Design of PVDF sensor array for determining airflow direction and velocity.

An airflow sensor comprised of an array of piezoelectric polyvinylidene fluoride (PVDF) cantilever sensors mounted on a sensor ring is fabricated. A fluid-solid-electric coupling model based on the finite element method is presented to obtain the mathematical relationship between the normal airflow velocity and the response voltage. According to the response voltages from all pieces of PVDF cantilevers in the array, the values of the airflow direction and the velocity can be calculated. Furthermore, to find a suitable algorithm for error calculations and to achieve high accuracy, a method of reducing the flow angle error ( Eαn,cal¯ ) and flow velocity error ( Δvn,cal¯ ) by extracting Um of the effective cantilevers can be established. The experimental results show that the maximum value of Eαn,cal¯ is 1.2° (at 270° with 11.1 m/s) and the minimum value of Eαn,cal¯ is 0.3° (at 135° with 11.1 m/s) based on the PVDF sensor array with eight cantilevers. Meanwhile, the maximum value of Evn,cal¯ is 3% (at 315° with 11.1 m/s), and the minimum value of Evn,cal¯ is 1.5% (at 360° with 11.1 m/s). In addition, under 20 random airflow angles at 8 m/s, the error range in airflow velocity is from 1.27% to 2.67%, the error range in airflow angle is from 0.34° to 1.24°, and the response time is 20 ms. Therefore, the proposed design for an airflow sensory ring array can be used to determine the airflow direction and velocity, and the airflow sensor can be miniaturized as a bionic antennae, which is mounted on the skin of a piezoelectric autonomous mobile robot for sensing and escaping from an attack of the natural enemy.