Nondestructive Testing by Frequency-Domain Continuous-Wave Ultrasound Reflectometry

Currently, the primary method employed by ultrasound inspection systems is based on applying pulsed sound/ultrasound energy to the inspected part, and detecting reflected/transmitted pulses. Typically, pulse-based methods are essentially time-domain back-reflection methods, and time-of-flight is the main measured parameter. Recently, continuous-wave frequency-domain back-reflection meters were developed in the radar and in the fiber optics fields, which demonstrate significantly better spatial resolution, higher SNR, and ability to detect reflecting objects at very short distances. The same approach was used in this paper to develop a prototype continuous-wave ultrasound inspection system. The parameters of the prototype system are described, and the advantages and limitations of the continuous-wave ultrasound inspection method are discussed. Examples of the use of the system are presented.