Speaker: Aaron Khan, Boston University
Title: Thermal Wave Sensing for Operando Measurement of Subsurface Electrochemical, Mechanical, and Thermal Transport Properties in Next-Generation Energy Materials
Abstract: Thermal Wave Sensing (TWS), an extension of the 3-Omega method, offers a powerful, frequency-domain approach for noninvasively probing thermal and nonthermal properties in complex materials and devices. By applying a sinusoidal current to a high-aspect-ratio metal sensor, TWS induces periodic Joule heating and measures the resulting temperature oscillations. These oscillations are governed by the thermal transfer function of the sample, which encodes information about thermal conductivity, heat capacity, and interfacial resistance. Through the sensor's temperature-dependent resistance, this thermal information is inherited by the voltage response, enabling precise extraction of subsurface thermal properties from the third harmonic signal.
TWS is able to sense dynamic processes such as lithium-ion diffusion, microcrack evolution, and gas adsorption. Applications include architected battery electrodes, high-temperature thermal energy storage composites, and metal-organic frameworks for direct air capture. In each case, thermal conductivity serves as a proxy for a property of interest, enabling operando diagnostics.
This talk details the theoretical foundations of TWS, sensor fabrication constraints, system instrumentation, and analysis. It also outlines experimental workflows for calibration, validation, and application-specific measurements. The talk aims to establish TWS as a general-purpose, scalable platform for in situ and operando materials characterization, with broad implications for energy storage, thermal management, and noninvasive sensing.