Study of the effect of angle errors in conical ultrasonic sensors

Many ultrasonic sensors intended for non-destructive testing include a plastic or metal element, known as buffer rod, between the ultrasonic transducer and the material under analysis. Buffer rods are often terminated in the form of a conical tip for ultrasonic inspection of liquid-like substances. The conical tip is carefully shaped in a 45° angle to favour the in phase reception of all the components of the ultrasonic wave reflected at the buffer tip, obtaining thus a maximum amplitude measurement signal. The effect of the buffer rod cone angle on measurement signals is studied in this work. A straightforward approximate formula for the effect of the error angle on measurement signal amplitude is used. Simulations are performed using a two-dimensional finite differences tool. Measurements are conducted with the same operating conditions and buffer rod materials and dimensions as those defined for both approximate formula evaluation and simulations. Thus, a comparison of the approximate formula, simulation and measurement results are established. Furthermore, the significance of some parameters such as ultrasonic transducer operating frequency and diameter, and buffer rod material are also analysed. The obtained results show that significant loss of the measurement signal amplitude is found only for cone error angles beyond the range of usual machining errors.