Marcus Engholm

Licentiate Thesis, Signals and Systems, Uppsala University, September 2006.

The thesis is available from Signals and Systems, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden.

Thesis in pdf (2.4M)

Abstract:

This thesis introduces a narrowband ultrasonic spectroscopy (NBUS) technique for non-destructive testing. NBUS is most commonly used for inspection of multilayered structures. Inspections are performed by monitoring the electrical impedance of a transducer at a single frequency,the working frequency. A transducers electrical impedance depends on the mechanical load on its surfaces. Acoustically coupling a transducer to an object changes its electrical impedance depending on the objects condition. This is utilized to detect defects in inspected objects.

Optimal transducer design and working frequency selection is addressed using modelling. Simulation results from a transfer matrix model of an evaluation setup is compared to results from FEA simulations. The transfer matrix model is used to calculate kinetic and elastic energy distributions in the inspected object as well as the effective electromechanical coupling coefficient (EMCC) of the setup. Transducer performance is explained using these quantities making it possible to optimize the transducer design.

NBUS has been successfully used for the inspection of carbon fibre reinforced panels (CFRP) and multilayered structures. Results from these inspections are presented.