Directional-sensitive differential laser Doppler vibrometry for in-plane motion measurement of specular surface

Kusuma Agusanto, Gih Keong Lau, Kun Wu, Ting Liu, Chuangui Zhu, Ling Yuan

Research output: Chapter in Book/Report/Conference proceedingConference contribution

3 Scopus citations


A new method for measuring in-plane vibration velocity of glossy and specular surface using differential laser Doppler vibrometer (LDV) is proposed in this work. A standard tangential LDV using similar differential configuration is only able to measure in-plane velocity of objects with rough surface, due to its inherent on-axis optical design that collects backscatter light along its optical axis. The proposed method adopts an off-axis detection scheme, in which the photodetector is decoupled from LDV, and placed along the dominant direction of the scattered light. For optimal placement, the bidirectional reflectance distribution function (BRDF) of the sample must be considered ideally, but in our measurement tests, the off-axis detection along the direction of specular reflection is sufficient to obtain good measurement results. Another advantage with this setup is that it also works with the objects with rough surface. Experimental works using the standard tangential LDV and a prototype of this method were conducted to measure the in-plane motion of four different samples representing rough, glossy and mirror-like surface. An electrodynamic shaker was used to provide the in-plane motion of the samples at three different frequencies. A single point axial vibrometer was used to validate the in-plane velocity of the measurement from both in-plane LDVs. Some preliminary results showed that the in-plane motion of the object with glossy and specular surface can be measured using the proposed method.

Original languageEnglish
Title of host publicationInternational Conference on Experimental Mechanics 2014
EditorsAnand Asundi, Fook Siong Chau, Chenggen Quan, Kemao Qian
ISBN (Electronic)9781628413885
StatePublished - 1 Jan 2015
EventInternational Conference on Experimental Mechanics 2014, ICEM 2014 - Singapore, Singapore
Duration: 15 Nov 201417 Nov 2014

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceInternational Conference on Experimental Mechanics 2014, ICEM 2014


  • BRDF
  • In-plane motion
  • Laser Doppler vibrometry
  • Surface condition

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