Non-contact operational modal analysis of an optical membrane for space application

In recent years, a number of studies have addressed the possibility of replacing the conventional rigid mirrors that are used in space-based telescopes with optical membranes. Weight reduction, reduced cost of transportation and ability to provide a continuous surface for the attenuation of wave front aberrations are some of the benefits given by optical membranes. Given the harsh environmental loading conditions represented by thermal radiation, debris impact and slewing maneuvers, the ability to characterise fully the dynamics of such low-density thin-film membranes is essential. Nevertheless, the testing of membrane-like structures has proven to be a non-trivial process, and requires a considerable amount of work to achieve accurate results, as well as validating experiments against numerical models. Despite typical testing, the inherent low-density feature of membranes requires the use of non-invasive, non-contact sensors and excitation capability. The work presented here, investigates the possibility of using Operational Modal Analysis (OMA) techniques to extract modal parameters from an acoustically-exited membrane, where responses are collected by using a Scanning Laser Doppler Vibrometer (SLDV) as a non-contact velocity transducer. Results from this experiment are validated against an impedance-based numerical model.