Liquid Metal-Elastomer Composites with Dual-Energy Transmission Mode for Multifunctional Miniature Untethered Magnetic Robots

Abstract

Miniature untethered robots attract growing interest as they have become more functional and applicable to disruptive biomedical applications recently. Particularly, the soft ones among them exhibit unique merits of compliance, versatility, and agility. With scarce onboard space, these devices mostly harvest energy from environment or physical fields, such as magnetic and acoustic fields and patterned lights. In most cases, one device only utilizes one energy transmission mode (ETM) in powering its activities to achieve programmed tasks, such as locomotion and object manipulation. But real-world tasks demand multifunctional devices that require more energy in various forms. This work reports a liquid metal-elastomer composite with dual-ETM using one magnetic field for miniature untethered multifunctional robots. The first ETM uses the low-frequency (<100 Hz) field component to induce shape-morphing, while the second ETM employs energy transmitted via radio-frequency (20 kHz-300 GHz) induction to power onboard electronics and generate excess heat, enabling new capabilities. These new functions do not disturb the shape-morphing actuated using the first ETM. The reported material enables the integration of electric and thermal functionalities into soft miniature robots, offering a wealth of inspirations for multifunctional miniature robots that leverage developments in electronics to exhibit usefulness beyond self-locomotion.

Keywords: liquid metal; magnetic soft composite; miniature mobile robotics; soft robotics; wireless energy transmission.

Figure 1

Schematics illustrating the design and two working principles of the reported soft composite material. A) Schematic illustration of the reported magnetic liquid metal‐elastomer composite. B) An optical top‐view microscope image of the composite material. C) The first energy transmission mode is established by a low‐frequency component of the magnetic field to deliver mechanical energy for shape‐morphing. D) The newly enabled second energy transmission mode is established by an RF fast‐changing component of the magnetic field to deliver heat and electric current for hyperthermia and onboard electronics.

Figure 2

Electrical and mechanical characterization of the soft composite material. A) Measurement of the resistivity of the reported material (35  ×  18  ×  0.22 mm³). Each data point represents the average of three measured values. The variation is smaller than the marker size. B) Measurement of Young's moduli of the reported material and two other reference materials, i.e., PDMS (10:1 mass ratio between base and curing agents) and PDMS mixed with NdFeB MMPs at 1:1 weight ratio.

Figure 3

A sheet‐shaped, untethered miniature magnetic soft robot performing heat treatment on chicken breast meat in water. A) Video snapshots of the robot walking inside the tissue‐covered chamber (see Video S1, Supporting Information). B) 3D schematic illustrating the experimental setup. The untethered robot moved inside a chamber filled with distilled water preheated to 37 °C with walls made of chicken meat. The inset shows the side‐view sinusoidal magnetization profile of the robot. C) Top‐view images of the bottom and top surfaces of the chamber after the experiment. D) Experimentally measured temperature profile of the treatment site during the experiment in response to a ${\vec{B}}_{\mathrm{rf}}$ with a strength of 86.2 kA m^–1 alternating at a frequency of 337 kHz.

Figure 4

Untethered miniature soft robot surface‐crawling into an enclosed space using magnetic field‐based actuation and powering its onboard electronics using RF power transfer. A) The soft robot deformed its body for surface‐crawling locomotion using an external low‐frequency magnetic field waveform. B) The robot generated onboard electric current for powering an LED via the externally exerted RF fast‐changing magnetic field. C) Schematics illustrating two robot designs and their equivalent circuit. Two robots were fabricated, with the only difference being the onboard electronic units. A series of experimental snapshots are presented to show a robot moved into an enclosed space and powered a D) laser diode and E) an LED. The ${\vec{B}}_{\mathrm{rf}}$ has a frequency of 337 kHz. It has a strength of 46.8 and 24.3 kA m^–1 for the laser diode and the LED experiments, respectively. Videos of (D) and (E) are available in Videos S2 and S3 (Supporting Information), respectively.