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This paper reports a novel shear stress sensor utilizing flexible membrane and double SU-8 resist structures as a Fabry-Perot interferometer. Through UV lithography on thick resist, the surface roughness of the reflection surface was better than 7 nm (Ra value trough 10*10 μm2 area), suitable for optical application. A single mode optical fiber was employed for detecting the displacement of the floating element representing the shear stress force on the flexible membrane. A test has been successfully carried out and demonstrated the possibility of detection of a 10 nm displacement, representing a minimum detectable wall shear stress of 0.065 Pa from simulation, comparable to its counterparts with resolutions from 0.1-1 Pa.