How It Works
Conceptually, you could say that EARS is like an "acoustic microscope". You can use a microscope to "visually" observe a tiny area of the world in very rich detail with color, luminosity and, contrast. Similarly, EARS is a method to "acoustically" observe small areas of metals in order to learn about the key details which come to bear on their resonant spectral properties. More formally, the technology is a measurement of local elastic constants and velocities of sound. As such it is also a highly resolved and rapid survey of the complete spectrum of physical and chemical properties that affect material elastic behavior.
A sensor technology and a spectroscopy method work together to make up the EARS technique and the ARIS line of NDT systems. Hardware and software excite, detect, and analyze high frequency and highly localized resonant modes in tested parts, doing so continuously and in real-time.
- A transmitting RM-EMAT sensor, using a continuously swept sine wave, excites electric surface eddy currents in the material and then transforms them into mechanical sound waves via the Lorenz force to bring about a stable acoustic resonance.
- A receiving sensor detects the resonance in the material with the opposite operation, and presents the modulated signal for processing.
The difference between EARS and traditional RUS or PCRT is in the use of EMAT sensors which do not force the entire part into resonance but instead create carefully bounded, acoustic fields in the areas directly under sensor faces.
Highly versatile, integrated ARIS systems, which very often include motion controlled sensors or moving test subjects, work by examining many small, bounded areas in rapid succession to get a comprehensive look at longer or more geometrically complex parts.
We can adjust our understanding of the theoretical vibrating string to reflect the new approach to resonance NDT. Instead of an engine valve stem resonating as a single string would, consider that the stem is comprised of hundreds of smaller strings that vibrate at significantly higher frequencies.
A non-destructive "test" of metals is made by observing changes to resonant signals within a part or from part to part. The analytical methods can be made to include both supervised training algorithms and calibrated quantitative measurements which are extremely responsive to small changes in material properties.