Vibration Analysis

The Problem: To Identify and Characterize Vibration Modes


The K100/HOL optical head using the HoloFringe300 interferometry program allows quick identification of vibration modes of a test structure as it is subjected to a vibratory excitation. The vibration modes show up as Bessel function fringes. These fringes are dark bands on the image that read like a topographical map showing the peaks and valleys of the vibration amplitude. The program controls a dual frequency generator via the PC host computer to provide excitation.  The second signal can be used to produce wrapped phase fringes, which are easily converted to numerical data.  No scanning of the object is required, resonant frequencies are easily located, and resonant bandwidths can also be obtained.


Vibration Mode Analysis of a Rectangular Plate. The upper left image shows the vibration mode of the plate as a set of zero-order Bessel function fringes. This is what the system displays in real-time for mode identification. Upper right shows that fringe pattern converted to the wrapped phase function. Lower left shows the unwrapped phase function, otherwise known as the fringe locus function. Lower right shows a 3D plot of the vibration mode. Note that the plate has four holes in it that present no problem to the unwrapping program.


Read paper "Two-Dimensional Vibration Analysis via Digital Holography"

ABSTRACT: A simple modification is described to allow capture of digital holograms with two separated illuminations of a vibrating object using a standard digital holography system. The object is a small wine glass vibrating in a two-diameter mode and a three-diameter mode. Image data is resolved into axial and transverse components, and horizontal data scans are resolved into magnitude and angular direction.


2-Diameter Vibration Mode of a Circular Saw Blade
3-Diameter Vibration Mode of a Circular Saw Blade
4-Diameter Vibration Mode of a Circular Saw Blade