Dual‐Frequency Ultrasonic Pulse‐Echo Testing

The problem of defect‐size determination by means of ultrasonic pulse‐echo testing and the benefits accrued from the utilization of a system that permits simultaneous testing at two different frequencies are discussed. The design of a dual‐frequency pulse‐echo test system employing only a single ultrasonic transducer is described, and its usefulness is examined for discriminating between disklike discontinuities (flat‐bottom holes) of various diameters. In addition, experiments are described that indicate that the frequency dependence of ultrasonic‐energy losses and the longitudinal‐wave velocities in materials can be determined faster and with a higher degree of reliability by dual‐frequency testing than by conventional methods. Also reported is an experimental investigation of the frequency dependence of transducer coupling in contact testing involving interposed layers of liquid couplant.