Flexible, printable and self-healable magnetic field sensors for soft robotics and human-machine interfaces

Composites consisting of magnetic fillers in polymers and elastomers enable new types of applications in soft robotics, reconfigurable actuation and sensorics. In particular, soft-bodied robots emerge as the closest synthetic system analogous to living organisms mimicking their mechanical behavior and going beyond in performance. We will introduce lightweight, durable, untethered and ultrafast soft-bodied robots performing large amplitude of deformations at high frequencies of up to 100 Hz and exhibit high specific energy density [1]. Our soft-bodied robots can walk, swim, levitate, and transport cargo being driven using external magnetic fields. This inspires new classes of soft robots that impact biosensorics, biological tissue engineering, confined and high-speed mechanical (tissue) manipulation, and serve as working models to study fast biomechanical processes like hydro- and aero- dynamics of fast-moving organisms.

These mechanically active structures are typically designed to work in a specific prior defined parameter range and can malfunction when the conditions are changed. Specifically for magnetic soft robots, the change of the intrinsic magnetic properties due to temperature activations or time relaxation can lead to modifications in the actuation pattern. We present ultrathin and reconfigurable magnetic origami actuators based on a composite consisting of shape memory polymers and magnetic microparticles [2]. Self-sensing is achieved by laminating ultrathin magnetosensitive e-skins [3] on soft origami actuators. The sensor assesses the magnetic state of the actuator (magnetized vs. non-magnetized) and decides on its actuation pattern even before the actual actuation is done experimentally. Furthermore, the sensor enables communication of the actuator with external devices (rotation stage, electromagnets) for self-guided assembly of an initially flat layout and provides the possibility to control the sequentiality and quality of the folding process.

Magnetic composites can be readily used to realise not only actuators but also magnetic field sensors. We demonstrate that printed magnetoelectronics can be stretchable, skin-conformal, capable of detection in low magnetic fields and withstand extreme mechanical deformations [4,5]. We feature the potential of our skin-conformal sensors in augmented reality settings [6,7], where a sensor-functionalized finger conducts remote and touchless control of virtual objects manageable for scrolling electronic documents and zooming maps under tiny permanent magnet.
Furthermore, we put forth technology to realise magnetic field sensors, which can be printed and self-heal upon mechanical damage [8]. This opens exciting perspectives for magnetoelectronics in smart wearables, interactive printed electronics. Furthermore, this research motivates further explorations towards the realisation of 3D printed magnetic field sensors.

[1] X. Wang et al., Untethered and ultrafast soft-bodied robots. Communications Materials 1, 67 (2020).
[2] M. Ha et al., Reconfigurable magnetic origami actuators with on-board sensing for guided assembly. Adv. Mater. 33, 2008751 (2021).
[3] G. S. Canon Bermudez et al., Magnetosensitive e-skins for interactive devices. Adv. Funct. Mater. 31, 2007788 (2021).
[4] M. Ha et al., Printable and Stretchable Giant Magnetoresistive Sensors for Highly Compliant and Skin-Conformal Electronics. Adv. Mater. 33, 2005521 (2021).
[5] E. S. Oliveros Mata et al., Dispenser printed bismuth-based magnetic field sensors with non-saturating large magnetoresistance for touchless interactive surfaces. Adv. Mater. Technol. 7, 2200227 (2022).
[6] J. Ge et al., A bimodal soft electronic skin for tactile and touchless interaction in real time. Nature Communications 10, 4405 (2019).
[7] G. S. Canon Bermudez et al., Electronic-skin compasses for geomagnetic field driven artificial magnetoception and interactive electronics. Nature Electronics 1, 589 (2018).