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The dc power collected by radio frequency energy harvesting (RFEH) absorbing surfaces is limited by their physical aperture. Here, a compact, conformable, and ultrathin sub-1 GHz large-area RFEH surface is proposed based on electrically small ($ka=0.58$) “wire-type” rectenna elements, with an effective area exceeding its physical aperture size. Using optimized large-signal complex source tuning, the rectifiers achieve up to 36% measured power conversion efficiency (PCE) at =20 dBm. The proposed 15 cm-diameter six-element array generates a 27.5 $\mu \text{W}$ at 1 V output from a $0.17~\mu \text{W}$ /cm2 incident power density across a 40 $\text{k}\Omega $ load. Owing to its series connection, the voltage output is boosted, and the load resistance dependence is suppressed enabling over 60% of the maximum RF-to-dc PCE to be preserved for loads between 7 and 100 $\text{k}\Omega $ , with an area-normalized figure-of-merit nearly 100% higher than previous arrays. The proposed array is integrated with a commercial DC-DC converter and demonstrated powering a Bluetooth low energy (BLE) wireless sensor node (WSN) from an unprecedented incident power density of 0.25 $\mu \text{W}$ /cm2. A practical demonstration using a commercial 3 W, 915 MHz Powercast source is presented, showing an 11 m operation range with a 1 V output and illustrating the impact of polarization mismatch on the proposed array. [ABSTRACT FROM AUTHOR]

In microwave wireless power receivers, impedance matching networks can maximize power transmission from RF to dc. However, they require circuit components and physical space to implement. To circumvent the problem, we present two compact patch rectennas that do not require matching networks. They comprise a patch antenna and rectifying Schottky diodes which are mounted on the ground plane and connected to the patch antenna through metallic vias. The positions of the vias are chosen in such a way that the input impedance of the antenna and that of the rectifying units are conjugately matched. The two rectenna types are all fabricated and tested: one with one rectifying unit and the other with double rectifying units, respectively. Measurements show that the rectenna with the single rectifying unit has the peak RF-dc conversion efficiency of 77% at 2.45 GHz and the dynamic power range (>60%) is 10 dB. The rectenna with the double rectifying units has the peak conversion efficiency of 74.14% at 2.45 GHz and the dynamic power range (>60%) is 10 dB. Both rectennas are good candidates for integrated microwave wireless power receivers due to the removal of the impedance matching networks and the suppression of harmonic components. [ABSTRACT FROM AUTHOR]

A new GaN Nano-Schottky diode rectifier is introduced with capacitance per unit gate width of 381 fF/mm, and series resistance is 0.45 $\Omega \cdot $ mm leading to transition frequency ($f_{\mathrm {T}}$) of 928 GHz. The associated forward current is 1.8 A/mm with breakdown voltage of 30 V. The new device was modeled and an on-wafer voltage doubler rectenna circuit was designed and fabricated on GaN/SiC wafers. A $W$ -band small and large signal characterization was performed to highlight the integrated rectenna performance. An RF-dc efficiency of 61.5% was measured at 95 GHz with associated input power density of 3.61 kW/m2. The latter represents a 15.7% increase in efficiency over the state-of-the-art $W$ -band rectenna circuit. The input power handling has also increased by a factor of 1.5 and 9.5 from reported GaAs and CMOS-based rectenna circuits at 94 GHz. The result highlights key improvements in the rectenna metrics for wireless power beaming demonstrations of the future. [ABSTRACT FROM AUTHOR]

The design of an ambient radio frequency (RF) energy harvesting system is introduced to replace the battery of the mass Internet-of-Things devices. This system can achieve high sensitivity with high efficiency over a wide input power range by optimizing the differential-drive cross-coupled (DDCC) rectifier and the load. The impedance of the dual-band four-port loop antenna array is directly conjugated to match with the rectifier, which reduces insertion loss of the matching network to improve efficiency. At 915 and 945 MHz for ISM and GSM bands, the rectenna can achieve high sensitivity of −30 dBm with 22% and 24% efficiency, high efficiency of 65% and 48% with −20-dBm input power, and a wide input power range from −30 to −18 dBm with 22–65% and 24–48% efficiency. The dual-band design explores the frequency diversity to harvest more RF energy from the environment, while the cross-shaped antenna array utilizes the space diversity to harvest RF energy from different directions with a compact size of $0.15\lambda \times 0.15\lambda $ per antenna element (where $\lambda $ is the free space wavelength at 915 MHz). This new harvesting system can provide output dc power of 21.4 and $2.95~\mu \text{W}$ in real-world outdoor and indoor ambient environments, respectively. [ABSTRACT FROM AUTHOR]

The RF to dc conversion efficiency of a rectenna often varies dramatically with the operating frequency, input power, and polarization tilt angle. To stabilize the efficiency, this article presents a polarization-independent rectifier, which employs a novel six-port Lange-based coupler with a grounded isolation point, as well as four subrectifiers. By the adoption of the novel six-port Lange-based coupler, the rectifier not only achieves stable efficiency at varied polarization tilt angles, but also widens operating frequency and input power ranges. In this case, when developing a dual-polarized rectenna with such a rectifier, the rectenna can receive incident energy at any polarization tilt angles with stable efficiency. For verification, the mechanism of the proposed rectifier is analyzed and a prototype is implemented. Measured results show that the rectifier operates efficiently at a frequency band from 1 to 2.7 GHz and an input power range beyond 18.5 dB. Furthermore, when the polarization tilt angle varies from 0° to 90°, the rectifier can work stably. [ABSTRACT FROM AUTHOR]

We present a dual-polarized electromagnetic (EM) energy-harvesting system that consists of a periodic absorber surface and a full-wave rectifier. The unit cell of the absorber is constructed using concentric bow-tie dipoles and channeling features that make it possible to efficiently combine and transfer the collected power from multiple unit cells. Simulation results are provided together with experimental verification demonstrating the strong absorption characteristics of the proposed energy harvesting surface. Overall radiation-to-DC conversion efficiency of the fabricated prototype was measured to be more than 60% under two perpendicular polarizations. The performance of the structure was further evaluated under various polarization angles and the results demonstrate that the proposed concept can be used to construct a scalable and polarization insensitive energy-harvesting system. [ABSTRACT FROM AUTHOR]

This article describes a 5.8-GHz band highly efficient 1-W rectenna that consists of a bridge diode, directly connected to a short-stub-connected high-impedance dipole antenna, with a designed antenna resistance of $580~\Omega $. The proposed antenna topology realizes circuit functionalities of impedance transform, impedance matching, harmonic reaction, and dc blocking while maintaining a high antenna radiation efficiency. Lossy circuit components between the antenna radiator and the bridge diode can be eliminated for a highly efficient rectification. In experimental investigations, the measured rectification efficiency of the 5.8-GHz band rectifier is 92.8% at an input power of 1 W, and the estimated antenna radiation efficiency from the measured antenna gain is 96.9%, including loss due to circuit functionalities and interconnection. With lesser additional losses, the proposed antenna can be integrated with circuit functionalities to achieve a highly efficient rectenna. The measured rectification efficiency is almost the same as the fundamental limitation restricted by the rectifier diodes’ performance. [ABSTRACT FROM AUTHOR]

An ultra-wideband (UWB) rectenna (fractional bandwidth >100%) using a novel wideband complementary matching stub is proposed for microwave power transmission and energy harvesting. A simple resonant structure, i.e., LC series–parallel resonant circuit, is embedded to the L-shaped complementary matching stub. Due to the unique frequency response of the LC resonant circuit, the proposed matching stub can exhibit “open” and “short” circuits as a function of frequency, thereby acting as a complementary matching circuit covering a relatively wide frequency range. Having utilized the proposed matching stub, the nonlinear input impedance of the rectifier can be tuned to conjugately match the antenna impedance throughout the frequency band of interest. Simulated and measured results show that the proposed rectenna has good matching performance ($S_{11} < -10$ dB) and high RF-dc conversion efficiency (>50%) over a relatively wide frequency range from 0.9 to 3 GHz (for GSM, Wi-Fi, and WLAN bands). The maximum conversion efficiency of 73.4% is realized at 3-dBm input power. It is evident that the proposed resonant structure-based matching scheme is a promising and effective solution to facilitate the UWB rectenna design with stably high efficiency over a very wide frequency band. [ABSTRACT FROM AUTHOR]

Microwave wireless power transmission (MWPT) via radio waves has been an important research topic of the WPT systems, where the overall power transfer and conversion efficiency is a key factor to evaluate the system performance. The state-of-the-art work on MWPT has only taken the end-to-end power transfer efficiency in free space or the power conversion efficiency of the receiver (rectenna) into consideration separately when optimizing the power transfer efficiency of the overall system. To comprehensively consider the system-level matching of the entire MWPT system, a novel space matching concept, including aperture field matching, power matching, and impedance matching, is proposed for optimizing the overall power transfer efficiency. By using the space matching method in this work, the optimal designs of the subsystem components such as the transmitting antenna, receiving antenna, and rectifying circuit can be separately obtained to avoid the complex systematic optimization of the large-scale and complicated MWPT system, therefore, significantly improving the overall power transfer efficiency by 19.4% compared with the traditional methods, and reducing the complexity in large-scale system-level design. This work will have valuable implications in the system design of MWPT applications. [ABSTRACT FROM AUTHOR]

A dual-band and polarization-angle-independent rectifying metasurface (MS) with a miniaturized dimension and a wide incident angle range are presented in this article. The proposed structure consists of a single layer of periodic cell arrays with integrated diodes, a $dc$ feed, and a load. A novel method of incorporating surface-mount components (e.g., diodes) into the texture is developed to simplify the structure. The matching network between MS and the nonlinear rectifier can be eliminated directly due to the multimode resonance and adjustable high-impedance characteristics of the MS. Moreover, the proposed MS can maintain high conversion efficiency by using different diodes without changing the overall topology. In addition, the proposed design can effectively capture incoming waves with arbitrary polarizations and a wide incident angle range of 60°. The $4\times 4$ MS array is fabricated and measured. Experimental results show that the proposed structure can achieve maximum efficiency of 58% at 2.4 GHz and 50% at 5.8 GHz with an input power of 0 dBm under different polarizations and incident angles. Importantly, it is also shown that the rectifying MS can maintain high efficiency over a wide power range from −3 to 10 dBm. The proposed design concept is very suitable for the adaptive wireless power supply of portable devices. [ABSTRACT FROM AUTHOR]

In this article, a novel duplexing rectenna with harmonic feedback capability is proposed for efficient wireless power transfer (WPT) applications. The proposed duplexing rectenna can harvest the incoming radio frequency (RF) energy efficiently and also make use of an inherent harmonic signal, which is sent back to the RF transmitter (Tx) for positioning in order to guide the radiation patterns from Tx antenna array for optimum WPT. A novel duplexing dipole antenna is designed based on the top loading and capacitive gap effects. It is used to receive RF power at fundamental frequency 0.915 GHz and transmit the second harmonic signals at 1.83 GHz as a feedback. Experimental validation of a complete WPT system with beam-scanning capability has been carried out. It is shown that the fabricated rectifier has realized a maximum RF-dc conversion efficiency of 71% (at 15-dBm input power) and a measured peak second harmonic power of −1 dBm. Thus, the proposed duplexing rectenna can form a closed-loop system by providing its location information for efficient WPT applications. [ABSTRACT FROM AUTHOR]

This article presents a $W$ -band rectenna unit that incorporates a novel CMOS switching rectifier and a print tapered slot antenna. The operation principle of the switching rectifier is analyzed. The proposed rectifier topology shows improved reliability, and it utilizes the body-diode effect (BDE) to improve power conversion efficiency (PCE). Besides, a high-gain $W$ -band antipodal linearly tapered slot antenna is implemented on PCB to improve the overall efficiency. In order to demonstrate the utility of the proposed rectenna unit for large-scale rectenna array, a $1\times 2$ (parallel) and $2\times 2$ (series-parallel) rectenna arrays in 40-nm bulk CMOS technology and PCB process have been implemented. The switching rectifier achieves a peak PCE of 45.8% at 94GHz with improved reliability. Occupying only 0.0756 mm2, the overall PCEs of the rectenna unit and the $2\times 2$ rectenna array are 25% and 23%, delivering 5.6- and 20-mW output dc power, respectively, at 90-mW/cm2 incident power density. The proposed rectifier and rectenna array achieve the highest PCE among recently reported $W$ -band rectifiers and rectenna arrays with different technologies. [ABSTRACT FROM AUTHOR]

Millimeter-wave (mmWave) bands, a key part of future 5G networks, represent a potential channel for RF energy harvesting, where the high-gain antenna arrays offer improved end-to-end efficiency compared with sub-6-GHz networks. This article presents a broadband mmWave rectenna, the first rectenna realized on a flexible textile substrate for wearable applications. The proposed novel antenna’s bandwidth extends from 23 to 40 GHz, with a minimum radiation efficiency of 67% up to 30 GHz, over 3-dB improvement compared with a standard patch. A stable gain of more than 8 dB is achieved based on a textile reflector plane. The antenna is directly connected to a textile-based microstrip voltage doubler rectifier utilizing commercial Schottky diodes. The rectifier is matched to the antenna using a tapered line feed for high-impedance matching, achieving broadband high voltage sensitivity. The rectifier has a peak RF–dc efficiency of 12% and a 9.5-dBm 1-V sensitivity from 23 to 24.25 GHz. The integrated rectenna is demonstrated with more than 1.3-V dc output from 12 dBm of mmWave wireless power across a 28% fractional bandwidth from 20 to 26.5 GHz, a 15% half-power fractional bandwidth, and a peak output of 6.5 V from 20 dBm at 24 GHz. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) has grown rapidly in the past decade to power up devices such as radio frequency identification (RFID) tags, sensors, and medical implants. In recent years, miniaturization has become a new key requirement for some emerging applications such as the Internet of Things (IoT) and biomedical devices. Targeting at a miniaturized receiving (Rx) coil, conventional-inductive WPT (IWPT) has insufficient power transfer gain. The multi-coil transmitting (Tx) array techniques mainly aim at improving the misalignment tolerance, but the power gain (or efficiency) is significantly limited by the mutual coupling among the Tx elements. In this article, we propose a new Tx array structure formed by lines instead of coils. The line-array technique keeps the antimisalignment character of the conventional multi-coil arrays, while the power gain is enhanced in two ways: 1) the lossy adjacent sides are removed in the line array, and 2) the mutual coupling among the array elements is alleviated. To validate the proposed technique, we demonstrate a Ku-band WPT prototype, including a CMOS Rx rectenna and a printed circuit board (PCB) Tx line array. The rectenna is fabricated in a 65-nm CMOS technology, with a coil antenna measuring $100 \mu \text{m} \times 100 \mu \text{m}$. At varying power transfer ranges, the power transfer gain and misalignment tolerance are measured for both the single-coil and line-array systems, respectively. In comparison to the conventional single-Tx-coil IWPT, the overall power gain can be improved by 17.3 dB at a typical power transfer range of 2.5 mm, while a 1-mm misalignment only reduces the gain by 1.3 dB. [ABSTRACT FROM AUTHOR]

The design of a hybrid radio frequency (RF) and solar energy harvesting (EH) system utilizing a transparent multiport antenna for indoor applications is described. The system incorporates an eight-port transparent antenna, operating in the unlicensed 2.4-GHz band, and is constructed from transparent copper micromeshed planar conductor. The antenna is integrated on the top surface of a solar cell with rectifiers positioned underneath to form a hybrid RF-solar indoor EH system. A key advantage of this approach is that the surface area of the solar cell is reused for the antenna saving space. Another novelty is the use of a multiport antenna for increasing the RF harvested energy. It is demonstrated that with a light intensity of 360 lux, the solar cell can obtain 1.68-mW power while the rectenna can achieve an additional 4.8%–45.8% harvested power when the incident RF input power density is varied from 13.30 to 52.96 mW/m2. The transparent antenna achieves 72.4% efficiency and is one of the highest reported results. In addition, the rectifiers obtain 53.2% RF-to-dc conversion efficiency for an RF input power of −10 dBm. These results demonstrate that the proposed RF-solar energy harvester can increase harvested energy and provide energy diversity. [ABSTRACT FROM AUTHOR]

In this paper, a proof-of-concept high-efficiency rectifier-booster regulator (RBR) with an impedance matching converter operating at 2.45 GHz is proposed. An entire WLAN energy harvesting system is demonstrated. A flower-shaped broadband dual-polarized cross dipole antenna with a full-wave matching network is employed to harvest electromagnetic energy from a WiFi router. A novel RBR is proposed to rectify the RF energy to dc and boost the output voltage. It is evolved from a Greinacher rectifier and two Cockcroft–Walton charge pumps to form a full-wave rectifier. An equivalent resistance model is established to evaluate the optimal stage of the RBR. Furthermore, a boost converter is designed as an impedance matching converter to harvest as much energy as possible from the RBR and store the energy into a 1-mF supercapacitor. Experimental results show that the RBR can provide 1.7-V output voltage under −10-dBm input power. In addition, the RBR can achieve up to $\times 3.4$ voltage boosting with 85% voltage conversion rate (VCR) and provide a higher than 1-V output voltage within a distance of 50 cm between an antenna with 20-dBm transmitting power and the rectenna. The excellent performance shows the wide practicality of the proposed design method for the Internet-of-Things (IoT) applications. [ABSTRACT FROM AUTHOR]

In this paper, a novel high-efficiency, low-cost, and low-complexity RF-to-dc converter was designed for RF energy harvesting in the 2.4-GHz band. The proposed design has two RF inputs and maintains high efficiency over a wide range of incoming incident wave angles. The circuit is based on a Wilkinson power combiner and has two single-diode rectifiers. One rectifier is connected at the combiner’s output and collects the energy coming from the two inputs. The second rectifier replaces the isolation resistor of the combiner in order to collect the power that would, otherwise, be dissipated in it. The second rectifier is used for recycling the wasted power when the input signals do not have the same phase. The novel RF-to-dc converter was fabricated using the commercially available components and a low-cost FR-4 substrate. A prototype was designed, and its efficiency was optimized for low-power input levels. The measured system efficiency was 16.2% for in-phase input signals with an available input power of −17 dBm. When the relative phase of input signals varied from 0° to 360°, a variation in efficiency between 15.3% and 22% was observed. For an input power of 3 dBm, the efficiency varies from 26% to 39% between 0° and 360° phase difference. [ABSTRACT FROM AUTHOR]

This paper addresses the design and characterization of compact rectennas for wireless power transmission application in the industrial, scientific, and medical 868-MHz/915-MHz band. These rectennas are designed for supplying power to a dc-to-dc boost converter. The proposed low-profile rectenna exhibits a good tradeoff between compactness ($0.06\lambda ^{2}$ at 900 MHz) and RF-to-dc conversion efficiency, which is higher than 25% for RF power densities of at least $0.25~\mu \text{W}$ /cm2 and 37% for $2.1~\mu \text{W}$ /cm2. It is shown that this rectenna can activate the standard Bq25504 dc-to-dc boost converter for an RF power density higher than $0.6~\mu \text{W}$ /cm2. Moreover, through using a storage capacitor of $220~\mu \text{F}$ , a light emitting diode (LED) can be turned on for a duration of 60 ms with power consumption of 9.45 mW and a dc voltage of 3 V. The LED allows emulating the dc consumption of the QN908x ultra-lower-power Bluetooth 5 module which operates in the transmission mode with −4 dBm of output power. [ABSTRACT FROM AUTHOR]

We present an energy harvesting surface (EHS) designed for electromagnetic energy harvesting and wireless power transfer consisting of an array of cross-dipole metallic elements. The EHS unit cell of the proposed harvester is based on two cross-dipoles that enable capturing the energy from various angles of illuminations at an operating frequency of 3 GHz. The simulation results yielded a radiation to ac efficiency of 94% at multiple angles of polarization. As a proof of concept, a finite array of $7\times 7$ unit cells was fabricated and tested experimentally. The experimental results of the EHS energy harvesting array show an overall radiation to dc harvesting efficiency of 74% at various polarization angles. A critical design feature of the proposed cross-dipole EHS array is that it allows direct matching to a rectifying circuitry at the dipoles plane. The design also enhances the available power per diode, thus, maximizing the rectifying diodes’ turn-on time. [ABSTRACT FROM AUTHOR]

It is difficult to effectively rectify or convert low power in the circuit stage of harvesters. The high-gain antenna can offer a higher level of power and is beneficial to RF power harvesting in a low power density environment. To extend the narrow beam of the conventional high-gain rectenna, the multiport and multibeam antenna is promising. To pursue a simple configuration and avoid extra beamforming networks, a traveling-wave grid-array antenna (GAA) with two isolated ports and two symmetrically tilted beams is proposed. A prototype is designed and fabricated after a detailed analysis of the GAA with tilted beams and the coplanar stripline-based rectifier. The measured results show that the proposed rectenna is sensitive and effective in a wide-angle range. The harvesting angle range is extended by combining two tilted beams and can be greater than 70°, where the level of dc power exceeds $100~\mu \text{W}$ when the power density is as low as $1~\mu \text{W}$ /cm2. A maximum dc output of 3.6– $203.8~\mu \text{W}$ and a maximum RF-to-dc conversion efficiency of 16.3%–45.3% are available at 2.45 GHz, under the condition that the power density ranges from 0.052 to $1~\mu \text{W}$ /cm2. [ABSTRACT FROM AUTHOR]

This paper proposes an extensive study of multisine excitations to enable high-accuracy localization of battery-less tags, by harvesting the higher order harmonics, generated by the rectifier nonlinearity. Usually, these harmonics are either filtered out or terminated, to increase the conversion efficiency. A dual-mode rectifier with the output section splitted into two paths is designed. One dc path is the common one used to deliver the converted dc power to an optimum load and the second path is broadband and collects the higher harmonics obtaining an ultrawideband radiated signal to communicate with the receivers for tag localization. To this purpose, a variety of multisine excitation signals, with different tones, spacing among tones and bandwidth, is accurately evaluated to characterize the system-level localization performance. Both the modeled and experimental results are presented demonstrating the excellent performance of such a dual-mode rectifier, despite of the limited add-on circuitry if compared to those used in standard rectennas. For an average received power of −10 dBm, measurements show that the localization of a tag with centimeter-level accuracy can be achieved at more than 10 m distance from the receivers having a 4 dB noise figure. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

This work presents an analytical approach for optimizing the single-ended (SE) and differential (DF) reader coils and miniature rectenna designs in near-field inductive power transfer (IPT) systems. In this design context, the appropriate operation frequency is in the gigahertz range, and the nonuniform current distribution on the reader coil and the radiation resistance must be considered and are included in this paper. Utilizing the rectenna miniaturization, the reader coil and the rectenna designs can be decoupled and their figure of merits (FOMs) are identified. The equation-based approach optimizes the IPT design rapidly, and the optimized reader-coil FOM and the optimized rectenna FOM, both plotted versus the IPT frequency, co-decide the optimal IPT frequency and the coil geometries for the highest RF-dc power transfer efficiency. The analytical method is verified by EM-simulation and measurement, and the DF reader coil topology is demonstrated to be more efficient than the commonly used SE coils. An optimized 2.2-mm IPT with a DF coil is realized at 4.8 GHz and significantly outperforms the previous works. Under a total RF power of 33.1 dBm, the CMOS rectenna, with a coil size of only 0.01 mm2, harvests the designed dc conditions of 1 V/0.1 mA. [ABSTRACT FROM PUBLISHER]

We present a design of an electromagnetic energy harvesting surface inspired by an array of printed metallic dipolar elements. The unit cell of the proposed harvester is based on two printed asymmetric off-center fed dipoles. As a proof of concept, a finite array of $9 \times 3$ unit cells was analyzed numerically and experimentally. The array was first analyzed for maximizing radiation to ac absorption where each dipole was terminated by a resistor across its gap. For dc conversion, the resistors were the replaced by Schottky diodes. The simulation results show radiation to ac harvesting efficiency of 99%. An overall radiation to dc harvesting efficiency of 76% was obtained experimentally, which, to the best of the authors’ knowledge, exceeds the performance of all previous energy harvesting surfaces. Another critical feature of the proposed designs is enhancing the power per diode in order to maximize its turn-ON time. [ABSTRACT FROM PUBLISHER]

A novel rectifying circuit topology is proposed for converting electromagnetic pulse waves (PWs), that are collected by a wideband antenna, into dc voltage. The typical incident signal considered in this paper consists of 10-ns pulses modulated around 2.4 GHz with a repetition period of 100 ns. The proposed rectifying circuit topology comprises a double-current architecture with inductances that collect the energy during the pulse delivery as well as an output capacitance that maintains the dc output voltage between the pulses. Experimental results show that the efficiency of the rectifier reaches 64% for a mean available incident power of 4 dBm. Similar performances are achieved when a wideband antenna is combined with the rectifier in order to realize a rectenna. By increasing the repetition period of the incident PWs to 400 ns, the rectifier still operates with an efficiency of 52% for a mean available incident pulse power of −8 dBm. Finally, the proposed PW rectenna is tested for a wireless energy transmission application in a low- $Q$ cavity. The time reversal technique is applied to focus PWs around the desired rectenna. Results show that the rectenna is still efficient when noisy PW is handled. [ABSTRACT FROM PUBLISHER]

This paper presents a flexible 2.45-GHz wireless power harvesting wristband that generates a net dc output from a −24.3-dBm RF input. This is the lowest reported system sensitivity for systems comprising a rectenna and impedance-matching power management. A complete system has been implemented comprising: a fabric antenna, a rectifier on rigid substrate, a contactless electrical connection between rigid and flexible subsystems, and power electronics impedance matching. Various fabric and flexible materials are electrically characterized at 2.45 GHz using the two-line and the T-resonator methods. Selected materials are used to design an all-textile antenna, which demonstrates a radiation efficiency above 62% on a phantom irrespective of location, and a stable radiation pattern. The rectifier, designed on a rigid substrate, shows a best-in-class efficiency of 33.6% at −20 dBm. A reliable, efficient, and wideband contactless connection between the fabric antenna and the rectifier is created using broadside-coupled microstrip lines, with an insertion loss below 1 dB from 1.8 to over 10 GHz. A self-powered boost converter with a quiescent current of 150 nA matches the rectenna output with a matching efficiency above 95%. The maximum end-to-end efficiency is 28.7% at −7 dBm. The wristband harvester demonstrates net positive energy harvesting from −24.3 dBm, a 7.3-dB improvement on the state of the art. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel compact ultralightweight 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. [ABSTRACT FROM PUBLISHER]

This paper discusses a new design approach that uses hybrid power combining rectenna array in radio frequency (RF) energy transfer systems to receive more energy in a wide incident angle range. A beam-forming matrix and a dc power management network (PMN) are introduced to the hybrid power combining. The normalized dc output power of the proposed hybrid power combining array is compared to the conventional power combining methods with regard to the incident wave angle, and the average received dc power is also calculated and compared. To experimentally verify the proposed hybrid combining array performance, four suspended patch antennas are attached to RF energy receiving architecture. A $4 \times 4$ Butler matrix and quadrature hybrids are used for the beam-forming matrix in a hybrid power combining rectenna array. A reconfigurable voltage doubler rectifier with a dc PMN is used to convert RF energy to dc energy and delivers proper voltage to the load. The measured results of each component are presented. Moreover, an experimental verification using fabricated components for RF energy transfer is presented and the measured received dc output power of conventional and proposed structures is presented and compared. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to realizing full-wave rectification for electromagnetic energy harvesting. Instead of using one antenna to feed one rectifier circuit, we propose utilizing two antennas connected to one rectifier to form a full-wave rectenna. This balanced configuration allows the received power to be rectified and transferred to a dc load between two antennas, making it very easy to channel the harvested power in rectenna arrays. The proposed concept is demonstrated in the microwave regime using an array of full-wave rectennas optimized for 2.45 GHz. The full-wave rectenna array is compared with an array of half-wave rectennas that occupy the same footprint and are optimized to maximize power absorption at the same frequency. Measurements showed that the proposed full-wave rectifier performed better than the half-wave rectifier and achieved 74% radiation-to-dc conversion efficiency. Here, without loss of generality, the proposed concept is demonstrated using T-matched dipole antennas at a specific frequency, but the concept can be applied to other antenna types and other frequencies. [ABSTRACT FROM AUTHOR]

This paper discusses the design of a novel dual (solar + electromagnetic) energy harvesting powered communication system, which operates at 2.4 GHz ISM band, enabling the autonomous operation of a low power consumption power management circuit for a wireless sensor, while featuring a very good “cold start” capability. The proposed harvester consists of a dual port rectangular slot antenna, a 3-D printed package, a solar cell, an RF-dc converter, a power management unit (PMU), a microcontroller unit, and an RF transceiver. Each designed component was characterized through simulation and measurements. As a result, the antenna exhibited a performance satisfying the design goals in the frequency range of 2.4–2.5 GHz. Similarly, the designed miniaturized RF-dc conversion circuit generated a sufficient voltage and power to support the autonomous operation of the bq25504 PMU for RF input power levels as low as −12.6 and −15.6 dBm at the “cold start” and “hot start” condition, respectively. The experimental testing of the PMU utilizing the proposed hybrid energy harvester confirmed the reduction of the capacitor charging time by 40% and the reduction of the minimum required RF input power level by 50% compared with the one required for the individual RF and solar harvester under the room light irradiation condition of 334 lx. [ABSTRACT FROM AUTHOR]

To reduce the weight of a satellite, an internal wireless system (IWS) for satellites was proposed in a previous study. It is a system that can communicate between the satellite’s subsystems by using wireless communication modules. In this paper, we propose a complete IWS for a satellite using microwave wireless power transmission technology. The design of a 5.8-GHz high efficiency rectifier circuit-based charge pump circuit is also presented. Furthermore, we introduced a class-F load that can process the third harmonic components. The rectifying efficiencies of a normal charge pump rectifier and a charge pump rectifier with the class-F load are theoretically compared. To improve the conversion efficiency of the charge pump rectifier, the applied voltages of diodes are adjusted. Owing to inserting the class-F load and adjusted the applied voltage of diodes in this circuit, the conversion efficiency of the charge pump circuit at 30 mW increases to about 78% at 30 mW in the simulation, and to about 71% conversion efficiency in the experiment. In addition, the output voltage is higher than 5 V at an optimal load 1300 $\Omega $ . [ABSTRACT FROM PUBLISHER]

This paper describes the voltage doubler (VD) behavior of a 2.45-GHz VD-type rectenna. An important feature of the developed VD-type rectenna is the absence of the charge pump capacitor that is present in conventional VDs. Based on the circuit simulation and measurement results, the developed VD-type rectenna shows drastic improvement to the radio frequency-to-direct current (RF–dc) conversion efficiency in comparison with a half-wave rectifier (HWR)-type rectenna at output loads exceeding $100~\Omega $ . From the simulation, both the VD- and HWR-type rectennas show VD behavior, even without the charge pump capacitor. This behavior was found to be attributable to the electric charge stored in the junction and package capacitances of the Schottky barrier diode in the rectennas. Additionally, it was found that the improvement of the RF–dc conversion efficiency is caused by the voltage conservation in the series diode. This improvement is dependent on the microwave period and the electric discharge time constant. When the microwave period is comparable with the electric discharge time constant, the VD-type rectenna conserves a dc voltage even when the input microwave voltage is negative. These phenomena were observed by analyzing the voltage and current waveforms of the rectenna equivalent circuit obtained via circuit simulation. [ABSTRACT FROM AUTHOR]

This paper presents a differential rectifier with high radio frequency (RF)-dc conversion efficiency over an extended input power range by using resistance compression network (RCN). The RCN is cascaded with a typical differential rectifier. It can reduce the variation range of rectifier input impedance, which changes with input power levels, and better impedance matching can be realized. Thus, the loss due to impedance mismatch is reduced, and high efficiency can be obtained in a wider input power range. First, the theoretical analysis of the RCN is carried out. Then, the detailed analysis of the rectifier input impedance and efficiency is derived in closed form. Based on the analytical results, a 915-MHz rectifier incorporating RCN is implemented. The measured results show that the RF-dc conversion efficiency keeps above 50% and 70% in the input power range 5.5–33.1 and 13.5–31.3 dBm, respectively. The maximum efficiency is 84.8%. Compared with the counterpart without RCN, the efficiency at lower input power levels is improved without degrading the peak efficiency. [ABSTRACT FROM AUTHOR]

The first reported full-system 60-GHz wireless power transfer (WPT) solution that can power batteryless and charge coil-free compact WPT devices is presented. The system is fabricated in a 40-nm digital CMOS process and an inexpensive packaging material. In the rectenna (RX), a grid antenna is integrated with a complementary cross-coupled oscillator-like rectifier. At a 4-cm spacing from the transmitter (TX), the RX harvests energy at a rate of 1.22 mW with a 32.8% efficiency, which is significantly higher than the prior state of the art. A novel theoretical analysis of the rectifier operation is presented that formulates all key specifications. The TX is equipped with a quad-core PA that produces a saturated output power ( P\mathrm{ sat} ) of 24.6 dBm, which is the highest power delivery in digital CMOS at millimeter-wave bands. The TX peak power-added efficiency is 9.4%. In the TX, a $4 \,\, \times \,\, 8$ -way differential power combining and a binary-tree architecture are implemented. The designed $2 \times 2$ grid array antenna helps the TX produce 35.3-dBm peak equivalent isotropically radiated power. The results of the performance characterizations of the full-system and all individually fabricated blocks are reported. The quad-core PA supports power control and beam steering. A four-port TX antenna is designed that shows a 70° steering range in simulations. [ABSTRACT FROM AUTHOR]

A time reversal (TR) method is investigated for wireless power transmission in an indoor environment. Experiments performed with nanosecond pulses modulated at the frequency of 2.45 GHz reveal that the temporal and spatial focusing makes this technique valuable for applications of wireless power transmission. It is shown that the TR scheme avoids the fading phenomena that usually appear in an indoor environment when the power transmission is realized with a continuous wave: the voltage gain (respectively, the energy gain) can reach 30 dB (respectively, 20 dB) for the proposed scenarios. Moreover, it is theoretically proved that the TR technique is the optimal solution for an energy transmission, whatever the density of the multipath environment. In addition, simulations show that the voltage gain (respectively, the energy gain) of the TR technique is 3 dB (respectively, 9 dB) compared with the inverse filtering technique for a representative scenario. Other potential benefits of the method are discussed, notably concerning the power management of rectennas. [ABSTRACT FROM PUBLISHER]

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 \mu \W/cm^2. 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. [ABSTRACT FROM PUBLISHER]

The aim of this paper is to show the possibility to harvest RF energy to supply wireless sensor networks in an outdoor environment. In those conditions, the number of existing RF bands is unpredictable. The RF circuit has to harvest all the potential RF energy present and cannot be designed for a single RF tone. In this paper, the designed RF harvester adds powers coming from an unlimited number of sub-frequency bands. The harvester’s output voltage ratios increase with the number of RF bands. As an application example, a 4-RF band rectenna is designed. The system harvests energy from GSM900 (Global System for Mobile Communications), GSM1800, UMTS (Universal Mobile Telecommunications System) and WiFi bands simultaneously. RF-to-dc conversion efficiency is measured at 62% for a cumulative -\10-dBm input power homogeneously widespread over the four RF bands and reaches 84% at 5.8 dBm. The relative error between the measured dc output power with all four RF bands on and the ideal sum of each of the four RF bands power contribution is less than 3%. It is shown that the RF-to-dc conversion efficiency is more than doubled compared to that measured with a single RF source, thanks to the proposed rectifier architecture. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a new load-modulated two-branch rectifier, designed to dynamically cooperate with an ultra-low power management unit (PMU), interposed between the rectenna and application circuits. The design targets batteryless RF energy harvesting applications with typical input power ranging from \sim10 to \sim \ 100\ \mu\W. Energy is stored in a low leakage capacitor. In order to allow activation in discharged states, the PMU implements a low-voltage start-up stage, whose current consumption is specifically optimized for biasing the rectifier accordingly. When a sufficient voltage is reached, the PMU activates a more efficient boost converter stage with maximum power point tracking capabilities and micro-power consumption. Such two circuits are designed to provide two very different loading conditions to the rectifier. A joint design of the nonlinear rectifier paths and of the two PMU subsystems based on two specific optimizations of the matching networks is proposed, along with a circuit solution for automatically switching between the start-up stage and the boost converter. In order to validate the concept, a microstrip prototype operating at 900 MHz with a discrete components PMU is characterized, although the proposed idea is fully technology independent. With respect to a conventional rectifier, the proposed design allows the system to operate with significantly lower input power, while preserving efficiency during steady-state power conversion. [ABSTRACT FROM AUTHOR]

This paper addresses the microwave energy harvesting on board of geostationary satellites for health satellite monitoring. To prove the feasibility of such a concept, we investigated the electromagnetic environment existing on antenna panels. Based on established cartographic maps, three designs of rectennas are proposed. Measured dc powers ranging from 0.256 to 1.28 mW can be harvested for electric field levels ranging from 91 to 121 V/m and by using very simple and compact designs. The harvesting structures consist of only one Schottky diode per rectenna and present a total surface of 2.4 cm^2. They are suitable for powering the new generation of ultra-low power transceivers, thus enabling autonomous wireless power networks for satellite health monitoring. [ABSTRACT FROM AUTHOR]

Wireless power transmission (WPT) is an emerging technology that is gaining increased visibility in recent years. Efficient WPT circuits, systems and strategies can address a large group of applications spanning from batteryless systems, battery-free sensors, passive RF identification, near-field communications, and many others. WPT is a fundamental enabling technology of the Internet of Things concept, as well as machine-to-machine communications, since it minimizes the use of batteries and eliminates wired power connections. WPT technology brings together RF and dc circuit and system designers with different backgrounds on circuit design, novel materials and applications, and regulatory issues, forming a cross disciplinary team in order to achieve an efficient transmission of power over the air interface. This paper aims to present WPT technology in an integrated way, addressing state-of-the-art and challenges, and to discuss future R&D perspectives summarizing recent activities in Europe. [ABSTRACT FROM AUTHOR]

This paper discusses harvesting of low-power density incident plane waves for electronic devices in environments where it is difficult or impossible to change batteries and where the exact locations of the energy sources are not known. As the incident power densities vary over time and space, distributed arrays of antennas with optimized power-management circuits are introduced to increase harvested power and efficiency. Scaling in array size, power, dc load, frequency, and gain is discussed through three example arrays: a dual industrial–scientific–medical band Yagi-Uda array with a low-power startup circuit; a narrowband 1.96-GHz dual-polarized patch rectenna array with a reconfigurable dc output network designed for harvesting base-station power; and a broadband dual-polarized 2–18-GHz array with multi-tone performance. The efficiency of rectification and power management is investigated for incident power densities in the \1–100-\mu \W/cm^2 range. [ABSTRACT FROM AUTHOR]

This paper discusses a shielded over-moded conductive cavity for wirelessly powering multiple electronic devices simultaneously. The demonstrated cavity is designed for 10-GHz powering with a subwatt transmitter. A study of methods to increase power density uniformity within the cavity is presented, including mechanical stirring, conductive and absorptive object loading, and frequency modulation. It is found that very small frequency modulation of less than 0.1% is sufficient to provide a practical level of power uniformity. A device-under-charge (DUT) consisting of a rectenna, microcontroller, power management circuit, solid-state battery, and ISM-band wireless transceiver is used to validate the study by monitoring the battery charging at various locations within the cavity. The demonstrated shielded three-dimensional charging method is scalable in frequency, volume, power, and number of devices that can be charged. [ABSTRACT FROM AUTHOR]

Wireless power transmission (WPT) is actively being researched and developed. WPT transfers power to electrical load without a wire. One of the problems is that the efficiency is easily affected by load resistance and input power. Therefore, an impedance matching circuit becomes crucial for realization of high-efficiency wireless power systems. In this study, we proposed a maximum power point tracking (MPPT) method for a low-power milliwatt-level RF-dc rectifying circuit using a dc–dc converter. We proposed an RF-dc–dc circuit that consists of an RF-dc rectifier circuit and a dc–dc converter. We measured the RF-to-dc conversion efficiency of the RF-dc–dc circuit using 2.45-GHz microwave power. When the buck–boost converter is connected to the rectifying circuit, the RF-to-dc efficiency of rectifier is approximately steady at 75%, despite the load resistance changing from 100 to 5000 \Omega. The overall efficiency of the RF-dc–dc circuit is still over 60%, even though the load resistance varied from 100 to 5000 \Omega and the input power changed from 40 to 100 mW. [ABSTRACT FROM AUTHOR]

Infrared (IR) detectors have been fabricated consisting of antenna-coupled metal–oxide–metal diodes (ACMOMDs). These detectors were defined using electron beam lithography with shadow evaporation metal deposition. They are designed to be sensitive to the IR range and work at room temperature without cooling or biasing. In order to achieve large arrays of ACMOMDs, nanotransfer printing have been used to cover a large area with metal–oxide–metal (MOM) diodes and with antenna structures. The printed antenna structures consist of gold and aluminum and exhibit a low electrical resistivity. A large area array of MOM tunneling diodes with an ultrathin dielectric (\sim3.6-nm aluminum oxide) has also been fabricated via the transfer-printing process. The MOM diodes exhibit excellent tunneling characteristics. Both direct and Fowler–Nordheim tunneling has been observed over eight orders of magnitude in current density. Static device parameters have been extracted via kinetic Monte Carlo simulations and have confirmed the existence of a dipole layer at the aluminum/aluminum oxide interface of the printed tunneling diodes. The mechanical yield of the transfer-printing process for the MOM tunneling diodes is almost a 100%, confirming that transfer printing is suitable for large area effective fabrication of these quantum devices. [ABSTRACT FROM AUTHOR]

This paper proposes a high-efficiency dual-band on-chip rectifying antenna (rectenna) at 35 and 94 GHz for wireless power transmission. The rectenna is designed in slotline (SL) and finite-width ground coplanar waveguide (FGCPW) transmission lines in a CMOS 0.13-\mu\ m process. The rectenna comprises a high gain linear tapered slot antenna (LTSA), an FGCPW to SL transition, a bandpass filter, and a full-wave rectifier. The LTSA achieves a VSWR=2 fractional bandwidth of 82% and 41%, and a gain of 7.4 and 6.5 dBi at the frequencies of 35 and 94 GHz. The measured power conversion efficiencies are 53% and 37% in free space at 35 and 94 GHz, while the incident radiation power density is 30 \mW/cm^2. The fabricated rectenna occupies a compact size of 2.9 \ mm^2. [ABSTRACT FROM AUTHOR]