Abstract: A system and method for sizing defects in solid structures using guided waves. The system includes a magnetostrictive-strip EMAT transducer comprising at least one biasing static magnetic field, at least one RF coil for fixed-wavelength measurements, at least one RF coil for variable-wavelength measurements, and a strip of highly magnetostrictive material that is coupled with the structure. The fixed-wavelength RF coil permits obtaining measurements of amplitude and frequency content of signals reflected and/or attenuated when traveling through the structure which are used to estimate the size and geometry of any defects in this structure. The variable-wavelength RF coil permits recording the frequencies that are cut off or pass through the structure to also estimate the size of any defects in the structure. The fixed-wavelength sizing and geometry assessment is used to determine whether the variable-wavelength estimate is valid.