Application of ESPI to three-dimensional vibration measurements

There are many situation in vibration analysis where it is necessary or desirable to make three-dimensional measurements. By using three different illumination geometries around a single imaging system, electronic speckle pattern interferometry (ESPI) can be used to measure the orthogonal components of vibration amplitude independently. These can be combined to determine the three-dimensional amplitude and mode shape. Examples of experimental results are presented for volume vibrations of a thick cylinder, identification of vibration modes of a turbocharger blade, and observation of in-plane modes in a thin plate.