Density Matters: The Effect of SPION Sedimentation on Molecular Communication

Abstract

Superparamagnetic iron-oxide nanoparticles (SPIONs) have emerged as promising information carriers in the field of molecular communication (MC). However, a critical discrepancy exists between theoretical models and experimental realities: while theoretical frameworks typically assume neutral buoyancy and neglect gravitational forces, practical implementations exhibit significant gravity-induced sedimentation. This oversight leads to substantial prediction errors and system unreliability. To address this, we developed an experimental testbed featuring a vertically oriented bifurcated channel, specifically designed to isolate and quantify the impact of gravity on signal propagation. Our experimental results empirically demonstrate that sedimentation causes significant deviations in channel impulse response (CIR), contradicting the simplifying assumptions found in existing literature. Furthermore, we elucidate the physical mechanism of sedimentation based on hydrodynamic instability to clarify the factors driving this settling behavior. This work highlights the necessity of incorporating gravitational effects into system modelling to ensure accurate performance assessment in realistic MC environments.