Liquid‐Metal‐Enabled Flexible Metasurface with Self‐Healing Characteristics

Abstract

an emerging material, liquid metal when used in combination with polydimethylsiloxane (PDMS) finds applications in soft/ flexible and wearable electronics. [2] Due to its flexibility and deformability, liquid metal encapsulated in PDMS has recently shown self-healing characteristics after damage on the device. [7][8][9] Gallium-based liquid metal has been explored in various applications ranging from electrocardiogram, [10] microcooling, [11] thermometers, [12] flexible electrodes, [13,14] flexible interconnection, [15] strain sensors, [16] pressure sensors, [17] inkjet printing, [18] energy harvesting, [19,20] and magneto-hydrodynamic pumps. [21] Metasurface-based frequency selective surface (FSS) exists in 1D or 2D as periodic arrays of sub-wavelength metallic elements on dielectric surfaces. [22,23] Based on material, physical construction, [24] and geometry, [25] the FSSs are classified into high-pass, low-pass, band-pass, and bandstop filter. [25,26] The performance and behavior of the FSS is dependent on the geometry, periodicity, array size, and choice of materials (conductivity and permittivity). [24] The FSSs have been extensively studied [27] since 1960s, however its fundamental origin can go back to Marconi and Franklin's patent of reflectors in 1919. [28] The ability to tailor FSSs to curtail certain frequency band makes it a vital component in communication applications including radar, [23,29,30] microwave absorber, [29] satellite, [23,31] electromagnetic interference shielding, [32] dichroic sub reflectors, [33] reflect array lenses, [34] lens antenna, [35] polarizers, [36] stealth blankets, [37] and wireless networks. [23,38] Traditional metasurfaces have been realized on rigid substrates using materials such as glass, [23] quartz, [39] polytetrafluoroethylene (PTFE) reinforced with glass, [40] commercially available FR-4-based printed circuit boards, [41][42][43] Rogers 5880 PTFE composites supported with glass microfibers. [44] The varactor diodes like BB 837 or BB 857-02 V, [41,45] liquid crystal, [40,46] and silver paint were either soldered, [41] filled/deposited, [40,46] or painted into these mechanically rigid substrates. [23,47] Recently, liquid metal injection in all connected microfluidic channels in PDMS has been used to realize physically flexible metasurfaces with or without incorporation of soldered chip resistors. [48,49] While the metasurface is flexible, serial injection/withdrawal of liquid metal in all connected microfluidic channels may limit its application (e.g., metasurface that needs unconnected patterns). Injection filling is also known for leaving airgaps and may cause device delamination. [50] A flexible self-healing metasurface using gallium-based liquid metal encapsulated in polydimethylsiloxane (PDMS) operating in the X-band (8-12 GHz) is reported. A band-stop metasurface with center frequency at 9.82 GHz is designed using floating patches surrounding the respective end cap of a Jerusalem cross. A large-scale (up to 10 × 10 array) metasurface is patterned in PDMS and ...

Machine learning (ML)-assisted surface tension and oscillation-induced elastic modulus studies of oxide-coated liquid metal (LM) alloys

“…The software, DropImage, calculated axisymmetric pendant droplets and provided the surface tension value with the associated shape parameters. The area and surface tension values over time are supposed to be fitted in equations (7) and (8) to get the A 0 , A a , γ 0 , γ a , and δ values to calculate the E ′ and E ′′ values. We developed our own Python script to process the data and used the default curve_fit optimization package from the Scipy library.…”

“…Numerous techniques are currently available in the literature to study the elastic modulus and surface tension of gallium alloys; however, the utility of pendant droplets (symmetric and asymmetric) for (a) machine-learning (ML) assisted surface tension and (b) oscillation-induced elastic modulus studies have remained unexplored. Gallium and its alloys at low melting points [1][2][3] have emerged as the most promising soft conductor for sensors, actuators, pumps, flexible electronics, and other microfluidics applications [3][4][5][6][7][8][9][10]. High electrical conductivity, low toxicity, low vapor pressure, biocompatibility, and tunable surface tension (∼600 mN m −1 -100 mN m −1 ) are some of the notable properties at room temperature [11,12]of these alloys; however, the unique behavior of these alloys arise from their native 1-5 nm thick, and passivating Ga 2 O 3 layer [13].…”

Surface Optics and Color Effects of Liquid Metal Materials

“…[11] LMs have emerged as a functional material with great development potential because of their unique properties, including fluidity, printability, conductivity, thermal conductivity, flexible, and liquid phase at room temperature. [12,13] These properties have endowed them to overcome many conventional technical bottlenecks and open applications in diverse fields. [14] including flexible optoelectronic devices, [15] healthcare, [16,17] printing, [18] energy security, [19] flexible sensors, [20] batteries, [21] wearable device, [22] and microfluidics.…”

Liquid metal droplet motion transferred from an alkaline solution by a robot arm

“…1–6 As emerging soft materials, gallium-based liquid metal alloys, such as eutectic EGaIn (75.5 wt% gallium and 24.5 wt% indium), have demonstrated enormous potential for developing high-performance small-scale devices in many important fields. 7–11 They have many unique physicochemical properties, such as high interface tension, 12 excellent thermal/electrical conductivity, 13–17 extreme flexibility, 4,18–20 low vapor pressure, 21 biocompatibility, 22 and low toxicity. 23,24 In addition, liquid metals (LMs) can be actuated under the methods of magnetic, 25,26 ultrasound, 20 optical, 27 and each method has its advantages in different applications.…”