Broadband dielectric characterization of liquid media at physiological cell-culture temperature (36.5 °C) with Debye–ionic modeling for RF exposure assessment

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Unlike most existing dielectric databases, which primarily focus on biological tissues, water, saline solutions, or tissue-equivalent materials, this study establishes a validated dielectric dataset for widely used cell-culture media measured directly under physiological culture conditions. In this work, the dielectric properties of four liquid media (DI water, PBS, DMEM, and RPMI-1640) were experimentally characterized at the physiological cell-culture temperature (36.5°C) using a temperature-controlled chamber. The relative permittivity and loss tangent of each medium were measured over the frequency range of 0.3–20 GHz. To provide a physically interpretable description of the measured dielectric behavior, a Debye–ionic conduction model for the four media was developed. The corresponding model parameters—static permittivity ( ε s ), infinite-frequency permittivity ( ε ∞ ), relaxation time ( τ ), and ionic conductivity ( σ )—were extracted by fitting the measured data. The results demonstrate that the PBS, DMEM, and RPMI-1640 exhibit dielectric behavior characteristic of saline-based aqueous media. Although the differences in the real part of the relative permittivity ( ε ′) among them are relatively small, the imaginary part of the relative permittivity ( ε ″) and the ionic conductivity are substantially higher, reflecting the dominant contribution of ionic conduction . These findings indicate that loss-related parameters are critical for predicting RF-induced power absorption and specific absorption rate (SAR) under otherwise identical local electric field conditions. Furthermore, by integrating uncertainty-quantified measurements with physically interpretable Debye–ionic conduction parameters, the proposed framework provides an engineering resource for reproducible RF dosimetry, reliable SAR estimation, and realistic in vitro bioelectromagnetic simulations.