Harbor seal whisker inspired self-powered piezoelectric sensor for detecting the underwater flow angle of attack and velocity

Nowadays, there are high demands for robust, low-powered, miniaturized and light-weight sensors which can assist unmanned underwater vehicles (UUVs) in detecting hydrodynamic flow phenomena. Inspired by harbor seal whisker, this work presented a novel self-powered sensor for sensing the flow angle of attack and velocity, which provided a fine application foreground for UUVs' navigation. The sensor featured a pillar emulating the whisker interaction with water flow, and a d33 mode piezoelectric diaphragm imitating the nerve in cheek of the harbor seal. The pillar had a high aspect ratio (height/diameter) and an ellipse cross section whose ratio of the minor axis to the major axis was around 0.484. The polarization reorientation realized by interdigitated electrodes and the resonant property of the sensor were numerically calculated. Prototype fabrication was accomplished by utilizing stereolithography and microfabrication. Impedance and phase spectra of the sensor under different electrode configurations were tested to illustrate its dynamic property. By employing an oscillating sphere to emulate underwater perturbations, sensor output under the excitation of oscillatory flows was examined. Its capability of detecting distinct water flow angles of attack was verified by experimental results. The sensitivity of the sensor in sensing water flow velocity was as high as 1.445 V/(m/s).