Stretchable electronics represents a relatively recent class of technology [1,2] of interest partly due to its potential for applications in sensory robotic skins, [3,4] conformal photovoltaic modules, [5,6] wearable communication devices, [7,8] skin-mounted monitors of physiological health, [9][10][11] advanced, soft surgical and clinical diagnostic tools, [11,12] and bioinspired digital cameras. [13,14] A key challenge in each of these systems is in the development of strategies in mechanics that simultaneously allow large levels of elastic stretchability and high areal coverages of active devices built with materials that are themselves not stretchable (e.g., conventional metals) and are, in some cases, highly brittle (e.g., inorganic semiconductors). For design approaches that embed stretchability in interconnect structures that join rigid device islands, the system level stretchability ε system is much smaller than the interconnect stretchability ε interconnect . Zhang et al. [15] identified the following relationship between the interconnect and system stretchability:, where f dev = (area of active device components)/(total area of the system) is the areal coverage ratio of active device components. Structure designs for stretchable interconnects have evolved from straight [13,16] to curvilinear interconnects, [17] from those bonded to or embedded in the supporting substrate [11,18] to free-standing designs housed in microfluidic enclosures, [19] and from simple structures [17] to fractal/self-similar designs. [15,[20][21][22] All such cases, including a broad variety of shapes, sizes, and geometric arrangements, share the same underlying mechanisms, i.e., out-of-plane buckling of thin structures (metals, insulators, or semiconductors with thickness typically between ≈100 nm and ≈1 µm) provides the basis for elastic stretchability. The most advanced interconnects achieve elastic (reversible)

Wireless functionality is essential for the implementation of wearable systems, but its adaptation in stretchable electronic systems has had limited success. In this paper, the electromagnetic properties of stretchable serpentine mesh-based systems is studied, and this general strategy is used to produce high-performance stretchable microwave systems. Stretchable mechanics are enabled by converting solid metallic sections in conventional systems to subwavelength-scale serpentine meshes, followed by bonding to an elastomeric substrate. Compared to prior implementations of serpentine meshes in microwave systems, this conversion process is extended to arbitrary planar layouts, including those containing curvilinear shapes. A detailed theoretical analysis is also performed and a natural tradeoff is quantified between the stretching mechanics and microwave performance of these systems. To explore the translation of these concepts from theory to experiment, two types of stretchable microwave devices are fabricated and characterized: a stretchable far-field dipole antenna for communications and a stretchable midfield phased surface for the wireless powering of biomedical implanted devices.

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Scissoring/nonbuckling interconnects are proposed as a different route to stretchable structures, in which thick bar geometries replace thin ribbon layouts, to yield scissor‐like/nonbuckling deformations instead of in or out of plane buckling, as discussed in article number 1604989 by Shuodao Wang, John A. Rogers, and co‐authors. Metal and silicon structures with scissoring design can be stretched as much as 350% (previous maximum value 54%) and 90%, respectively, without fracture. Image designed by Zhenhai Li.

A novel stable beamwidth, ultrawide-bandwidth low-scattering antenna is presented in this paper. This antenna is a modified version of the conducting slotline bowtie hybrid (SBH) antenna with resistive sheets (Rcards) introduced into the guiding structure design. Since the resistive sheets can attenuate creeping wave fields, much smaller rolled edges are needed in the Rcard SBH antenna. Moreover, due to the Rcard's partially transparent nature with respect to electromagnetic fields, the radar cross section (RCS) associated with this new antenna is smaller than the original conducting rolled edge one. By employing an optimization process based on the concept of the genetic algorithm, one can easily design the Rcard SBH antenna to obtain a very stable antenna beamwidth and phase center in both the -and -planes across the entire operating frequency bandwidth. Because of its constant beamwidth, low RCS, and broad-band features, the Rcard SBH antenna is an ideal antenna for many applications such as a compact range feed. Calculated and measured results are presented to demonstrate the performance of this new antenna.