Surface-normal vector velocity measurement using a five-axis contour scanning laser vibrometry system

Abstract

A novel system for using a single-point Laser Doppler vibrometer (LDV) to measure surface normal velocity components of non-planar targets has been developed. A description of this measurement system is presented, along with a discussion of results and relative merits compared with conventional scanning LDV systems. Data from sample measurements taken on an anti-tank landmine buried in sand are presented. It is shown that measurements of the same surface wave using this system and a conventional system can differ by as much as 75%.

Five-axis scanning laser vibrometry for three-dimensional measurements of non-planar surfaces

“…The second rotation stage, R-2, is mounted on R-1 such that the axis of rotation of R-2 in the global coordinate system is a function of the angle, θ R1 , at which stage R-1 is positioned. The mirror can thus be oriented to direct the LDV beam to the target along a desired vector [6]. A photo of the rotation stage and mirror assembly is shown in figure 4.…”

“…If surface-tangent motion is non-negligible, such as in measurements of bulk solids or complicated structures, full 3D measurements are typically desirable, although surfacenormal measurements may still be preferable to measurements along a constant direction. In an earlier work, the authors [6] demonstrated how additional information was revealed about a target (a mine buried in sand) when the surface normal directions were measured rather than a conventional straightdown measurement of the sand surface.…”