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The lack of broadband impedance measurements has restricted the potential capabilities of ferromagnetic wire composites, which have been mainly evaluated through theoretical impedance calculated from existing models without considering wire domain microstructure. Here, we have developed an accurate method for measuring the impedance of ferromagnetic wires in a wide frequency range, from 100 kHz up to 15 GHz, under magnetic and stress stimuli. The broadband measurements were ensured by a more accurate microwave calibration on the PCB cell, extending the reference planes up to the wire sample ends and by compensating the sample waveguide properties using the phase unwrapping technique proposed in this work. In addition, a specially designed dogbone PCB measurement cell allows both field-and stress-dependent impedance measurements, efficiently transferring the tensile stress from the cell to the wire sample fixed onto it. The measured wire impedance can be then recalculated into the surface impedance, which constitutes the boundary condition in the antenna equation, describing the microwave scattering properties of a wire. The developed approach will make it possible to build a practically predictive scattering theory in composite materials with embedded wire inclusions and thus their implementation in real-world applications, such as remote stress monitoring.

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Self-sensing composites' performance largely relies on the sensing fillers' property and interface. Our previous work demonstrates that the microwires can enable self-sensing composites but with limited damage detection capabilities. Here, we propose an optimization strategy capitalizing on dual interfaces formed between glass-coat and metallic core (inner interface) and epoxy matrix (outer interface), which can be decoupled to serve different purposes when experiencing stress; outer interfacial modification is successfully applied with inner interface condition preserved to maintain the crucial circular domain structure for better sensitivity. We found out that the damage detection capability is prescribed by periodical structural integrity parameterized by cracks number and location in the case of damaged wires; it can also be optimized by stress transfer efficiency with silane treated interface in the case of damaged matrix. The proposed self-sensing composites enabled by a properly conditioned dual-interfaces are promising for real-time monitoring in restricted and safetycritical environments.