Remote vibration measurements: compensation of waveform distortion due to whole body translations

Remote vibration measurements using the laser Doppler technique are a practical and increasingly popular alternative to the use of contacting transducers. This study concerns aspects of non-contact measurements that result when the vibrating target additionally undergoes larger scale whole body translation. The characteristics of a single remote measurement of steady state vibration on a body undergoing whole body translation are investigated in both the time and frequency domains, where waveform distortion and whole body target displacement induced harmonics are observed. A technique which compensates for the relative whole body displacement between the target and a remote transducer is introduced, in which two simultaneous remote measurements are combined to derive a closer estimate of the measurement which would be made by a contacting transducer attached to the target surface. A substantial improvement in the data quality obtainable from a single remote measurement is demonstrated using a numerical simulation and in experimental data captured remotely from a golf club head during and immediately following an impact with a golf ball. Remote measurements are particularly suited to analysis of impacting bodies and the displacement compensation technique is thus developed in this paper to investigate transient pulse propagation effects. The improvement in data quality obtained is demonstrated using data pertaining to the deformation of a golf ball during an impact in which the whole ball accelerates forwards rapidly.