RECIPROCITY CALIBRATION OF ULTRASONIC CONTACT TRANSDUCERS

The extension of the reciprocity calibration method widely used in medical ultrasonics to nondestructive pulse-echo transducers is presented. It is shown that the self-reciprocity procedure originally developed for immersion transducers can also be applied to contact transducers, which are mainly used for the investigation of solids. The sensitivity of the contact transducers used was calculated with the help of two models which simulate the behavior of the transmitter-receiver arrangement within the whole frequency range investigated, namely 2-12 MHz. The procedure needed to determine the diffraction losses associated with the test objects such as half cylinders and half spheres is also presented. Half cylinders or half spheres are needed when the ultrasonic wave does not have a normal incidence on the test object. The calculated diffraction loss for the half cylinder was also experimentally verified. Good agreement obtained between diffraction loss measurements and the model predictions confirms that the calculated diffraction loss of the half cylinder is suitable for use in practical investigations. The calibration procedure described enables ultrasonic measurements performed with different contact transducers and devices to be compared. This is of great importance in many applications, as for example in periodic routine inspections of the components of nuclear facilities.