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  Our resolution is the wavelength of light  

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 The basic principles  of the measurement method are

                                 interferometry    and     correlation    techniques. 

Interferometry is determination of fractional relative phase difference between light waves traversing different paths. Phenomena which can be measured are those which influence the phase of the light beams. In practice this is e. g. surface deformation or density variation of a fluid.

Conventional techniques determine the relative light phase against a fixed reference beam. This is sensitive to ambient disturbances such as rigid body motion. isi-sys sensors determine the differences between neighbouring beams. This compensates ambient disturbances, which affect both beams to equal extent.

 This is the principle of shearography, which results in maximum sensitivity without need for vibration isolation.

 
Digital Image Correlation is a data analysis method, which uses a proprietary mathematical correlation method to analyse digital image data taken while samples are subjected to mechanical stresses. Consecutive image captures taken during the testing phase will “show” a change in surface characteristics as the specimen is effected by the mechanical stresses imposed upon it. 


Digital Image Correlation is an optical method to measure deformations on an object surface by determination the displacements of gray value patterns in digital images. The method tracks the gray value pattern in small neighbourhoods called subsets (indicated in red in the figure) during deformation.


When applied to mechanical components, full-field 2D and 3D displacements and strains due to loading of the structure can be measured on the entire object surface.  It also can be applied to vibration object by the vibro-correlation system, which is a  joint venture of LIMESS and isi-sys)

Some of the advantages of the method are the simple specimen preparation, the insensitivity to vibrations as no lasers are required, the capability to measure large strains (>500%) and the possibility to measure specimen shape and surface displacements in three dimensions