Moiré gauging of in-plane displacement using double aperture imaging

An easily implemented method of measuring in-plane surface displacement by photographing an object through two laterally displaced apertures is described and the experimental results are presented. The displacement is displayed as a pattern of moiré fringes over the image. No previously constructed grids or rulings are required as in normal moiré devices. The method is noncontacting and requires no special surface preparation. The sensitivity is easily adjusted and is shown to be equivalent to that obtained using double-exposure holography or speckle pattern interferometry techniques. The method has potential application in mechanically unstable environments or where the conditions are such that grids or strain gauges cannot be attached to the object.