A method for obtaining more information from attenuation based material testing techniques

With reference to a well-known technique which detects the presence of air gaps inside materials on the basis of attenuation measurements of an ultrasound beam, a modification of the standard procedure is proposed which allows the determination of the thickness of the air gap itself. The method requires only a simple modification of the commonly used attenuation measuring setup. The technique requires a frequency-variable signal source for ultrasound generation and a receiver and transducers with a correspondingly wide bandwidth. There are no strict performance requirements for the flatness of the amplitude versus frequency characteristics of the source, transducers, and receivers, as the thickness estimation procedure is simply based on the detection of relative dips in the attenuation versus frequency response of the tested material