Vertically aligned dual-sensing multi-harmonic system for non-invasive thermal measurement of freestanding layers

A multi-harmonic frequency-domain thermal characterization system based on a vertically aligned dual-sensing configuration was developed to address the substrate dependence and parameter-coupling limitations inherent in conventional 3ω techniques. The system integrates two flexible film sensors positioned on opposite sides of a freestanding layer, enabling non-invasive out-of-plane thermal measurements. By synchronously acquiring 1ω, 2ω, 3ω, and DC harmonic signals and integrating them with an improved multilayer thermal diffusion model, the proposed method enables the simultaneous determination of thermal conductivity, volumetric heat capacity, and contact thermal resistances with high accuracy. Experimental validation using SiO2, copper, and polydimethylsiloxane films confirms the accuracy and stability of the proposed system, demonstrating its strong capability for resolving interfacial heat-transfer behavior. This work establishes a compact and reliable platform for the precise thermal metrology of flexible and multilayer materials, providing new methodological support for advanced thermal management and flexible electronic applications.