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This paper introduces a novel compact ultra-lightweight multiband RF energy harvester fabricated on a paper substrate. The proposed rectenna is designed to operate in all recently released LTE bands (range 0.79-0.96 GHz; 1.71-2.17 GHz; and 2.5-2.69 GHz). High compactness and ease of integration between antenna and rectifier are achieved by using a topology of nested annular slots. The proposed rectifier features an RF-to-dc conversion efficiency in the range of 5%-16% for an available input power of -20 dBm in all bands of interest, which increases up to 11%-30% at -15 dBm. The rectenna has been finally tested both in laboratory and in realistic scenarios featuring a superior performance to other state-of-the-art RF harvesters on flexible substrates.

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.

The purpose of this study is to outline the main guidelines for the design of arrays of optical rectennas aiming to harvest energy and for the optimization of the power transfer to an external load. In particular, the novelty of this study consists in introducing the concept of the integrated design between the array of optical rectennas and the harvesting circuit able to exploit the available energy. The design of the array represents the crucial point in order to optimize the power transfer between the antenna and the load and can influence the rectenna design. On the other hand, the maximum power transfer to the load has to be obtained under matching conditions between the array and the load and can influence both the design of the array and of the converter to supply a load. A previous study of the main type of nanoantennas and their relative structures will be fulfilled in order to choose the particular structure, which will be analysed in this work. Therefore, a numerical analysis of the chosen structure, a dipole nanoantenna, and a description of the rectenna topology will be performed. The exploitation of the available energy requires the use of the DC-DC boost converter, which allows to interface a rectenna system with a downstream load. The choice of the commercially DC-DC boost converter will allows to design an array of optical rectennas in order to achieve the impedance matching conditions to a harvesting circuit. Finally, since the equivalent impedance of the array of optical rectennas changes with the solar radiation during a day, the optimization of the maximum power transfer between the array and the harvesting circuit will be investigated.

Wireless power transmission presents itself as being a solution to some common problems of the extensive use of electronic devices such as the removal of parasitic components present in feeding pads and the constant charge of electronic devices without the need of wires. This solution becomes attractive, for example, as a means of increasing the flight time of battery dependent unmanned aerial vehicles. Microstrip antenna due to their ease of manufacturing, low fabrication cost, support of different polarizations and conformability to irregular surfaces and different substrates, seem very advantageous in being used for microwave power transmission. This paper presents a linearly polarized 16-element antenna array with uniform amplitude and phase excitation proposed for power transmission while both a linearly and circularly polarized single element patch are proposed for reception., Grant numbers : We would like to acknowledge the financial Support of COST IC1301, referring that A. Georgiadis was supported by the Spanish Ministry of Economy and Competitiveness project TEC 2012-39143 (SOSRAD), and the Generalitat de Catalunya under grant 2014 SGR 1551.© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

This paper presents the design of an integrated and differential rectenna on silicon, operating at 24 GHz. The antenna is dual-polarized and composed by four patches on a synthetized low effective permittivity dielectric. The substrate is a structure composed of three layers of high-resistivity silicon (εr= 11.9) where the central layer has an air cavity equal to the dimensions of the antennas. The feeding solution is performed by planar microstrip lines with inset feeds. A shunt configuration was chosen for the rectifier with GaAs diodes. The silicon substrate assures the complete integration for on-chip systems and despite the lossy material chosen as substrate, each patch antenna presents 83% of radiation efficiency with a maximum gain of 4.82 dBi. The overall efficiency of the rectenna is 44% at a received power level of 10 dBm.

Summarization: This work presents an efficient and high-sensitivity radio frequency (RF) energy harvesting supply. The harvester consists of a single-series circuit with one double diode on a low-cost, lossy FR-4 substrate, despite the fact that losses decrease RF harvesting efficiency. The design targeted minimum reflection coefficient and maximum rectification efficiency, taking into account not only the impedance matching network, but also the rectifier microstrip trace dimensions and the load. The simulated and measured rectenna efficiency was 28.4% for-20-dBm} power input. In order to increase sensitivity, i.e., ability to harvest energy and operate at low power density, rectennas were connected in series configuration (voltage summing), forming rectenna arrays. The proposed RF harvesting system ability was tested at various input power levels, various sizes of rectenna arrays, with or without a commercial boost converter, allowing operation at RF power density as low as 0.0139 μ W/cm2. It is emphasized that the boost converter, whenever used, was self-started, without any additional external energy. The system was tested in supplying a scatter radio sensor, showing experimentally the effect of input power density on the operational cold start duration and duty cycle of the sensor. Presented on: IEEE Transactions on Microwave Theory and Techniques

This paper presents the design of an integrated and differential rectenna on silicon, operating at 24 GHz. The antenna is dual-polarized and composed by four patches on a synthetized low effective permittivity dielectric. The substrate is a structure composed of three layers of high-resistivity silicon (εr = 11.9) where the central layer has an air cavity equal to the dimensions of the antennas. The feeding solution is performed by planar microstrip lines with inset feeds. A shunt configuration was chosen for the rectifier with GaAs diodes. The silicon substrate assures the complete integration for on-chip systems and despite the lossy material chosen as substrate, each patch antenna presents 83% of radiation efficiency with a maximum gain of 4.82 dBi. The overall efficiency of the rectenna is 44% at a received power level of 10 dBm.