Lock-in thermography using miniature infra-red cameras and integrated actuators for defect identification in composite materials

Geir Olafsson*, Rachael Tighe, Stephen Boyd, Janice M Dulieu-Barton

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

13 Citations (Scopus)
120 Downloads (Pure)


A novel approach for thermographic Non-Destructive Evaluation (NDE) of laminated polymer composite structures is presented. The technique is based on Lock-In Thermography (LIT), which traditionally uses an external heat source. Here a new means of internal heating, via a lightweight embedded actuator capable of providing highly repeatable and uniform heating is presented. The equipment cost, complexity and hence size is reduced by removing the need for high power external thermal excitation. Instead, the necessary temperature modulation of the internal actuator is achieved with a compact and low-cost Arduino controlled circuit. The size and cost of the equipment is further reduced by demonstrating that a miniature printed circuit board mounted thermal core type micro-bolometer can be used effectively for LIT. The performance of the thermal core is quantitatively compared with the more expensive and bulky traditional infra-red cameras. It is shown that the thermal core can detect defects with similar overall performance as a cooled photon detector and an uncooled micro-bolometer. The low-cost, compact nature and small mass of the thermal core offers great potential in thermographic inspection opening the possibility of deploying devices permanently on structures in conjunction with the embedded actuators for in-situ monitoring in the service environment.
Original languageEnglish
Article number107629
Number of pages11
JournalJournal of Optics and Laser Technology
Early online date19 Nov 2021
Publication statusPublished - 1 Mar 2022

Bibliographical note

Funding Information:
The authors would like to thank the Engineering and Physical Sciences Research Council (EPSRC) and BAE Systems Naval Ships for funding the work with an industrial PhD CASE studentship. The work described in the paper was conducted in the Testing and Structures Research Laboratory (TSRL) at the University of Southampton and the authors are grateful for the support received from Dr Andy Robinson, the TSRL Experimental Officer. The authors thank Mr. Michael Caton of TFP for supplying the material to develop the embedded actuator. The authors also appreciate the guidance and support of the student electronics workshop at the University of Southampton during the development of the modulation circuitry. The authors also thank Dr Cedric Devivier for contributing to the lock-in processing used in this study.

Publisher Copyright:
© 2021 The Authors


  • Non-Destructive Evaluation (NDE
  • Lock-in Thermography (LIT)
  • Bolometer
  • Internal Heating
  • Embedded Actuator


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