An innovative wireless power transfer (WPT) system utilizing millimeter wave (mmWave) power for multi-node charging and tracking is presented in this paper. The core concept of the system revolves around the utilization of frequency-dispersive leaky-wave antenna transmitters, enabling passive beam scanning in the far-field without the need for active phased arrays. However, such a system requires a breakthrough in receiving rectenna design at mmWave frequencies, encompassing a wide frequency bandwidth, wide beam width, and high RF-DC conversion efficiency beyond 20 GHz. In this work, we introduce a pioneering mmWave rectenna design achieved through the co-design integration of a magnetoelectric dipole and high-frequency diodes, eliminating the need for complex impedance matching networks at mmWave frequencies. The proposed rectenna operates in the frequency range of 24-34.5 GHz, achieving over 50% RF-DC conversion efficiency for input powers exceeding 15 dBm. Additionally, the rectenna demonstrates improved gain and beamwidth compared to conventional designs, enabling wide-angle reception of frequency-scanning passively beamformed mmWave signals. A practical demonstration of the proposed system showcases simultaneous wireless charging of three nodes, highlighting its notable advantages in terms of mobility, cost-effectiveness, and simplicity over conventional WPT technologies.

A low-cost hybrid textile/PCB wearable rectenna is designed for smart on-body applications. It is an integration of a textile patch antenna and a highly efficient rectifier on a small PCB substrate, where the feeding aperture of the antenna is significantly miniaturized by exploiting an LC loading technique in order to have an effective integration with the rectifier. The feeding-rectifying circuitry is attached to the back of the antenna by normal sewing threads. The essential components are soldered on the small rigid PCB for a robust connection. The size of the rectenna is 0.817 × 0.817 λ ₀ ² while the rigid substrate area for the feeding-rectifying circuitry is only 0.278 × 0.147 λ ₀ ² (3.4 cm × 1.8 cm) at 2.45 GHz. The intrinsic dielectric/conduction loss of textile feedlines, the loss of antenna-to-rectifier interconnectors, the loss of soldering or gluing on textiles, and the loss due to body absorption from typical large feeding slots are constitutively reduced. The soldering points and the consequent hard-to-be-characterized parasitic effects on textiles are avoided. The proposed integration approach reduces the cost and eases the rectenna design, fabrication, and integration. As a result, the power conversion efficiency (PCE) of the rectifier reaches up to 39.5% at -20 dBm input power level whilst the experimental rectenna prototype achieves the state-of-the-art PCE of 41% at an extremely low incident power density of 0.4 μW/cm ² . The maximum PCE is 56% at the -5 dBm input power. Finally, the possibility of harvesting datalink energy from PC/mobile phones as power source for wearable electronics is investigated.

A wearable antenna functioning in the 2.4 GHz band for health monitoring and sensing is proposed. It is a circularly polarized (CP) patch antenna made from textiles. Despite its low profile (3.34 mm thickness, 0.027 λ₀), an enhanced 3-dB axial ratio (AR) bandwidth is achieved by introducing slit-loaded parasitic elements on top of analysis and observations within the framework of Characteristic Mode Analysis (CMA). In detail, the parasitic elements introduce higher-order modes at high frequencies that may contribute to the 3-dB AR bandwidth enhancement. More importantly, additional slit loading is investigated to preserve the higher-order modes while relaxing strong capacitive coupling invoked by the low-profile structure and the parasitic elements. As a result, unlike conventional multilayer designs, a simple single-substrate, low-profile, and low-cost structure is achieved. While compared to traditional low-profile antennas, a significantly widened CP bandwidth is realized. These merits are important for the future massive application. The realized CP bandwidth is 2.2–2.54 GHz (14.3%), which is 3–5 times that of traditional low-profile designs (thickness < 4 mm, 0.04 λ₀). A prototype was fabricated and measured with good results.

Stretchable and flexible antennas are pivotal in wearable electronics and soft robotics, but achieving consistent resonant frequency under mechanical strain is a fundamental problem that remains to be solved. This paper introduces, for the first time, a strain-invariant patch antenna fabricated with a liquid metal conductor, EGaIn, and a soft elastomeric substrate, Ecoflex 00-30, with overall dimensions of 90 × 90 × 1.5 mm³. By strategically employing slot-induced surface current redistribution and leveraging Poisson’s effect, the proposed design achieves an exceptional level of frequency stability. Experimental results demonstrate a maximum frequency shift of only 0.8% under strains up to 58.8%, significantly outperforming existing straininvariant stretchable antennas, which typically exhibit significant frequency shifts for strains higher than 30%. Unlike conventional approaches that rely on specialized materials or complex 3D structures, our planar antenna offers remarkable scalability and versatility, presenting a transformative solution for next-generation wireless communication and sensing systems for soft electronics.

To address the fundamental tradeoffs between antenna efficiency, directivity and size of superdirective antennas, a compact microstrip antenna array using a high dielectric substrate (ϵr = 24) is presented. Leveraging the quasi-Yagi-Uda principle, we construct the antenna elements using capacitively loaded loops (CLLs) and arc-shaped monopoles for high directivity. A pair of monopoles are placed in parallel to achieve good impedance matching. A two-element superdirective antenna array is designed based on the magnetic coupled-mode. The antenna elements perpendicularly stand on the metal ground face to face, and a power divider is introduced for equal amplitude and in-phase excitation through the respective arc-shaped monopoles. The maximum directivity is achieved when the antenna elements are in resonance, where the distance between the monopole elements is optimized to be 24 mm for the maximum directivity of 7.32 dBi.