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Articles you may be interested inEffect of a vacuum ion gauge on the contamination of a hydrogenpassivated silicon surface Most techniques for levitating small objects in a vacuum employ fluctuating electric or magnetic fields, often controlled by feedback from a position-sensing device to obtain the desired stability. We describe an alternative technique, diamagnetic levitation, which is particularly useful where compactness and simplicity are important. Diamagnetic levitation is passive in that steady magnetic fields are used and no position sensing or feedback are required. The theoretical background and prior developments are summarized. Two basic configurations, in which the magnetic fields are either vertical or horizontal, are distinguished. Particles of graphite and bismuth in sizes down to the micron range have been levitated in experimental systems of these types. Observations of particle motion as a result of interactions with the surrounding gas molecules are discussed. Many of the observed effects are pressure dependent. Several types of vacuum gauges based on these principles are suggested.

A novel method of levitation, using an actively controlled electric field, launches, captures, and stably suspends a microscopic (∼15 μm) particle in high vacuum. While held to within one diameter in the vertical direction, the particle is allowed to oscillate nearly freely in the horizontal plane under the influence of a central restoring force. The damping of horizontal oscillations was measured over the pressure range from 10−2 to 10−8 Torr. The damping was observed to be proportional to pressure down to less than 10−6 Torr, where residual (pressure independent) damping became significant. An absolute high vacuum gauge based on the pressure-dependent damping observed with this apparatus could operate linearly throughout at least a six decade range. A prototype gauge design is suggested.

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Articles you may be interested inA model of laminar-turbulent transition based on viscous stream buckling AIP Conf.The field of fluid mechanics has long held that the transition from laminar to turbulent flow can be sufficiently described using the classical, continuum formulation of the Navier-Stokes equation and dimensionless parameters such as the Reynolds number. Recent theoretical and experimental challenges to the continuum description of this transition have led to controversial claims. To help resolve this debate, we have developed apparatus specifically designed to produce repetitive laminar-turbulent transitions so that the details of the transitions with respect to a variety of parameters can be studied. Since the laminar-turbulent transition is by its nature chaotic, it is desirable to have numerous events-each occurring in rapid succession under essentially identical conditions-for a fuller understanding of this phenomenon. The apparatus and method described here produce these repeated transitions spontaneously by exploiting the fact that for gases the conductance in the turbulent regime is higher than that in the laminar regime. It is accomplished with relatively simple, compact, and readily available equipment. Initial operation of the apparatus has produced data which show interesting and characteristic behavior for several gasses.