MATERIALS SCIENCE

What is RUS?

Given a sample's composition, dimensions, and elastic constants, a spectrum of resonant frequencies can be calculated for a given set of boundary conditions (the forward problem).  It is the job of RUS to measure these resonant frequencies and use them along with sample properties and a nonlinear inversion algorithm to compute elastic constants (the inverse problem).

In an RUS measurement the sample is held at its corners between piezoelectric transducers.  A minimal amount of pressure is used to avoid perturbing the resonances of the sample. One transducer is used to excite the sample while the other measures its response.  The driving frequency is typically swept from about 100 kHz to over 1 MHz until a sufficient number of resonances is obtained to provide a reliable solution to the inverse problem. 

These elastic constants are very valuable as probes to study phase transitions, and are closely related to thermodynamic properties such as specific heat and thermal expansion.

Advantages of RUS for determination of elastic constants:

• Sample sizes may vary from less than 1 mm³ (essential for single crystal samples) to several cm³. 
• All elastic constant are obtained from a single measurement, with no need to remount the sample.
• No bonding between sample and transducer and minimal loading closely simulate stress-free boundary conditions, resulting in accurate measurements of elastic constants.

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