We developed a fast response and high-resolution plasmonic waveguide sensor for sensing environmental humidity by converting the optical signal in the visible light region. The sensor was designed as a layer-on-layer film structure in which the hydrophilic polymer of polyvinylpyrrolidone (PVP) film served as the waveguide layer and was dip-coated onto the plasmonic gold (Au) nanofilm for sensing the environmental humidity. The amount of the absorbed water molecules on the PVP layer could affect the refractive index and thickness of the PVP, leading to a shift of the surface plasmon resonance peak position of Au nanofilm at the different order modes of the waveguide. The theoretic calculations indicated that the optimal thickness of the waveguide layer on the Au nanofilm ranged from 550 to 650 nm. By adjusting the thickness of the PVP layer to 560 nm, the high-resolution optical signals were observed in the visible light region with the humidity shifts ranging from 11% to 85% relative humidity (RH). Our work details a successful attempt to design and prepare the plasmonic waveguide sensor with the lost-cost polymer as the sensing layer for real-time detection of environmental humidity.
An investigation of diffuser/nozzle micropumps is presented. Numerical simulations are done using CFD program
ANSYS/Flotran. The simulations show when the opening angel is small, the flow in the diffuser/nozzle is steady, the
mass flow is increasing with the adding opening angle. But when the opening angel continues increasing, the pressure
grads will be bigger than zero. It means that the static pressure is gradually going up along the diverging direction. The
fluid near the wall stops flowing because the velocity decreases rapidly and the dynamic pressure is not big enough to
overcome the increasing of the static pressure. Finally the fluid flows reversely from the backward position of higher
pressure area, this makes the separation flow of fluid, the diffuser is full of reverse fluid. And this results in the dropping
of mass flow at last. The simulations also show that the performance of diffuser with a round inlet is better than that with
a sharp inlet. The mass flow of micropumps with different opening angles, different inlets are measured. The
experimental results agree well with the simulations.