بهره برداری از اثرات لاستیکی برای کاهش رانش، در یک سنسور جریان هوای تمام پلیمری

This paper presents a vibration amplitude measurement method that greatly reduces the effects of baseline resistance drift in an all-polymer piezoresistive flow sensor or microtuft. The sensor fabrication is based on flexible printed circuit board (flex-PCB) technology to enable the potential for low-cost and scalable manufacture. Drift reduction is accomplished by discriminating the flow-induced vibration (‘flutter’) amplitude of the microtuft-based sensor as a function of flow velocity. Flutter peak-to-peak amplitude is measured using a microcontroller-based custom readout circuit. The fabricated sensor with the readout circuitry demonstrated a drift error of 2.8 mV/h, which corresponds to a flow-referenced drift error of 0.2 m/s of wind velocity per hour. The sensor has a sensitivity of 14.5 mV/(m/s) with less than 1% non-linearity over the velocity range of 5–16 m/s. The proposed vibration amplitude measurement method is also applied to a sensor array with a modified structure and a reduced dimension, which demonstrated a sensitivity of 13.2 mV/(m/s) with a flow-referenced drift error of 0.03 m/s of wind velocity per hour.

Flow sensors are of great interest to applications such as process control, metrology [1] and flight control involving unmanned aerial vehicles (UAVs) [2]. Among different types of flow sensors, bio-mimetic flow sensors mimicking fish hairs and cricket filiform hairs are the subject of much research. Typically, the nature-inspired bio-mimetic flow sensor has a three-dimensional (3D) out-of-plane cantilever with a sensing element to detect the air flow around it. Advances in microelectronics and micromachining technologies enable the fabrication of MEMS bio-mimetic flow sensors with good performance, based on silicon and/or polymer micromachining technologies. A bio-mimetic silicon-based capacitive flow sensor array with high-aspect ratio SU-8 microtufts was recently reported and demonstrated sensitivities of the order of 1 mm/s [3]. A silicon-based piezoresistive air flow sensor with SU-8 cilia has also been reported [4]. Although these approaches demonstrate good sensitivity, they require relatively complex fabrication sequences. Further, being silicon-based, it is challenging to cover large areas of vehicle wings with these flow sensors in a cost-effective manner. Polymer-based devices may overcome these challenges, at the expense of specific performance, and further exhibit good flexibility and scalability. These features are extremely important in applications requiring distributed sensor arrays in large and uneven surfaces such as UAV applications [2]. We have already demonstrated a 3D out-of-plane micromachined flexible piezoresistive all-polymer flow sensor array based on low-cost flexible-PCB technologies [5]. The piezoresistive all-polymer sensor provided a large resistance change without complex sensing circuitry for compensation and amplification of the sensor output. However, a significant resistance drift in the sensor output was observed [5], potentially limiting the applicability of the sensor. In this paper, we propose a reduced-drift sensor measurement method that exploits aeroelastic ‘flutter’ effects [6] and [7] and demonstrate its application to a flex-PCB-based all-polymer flow sensor. The sensor comprises a 3D out-of-plane polymer cantilever member that can protrude into an embedding flow, and a piezoresistive readout element in the polymer member. Positioning the flexible polymer sensor in a flow results in a static deflection of the sensor, as well as a vibratory sensor flutter caused by aeroelastic effects. The amplitude of the flutter depends on the surrounding flow velocity and is empirically characterized. Microcontroller-based circuitry is used to extract the peak-to-peak vibration amplitude from the sensor output. Since the sensor output is now primarily dependent on the vibration-induced resistance change, as opposed to static deflection, the sensor output is relatively insensitive to DC resistance drift.

This paper proposes a peak-to-peak vibration amplitude measurement method for wind velocity sensing as a baseline resistance drift-reduction method. The proposed method exploits aeroelastic flutter-based flow-induced vibration and has been validated by the wind tunnel test of a flexible-PCB-based all-polymer piezoresistive air flow sensor. The measured characteristics demonstrate a significant reduction of output drift using the proposed measurement method, when compared to that of the conventional direct measurement method. In addition, sensors with different geometries were tested with the proposed measurement method as shown in Table 1. The proposed measurement method is promising since it significantly reduces the drift caused by the intrinsic property of the materials as well as environmental changes.