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. This Review examines the development of novel physical effects and materials for wireless power transfer, considering techniques based on coherent perfect absorption, parity–time symmetry and exceptional points, and on-site power generation, as well as the use of metamaterials and metasurfaces, and acoustic power transfer.

Wireless power transfer based on novel physical concepts

We propose and implement a novel 1-bit coding metasurface that is capable of focusing and steering beam for enhancing power transfer efficiency of the electromagnetic (EM) wave-based wireless power transfer systems. The proposed metasurface comprises 16 × 16 unit cells which are designed with a fractal structure and the operating frequency of 5.8 GHz. One PIN diode is incorporated within each unit cell and enables two states with 180 ° phase change of the reflected signal at the unit cell. The two states of the unit cell correspond to the ON and OFF states of the PIN diode or “0” and “1” coding in the metasurface. By appropriately handling the ON/OFF states of the coding metasurface, we can control the reflected EM wave impinged on the metasurface. To verify the working ability of the coding metasurface, a prototype metasurface with a control board has been fabricated and measured. The results showed that the coding metasurface is capable of focusing beam to desired direction. For practical scenarios, we propose an adaptive optimal phase control scheme for focusing the beam to a mobile target. Furthermore, we prove that the proposed adaptive optimal phase control scheme outperforms the random phase control and beam synthesis schemes.

https://www.mdpi.com/1996-1073/12/23/4488/pdf

A Novel Coding Metasurface for Wireless Power Transfer Applications

Wireless energy transmission and harvesting techniques have recently emerged as attractive solutions to realize wireless powered networks. By eliminating fundamental power constraints arising from the use of conventionally battery sources, wireless modes of energy transmission provide viable means to power wireless network devices away from the grid. Metasurfaces have emerged as key enablers for the use of microwave energy as a power source. Their unique abilities to tailor electromagnetic waves have motivated significant research interest into their use for power-focused microwave systems. This article provides an overview of progress in the development of metasurface implementations for microwave energy transmitters and energy harvesters. First, the paper provides a basic introduction to metasurfaces, after which it reviews research progress in metasurfaces for microwave energy transmission and harvesting. Also highlighted are key parameters by which the performance of such metasurface designs are characterized. In addition, an overview of studies on metasurfaces as reconfigurable intelligent surfaces in wireless networks supporting the simultaneous transmission of information and energy is presented. Finally, the paper highlights existing challenges, and explores future directions, including opportunities to control radio environments through ambiently energized reconfigurable intelligent surfaces in next-generation wireless networks.

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A Review of Metasurfaces for Microwave Energy Transmission and Harvesting in Wireless Powered Networks

Future wireless systems are envisioned to create an endogenously holography-capable, intelligent, and programmable radio propagation environment, that will offer unprecedented capabilities for high spectral and energy efficiency, low latency, and massive connectivity. A potential and promising technology for supporting the expected extreme requirements of the sixth-generation (6G) communication systems is the concept of the holographic multiple-input multiple-output (HMIMO), which will actualize holographic radios with reasonable power consumption and fabrication cost. The HMIMO is facilitated by ultra-thin, extremely large, and nearly continuous surfaces that incorporate reconfigurable and sub-wavelength-spaced antennas and/or metamaterials. Such surfaces comprising dense electromagnetic (EM) excited elements are capable of recording and manipulating impinging fields with utmost flexibility and precision, as well as with reduced cost and power consumption, thereby shaping arbitrary-intended EM waves with high energy efficiency. The powerful EM processing capability of HMIMO opens up the possibility of wireless communications of holographic imaging level, paving the way for signal processing techniques realized in the EM-domain, possibly in conjunction with their digital-domain counterparts. However, in spite of the significant potential, the studies on HMIMO communications are still at an initial stage, its fundamental limits remain to be unveiled, and a certain number of critical technical challenges need to be addressed. In this survey, we present a comprehensive overview of the latest advances in the HMIMO communications paradigm, with a special focus on their physical aspects, their theoretical foundations, as well as the enabling technologies for HMIMO systems. We also compare the HMIMO with existing multi-antenna technologies, especially the massive MIMO, present various...

Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions

Systems, methods, and apparatus are described to provide a large emittance angle and a large beamforming aperture for radiation emitted by a relatively small transmit aperture. For example, a diffractive concentrator structure can provide a large emittance angle and a large beamforming aperture for radiation emitted by a small transmit aperture and delivered to a larger exit aperture.

Diffractive concentrator structures

We present a 5.8 GHz Fresnel-zone microwave wireless power transfer experiment leveraging a large planar holographic metasurface reflectarray to form a focused spot at a distance of 6.5 m. The 1.5 $\mathbf{m}^{2}$ holographic metasurface is fabricated from 15 panels having total dimensions of $\mathbf{122}\times \mathbf{127}$ cm, and is comprised of over 4,000 reflective patch resonators on the top surface of a 3.0 mm thick FR-4 substrate. A constrained hologram approach is used to discretize the desired hologram and approximate the desired focal spot given the Lorentzian coupled amplitude-phase response of the patch resonators. When the metasurface is illuminated by a 20 dB standard-gain horn 1.8 $\mathbf{m}$ away, it produces a spot with a 3 dB beam waist (FWHM) of approximately 50 cm. The experimentally measured beam profile matches the simulated beam profile to ± 1 dB within the beam, and we estimate almost 40% of the transmitted power was incident onto the receiver at the focus point.

A Large Planar Holographic Refiectarray for Fresnel-Zone Microwave Wireless Power Transfer at 5.8 GHz

In some embodiments, an antenna system includes antenna elements for transmitting and/or receiving electromagnetic radiation. The antenna elements may be connected to a feed via a plurality of tunable impedance elements. At least some of the tunable impedance elements may have nonlinear responses to impedance tuning that can be numerically approximated by nonlinear impedance-tuning parameter curves with a cumulative number of selectable nonlinear coefficients. Control inputs to nonlinearly vary impedance values of the tunable impedance elements allow for the selection of distinct impedance patterns that correspond to distinct field patterns attainable by the antenna system. The number of field patterns attainable is a function of the number of control inputs and a cumulative number of selectable nonlinear coefficients. Thus, a selection of tunable impedance elements and control inputs may be made to attain a target number of field patterns to serve a desired coverage area.

Systems and methods for reduced control inputs in tunable meta-devices

An antenna system includes a tunable medium, rectifier circuitry, combining circuitry, and control circuitry. The tunable medium includes antenna elements corresponding to lumped impedance elements and variable impedance control inputs configured to enable selection of an impedance value for each of the lumped impedance elements. The control circuitry is configured to determine a scattering matrix (S-matrix) relating field amplitudes at lumped ports including internal lumped ports and lumped external ports. The internal lumped ports correspond to the lumped impedance elements, and the lumped external ports correspond to at least one of the rectifier circuitry inputs, the combined output of the combining circuitry, and the at least one transmitting element. A method includes determining at least a portion of component values of a desired S-matrix, and adjusting the variable impedance control inputs to at least approximate at least a portion of the desired S-matrix.

Systems and methods for tunable medium rectennas

System and methods are described herein for providing wireless power to a target device, such as a laptop computer, a mobile phone, a vehicle, robot, or an unmanned aerial vehicle or system (UAV) or (UAS). A tunable multi-element transmitter may transmit electromagnetic radiation (EMR) to the target device using any of a wide variety of frequency bands. A location determination subsystem and/or range determination subsystem may determine a relative location, orientation, and/or rotation of the target device. For a target device within a distance range for which a smallest achievable waist of the Gaussian beam of the EMR at an operational frequency is smaller than the multi-element EMR receiver of the target device, a non-Gaussian beamform may be determined to increase efficiency, decrease overheating, reduce spillover, increase total power output of rectenna receivers on the target device, or achieve another target power delivery goal.

Non-Gaussian beamforming for wireless power transfer optimization

The present technology pertains to a system and method of operation of a metamaterial phase shifter having various use applications. In one aspect of the present disclosure, a phase shifter includes a network of tunable impedance elements and a controller. The controller is coupled to the network of tunable impedance elements and configured to receive a phase shift input value and determine a corresponding tuning voltage to be supplied to each tunable impedance element of the network of tunable impedance elements based on the phase shift input value, the network of tunable impedance element being configured to shift a phase of an input signal based on tuning voltages supplied to the network of tunable impedance elements by the controller.

Hagerty Joseph

Papers

A Large Planar Holographic Refiectarray for Fresnel-Zone Microwave Wireless Power Transfer at 5.8 GHz

Systems and methods for reduced control inputs in tunable meta-devices

Systems and methods for tunable medium rectennas

Non-Gaussian beamforming for wireless power transfer optimization

Metamaterial phase shifters