A moiré micro strain gauge

We have built a new strain gauge based on the moiré technique. This strain gauge mainly consists of two frames that can move with respect to each other. Displacements are recorded by using the moiré technique. We use a pair of similar gratings attached to the frames. The gratings are installed in parallel without physical contact and their lines making a small angle with one another. A moiré pattern is formed due to superimposing of the gratings. A diode laser light passes through the moiré pattern and a narrow slit, and hits on a light sensor. In response to external stress, one of the gratings is displaced and, as a result, the moiré fringes move in front of the slit. Due to the fringes movements, the light intensity on the detector varies and is recorded as voltage. The voltage output can be used to measure the strain. This instrument can detect displacements of the order of micron. In this paper we show the experimental results of our instrument.