MEASUREMENT OF HIGHER HARMONICS IN PERIODIC VIBRATIONS USING PHASE-MODULATED TV HOLOGRAPHY WITH DIGITAL IMAGE-PROCESSING

We separately measure the higher harmonics vibration patterns of a per iodic vibrating object by using time-average TV holography and phase m odulation. During measurements the frequency of the phase modulation i s adjusted to each harmonic component while the excitation of the obje ct is set low enough to record all components on the linear part of th e fringe function. Using acoustical phase stepping and calibration of the fringe function, we compute the amplitude and phase distributions of the frequency component. We measure components up to the 65th harmo nic by using square-wave excitation.