Pressure measurement by low coherence speckle interferometry membrane shaping with tunable diode lasers

Non-contact evaluation of object deformation is of great importance in several industrial and scientific processes. In this work the demonstrate that low-coherence digital speckle pattern interferometry can be employed for pressure measurement by the analysis of a 0.4-mm thickness, 55-mm diameter circular aluminum membrane submitted to a pressure differential ranging from 0 to 90 kPa. The membrane deformation was measured with a tunable red diode laser emitting simultaneously two wavelengths. The resulting speckle image of the membrane appeared covered with interference fringes which correspond to the contour lines of the studied surface. By means of conventional fringe pattern evaluation methods like 4-stepping and unwrapping methods the membrane deformation was determined. The experimental results were compared with the ones obtained by a numerical algorithm.