The extreme properties that metamaterials provide can protect optical and electromagnetic systems from surrounding “ordinary” materials and substances – a feature never explicitly used yet. Wireless energy transfer, i.e., the transmission of electromagnetic energy without physical connectors9, demands reliable and stable solutions for charging high-power systems like electric vehicles with no effect on people, animals, plants, etc. Here we tackle this challenging problem and suggest a novel approach of using metamaterials with extreme parameters to enable targeted and protected wireless energy transfer. We design and experimentally implement epsilon-near-zero (ENZ) and epsilon-and-mu-near-zero (EMNZ) metamaterials that provide an energy transmission if and only if both the transmitter and the receiver are equipped with these metamaterials. The fact of absence of materials with such extreme parameters protects the system against surrounding objects, which cause neither noticeable change in the system operation nor experience any detrimental effect. The system behind the proposed approach can be realised in virtually any frequency band by appropriate scaling and suitable choice of material. This technology will find applications in targeted wireless energy transfer systems, especially where high power is needed, including electric vehicles.
Extraction of electromagnetic energy by an antenna from impinging external radiation is at the basis of wireless communications and wireless power transfer (WPT). The maximum of transferred energy is ensured when the antenna is conjugately matched, i.e., when it is resonant and it has an equal coupling with free space and its load. This condition, however, can be easily affected by changes in the environment, preventing optimal operation of a WPT system. Here, we introduce the concept of coherently enhanced WPT that allows us to bypass this difficulty and achieve dynamic control of power transfer. The approach relies on coherent excitation of the waveguide connected to the antenna load with a backward propagating signal of specific amplitude and phase. This signal creates a suitable interference pattern at the load resulting in a modification of the local wave impedance, which in turn enables conjugate matching and a largely increased amount of extracted energy. We develop a simple theoretical model describing this concept, demonstrate it with full-wave numerical simulations for the canonical example of a dipole antenna, and verify experimentally in both near-field and far-field regimes.
Wireless power transfer—the transmission of electromagnetic energy without physical connectors such as wires or waveguides—typically exploits electromagnetic field control methods that were first proposed decades ago and requires some essential parameters (such as efficiency) to be sacrificed in favour of others (such as stability). In recent years, novel approaches to electromagnetic field manipulation have been developed that can be used to create advanced forms of wireless power transfer. Here we review the development of novel physical effects and materials for wireless power transfer. We explore techniques based on coherent perfect absorption, parity–time symmetry and exceptional points, and on-site power generation. We also explore the use of metamaterials and metasurfaces in wireless power transfer, and the use of acoustic power transfer. Finally, we highlight potential routes for the further development of wireless power transfer technology.