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6 Dec 2010

Volume 97, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 97, 233101 (2010); http://dx.doi.org/10.1063/1.3523252 (3 pages)

Hoonkyung Lee, Marvin L. Cohen, and Steven G. Louie
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A low profile vibro-impacting energy harvester with symmetrical stops

Scott Moss, Alex Barry, Ian Powlesland, Steve Galea, and Gregory P. Carman

Appl. Phys. Lett. 97, 234101 (2010); http://dx.doi.org/10.1063/1.3521265 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2010

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This paper reports on an investigation into the use of a vibro-impact approach to construct a relatively broadband kinetic energy harvester. Potentially, the vibro-impacting process may be exploited as an autotuning mechanism for energy harvesting in an environment where the source vibration spectrum varies in time, such as an aircraft in flight. The energy harvester examined in this paper is based on a vibro-impacting oscillator with double-sided, symmetrical, piezoelectric bimorph-stops. The energy harvester operates in the frequency range of 100–113 Hz and has a (non-optimized) maximum energy of 5.3 mW from an rms host vibration of 450 mG.
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84.60.-h Direct energy conversion and storage
84.30.Ng Oscillators, pulse generators, and function generators
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Frost formation and ice adhesion on superhydrophobic surfaces

Kripa K. Varanasi, Tao Deng, J. David Smith, Ming Hsu, and Nitin Bhate

Appl. Phys. Lett. 97, 234102 (2010); http://dx.doi.org/10.1063/1.3524513 (3 pages) | Cited 2 times

Online Publication Date: 7 December 2010

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We study frost formation and its impact on icephobic properties of superhydrophobic surfaces. Using an environmental scanning electron microscope, we show that frost nucleation occurs indiscriminately on superhydrophobic textures without any particular spatial preference. Ice adhesion measurements on superhydrophobic surfaces susceptible to frost formation show increased adhesion over smooth surfaces with a strong linear trend with the total surface area. These studies indicate that frost formation significantly compromises the icephobic properties of superhydrophobic surfaces and poses serious limitations to the use of superhydrophobic surfaces as icephobic surface treatments for both on-ground and in-flight applications.
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64.70.D- Solid-liquid transitions
64.60.qj Studies of nucleation in specific substances
68.35.Np Adhesion
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Controlled microbubble generation on a compact disk

Debapriya Chakraborty and Suman Chakraborty

Appl. Phys. Lett. 97, 234103 (2010); http://dx.doi.org/10.1063/1.3524518 (3 pages) | Cited 2 times

Online Publication Date: 7 December 2010

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We develop a rotationally actuated fluidic device for controlled generation of microbubbles in a lab-on-a-compact-disk based environment. Use of such a strategy essentially implicates that one may employ simplistic, versatile, flexible, and economized microfabrication as well as fluidic actuation techniques, instead of more complex traditional methodologies, for microbubble generation and control. We further demonstrate that the spatio-temporal frequencies and size distributions of the generated bubbles may be judiciously controlled by simply tailoring the rotational speeds, corresponding to given channel dimensions and fluid-substrate combinations.
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47.55.D- Drops and bubbles
47.60.Dx Flows in ducts and channels
47.32.Ef Rotating and swirling flows

Carbon nanotube composite optoacoustic transmitters for strong and high frequency ultrasound generation

Hyoung Won Baac, Jong G. Ok, Hui Joon Park, Tao Ling, Sung-Liang Chen, A. John Hart, and L. Jay Guo

Appl. Phys. Lett. 97, 234104 (2010); http://dx.doi.org/10.1063/1.3522833 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2010

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We demonstrate carbon nanotube (CNT) composite-based optoacoustic transmitters that generate strong and high frequency ultrasound. The composite consists of CNTs grown on a substrate, which are embedded in elastomeric polymer used as an acoustic transfer medium. Under pulsed laser excitation, the composite generates very strong optoacoustic pressure: 18 times stronger than a Cr film reference and five times stronger than a gold nanoparticle composite with the same polymer. This enhancement persists over a broadband frequency range of up to 120 MHz and is confirmed by calculation. We suggest the CNT-polymer composites as highly efficient optoacoustic transmitters for high resolution ultrasound imaging.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
62.65.+k Acoustical properties of solids
43.38.-p Transduction; acoustical devices for the generation and reproduction of sound

Far-ultraviolet signatures of the 3He(n,tp) reaction in noble gas mixtures

Patrick P. Hughes, Michael A. Coplan, Alan K. Thompson, Robert E. Vest, and Charles W. Clark

Appl. Phys. Lett. 97, 234105 (2010); http://dx.doi.org/10.1063/1.3521285 (3 pages)

Online Publication Date: 8 December 2010

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Previous work showed that the 3He(n,tp) reaction in a cell of 3He at atmospheric pressure generated tens of far-ultraviolet photons per reacted neutron. Here we report amplification of that signal by factors of 1000 and more when noble gases are added to the cell. Calibrated filter-detector measurements show that this large signal is due to noble gas excimer emissions and that the nuclear reaction energy is converted to far-ultraviolet radiation with efficiencies of up to 30%. The results have been placed on an absolute scale through calibrations at the NIST SURF III synchrotron. They suggest possibilities for high-efficiency neutron detectors as an alternative to existing proportional counters.
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25.40.Kv Charge-exchange reactions
27.10.+h A ≤ 5

Unique flow transitions and particle collection switching phenomena in a microchannel induced by surface acoustic waves

Ming K. Tan, Leslie Y. Yeo, and James R. Friend

Appl. Phys. Lett. 97, 234106 (2010); http://dx.doi.org/10.1063/1.3524511 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2010

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We present an experimental approach for controlled switching between uniform flow for pumping and vortical flow for mixing in a microchannel fabricated onto a piezoelectric substrate. For particle laden fluids, this arrangement permits a choice between transport and alignment of microparticles. Using surface acoustic waves with amplitudes beyond 1 nm, the transition from uniform to mixing flows occurs when the acoustic wavelength in the fluid is reduced to a dimension smaller than the channel width, i.e., λf ≥ Wch for uniform flow and λf<Wch for mixing flow. On the other hand, using relatively weak surface acoustic waves with amplitudes below 1 nm, particles in an initially homogeneous suspension agglomerate into equally spaced lines with a separation of λf/2. Switching the transducer between its fundamental resonant frequency f0 and its first harmonic frequency f1+ ∼ 2f0 causes a switch between uniform and mixing flow, while switching between large and small amplitude excitation allows one to choose whether to collect the particles in the flow along nodal lines parallel to the channel. These results are uniquely achieved without requiring the microfabrication of complex microchannel architectures and control schemes; the switching is simply achieved by adjusting two parameters: the acoustic excitation frequency and amplitude.
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43.35.Pt Surface waves in solids and liquids
47.32.-y Vortex dynamics; rotating fluids
47.51.+a Mixing
47.60.Dx Flows in ducts and channels
47.61.Ne Micromixing
43.25.Fe Effect of nonlinearity on acoustic surface waves
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