HALVE Actuators | Project Page

Abstract

Electrohydraulic artificial muscles can offer high speed and power density, but conventional designs often need several kilovolts and exposed high-voltage electrodes. This work introduces HALVE actuators, a multilayer electrohydraulic actuator design that lowers the operating voltage to around 1100 V while remaining safe to touch, waterproof, and self-clearing after dielectric breakdown. The actuators reach muscle-like average power density and peak strain rate, then demonstrate practical use in an untethered gripper and a soft robotic swimmer.

Overview

HALVE actuators combine a structural shell, an electrode, a high energy density dielectric layer, and liquid dielectric amplification. By decoupling mechanical load-bearing from the dielectric layer, the actuator can use thin high-permittivity materials to lower voltage while keeping the electrohydraulic contraction mechanism.

Lower voltage operation around 1100 V, roughly 5 to 7 times lower than comparable paraelectric electrohydraulic actuators.
Muscle-like performance with 50.5 W kg^-1 average power density and 971% s^-1 peak strain rate.
Untethered demonstrations in a compact gripper and an artificial fish powered by onboard electronics.

HALVE actuator mechanism, specific power plot, and robot demonstrators — Overview of the HALVE mechanism and its gripper and underwater fish demonstrators.

Design Principles

Multilayer Actuator

A force-bearing shell and a separate high energy density dielectric layer let electrical and mechanical properties be tuned independently.

Low-Voltage Drive

Thin PVDF-based dielectric layers increase capacitance, reducing the voltage needed for useful electrohydraulic contraction.

Robotic Integration

Compact power electronics drive independent muscle packs in untethered systems without bulky off-board supplies.

HALVE actuator force, strain, response, and strain-rate characterization — Performance characterization compares HALVE actuators against traditional Peano-HASEL devices across voltage, force, strain, and response speed.

Results

1100 V

Operating Voltage

Useful contraction at substantially reduced voltages for electrohydraulic actuation.

50.5 W kg^-1

Average Power Density

Comparable to the typical average power density of mammalian skeletal muscle.

971% s^-1

Peak Strain Rate

Fast contraction dynamics at low voltage with lightweight electrohydraulic muscles.

3 cm s^-1

Fish Speed

The untethered swimmer reaches 3 cm s^-1 after 14 seconds.

HALVE actuator touch safety, waterproof behavior, power supply lifting, and self-clearing — Implementation features include touch safety, waterproof operation, onboard power-supply lifting, and self-clearing recovery.

Untethered artificial fish assembly and swimming sequence — The untethered artificial fish integrates HALVE muscles, buoyancy, and embedded high-voltage power supply hardware.

Why It Matters

Challenge	HALVE Contribution	Robotic Impact
High electrohydraulic actuation voltages	Thin high-permittivity dielectric layer lowers the required drive voltage.	Smaller, lighter, and more practical onboard electronics.
Safety and environmental exposure	Insulated, waterproof, and self-clearing actuator construction.	More robust operation near humans, wearables, and water-based robots.
Untethered soft robotic demonstrations	Compact muscle packs integrated with power supplies.	Functional gripper and underwater swimmer without external actuation tethers.

Citation

Use the following BibTeX entry when citing this work.

@article{gravert2024lowvoltage,
  title = {Low-voltage electrohydraulic actuators for untethered robotics},
  author = {Gravert, Stephan-Daniel and Varini, Elia and Kazemipour, Amirhossein and Michelis, Mike Y. and Buchner, Thomas and Hinchet, Ronan and Katzschmann, Robert K.},
  journal = {Science Advances},
  volume = {10},
  number = {1},
  pages = {eadi9319},
  year = {2024},
  doi = {10.1126/sciadv.adi9319}
}