Experimental Characterization of Hydrodynamic Gating-Based Molecular Communication Transmitter

TL;DR

The paper addresses the challenge of generating reliable, high-fidelity molecular concentration pulses in microfluidic molecular communication by experimentally validating a hydrodynamic gating-based transmitter enhanced with a zig-zag passive mixer. By controlling input pressures, it achieves programmable, reproducible pulses and demonstrates linear relationships between gating time $T_g$ and pulse width $w_p$, as well as between input inter-pulse duration $T_{pi}$ and measured inter-pulse duration $T_{pm}$, while mitigating inter-symbol interference through improved cross-sectional mixing. The work provides a practical MCU-like testbed for MC and IoBNT research, enabling more accurate pulse shaping and potentially multi-waveform transmissions in microchannels. These findings advance MC experimentation by delivering a simpler, tunable, and more reliable transmitter architecture aligned with microfluidic fabrication capabilities and pressure-driven operation.

Abstract

Molecular communication (MC) is a bio-inspired method of transmitting information using biochemical signals, promising for novel medical, agricultural, and environmental applications at the intersection of bio-, nano-, and communication technologies. Developing reliable MC systems for high-rate information transfer remains challenging due to the complex and dynamic nature of application environments and the physical and resource limitations of micro/nanoscale transmitters and receivers. Microfluidics can help overcome many such practical challenges by enabling testbeds that can replicate the application media with precise control over flow conditions. However, existing microfluidic MC testbeds face significant limitations in chemical signal generation with programmable signal waveforms, e.g., in terms of pulse width. To tackle this, we previously proposed a practical microfluidic MC transmitter architecture based on the hydrodynamic gating technique, a prevalent chemical waveform generation method. This paper reports the experimental validation and characterization of this method, examining its precision in terms of spatiotemporal control on the generated molecular concentration pulses. We detail the fabrication of the transmitter, its working mechanism and discuss its potential limitations based on empirical data. We show that the microfluidic transmitter is capable of providing precise, programmable, and reproducible molecular concentration pulses, which would facilitate the experimental research in MC.

Figures (6)

• Figure 1: An illustration of different states of the hydrodynamic gating process: (a) Gating state (barricading the entrance of information molecules), (b) Injection state (allowing the entrance of information molecules). Note: The zig-zag mixing channel in this chip, which shows a single transition from left to right, is extended in subsequent designs to increase the hydraulic resistance by having multiple transitions.
• Figure 2: Schematic representation of the Hydrodynamic Gating-Based MC Transmitter and parameters of the zig-zag mixing sturcture. $L$ is the total linear length, $s$ is the length of each periodic zig-zag step, and $w$ is the channel width.
• Figure 3: An illustration of the fabricated PDMS chip for the MC transmitter, integrated to the experimental setup.
• Figure 4: An illustration of consecutive pulses with different gating times ($T\textsubscript{g}$): (a) t = 90 ms, (b) t = 120 ms and (c) t = 150 ms. The dashed lines indicate the pulse width values ($w_{p}$), determined using the FWHM method, while the peak points mark the maximum concentration points. NCIP stands for normalized concentration intensity profile. Processed with MATLAB.
• Figure 5: An illustration of consecutive pulses with different input inter-pulse durations ($T\textsubscript{pi}$): (a) t = 7 s, (b) t = 11 s and (c) t = 17 s. NCIP stands for normalized concentration intensity profile. Processed with MATLAB.