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Design and Performance Analysis of a Planar Microstrip Filter Sensor for Non-Invasive Human Tension and Physiological Stress Detection

Authors:

Nabaa S.M. Abed

DOI:

  • https://doi.org/10.65983/ijhec.2026.01.0003

Abstract:

Psychological stress is accompanied by autonomic changes that can modify sudomotor activity, skin hydration, and the ionic environment at the skin surface. Because tissue water content and conductivity contribute to microwave dielectric behavior, these physiological changes can perturb the electromagnetic loading experienced by a resonant sensor. This study presents a compact planar microstrip band-stop sensor operating near 2.45 GHz for non-invasive monitoring of stress-related physiological changes. The sensor uses a modified split-ring resonator (SRR) coupled to a 50-Ω microstrip line on Rogers RT/duroid 5880 (εr = 2.2, tanδ = 0.0009, h = 1.57 mm) and occupies 30 × 25 mm². HFSS simulations were performed using a three-layer skin model and the dielectric states reported in the original study. Across the modeled tissue range, ε′ increased from 38.0 to 46.5 and conductivity from 1.45 to 1.95 S/m, while the resonance shifted from 2.312 to 2.185 GHz, corresponding to a 127 MHz shift and an average sensitivity of 14.94 MHz per unit change in ε′. The unloaded-to-resting transition produced an additional 138 MHz shift and should not be confused with the tissue-state sensitivity range. Experimental measurements on 12 healthy adults used a two-port VNA and GSR as a reference physiological signal. The manuscript reports phase-level values of 2.14 ± 0.35 μS at baseline, 6.85 ± 0.92 μS during the Stroop task, and 2.80 ± 0.41 μS during recovery, with corresponding measured resonances of 2.315, 2.242, and 2.301 GHz. The previously reported R² = 0.984 is retained only as a reported experimental association because individual-level raw data are not supplied in the manuscript; confidence intervals, subject-level RMSE/MAE, and repeated-measures inference require the original paired measurements. The revised interpretation therefore treats the microwave response as a stress-related physiological proxy rather than a direct or diagnostic measure of psychological stress.

Keywords:

microwave sensor, microstrip filter, split-ring resonator, skin permittivity, electrodermal activity, physiological stress, non-invasive sensing, 2.45 GHz

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