An All Polymer Air-Flow Sensor Array using a Piezoresistive Composite Elastomer

This paper presents an out-of-plane micromachined piezoresistive flow sensor array based on laser micromachining of polymer films, microstencil printing, and stress-engineered curvature. The developed process is suitable for low cost, large-area sensor array fabrication, and can leverage traditional flex-circuit fabrication. Each device is composed of an out-of-plane curved microtuft formed from laser-machined Kapton^reg polyimide and PECVD-deposited SiO₂, and a conductive elastomer piezoresistor with a measured gage factor of 7.3 located at the base of the microtuft. The fabrication and performance of a prototype array and a fabrication sequence for large-area arrays on flexible substrates is demonstrated, for flow field mapping across an airfoil. The fabrication sequence also enables backside interconnects without adding further process complexity, which facilitates integration and enables the sensing of airflow with minimum interference due to the sensing circuitry. Individual microtufts as small as 1.5 mm in length and 0.4 mm in width, with 70 m wide piezoresistor lines have been fabricated. Wind tunnel testing demonstrated sensitivities as high as 66 Omega/(m/s).