Hakim Takhedmit

Low-cost converter for harvesting of microwave electromagnetic energy

Energy harvesting receives a lot of attention whatever the physical domain of energy. Microwave electromagnetic energy represents a large reserve to harvest. Present papers details conversion schemes depending on the value of the electromagnetic field. Practical measurements show that fields from 1.5V/m to 30V/m may be encountered. There is a need for high-efficiency converters and various architectures are considered depending on the field range. Simulation results give the analysis of the architectures and the attainable efficiency. Experiments confirm the results. Associated to multiantenna system, it is possible to design a harvesting converter for various consumers.

A 2.45-GHz localized elements rectenna

This paper presents new methodology of rectenna circuit conception. Succeeding sources theory, generally used for power electronics conversion, is presented here and integrated to rectenna circuit design. Circuit simulation based on good filter dimensioning which is sufficient for rectenna design is presented. Localized elements technology is employed here to make the circuits instead of micro strip lines technology usually used to make rectenna circuits. Simulation results are presented and validated by measurement results.

An Efficient Dual - Circularly Polarized Rectenna for RF Energy Harvesting in the 2 . 45 GHz ISM Band

This paper reports a 2.45 GHz, low power dual circularly polarized (DCP) and dual access rectenna. It contains two dc-recombined rectifiers and a cross-slot coupled square patch antenna fed by a microstrip line. A judicious dc recombination scheme allows to minimize the RF power imbalance between accesses caused by multipath effects and consequently arbitrary polarized incident waves. The proposed rectenna is then able to harvest linearly polarized, right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) electromagnetic waves, with nearly stable performances. The rectenna has been optimized at -15 dBm per access and dedicated to remote and contactless supply low consumption sensors. It has been experimentally tested with very low power densities from 0.057 μW/cm2 (Erms=0.46 V/m) to 2.3 μW/cm2 (Erms=2.95 V/m). At 1.49 μW/cm2 (-15 dBm on each rectifier), the structure exhibits an output dc voltage and a global efficiency of 189 mV and 37.7%, respectively when the azimuthal angle (Φ) of the incident field is equal to 0°. Due to the nearly constant total gain of the DCP antenna and an appropriate dc recombination of the two rectifiers, the global efficiency slightly varies between 37.7% and 41.4% when the azimuthal angle (Φ) varies between -90 and 90°.

A 2.45-GHz dual-diode rectenna and rectenna arrays for wireless remote supply applications

This paper describes a compact and efficient rectenna based on a dual-diode microstrip rectifier at 2.45 GHz. This circuit has been designed and optimized using a global analysis technique which associates electromagnetic and circuit approaches. Due to the differential topology of the rectifier, neither input low-pass filter nor via-hole connections are needed. This makes the structure more compact reducing losses. Measurements of a single rectenna element show 83% efficiency over an optimal load of 1050 V at a power density of 0.31 mW/cm2. To increase the received RF power and then increase dc power over the load, identical rectennas have been interconnected to form arrays. Two and four elements rectenna arrays, connected either in parallel or in series, have been developed. It was shown that by properly choosing the interconnection topology and the optimal output load, higher dc voltage or dc power have been obtained. The four-element series-connected array can provide experimentally up to 3.85 times output dc voltage compared to the single rectenna. The parallel-connected rectenna arrays generate approximately 2.15 and 3.75 times output dc power for two and four elements, respectively.

Ultra-Low Power, Low Voltage, Self-Powered Resonant DC-DC Converter for Energy Harvesting

This article presents a resonant DC-DC converter suitable for ultra-low power and low voltage sources. This original topology allows a self-starting and a self-operation under harsh conditions of input voltage and power without any additional start-up assistance. A global theoretical modeling of the converter which includes start-up and steady-state phases is presented and a methodology for optimal design is detailed. It is based on the combination of both theoretical calculations and circuit simulations. Experimental tests based on discrete prototypes are carried out in order to demonstrate the good operation of the converter. Experimental tests have been achieved using an RF energy harvesting source. Ultra-low power and low voltage conditions as low as 3 μW and 100 mV respectively can be achieved as demonstrated by the experimental measurements. The input low voltage is stepped-up to a conventional level of some volts, what allows to power autonomously and solely low power circuits from energy harvesting sources.

A HIGH-PERFORMANCE CIRCULARLY-POLARIZED RECTENNA FOR WIRELESS ENERGY HARVESTING AT 1.85 AND 2.45 GHZ FREQUENCY BANDS

This paper deals with the design and experiments of a dual-band circularly polarized rectenna at 1.85 and 2.45 GHz. It uses a single antenna and a single RF-to-dc rectifier. The circuit contains a dual-band circularly polarized antenna and a dual-band RF-to-dc rectifier based on a miniaturized 180◦ hybrid ring junction. The ring junction is used to independently match the subrectifiers at each frequency. The proposed rectenna was experimented with single-tone and multi-tone incident waves. It achieves more than 300 mV and 40% efficiency, across a 4-kΩ resistive load, at very low power density of 1.13 μW/cm2 at 1.85 GHz and 1.87 μW/cm2 at 2.45 GHz. It also achieves more than 150 mV under the same load condition and in the critical case when receiving only one of the two frequency bands. It is dedicated to harvest RF energy in the GSM 1800 and the 2.45-GHz ISM bands, regardless the polarization angle of the incident waves.

Design and experiments of transparent rectennas for wireless power harvesting

This paper reports the design, optimization and experiments of rectenna circuits, on transparent substrates, dedicated for wireless power harvesting and operating at different frequency bands: GSM, UMTS and Wi-Fi. The proposed circuits are etched on 1.7-mm thickness optically transparent plexiglas, and show more than 95 % transparency. Each circuit contains a linearly-polarized circular loop antenna and a coplanar stripline RF-to-dc rectifier, based on shunt SMS7630 Schottky diode. For 1 μW/cm2 (E = 1.94 V/m) power density, the prototypes offer approximately 300, 200, 100 and 100 mV output DC voltage at 940, 1860, 2140 and 2490 MHz, respectively. For the same power density, overall efficiencies of 50, 30, 30 and 25 % were achieved at the same frequencies.

Electrostatic Vibration Energy Harvester Pre-charged Wirelessly at 2.45 GHz

This paper reports the design, fabrication and experiments of an electrostatic vibration harvester (e-VEH), pre-charged wirelessly for the first time by using an electromagnetic waves harvester at 2.4 GHz. The rectenna uses the Cockcroft-Walton voltage doubler rectifier. It is designed and optimized to operate at low power densities and provides high voltage levels: 0.5 V at 0.5 μW/cm2 and 0.8 V at 1 μW/cm2 The e-VEH uses the Bennet doubler as conditioning circuit. Experiments show 23 V voltage across the transducer terminal when the harvester is excited at 25 Hz by 1.5 g of external acceleration. An accumulated energy of 275 μJ and a maximum power of 0.4 μW are available for the load.