|
UPSI Digital Repository (UDRep)
|
|
| ||||||||||||||
| Abstract : |
| Particle image velocimetry (PIV) technique in its original form is limited to in-plane two-dimensional two-component (2D-2C) displacement and velocity measurements. Although it is possible to extract the out-of-plane component through stereoscopic viewing, the useful measurement volume remains limited to a light sheet of several millimeters thick. On the other hand, integration of holographic recording in PIV (HPIV) has finally realised whole-field, three-dimensional three-component (3D-3C) displacement and velocity measurements. In comparison to in-line particle holography, off-axis particle holography offers a relatively higher signal-to-noise ratio (SNR) although it demands long coherence and high laser energy for flow diagnostics. In-line particle holography relaxes the requirements of such a system but at the expense of image (signal) degradation due to superposition of virtual image waves, the directly transmitted reconstruction wave and the real image. On this basis, off-axis setup is favourable, as in theory, the only influencing noise is the out-of-focus real images. This paper introduces a new approach of SNR analysis which considers the position of out-of-focus real images based on the paraxial approximation to spherical wavefronts. It was shown that the formulated off-axis SNR agrees well with other established expressions found in the literature. The SNR was shown dependent on particle number density, square of particle diameter and depth volume. |
| This material may be protected under Copyright Act which governs the making of photocopies or reproductions of copyrighted materials. You may use the digitized material for private study, scholarship, or research. |