Embedding liquid metals (LMs) into an elastomer is emerging as a promising strategy for stretchable conductors. Existing manufacturing techniques are struggling between spatial resolution and proce...

https://pubs.acs.org/doi/pdf/10.1021/acsaelm.1c00884

Stretchable Conductors Fabricated by Stencil Lithography and Centrifugal Force-Assisted Patterning of Liquid Metal

This study presents a dielectrophoresis-based liquid metal (LM) droplet control microfluidic device. Six square liquid metal electrodes are fabricated beneath an LM droplet manipulation pool. By applying different voltages on the different electrodes, a non-uniform electric field is formed around the LM droplet, and charges are induced on the surface of the droplet accordingly, so that the droplet could be driven inside the electric field. With a voltage of ±1000 V applied on the electrodes, the LM droplets are driven with a velocity of 0.5 mm/s for the 2.0 mm diameter ones and 1.0 mm/s for the 1.0 mm diameter ones. The whole chip is made of PDMS, and microchannels are fabricated by laser ablation. In this device, the electrodes are not in direct contact with the working droplets; a thin PDMS film stays between the electrodes and the driven droplets, preventing Joule heat or bubble formation during the experiments. To enhance the flexibility of the chip design, a gallium-based alloy with melting point of 10.6 °C is used as electrode material in this device. This dielectrophoresis (DEP) device was able to successfully drive liquid metal droplets and is expected to be a flexible approach for liquid metal droplet control.

A Study of Dielectrophoresis-Based Liquid Metal Droplet Control Microfluidic Device.

Fabrication of flexible microheater with tunable heating capabilities by direct laser writing and selective electrodeposition

Metal coils are typically used as motors, inductors, transformers, and loop antennas, which are essential and ubiquitous elements in electronics. With the improvement of living standards and the demand for compliant technologies, flexible electronics are thriving as new frontiers in diverse areas. Along with that, various soft circuits and electronic components are urgently required to replace those traditional rigid ones, in order to tackle existing challenges. Among those materials to realize device flexibility, room temperature liquid metals are playing ever important roles instead of conventional metal components due to their outstanding fluidity, large conductivity, and non-toxicity. In this review, we summarized and classified the transformable properties of liquid metal coils (LMCs) as four fundamental passive electronic components: resistor, capacitor, inductor, and memristor. The fabrication methods of LMCs are illustrated. Then we concluded LMCs’ contributions to soft actuation, flexible sensing, antenna, and so on, which would be conducive to the fields such as wearable and implantable devices, soft robotics, and medical instruments. Finally, the current challenges in LMC’s practical applications and outlook have been discussed. 

Liquid Metal Coil

Soft magnetic sensors for tactile and pressure sensing based on the intensity change of the magnetic field has been drawing attentions recently due to the simplicity in manufacturing using commercial Hall effect sensors with high linearity and sensitivity. However, these sensors usually show relatively narrow sensing ranges due to fast saturation of the output signals from the magnetic field. In addition, rigid components for creating the magnetic field often limit the structural compliance. In this study, we propose a soft pressure sensor not only sensitive in a small pressure range but also has a large dynamic range using a hybrid mechanism of two different sensing modes: electromagnetic and piezoresistive sensing. By directly printing eutectic gallium-indium (EGaIn) to form a double-layered pancake coil pattern on a silicone elastomer, we fabricate a microfluidic soft coil that can be used as either an electromagnet or a variable resistor. Parameters, such as the sensor height, the stiffness of the material, and the resistance of the soft coil are configured for an enhanced sensitivity, a short recovery time from deformation, and reduction in electrical failures during operation. In this letter, we introduce the design and fabrication of the proposed sensor and characterizes a single sensor prototype. An array of the proposed sensors is also demonstrated as an application. 

A Hybrid Mechanism of Electromagnetic and Piezoresistive Sensing Using A Soft Microfluidic Coil

Gallium-based liquid metal can be used as a material for microheaters because it can be easily filled into microchannels and electrified to generate Joule heat, but the liquid metal-based microheater will suffer breakage induced by voids forming within the liquid metal when the temperature normally gets higher than 100 °C. To resolve this problem, a novel liquid metal-based microheater with parallel ventilating side-channels is presented. It consists of a liquid-metal heating channel and two parallel ventilating side-channels. The heating channel is connected with the side-channels by small gaps between polydimethylsiloxane (PDMS) posts. Experimental results show that this novel microheater can be heated up to 200 °C without damage. To explain its excellent performance, an experiment is performed to discover the development of the voids within the liquid-metal heating channel, and two reasons are put forward in this work on the basis of the experiment. Afterward pressing and bending tests are conducted to explore the mechanical stability of the novel microheaters. Finally, the microheaters are applied to warm water to show their good flexibility on non-flat surfaces. In consequence, the novel liquid metal-based microheater is believed to be widely applicable to soft micro-electro-mechanical system(MEMS) heating devices.

https://www.mdpi.com/2072-666X/11/2/133/pdf

A Performance-Enhanced Liquid Metal-Based Microheater with Parallel Ventilating Side-Channels.

The embodiment of the invention provides a liquid metal flexible pressure sensor and a preparation method thereof. The sensor comprises a pressure sensing unit and a flexible fixed unit; the flexiblefixed unit is made of insulating materials; hollow micro-channels are arranged in the flexible fixed unit, and the micro-channels are symmetrically distributed around the pressure sensing unit; the micro-channels are filled with liquid metal electrodes which are not disconnected, and the liquid metal electrodes are in contact with the pressure sensing unit; and the pressure sensing unit is a flexible conductive polymer. According to the liquid metal flexible pressure sensor and the preparation method thereof provided by the embodiment of the invention, a resistive flexible pressure sensor is provided, which can maintain the original performance under large deformation while achieving achieve accurate pressure measurement; and besides, the manufacturing is simple and the application range is wide.

Li Zhenming

Papers

A Performance-Enhanced Liquid Metal-Based Microheater with Parallel Ventilating Side-Channels.

Liquid metal flexible pressure sensor and preparation method thereof