Date of Award
M.S. in Engineering Science
Interferometric vibration sensors are widely used for ground vibration measurements where traditional contact sensors are not desired. Laser Doppler vibrometers (LDV) and digital speckle pattern interferometers are studied in this thesis. The working principle of laser Doppler vibrometry and digital shearography is described. The effect of vibration of the unconsolidated sand on the performance of both sensors is experimentally investigated.
The vibration of unconsolidated sand can cause an increase of noise in the laser Doppler vibrometer output and cause speckle decorrelation in digital speckle pattern interferometry (referred to as digital shearography). An experimental investigation of the effect of varying the grain size and the vibration amplitude of sand is conducted. The experiments are two-fold: the first experiment focuses on digital shearography ground vibration measurements on ten different sands with varying grain size ranges to study the effect of speckle decorrelation on the performance of digital shearography; and, the second experiment utilizes the LDV to measure the same ten sands at incrementally higher vibration amplitudes to see the effect of sand particle motion on the performance and noise of the LDV.
It was found that for digital shearography, the vibration amplitude necessary to cause speckle decorrelation decreased from 4.18μ to 2μ for the increase in grain size from 0.15mm to 1mm. For the LDV, it was found that the average increase in noise is between 34.2dB and 45.6dB for an increase in vibration amplitude of 2μ to 22μ.
Berrey, Cody, "Effect of Vibration of Unconsolidated Sand on the Performance of Interferometric Vibration Sensors" (2017). Electronic Theses and Dissertations. 1332.