Reflection spectrum distortion due to Bragg‐frequency variation in tapered highly reflective surface‐wave gratings

P. S. Cross

doi:10.1063/1.89807

Reflection spectrum distortion due to Bragg‐frequency variation in tapered highly reflective surface‐wave gratings

Applied Physics Letters ◽

10.1063/1.89807 ◽

1977 ◽

Vol 31 (9) ◽

pp. 562-564 ◽

Cited By ~ 1

Author(s):

P. S. Cross

Keyword(s):

Surface Wave ◽

Reflection Spectrum ◽

Frequency Variation ◽

Reflective Surface ◽

Bragg Frequency

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Long Time Delay Reflective Surface Wave Dispersive Delay Line

10.1109/ultsym.1973.196250 ◽

1973 ◽

Cited By ~ 5

Author(s):

P.C. Meyer ◽

R.H. Tancrell ◽

J.H. Matsinger

Keyword(s):

Surface Wave ◽

Time Delay ◽

Delay Line ◽

Reflective Surface ◽

Long Time

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Field Investigation on the Effects of Base Plate Material on Experimental Surface Wave Data with MASW

Journal of Environmental and Engineering Geophysics ◽

10.2113/jeeg18-056 ◽

2020 ◽

Vol 25 (2) ◽

pp. 255-274

Author(s):

Siavash Mahvelati ◽

Joseph Thomas Coe ◽

Philip Asabere

Keyword(s):

Surface Wave ◽

Power Spectra ◽

Base Plate ◽

Field Investigation ◽

Signal Frequency ◽

Frequency Variation ◽

Frequency Content ◽

Promising Alternative ◽

Masw Method ◽

Base Plates

Source characteristics significantly affect the signals generated during seismic testing. Proper source selection plays a major role in data quality and can potentially improve investigation outcomes. This is particularly true for surface wave testing where the goal is to establish the frequency variation of phase velocity. Little research has compared the input energy caused by different base plates when impact sources are used. Consequently, data were collected using the Multichannel Analysis of Surface Waves (MASW) method with three base plate configurations (aluminum, aluminum over a rubber mat, and polyethylene) and two different sledgehammers. The variations in signal frequency content and amplitude spectra, energy, and dispersion images were systematically analyzed. There were appreciable differences in the energy introduced by different base plate configurations. Both the aluminum/rubber and the polyethylene base plates led to power spectra increases relative to the aluminum base plate. Subsequently, the aluminum/rubber and polyethylene base plates typically transferred more energy into the subsurface. This was not necessarily the case when the base plates were used on soft surficial soils. The variations in predominant frequency content were also less substantial, though the aluminum/rubber and polyethylene base plates developed slightly lower-frequency content at the expense of higher-frequency components in the dispersion curves. Despite the noticeable differences in energy transfer and frequency content, the base plate materials did not appreciable alter interpretation of the dispersion behavior at the sites given the uncertainty present in the dispersion images. This highlights that the selection of MASW base plate materials can be correspondingly driven by practical considerations such as noise, portability, and durability. Consequently, base plate materials with viscoelastic characteristics are a promising alternative to conventional metallic plates for coupling impact sources in surface wave testing, though care should be exercised when employing them at sites with soft ground conditions.

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Exit-surface wave reconstruction using a focal series

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100129577 ◽

1992 ◽

Vol 50 (2) ◽

pp. 988-989

Author(s):

W.J. de Ruijter ◽

M.R. McCartney ◽

David J. Smith ◽

J.K. Weiss

Keyword(s):

Surface Wave ◽

Spherical Aberration ◽

Data Extraction ◽

High Sensitivity ◽

Geometric Distortion ◽

Variation Method ◽

Objective Lens ◽

Immediate Reconstruction ◽

Exit Surface ◽

Electron Microscopes

Further advances in resolution enhancement of transmission electron microscopes can be expected from digital processing of image data recorded with slow-scan CCD cameras. Image recording with these new cameras is essential because of their high sensitivity, extreme linearity and negligible geometric distortion. Furthermore, digital image acquisition allows for on-line processing which yields virtually immediate reconstruction results. At present, the most promising techniques for exit-surface wave reconstruction are electron holography and the recently proposed focal variation method. The latter method is based on image processing applied to a series of images recorded at equally spaced defocus.Exit-surface wave reconstruction using the focal variation method as proposed by Van Dyck and Op de Beeck proceeds in two stages. First, the complex image wave is retrieved by data extraction from a parabola situated in three-dimensional Fourier space. Then the objective lens spherical aberration, astigmatism and defocus are corrected by simply dividing the image wave by the wave aberration function calculated with the appropriate objective lens aberration coefficients which yields the exit-surface wave.

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