Wireless charging is a cornerstone technology for next-generation mobile and ubiquitous computing. However, its practical deployment has long been constrained by short range, poor flexibility, and lack of support for dynamic multi-device scenarios. In this paper, we propose ChargeX—a system that enables long-range and mobility-resilient wireless charging for multiple small devices. ChargeX pioneers the integration of metasurface-assisted magnetic beamforming, a high-frequency compact transceiver design, and a real-time closed-loop feedback-control mechanism. It further advances the field by introducing a joint optimization framework for dynamically allocating energy across mobile receivers with heterogeneous priorities and spatial-temporal demands. Experimental results demonstrate that it achieves meter-level charging distance, real-time response to device movement, and efficient coordination among multiple receivers, significantly outperforming state-of-the-art prototypes.

The widespread adoption of WiFi has driven numerous WiFi-based wireless sensing applications. Researchers have utilized Channel State Information (CSI) from WiFi communications to develop various applications and systems, such as activity recognition, gesture recognition, and user authentication. However, unlike the payload data of packets, the CSI in WiFi packet headers lacks effective encryption mechanisms, posing a risk of privacy leakage. This paper proposes a privacy protection method for WiFi-based wireless sensing applications by controlling CSI through the modification of pilot symbols, specifically the Long Training Sequence (LTS), in WiFi packet headers. This approach affects the results of wireless sensing applications. To achieve encrypted protection of CSI, we designed a virtual channel model implemented at the FPGA level based on the OpenWiFi architecture. We simulate multipath effects to encrypt the IQ signal before its analog conversion. After passing through this virtual channel, the signal is transmitted through the real physical channel and collected by the receiver. Additionally, to further protect data privacy, we implemented a targeted protection algorithm for customized precise control of CSI in the current physical environment. Based on the current CSI data and the target CSI data, the algorithm customizes the parameter selection of the virtual channel model to generate a specific virtual channel for targeted encryption. Finally, our research verified the existence of privacy leakage issues in wireless sensing systems through experiments on respiration detection and human activity recognition based on CSI. We also validated the effectiveness of our designed virtual channel model in privacy protection.

Wireless charging has achieved promising progress in recent years. However, the severe bottlenecks are the small charging range and poor flexibility. This paper presents ChargeX to enable smart and long-range wireless charging for small mobile devices. ChargeX incorporates emerging smart metasurface into the magnetic resonance coupling-based wireless charging to extend the charging range and accommodates the mobility of charging device. Unlike previous endeavors in metasurface-assisted wireless charging that focused on simulation, ChargeX makes efforts across software and hardware to meet three crucial requirements for a practical wireless charging system: (i) realize high-freedom and accurate metasurface control under the premise of low loss; (ii) obtain real-time feedback from the receiver and make effective manipulation for transmitted magnetic flux; and (iii) generate a proper AC signal source at the desired frequency band. We developed a prototype of ChargeX, and evaluated its performance through controlled experiments and real-world phone charging. Extensive experiments demonstrate the great potential of ChargeX for long-range and flexible wireless charging with a compact receiver design.

Sub-6GHz and mmWave complement each other in the next generation of wireless communications for wide coverage and high capacity. However, there is still a gap between current network technology and seamless connection in indoor environments due to the inevitable occlusions that particularly affect higher frequency bands like Wi-Fi 5GHz and mmWave. To overcome this gap, economical tunable metasurfaces offer a promising solution by redirecting the beam direction of incoming waves to bypass blockages. However, existing metasurface technologies focus on a single frequency band and lack a theoretical framework to guide surface design for multiple desired bands, limiting their potential for diverse applications.