Wireless energy harvesting enables the conversion of ambient energy into electrical power for small wireless electronic devices. This technology offers numerous advantages, including availability, ease of implementation, wireless functionality, and cost-effectiveness. Radio frequency energy harvesting (RFEH) is a specific type of wireless energy harvesting that enables wireless power transfer by utilizing RF signals. RFEH holds immense potential for extending the lifespan of wireless sensors and wearable electronics that require low-power operation. However, despite significant advancements in RFEH technology for self-sustainable wearable devices, numerous challenges persist. This literature review focuses on three key areas: materials, antenna design, and power management, to delve into the research challenges of RFEH comprehensively. By providing an up-to-date review of research findings on RFEH, this review aims to shed light on the critical challenges, potential opportunities, and existing limitations. Moreover, it emphasizes the importance of further research and development in RFEH to advance its state-of-the-art and offer a vision for future trends in this technology.

In this paper, a novel cylindrical metamaterial with helical cell exhibiting zero Poisson’s ratio (ZPR) in two different directions is introduced. Detailed Computer-aided design modelling of a curved optimised spring element is demonstrated for numerical and experimental analysis. High fidelity finite element models are developed to assess the homogenisation study of Poisson’s ratios, normalised Young’s modulus and torsion behaviour, demonstrating the curvature effect and independency of mechanical behaviour of cylindrical optimised spring element metamaterial from tessellation numbers. Buckling and frequency analysis of the cylindrical metamaterial with spring element are compared with equivalent shell cylinders. Moreover, experimental analysis is performed to validate the large strain ZPR and deformation mechanism demonstrated in numerical simulations. Finally, radical shape morphing analysis under different bending conditions for cylindrical metamaterial with helical cell is investigated, including deformation and actuation energy and compared with positive and negative Poisson’s ratio cylinders formed by honeycomb and auxetic cells.

Mechanical metamaterials with zero Poisson’s ratio (ZPR) offer unique advantages in applications requiring dimensional stability under large deformations. Here we present a three-dimensional, large strain ZPR metamaterial composed of shape-optimized helical ligaments arranged in a hierarchical lattice. The design reduces stress concentrations at the joints and supports substantial elastic deformation in tension, compression and shear, while maintaining orthotropic, decoupled stress-strain behaviour. Finite element analyses assess homogenized properties, buckling behaviour, and vibrational modes through the analysis of the phononic band gaps, showing low normalized Young’s modulus and strain-invariant Poisson’s ratios. We further examine the influence of ligament cross-sectional diameter and the effect of different base materials on stiffness and strain range. Experimental tests on 3D-printed specimens confirm the predicted ZPR behavior and deformation capacity. The metamaterial’s elastic isotropy, fatigue resistance, and tailorable stiffness make it suitable for multifunctional applications including adaptive actuators, morphing structures, and energy-absorbing systems.