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Abstract: In this paper, we introduce the use of thin mesoporous mixed cellulose ester (polymer) membranes as the enabling element of miniature, motionless gas pumps. The pores within these membranes serve as channels that constrain gas molecules to the free molecular or transitional gas flow regimes. A temperature gradient across the membranes causes a transpiration based gas flow from the cold side to the hot side; this type of flow is the basis of Knudsen pumps. Gas flow characteristics and vacuum generation capabilities of polymer membranes with three different pore-sizes are reported. In this group, membranes with 25nm pore-size provide superior functionality. For an input power of 1.4W/cm2, Knudsen pump test structures based on this membrane material provide a typical gas flow rate of ≈0.93sccm/cm2 in the absence of pressure load. The transient pressure response is used to quantify various non-idealities. Experiments suggest that these polymer membranes are relatively defect-free as compared to bulk microporous ceramics that were previously evaluated for similar applications. In longevity tests performed to date, a polymer pump has operated continuously for ≈6000h without significant deterioration in its performance. [Copyright &y& Elsevier]

Abstract: This paper describes an investigation of microfluidic actuation of doublet patterns in samples of water on blank substrates, using singular and arrayed microfabricated thermal probes. A doublet is a two-dimensional flow pattern consisting of adjacent, opposing vortices with linear streamlines between them. In this work, each probe consists of a polyimide thin film cantilever with a metal heater near the tip which generates a temperature gradient up to 1°C/μm along its length. The probes are 360μm long, 42–120μm wide, and 3.5μm thick, and the tips are typically <1mm away from the liquid surface. The velocity of the doublet flow can be controlled by adjusting the temperature of the heat source or by controlling the gap or attack angle between the heat source and the liquid surface. Linear flow velocities exceeding 5mm/s and rotational velocities exceeding 1200rpm are reported. [Copyright &y& Elsevier]

Abstract: This paper presents a preliminary exploration of high-speed contact mode performed with a polyimide probe. The probe is batch micromachined by a lithographic manufacturing process. It offers a spring constant of <0.1N/m, a resonance frequency of about 50kHz, and a tip diameter of 50–100nm. The probe is particularly suitable for scanning soft specimens such as biological and polymeric samples. Topographical contact mode imaging at high scanning rates of 48Hz (1.47mm/s) has been demonstrated, detecting features <100nm over a 15μm scan, yielding >7 bit resolution at 48Hz. Scanning rates of 16Hz (0.5mm/s) have been demonstrated for lateral force imaging with spatial resolution of 100nm over a 15μm scan, which translates into >7 bit resolution at 16Hz. These results suggest that the probe can be used in high throughput applications. [Copyright &y& Elsevier]

Abstract Miniaturized magnetron gauges are necessary for monitoring vacuum level in miniature vacuum chambers. This paper addresses the challenges of designing the magnetron cavity and configuring the electric and magnetic fields within it while meeting the contradictory constraints of small size and high vacuum level that make electron confinement and accumulation difficult. The resulting gauge has an internal volume of 0.3 cm3 and is designed for and fabricated by advanced 3D printing – including direct metal laser sintering of 316 L stainless steel. Additionally, it is capable of directly attaching to a standard vacuum electrical feedthrough. A particle tracing simulation is used to assess the electron confinement for a range of operating conditions. Experimental characterization shows that the operating pressures extend from 10 nTorr (1.33 μPa) to 1 mTorr (133 mPa). The gauge current is repeatable over the characterized pressures at various values of supply source voltage, V S , from −1000 V to −2500 V, and ranges from ≈1 nA to ≈100 μA over these pressures and voltages. The effects of V S and pressure are examined and compared to prior work. This gauge is at least 30× smaller than commercially available magnetron gauges (e.g., a typical inverted magnetron transducer has an internal volume of 15 cm3). Highlights • A 3D-Printed Miniature Magnetron Gauge for Ultra-High Vacuum Environments. • A 0.3 cm3 magnetron gauge is presented, ∼30× smaller than commercial gauges. • 3D-printing of gauge from 316 L stainless steel facilitates miniaturization. • The gauge is capable of measuring from 10 nTorr (1.33 μPa) to 1 mTorr (133 mPa). • The gauge sensitivity is linear over a wide range, at 0.416 A/Torr (3.13 mA/Pa). [ABSTRACT FROM AUTHOR]

An enhancement of membrane gas separation, which makes use of the temperature difference in addition to the pressure difference across the porous membrane, is proposed. The thermal transpiration flow through the membrane induced by the temperature difference enables control of two physical quantities of the permeate flow, since the temperature difference is controllable separately from the pressure difference. It is possible to establish the molecular exchange state of the permeate flow, where a component gas of binary mixture flows in the opposite direction from the flows of the other component. A model gas separation device, which makes use of the counter flow arrangement to accumulate the molecular exchange of the micro-channels in the membrane, is devised using a single mixed cellulose ester membrane of 110 μm thickness and 3 × 3 cm size. The device induces 15% variation of mole percentage of a helium–argon mixture by a temperature difference of 45 K when the speed of the counter flow is around 50 cm/s. The performance of the device is well represented by numerical simulations that use the results of molecular gas dynamics for mixture flow in micro-channels. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a steady numerical flow model and experimental gas flow results of a self-encapsulated, piezoelectrically actuated, cryogenic micro-valve for distributed cooling applications. Experimental flow data of the prototype micro-valve design is obtained for various gases at room temperature and for helium at near liquid nitrogen temperature. With a pressure differential of 100kPa across the inlet and outlet, a prototype micro-valve is shown to modulate the flow of room temperature helium from 1200 to 0sccm. Numerical flow results and experimental data agree well, with 60% of the data points falling within the range of ±10%. [Copyright &y& Elsevier]