Multiphysical Characterization of a Tissue-Mimicking Phantom: Composition, Thermal Behavior, and Broadband Electromagnetic Properties from Visible to Terahertz and Microwave Frequencies
Description
This article presents a comprehensive multiphysical characterization of a muscle-equivalent tissue-mimicking phantom intended for biomedical electromagnetic and thermal studies. The phantom’s chemical composition, thermophysical properties, and broadband electromagnetic response are systematically analyzed across visible, microwave, and terahertz frequency ranges. Optical properties are evaluated in the VIS–NIR spectrum, dielectric properties are extracted in the microwave band, and terahertz response is characterized using reflection-mode THz spectroscopy. Thermal stability and heat transport properties are assessed under physiologically relevant conditions and validated through controlled microwave hyperthermia experiments. The results provide an integrated materials-level understanding of the phantom’s behavior, supporting its suitability for broadband electromagnetic exposure, dosimetry, and hyperthermia applications.
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The dataset was generated through controlled fabrication and multimodal experimental characterization under reproducible laboratory conditions. The muscle-equivalent phantom was prepared following the formulation proposed by Ito et al., using deionized water, agar, polyethylene powder (~500 µm), sodium chloride (NaCl), TX-151 emulsifier, and sodium azide. NaCl and sodium azide were dissolved in heated water under magnetic stirring. The mixture was raised to 70 °C to incorporate agar, then homogenized with polyethylene and TX-151 using mechanical mixing. The material was cast in sealed molds, rested 24 h, wrapped to reduce dehydration, and stored at room temperature before testing. Elemental composition was analyzed by energy-dispersive X-ray spectroscopy (EDS) coupled to field-emission scanning electron microscopy (FE-SEM) at 20 kV. Ten spatially separated measurements were acquired and averaged. Thermal stability was assessed by thermogravimetric analysis (Discovery 550, TA Instruments) from room temperature to 800 °C at 10 °C/min in air. Thermal conductivity and volumetric heat capacity were measured using a KD2 Pro analyzer with a dual-needle probe inside a climatic chamber (Memmert HPP 110) at 25 °C, 35 °C, and 45 °C (65 % RH). The probe was inserted 3 cm into the phantom, equilibrated 15 min, and each condition was repeated four times. VIS–NIR diffuse reflectance (350–1200 nm) was acquired using a laser-driven broadband source (Energetiq EQ-99-FC) and an optical spectrum analyzer (Yokogawa AQ6373) coupled via a bifurcated fiber probe at 45° incidence. Calibration used a certified reflectance standard (Labsphere USRS-99-010). Spectra were collected at multiple surface positions under fixed geometry. Principal component analysis in Python was applied after mean-centering. Microwave dielectric properties (1.5–4.0 GHz) were extracted using a coplanar waveguide on Rogers RO3003 substrate. Two-port S-parameters were measured with a Rohde & Schwarz ZNA26 vector network analyzer after SOLT calibration. Relative permittivity and conductivity were derived from the complex propagation constant. Seven repeated measurements were performed. Terahertz characterization was conducted in reflection mode using a BATOP TDS1008 system (0.05–4.5 THz). A baseline–mirror–sample sequence ensured consistency. Time-domain scans were recorded every 30 min over 7.5 h to assess temporal stability. Microwave heating at 2.45 GHz was applied using a National Instruments USRP-2922 with external amplification. Surface temperature was monitored using an Optris PI 450i infrared camera (emissivity 0.98). Fixed antenna–sample spacing (5 mm) and repeated acquisitions ensured reproducibility under defined laboratory conditions.