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This study proposed, for the first time, a newly developed metal–insulator-insulator–metal (MIIM)-based log-spiral rectenna for energy harvesting applications. The designed resonant log-spiral antenna at 28.3 THz forwards the absorbed infrared (IR) electromagnetic (EM) radiations to the installed double insulator-based MIIM rectifying diode. The realized MIIM diode is formed by sandwiching the two insulators among the designed resonant antenna terminals (hot spot region). Antenna terminals are used as the electrodes of the rectifying diode. This novel approach ensures the maximum transfer of captured IR EM radiations by the antenna to the rectifying part with good impedance matching and thus increases the overall conversions efficiency. The study presents an in-depth analysis of the impact of the changing metal types (Au, Al, Ag, and Cu) and insulating materials (Al 2 O 3 , Cu 2 O, Ta 2 O 5 , TiO 2 , and ZnO with10 different formations) on the realized rectenna performance in terms of captured E-field enhancement, I/V , resistivity, and responsivity characteristics. It is found that the overall performance of the proposed double insulator-based rectenna system is better for the asymmetric configuration of Au- Al 2 O 3 - Cu 2 O –Cu and it exhibits 100% enhanced non-linearity as compared to MIM-based configuration. [ABSTRACT FROM AUTHOR]

The harvesting of ambient RF power would be a promising respond to the requirement of continuous power support the sensors of wireless networks, without using batteries. The devices used for scavenging the RF power are known by the term rectennas and their first unit is an antenna which captures the power of impinging RF signals and then guide it to be rectified and stored by the rest of rectennas' grades. This article proposes an antenna scheme suitable for rectenna applications at the Universal Mobile Telecommunication System (UMTS), from 1.92 GHz to 2.17 GHz. The antenna is composed of planar dipoles with specific layout, printed on dielectric substrate with Double Negative (DNG) electromagnetic properties. The DNG substrate is composed of dielectric spherical particles that are hosted in a medium of very low dielectric constant and have suitable size in order to resonate at the UMTS band, thus developing high intensity electromagnetic fields. The dipoles embedded to this hybrid structure gather amounts of RF power larger than in case of an ordinary dielectric. Moreover, the antenna was synthesized with intend a matching network between it and the rectifier not to be used, thus avoiding potential losses and complexity. Considering that the rectenna will work in mobile telecommunication environment, where the incoming signals are of statistical nature, its performance was studied using its Mean Effective Gain (MEG), the Cross Polarization Power Ratio (XPR) and the Directions of Arrival (DoAs) of the incoming waves. Statistical mean values for DC voltages and power equal to 172 mV and 65 μW respectively and with mean efficiency 58% were obtained for incident power 0.2 mW, while, depending on case, the DC voltage may exceed the 300 mV and the power the 160 μW. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a novel compact broadband rectifying antenna (rectenna) is presented for ambient radio frequency (RF) energy harvesting. Slot antennas with excellent bandwidth and matching characteristic are designed by etching fractal geometries with different iteration order on a radiation patch. A rectifier with a single stub matching network is investigated for impedance matching and the RF to DC conversion efficiency is improved at low input power. Simulation and the experiments have been carried out to evaluate the performance of antenna and rectifier respectively. A good match is observed between the simulated and measured results. The experimental results show that antenna features a broad bandwidth from 2.15 GHz to 2.9 GHz and the maximum conversion efficiency of rectifier is up to 64% at 0 dBm. The highest conversion efficiency of rectenna is 62% and the maximum output voltage is 1.5 V at the input power of 0 dBm. [ABSTRACT FROM AUTHOR]

The paper presents a multiband dual polarized rectenna for RF energy harvesting in C-band application range. The receiving antenna of the designed rectenna is consisting of a truncated corner square patch loaded with several circular slots, L-slots and U-slot. A proximity coupled feeding arrangement is used for obtaining a wide impedance bandwidth so that the complete C-band from 4 to 8 GHz can be covered. The proposed antenna has the advantage of compact size and dual polarization since circular polarization is realized at three bands (5.42 GHz, 6.9 GHz and 7.61 GHz) in the −10 dB impedance bandwidth range. For efficient RF to DC conversion a two-stage voltage doubler rectifier is used considering that it provides a higher voltage multiplication with a small threshold voltage at its primary stage. For ensuring maximum RF to DC conversion efficiency; a matching network has been designed and is connected in between receiving antenna and the rectifier circuitry in order to match the antenna and load in different frequency bands. It is observed that a maximum conversion efficiency of 84% is achieved at 5.76 GHz. The proposed rectenna has been fabricated and it is found that measured results are in good match with the simulated results. [ABSTRACT FROM AUTHOR]

Theoretical photoelectric conversion efficiency is higher in energy conversion using nano-rectifying antennas compared to traditional photovoltaic cell conversion technology. This paper presents the design of a wide-band metal rectifying antenna based on a concave bow tie structure to achieve efficient and wide-band solar energy collection. Firstly, the concave bow tie nanoantenna's structure is designed using the finite difference time domain method. The optimization of the antenna structure considers the influence of parameters such as antenna gap, concave corner radius, thickness, and substrate thickness on absorption efficiency. The resulting absorption efficiency is 94.6% within the wavelength range of 400 nm–1600 nm. Subsequently, the design, preparation, and experiment of the metal–insulator–insulator–metal​ ( Ag-Al 2 O 3 − HfO 2 − Au) rectification based on Ag particle antenna are carried out, and a rectification system test platform is established. The correctness of the proposed transfer matrix method tunneling model and rectification antenna design approach in this paper is verified, yielding a photoelectric conversion efficiency of 5.14 × 10−9. • Design of a wide-band metal rectifying antenna based on a concave bow tie structure for efficient and wide-band solar energy collection. • Optimization of the concave bow tie nanoantenna structure,Achieved absorption efficiency of 94.6% within the wavelength range of 400 nm–1600 nm. • Design, preparation, and experimental validation of a metal–insulator–insulator–metal (MIIM) rectification system. • Establishment of a rectification system test platform to evaluate the performance of the proposed design. • Verification of the proposed transfer matrix method tunneling model and rectification antenna design approach. • Demonstration of a photoelectric conversion efficiency of 5.14×10-9 using the developed rectification system. [ABSTRACT FROM AUTHOR]

This work illustrates the effect of nano-antenna shape on the efficiency of a complete nano-rectenna system for one specific geometry: the bowtie. The bowtie geometry is very well known for its wider band characteristics compared to the straight dipole. Based on full wave electromagnetic field solvers, the radiation efficiency and maximum matching efficiency for nano-bowties with different lengths and base angles are calculated. The results demonstrate that by adopting the bowtie topology, the radiation efficiency for an aluminum dipole can be improved from 51% to 61%, while the relative total efficiency can be improved from 46% to 57%, compared to the common straight nano-dipole mainly used in literature. [ABSTRACT FROM AUTHOR]

Before designing a detector circuit, the electrical parameters extraction of the Schottky diode is a critical step. This article is based on a Monte-Carlo (MC) solver of the Boltzmann Transport Equation (BTE) including different transport mechanisms at the metal-semiconductor contact such as image force effect or tunneling. The weight of tunneling and thermionic current is quantified according to different degrees of tunneling modelling. The I-V characteristic highlights the dependence of the ideality factor and the current saturation with bias. Harmonic Balance (HB) simulation on a rectifier circuit within Advanced Design System (ADS) software shows that considering non-linear ideality factor and saturation current for the electrical model of the Schottky diode does not seem essential. Indeed, bias independent values extracted in forward regime on I-V curve are sufficient. However, the non-linear series resistance extracted from a small signal analysis (SSA) strongly influences the conversion efficiency at low input powers. [ABSTRACT FROM AUTHOR]

The small wavelength utilizable range used for determining the optimum performance of photovoltaic and rectenna devices, compared to the broad band spectrum of solar or other heat sources, limits the energy conversion efficiency of such technologies. A selective emitter, with an emissivity profile that matches the receiver's characteristic bandwidth, can be used to improve the overall efficiency of such energy harvesting devices. This paper compares simulated and experimental results of the design and fabrication of a selective emitter that can be used in the 8–12 µm frequency range. The matrix transform method is used to calculate the radiative properties of one dimensional metal-dielectric photonic structures. By using genetic algorithm as a powerful optimization tool, the simulated design characteristics of such structure are adjusted to minimize the mean square deviation of the actual spectral emissivity from the target emissivity profile. Specifically, this paper presents and compares results of the simulated design and fabrication of selective emitters composed of alternating layers of Al 2 O 3 -SiO 2 or Al 2 O 3 -SiC on an aluminum substrate. The output radiation of these selective emitters could be used as the input radiation to high efficiency rectenna devices. [ABSTRACT FROM AUTHOR]

The present study provides a series–parallel combination of connected rectenna arrays using SMS7621-001LF Skyworks Schottky diodes at 5.8 GHz to harvest wireless systems' power. The proposed configuration is an array of patch antennae with a rectifying circuit, while in the array connection, the rectenna system works with the most optimal conversion efficiency. Based on the results obtained from the fabricated proposed rectenna's optimal efficiency, an RF power density ranging from 30 to 160 µW/cm2 has been obtained. Also, the conversion efficiency of RF-to-DC power is more than 77%. The measured output DC voltage of 10 elements in a parallel-series connection is 9.1 V, and their output current has been measured at 130 mA. The highest power conversion efficiency in the proposed rectenna system is 75.2 at a power density of 90 µW/cm2. The conversion efficiency is almost constant in this rectenna as the number of elements increases. Also, during this experiment, it was proven that the addition of a rectifier to the receiving antenna has not only a very small effect on the radiation efficiency but also has not much effect on the features of the main beam of the antenna system. The prototype unit cell rectenna and array are fabricated, and their performance is validated using measurements. [ABSTRACT FROM AUTHOR]

This paper presents the development of an energy harvesting circuit for use with a head-mountable deep brain stimulation (DBS) device. It consists of a circular planar inverted-F antenna (PIFA) and a Schottky diode-based Cockcroft-Walton 4-voltage rectifier. The PIFA has the volume of π × 10 2 × 1.5 mm 3 , resonance frequency of 915 MHz, and bandwidth of 16 MHz (909–925 MHz) at a return loss of −10 dB. The rectifier offers maximum efficiency of 78% for the input power of −5 dBm at a 5 kΩ load resistance. The developed rectenna operates efficiently at 915 MHz for the input power within −15 dBm to +5 dBm. For operating a DBS device, the DC voltage of 2 V is recorded from the rectenna terminal at a distance of 55 cm away from a 26.77 dBm transmitter in free space. An in-vitro test of the DBS device is presented. [ABSTRACT FROM AUTHOR]

• Atomic layer deposition was used to deposit 1–5 nm ultra-thin insulators. • Au/Al 2 O 3 /Ti diode exhibited a zero-bias responsivity of −0.6 A/W. • Resonant tunneling effect was observed in triple insulator MI3M rectifiers. • Experimental I-V characteristics of MI3M rectifiers are simulated. • Asymmetry of 6 and responsivity of 4.3 A/W at sub-V were obtained for MI3M diodes. Tunnel-barrier rectifiers comprising single and triple insulator configurations have been fabricated by atomic layer deposition (ALD) to investigate the insulator (Al 2 O 3 , Ta 2 O 5 , Nb 2 O 5) layer quality and rectification performance for inclusion in rectenna arrays for infrared energy harvesting. ALD has provided superior control of nanometer film thickness (1–3 nm) as well as insulator film quality as tunneling has been found to be the dominant conduction mechanism for all fabricated devices. The key rectifier properties, such as asymmetry, non-linearity, responsivity and dynamic resistance have been assessed from current-voltage (I-V) measurements. The Au/Al 2 O 3 /Ti diode exhibits zero bias responsivity of −0.6 A/W, showing that it can be used for energy harvesting applications without the aid of external bias. The effect of resonant tunneling on rectification performance of triple insulator non-cascaded (Ta 2 O 5 /Nb 2 O 5 /Al 2 O 3) and cascaded (Nb 2 O 5 /Ta 2 O 5 /Al 2 O 3) rectifiers has been observed from experimental I-V characteristics and substantiated by theoretical simulations. Superior low-voltage asymmetry (6 at 0.1 V) and responsivity (4.3 A/W at 0.35 V) for triple insulator MI3M rectifiers have been observed. The resonant tunneling does not provide enhanced rectification at low bias as previously reported, rather it has much smaller effect. The latter indicates that dissimilar metal electrodes rectifier configurations are more promising for inclusion in optical rectenna. [ABSTRACT FROM AUTHOR]

Despite the high number of scientific reports on rectenna applications, the influences of antenna/rectifier interface over the power conversion efficiency have not yet been profoundly debated in the literature. In this context, equations that fully characterize the matching and power transmission processes within the antenna/rectifier interface are developed and presented in this work, applying the Two-Port Power Gain definitions in rectenna analysis. Rectenna designs presented in previous works were used here as test cases to introduce the problem and experimentally validate the revised methodology and results. The overall rectenna power conversion efficiency was equated as a function of the antenna/rectifier interface matching losses, which proved to be responsible for 20–50% of the power conversion efficiency reduction for the tested cases. In conclusion, the equations presented, based only on conventional power, S -Parameter and DC voltage measurements, represent an alternative tool in the design of matching and rectification solutions for rectennas. [ABSTRACT FROM AUTHOR]

This paper introduces a novel device composed by a wide band rectifying antenna array coupled with a modified resonant amortized Armstrong oscillator with increased efficiency, used as step-up micro-converter. The aim of the device is to harvest ambient electromagnetic energy and convert it into useful energy. Experimental methods and simulations were used to design the microstrip rectenna and the micro-converter prototypes. One rectenna array composed by 48 microstrip antennas and five step-up micro-converters were designed, manufactured and tested. The microstrip rectenna has a unique design with a geometrical area of 36 cm2 and high frequency to direct current power conversion efficiency of 17.5%–74% measured at 0.6 μW/cm2 to 55 μW/cm2 input power density in 860–890 MHz band and a large bandwidth of 800 MHz-13GHz range. The micro-converters were supplied from the rectenna array output with 300mV–1200mV, charging each one 3 V/6 mAh accumulator. The DC to DC conversion efficiency of the micro-converters falls in 43%–59% range. Our micro-converter has an average increased conversion efficiency of about 15% higher than any published solutions, measured below one miliwatt input power. Our micro-converter can be used for other energy harvesting devices such as low light indoor photovoltaic cells or ultra low power thermoelectric generators. • Novel rectenna array coupled with micro-converters harvests electromagnetic energy. • 48 ultra large bandwidth 800 MHz-13GHz microstrip antennas equip the array. • Conversion efficiency of each rectenna reaches 75% at 55 μW/cm2 input power density. • 59% efficiency was measured on sub milliwat pulse width modulated micro-converter. • Two resonant oscillation modes of the micro-converter are deeply analyzed. [ABSTRACT FROM AUTHOR]

To wirelessly harvest RF energy at LTE band, a novel compact and efficient dual-port microstrip rectenna is proposed. An antenna designed with two ports and featured by arrow-shaped, circular and rectangular slots is presented. A broadband rectifier including a voltage doubler rectifying circuit and a novel matching network is developed to convert the RF power captured by the antenna into DC power. For well matching between the antenna and the rectifying circuit, the matching network which consists of double 70-deg fan-shaped stubs, no-uniform transmission line and double 55-deg fan-shaped stubs is designed. The prototypes of the proposed antenna and rectifier are respectively fabricated. The simulation and experimental results show that the antenna is able to harvest energy from different frequencies when fed by separate microstrip feeding line. The distribution of current density along with the radiation pattern in E-plane and H-plane is investigated. Besides, the conversion efficiency and output voltage of the rectifier are studied. To test the performance of the proposed rectenna, an indoor measurement is conducted. The results demonstrate that the RF-to-DC conversion efficiency of the proposed antenna is around 42% and the output voltage is around 0.9 V, indicating its potential application in the RF energy harvest. [ABSTRACT FROM AUTHOR]

Rectifying antennas are often prensented as a potentiel technological breakthrough for energy harvesting. First theorized in the 1970's, the downsizing of an antenna coupled with a rectifier has become technologically achievable with the progresses of fabrication techniques such as electron beam or photolithography. However, reaching infrared or visible region of the electromagnetic spectra still entails challenges on the integration of a rectifier operating in the terahertz range. New bottom up approaches are likely to bring a promising solution to this issue. To improve our understanding of the key points of rectifying antennas' design for the infrared and visible light, and the challenges of device fabrication, this work reviews the progresses of this technology, going back from the first historical RF energy harvesting systems and covering the most innovative trends to this date. [ABSTRACT FROM AUTHOR]

In this paper a preliminary study on an array configuration of rectified optical nanoantennas for energy harvesting application is proposed. Currently, the major impediments for the use of the rectified optical nanoantenna known as rectenna are the relatively low conversion efficiency and low power transfer to the load, both of them caused mainly by the mismatch between the impedance of the rectifier (several kilo ohms) and that of the antenna (hundreds of ohm). For this reason, the design of the array represents a crucial point to obtain the maximum energy transfer from the rectenna to the load, represented as a typical DC/DC boost power converter, and modeled by an equivalent input impedance. The novelty of this study confirms that it is possible to obtain dynamically an impedance matching between the array of optical rectennas and the load. According to this method, in the proposed rectenna array, N elements can be serially connected so to allow to the open circuit voltage to be increased and M elements can be parallel connected to give the degree of freedom needed to achieve the impedance matching with the load. Finally, a case study for Structural Health Monitoring (SHM) application is presented. [ABSTRACT FROM AUTHOR]