High-speed generation of digital holographic interferograms and shearograms for non-destructive testing

Authors: Thomas, B P; Pillai, S A

Source: Insight - Non-Destructive Testing and Condition Monitoring, Volume 51, Number 5, May 2009 , pp. 252-256(5)

Publisher: The British Institute of Non-Destructive Testing

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Digital holographic interferometry is the state-of-the-art technique in holography having applications in the fields of non-destructive testing, flow analysis and vibration measurement covering a wide range from huge aerospace structures to micro objects such as MEMS[1,2,3].

In holographic non-destructive testing (HNDT), transient thermal loading is an extensively used method of stressing the objects for defect detection[4]. Test objects are stressed thermally using infrared lamps, flat heater or hot-water tanks depending on the object configuration and geometry, defect type and nature and the safety aspects. Holograms at different stress states of the object are recorded continuously, either during heating or during cooling after the removal of the heating element, to obtain interferograms. However, in order to capture and analyse the fast transient response of the structures upon thermal stressing, a system that records holograms and generates holographic interferograms in high speed is essential. Added to this, if the system can simultaneously generate shearograms, which provide a displacement derivative fringe pattern, this would increase its defect detection capability during NDT.

In this paper the development of a digital hologram processing system which can record a digital hologram in high speed and generate holographic interferograms and shearograms simultaneously is reported. The design of the high-speed image processing system and selection of digital camera is also explained. The paper also gives details of the software developed and its features. The need for the high-speed system to record and generate interferograms during NDT of highly porous materials is also demonstrated in this paper.

Keywords: NDT; digital holographic interferometry; image processing; transient thermal stressing

Document Type: Research Article

DOI: http://dx.doi.org/10.1784/insi.2009.51.5.252

Affiliations: 1 Experimental Mechanics Division, Vikram Sarabhai Space Centre, Thiruvananthapuram 695 022, Kerala, India. binu_thomasvssc.gov.in, Tel: 91 (0)471 2565245

Publication date: May 1, 2009

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