In intracavity microwave power transfer (MPT) applications, receiver rotations cause fluctuations and a decrease in over-the-air (OTA) efficiency. To address this issue, we propose an intracavity MPT system incorporating metasurfaces that are programmable in both phase and polarization. Programmable metasurfaces (PMS) manipulate both the reflection phase and the polarization direction of microwaves within the cavity, thereby altering the electric field strength and polarization direction at the receiver. Subsequently, we develop an adaptive receiver orientation algorithm that integrates genetic algorithms with time reversal (TR) theory to optimize the PMS pattern. For experimental validation, an intracavity MPT system, incorporating 147 meta-atoms and operating at 2.4 GHz, was designed, fabricated, and tested. Experimental results indicate that our system achieved an improvement of at least 11 dB in the OTA efficiency, reaching an efficiency of 13% or more at the measurement orientation, compared to systems using a fixed PMS pattern. This improvement significantly enhances the robustness of the intracavity MPT system against variations in receiver orientation.

In a practical wireless power transfer (WPT) system with multiple nonlinear receivers and a power-limited transmitter, rectification efficiency may be low because the received radio frequency (RF) power of the receiver does not match the optimal rectified power. To tackle the challenge that a power-limited transmitter actively transmits RF power to satisfy different power demands with high efficiency and large average output direct current (dc) power, this article proposes a novel high-efficiency multiuser WPT. In this scheme, the transmission signals are optimized based on the received RF signals with power equal to the optimal rectified power from the selected receivers, so the selected receivers can track the optimal rectified power within a time slot. Then, we formulate a bilevel optimization problem under the constraint of transmit power to group all receivers and optimize the transmission signals of each group. Multiple groups sequentially track the optimal rectified power across multiple time slots with a power-limited transmitter, thereby tackling the challenge. In order to solve the nonconvex bilevel optimization problem, a bilevel genetic algorithm is adopted to obtain the optimal solution. Numerical and experimental results show that the RF-RF-dc efficiency and output dc power of the proposed scheme are up to 2.6 and 3.7 times higher than those of the traditional schemes. Additionally, only our scheme meets the different power demands of multiple receivers, ensuring the same survival time. Furthermore, our scheme can also provide guidance for practical WPT system design and has the potential of compatibility with other existing systems.

In actual microwave power transmission (MPT) scenarios such as smart factory, the system efficiency and output dc power will decrease when the receiving antenna array of the multi-posture receiver does not face the transmitting antenna. To address the challenge of efficiently transmitting energy from the transmitter to a multi-posture receiver, a multi-posture MPT scheme based on forward and backward time reversal (TR) is proposed. This letter introduces phase shifters in the multi-posture receiver, enabling the beam of receiver to have steering capabilities. Importantly, inspired by the adaptive beam alignment characteristic of TR, the phase shifters of receiver are configured to align the beam of the offset receiver with the transmitter using the backward TR method, while the phase shifters of transmitter are configured to align the beam of the transmitter with the receiver using the forward TR method. So, dual alignment of the transmitting and receiving beams is achieved. A prototype of the multi-posture MPT system is established. The experiment results show that the output dc power of the multi-posture MPT scheme is 30.6 dB higher than the traditional MPT scheme when the multi-posture receiver changes its orientation, demonstrating the effectiveness of the multi-posture MPT scheme.

In intracavity microwave power transfer (MPT) scenarios such as shipping containers and closets, the over-the-air (OTA) efficiency at some regions will decrease due to antenna impedance mismatch and the nodal points of eigenmodes. To solve this issue, a microwave power transfer (MPT) system within the metallic cavity based on reconfigurable metasurfaces is proposed. First, the effect of meta surfaces on the over-the-air (OTA) efficiency of the system is analyzed based on the eigenmode, and a 2-bit reconfigurable metasurface which has two states: polarization-rotation (PR) and non-PR was designed. Then, we proposed an iterative algorithm to acquire the optimal patterns of metasurfaces by minimizing the reflection coefficient of the transmitting antenna. Last, Full-wave simulations were carried out to demonstrate the system's validity. This system can simultaneously form a focusing field at the receiver and realize antenna impedance matching to improve the OTA efficiency. Furthermore, the receiver can operate for a longer time without requiring the transmission of pilot or feedback signals.

In order to continuously power movable sensors, we present an autotracking continuous-wave time reversal (TR) wireless power transfer (ACTR-WPT) system of a novel low-profile planar transmitter. The new transmitter is designed with a radio-frequency (RF)–channel cascaded structure, which couples only a little energy of the amplified feeding signal of each radiating element to the following cascaded one. Such RF-channel cascaded transmitter makes the decrease or increase of the number of the radiating elements quite flexible. The transmitting circuits are highly integrated with a microstrip antenna for every radiating element, which benefits the planar transmitter with the profile of less than 3 mm and the weight of each radiating element of less than 40g. Meanwhile, we develop an autotracking algorithm for the ACTR-WPT system, which inherently depends on the adaptive focusing mechanism of the TR technique. With the newly developed autotracking algorithm, we successfully demonstrate the experiments of powering the devices arbitrarily moving within a range from 1m to 7 m and the angle from -45° to +45°. The received dc power ranges from 1mW to 250 mW. The demonstration results are exciting for applications in charging or powering the movable sensors of low power consumption within a mid-range region.

This letter proposes a 360(degrees)-beam-steering low-sidelobe time reversal microwave power transfer (TR-MPT) method. The beam steering is implemented by only one circular patch antenna fabricated with multiple feeding ports. The multiple feeding ports are designed to stimulate different radiation modes and their combinations to steer the beam within 360(degrees) in the azimuth plane. To depress the sidelobe levels and enhance the beam gain, a disc-top-loaded monopole antenna is added at the center of the patch antenna, which is used to excite an additional mode out of phase with the maximal sidelobe but in phase with the main lobe. Finally, time reversal (TR) is adopted for optimally weighting the stimulated modes and focusing the power beam adaptively to the desired receiver. A prototype of the TR-MPT system based on the proposed method is established. The experiments demonstrate that the new method can not only adaptively focus the power at the receiver placed at any azimuth angle within 360(degrees), but also achieve a low sidelobe level of smaller than -8.57 dB under a 0.7-wavelength aperture. Additionally, the power transferred to the receiver at different angles has a small fluctuation of less than 0.7 dB.

Wireless Power Transfer (WPT) can completely eliminate the constraints of transmission cables, providing uninterrupted power to energy-consuming devices conveniently and flexibly. It is a revolutionary energy transmission technology with the potential to lead humanity into a truly wireless era. However, it is still challenging to realize in-phase superposition of the focus signal and the sidelobe signals received by one user in a multi-user WPT system. In this paper, we present an efficient double in-phase superposition time reversal (TR) method for multi-user WPT. First, we use TR technology to make the focus signals received by the receiver superimpose in phase. Then, the sidelobe signals of other receivers and the focus signals of this receiver are superimposed in phase through the vector group synchronous rotation (VGSR) method. We also show as the performance of the proposed method outperforms the traditional TR method.

The issue of accurately distinguishing and selectively powering multiple closely spaced devices is challenging but vital for wireless power transfer (WPT). In this article, a continuous-wave time-reversal selective radiative wireless power transfer (CWTR-SRWPT) method based on a multipoint focusing idea is proposed. With the proposed method, we realize a selective radiative WPT prototype system, which can arbitrarily select multiple devices spaced at a diffraction limited distance and power them simultaneously. The accurate positioning and high-precision spatial selection of the closely spaced energy-dissipated devices are achieved by the multipoint focusing field (MPFF) without any auxiliary positioning equipment. The MPFF is produced by a set of weight-optimized single-point focusing fields that are generated by the fundamental time-reversal technique. Theoretical analysis and full-wave simulations to the performances of the CWTR-SRWPT system are presented. The experimental demonstrations of selectively powering multiple LEDs are also conducted. The results indicate that the proposed method exhibits exciting performances of high-precision selectivity, accurate positioning, and satisfactory over-the-air efficiency. It demonstrates potential applications in selectively powering the wireless sensors distributed densely in future intelligent factories.

Time reversal wireless power transfer (TR-WPT) provides an efficient radiated method for wirelessly transferring power to multiple users at a middle distance in complicated multipath environments. However, TR-WPT based on the direct time reversal scheme cannot ensure each user to have the equal received power although the maximum transfer efficiency can be achieved. In order to realize the same received power assignment for each user as well as high transfer efficiency, an asynchronous focusing time reversal (AFTR) scheme is proposed in this paper. Different from the TR-WPT based on the direct time reversal technique, the radiated power does not focus on multi-users at the same time. Instead, the AFTR-WPT system operates in an asynchronous focusing mode. For the continuous-wave wireless power transfer, asynchronous focusing means that the phases of the focused power signals received by multi-users are different. By optimizing the phase of the focused signal received by each user, the AFTR-WPT system can not only transfer the equal power to each user but also achieve the optimal transfer efficiency. To demonstrate the proposed scheme, a porotype of multi-user AFTR-WPT system of 16 transmit antennas and 9 receive antennas is developed with the continuous-wave power transfer in an indoor laboratory environment. Utilizing the proposed asynchronous focusing scheme, we successfully demonstrate the equal power assignment for multiple users and achieve the optimal transfer efficiency, approaching the maximum efficiency of the TR-WPT based on direct time reversal scheme for all studied cases.

为了满足微波输能系统的大功率整流要求,本文基于多支路共用匹配阻抗的方法设计了一种微带线结构的大功率微波整流电路.首先采用微带线结构的功分器将输入的大功率微波能量分为较小功率的微波能量,然后在功分器的每一条支路上利用肖特基二极管阵列将微波能量转换为直流能量,且所有的支路共用阻抗匹配电路.最后将所有支路的直流能量合并输出,实现大功率微波整流.实验结果表明,当输入功率大于34 dBm时,实测直流输出功率大于1w;在输入功率为39.28 dBm时,整流电路的最高实测效率为44.27％;在输入功率为41.42 dBm时,整流电路的最高实测直流输出功率达到了5.84w.该微波整流电路工作于2.45GHz,尺寸为40mm×80mm,具有尺寸小、整流后直流输出功率大,易于集成的特点,可为易于集成的大功率微波整流电路提供设计指导.