A study of the transmission of ultrasound across real rough solid-solid interfaces

A link between reflection coefficient, surface roughness and interfacial pressure is described for the case of elastic contact, the example chosen being contact between rubber and metal or plastic. This case is of practical interest for the dry coupling of ultrasonic transducers using a rubber contact tip. Real measured surface profiles are used in a numerical elastic contact model to predict the size and distribution of contacts and gaps between two contacting bodies under a given load. In addition to this modelling, reflection coefficients from rubber-solid interfaces have been measured at varying contact pressures. From the combination of the contact model and these experimental results, the variation of reflection coefficient with size and distribution of contacts and gaps (percentage contact) can be found. Results are presented for contact between surfaces of different roughness. These results are then compared with the predictions of various simple quasi-static models of the interface such as the Balk and Thompson representation