A 2.45/5.8 GHz high-efficiency dual-band rectifier for low radio frequency input power

This article proposes a concurrent rectifier for radio frequency (RF) energy harvesting from the popular ambient RF sources wireless fidelity (WiFi) 2.45 and 5.8 GHz bands. A voltage doubler-based converter circuit with the Schottky SMS7630 diode is used, this chosen diode has shown good results for low power levels. To ameliorate the resulting circuit, we used an interdigital capacitor (IDC) instead of a lumped component; and then we added a filter to reject the 3rd harmonics of each operating frequency. A dual-band impedance transformer with a direct current (DC) block function is used and optimized at low input power points for more harvested DC power. The final circuit was, therefore, more efficient and more reliable. The maximum conversion efficiencies obtained from the resulting circuit are about 60.321% for 2.45 GHz and 47.175% for 5.8 GHz at 2 dBm of input power. Compared to other previous rectifiers presented in the literature, our proposed circuit presents high efficiencies at low power levels and at these operating frequencies

Improvement On Rectification And Regulation Of Power Conditioning Circuit For RF Energy Harvesting

Power management is one of critical issues in most of integrated circuit (IC) applications as it determines the ability of a device to maintain its operating time. Power management system can be divided into two parts, energy harvesting and low dropout (LDO) voltage regulator circuits. Due to the increase of radio frequency (RF) sources around the globe, RF energy harvesting system which mainly composes of a rectifier becomes promising solution to power the low-powered electronic devices as it offers low power density and smaller size of energy converter make it easily to be integrated into a chip. The sensitivity, efficiency, and output voltage play an important role in the design of rectifier for energy harvesting. High efficiency conventional rectifiers typically provide either high sensitivity or high output voltage characteristics. Due to the limitation in rectifier architectures and the physical structure of transistor that causing large voltage drop across the rectifier over a wide range of sensitivity and output voltage, improving one of the characteristics trades off the other. The objective of this research is to design a high efficiency rectifier that operates at high sensitivity, targeting urban and rural areas and producing large output voltage that is sufficient to supply low-power electronic devices. The proposed rectifier comprises bulk-to-source BTMOS differential-drive based rectifier to produce a high efficiency RF energy harvesting system. Low-pass upward matching network is applied at the rectifier input to minimize the power loss between antenna and the rectifier hence increasing the sensitivity and output voltage. Dual-oxide-thickness transistors are used in the rectifier circuit to optimize the power efficiency at each of the rectifier’s stage over a wide range of output voltage and sensitivity. The system is designed using 0.18μm Silterra RF in deep n-well process technology and produces 3.997V output at -15dBm sensitivity without the need of complex auxiliary control circuit and DC – DC charge-pump circuit. Meanwhile, technology scaling in modern IC industries causing the ripple noise from power supply become dominant for analogue and RF circuits. RF circuit demands for voltage regulator that has high power supply rejection ratio (PSRR) and low temperature coefficient as this circuit is very sensitive to noise. Small changes in its supply voltage may cause the circuit not functioning properly. Conventional regulators provide high PSRR, but it typically focuses on low frequency application. Due to this reason, LDO with high PSRR at high frequency and low temperature coefficient over a wide range of temperature is proposed. The proposed LDO uses rail-to-rail folded cascode amplifier to achieve high PSRR while obtaining good open-loop gain and stability. Large 1μF off-chip load capacitor is used to further increase the PSRR. The LDO uses transistors operating in weak and strong inversions at the voltage reference circuit to achieve 2nd order voltage-temperature characteristic hence reducing the temperature coefficient. The LDO is designed using 0.18μm Silterra thick-oxide technology and produces a constant 1.8V output voltage for input voltage between 3.2V to 5V and load current up to a 128mA at temperature between -40°C to 125°C. The LDO achieves more than 100dB PSRR for frequency greater than 900MHz and obtained temperature coefficient of lower than 5ppm/°C within the desired temperature range

A Novel Transparent UWB Antenna for Photovoltaic Solar Panel Integration and RF Energy Harvesting

A novel transparent ultra-wideband antenna for photovoltaic solar-panel integration and RF energy harvesting is proposed in this paper. Since the approval by the Federal Communications Committee (FCC) in 2002, much research has been undertaken on UWB technology, especially for wireless communications. However, in the last decade, UWB has also been proposed as a power harvester. In this paper, a transparent cone-top-tapered slot antenna covering the frequency range from 2.2 to 12.1 GHz is designed and fabricated to provide UWB communications whilst integrated onto solar panels as well as harvest electromagnetic waves from free space and convert them into electrical energy. The antenna when sandwiched between an a-Si solar panel and glass is able to demonstrate a quasi omni-directional pattern that is characteristic of a UWB. The antenna when connected to a 2.55-GHz rectifier is able to produce 18-mV dc in free space and 4.4-mV dc on glass for an input power of 10 dBm at a distance of 5 cm. Although the antenna presented in this paper is a UWB antenna, only an operating range of 2.49 to 2.58 GHz for power scavenging is possible due to the limitation of the narrowband rectifier used for the study

Rectennas for RF wireless energy harvesting

There is an increasing interest in energy harvesting. The rectenna, which is a combination of a rectifier and an antenna, is a device to harvest wireless energy in the air. This thesis is concentrated on the analysis, design and measurement of compact rectennas for radio frequency (RF) wireless energy harvesting applications, and the thesis can be divided into three parts. The first part is about broadband planar dipole antennas with an unidirectional radiation pattern which is suitable for wireless energy harvesting applications. With the rapid development of various wireless systems, there is a need to have a broadband rectenna for energy collection. The antenna is optimized by changing the dipole shape, diameter, feed gap and the spacing between the antenna and the ground plane. It is shown the optimized antenna has a broad (from 2.8 to at least 12 GHz) with the ability to produce unidirectional radiation pattern. It is a good candidate to form a wideband dual-polarized antenna array for applications such as the wireless power transmission and collection. In addition, a simple rectenna and duel-polarized rectenna arrays are presented. The measurement of the rectenna array is shown that the design has produced the desired DC power with reasonable efficiency. The study is confirmed that the more elements in the array, the higher output voltage although the bandwidth is not as wide as expected because of practical limits. The second part is about a novel wideband cross dipole rectenna for RF wireless energy harvesting. The proposed device consists of a cross dipole antenna, low-pass filter (LPF) and voltage doubling rectifier circuit using Shottcky diodes as rectifying elements. It works over the frequency range from 1.7 to 3 GHz for the reflection coefficient less than -10 dB. Besides, the proposed rectenna can convert the RF energy into DC energy with a good conversion efficiency of up to 75% for high input power density levels (>5 mW/cm^2). In addition, another wideband rectenna built on FR4 substrate is optimized for low input power and the rectenna is optimized, built and measured. A further investigation for the input impedance of rectifier is also conducted. Experimental results demonstrate the rectenna has wideband rectification performance and the maximum rectenna conversion efficiency at 1.7 GHz is more than 50% for the power density of 0.1 mW/cm^2. The third part is about improving rectenna conversion efficiency for low input power density. Increasing the rectenna conversion efficiency for low power density is significant for improving rectenna performance. Currently, there are few of research focused on wideband rectenna arrays for low input power. A new wideband rectenna array with a reflector is developed to increase the rectenna conversion efficiency and output voltage through increasing the gain of the antenna. In addition, two connection methods are used to build the rectenna array and advantages and disadvantages for each method are presented. The RF to DC conversion efficiency of proposed rectenna arrays is much improved for low input power density over a wide bandwidth. This research has produced some important designs and results for wireless energy harvesting, especially in wideband rectennas, and is a solid step towards possible widespread applications of rectennas in the near future

Wireless Information and Power Transfer: Architecture Design and Rate-Energy Tradeoff

Simultaneous information and power transfer over the wireless channels potentially offers great convenience to mobile users. Yet practical receiver designs impose technical constraints on its hardware realization, as practical circuits for harvesting energy from radio signals are not yet able to decode the carried information directly. To make theoretical progress, we propose a general receiver operation, namely, dynamic power splitting (DPS), which splits the received signal with adjustable power ratio for energy harvesting and information decoding, separately. Three special cases of DPS, namely, time switching (TS), static power splitting (SPS) and on-off power splitting (OPS) are investigated. The TS and SPS schemes can be treated as special cases of OPS. Moreover, we propose two types of practical receiver architectures, namely, separated versus integrated information and energy receivers. The integrated receiver integrates the front-end components of the separated receiver, thus achieving a smaller form factor. The rate-energy tradeoff for the two architectures are characterized by a so-called rate-energy (R-E) region. The optimal transmission strategy is derived to achieve different rate-energy tradeoffs. With receiver circuit power consumption taken into account, it is shown that the OPS scheme is optimal for both receivers. For the ideal case when the receiver circuit does not consume power, the SPS scheme is optimal for both receivers. In addition, we study the performance for the two types of receivers under a realistic system setup that employs practical modulation. Our results provide useful insights to the optimal practical receiver design for simultaneous wireless information and power transfer (SWIPT).Comment: to appear in IEEE Transactions on Communication

Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation

A new line of research on communications and signals design for Wireless Power Transfer (WPT) has recently emerged in the communication literature. Promising signal strategies to maximize the power transfer efficiency of WPT rely on (energy) beamforming, waveform, modulation and transmit diversity, and a combination thereof. To a great extent, the study of those strategies has so far been limited to theoretical performance analysis. In this paper, we study the real over-the-air performance of all the aforementioned signal strategies for WPT. To that end, we have designed, prototyped and experimented an innovative radiative WPT architecture based on Software-Defined Radio (SDR) that can operate in open-loop and closed-loop (with channel acquisition at the transmitter) modes. The prototype consists of three important blocks, namely the channel estimator, the signal generator, and the energy harvester. The experiments have been conducted in a variety of deployments, including frequency flat and frequency selective channels, under static and mobility conditions. Experiments highlight that a channeladaptive WPT architecture based on joint beamforming and waveform design offers significant performance improvements in harvested DC power over conventional single-antenna/multiantenna continuous wave systems. The experimental results fully validate the observations predicted from the theoretical signal designs and confirm the crucial and beneficial role played by the energy harvester nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication

Multi-service highly sensitive rectifier for enhanced RF energy scavenging

Due to the growing implications of energy costs and carbon footprints, the need to adopt inexpensive, green energy harvesting strategies are of paramount importance for the long-term conservation of the environment and the global economy. To address this, the feasibility of harvesting low power density ambient RF energy simultaneously from multiple sources is examined. A high efficiency multi-resonant rectifier is proposed, which operates at two frequency bands (478-496 and 852-869 MHz) and exhibits favorable impedance matching over a broad input power range (40 to 10 dBm). Simulation and experimental results of input reflection coefficient and rectified output power are in excellent agreement, demonstrating the usefulness of this innovative low-power rectification technique. Measurement results indicate an effective efficiency of 54.3%, and an output DC voltage of 772.8 mV is achieved for a multi-tone input power of '10 dBm. Furthermore, the measured output DC power from harvesting RF energy from multiple services concurrently exhibits a 3.14 and 7.24 fold increase over single frequency rectification at 490 and 860 MHz respectively. Therefore, the proposed multi-service highly sensitive rectifier is a promising technique for providing a sustainable energy source for low power applications in urban environments

A Dual-Band Rectifier for RF Energy Harvesting

Our cities are surrounded by a large number of radio frequency (RF) signals broadcasted by various wireless systems. In order to enhance the efficiency of energy usage in addition to the purpose of communication, ambient RF energy harvesting systems are designed to harvest and recycle wireless energy for many applications such as battery chargers, sensor devices and portable devices. The main element of the ambient RF energy harvesting system is a rectenna which is the combination of an antenna and a rectifying circuit. Even though the ambient RF energy is widely broadcasted by many systems, the energy is extremely low. Therefore, high performance antenna and rectifying circuits have to be designed for supporting small incident power; also the number of frequency channels of the rectenna can enhance the performance and support different harvesting locations. This paper proposes a dual-band rectifier for RF energy harvesting which is designed to operate at 2.1 GHz and 2.45 GHz. The first channel can provide the maximum efficiency of 24% with 1.9 V of the output voltage at 10 dBm of input power. On the other hand, a maximum efficiency of 18% and 1.7 V of the output voltage can be achieved by the second channel at 10 dBm of input power

Current Developments of RF Energy Harvesting System for Wireless Sensor Networks

Energy harvesting or energy scavenging is basically a conversion process of the ambient energy into the electrical energy. The ambient energy exists around us in many different forms including thermal, chemical, electrical and radio frequency (RF). This technique significantly reduces the costs of replacing batteries periodically. Hence, energy harvesting offers various environmental friendly alternative energy sources, which include the vibration, electromagnetic wave, wind energy and solar power. This study will focus on RF energy harvesting that involves the generating of a small amount of the electrical power to drive circuits in wireless communication electronics devices. Recently, wireless sensor network (WSN) has been a crucial part of our daily life. The importance of WSN can be described by the use of sensors in many devices for home security including light sensors, room thermostat and alarm systems. This paper presents an overview and the progress achieved in RF energy harvesting, which involves the integration of antenna with rectifying circuit. Different combinations of antenna and rectifier topologies yield diverse results. Therefore, this study is expected to give an indication on the appropriate techniques to develop an efficient RF energy harvesting system