Solid state bonds are being extensively developed and used in aerospace structures. As with any other bonding technology, a reliable method for estimating bond strength is needed in order to establish confidence levels in the process routes and the finished bonded products. Ultrasonic nondestructive evaluation (NDE) methods are currently being investigated for detection and characterisation of anomalies at diffusion bonds between similar or dissimilar metallic layers [1], There is large gap in the understanding of the nature and behaviour of imperfect bonds. These are diffusion bonds which do not show up as good reflectors of ultrasonic energy, but at the same time have very low bond strengths. A purely experimental approach to developing an NDE method is often hampered by the difficulties in fabricating samples with controlled defects, and other experimental uncertainties. The objectives of this study are thus to develop a computer model to determine whether ultrasound could be used for characterisation of imperfections at a diffusion bond, and what would be the optimum set-up for obtaining the most reliable information about the condition of the bond line.