All-soft multiaxial force sensor based on liquid metal for electronic skin

Abstract

Electronic skin (E-skin) capable of detecting various physical stimuli is required for monitoring external environments accurately. Here, we report an all-soft multiaxial force sensor based on liquid metal microchannel array for electronic skin applications. The proposed sensor is composed of stretchable elastomer and Galinstan, a eutectic gallium-indium alloy, providing a high mechanical flexibility and electro-mechanical durability. Liquid metal microchannel arrays are fabricated in multilayer and positioned along a dome structure to detect multi-directional forces, supported by numerical simulation results. By adjusting the height of the dome, we could control the response of the multiaxial sensor with respect to the deflection. As a demonstration of multiaxial force sensing, we were able to monitor the direction of multidirectional forces using a finger by the response of liquid metal microchannel arrays. This research could be applied to various fields including soft robotics, wearable devices, and smart prosthetics for artificial intelligent skin applications.

Liquid Metal-Based Devices: Material Properties, Fabrication and Functionalities

“…Due to its natural advantages of high electrical conductivity, high thermal conductivity, fluidity, and controllable deformation, LM has been widely used in switches [39][40][41][42][43], reconfigurable antennas [48][49][50][51][52][53][54][55], microwave devices [10][11][12][13], sensors [57][58][59][60], and wearable devices and flexible circuits [62][63][64]. Gallium-based LM can be used as a substrate integrated waveguide switch [39] and can also be used as a thermal switch controlling heat transfer spatially and temporally [42].…”

“…The strain sensors proposed in [16,26] had good mechanical stability and a high measurement factor. A soft multi-axis force sensor based on an LM microchannel array could detect multi-directional force [59]. A wearable tactile sensor based on LM (Galinstan) had high flexibility and stretchability, and could sense temperature and contact force simultaneously [60].…”

“…The results obtained proved the feasibility of using LM-based electrodes to fabricate flexible pressure sensing devices. To be able to accurately monitor the external environment, a full-soft multiaxis force sensor based on a LM microchannel array consisted of a stretchable elastomer and Galinstan, as shown in Figure 17 [59]. The LM microchannel array was fabricated in multiple layers and positioned along the three-dimensional dome structure to detect multidirectional forces.…”

Multifunctional liquid metal polymer composites

“…A valuable demonstration of this type of sensor is shown in Figure 12C, where researchers were able to code American Sign Language to hand gestures via a resistive sensing device. Injection‐based LMPCs can also deform with more predictability due to the simplicity of the traces, making them excellent for accurately detecting forces and pressures 171,172 . Furthermore, several recent studies have shown LMPCs potential for thermal‐resistive sensing.…”

“…Injectionbased LMPCs can also deform with more predictability due to the simplicity of the traces, making them excellent for accurately detecting forces and pressures. 171,172 Furthermore, several recent studies have shown LMPCs potential for thermal-resistive sensing. While remaining both stretchable and conductive, these composites experience magnitudes of change in resistance when exposed to temperature changes, highlighting their potential for overheating protection and other thermally driven smart devices.…”