An artificial muscle capable of shape programmability, deformation-locking capacity without needing continuous external energy, and self-sensing capability is highly desirable yet challenging in applications of reconfigurable antenna, deployable space structures, etc. Inspired by coupled behavior of the muscles, bones, and nerve system of mammals, a multifunctional artificial muscle based on polydopamine-coated liquid crystal elastomer (LCE) and low–melting point alloy (LMPA) in the form of a concentric tube/rod is proposed. Thereinto, the outer LCE is used for reversible contraction and recovery (i.e., muscle function); the inner LMPA in the resolidification state is adopted for deformation locking, and that in the melt state is adopted for angle variation monitoring by detecting resistance change (i.e., bones and nerve functions, respectively). The proposed artificial muscle demonstrates multiple performances, including controllable bending angle, position, and direction; deformation locking for supporting heavy objects; and real-time monitoring of angle variation, which also provides a straightforward and effective approach for designing soft devices.

This paper presents a novel approach to design compact wearable antennas based on metasurfaces. The behavior of compact metasurfaces is modeled with a composite right-left handed transmission line (CRLH TL). By controlling the dispersion curve, the resonant modes of the compact metasurface can be tuned efficiently. A printed coplanar waveguide (CPW) monopole antenna is used as the feed structure to excite the compact metasurface, which will result in a low profile antenna with low backward radiation. Following this approach, two compact antennas are designed for wearable applications. The first antenna is designed to operate at its first negative mode (-1 mode), which can realize miniaturization, but maintain the broadside radiation as for a normal microstrip antenna. The proposed prototype resonates around 2.65 GHz, with a matching bandwidth of 300 MHz. The total dimensions of the antenna are 39.4x33.4 mm2 (0.1 λ02), and its maximum gain is 2.99 dBi. The second antenna targets dual-band operation at 2.45 GHz and 3.65 GHz. A pair of symmetric modes (±1 modes) are used to generate similar radiation patterns in these two bands. The size of the antenna is 55.79x52.25 mm2 (0.2 λ02), and the maximum gains are 4.25 dBi and 7.35 dBi in the two bands, respectively. Furthermore, the performance of the antennas is analyzed on the human body. The results show that the proposed antennas are promising candidates for Wireless Body Area Networks (WBAN).

Wireless Body Area Network (WBAN) has attracted more and more attention in many sectors of society. As a critical component in these systems, wearable antennas suffer from several serious challenges, e.g., electromagnetic coupling between the human body and the antennas, different physical deformations, and widely varying operating environments, and thus, advanced design methods and techniques are urgently needed to alleviate these limitations. Recent developments have focused on the application of metamaterials in wearable antennas, which is a prospective area and has unique advantages. This article will review the key progress in metamaterial-based antennas for WBAN applications, including wearable antennas involved with composite right/left-handed transmission lines (CRLH TLs), wearable antennas based on metasurfaces, and reconfigurable wearable antennas based on tunable metamaterials. These structures have resulted in improved performance of wearable antennas with minimal effects on the human body, which consequently will result in more reliable wearable communication. In addition, various design methodologies of meta-wearable antennas are summarized, and the applications of wearable antennas by these methods are discussed.

This paper presents a compact textile antenna design based on a metasurface for wearable applications. It operates in the 2.45 GHz and 5.5 GHz industrial, scientific, and medical bands. A two-dimensional equivalent circuit model is proposed to provide insight into the working principle of the metasurface. The tuning of the radiator's resonant frequencies can be easily performed by adjusting the dispersion curve of the metasurface unit cell. The metasurface in this work consists of a 4 × 4 array of unit cells fed by a printed coplanar waveguide structure with a slot in its reverse side to maintain its low profile structure. The main innovations of this work are: (i) the −2 ^nd mode is employed to significantly miniaturize the antenna dimensions; (ii) the simultaneous excitation of the +1 ^st mode to enable dual-band operation; (iii) an integrated back reflector to reduce back radiation and lower SAR; and (iv) the use of full textile materials to guarantee user comfort, ease of fabrication and low cost. The proposed antenna's footprint is 44.1 × 44.1 mm ² (0.12 λ ² at 2.45 GHz), with an impedance bandwidth of 10.2% centered at 2.45 GHz and 22.5% at 5.5 GHz. The maximum gain is −0.67 dBi and 7.4 dBi in free space, and 9% of power gain attenuation is generated when used on the body, and is suitable as a miniaturized antenna for wearable applications.

This paper presents a metasurface (MS)-based wideband wearable circularly polarized (CP) antenna to communicate with in-body devices. The antenna consists of a crossed dipole, an MS plane and a CP feeding network. The feed network generates a quasi-90° phase delay between each adjacent arm of the crossed dipole. This produces CP radiation and reduces polarization mismatch between the telemetry antenna and the implantable antenna. The MS consisting of a 5×5 unit cell array functions as a reflector for the crossed dipole to improve forward radiation while maintaining a low profile structure. This is by designing the unit cells with a near-zero phase reflection over the operating band. To enable conformity with on-body usage, the antenna is designed fully using flexible materials. Textile conductive elements are embedded into a PDMS substrate. It is sized at 106×106×5mm3 (1.24λ×1.24λ×0.05λ at 3.5 GHz). Results indicated a -10 dB impedance bandwidth from from 2.25 to 6 GHz (90%). The 3-dB axial ratio bandwidth is from 2.9 to 4.95 GHz (52%), with a maximum on-body gain of - 10.5 dBi. Finally, the specific absorption rate (SAR) assessment of the antenna indicated values far lower than the limits of the FCC.

For the passive intermodulation (PIM) problem of nonlinear contact on microwave connectors, an effective method is presented to improve the computational accuracy of PIM. First of all, the contact stress distribution on contact surface is analyzed by finite-element method based on the Weierstrass-Mandelbrot model. The contact stress and real area of contact are evaluated under different loading conditions. Then, the electrical parameters of physical effects of nonlinear contact are derived based on the electric contact theory and the physical effects of metal-metal microcontact. Finally, the nonlinear I-V relation is established from the microcontact equivalent circuit, and the third-order PIM power level generated by contact nonlinearity is revealed in analytic form. The analytic results are verified by the PIM test experiments. This work provides a novel way for PIM calculation of rough surface contact.