A simple and inexpensive optical technique to help students visualize mode shapes.

An imaging technique is introduced that is suitable for visualizing the mode shapes of vibrating structures in an educational setting. The method produces images similar to those obtained using electronic speckle pattern interferometry (ESPI), but it can be implemented for less than 1/10 the cost of a commercial ESPI system, and the apparatus is simple enough that it can be constructed by undergraduate students. This technique allows for real-time visualization of the normal modes and deflection shapes of harmonically vibrating structures, including those with shapes that make generating Chladni patterns with sand or powder impossible. The theory of operation and construction details are discussed.