Oblique incidence ultrasonics

S. I. Rokhlin and D. Marom, Study of adhesive bonds using low frequency obliquely incident ultrasonic waves, J. Acoust. Soc. Am. 80, 585-590 (1986). 

Oblique incidence ultrasonic test techniques like those illustrated in Fig. 7 are also quite useful. In fact, it has been found in earlier studies that the normal beam shear wave incidence technique is often more sensitive to subtle interfacial weakness problems than a normal beam longitudinal incident wave. It is difficult, however, to produce shear wave incidence in a normal beam mode because of the somewhat permanent adherence to the substrate that is required. As a result, it was... 

ANL s ultrasonic viscometer is a nonintrusive in-line device that measures both fluid density and viscosity. The design of the viscometer is based on a technique that measures acoustic and shear impedance. The technique was first applied by Moore and McSkimin (1970) to measure dynamic shear properties of solvents and polystyrene solutions. The reflections of incident ultrasonic shear (1-10 MHz) and longitudinal waves (1 MHz), launched toward the surfaces of two transducer wedges that are in contact with the fluid, are measured. The reflection coefficients, along with the speed of sound in the fluid, are used to calculate fluid density and viscosity. Oblique incidence was commonly used because of better sensitivity, but mode-converted waves often occur in wedges that do not exhibit perfect crystal structure and lack well-polished surfaces. For practical applications, we use the normal-incidence arrangement. 

The theory can be generalized to the case of oblique incidence/ Martinoty and Candau found that the viscosity coefficients determined by the ultrasonic technique compare fairly well with those derived from capillary flow. 

A. Pilarski and J. L. Rose, Ultrasonic oblique incidence for improved sensitivity in interface weakness determination, NOT International 21, 241-246 (1988). 

A. Pilarski, J. L. Rose, J. Dale, K. Balasubramaniam, and D. Lecuru, An ultrasonic oblique incidence technique for adhesive bond quality evaluation. Proceedings of the 4th European NDT Conference, September 13-17, 1987, London, UK, Vol. 4, pp. 2237-2244 Pergamon Press, New York (1987). 

Fig. 3. Refraction principle for ultrasonic waves impinging upon an interface between two materials at oblique incidence.

Pilarski, A. and Rose, J.L., A transverse-wave ultrasonic oblique-incidence technique for interfacial weakness detection in adhesive bonds. J. Appl. Phys., 63, 300-307 (1988). 

Other ultrasonic techniques which show promise are oblique incidence waves (Pilarski et al, 1990) and Lamb waves (Bork and Challis 1995). Rose and co-workers (Puthillath and Rose 2010 Rose et al. 1996 Rose and Ditri 1992 Rose et al. 1995) have used guided ultrasonic waves to detect defects in adhesively bonded joints. 

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