A Compact Flexible Thermal Flow Sensor for Detecting Two-Dimensional Flow Vector

This paper presents a novel compact flexible thermal flow sensor on a polyimide (PI) substrate for detecting parameters of a two-dimensional (2-D) flow vector over a full range of 360°. Three or more thermal elements patterned as equally divided sectors of a round on a PI substrate compose the sensor probe, of which the three-element structure is the simplest design for 2-D flow detection. Each element works in constant temperature difference (CTD) mode, all of which form a common round CTD area while the heat power loss for each element is detected separately. The sensor probe contains thin-film Pt elements distributed in a round with a diameter of 2 mm fabricated on a flexible substrate using micromachining technique. Using a neural network to execute data fusion, the velocity and direction angle of the flow are deduced from the readouts of the sensor elements. Validities of the three-element and four-element designs were proven through experiments. Experimental results show that for the three-element sensor, the mean square error of the flow velocity reaches 0.65 m/s in the range of 3-30 m/s and the error of the flow direction reaches 2.69° in the range of 0°-360°. For four-element sensor in the same ranges of measurement, the mean square errors of the flow velocity and flow direction angle reach 0.59 m/s and 0.96°, respectively.