Remote measurements of the ultrasonic pressure distribution using focused transducer

Abstract

Measurements of the pressure distributions differences of the ultrasonic fields at different zones of the test object can be provided in order to estimate the dimensions of the defects, located in the test object. Such measurements of the field pressure distributions point-by-point can be done using hydrophones, e.g. ultrasonic transducers of a small diameter. The field is measured at the point where the hydrophone is located. The use of hydrophones for the ultrasonic field measurements is complicated due to the field distortions at the measurement points, induced by the hydrophone. In order to avoid for such distortions it is possible to use focused ultrasonic transducer. Presumption is done that the focused transducer measures the field, which is in the focus point of the transducer and the ultrasonic signals are obtained without placing the transducer at the exact point of the ultrasonic field. It is possible to measure remotely the distributions of the ultrasonic field pressure at different distances from the surface of the field radiating source.
There are no transducers, which would radiate the standard or a priori ultrasonic field, so the equivalent of the real field was theoretically calculated, which is tagged as a true field. Also the field pressure distribution, measured with the focused transducer, was calculated imitating the real measurement. The modelling results were verified and compared with the results, obtained during experimental measurements of the ultrasonic field distributions. Calculations and measurements were performed at three distances between the surface of the radiating plane transducer and receiving focused transducer.