Measuring sound speed and bulk modulus in liquids using ‘ultrasonic grating Moiré fringes’ in an educational laboratory

Abstract An intuitive educational experiment is demonstrated for measuring sound speed and bulk modulus in liquids using ultrasonic grating Moiré fringes. A low-cost optical setup, built from standard teaching-lab components, projects the ultrasonic standing wave into macroscopic Moiré patterns via geometric magnification and grating superposition. Fringe spacing is automatically analyzed by a Python program integrating a U-Net deep learning model for robust, high-throughput data processing. The method is validated with pure water at room temperature, yielding sound speed and bulk modulus values consistent with reference data. Its applicability is further shown through systematic studies of temperature (15 °C–60 °C) and solute concentration (glycerol, ethanol), capturing both monotonic and anomalous non-monotonic trends. By merging acoustics, optics, and modern AI, this approach offers an engaging, interdisciplinary platform for undergraduate physics education.