Magnetostrictive transducers are receiving growing attention as an alternative to piezoelectric transducers in generating guided torsional waves in cylindrical waveguides. A recent study shows that torsional wave generation is possible if a set of thin magnetostrictive nickel strips are bonded to the surface of a cylindrical waveguide at an oblique angle and a combination of static and dynamic magnetic fields is applied to the strips. The objective of this work is to experimentally investigate the intriguing effects of the angle on the transduction efficiency and to provide a physical explanation for the observed phenomena. Excitation frequencies used for wave experiments were between 40 and 100 kHz, for which the highest transduction was observed.

This investigation presents a new measurement technique for third-order elastic constants using the acoustoelastic effect. The cross-sectional resonance frequencies of a cylindrical rod are measured while the rod is stressed under tensional load. The Murnaghan's third-order elastic constants of the rod are determined by matching experimentally obtained resonance frequencies with those numerically obtained by a finite element model. Electromagnetic acoustic transducers (EMATs) are employed to measure cross-sectional resonance frequencies, enhancing the repeatability to minimize the variation of the contact condition between the transducer and the specimen. The present method was applied to specimens made of carbon steel (JIS-S20C) and aluminum (Al7075-T651), whose third-order elastic constants were calculated. It should be emphasized that the estimated Murnaghan's constants obtained by the proposed method showed very small coefficients of variation (CVs), less than 6.54%, for repeated tests conducted on several specimens, showing excellent repeatability and reproducibility that is almost unattainable by conventional methods using wave speeds or higher harmonics of an input wave.

Grout voids in the tendons of a post-tensioning bridge reduce their strength. Grout voids are also severe flaws causing corrosion of the steel strands in the tendons. Detecting voids during construction and operation of the tendons is essential to prevent tendon failure, which is critical to bridge safety. This study presents a method for inspecting external tendons for voids in the grout below the protective duct pipe using terahertz electromagnetic waves. Due to low attenuation in the high-density polyethylene duct and the large reflectivity difference between the duct/grout and the duct/void interfaces, terahertz waves are suitable for detecting voids in the grout inside tendons. For this study, we developed a mobile frequency-domain terahertz A-scanner that can be used to measure terahertz A-scan data in real time. It is shown that the mobile terahertz A-scanner can be used to assess the area of the grout void in external bridge tendons.