A Real-Time Tilt Sensor Based on a Piezoelectric MEMS Resonant Accelerometer Through Demodulated Amplitude Detection

This work presents a dual-axis differential static and dynamic tilt sensor using a thin-film piezoelectric on substrate (TPoS) resonant accelerometer with demodulated amplitude detection for a 336x improvement in normalized sensitivity and about 1.7x enhancement in resolution compared to typical frequency change detection. A commercial Lock-in amplifier with a Phase Locked Loop (PLL) was utilized to operate the resonant accelerometer in a closed-loop as an oscillator and the demodulated amplitude (A) was used to measure the tilt angle. The device has a resonant frequency of around 960 kHz for all four constituent resonators and is tilted at 60° in a clockwise and anticlockwise direction. The amplitude and frequency changes are induced by stiffness modulation (through stress/strain) due to tilting. A sensitivity of 357 ppm/deg in the x-axis (with cross-axis sensitivity < 5%), 324 ppm/deg in the y-axis (with cross-axis sensitivity of < 4%) and a resolution of 0.22° (X1 resonator) were measured through demodulated amplitude detection under a vacuum condition of <1 μTorr. This enhanced performance opens promising avenues for applications requiring high-precision tilt sensing in both static and dynamic environments. These types of resonant accelerometers are attractive candidates in fields where robustness and precision are required.