Flexible parylene-valved skin for adaptive flow control

This paper describes the first work of using wafer-sized flexible parylene-valved actuator skins (total thickness ~20 µm) for micro adaptive flow control. The check-valved actuator skins feature vent-through holes with tethered valve caps on the membrane to regulate pressure distribution across the skins. The skins were integrated onto MEMS wings and were tested in the low-speed wind tunnel for aerodynamic evaluation. The test results have shown very significant effects on the aerodynamic performances. Compare to the reference MEMS wings (no actuators), both the lift and thrust of the parylene check-valved wings were improved by more than 50%. This is the first experimental result to demonstrate that the application of MEMS actuator skins for flow control is very promising

A micromachined flow shear-stress sensor based on thermal transfer principles

Microhot-film shear-stress sensors have been developed by using surface micromachining techniques. The sensor consists of a suspended silicon-nitride diaphragm located on top of a vacuum-sealed cavity. A heating and heat-sensing element, made of polycrystalline silicon material, resides on top of the diaphragm. The underlying vacuum cavity greatly reduces conductive heat loss to the substrate and therefore increases the sensitivity of the sensor. Testing of the sensor has been conducted in a wind tunnel under three operation modes-constant current, constant voltage, and constant temperature. Under the constant-temperature mode, a typical shear-stress sensor exhibits a time constant of 72 μs

Micro thermal shear stress sensor with and without cavity underneath

Micro hot-film shear-stress sensors have been designed and fabricated by surface micromachining technology compatible with IC technology. A poly-silicon strip, 2 µm x 80 µm, is deposited on the top of a thin silicon nitride film and functions as the sensor element. By using sacrificial-layer technique, a cavity (vacuum chamber), 200 x 200 x 2 µm^3, is placed between the silicon nitride film and silicon substrate. This cavity significantly decreases the heat loss to the substrate. For comparison purposes, a sensor structure without a cavity has also been designed and fabricated on the same chip. Theoretical analyses for the two vertical structures with and without a cavity show that the former has a lower frequency response and higher sensitivity than the latter. When the sensor is operated in constant temperature mode, the cut-off frequencies can reach 130 k-Hz and 9 k-Hz respectively for the sensors without and with cavities

Prolonged mixed phase induced by high pressure in MnRuP

Hexagonally structured MnRuP was studied under high pressure up to 35 GPa from 5 to 300 K using synchrotron X-ray diffraction. We observed that a partial phase transition from hexagonal to orthorhombic symmetry started at 11 GPa. The new and denser orthorhombic phase coexisted with its parent phase for an unusually long pressure range, {\Delta}P ~ 50 GPa. We attribute this structural transformation to a magnetic origin, where a decisive criterion for the boundary of the mixed phase lays in the different distances between the Mn-Mn atoms. In addition, our theoretical study shows that the orthorhombic phase of MnRuP remains steady even at very high pressures up to ~ 250 GPa, when it should transform to a new tetragonal phase.Comment: 15 pages, 5 figures, supplementary materia

Analog VLSI system for active drag reduction

We describe an analog CMOS VLSI system that can process real-time signals from surface-mounted shear stress sensors to detect regions of high shear stress along a surface in an airflow. The outputs of the CMOS circuit are used to actuate micromachined flaps with the goal of reducing this high shear stress on the surface and thereby lowering the total drag. We have designed, fabricated, and tested parts of this system in a wind tunnel in laminar and turbulent flow regimes

A surface-micromachined shear stress imager

A new MEMS shear stress sensor imager has been developed and its capability of imaging surface shear stress distribution has been demonstrated. The imager consists of multi-rows of vacuum-insulated shear stress sensors with a 300 /spl mu/m pitch. This small spacing allows it to detect surface flow patterns that could not be directly measured before. The high frequency response (30 kHz) of the sensor under constant temperature bias mode also allows it to be used in high Reynolds number turbulent flow studies. The measurement results in a fully developed turbulent flow agree well with the numerical and experimental results previously published

Utilization of a magnetic field-driven microscopic motion for piezoelectric energy harvesting.

In spite of the recent advances in the development of high performing piezoelectric materials, their applications are typically limited to the direct conversion of mechanical impact energy to electrical energy, potentially risking mechanical failures. In this study, we developed piezoelectric poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) nanofibers integrated with SiO2-shelled Fe3O4 magnetic nanoparticles, to utilize magnetic energy to reliably drive the piezoelectric effect. Specifically, we show that the shape of the magnetic nanoparticles exerts a significant effect on the efficiency of the magneto-mechano-electrical energy conversion as magnetic nanorods exhibit approximately 70% enhancement in electric field generation under cyclic magnetic fields as compared to nanospheres. Under an alternating magnetic field of 200 mT, the magnetic nanorod-piezoelectric nanofiber composite generated a peak-to-peak voltage of approximately 30 mVp-p with a superior durability without any performance degradation after over 1 million cycles. This study demonstrates the potential of magnetic-field responsive, piezoelectric-based materials in energy harvesting applications from non-mechanical energy sources