Stretchable conductors based on three-dimensional microcoils for tunable radio-frequency antennas

Great efforts have been devoted to fabricate stretchable conductors due to their widespread potential applications in fields such as bionic skin, wireless transmission, and flexible electronics. Despite many strategies, it is difficult to achieve large deformation capability and stable conductivity simultaneously. In this work, a novel stretchable conductor has been fabricated using three-dimensional (3D) conductive microcoils made from Spirulina bio-templates. The microcoils, with 3D preferable deformable configuration, were aligned to form well-ordered structures via microgrooves and then nano-welded to construct electrically continuous networks, followed by immersion in polydimethylsiloxane (PDMS) for curing. The microcoil-based composites could maintain stable conductivity during the stretching (∼50%) and bending process (at a radius of ∼1 mm) or even during cyclic loading. This performance mainly relies on the 3D helical micro-structure, which could transform large uniaxial stretching (∼50%) into only small strain (∼1%) per structural unit. Additionally, the composites were explored for the fabrication of a tunable and deformable radio-frequency (RF) antenna. And the RF antenna could be tuned over a wide frequency range (from ∼1.72 GHz to ∼2.45 GHz) and maintain a high radiation efficiency (>95%), which may open new routes to the development of wireless mobile communication systems, wearable electronics, and smart remote sensing.