A Narrowband Ultrasonic Spectroscopy Technique for the Inspection
of Layered Structures
Licentiate Thesis, Signals and Systems,
Uppsala University, September 2006.
Licentiate Seminar Friday September 15, 2006, 10.15 - 12.00
Ångström Laboratory, Room 4001, Uppsala.
The thesis is available from Signals and Systems, Uppsala University,
Box 534, SE-751 21 Uppsala, Sweden.
Thesis in pdf (2.4M)
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
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.