We propose a flexible anti-metal radio frequency identification (RFID) tag antenna based on a high-conductivity graphene assembly film (HCGAF). The HCGAF has a conductivity of 1.82 × 10⁶ S m⁻¹, a sheet resistance of 25 mΩ and a thickness of 22 μm. The HCGAF is endowed with high conductivity comparable to metal materials and superb flexibility, which is suitable for making antennas for microwave frequencies. Through proper structural design, parameter optimization, semiautomatic manufacturing and experimental measurements, an HCGAF antenna could realize a realized gain of –7.3 dBi and a radiation efficiency of 80%, and the tag could achieve a 6.4 m read range at 915 MHz on a 20 × 20 cm² flat copper plate. In the meantime, by utilizing flexible polyethylene (PE) foam, good conformality was obtained. The read ranges of the tags attached to curved copper plates with different bending radii were measured, as well as those of those attached to several daily objects. All the results demonstrate the excellent performance of the design, which is highly favorable for practical RFID anti-metal applications.

Existing Internet of Things (IoT) devices face a significant challenge in terms of power consumption due to their limited battery life. Capturing and utilizing ambient radio frequency (RF) energy emerges as a promising solution for powering low-power sensors and electronic devices, given its unique spatial and temporal distributions. However, the low level of ambient RF power severely hampers the rectenna’s RF-to-direct current (DC) conversion efficiency, making it incapable of generating sufficient DC power. To address this issue and enhance the conversion efficiency of a broadband rectenna at low environmental power levels, this study introduces a novel technique called the meta-lens assisted technique (MAT). This technique leads to a substantial increase in the rectenna’s received RF power by more than 10 dB. As a result, the total conversion efficiency improves by over 30% across a wide frequency band ranging from 2.9 GHz to 3.63 GHz (with a fractional bandwidth of 22.3%), even when the initial RF power received (without the MAT) was as low as -20 dBm, which approaches the real-life ambient RF power level. Notably, the proposed MAT achieves a 40% to 60% efficiency improvement compared to state-of-the-art approaches. These remarkable results demonstrate the promising potential of the MAT rectenna as an alternative for harvesting low-density wireless energy and supporting low-power-required industrial IoT applications.

The continuous advancements in multimode detection and surveillance technologies have made multispectral-compatible camouflage increasingly vital for both defense and civilian applications. Meanwhile, stealth radomes require in-band communication of electromagnetic (EM) signals. This article presents a multifunctional metasurface that provides multispectral-compatible camouflage across visible, infrared (IR), and microwave regions while simultaneously enabling efficient transmission in the millimeter-wave (mm-Wave) band. The proposed system consists of bilayer indium tin oxide (ITO) patterned layers for low IR emissivity and broadband radar absorption along with a metal-meshed frequency-selective surface (FSS) layer for mm-Wave transmission. Both simulated and experimental results indicate that the fabricated sample exhibits more than 90% absorption over a wide microwave frequency band ranging from 7.6 to 16.4 GHz, while a transmission window with an insertion loss (IL) of 0.96 dB is realized at 27.9 GHz in the mm-Wave band. In the IR atmospheric window, the measured emissivity of the metasurface is 0.304 and 0.363 for 3–5 μm and 8–14 μm, respectively. Besides, the measured optical transparency reaches 51.7% in the visible wavelength range of 400–800 nm. This work presents promising opportunities for the engineering application of metasurfaces in optical windows, stealth radomes, and 5G mm-Wave communication systems.

The unpredictable propagation of ambient radio frequency (RF) waves may cause significant randomness in power densities against the propagation distance, time, and locations. To address this challenge, we propose a novel adaptive rectifier system with stabilized output dc power against dynamic power densities. A novel detection circuit is designed to identify the frequency range and receiving power level. Then the received RF power is amplified to the saturated level by referring to the detected frequency and power information for adaptive dc biasing control for an integrated power amplifier. Doing so makes the input power to the rectifier constant regardless of the power and frequency variations. The experimentally validated system can output a stabilized power under the time-varying power range of −10 to 0 dBm and location varying within 0.5 m at 1.8, 2.1, and 2.6 GHz. Compared with conventional designs, this system has realized stabilized and enhanced conversion efficiency (61% at 1.8 GHz, 64% at 2.1 GHz, and 53% at 2.6 GHz) and therefore could be adopted for wireless powering distributed sensors and Internet of Thing (IoT) devices continuously and steadily at flexible conditions.

Given the swift advancement of the Internet of Things (IoT) and wireless power transfer (WPT), there is an increasing need for incorporating new functionalities like wireless communication, recognition, sensing, and localization into existing systems. In response to these evolving demands, a transformative rectenna-based unified platform has been developed. This groundbreaking platform is engineered to harvest ambient wireless power while smartly managing the generated second-order harmonic signals. Illustrating its design, a multi-functional system has been implemented. This system can convert 52.9% of input radio frequency power into direct current power and achieve a state-of-the-art SH generation efficiency of 10.2% when the input RF power is set at 0 dBm. Concurrently, the harmonic signals can be re-radiated and automatically directed (steered) from –65° to 66°, facilitated by an 8×8 Butler matrix and an 8-way microwave switch, all controlled by a microcontroller unit (MCU). Notably, our platform extends beyond beamforming to embrace a broader spectrum of applications, including backscattering communication, simultaneous wireless information and power transfer (SWIPT), integrated sensing and communications (ISAC), and continuous wave detection. This expansion significantly enhances the scope and capability of rectification technology applications.

Radio frequency (RF) energy harvester as an efficient tool for capturing and converting the flourishing ambient RF energy provides a promising solution for long-term powering the wireless sensor networks and the Internet of things (IoTs). However, the actual distribution of the environmental RF signals is dynamically frequency-dependent due to the diverse wireless terminals only interacting with specified frequencies. To take full advantage of the RF energy carrying this characteristic, an intelligent RF energy harvester is in demand to automatically sense the frequency information of an incident signal and conduct the corresponding RF-to-direct current transformation process. Here, to the best of my knowledge, a frequency-self-adaptive RF harvester is first presented with the help of the shape-reconfigurable liquid metal, which can precisely identify and efficiently convert an arbitrary signal from the frequency span of 1.8 to 2.6 GHz. Companied with a microcontroller unit and a tensile system, the dynamic functionality of the entire system is comprehensively demonstrated, showing promising potential to significantly advance various fields, including sustainable IoT applications, green wearable technologies, and self-powered devices.