interactions.