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  • 1
    Electronic Resource
    Electronic Resource
    Ball SAW Sensors for Safety and Reliability of Fuel Cell Technologies (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 321-323 (Oct. 2006), p. 48-52 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Detection of hydrogen gas is a crucial task for establishing safety and reliability of fuelcells, a key technology for the environment and our society. However, hydrogen is difficult to detectand various hydrogen sensors have many drawbacks. Here we report a novel hydrogen gas sensor,the ball surface acoustic wave (SAW) sensor, using Pd or PdNi sensitive film. The ball SAW sensoris based on a novel phenomenon, diffraction-free propagation of collimated beam along an equatorof sphere. The resultant ultra-multiple roundtrips of SAW makes it possible to achieve highestsensitivity among SAW sensors. Moreover, it enables to use a very thin sensitive film, andconsequently the shortest response time (2s) was realized. In terms of the sensing range, it has thewidest range of 10 ppm to 100 % among any hydrogen sensors including FET or resistivity sensors.The ball SAW sensor can be applied not only to hydrogen but also to any gasses and possibly toliquids
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/51/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.321-323.48.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Nanoscale elasticity measurement with in situ tip shape estimation in atomic force microscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2403-2408 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: For a quantitative evaluation of nanoscale elasticity, atomic force microscopy, and related methods measure the contact stiffness (or force gradient) between the tip and sample surface. In these methods the key parameter is the contact radius, since the contact stiffness is changed not only by the elasticity of the sample but also by the contact radius. However, the contact radius is very uncertain and it makes the precision of measurements questionable. In this work, we propose a novel in situ method to estimate the tip shape and the contact radius at the nanoscale contact of the tip and sample. Because the measured resonance frequency sometimes does not depend so sensitively on the contact force as expected from the parabolic tip model, we introduced a more general model of an axial symmetric body and derived an equation for the contact stiffness. Then, the parameters in the model are unambiguously determined from a contact force dependence of the cantilever resonance frequency. We verified that this method is able to provide an accurate prediction of the cantilever thickness, the tip shape, and the effective elasticity of soft and rigid samples. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150627
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of excitation and coherent amplitude enhancement of surface acoustic waves by the phase velocity scanning method (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6511-6522 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a general theoretical formulation for the characteristics of surface acoustic waves (SAW) generated by the phase velocity scanning (PVS) method that employs a scanning single laser beam (SSB) or a scanning interference fringes (SIF). In the SSB approach, a broad band SAW pulse is generated and its amplitude is coherently enhanced when the laser scanning velocity V is equal to the phase velocity νR of the SAW. The amplitude of the SAW follows a resonance curve represented by a sinc function of the scanning velocity V, but different spatial frequency components in the SSB significantly suppress the side lobes of the resonance curve. In the SIF approach, the scanning velocity νf of the fringes is determined by the intersection angle and the frequency difference ωa of the laser beams. A narrow band tone burst of SAW with frequencies higher than 100 MHz can be excited. The SAW frequency ω depends upon a characteristic time t*, defined as a propagation time of the SAW across the laser beam spot. The SAW frequency ω is identical to the frequency difference ωa when the laser pulse width T is longer than the characteristic time t*. But, the SAW frequency ω is determined as a product kfνR of the wave number of the SIF and the SAW velocity when the laser pulse width is shorter than the characteristic time. Precise frequency measurement provided by the amplitude enhancement effect and the narrow frequency bandwidth in the SIF approach make the PVS method particularly promising for the noncontact SAW velocity measurement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355140
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  • 4
    Electronic Resource
    Electronic Resource
    Microscale evaluation of the viscoelastic properties of polymer gel for artificial muscles using transmission acoustic microscopy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6407-6412 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local viscoelastic properties and a micromechanical structure of polymer hydrogel were studied using transmission acoustic microscopy (AM) with a spatial resolution up to 5 μm. Utilizing various amplitude, phase, and pulse techniques provided by the transmission AM, a velocity and an attenuation of the acoustic wave in the local point of the polymer sample as well as a frequency dependence (dispersion) of these values were evaluated in the frequency range from 30 to 320 MHz. Using these facilities a poly(vinylalcohol) polymer hydrogel for the artificial muscle was studied at the succeeding steps of its manufacturing process of cyclic freezing–thawing. It was found that synchronously, with the increase of the compressional elasticity and acoustic attenuation, a micromechanical nonuniformity of the gel also profoundly enhances it. Fiber-like structures of 10–50 μm width possessing higher elastic modulus appear in the gel which can play a significant role in the macroscopic mechanical properties of the gel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355142
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  • 5
    Electronic Resource
    Electronic Resource
    Resonance frequency and Q factor mapping by ultrasonic atomic force microscopy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1939-1941 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We developed an improved ultrasonic atomic force microscopy (UAFM) for mapping resonance frequency and Q factor of a cantilever where the tip is in linear contact with the sample. Since the vibration amplitude at resonance is linearly proportional to the Q factor, the resonance frequency and Q factor are measured in the resonance tracking mode by scanning the sample in the constant force mode. This method enables much faster mapping of the resonance frequency and Q factor than the previous one using a network analyzer. In this letter, we describe the principle and instrumentation of the UAFM and show images of carbon-fiber-reinforced plastic composites. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357540
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  • 6
    Electronic Resource
    Electronic Resource
    Precise velocity measurement of surface acoustic waves on a bearing ball (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2797-2799 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using the photoacoustic effect of interference fringes scanned at the phase velocity of surface acoustic waves (SAW), we excited tone bursts of SAW with a center frequency of around 30 MHz on a 8 mm φ steel bearing ball. A surprisingly large number (around 20 turns) of round-trip propagations was observed. The time interval between the SAW at the first and the twelfth turn was as large as 93 μs, however it could be determined with a 2 ns resolution since an exact overlapping of the two wave forms was possible. Thus, we achieved a very high resolution of 0.002% in the velocity measurement, and a velocity change of 2 m/s due to the deposition of a 50-nm-thick Ag film was easily detected. Because of its noncontact nature, this method would be useful for nondestructive evaluation of bearing balls. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126481
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  • 7
    Electronic Resource
    Electronic Resource
    Excitation of high frequency surface acoustic waves by phase velocity scanning of a laser interference fringe (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2036-2038 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a novel method for generating 100 MHz band surface acoustic wave (SAW) by using a scanning interference fringe at the phase velocity of the SAW. The scanning interference fringe is obtained by intersecting two laser beams with different frequencies, and used as a thermoelastic source. The principle of this method is described, and experimentally demonstrated in the 110 MHz Rayleigh waves on an aluminum specimen generated by a long-pulse (140 ns) Q-switched Nd:YAG laser.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109471
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  • 8
    Electronic Resource
    Electronic Resource
    Selective excitation of single-mode acoustic waves by phase velocity scanning of a laser beam (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1591-1593 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel method for selective generation of single-mode acoustic waves in multimode media has been developed using a laser beam scanned at the phase velocity of a specified mode. In dispersive media, the acoustic frequency can be varied by changing the scanning velocity. The number of carriers in the generated wave packet is proportional to the difference between the phase and the group velocities. These features were experimentally verified in the fundamental symmetric and asymmetric Lamb waves on an aluminum plate generated by a long-pulse Nd:YAG laser. Applications to anisotropy and thickness measurements are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105134
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  • 9
    Electronic Resource
    Electronic Resource
    Ultrasonic force microscopy for nanometer resolution subsurface imaging (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 178-180 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a novel method for nanometer resolution subsurface imaging. When a sample of atomic force microscope (AFM) is vertically vibrated at ultrasonic frequencies much higher than the cantilever resonance, the tip cannot vibrate but it is cyclically indented into the sample. By modulating the amplitude of ultrasonic vibration, subsurface features are imaged from the cantilever deflection vibration at the modulation frequency. By adding low-frequency lateral vibration to the ultrasonic vibration, subsurface features with different shear rigidity are imaged from the torsional vibration of cantilever. Thus controlling the direction of vibration forces, we can discriminate subsurface features of different elastic properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111524
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  • 10
    Electronic Resource
    Electronic Resource
    Remote Nondestructive Evaluation of Delaminating Tiles by Using Photorefractive Vibration Imaging (2004)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 261-263 (Apr. 2004), p. 969-974 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/47/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.261-263.969.pdf
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