Resonant Ultrasound Spectroscopy (RUS) for Determining Elastic Moduli of Soft Materials.

The elastic moduli of materials are vital for engineering and scientific applications, and simple, non-destructive methods to measure them can greatly improve material design. Using the classical Resonant Ultrasound Spectroscopy (RUS) approach, we built an inexpensive instrument capable of determining the full elastic stiffness tensor with high accuracy. The sample is nearly freely suspended between two piezoelectric transducers—one excites an ultrasonic signal, and the other receives it. A Stanford Research Systems SR865A-DSP lock-in amplifier generates and cleans the signal, while custom Python code performs precise frequency sweeps to detect resonances. When the excitation frequency matches a natural resonance, the output signal spikes, allowing identification of resonant modes. Using the sample's geometry and lattice structure, these frequencies are used to calculate all elastic constants. Our design supports a broad frequency range and can characterize materials from very soft to very hard. We have successfully validated the setup using ferroelectric KTa0.6Nb0.4O3 (KTN), recovering its elastic moduli with high accuracy. Ongoing work is focused on extending this method to metallic samples such as aluminum, iron, and magnesium. This low-cost, high-performance system is designed to be accessible for undergraduate education and research.