BlueME: Robust Underwater Robot-to-Robot Communication Using Compact Magnetoelectric Antennas

Mehron Talebi, Sultan Mahmud, Adam Khalifa, and Md Jahidul Islam

Pre-print


BlueME Overview


Magnetoelectric (ME) antennas offer a promising solution to overcome the limitations of acoustic and optical communication in underwater environments. By leveraging the magnetoelectric effect, these antennas efficiently transmit and receive very-low-frequency (VLF) electromagnetic signals with a more compact design than traditional electrically small antennas (ESAs). This efficiency, combined with their resilience to multi-path interference, non-line-of-sight requirements, and Doppler effects, makes ME antennas well-suited for space- and power-constrained underwater applications.

In this project, we present the design, development, and validation of BlueME, a novel magnetoelectric (ME) antenna system for real-time data transmission between underwater robots. We use a compact array of ME antennas integrated into pressure-compensated enclosures for real-time data transmission and retrieval between robots and sensors underwater. While previous ME-based underwater communication efforts have primarily focused on basic connectivity tests in controlled water-tank environments, we validate BlueME by open-water trials, demonstrating its potential as a deployable communication system for marine robotics applications.

Overall, we make the following contributions:
 • We design, simulate, and fabricate an ME antenna array system (BlueME) for real-time underwater communication between mobile robots and/or sensor nodes. This is the first ME antenna array system tested in practical environments beyond controlled water-tank setups.
 • We present a seamless integration of BlueME into pressure-compensated enclosures to ensure reliable underwater operations. The enclosed system is compact and portable for use on low-power embedded devices.
 • We validate the system through simulation as well as open-water experiments, demonstrating its effectiveness for underwater communication. The system performs reliably when fully submerged and is unaffected by turbidity, line-of-sight obstacles, and shallow-water interference, which limit acoustic and optical systems.
 • Our field deployments reveal that we can achieve high-fidelity communications between mobile robots for up to 200 meters with a power footprint of only 1 watt.

The proposed BlueME system includes a novel ME antenna design; we use a 3x5 array of these antennas to enable real-time communications between underwater robots and wireless sensor nodes.


System Design and Integration


The Figure above illustrates an outline of our design showing how magnetostriction and piezoelectricity are coupled together in ME antennas. We investigate the fundamental mechanical resonance frequency of the ME antenna for underwater communication. Considering the requirements of compact size, low attenuation characteristics, and long propagation distances, we calculate a frequency of approximately 35 kHz. Please check out paper for detailed analyses.

To validate our theoretical analysis, we use COMSOL Multiphysics to simulate a three-layer ME structure. We evaluate the displacement magnitude of our antenna with a Metglas-PZT-Metglas thickness of 25-150-25 um. As shown above, we predict the eigenfrequency for the fundamental displacement mode to be 40.85 kHz.

As shown above, each ME antenna is housed in a custom 3D-printed enclosure. The upper shell of the enclosure contains a pogo pin and two vertical 18 AWG copper wires; the pogo pin is bonded to a designated hole on the antenna using a UV-curable cyanoacrylate adhesive. The 36 AWG wires from the antenna are twisted and soldered to the 18 AWG wires, which extend through the lower shell. The two shells are then enclosed and arranged in a 3x5 grid within a frame that includes 1/32 inch N52 neodymium magnets oriented north-to-south to maintain the required magnetic bias. The receiver and transmitter antennas are connected in series and parallel configurations, respectively.



Data Communication


In our experiments, a transmitter antenna array is mounted on an autonomous surface vehicle (ASV) (BlueRobotics BlueBoat), while a receiver array is mounted on an underwater remotely operated vehicle (ROV) (BlueRobotics BlueROV2). The transmitter array connects to a power amplifier driven by a signal from a Digilent Analog Discovery 2 (AD2) board.

The receiver array connects to a low-noise amplifier (AlphaLab LNA10) with configured gain and filtering, which is interfaced with a Digilent Analog Discovery 3 (AD3) board. Signal modulation and recording are performed on host computers tethered to the ASV and ROV via AD2 and AD3 devices. We capture signal strength, represented by the induced voltage on the ME receiving array, as a function of distance. This data was recorded using Digilent's WaveForms software on the host computers. Data communication and signal processing flow is shown on the right.


Field Experimental Analyses


We deploy the proposed system on ASVs and underwater ROVs for comprehensive performance evaluation and feasibility analysis. Our field experimental results demonstrate that the BlueME system offers a more robust, long-range, scalable, and efficient alternative to the traditional acoustic and optical communication modalities. We also analyze the antenna characteristics, underlying theory of operations, and relevant engineering constructs for practical deployments of ME antenna arrays underwater.


Impedance Measurement. The impedance measurements of the individual antennas are shown in the following Figure. These results match our simulations and proof-of-concept experiments, thus validating the proposed design. We observe that the parallel configuration of transmitter antennas resulted in an impedance close to the parallel sum of the individual antenna impedances within the target frequency range. Similarly, the series configuration of the receiver antennas yielded an impedance close to the sum of the individual impedances. These results demonstrate that wiring the antennas in parallel or series effectively adjusts the overall impedance and resonant response, which can improve bandwidth and signal strength. Furthermore, some antennas exhibited smaller resonant peaks near the primary resonant frequency of 35-36 kHz. We hypothesize that this is due to minor variations in the fabrication process or internal micro-cracks. Notably, certain antennas displayed approximately one order of magnitude lower impedance at resonance and higher quality factors than average, indicating stronger resonant responses. Conversely, some antennas had approximately one order of magnitude higher resonant impedance and lower quality factors than average, suggesting weaker resonant responses but wider bandwidths. These variations highlight the importance of consistent fabrication processes and the potential for optimization through mass manufacturing and binning.
For the results of impedance analyses above: (a-d) Rx impedance, reactance, resistance, and phase; (e-h) Tx impedance, reactance, resistance, and phase. The blue shaded areas indicate the bounds across all antennas tested individually, with the blue line showing the average value. The red line shows the result with all antennas connected in series (for Rx) or parallel (for Tx). All results are obtained from impedance analyzer sweeps performed on a DAD3 board from 33-38 kHz.
Signal Strength. The Figure above shows that received signals at various transmitter power levels and distances, a downward frequency shift is also observed. However, since the receiver experiences only the coupled power from the transmitter, these power levels are much lower, resulting in minimal nonlinear distortion at the receiver. Thus, the observed frequency shift primarily reflects the transmitter's nonlinear behavior combined with the receiver's nearly constant resonant response. These effects can be exploited to adjust for resonance mismatches between Tx/Rx arrays by varying the drive strength. We also observed that the antenna performance was not significantly affected by obstacles, water turbidity, or multipath propagation, which are major challenges for traditional acoustic and optical modalities.

Please checkout Our Paper for more details on the theoretical analyses of the data communication. We are currently focusing on optimizing the antenna fabrication process to ensure consistent performance and on tailored modulation schemes that extend the system's capabilities. This includes enabling applications in multi-robot cooperative tasks such as localization, navigation, and mapping, where reliable, low-latency, and low-power underwater communication is essential.


Acknowledgments


This work is supported in part by the NSF grants #2330416 and #2435009; and UF research grant #132763.