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arXiv · 2610.16026

Short-Range Microwave Interprobe Coupling in a Brain-Mimicking Phantom and Ex-Vivo Brain

Pouya Faeghi·Xiaoting Jia·Jeffrey S. Walling
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Abstract

A printed tapered-slot coupling probe with a partially inserted 12-mm wire element is characterized for short-range microwave coupling through a brain-mimicking agar--gelatin--saline phantom and \textit{ex vivo} brain. Simulated and measured free-space $S_{11}$ responses agree over a measured $-10$-dB band spanning 5.78 to 6.86~GHz, corresponding to a 1.08-GHz bandwidth and approximately 17.1~percent fractional bandwidth. In a controlled two-probe experiment, the phantom was introduced and removed while the probe arrangement and measurement conditions were retained. This comparison was repeated under the same retained arrangement, with the same general $S_{21}$ differential behavior observed across repetitions. Near 6.3~GHz, measured $S_{21}$ was approximately $-25$~dB with the phantom present and approximately $-40$~dB in air, corresponding to an $\approx 16~\mathrm dB$. \textit{Ex vivo} goat brain measurements repeated more than five times showed reproducible behavior. Across 5.78--6.86~GHz, the \textit{ex vivo} goat-brain $S_{21}$ response closely followed that of the phantom, with an approximately figure-derived maximum operating-band difference of about 1.5~dB. The observed increase in $|S_{21}|$ is interpreted as a property of the complete probe--medium--probe system, including loading, mutual coupling, interfaces, geometry, propagation, and material loss. The measurement does not uniquely identify a tissue-intrinsic mechanism.

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Pouya Faeghi, Xiaoting Jia, Jeffrey S. Walling. 2026-10-12. Short-Range Microwave Interprobe Coupling in a Brain-Mimicking Phantom and Ex-Vivo Brain. https://arxiv.org/abs/2610.16026

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