Electromagnetic ultrasonic (EMUS) probes: state of the art and developments for application in nuclear power plants
The excitation and detection of ultrasound by conventional piezoelectric techniques doesn't provide the full range of elastic wave modes which can be used for NDT. Besides this there is a limitation of the temperature range. This gap can be filled up using alternative techniques for the ultrasonic transduction. One of the most far developed alternative techniques is the electromagnetic ultrasonic (EMUS) excitation and detection. EMUS-probes work free of liquid couplants; hence they can be appplied for inspection and measurements at higher temperatures. The transduction of shear waves with horizontal polarization (SH-)waves can be more reliably performed by EMUS-probes for practical applications than by piezoelectric shear wave transducers using Y-cut quartzes. The contribution presents the performance of phased-array angle-probes. The application of these probe-type for the ISI of austenitic and dissimilar welds using SH-waves will be shortly highlighted. For the continous monitoring o f the liquid level in the vessel of BWR's from outside at temperatures of 300øC SV-wave angle probes are used. Their performance for operation in the mentioned temperature range and the principle of measurement of the liquid level will be described. Ongoing development work to enlarge the frequency range of EMUS-probes and for the automatic control of the lift-off will be shortly described.