Soccer ball modal analysis using a scanning laser doppler vibrometer (SLDV)

Soccer equipment manufacturers invest significant amounts of time and money researching and developing soccer balls, using advanced materials and constructions in an attempt to create a ball that has better flight and impact characteristics. An important consideration in any structure subject to dynamic or impact loading is its mechanical response. The recent development of non-contact optical vibration measurement tools such as the SLDV have made the accurate measurement of such responses possible. The technique of vibrometry utilises the Doppler principle to provide a measure of the surface velocity at the point at which a laser beam is incident. The SLDV benefits from its non-contact and non-marking method, and the speed and ease with which measurements can be recorded. This paper reports the method and results from a study aimed at determining the dynamic responses of two different soccer balls. The balls were excited using an acoustic source and the velocity of each ball's surface at a series of points was recorded. The natural frequencies and vibration mode shapes were identified and a comparison made between the responses of each ball. Significant mode shapes were observed between 150 Hz and 1500 Hz. At the lower frequencies, the mode shapes were observed to be independent of the outer panels, based more on the structure of the ball as a whole. At higher frequencies, one of the balls tested showed mode shapes centred on individual panel oscillations. The soccer balls tested show some noticeable differences in mode shapes.