Wireless RF Energy Research Articles

High-efficiency rectifying circuit for 5.8GHz wireless RF energy harvesting applications

High-efficiency rectifying circuit for 5.8GHz wireless RF energy harvesting applications

Van der Waals crystal radio with Pt/MoSe2 Schottky diode and h-BN capacitor for RF energy harvesting

Two-dimensional (2D) semiconductor-based devices are mostly using in-plane direction current in their device architecture, to justify the novelty of 2D-like ultrathin electron devices beyond conventional 3D devices. Those ultrathin 2D devices, however, would unavoidably meet high contact resistance issue. In the present study, thick 2D-layered crystals are rather chosen for a meaningful vertical device, which alleviates the contact resistance issue using a large contact area. Here, we have fabricated Pt/120 nm-thick MoSe2 Schottky diodes with different Ohmic metal contacts of Au, Ti/Au, and MoTi/Au. These diodes are then monolithically integrated with a capacitor of ~20 nm-thick h-BN or 50 nm-thick ALD Al2O3. This way, van der Waals crystal radios are successfully fabricated for wireless RF energy harvesting. In terms of crystal radio device performance, the best results come from Pt/n-MoSe2 Schottky diode with MoTi contact and h-BN capacitor combination. This superiority is attributed to the excellent Ohmic behavior of MoTi alloy contact. At last, when AM demodulation experiments are conducted with 1 MHz carrier frequency/audio frequency-mixed signals, the crystal radio with MoTi demonstrates the highest output DC voltage envelope, allowing loud audio sound.

Compact and Simple High-Efficient Dual-Band RF-DC Rectifier for Wireless Electromagnetic Energy Harvesting

(1) Background: This work presents a high-efficiency, high sensitivity, compact rectifier based on a dual-band impedance matching network that employs a simple and straightforward T-matching circuit, for sub-1 GHz license-free applications. The development of a low-cost RF energy harvester dedicated to the ISM bands is introduced. The proposed rectifier design is optimized to operate at the sub-GHz frequency bands (0.9 to 2.4 GHz), specifically those at the ISM 900 and 2400 MHz. The motivation for this band is due to the low attenuation, well-known fundamental electromagnetic theories and background, and several wireless communications are emitting at those bands, such as RFID (2). Methods: The rectifier design is based on a simple, balanced single-series diode connected with a T-matching circuit. The dual-band performance is achieved by deploying reactive elements in each branch. The full mathematical analysis and simulation results are discussed in the manuscript. (3) Results: The rectifier can achieve a 80 MHz bandwidth around 920 MHz frequency and 200 MHz around the higher band 2.4 GHz. The resultant conversion efficiency level is maintained above 45% at both bands with a peak efficiency reaches up to 70% at the higher band. The optimum terminal load attached to the circuit at which the peak efficiency is achieved, is given as 4.7 kΩ. (4) Conclusion: Due to the compactness and small footprint, simple design, and simple integration with microwave circuits, the proposed rectifier architecture might find several potential applications in wireless RF energy harvesting.

WiFED Mobile: WiFi Friendly Energy Delivery With Mobile Distributed Beamforming

Wireless RF energy transfer for indoor sensors is an emerging paradigm ensuring continuous operation without battery limitations. However, high power radiation within ISM band interferes with packet reception for existing WiFi devices. The paper proposes the first effort in merging RF energy transfer within a standards compliant 802.11 protocol, realizing practical and WiFi-friendly Energy Delivery with Mobile Transmitters (WiFED Mobile). WiFED Mobile architecture is composed of a centralized controller coordinating the actions of multiple energy transmitters (ETs), and deployed sensors that periodically requires charging. The paper first describes 802.11 supported protocol features that can be exploited by sensors to request energy and for ETs to participate in energy transfer. Second, it devises a controller-driven bipartite matching algorithm, assigning appropriate number of ETs to sensors for efficient energy delivery. Thirdly, it detects outlier sensors (OS), which have limited power reception from static ETs and utilizes mobile ETs (METs) to satisfy their charging cycles. The proposed in-band and protocol supported coexistence in WiFED Mobile is validated via simulations and partly in a software defined radio testbed, showing that METs reduce latency by 42% and improve throughput by 83% in scenarios where using only static ETs fails to satisfy charging cycles of OS.

A miniaturized printed rectenna for wireless RF energy harvesting around 2.45 GHz

This paper presents the design of a highly compact printed rectenna for ambient RF energy harvesting around 2.45 GHz. Its antenna structure comprises a rectangular patch with two etched U-shaped slots fed by a symmetric 50 Ω coplanar line. In spite of compact size, it has been directly integrated with a rectifying circuit on the same substrate only at the expense of a 15% frequency shift. The proposed rectenna overall dimension is only 24.9 × 8.6 × 1.6 mm3, the smallest so far reported with comparable performance, which can be easily integrated with any device for energizing low-power wireless sensor networks. It was fabricated and experimentally characterized, achieving a reasonable agreement with the expected simulated results. Measured results indicate that, at the resonant frequency, the antenna part of the proposed rectenna provides a good matching level (<−25 dB) and has a 0.8 dBi peak gain as well as nearly symmetrical radiation properties (in both E- and H-planes). The measured RF-to-DC conversion efficiency (DC output voltage) of the proposed rectenna at a low incident power of −20 dBm is about 20% (97 mV) with a load resistance of 4.7 kΩ. A demonstration experiment of a LED driven by the rectenna was also presented.

Q-Learning-Based Adaptive Power Control in Wireless RF Energy Harvesting Heterogeneous Networks

This article investigates adaptive power control in wireless radio frequency energy harvesting (EH) femtocell heterogeneous networks (HetNets), where some EH devices desire to harvest energy from the signals transmitted from both macro base stations (BSs), and femtocell BSs. An optimization problem is formulated to maximize the sum capacity of femtocells while satisfying the EH requirements of energy users, and information quality of service (QoS) requirements of macrocell users by adaptively controlling the transmit power of femtocell HetNets, where nonlinear EH model is adopted. Due to the discrete variables of transmit power, the formulated optimization problem is with combinatorial computational complexity, and cannot be solved with known solution methods. Thus, a Q-learning-based algorithm is presented, and a segmented reward function based on the distance factor, and the penalty parameter is designed. Simulation results show the effectiveness of the proposed Q-learning-based algorithm, and the presented segmented reward function. It is also demonstrated that by using the nonlinear EH model can effectively avoid the deviation brought by the traditional ideal linear EH model. Additionally, it shows that the convergence time of our proposed scheme grows linearly w.r.t. the number of femtocell BSs, and the number of selectable transmit power levels of femtocell BSs roughly.

Differential voltage octuple rectifiers for wireless energy harvesting

AbstractThis paper presents the design of a novel differential voltage octuple rectifier for wireless RF energy harvesting. Two rectifiers with common matching (CM) and two‐branch matching (TBM) are presented for the CDMA850/GSM900 bands operation. Measured maximum efficiencies of CM and TBM rectifiers reach 66.5% and 70.6%, respectively. The results also show that both matching network‐type rectifiers can produce higher output voltage. It is demonstrated that the designed rectifier‐antenna structure powers up a battery‐less LCD sensor by harvesting RF signal of a dialing cell phone. The proposed rectifier topology and matching mechanisms can be used for various energy harvesting applications, especially for those requiring high supply voltage.

Compensating Spectral Efficiency Loss of Wireless RF Energy Transfer With Analog Joint Source Channel Coding Compression

We investigate the use of discrete-time analog joint source channel coding (JSCC) in a wireless sensor network where the source of information is wirelessly powered by the destination. Wireless energy transfer and information transmission are multiplexed via a time-switching protocol. As a fraction of the time slot is spent for energy transfer, the source samples are saved and compressed using either parametric or non-parametric $N$ : $K$ dimension compression analog JSCC to transmit the information in the remaining fraction of the time slot. We analyze both matched and unmatched source and channel bandwidths. Moreover, we investigate the time-sharing parameter that optimizes the analog system performance and show that the proposed analog scheme can outperform a fully digital system.

원거리 무선 전력 하베스팅 테스트 시스템 개발

본고에서는 초고주파 대역에서의 무선 전력 포집 성능을 검증할 수 있는 테스트 시스템의 구성과 특성을 나타내었다. 개발된 무선 전력 포집 테스트 시스템은 900 MHz와 2.4 GHz 대역을 이용한 전력 전송과 데이터 통신 시스템뿐만이 아니라 2.4 GHz 대역에서의 전력 전송 및 데이터 통신 성능 평가가 가능하며, 효율적인 전력 포집 알고리즘 개발에 적합하도록 개발 되었다. This paper presents the system design, implement, and measurement results of the testbed for the wireless RF energy harvesting system. The developed testbed can be used for RF power transfer and data communication using the 2.4 GHz and 900 MHz frequency bands. It allows to evaluate the system performances for the RF power and data transmission. The testbed can also be used to develop algorithms for efficient energy harvesting.

Materials for Bioresorbable Radio Frequency Electronics

Materials, device designs and manufacturing approaches are presented for classes of RF electronic components that are capable of complete dissolution in water or biofluids. All individual passive/active components as well as system-level examples such as wireless RF energy harvesting circuits exploit active materials that are biocompatible. The results provide diverse building blocks for physically transient forms of electronics, of particular potential value in bioresorbable medical implants with wireless power transmission and communication capabilities.

A Battery-Free 217 nW Static Control Power Buck Converter for Wireless RF Energy Harvesting With $\alpha $-Calibrated Dynamic On/Off Time and Adaptive Phase Lead Control

A battery-free nano-power buck converter with a proposed dynamic on/off time (DOOT) control can achieve high conversion efficiency over a wide load range. The DOOT control can predict the on/off time at different input voltages without a power consuming zero current detection (ZCD) circuit, as well as suppress static power in idle periods. To adapt to the fluctuations in a harvesting system, the proposed α-calibration scheme guarantees accurate ZCD over process, voltage variation, and temperature (PVT) in the DOOT to improve power conversion efficiency. Furthermore, the adaptive phase lead (APL) mechanism can improve inherent propagation delay attributable to low-power and non-ideal comparator, thus improving load regulation by a maximum of 30 mV. The test chip was implemented in 0.25-μm CMOS process with a die area of 0.39 mm2. Experimental results showed 95% peak efficiency, low static power of 217 nW and good load regulation of 0.1 mV/mA, which are suitable for RF energy harvesting applications.

Wireless RF Energy Propagation in Multiply-Connected Reverberant Spaces

Electromagnetic compatibility of electronic systems in reverberant environments is an important issue in the deployment of wireless communications and sensor networks in below-deck compartments of ships and in aircraft cabins and bays. The cumulative buildup and full exchange of radiated electromagnetic energy between multiply-connected reverberant spaces are examined using a simple model adapted from the field of acoustics. Based on conservation of average energy in the diffuse fields, the general model formulation is valid for both weak and strong couplings between the cavities caused by window materials, open apertures, closed and open hatches, seams, and cable/pipe penetrations through bulkheads. Physical energy loss and coupling parameters in three connected chambers are determined from an overlay of model solutions to time-resolved received power measurements, and they can subsequently be used to assess wireless emission coverage and shielding of structures in the connected spaces.