ABSTRACT
The measurement of vibration of a solid surface is usually achieved with an accelerometer or some other form of surface-contacting transducer. There are, however, many cases of engineering interest where this approach is precluded. A prime example is that of loudspeaker vibration shown in Figure 13.1 which shows a loudspeaker in a ‘rocking’ mode at 3 kHz. In order to improve designs, vibration data are required both at a point (time-resolved) and over the whole surface. These data cannot be provided by contacting transducers. Other examples include very hot and rotating surfaces such as engine exhausts and rotating driveshafts, respectively. Since the advent of the laser in the early 1960s, optical metrology has provided engineering data for designers which, hitherto, would have been considered unobtainable. In this chapter we introduce the techniques of laser vibrometry and TV holography which are capable of providing remote timeresolved vibration data at a point on a surface in addition to both visualising and quantifying vibration behaviour over an area. We also address the difficult measurement problem of torsional vibration and show how this has been solved by laser technology. The basic physics of each technique is explained prior to descriptions of applications and a discussion of accuracy and limitations.
