7,997 research outputs found
Casimir probe based upon metallized high Q SiN nanomembrane resonator
We present the instrumentation and measurement scheme of a new Casimir force
probe that bridges Casimir force measurements at microscale and macroscale. A
metallized high Q silicon nitride nanomembrane resonator is employed as a
sensitive force probe. The high tensile stress present in the nanomembrane not
only enhances the quality factor but also maintains high flatness over large
area serving as the bottom electrode in a sphere-plane configuration. A fiber
interferometer is used to readout the oscillation of the nanomembrane and a
phase-locked loop scheme is applied to track the change of the resonance
frequency. Because of the high quality factor of the nanomembrane and the high
stability of the setup, a frequency resolution down to and a
corresponding force gradient resolution of 3 N/m is achieved. Besides
sensitive measurement of Casimir force, our measurement technique
simultaneously offers Kelvin probe measurement capability that allows in situ
imaging of the surface potentials
Characterization of noncontact piezoelectric transducer with conically shaped piezoelement
The characterization of a dynamic surface displacement transducer (IQI Model 501) by a noncontact method is presented. The transducer is designed for ultrasonic as well as acoustic emission measurements and, according to the manufacturer, its characteristic features include a flat frequency response range which is from 50 to 1000 kHz and a quality factor Q of less than unity. The characterization is based on the behavior of the transducer as a receiver and involves exciting the transducer directly by transient pulse input stress signals of quasi-electrostatic origin and observing its response in a digital storage oscilloscope. Theoretical models for studying the response of the transducer to pulse input stress signals and for generating pulse stress signals are presented. The characteristic features of the transducer which include the central frequency f sub o, quality factor Q, and flat frequency response range are obtained by this noncontact characterization technique and they compare favorably with those obtained by a tone burst method which are also presented
Wind tunnel measurements of surface pressure fluctuations at Mach numbers of 1.6, 2.0, and 2.5 using 12 different transducers
The turbulent boundary layer on the wall of a 9 by 7 foot wind tunnel was measured with 12 different transducers at Mach numbers of 1.6, 2.0, and 2.5. The results indicated that the wall surface-pressure-fluctuation field was more homogeneous at a Mach number of 2.5 than at Mach numbers of 1.6 or 2.0. A comparison of power-spectral-density data at Mach 2.5 with a summary of similar data (Mach 0.1 to 3.45) showed good agreement. The measurement uncertainty was greatest when frequencies were low and the surface-pressure-fluctuation field was homogeneous. The uncertainty at higher frequencies increased as the surface-pressure-fluctuation field became more inhomogeneous. Since transducer mounting effects and system noise levels were determined not to have contributed appreciably to measurement uncertainties, the result was attributed to an interaction between the surface-pressure-fluctuation field and the transducers. Corcos' correction for size effects improved the comparison between transducers at the high frequencies, but did not eliminate an apparent size effect at the lower frequencies
Dynamic sensor Patent
Dynamic sensor for gas pressure or density measuremen
Comment on "Anomalies in electrostatic calibration for the measurement of the Casimir force in a sphere-plane geometry"
Recently W. J. Kim, M. Brown-Hayes, D. A. R. Dalvit, J. H. Brownell, and R.
Onofrio [Phys. Rev. A, v.78, 036102(R) (2008)] performed electrostatic
calibrations for a plane plate above a centimeter-size spherical lens at
separations down to 20-30 nm and observed "anomalous behavior". It was found
that the gradient of the electrostatic force does not depend on separation as
predicted on the basis of a pure Coulombian contribution. Some hypotheses which
could potentially explain the deviation from the expected behavior were
considered, and qualitative arguments in favor of the influence of patch
surface potentials were presented. We demonstrate that for the large lenses at
separations of a few tens nanometers from the plate, the electrostatic force
law used by the authors is not applicable due to possible deviations of the
mechanically polished and ground lens surface from a perfect spherical shape. A
model is proposed which explains the observed "anomalous behavior" using the
standard Coulombian force.Comment: 9 pages, 3 figure
On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration
We report on measurements of forces acting between two conducting surfaces in
a spherical-plane configuration in the 35 nm-1 micrometer separation range. The
measurements are obtained by performing electrostatic calibrations followed by
a residual analysis after subtracting the electrostatic-dependent component. We
find in all runs optimal fitting of the calibrations for exponents smaller than
the one predicted by electrostatics for an ideal sphere-plane geometry. We also
find that the external bias potential necessary to minimize the electrostatic
contribution depends on the sphere-plane distance. In spite of these anomalies,
by implementing a parametrixation-dependent subtraction of the electrostatic
contribution we have found evidence for short-distance attractive forces of
magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss
the relevance of our findings in the more general context of Casimir-Lifshitz
force measurements, with particular regard to the critical issues of the
electrical and geometrical characterization of the involved surfaces.Comment: 22 pages, 15 figure
\u3cem\u3eIn Situ\u3c/em\u3e Nanomechanical Testing in Focused Ion Beam and Scanning Electron Microscopes
The recent interest in size-dependent deformation of micro- and nanoscale materials has paralleled both technological miniaturization and advancements in imaging and small-scale mechanical testing methods. Here we describe a quantitative in situ nanomechanical testing approach adapted to a dualbeam focused ion beam and scanning electron microscope. A transducer based on a three-plate capacitor system is used for high-fidelity force and displacement measurements. Specimen manipulation, transfer, and alignment are performed using a manipulator, independently controlled positioners, and the focused ion beam. Gripping of specimens is achieved using electron-beam assisted Pt-organic deposition. Local strain measurements are obtained using digital image correlation of electron images taken during testing. Examples showing results for tensile testing of single-crystalline metallic nanowires and compression of nanoporous Au pillars will be presented in the context of size effects on mechanical behavior and highlight some of the challenges of conducting nanomechanical testing in vacuum environments
Gradient of the Casimir force between Au surfaces of a sphere and a plate measured using atomic force microscope in a frequency shift technique
We present measurement results for the gradient of the Casimir force between
an Au-coated sphere and an Au-coated plate obtained by means of an atomic force
microscope operated in a frequency shift technique. This experiment was
performed at a pressure of 3x10^{-8} Torr with hollow glass sphere of 41.3 mcm
radius. Special attention is paid to electrostatic calibrations including the
problem of electrostatic patches. All calibration parameters are shown to be
separation-independent after the corrections for mechanical drift are included.
The gradient of the Casimir force was measured in two ways with applied
compensating voltage to the plate and with different applied voltages and
subsequent subtraction of electric forces. The obtained mean gradients are
shown to be in mutual agreement and in agreement with previous experiments
performed using a micromachined oscillator. The obtained data are compared with
theoretical predictions of the Lifshitz theory including corrections beyond the
proximity force approximation. An independent comparison with no fitting
parameters demonstrated that the Drude model approach is excluded by the data
at a 67% confidence level over the separation region from 235 to 420 nm. The
theoretical approach using the generalized plasma-like model is shown to be
consistent with the data over the entire measurement range. Corrections due to
the nonlinearity of oscillator are calculated and the application region of the
linear regime is determined. A conclusion is made that the results of several
performed experiments call for a thorough analysis of the basics of the theory
of dispersion forces.Comment: 35 pages, 14 figures, 1 table; to appear in Phys. Rev.
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