📡Pneumatically-Actuated Liquid Metal-Based Frequency Reconfigurable Antenna

Soft Machines Lab

PI: Prof. Carmel Majidi

Carnegie Mellon University

Pittsburgh, PA

Aug 2024 - May 2025

🎯 Objective

Develop a soft, pneumatically actuated antenna capable of autonomous frequency reconfiguration across the 0.9–5 GHz range, integrating robotic actuation, stretchable electronics, and closed-loop control for adaptive wireless communication.

Dual-branch pneumatically actuated soft antenna with McKibben muscles and 3D-printed liquid-metal conductors. Each branch tunes independently to achieve wideband operation (0.9–5 GHz) under closed-loop PID control.

💡 Motivation

Modern robotic systems demand lightweight, adaptive, and reconfigurable communication hardware capable of functioning in dynamic or deformable environments. Conventional rigid and flexible antennas lack real-time tunability and mechanical adaptability.

This project was driven by the goal of integrating soft actuation and liquid-metal electronics to realize a self-tuning antenna that autonomously adjusts its frequency response through pneumatic control and closed-loop feedback—bridging soft robotics and wireless communication for resilient, intelligent robotic platforms.

⚙️ Approach

Designed a dual-branch monopole geometry fabricated with 3D-printed Ag-EGaIn-SIS liquid-metal traces on silicone substrates.
Integrated McKibben actuators for independent pneumatic tuning of each branch
Implemented a PID-based control loop linked to a software-defined radio (SDR) for real-time signal-strength feedback.
Optimized impedance matching and radiation efficiency through multi-stage simulation and experimental validation.

Step-by-step fabrication of the pneumatically actuated soft antenna (PASTA). Silicone substrate is molded and plasma-treated (A–B), 3D-printed with Ag–EGaIn–SIS conductive ink (C), integrated with SMA connector (D), and attached to McKibben actuators for pneumatic control (E).

Fabricated PASTA prototype showing the dual-branch soft antenna with attached SMA connector (A), detailed 3D-printed liquid-metal traces (B), and microscopy view under strain (C). The model (D) illustrates the actuation direction of each branch for frequency tuning.

🧠Two-Stage Control Strategy

v1 antehnna actuating.mp4

Actuation test of version 1 of the soft antenna

Actuation test of version 2 of the soft antenna

📈 Key Findings

Achieved autonomous tuning across 0.9–5 GHz in under 1 s.
Demonstrated 10–16 dB improvement in return loss and received-signal strength over flexible patch antennas.
Delivered 2× wider frequency coverage with only 10 g antenna mass and compact actuation (~100 g system).
Maintained omnidirectional radiation and high efficiency under repeated actuation cycles.

Closed-loop control and self-configuration of the pneumatically actuated soft antenna. The system integrates an Arduino-based air pump and valve controller with a software-defined radio (SDR) for real-time feedback. Received-signal-strength (RSS) data guide PID-based actuation to tune frequency within < 1 s, maintaining stable performance across 0.9–5 GHz.

Measured return-loss performance showing frequency reconfiguration of the PASTA antenna. Independent actuation of each branch enables wide-band operation from 0.9 GHz to 5 GHz with strong impedance matching (S11 < –10 dB).

🌍 Impact

PASTA enables adaptive, soft electromagnetic systems that unify mechanical actuation and wireless control—paving the way for self-tuning robotic communication modules, wearable electronics, and autonomous sensing networks.

View the Paper Submission Here

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