Increasing the Performance of EHD Fiber Pumps by Scaling and by Changing to a More Sustainable Working Fluid

Electrohydrodynamic (EHD) fiber pumps are flexible millimeter-diameter tubes that generate fluid flow when a high voltage is applied. These pumps consist of a polymer shell in which two helical copper electrode wires are embedded, such that they are in electrical contact with the liquid. The fiber form factor is well-suited for integration in fluidic-driven wearable robots. In our earlier work (Smith et al., Science 379, 2023) we reported fluidic powers of approximately 20 mW/m at 6.4 kV, using the hydrofluoroether dielectric liquid novec-7100, which will however no longer be commercially available past 2028.<br/>Here we report 5x improved pump performance by two means: using different fluids and varying pump diameter. To measure the EHD fiber pump’s performance across a broad range of fluids, a change in the polymer shell material was necessary. By switching from thermoplastic polyurethane (TPU) to polypropylene (PP), we ensured chemical compatibility with a wide range of fluid candidates, including fluorinated organic fluids, nonfluorinated organic fluids, and organosilicon fluids, focusing on non-toxic choices. We built an automated test platform to systematically record pump metrics including generated pressure, flowrate, efficiency, and fluidic power, as a function of applied voltage. We also explored the effect of changing liquid and varying tube inner diameter and electrode spacing. Several liquids showed performance on par or even better than novec-7100.<br/>Using a nonfluorinated organic fluid (3-methoxybutyl acetate) and by scaling the pump diameter while keeping a constant inter-electrode spacing, we achieved a fivefold improvement in the maximum fluidic power output, reaching over 100 mW/m. Generating 1 W of fluidic power now requires 10 m of pump, nearly within reach of our manufacturing equipment.<br/>We used a 1-meter-long EHD fiber pump to drive a thin McKibben actuator, lifting a 500 g weight by 1.5 cm within 6 s, illustrating the promise of EHD fiber pumps for fluidic wearable robots.