Design and Acoustic Performance Study of Capacitive Acoustic Emission Sensors Based on MEMS Technology

A capacitive microelectromechanical system (MEMS) acoustic emission (AE) sensor was designed to address the growing demand for structural health monitoring (SHM) in miniature precision machinery. The response characteristics of the sensor in solid materials were investigated through finite element method (FEM) simulations and theoretical analysis, focusing on the characteristic frequency, frequency domain, and transient responses. Simulations, conducted at an operating voltage of 18 V, revealed a central frequency of approximately 3 MHz, with excellent agreement between theoretical and simulated results. Transient response analysis, influenced by boundary conditions, indicated a central frequency slightly above 3 MHz. The sensor was fabricated using wafer bonding technology. Packaging of the sensor is done by ceramic half-packaging. Performance testing was conducted by applying an 18 V dc bias and exciting the sensor with signals from a piezoelectric actuator, including continuous sine waves, five-cycle sine waves, and five-peak waves. Frequency spectrum analysis showed a central frequency of 2.8 MHz, slightly lower than the simulation due to manufacturing variations and the combined effects of multiple MEMS sensor cells. The sensor sensitivity was characterized using the system response function, which revealed maximum sensitivity at 2.8 MHz under a 10 V excitation signal at 2.7 MHz, corresponding to a system response function of −30.8 dB; the corresponding signal-to-noise ratio (SNR) reaches as high as 35.7 dB. The MEMS sensor effectively responds to both sine and five-peak wave signals. These results validate excellent performance of the sensor in solid materials and its capability to accurately detect both sine and five-peak wave signals.