Ambient RF Energy Harvesting Research Articles

Scalable Electromagnetic Energy Harvesting Using Frequency-Selective Surfaces

We present a frequency-selective surface (FSS) that is specially designed and optimized for ambient RF energy harvesting. The unit cell geometry incorporates channeling features in order to combine the collected power from multiple unit cells, allowing for efficient operation under low-power conditions. To demonstrate its performance, we designed and fabricated a matched full-wave rectifier integrated with the absorber FSS. Radiated measurements for the complete rectenna system are included in this paper demonstrating strong agreement with the simulation results. The proposed periodic structure absorbs 97% of the available energy at its resistive load, thus making it an ideal candidate for energy harvesting and channeling applications. Overall Radiation-to-dc conversion efficiency of the fabricated prototype was measured to be 61% when the collected power at the rectifier was 15 dBm.

Coexistence of RF-powered IoT and a Primary Wireless Network With Secrecy Guard Zones

This paper studies the secrecy performance of a wireless network (primary network) overlaid with an ambient RF energy harvesting Internet of Things (IoT) network (secondary network). The nodes in the secondary network are assumed to be solely powered by ambient RF energy harvested from the transmissions of the primary network. We assume that the secondary nodes can eavesdrop on the primary transmissions due to which the primary network uses secrecy guard zones . The primary transmitter goes silent if any secondary receiver is detected within its guard zone. Using tools from stochastic geometry, we derive the probability of successful connection of the primary network as well as the probability of secure communication. Two conditions must be jointly satisfied in order to ensure successful connection: 1) the signal-to-interference-plus-noise ratio (SINR) at the primary receiver is above a predefined threshold, and 2) the primary transmitter is not silent. In order to ensure secure communication, the SINR value at each of the secondary nodes should be less than a predefined threshold. Clearly, when more secondary nodes are deployed, more primary transmitters will remain silent for a given guard zone radius, which will in turn impact the amount of energy harvested by the secondary network. Our results concretely show the existence of an optimal deployment density for the secondary network that maximizes the density of nodes that are able to harvest sufficient amount of energy. Furthermore, we show the dependence of this optimal deployment density on the guard zone radius of the primary network. In addition, we show that the optimal guard zone radius selected by the primary network is a function of the deployment density of the secondary network. This interesting coupling between the performance of the two networks is studied using tools from game theory. We propose an algorithm that can assist the two networks to converge to Nash equilibrium. The convergence of this algorithm is verified using simulations. Overall, this paper is one of the few concrete works that symbiotically merge tools from stochastic geometry and game theory.

Multiport Pixel Rectenna for Ambient RF Energy Harvesting

We describe the design of a multiport pixel rectenna for ambient radio-frequency (RF) energy harvesting consisting of an optimized triple-port pixel antenna and a triple-port rectifier with dc combining. The advantages of the multiport pixel approach include enhanced harvested RF power for a given area as well as a reduction in the antenna matching requirements. We formulate the design of the triple-port pixel antenna as a binary optimization problem with an objective function related to harvested RF power in the GSM-1800 band for specified power angular spectrums without the need for antenna matching components. The optimization of the triple-port pixel antenna is obtained by using successive exhaustive Boolean optimization. The design for the triple-port rectifier with dc combining is also provided and a prototype is demonstrated. The rectenna measurement demonstrates that the proposed triple-port pixel antenna has dc output power over double that of single-port-based antennas of similar size. The overall RF-to-dc efficiency of the multiport pixel rectenna is also evaluated and shown to be 19% when the total input RF power is −20 dBm. The effects of nonuniformity in the input RF power across antenna ports are also investigated.

Compact Triple-Band Rectifier for Ambient RF Energy Harvesting Application

In this paper, a triple-band impedance matching network is introduced and applied to rectifier design. It can be used to realize impedance matching at three frequencies simultaneously. Theoretical analysis of the triple-band matching network is carried out, and a rectifier operating at 0.85, 1.77, and 2.07 GHz is designed, fabricated, and measured. Measurement results show that when the input power is 0 dBm, the measured maximum RF-to-dc power conversion efficiencies are 61.9%, 71.5%, and 60.5% at the frequencies of 0.85, 1.77, and 2.07 GHz, respectively. Compared with other related designs, the proposed rectifier features high efficiency and compactness. Thus, it is suitable for ambient RF energy harvesting application.

Design and experiments of a dual‐band rectenna for ambient RF energy harvesting in urban environments

Energy harvesting technologies are required for autonomous applications, like sensors, for which a long-time power sourcing from a battery is infeasible. An energy harvester converts different forms of environmental energy into electricity. It can replace, totally or partially, the batteries of certain micro-systems that have low-energy requirements. Therefore, the authors exploit the use of electromagnetic waves from broadcasters to power wireless sensors. The authors propose to realize harvesting operation at typical ambient radio frequency power levels found within urban environments. To explore the potential for ambient RF energy harvesting, an RF spectral survey was undertaken from outside in Paris. The average RF power in the frequency range 0.9-3 GHz is about -12 dBm. The harvester includes an antenna, an impedance-matching network, and a rectifier; it was designed to cover two frequency bands from the largest RF contributors (GSM1800 and UMTS Band 1). A prototype is designed, fabricated, and measured. The RF-to-DC rectifier and the choice of the load to optimize the amount of DC power are presented. An efficiency of ~45% was observed experimentally for the UMTS Band 1 and 33% for the GSM1800, whenever the incident power is -7 dBm. Numerical and experimental data are reported and discussed.

On-Body Long-Range Wireless Backscattering Sensing System Using Inkjet-/3-D-Printed Flexible Ambient RF Energy Harvesters Capable of Simultaneous DC and Harmonics Generation

A novel wearable and flexible energy autonomous on-body sensing network is proposed featuring full operability through energy harvesting from a hand-held 464.5-MHz UHF two-way talk radio. Three different functions are provided utilizing the hand-held two-way talk radio as the only energy source for our proposed system. There are two types of energy harvesters (EHs) proposed for the presented system. The first EH that is mounted on the sensing capable backscattering RFID tags harvests the 464.5-MHz signal energy to drive the tags; the second EH that can be worn on hands harvests the same 464.5-MHz signal to produce both the dc power and the carrier signal. The second EH is more efficient than conventional ambient RF energy harvesting architectures because for the first time, both the dc and the second harmonics generated by the rectifier are utilized to enable two additional functions. The generated second harmonic is used to interrogate backscattering RFID tags for on-body sensing, while the dc power is used to power an RF amplifier in order to enhance the second harmonic to effectively extend the sensing and communication range. For the proof-of-concept demonstration, the measured dc and the second harmonic, 929 MHz, output power from the proposed EH are 17.5 and 1.43 dBm, respectively, while a two-way talk radio is 9 cm away. The measured second harmonic output power is increased to 13 dBm utilizing the harvester-powered RF amplifier, and the reading range of the custom backscattering sensor tag is extended to more than 70 m. Also, the interrogation of multiple sensor tags and the wireless detection of ammonia gas utilizing an inkjet printed flexible ammonia sensor are demonstrated showing the wide range of applications of the proposed approach.

Octave and Decade Printed UWB Rectifiers Based on Nonuniform Transmission Lines for Energy Harvesting

Ambient RF energy harvesting is a potential energy source for low-power and battery-less wireless sensors, enabling a range of applications from monitoring to security as part of the Internet-of-Things (IoT) scenario. One of the main challenges of ambient RF energy harvesting is the requirement of operation over a multitude of frequency bands of low ambient power densities resulting in a very wide aggregate operating bandwidth. In this paper, design examples of novel ultra-wideband energy harvesters are demonstrated with octave and decade bandwidths in the UHF and low microwave spectrum. The RF-dc conversion efficiency is maximized by tailoring the dimensions of a nonuniform transmission line used to provide broadband impedance matching. The design challenges in terms of impedance matching based on the Bode-Fano theoretical limit, losses and miniaturization are highlighted. Two prototypes are presented and their performance is evaluated. The octave band rectifier showed a measured RF-dc conversion efficiency of more than 60% over a frequency band of 470 to 860 MHz at 10-dBm input power. The decade band rectifier fabricated on Kapton substrate using inkjet printing featured a higher than 33% efficiency over a frequency band from 250 MHz to 3 GHz at 10-dBm input power.

Energy-Efficient Sub-Carrier and Power Allocation in Cloud-Based Cellular Network With Ambient RF Energy Harvesting

Due to the limited battery energy of mobile devices, the issue of energy-efficient resource allocation has drawn significant interest in the mobile cloud computing area. Simultaneous wireless information and power transfer (SWIPT) is an innovative way to provide electrical energy for mobile devices. Extensive research on the resource allocation problem is conducted in SWIPT systems. However, most previous works mainly focus on energy harvesting over a relatively narrow frequency range. Due to small amounts of energy harvested by the users, the practical implementations are usually limited to low power devices. In this paper, an energy-efficient uplink resource allocation problem is investigated in a cloud-based cellular network with ambient radio frequency (RF) energy harvesting. In order to obtain sufficient energy, a broadband rectenna is equipped at the user device to harvest ambient RF energy over six frequency bands at the same time. From the viewpoint of service arrival in the ambient transmitter, a new energy arrival model is presented. The joint problem of sub-carrier and power allocation is formulated as a mixed-integer nonlinear programming problem. The objective is to maximize the energy efficiency while satisfying the energy consumption constraint and the total data rate requirement. In order to reduce the computational complexity, a suboptimal solution to the optimization problem is derived by employing a quantum-behaved particle swarm optimization (QPSO) algorithm. Simulation results show that more energy can be harvested by the user devices compared with narrow band SWIFT systems, and the QPSO method achieves higher energy efficiency than a conventional particle swarm optimization approach.

A Dual-Port Triple-Band L-Probe Microstrip Patch Rectenna for Ambient RF Energy Harvesting

A dual-port triple-band L-probe microstrip patch rectenna design for ambient RF energy harvesting using the GSM-900, GSM-1800, and UMTS-2100 bands is described. The compact dual-port L-probe patch antenna is implemented by stacking two single-port patch antennas back to back. Each port can independently harvest RF signal from a half-space with gain greater than 7 dBi, and together with both ports in a dc combining configuration, the antenna can acquire RF energy from nearly all directions. We also provide a design for a high-efficiency triple-band rectifier operating at GSM-900, GSM-1800, and UMTS-2100, which is replicated on each port and concatenated together to allow dc combining and near doubling of the output dc voltage. Measurement results show that our prototyped dual-port triple-band rectenna can receive RF power from nearly all directions with an efficiency of greater than 40% and an output voltage of more than 600 mV when the power density is greater than 500 $\mu \mathrm{W}/\mathrm{m}^{2}$ .

Exact Performance Analysis of Ambient RF Energy Harvesting Wireless Sensor Networks With Ginibre Point Process

Ambient radio frequency (RF) energy harvesting methods have drawn significant interests due to their ability to provide energy to wireless devices from ambient RF sources. This paper considers ambient RF energy harvesting wireless sensor networks where a sensor node transmits data to a data sink using the energy harvested from the signals transmitted by the ambient RF sources. We analyze the performance of the network, i.e., the mean of the harvested energy, the power outage probability, and the transmission outage probability. In many practical networks, the locations of the ambient RF sources are spatially correlated and the ambient sources exhibit repulsive behaviors. Therefore, we model the spatial distribution of the ambient sources as an $\alpha $ -Ginibre point process ( $\alpha $ -GPP), which reflects the repulsion among the RF sources and includes the Poisson point process as a special case. We also assume that the fading channel is Nakagami- $m$ distributed, which also includes Rayleigh fading as a particular case. In this paper, by exploiting the Laplace transform of the $\alpha $ -GPP, we introduce semi-closed-form expressions for the considered performance metrics and provide an upper bound of the power outage probability. The derived expressions are expressed in terms of the Fredholm determinant, which can be computed numerically. In order to reduce the complexity in computing the Fredholm determinant, we provide a simple closed-form expression for the Fredholm determinant, which allows us to evaluate the Fredholm determinant much more efficiently. The accuracy of our analytical results is validated through simulation results.

Energy Harvesting from Ambient Radio Frequency: Is it Worth it?

Ambient energy harvesting has been an attractive area of research due to its prospective applications in several modern low-power systems. The paper reports on the feasibility assessment of energy harvesting from ambient radio frequency signals radiated by different communication sources. The rectenna efficiency and leakage current of a storage capacitor are identified as major sources limiting the harvested power and hence considered as core elements in the development of a practical ambient RF energy harvester. A couple of experiments were performed to analyze the spectrogram of ambient RF energy and the effect of capacitor leakage as well as the level of harvested energy that may be needed by low consumption applications.

A Novel Six-Band Dual CP Rectenna Using Improved Impedance Matching Technique for Ambient RF Energy Harvesting

A novel six-band dual circular polarization (CP) rectenna for ambient radio frequency (RF) energy harvesting is presented. Due to the nonlinearity and complex input impedance of the rectifying circuit, the design of a multiband and/or broadband rectenna is always challenging and its performance can be easily affected by variation in the input power level and load. Therefore, an improved impedance matching technique is introduced, which is aimed to improve the performance of the rectifier with a varying condition. A broadband dual CP receiving antenna is proposed, which has a very wide bandwidth (from 550 to 2.5 GHz) and a compact size. An annular ring structure and a novel feeding technique are employed in order to reduce the size and improve the antenna performance. As a result, the proposed rectenna is the first design that covers six frequency bands, including part of the digital TV and most cellular mobile and WLAN bands in the U.K., while the optimal load range for a constant conversion efficiency is from 10 to 75 $\text{k}\Omega $ . The measured results show that the maximum harvested dc power of the rectenna in typical outdoor and indoor environments are 26 and 8 $\mu \text{W}$ , respectively; it can therefore be applied to a range of low-power wireless applications.

Ambient RF energy harvesting in ultra-dense small cell networks: performance and trade-offs

In order to minimize electric grid power consumption, energy harvesting from ambient RF sources is considered as a promising technique for wireless charging of low-power devices. To illustrate the design considerations of RF-based ambient energy harvesting networks, this article first points out the primary challenges of implementing and operating such networks, including non-deterministic energy arrival patterns, energy harvesting mode selection, energy-aware cooperation among base stations (BSs), etc. A brief overview of the recent advancements and a summary of their shortcomings are then provided to highlight existing research gaps and possible future research directions. To this end, we investigate the feasibility of implementing RF-based ambient energy harvesting in ultra-dense small cell networks (SCNs) and examine the related trade-offs in terms of the energy efficiency and signal-to-interference-plus-noise ratio (SINR) outage probability of a typical user in the downlink. Numerical results demonstrate the significance of deploying a mixture of on-grid small base stations (SBSs)~(powered by electric grid) and off-grid SBSs~(powered by energy harvesting) and optimizing their corresponding proportions as a function of the intensity of active SBSs in the network.

Feasibility of Ambient RF Energy Harvesting for Self-Sustainable M2M Communications Using Transparent and Flexible Graphene Antennas

Lifetime is a critical parameter in ubiquitous, battery-operated sensors for machine-to-machine (M2M) communication systems, an emerging part of the future Internet of Things. In this paper, the performance of radio frequency (RF) to DC energy converters using transparent and flexible rectennas based on graphene in an ambient RF energy-harvesting scenario is evaluated. Full-wave electromagnetic (EM) simulations of a dipole antenna assuming the reported state-of-the-art sheet resistance for few-layer, transparent graphene yields an estimated ohmic efficiency of 5%. In the power budget calculation, the low efficiency of transparent graphene antennas is an issue because of the relatively low amount of available ambient RF energy in the frequency bands of interest, which together sets an upper limit on the harvested energy available for the RF-powered device. Using a commercial diode rectifier and an off-the-shelf wireless system for sensor communication, the graphene-based solution provides only a limited battery lifetime extension. However, for ultra-low-power technologies currently at the research stage, more advantageous ambient energy levels, or other use cases with infrequent data transmission, graphene-based solutions may be more feasible.

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.

Performance Analysis of Ambient RF Energy Harvesting with Repulsive Point Process Modeling

Ambient RF (Radio Frequency) energy harvesting technique has recently been proposed as a potential solution to provide proactive energy replenishment for wireless devices. This paper aims to analyze the performance of a battery-free wireless sensor powered by ambient RF energy harvesting using a stochastic geometry approach. Specifically, we consider the point-to-point uplink transmission of a wireless sensor in a stochastic geometry network, where ambient RF sources, such as mobile transmit devices, access points and base stations, are distributed as a Ginibre alpha-determinantal point process (DPP). The DPP is able to capture repulsion among points, and hence, it is more general than the Poisson point process (PPP). We analyze two common receiver architectures: separated receiver and time-switching architectures. For each architecture, we consider the scenarios with and without co-channel interference for information transmission. We derive the expectation of the RF energy harvesting rate in closed form and also compute its variance. Moreover, we perform a worst-case study which derives the upper bound of both power and transmission outage probabilities. Additionally, we provide guidelines on the setting of optimal time-switching coefficient in the case of the time-switching architecture. Numerical results verify the correctness of the analysis and show various tradeoffs between parameter setting. Lastly, we prove that the sensor is more efficient when the distribution of the ambient sources exhibits stronger repulsion.

Ambient RF energy harvesting trial in domestic settings

This study investigates the feasibility of ambient radio frequency (RF) energy harvesting for powering low-power electronic devices, in domestic environments. An RF spectrum survey was carried out in a variety of locations around the city of Bristol, UK between 500 MHz and 6 GHz. Locations are limited to indoor residential environments, and as a comparison an office. The measurement setup consists of an omnidirectional, broadband, discone antenna and a handheld spectrum analyser. On the basis of the measured power consumption of a number of low-power electronic devices and the analysed results, the required harvesting time to power each device is calculated. The results show that in order to harvest enough energy to power-up a small calculator (2 μW) for 1 s, an antenna array covering 1.7–2.5 GHz with effective area of 1 m2 requires on average about 10 min of harvesting.

Inkjet-Printed Wideband Planar Monopole Antenna on Cardboard for RF Energy-Harvesting Applications

We present a fully inkjet-printed novel wideband planar monopole antenna on thin packaging cardboard available in bulk for low-cost and environmentally-friendly mass manufacturing. We outline the characterization and the dielectric properties of the cardboard that are imperative for the successful design of an antenna on a paper-based substrate. To achieve highly conductive inkjet-printed pattern on the fibrous and porous cardboard, we deposit thin dielectric coating on the cardboard in the same inkjet process. The operation of the antenna is attested through simulations and measurements in the frequency range of 600-1500 MHz, where there are several strong radio signals present for ambient RF energy harvesting.

Enhancing RF-to-DC conversion efficiency of wideband RF energy harvesters using multi-tone optimization technique

In this paper, a 1.8–2.6 GHz wideband rectenna is designed for radio frequency (RF) energy harvesting in the context of wireless sensor nodes (WSN). To assess the feasibility of ambient RF energy harvesting, the power density from RF base stations is analyzed through statistical measurements. Power density measurements are also performed close to Wi-Fi routers. Using these results, a methodology based on impedance matching network adaptation and maximum power transfer is proposed to design the wideband RF harvester. Using this method, three RF bands,i.e.GSM1800, UMTS and WLAN, are covered. The theoretical analysis is confirmed by simulations and measurements. From measurements results, the prototype RF-to-DC conversion efficiency is 15% at −20 dBm from 1.8 to 2.6 GHz. It is shown that with three RF sources in the chosen bands, each emitting at 10 dBm, the RF-to-DC conversion efficiency is 15% better compared to that measured with a single RF source. Finally, 7 µW is harvested at 50 m from a GSM1800 and UMTS base station. This value confirms the RF harvester workability to supply small sensors.

Ambient RF Energy Harvesting in Urban and Semi-Urban Environments

RF harvesting circuits have been demonstrated for more than 50 years, but only a few have been able to harvest energy from freely available ambient (i.e., non-dedicated) RF sources. In this paper, our objectives were to realize harvester operation at typical ambient RF power levels found within urban and semi-urban environments. To explore the potential for ambient RF energy harvesting, a city-wide RF spectral survey was undertaken from outside all of the 270 London Underground stations at street level. Using the results from this survey, four harvesters (comprising antenna, impedance-matching network, rectifier, maximum power point tracking interface, and storage element) were designed to cover four frequency bands from the largest RF contributors (DTV, GSM900, GSM1800, and 3G) within the ultrahigh frequency (0.3-3 GHz) part of the frequency spectrum. Prototypes were designed and fabricated for each band. The overall end-to-end efficiency of the prototypes using realistic input RF power sources is measured; with our first GSM900 prototype giving an efficiency of 40%. Approximately half of the London Underground stations were found to be suitable locations for harvesting ambient RF energy using our four prototypes. Furthermore, multiband array architectures were designed and fabricated to provide a broader freedom of operation. Finally, an output dc power density comparison was made between all the ambient RF energy harvesters, as well as alternative energy harvesting technologies, and for the first time, it is shown that ambient RF harvesting can be competitive with the other technologies.