Recording receptance of flat plates by holographic interferometry

In the study of mechanical vibrations of structures, the complex ratio of the displacement of the structure at a point divided by the force input to the structure at the same point or a different point is called receptance. This ratio is usually recorded in magnitude and phase by using piezoelectric transducers attached to the structure. This paper describes a study of the feasibility of recording the displacement of a square cantilevered plate not just at one point but over the entire plate surface, by using holographic interferometry. For purposes of comparison of the two techniques a piezoelectric transducer was attached to a free corner of the plate and the displacements at that point were recorded over the frequency range of interest. Although the dynamic range of the holographic technique was found to be somewhat limited, it was found that it is quite feasible to calculate at least the magnitude of the receptance by recording displacements holographically. Since the holographic fringe formation is an integrated effect in time, it was not possible to record the phase by holographic means. The displacements recorded at the corner of the plate by the two methods agreed very well.