How to learn physics using an ultrasonic 'tuning fork'
| Date/Time: | Thursday, 18 May 2017 from 4:10 pm to 5:00 pm |
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| Location: | Physics 3 |
| Phone: | 515-294-7377 |
| Channel: | College of Liberal Arts and Sciences |
| Actions: | Download iCal/vCal | Email Reminder |
Tuning forks are used to determine a pure musical tone (fixed pitch). Physically, a tuning fork is an acoustic resonator in a U-shaped metallic bar. Once the overtones have subsided, it resonates at a specific frequency set by the fork's length and elastic properties of the material it is made of. We can use the same principle to study the elastic properties of a material if we know its dimension and mass. Elastic moduli are of great significance because they are fundamental thermodynamic susceptibilities that connect directly to thermodynamics, electronic structure as well as mechanical properties. Resonant Ultrasound Spectroscopy (RUS) measures non-destructively all fundamental elastic properties, by determining the natural frequencies at which a 3D object resonates when is mechanically excited (normal modes, see Figure). By using an inversion scheme it is possible to extract the entire elastic tensor of a material with extreme sensitivity (better than 10-8) in a single frequency sweep using only one sample. This makes RUS particularly advantageous to study physical properties of low-symmetry small single crystals materials. RUS can be used to study elastic properties of conducting or insulating materials as long as the acoustical loses are not too large.
In this talk I will present the basis of the RUS measurement technique and examples of its applications to thermodynamic and materials science problems. First, the detection and study the skyrmion lattice in the cubic system MnSi under magnetic field where we extract six independent elastic moduli. The elastic moduli displays a much larger compression than shear one, contrary to what it is theoretically expected but similar to what it is found in superconducting vortex lattices. Second, the study of Plutonium, the most intriguing metal that even more than 70 years after its discovery still hides many secrets. By measuring the temperature and time dependences of the elastic moduli, we can unravel key aspects of Pu electronic structure and bring light to its self-irradiation process.