Abstract: A portable optical sensor for measuring surface strain in an object, such as pre-stressed concrete articles, is provided. The sensor is a modular device comprising at least first and second modules, each of which includes a laser and image sensor. When placed adjacent to the object, the laser of each module illuminates respective, spaced-apart areas of the object's surface and each module's image sensor captures at least a portion of the light reflected from the illuminated area and generates a speckle image of the area. Speckle images of the areas taken at various times and/or under various object stress conditions are compared to arrive at a surface strain measurement for the object.

Abstract: A portable optical sensor for measuring surface strain in an object, such as pre-stressed concrete articles, is provided. The sensor is a modular device comprising at least first and second modules, each of which includes a laser and image sensor. When placed adjacent to the object, the laser of each module illuminates respective, spaced-apart areas of the object's surface and each module's image sensor captures at least a portion of the light reflected from the illuminated area and generates a speckle image of the area. Speckle images of the areas taken at various times and/or under various object stress conditions are compared to arrive at a surface strain measurement for the object.