Research On Micro Flexible Thermal Shear Stress Sensor Array With Floating Structures

The control of the flow field has extremely important applications and has become the hotspot of research. Efficient flow control system not only can save billions of dollars on the fuel consumption of ground, air and sea transport each year, but also make the industry production process more economical, environmentally friendly and more competitive. We can get the characteristics of flow field by measuring the shear stress distribution of the wall. The control and application of the flow can be achieved by transmitting the signal of shear stress to the micro-actuators. Some measurements of non-planar surface are very important, so the flexible shear stress array that can be bent get more and more attention.The thermal shear stress sensors using MEMS technology are easy to process and integrate. This paper presents a micro thermal shear stress sensor array with double hot line resistors in close proximity using flexible MEMS technique. Prepared on flexible polyimide substrate, the sensor array can be used to detect direction and magnitude of shear stress on the complicated surface.(1) The principle of double hot-line structure of micro-thermal shear stress sensor has been analyzed and simulated using COMSOL multi-physics software. We did simulations of micro thermal shear stress sensor which include the thermal field and the coupling of flow and thermal field to understand the heat distribution of the sensor when the sensor under constant current and the influence of flow velocity on the heat distribution. The critical parameters of simulation including: the current, the minimum line width, the TCR of the thermal resistance and the velocity of the fluid.(2) The thermal shear stress sensor array with a floating structure has been produced with two different processes. The sensor was 30μm wide, 800μm long and 2μm thick and using nickel as the thermal resistance. The photoresist was used as a sacrificial layer to release the floating structure. Designed the flexible substrate to test the shear stress of non-planar surface object; Design the floating structure to reduce the thermal lose from substrate; Design the double hot-line structure to test the speed and direction of the flow field.(3) The traditional release process of the flexible devices, which using the sacrificial layer, is very complex, and has the possibility of causing damage to the device. Polyimide is easily to peel off from PDMS after socked in alcohol, so we chose it in our release process. The experiments of both traditional and our new method processes were carried out and the process parameters were obtained. The advantage and disadvantage of both methods have been compared.(4)The sensor's temperature coefficient of resistance (TCR) and response frequency have been tested. The temperature coefficient of resistance of the sensor is 0.49%/℃. The response frequency is greater than 5KHz. The time constant is less than 200μs. Experimental results show that the process route and parameter structure of the sensor are reasonable, can achieve the required shear stress sensor array. The control system solution of the sensor has been designed using ARM.