Surface-mountable VZO film-based piezoelectric sensors array in foil for underwater fluctuating pressure measurements

Wall fluctuating pressure in the boundary layer is critical for physical understanding of the surface flow and detection resolution optimization of the underwater vehicle. In this study, a flexible MEMS vanadium-doped zinc oxide (VZO) film piezoelectric pressure sensor array is developed for underwater applications. 2% vanadium-doped zinc oxide film achieves figure of merit of -54.5, far higher than the previous records of the contemporary thin films, indicating excellent receiving sensitivity. The sensors are designed and fabricated using a 4-mask VZO-on-SOI process. An array of 2×5 sensors is flexibly integrated on a polyimide foil and insulated by a parylene C waterproof cover. Calibrations in a plane wave tube are demonstrated. About 0.64± 0.06 mV/Pa pressure sensitivity at the frequency of 10 Hz to 2 kHz and the maximum nonlinearity of 0.3% from 0 to 50 Pa are achieved. The capabilities of the flexible sensors array in a real-time sensing situation on an underwater vehicle model are validated. The laminar, transition and turbulent flow at different positions of the vehicle model are detected successfully from the sensor outputs. The result shows that the amplitude and power energy of the fluctuation pressure at the transition case are higher than that of the laminar and turbulent flow. The presented sensors array with merits of low power, miniature size and low foot-print, offers a flexible and readily surface-mountable system, exhibiting promising potentials in underwater applications.