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A new compact patch rectenna is presented in this letter. It consists of a rectangular patch antenna, a Schottky diode, and a harmonic filter with impedance matching to improve the rectifying efficiency. The filter is realized by a series short-ended one-eighth-wavelength microstrip transmission line, which also balances the capacitive impedance of the diode. The impedances of the diode and patch antenna are matched well by tuning the patch antenna and short-ended transmission line. A meander line is used to build a dc output path. For validation, a rectenna working at 2.45 GHz is designed, manufactured, and measured. A maximum rectifying efficiency of 82.2% is realized when the dc load is 400 Ω at an input power of 22.5 dBm. The proposed patch rectenna has potential applications such as rectenna arrays in wireless power transmission. [ABSTRACT FROM AUTHOR]

In this article, a seven-band omnidirectional rectenna is proposed for the first time to harvest RF energy. The designed rectenna operates in the following practical and up-to-date frequency bands: GSM1800 (1.8 GHz), LTE (2.1 GHz), WLAN/Wi-Fi (2.4 and 5.8 GHz), and 5G bands (2.6, 3.5, and 4.9 GHz). To obtain the multiband rectenna, a novel seven-band rectifier is introduced and composed of three optimized single shunt diode rectifiers in parallel. Overall RF-to- dc conversion efficiencies as high as 44.4% @ 1.84 GHz, 43.9% @ 2.04 GHz, 45.4% @ 2.36 GHz, 43.4% @ 2.54 GHz, 36.1% @ 3.3 GHz, 32.4% @ 4.76 GHz, and 28.3% @ 5.8 GHz are achieved at an input power level of −10 dBm. Moreover, a broadband omnidirectional monopole antenna is further codesigned with elaborate impedance matching to the rectifier. The antenna can harvest RF energy in the bandwidth of 1.67–5.92 GHz ($\text{S}_{\mathbf {11}}$ no more than −10 dB) with stable omnidirectional radiation patterns. By integrating the rectifier and the monopole antenna in a low profile, a prototype of the rectenna was manufactured and tested. The experimental results demonstrate that the proposed rectenna has competitive performance in terms of RF-to- dc conversion efficiency and band coverage, indicating enormous potential for numerous battery-free or low-power-needed applications in the real world. [ABSTRACT FROM AUTHOR]

This work describes a novel fully integrated rectenna circuit using tunnelling-based devices for implanted medical devices. An ASPAT (Asymmetric Spacer Layer Tunnel Diode) was used as the active rectifier due to its high non-linearity and temperature insensitivity features. A miniaturized geometry rectenna ($1 \times 5$ mm2) with improved matching characteristics was demonstrated, by integrating a Cockcroft-Walton rectifier with an L-shaped planar folded antenna structure operating at ISM frequency bands. The circuit performance was experimentally explored at various separation distance between transmitter and receiver units. For a 5cm transmission set-up, the rectenna with a single-stage rectifier delivered 0.8V output at 20dBm transmit power. An extended doubler configuration exhibited enhanced performance when multiple stages are used, is predicted to reach 0.24mW output power at 23dBm transmit power and yielding ~1.6V output voltage with an efficiency of 0.12%. These findings can assist in compensating for the degraded antenna gain attributed to the extremely small effective-radiating area of $0.04\lambda $. Furthermore, the ability of controlling the antenna input impedance helps in circumventing the requirement for a matching circuitry thereby offering further reduction in chip size. [ABSTRACT FROM AUTHOR]

Rectifier is a fundamental element of a rectenna system that converts RF energy to direct current (dc). We proposed a triple-band rectifier using a novel matching technique and single series diode topology. First, we designed a single band rectifier and then converted it into a dual- and triple-band rectifier by introducing an appropriate transmission line and shorted stub, respectively, to convert simultaneously multiple RF signals into dc. The proposed rectifier operates at the popular frequency bands of 1.95, 2.7, and 5.8 GHz with power conversion efficiency (PCE) of 65.5%, 62%, and 57.1%, respectively, using a single impedance matching circuit. [ABSTRACT FROM AUTHOR]

The efficiency of a rectenna varies under the influences of receiving polarization tilt angle, operating frequency, input power, and load value in different applications. Yet, no reported rectenna can realize stable efficiency when all these factors vary within a wide range. To solve this problem, an all-polarized rectenna is proposed in this article, composed of a dual-input rectifier and a dual-polarized (DP) antenna. By introducing a novel six-port coupler, the rectifier maintains stable efficiency at wideband, wide input power, and dc load ranges. Moreover, the efficiency of the rectifier keeps stable when the antenna receives power at different polarization tilt angles. Accordingly, a DP antenna with extended bandwidth and 3-dB beamwidth is implemented. Finally, the rectenna is formed. The prototype can maintain beyond 70% of the peak efficiency from 1.7 to 2.5 GHz. At a power density as low as 1 μW/cm2, efficiency can reach 24.4%. Furtherly, the rectenna is demonstrated by forming a battery-less digital clock. The clock can be powered wirelessly by a WiFi router or cellular base station with maximum distances of 1 or 70 m respectively. Besides, the clock can successfully function under significant transmitting-direction deviation or polarization misalignment between the power source and the rectenna. [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]

In this letter, a compact dual-band rectenna is modeled and developed for low radio frequency (RF) power harvesting. The proposed theoretical model can provide a comprehensive analysis of the rectenna, including the power conversion efficiency (PCE) of the diode, matching efficiency of the rectifier, and total PCE of the rectenna. In the rectenna design, a very compact omnidirectional dielectric resonator antenna (DRA) is proposed with a broad bandwidth exceeding 40%. Meanwhile, a dual-band rectifier is designed based on a single branch in the low-power range with bandwidths covering the two fifth-generation (5G) frequency bands in China (2.515–2.675 and 3.4–3.6 GHz). It was found that the theoretical model can show a high accuracy with the calculation error within 5% in analyzing the dual-band rectifier. The DRA and the dual-band rectifier are integrated to form a compact dual-band rectenna. It shows a higher PCE than those of the existing multiband designs working at similar low-power levels. It is hoped to be implemented in 5G-enabled Internet of Things (IoT) applications for powering wireless sensor nodes. [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]

This article presents a textile antenna for dual-band simultaneous wireless information and power transfer (SWIPT). The antenna operates as a 2.4 GHz off-body communications antenna and a sub-1 GHz (785–875 MHz) broad-beam rectenna. Incorporated within the broadside microstrip antenna is a high-impedance rectenna for sub-1 GHz power harvesting. Utilizing antenna-rectifier co-design, the rectenna eliminates the rectifier matching network. The textile antenna is fabricated on a felt substrate and utilizes conductive fabrics for the antenna. At 2.4 GHz, the antenna achieves a realized gain of 7.2 dBi on a body phantom and a minimum radiation efficiency of 63%, with and without the rectifier. The rectenna achieves a best-in-class RF to dc efficiency of 62% from 0.8 $\mu \text{W}$ /cm2, representing over 25% improvement over state-of-the-art textile rectennas and demonstrating that SWIPT does not detrimentally affect the energy harvesting or communications performance. The antenna/rectenna occupies an electrically small area of $0.213\times 0.19\,\,\lambda ^{2}_{0}$. This antenna is the first dual-band, dual-mode antenna demonstrated on textiles for SWIPT applications and the first dual-band matching network-free SWIPT rectenna. [ABSTRACT FROM AUTHOR]

A novel aperture-coupled patch rectenna backed by a substrate integrated waveguide (SIW) cavity operated at 35 GHz for millimeter-wave power transmission (MMPT) with high conversion efficiency is presented in this article. A four-element SIW patch array with a harmonic suppression function based on the barbell-type defect ground structure (DGS) is proposed as the receiving antenna; thus, the low-pass filter in the rectifying circuit can be omitted. The Schottky diode is parallel-mounted in the rectifying circuit, which has a measured rectifying efficiency of 61.2% with a $500~\Omega $ load when the received power is 100 mW. The maximum conversion efficiency of the rectenna element is 60.9% when the received power is 79.4 mW. Additionally, 4–8-and 16-element rectenna arrays are also investigated to obtain high direct current power. When the power density is 9.2 mW/cm2, the conversion efficiencies of the rectenna element, $2\times2$ array, $2\times4$ array and $2\times8$ array are 50.5%, 44.1%, 41.9%, 38.9%, respectively. The measured conversion efficiency of the $2\times8$ rectenna array at 35 GHz is 49.2% when the input power is 1259 mW. The low profile and easy integration of the studied rectenna will make it easy to expand its use to large-scale arrays for high-power MMPT applications. [ABSTRACT FROM AUTHOR]

A novel highly efficient radio-frequency (RF) energy harvester (rectenna) array with multifrequency coverages (1.7–1.8 GHz and 2.1–2.7 GHz) as well as an omnidirectional 3-D radiation pattern is presented. The harvester array is very compact and of low-profile, which strategically combines 12 single Vivaldi slot rectenna elements. More importantly, the proposed rectenna array is significantly simplified through a codesigned effective impedance tuning and array combination method to reduce the overall circuit complexity whilst maintaining high energy conversion efficiency (up to 67%) over the desired frequency band under different input powers (−25–5 dBm) and circuit loads (0.2–8 kΩ). Having utilized the proposed wireless energy harvester array, a complete system-level demonstration of ambient RF energy-powered, a self-sustainable IoT sensor node is demonstrated for reliably operating in a typical indoor environment. Such a demonstration has never been reported before. In addition, the proposed rectenna array has novel features in terms of simplified Vivaldi rectenna matching, compact array combination and optimal beam shaping, which has proven to be an effective energy harvester in most domestic environments; therefore, having significant implications in powering small electronics for real-world Internet-of-Things (IoT) and industrial Internet-of-Things (IIoT) applications. [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]

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]

An electrically small, single-substrate Huygens dipole rectenna with exceptional physical and radiation performance characteristics is reported. A highly efficient rectifier circuit is seamlessly integrated with an ultrathin, electrically small, Huygens dipole antenna (HDA) on a single piece of Rogers 5880 substrate. It consists of two metamaterial-inspired near-field resonant parasitic (NFRP) elements, an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL) that are etched on the top and bottom metallization layers of the substrate, respectively. A printed receiving dipole is amalgamated tightly with the rectifier on the CLL layer. This ultracompact rectenna system has a large electromagnetic wave capture capability and achieves nearly complete conversion of the incident energy into dc power. The HDA prototype has a realized gain of 4.6 dBi and a half power beamwidth (HPBW) greater than 130°. The entire rectenna is electrically small with ka =0.98, is low cost and easy to fabricate, and has a measured 88% ac-to-dc conversion efficiency. The developed rectenna system is the ideal candidate for ultracompact far-field wireless power transfer (WPT) applications. [ABSTRACT FROM AUTHOR]

In this paper, we study simultaneous wireless information and power transfer (SWIPT) systems employing practical non-linear energy harvester (EH) circuits. Since the voltage across the reactive elements of realistic EH circuits cannot drop or rise instantaneously, EHs have memory which we model with a Markov decision process (MDP). Moreover, since an analytical model that accurately models all non-linear effects and the unavoidable impedance mismatch of EHs is not tractable, we propose a learning based model for the EH circuit. We optimize the input signal distribution for maximization of the harvested power under a constraint on the minimum mutual information between transmitter (TX) and information receiver (IR). We distinguish the cases where the MDP state is known and not known at TX and IR. When the MDP state is known, the formulated optimization problem for the harvested power is convex. In contrast, if TX and IR do not know the MDP state, the resulting optimization problem is non-convex and solved via alternating optimization, which is shown to yield a limit point of the problem. Our simulation results reveal that the rate-power region of the considered SWIPT system depends on the symbol duration, the EH input power level, the EH impedance mismatch, and the type of EH circuit. In particular, a shorter symbol duration enables higher bit rates at the expense of a significant decrease in the average harvested power. Furthermore, whereas half-wave rectifiers outperform full-wave rectifiers in the low and medium input power regimes, full-wave rectifiers are preferable if the input power at the EH is high. [ABSTRACT FROM AUTHOR]

This article presents a new compact lightweight radio frequency (RF) energy harvesting system. The system relies on a dual-tapered transmission line-based matching network that stretches the rectification capability of an integrated Schottky diode. This topology is demonstrated on a 2.4 GHz rigid harvesting system with a resulting power conversion efficiency that reaches up to 58% over 0 dBm input RF power. Its performance is compared with a reference rectifier that relies on a typical open circuit shunt-stub matching network. The rectifier along with a miniaturized monopole antenna is then tailored for a flexible substrate with a resulting efficiency around 50% at 0 dBm input power. The rectifier exhibits an almost flat efficiency over the 2.3–2.5 GHz frequency span despite wide load variations. The system is characterized in multiple bent configurations featuring high and stable performance. It is demonstrated that for different bent states, the proposed flexible harvester does not display large variations in harvested power. Thus, the presented rectenna demonstrates the remarkable combination of compactness, flexibility, and stability. Equipped with these features, such rectifier can be plugged into a variety of sensors, even on wearable surfaces, which makes it ideal for Internet of Things (IoT) applications. [ABSTRACT FROM AUTHOR]

An electrically small Huygens circularly polarized (HCP) rectenna whose antenna is directly matched to its rectifying circuit is developed and experimentally validated in the ISM band at 915 MHz. The HCP antenna is a near-field resonant parasitic (NFRP) design consisting of a driven element and a crossed pair of balanced electric and magnetic NFRP dipole elements. The rectifier circuit is highly capacitive. It is a full-wave design based on two HSMS286C Schottky diodes. Two innovative driven element designs are explored that facilitate the effective conjoin of the antenna to different classes of external circuits. An HCP antenna with a driven spiral line element is demonstrated. Its input impedance is capacitive and, hence, the system is ideal for matching directly to an inductive external circuit. An HCP antenna with a driven loop element is investigated in a similar manner. The system has an inductive input impedance that is subsequently optimized to be conjugately match to the capacitive rectifier directly. The measured HCP rectenna prototype has broad-angle capture capacity, avoids any polarization mismatch issues, and has exceptional ac to dc conversion efficiency, the maximum reaching 90.6%. It is an ideal candidate for wireless power transfer (WPT)-enabled Internet-of-Things (IoT) applications. [ABSTRACT FROM AUTHOR]

A pattern reconfigurable rectenna, consisting of a pattern reconfigurable receiving antenna and a low-/medium-power rectifying circuit, is proposed for microwave power transmission with multiple transmitting antennas. By controlling the states of p-i-n switch groups, the receiving antenna can work at one omni-directional mode and eight directional modes with flattened wide main beams for the arbitrary direction of incoming waves. In order to achieve good impedance matching at different modes, where the received power fluctuates severely, a complex impedance compression network (CICN) is introduced to the rectifying circuit. Since the proposed rectenna has a versatile structure, it can be used for multiple transmitting antennas in conformity with the incoming waves’ direction. [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]

An impedance matching network inserted between an antenna and a rectifier is essential for rectennas, but few studies have characterized the insertion loss of the matching network if nonideal matching elements are considered. In general, the matching elements, including lumped capacitors, lumped inductors, and transmission lines, are approximated as lossless; if the overall conversion efficiency decreases, the underlying reason seldom attributes to the loss of the matching network. In this paper, we derive the insertion loss of the matching network comprising actual lumped elements and transmission lines. The loss is quantified using the operating power gain of a two-port network, which varies with different levels of input power. When the input power ranges between −30 and 0 dBm, more than 95%, 90%, and 75% of power dissipates at 900 MHz, 1.8 GHz, and 2.4 GHz, respectively, due to the use of actual matching elements. The numerical results are verified by experimental data, and all the analyses demonstrate that the loss of the matching network becomes very serious as the input power is low. These observations are explained using the contour plot of operating power gain. Accordingly, this study provides a theoretical development for rectenna designers. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) and wireless energy harvesting (WEH) using rectennas are becoming an emerging technology. This paper presents a novel design method for a rectenna suitable for a wide range of selectable operating frequency band, input power level, and load impedance. Most importantly, it is realized without using complex impedance matching networks which shows significant advantages over existing rectennas in terms of the structure and cost. A rectenna example has been designed, made, and tested using this novel method. The proposed rectenna has a compact size of $90 \times 90 \times 1.58$ mm3 and operates at four different frequency bands that are selectable from 1.1 to 2.7 GHz. Over 60% (up to 85%) energy conversion efficiency is achieved for the input power from 0 to 15 dBm and load impedance between 700 and $4500~\Omega $. The rectenna shows excellent performance for the target applications (WPT and WEH) with a much-simplified structure and reduced cost. [ABSTRACT FROM AUTHOR]

The output power level and the power conversion efficiency (PCE) rate of the energy-harvesting systems are vital factors in realizing effective millimeter-wave wireless power transfer solutions that can power battery-less and charge coil-free smart everyday objects. Two 60-GHz energy harvesters that use a tuned complementary cross-coupled oscillator-like rectifying circuitry in 40-nm digital CMOS process are presented. They harvest energy at power rates and peak PCE levels in excess of 1 mW and 30%. These figures are significantly higher than those of the prior art. In one design, two rectifier stages are in a cascode configuration to produce higher dc output voltage levels at the low-current regime. Novel theoretical analyses of the unique rectifying circuitry of the single-stage and two-stage cascode harvesters are presented, which formulate all of the key specifications. [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]

Impedance matching networks for nonlinear devices such as amplifiers and rectifiers are normally very challenging to design, particularly for broadband and multiband devices. A novel design concept for a broadband high-efficiency rectenna without using matching networks is presented in this paper for the first time. An off-center-fed dipole antenna with relatively high input impedance over a wide frequency band is proposed. The antenna impedance can be tuned to the desired value and directly provides a complex conjugate match to the impedance of a rectifier. The received RF power by the antenna can be delivered to the rectifier efficiently without using impedance matching networks; thus, the proposed rectenna is of a simple structure, low cost, and compact size. In addition, the rectenna can work well under different operating conditions and using different types of rectifying diodes. A rectenna has been designed and made based on this concept. The measured results show that the rectenna is of high power conversion efficiency (more than 60%) in two wide bands, which are 0.9–1.1 and 1.8–2.5 GHz, for mobile, Wi-Fi, and ISM bands. Moreover, by using different diodes, the rectenna can maintain its wide bandwidth and high efficiency over a wide range of input power levels (from 0 to 23 dBm) and load values (from 200 to 2000 Ω). It is, therefore, suitable for high-efficiency wireless power transfer or energy harvesting applications. The proposed rectenna is general and simple in structure without the need for a matching network hence is of great significance for many applications. [ABSTRACT FROM AUTHOR]

This communication presents a novel hybrid resistance compression technique (HRCT) to improve the performance of broadband rectennas. The HRCT can offer resistance compression characteristic by reducing the nonlinear effects of the rectifier and provide improved impedance matching performance over a wide frequency range. Two ultrawideband rectennas (with/without using the HRCT) have been designed, made, and tested. The proposed rectennas have a very wide bandwidth from 450 to 900 MHz (covers the entire DTV, LTE700, and GSM900 bands in the U.K.) with relatively high conversion efficiency (up to 77%). The HRCT can maintain the high efficiency of the rectenna in a wide load impedance range (from 5 to 80 \textk\Omega ) . The measured harvested dc power of the rectenna from an outdoor ambient environment is about 66.7 \mu \textW with an overall conversion efficiency of 42.2%, which is therefore suitable for wireless energy harvesting to power low power electronic devices with different load impedance. [ABSTRACT FROM PUBLISHER]

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]

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 \textk\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 \textW , respectively; it can therefore be applied to a range of low-power wireless applications. [ABSTRACT FROM AUTHOR]

We present the concept and design of vertically stacked electromagnetic energy-harvesting system using folded dipole antennas. The proposed system is composed of stacked rectenna arrays or panels that are connected in various ways to channel the collected ac power to a single dc load. We show through experiments that by vertically stacking rectenna panels, the power collected per footprint is enhanced significantly. In fact, an improvement of up to 5 times is achieved in comparison to a single panel occupying the same two-dimensional footprint. [ABSTRACT FROM PUBLISHER]

In this communication, a novel stacked differential rectenna is proposed and its characteristics are experimentally investigated. The proposed rectenna can effectively convert RF power to dc due to its differential operation. The conversion efficiency of 44.1% was obtained when the received power density was as low as 0.041\,\text W/\text m^2. The proposed rectenna can easily achieve large-scale rectenna arrays effectively using its simple structure. The rectenna array with DC connection provides almost the same conversion efficiency and incident angle characteristics in comparison with a single rectenna. [ABSTRACT FROM PUBLISHER]

This paper studies loop antennas over artificial magnetic conductor (AMC) surfaces with the objective of designing a dual-band RF energy harvesting antenna. The AMC surface is well known to achieve low-profile and higher gain wire antennas. From a practical point of view, impedance matching is of paramount importance to achieve highly efficient reception of weak ambient RF energy. First, the driving-point impedance of a loop antenna over an AMC surface was studied, where a conventional method using image theory to estimate the impedance was found to be not always useful for loop antennas. As the AMC surface is within the reactive near field, mutual coupling between the antenna and the AMC unit cells is significant, which the conventional method does not take into account. Then, we proposed a novel use of a polarization-dependent AMC surface for dual-band RF energy harvesting. An AMC surface with a rectangular unit cell was adopted for two orthogonal polarizations with different frequencies. Finally, the AMC surface and the loop antennas were successfully implemented as a dual-band energy harvesting panel together with RF-to-dc conversion circuits and a power management circuit. [ABSTRACT FROM PUBLISHER]

In this work, a novel, compact, single-port antenna combining both UWB and UHF bands is presented. This solution is proposed for next-generation passive RFID tags, performing communication and localization through UWB technology and efficient energy harvesting in the UHF band, but it is also designed to keep compatibility with previous tags generations. The UWB communication is deployed by means of an Archimedean spiral topology, while energy harvesting at UHF is obtained by suitably extending the spiral outer arms, thus realizing a meandered dipole, without affecting the UWB behavior. The single-port architecture provides an overall size reduction, while preserving the radiation performance in both the operating bands. This solution allows a direct connection to future integrated UWB–UHF chips, to standard RFID chips, or to a diplexer for suitably combining the UWB and the UHF functionalities. A prototype of this new antenna, realized on a standard FR-4 substrate, is first presented to validate the proposed novel design. As a second step, the same architecture is scaled on a paper substrate in view of its fully ecocompatible realization to be exploited by future pervasive RFID applications. The compact design of the antenna-feeding network in discrete technology is also presented. [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, a rigorous procedure for the circuit-level analysis and design of entire systems, developed to provide power wirelessly, is presented. A unified theoretical approach is first introduced, based on a two-port-equivalent circuit representation, to describe the wireless power transfer link when the transmitter and the receiver are either in the near-field or in the far-field region reciprocally. This approach allows one to compute in a straightforward manner the system figure of merit, namely the power transfer efficiency. Specific guidelines for the two configurations are then intensively discussed together with the adopted software tools based on the combination of full-wave analysis and nonlinear harmonic balance techniques. Several practical examples based on this design procedure are presented, demonstrating predicted and experimental behavior of unconventional devices for both near-field and far-field power transfer usage. [ABSTRACT FROM AUTHOR]

In this paper, rectennas formed from nanodipole antennas terminated by plasmonic metal–insulator–metal (MIM) travelling wave transmission line rectifiers are developed for ambient thermal energy harvesting at 30 THz. The transmission lines are formed from two strips coupled either vertically or laterally. A systematic design approach is presented, that shows how different components can be integrated with each other with maximum radiation receiving nantenna efficiency, maximum coupling efficiency between nantenna and rectifier, and maximum MIM diode rectifier efficiency. The tunneling current of the rectifier is calculated using the transfer matrix method and the nonequilibrium Green's function. A detailed parametric study of the coupled strips plasmonic transmission lines is presented and thoroughly discussed. The overall efficiencies of the proposed travelling wave rectennas are fully expressed and compared. [ABSTRACT FROM PUBLISHER]

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]

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]

The second annual Student Wireless Energy Harvesting (WEH) Design Competition was held during the 2013 IEEE Microwave Theory and Techniques Society (MTT_S) International Microwave Symposium (IMS2013) in Seattle, Washington, United States. This year, the competition parameters were modified from those of last year [1], and a new figure of merit (FoM) was established. The overall goal of the competition was to demonstrate low-mass hardware that can efficiently receive and rectify extremely low-incident power densities at two frequencies, with a fixed dc load. As the radio-frequency (RF) environment gets more saturated with spurious power, designs from this competition will become a feasible way to energize ultralow-powered or low-duty-cycle hard-to-reach sensors. Concepts such as Internet-of-Things, in which small ubiquitous devices and sensors will log data and send it to the cloud, could benefit from wireless energy harvesters. These sensors will not have convenient ways to stay powered unless power harvesting circuits are used for the sensor hardware. [ABSTRACT FROM PUBLISHER]

We present progress toward a wirelessly-powered active contact lens comprised of a transparent polymer substrate, loop antenna, power harvesting IC, and micro-LED. The fully integrated radio power harvesting and power management system was fabricated in a 0.13~\mum CMOS process with a total die area of 0.2~mm^2. It utilizes a small on-chip capacitor for energy storage to light up a micro-LED pixel. We have demonstrated wireless power transfer at 10 cm distance using the custom IC and on-lens antenna. [ABSTRACT FROM PUBLISHER]