Percolation-Driven ε–μ Co‑Tuning in Ag/Epoxy Nano-Composites from X‑Band to Terahertz

Bo-Wei Tseng^1*, Hua-Yan Chen¹, Po-Hsiang Chuang², Chan-Shan Yang², Tsun-Hsu Chang^1,3

¹College of Semiconductor Research, National Tsing Hua University, Hsinchu, Taiwan
²Institute and Undergraduate Program of Electro-Optical Engineering, National Taiwan Normal University, Taipei, Taiwan
³Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Bo-Wei Tseng, email:webbertseng20010125@gmail.com

This work consolidates two companion studies on silver/epoxy (Ag/Epoxy) conductor–insulator nanocomposites characterized across microwave X‑band (8.2–12.4 GHz) and terahertz (0.2–2.0 THz) frequencies. By extracting complex permittivity ε(ω) and permeability μ(ω) versus silver volume fraction p, both studies reveal a shared percolation window near the critical threshold p_c in which ε' and ε'' surge while μ' dips below unity due to percolation‑induced diamagnetic loop currents. Power‑law scaling of ε and the magnetic susceptibility χ_b =1-μ' indicates an effective two‑dimensional (2D) universality class governed by sample geometry and measurement configuration. The combined GHz–THz picture demonstrates that assuming μ'≈1 near p_c can misestimate impedance and refractive index, and that co‑tuning ε and μ is achievable through composition enabling compact RF/THz absorbers, impedance‑matched coatings, and meta‑surfaces without lithographic resonators.

Keywords: Percolation, THz-TDS, Complex permittivity, Complex permeability