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

Abstract

Objectives: Short-range wireless links (microwave range) between closely spaced devices in brain tissue are relevant to neural interfaces and intracranial sensing, yet the change in coupling between two such devices caused by a finite volume of brain-like tissue has rarely been measured directly. Technology or Method: This work characterizes a printed, microstrip-fed, parasitic-strip-loaded tapered-slot coupling probe in which only a partially inserted 12-mm wire enters the medium, while the printed structure remains outside. Results: Two fabricated probes showed a measured free-space -10-dB reflection band of 5.78 to 6.86 GHz and a fractional bandwidth of approximately 17.1%, consistent with full-wave simulation. In a controlled two-probe experiment, a homogeneous agar-gelatin-saline brain-mimicking phantom was introduced and removed while the probe arrangement and measurement conditions were retained. Introducing the phantom increased the measured transmission coefficient near 6.3 GHz by approximately 16 dB, and this differential was reproduced across repeated trials. More than five measurements in ex vivo goat brain followed the phantom transmission response within approximately 1.5 dB across the 5.78-6.86-GHz band. Time-domain analysis of the phantom-present link gave a system root-mean-square delay spread of approximately 210 ps. Full-wave dosimetry predicted a peak 1-g-averaged specific absorption rate of 1.05 W/kg for approximately 0.49 W accepted power. Conclusions and Clinical or Biological Impact: These results provide an experimentally validated reference for short-range probe coupling in brain-like media and support phantom-based bench evaluation of minimally invasive intracranial probes before in vivo studies.

arXiv comment8 pages, 10 figures, 3 tables