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 — Panel A shows the HALVE actuator architecture and voltage-driven strain. Panel B compares average specific power versus actuation voltage. Panel C shows untethered demonstrations, with subpanel i showing gripper lifting and subpanel ii showing underwater fish integration and tail motion.

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 — Panel A shows low-voltage contraction under load. Panel B compares the HALVE layer stack with a traditional HASEL stack. Panels C, D, and E quantify force-strain behavior, transient strain response, and the voltage/force tradeoff at increasing peak strain rates.

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 — Panel A shows touch safety at 800 V. Panel B demonstrates waterproof operation in tap water. Panel C shows HALVE actuators lifting an onboard 13 g power supply, and Panel D shows self-clearing recovery after repeated dielectric breakdowns.

Untethered artificial fish assembly and swimming sequence — Panel A diagrams the untethered artificial fish architecture. Panel B shows the assembled components and embedded high-voltage power supply. Panel C plots alternating HALVE actuation and tail motion, and Panel D shows the swimming sequence from rest to 3 cm s^-1.

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}
}