Experimental investigation on natural frequencies of thin rectangular plates using contact and non-contact methods

In this paper, two excitation methods, namely contact and non-contact methods were used to excite a thin rectangular plate with clampled boundary conditions at all four edges. A modal hammer was used to apply an impact on the surface of the plate in the contact method while for the non-contact method, three loudspeakers were utilized to excite the plate by emitting a white noise signal. The loudspeakers covered low, medium and high ranges of frequency. Different positions for excitation point were suggested in order to find the best position in which the accelerometer is more capable of measuring the vibration of plate surface at natural frequencies. By comparing two types of excitation, the non-contact method was discovered to have advantages over contact method in medium and high frequency ranges and the contact method had better performance in low frequency range. An approximate analytical method based on Rayleigh-Ritz method was also studied in order to compare and validate the experimental results in predicting natural frequencies of a thin rectangular plate.