Low Input Power Levels Research Articles

Low-Power Energy Harvesting Voltage Doubler Using CTLs Based on Inverse Class-F Configuration Compatible with Fifth Generation

This paper introduces a highly efficient and low-power inverse class-F voltage doubler (VD) designed for radio frequency (RF) energy harvesting systems. Specifically tailored for mid-band 5G technology, the VD is designed for operation within the 1240–1300 MHz satellite band. The innovative design employs an inverse class-F architecture, incorporating a λ/8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda /8$$\\end{document} short-ended transmission line (TL) connected to the diode anode and a (λ/12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda /12$$\\end{document}) open-ended transmission line linked to the input of the voltage doubler. This configuration aims to reshape voltage and current waveforms, effectively reducing losses and series resistance in the diode. Dual-coupled transmission lines (CTLs) are utilized to provide passive voltage boosting at low-input power levels. The suggested voltage doubler is implemented using RO4003C substrate material with a dielectric relative permittivity (εr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\upvarepsilon }_{r}$$\\end{document}) of 3.38 and a thickness of 0.81 mm. Measured results demonstrate a minimum input return loss of − 29.3 dB at 1.25 GHz, operating seamlessly within a frequency band from 1.18 to 1.32 GHz. The measured conversion efficiency is 45.2% at an input power (Pin) of − 4dBm. Furthermore, the peak RF–DC efficiency reaches 50% at an input power of 0dBm. Simulated results predict a remarkable conversion efficiency of 60% and 68.7% at − 4dBm and 0 dBm, respectively. In addition to its exceptional performance, the suggested voltage doubler exhibits an experimental DC output voltage of 0.53 V at Pin=-10dBm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P_{{{\ ext{in}}}} = - 10{\ ext{dBm}}$$\\end{document} and a saturated DC voltage of 3.4 V at an input power of 10dBm under a load terminal resistance of 8 KΩ. Finally, the dimensions of the proposed voltage doubler are 25.3×10.5mm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$25.3 \ imes 10.5 {\ ext{mm}}^{{2}}$$\\end{document}.

Design and optimization of broadband CPW rectenna for RF energy harvesting

ABSTRACT Wireless sensor networks (WSNs) are widely used in a variety of sectors, including the surveillance, healthcare, and military, and so on. The high cost and short lifespan of wireless sensor networks prohibit emerging and low-income nations for using their benefits. This article proposes a compact, low cost, and broadband coplanar waveguide rectenna with a simple novel ground plane operate in band range of 4.8–5.5 GHz (700 MHz) for an effective solution to radio frequency (RF) energy harvesting applications in WSNs. A parametric study of distinct antennas is also conducted to strengthen the attributes of the proposed antenna. The defected ground structure created on the co-plane offers 105° measured half power beamwidth (HPBW) in the H-plane for wide angular coverage. As a result, design alignment does not need to be extremely perfect in order to make conversion efficiency constant. The rectifying circuit is made compact by using a two-stub impedance matching network. At load resistance of 1k Ω, the power conversion efficiency of the proposed rectenna for a low input power level of −10 dBm is 27.2% (simulated) and 20.1% (measured) while its maximum value is 52.5% (simulated) and 50.1% (measured) for input power level of 10 dBm.

A novel method for supersonic plasma measurement using a double-jacketed enthalpy probe

A novel method to characterize a supersonic plasma jet using a double-jacketed enthalpy probe is presented and applied to Ar supersonic plasma jets generated by a plasma torch operated at an input power level of 5.7 kW and a chamber pressure of 2.3 kPa. The basis of this method is to measure total stagnation pressure, total enthalpy, and static pressure at the backside of a shock wave formed in front of the probe with a single insertion of the probe. Once these three variables are known, normal shock relations before and after the shock wave can disclose information on static pressures, Mach numbers, temperatures, and velocities of the supersonic plasma jet under a calorically perfect gas assumption. For example, measurement experiments carried out with the proposed probe revealed that static pressure of Ar supersonic plasma jet oscillated around the chamber pressure of 2.3 kPa in a range of 1–5 kPa along the jet axis, clearly showing an aerodynamic non-equilibrium. Corresponding to the behaviors of static pressures, Mach numbers also oscillated in the range of 1.1–3.5 along the jet axis. In addition, oscillation patterns of static pressures and Mach numbers agreed well with those of compression and expansion wave zones observed in the photograph of an over-expanded Ar supersonic plasma jet. Although relatively large errors were accompanied due to a low input power level, plasma temperatures and velocities were measured to be decreasing and increasing, respectively, in the expansion wave zone while opposite behaviors were observed in the compression wave zone.

Advancing IoT wireless sensor nodes with a low profile multiband RF rectifier based on multi-stub J-Inverter network

In this paper, a unique RF rectifier design is introduced, employing a multi-stub J−Inverter impedance matching network (IMN). The structure of the IMN comprises a series of three sections with multiple stub tuning elements interconnected via a meandered line (MDL) to form multi-frequency susceptance blocks. The rectifier has been developed to work at frequency bands: 1.84, 2.10, and 2.45 GHz. These frequencies align with the designated bands for GSM/1800, UMTS/2100, and Wi-Fi, respectively. By implementing a complete ground architecture, the rectifier utilizes a minimal space of 0.57λg×0.3λg on the RT/Duroid 5880 PCB board. The experiment’s outcomes show the proposed RF rectifier’s effectiveness in converting radio frequency (RF) signals into direct current (DC) power (RF-to-DC). The results indicate PCE values of 32.70%, 27.60%, and 24.50%, corresponding to input powers of -20 dBm at the targeted operational frequencies. Additionally, the rectifier design proposed within this study achieves its peak RF-to-DC PCE of 75.30% when energized by an input power of 3 dBm. Moreover, notable stability is demonstrated by the rectifier, sustaining an RF-to-DC PCE surpassing 50% throughout the frequency range spanning 1.7 to 2.4 GHz. This robust performance remains consistent even at lower input power levels, such as -10 dBm Furthermore, the rectifier can produce a direct current (DC) voltage output ((VDC)), measured at 0.411 V in an ambient context. The integration of the rectifier with the power management module (PMM), facilitated through the utilization of the bq25504-674 evaluation module (EVM), successfully established a connection within the PMM system. This integration yielded a (VDC) of 1.270 V. Hence, through proficient management of the proposed RF rectifier, it becomes feasible to utilize ambient RF signals to energize a range of low-energy devices effectively.

Compact Single-Port Harmonic Transponder for Backscattering Communications and Energy Harvesting Applications

This article proposes a novel architecture for the design of a single-port harmonic transponder. The need for a diplexer is eliminated by adding a quarter-wave and a one-eighth-wave transmission line, combined with the two quarter-wave stubs that are usually needed in a conventional harmonic transponder. The proposed architecture provides isolation between the fundamental and the second harmonic signals and sends them to the desired port, while only introducing extremely low insertion loss. Compared with a single-resonator-based diplexer, it has a much wider bandwidth and a much more compact size than the conventional dual-port design. The proposed diplexing structure can also be used in the design of a compact single-port harmonic transponder with dc power supply capability. With such a design, the harmonic transponder can not only generate harmonics for communication purposes, but also provide power for the operation of communication modules, while being small in size and working with a single antenna. A harmonic tag with a simple modulation module based on this architecture is designed to demonstrate its practical value. The proposed design can work at a low input power level and is very suitable for future low-power Internet of Things (IoT) applications.

Harvesting microwave energy using pyroelectricity of nanostructured graphene/zirconium-doped hafnium oxide ferroelectric heterostructures

In this work, we present the design, atomistic/circuit/electromagnetic simulations, and the experimental results for graphene monolayer/zirconium-doped hafnium oxide (HfZrO) ultra-thin ferroelectric-based field effect transistors fabricated at the wafer scale, regarding the pyroelectricity generation directly from microwave signals, at room temperature and below it, namely at 218 K and at 100 K. The transistors work like energy harvesters, i.e. they collect low-power microwave energy and transform it into DC voltages with a maximum amplitude between 20 and 30 mV. The same devices function as microwave detectors in the band 1–10.4 GHz and at very low input power levels not exceeding 80 μW when they are biased by using a drain voltage, with average responsivity values in the range 200–400 mV mW−1.

A Self-Packaged SISL Low-Power Rectifier Based on a High-Impedance Line for C-Band Applications

In this letter, a self-packaged substrate-integrated suspended line (SISL) rectifier is proposed. The rectifier consists of a quarter-wavelength high-impedance transmission line, a diode, a tuning inductor, and a dc pass filter. The lower the power is, the lower the rectifying efficiency is. At a low input power level, the diode impedance real part is almost zero. A tuning inductor is introduced to form a parallel resonator to enhance the diode voltage. A quarter-wavelength high-impedance line is presented to match the rectifying diode to the source. In addition, due to the self-packaging characteristics and air cavity of SISLs, the radiation loss and dielectric loss of the proposed rectifier are reduced. A rectifier was designed, fabricated, and measured at 5.8 GHz. The radio frequency (RF)-dc conversion efficiency reaches 3.5% at −30 dBm, which is close to its theoretical estimated efficiency at 5.8 GHz. This ultralow power rectifier may be used in energy harvesting at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$ </tex-math></inline-formula> -band.

Wireless power transfer system prototype with a wide input power range rectifier and power‐optimized waveforms

AbstractThis paper describes a wireless power transfer (WPT) system operating at 2.4 GHz, which is based on waveform optimization technique and a wide input power range rectifier. This latter consists of an RF‐to‐dc power conversion circuit based on circulators. The waveform optimization is then applied in order to enhance the power conversion efficiency at very low input power levels. The proposed WPT system was prototyped and tested in open and closed loop configurations with different types of obstacles placed between the transmitter and the receiver. The generation of power‐optimized waveforms and the control process in the closed loop configuration were carried out using software‐defined radio. The obtained experimental results validate the wide input power behavior of the two proposed WPT systems especially when dealing with very low input power levels and relatively dynamic environments. In fact, for the two WPT systems featured a distance of 1 m and a transmitted power of 50mw, dc power levels of about 38 and 11 μW are harvested in the cases of no obstacle and low attenuation obstacle respectively.

A Self Threshold Voltage Compensated Rectifier for RF Energy Harvesting using 45nm CMOS Technology

A high frequency rectifier is the core of a RF energy harvesting system. It should offer a very good efficiency at low input power levels and to obtain that compensation of threshold voltage is a very important aspect. A threshold compensation scheme for MOSFETS for RF rectifier applicable in RF energy harvesting system is presented in this paper. The switching of the MOSFET is improved with overall enhancement of output rise time of the system. The design emphasis is to have a simplified circuit without the requirement of any external source so as to achieve self-sustainability in the true sense. The rectifier circuit is derived from the basic Dickson charge pump model and is evaluated using 45nm CMOS process. The design has utilized Metal Oxide Semiconductor Field Effect Transistor instead of basic diodes which ensures low power along with fabrication feasibility. The maximum measured PCE of the design is obtained to be 33% at 4dBm input power level at 500Mhz frequency with 1 Kilo Ohm load resistance. The output transient response rise time has been measured to be 85ns at 500MHz and 50.10ns at 1Ghz.

Simple Adaptive Rectifier with High Efficiency over a Range of 21 dBm Input Power for RF Energy Harvesting Applications

This paper presents a novel simple adaptive and efficient rectifier for Radio Frequency (RF) energy harvesting applications. Traditional rectifiers have maximum RF-DC Power Conversion Efficiency (PCE) over a narrow range of RF input power due to diode breakdown voltage restrictions. The proposed adaptive design helps to extend the PCE over a wider range of RF input power at 2.45GHz using a simple design. Two alternative paths arecontrolled depending on the RF input power level. Low input power levels activate the first path connected to a single rectifier; low power levels make the diode operate below its breakdown voltage and therefore avoiding PCE degradation. High input power levels activate the second path dividing it into three rectifiers. This keeps input power at each rectifier at a low power level to avoid exceeding the diode break down voltage. Simulated PCE of this work is kept above 50% over a range of 21.4 dBm input power from -0.8dBm to 20.6dBm.

Analysis, Design and Implementation of a Fully Integrated Analog Front-End for Microwave RFIDs at 5.8 GHz to Be Used With Compact MIMO Readers

In this paper we present the system and circuit level analysis and feasibility study of applying microwave Radio Frequency Identification (RFID) systems with multipleinput multiple-output (MIMO) reader technology for tracking machining tools in multipath fading conditions of production environments. In the proposed system the MIMO reader interrogates single-antenna tags, and a high RFID frequency of 5.8 GHz is chosen to reduce the size of the reader's antenna array. According to the requirements dictated by the performed system analysis at 5.8 GHz, a low power fully integrated analog frontend (AFE) is designed and fabricated in a standard 65-nm CMOS technology for low power passive transponders. Performance of the Differential Drive Rectifier (DDR) topology as the core of the energy harvesting unit is investigated in detail. A multi-stage DDR power scavenging unit is dimensioned to provide a 1.2 V rectified voltage for 20-30 kQ load range, with a high power conversion efficiency (PCE) for high frequency and low input power level signals. The rectified voltage is then converted to a 1 V regulated voltage for the AFE and the baseband processor with 30 to 50 μW of estimated power consumption. Transistors with standard threshold voltage (VT) have been used for implementation. Measurements of the fabricated multi-stage configuration of the circuit show a maximum PCE of 68.8% at -12.46 dBm, and an input quality factor (Q-factor) of approximately 10. Amplitude-shift keying (ASK) demodulator and backscattering modulator with 80% modulation index, operating according to EPC-C1G2 protocol are applied for data transfer. The AFE consumes less than 1 μW in the reading mode. The AFE tag chip is 0.55 × 0.58 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Design of a 900 MHz Dual-Mode SWIPT for Low-Power IoT Devices

This paper presents a duty cycle-based, dual-mode simultaneous wireless information and power transceiver (SWIPT) for Internet of Things (IoT) devices in which a sensor node monitors the received power and adaptively controls the single-tone or multitone communication mode. An adaptive power-splitting (PS) ratio control scheme distributes the received radio frequency (RF) energy between the energy harvesting (EH) path and the information decoding (ID) path. The proposed SWIPT enables the self-powering of an ID transceiver above 20 dBm input power, leading to a battery-free network. The optimized PS ratio of 0.44 enables it to provide sufficient harvested energy for self-powering and energy-neutral operation of the ID transceiver. The ID transceiver can demodulate the amplitude-shift keying (ASK) and the binary phase-shift keying (BPSK) signals. Moreover, for low-input power level, a peak-to-average power ratio (PAPR) scheme based on multitone is also proposed for demodulation of the information-carrying RF signals. Due to the limited power, information is transmitted in uplink by backscatter modulation instead of RF signaling. To validate our proposed SWIPT architecture, a SWIPT printed circuit board (PCB) was designed with a multitone SWIPT board at 900 MHz. The demodulation of multitone by PAPR was verified separately on the PCB. Results showed the measured sensitivity of the SWIPT to be −7 dBm, and the measured peak power efficiency of the RF energy harvester was 69% at 20 dBm input power level. The power consumption of the injection-locked oscillator (ILO)-based phase detection path was 13.6 mW, and it could be supplied from the EH path when the input power level was high. The ID path could demodulate 4-ASK- and BPSK-modulated signals at the same time, thus receiving 3 bits from the demodulation process. Maximum data rate of 4 Mbps was achieved in the measurement.

Dual-Band Transmission-Line Resistance Compression Network and Its Application to Rectifiers

In this paper, a dual-band transmission-line resistance compression network (TLRCN) is introduced and applied to the rectifier design to enhance the power conversion efficiency at low input power levels, leading to wider dynamic power range of the rectifier. It can be used to reduce the sensitivity of the rectifying efficiency to input power variation at two frequencies. The analytical expressions for the dual-band TLRCN are derived. In order to validate the proposed idea, two dual-band rectifiers with different frequency spacing ( $\Delta f$ ) are designed, fabricated, and measured. One works at 0.915 GHz/2.45 GHz ( $\Delta f = 1.535$ GHz) and the other at 1.80 GHz/2.40 GHz ( $\Delta f = 0.6$ GHz). For comparison, their counterparts, without the dual-band TLRCN, are also designed and implemented. The measured results show that the proposed dual-band TLRCN can be used to extend the input power range at two frequencies without decreasing the maximum power conversion efficiencies.

Two-Scale Envelope-Domain Analysis of Injected Chirped Oscillators

The response of chirped oscillators under the injection of independent signals, for spectrum sensing in cognitive radio, and under self-injection, for radio frequency identification, is analyzed in detail. The investigation is performed by means of a semianalytical formulation, based on a realistic modeling of the free-running oscillator, extracted from harmonic-balance simulations or from experimental measurements, through a new characterization technique. In the new formulation, the oscillator is linearized about a free-running solution that varies with the control voltage. This enables its application to oscillators having a frequency characteristic that deviates from the linear one. In the case of injection by independent signals, the two-scale envelope-domain formulation will enable an efficient handling of the difference between the slow chirp frequency and the beat frequency. The input carriers can be detected from their dynamic synchronization intervals or, at lower input-power levels, from the dynamics of the beat frequency. Noise perturbations are introduced into the formulation, which enables an estimation of the minimum detectable signal. In the case of a self-injected oscillator for radio frequency identification, an insightful formulation is derived to predict the propagation and tag-resonance effects on the instantaneous oscillation frequency. The tag-resonance signature gives rise to a distinct modulation of the oscillation frequency during the chirp period, which can be detected from the variation of the oscillator bias current. The analysis methods are illustrated through their application to a chirped oscillator, operating in the band 2–3 GHz.

A Coherent Homodyne TO-Can Transceiver as Simple as an EML

The introduction of low-cost coherent signal reception is one of the great challenges in optical telecommunications since its opto-electronic sub-systems are associated with a high degree of complexity. In this work, we propose a disruptive approach: the re-use of widely deployed direct-detection technology for simultaneous coherent homodyne reception and transmission. We first show that an externally modulated laser (EML) is sufficient to perform both, coherent reception and transmission functionality. Second, we prove that homodyne detection applies to the EML-based scheme in virtue of an injection-locked local oscillator, which for low input power levels is pulled to the optical carrier frequency of the incident data signal. The proposed methodology for coherent reception enables a greatly simplified transceiver as optical layer hardware. As we will demonstrate, it just requires single fiber access, a single radio frequency port, and can be implemented in a transistor-outline package. Full-duplex transmission with coherent homodyne reception is experimentally validated, showing 2.5 Gb/s transmission over 27.5 km reach and a loss budget of 28 dB, and coherent Gigabit Ethernet connectivity—without the use of optical layer digital signal processing functions.

High-Efficiency Single- and Dual-Band Rectifiers Using a Complex Impedance Compression Network for Wireless Power Transfer

In this paper, novel single- and dual-band complex impedance compression networks (ICNs) are proposed and applied to the design of rectifying circuits for efficiency improvement. The proposed ICNs are connected to the microwave input of two parallel subrectifiers. They reduce the variation ranges of the rectifier input impedance, which change with input power. Thus, the loss due to impedance mismatch is reduced, and high conversion efficiency can be obtained over wider input power ranges. Compared with the resistance compression networks (RCNs), the proposed ICNs are able to compress the variation range of the complex impedance, rather than that of the resistance, featuring design flexibility. A detailed analysis is carried out. For demonstration, a 2.45-GHz rectifier and a dual-band rectifier working at 2.45 and 5.8 GHz for the industrial, scientific, and medical band are implemented based on the ICN. The experimental results show that, in comparison to the counterparts without the ICN, the proposed rectifiers with the ICN can improve the efficiency at low input power levels without degrading the maximum conversion efficiency. Besides, the ICN-based rectifiers have a much simpler circuit structure than the RCN-based rectifiers.

Frequency tuning hysteresis of a dual‐resonance divide‐by‐three cross‐coupled injection‐locked frequency divider

This paper studies the frequency tuning effect on the locking range property of a dual-resonance 3:1 injection-locked frequency divider (ILFD) fabricated in a foundry 0.18 μm BiCMOS process. The ILFD architecture is based on a capacitive cross-coupled oscillator in conjunction with a resistor-degraded dual-resonance resonator for the locking range improvement. At a power consumption of 5.26 mW and at injection power of P inj = 0 dBm the locking range from the measurement is from 6.2 to 12.6 GHz (68.09%). The frequency tuning range of the free-running ILFD shows a frequency tuning hysteresis effect; at low input power level the locking range shows bipolar locking ranges and at high injection power the locking range is independent of the measured voltage tuning direction.

High Efficiency Energy Harvesters in 65nm CMOS Process for Autonomous IoT Sensor Applications

Two integrated, highly efficient RF-to-dc rectifier circuits are presented. The rectifier circuits are based on improved Dickson charge pump models and are fabricated using 65-nm CMOS GlobalFoundries process. The designs utilize diode-connected metal–oxide–semiconductor field-effect transistors instead of the conventional Schottky diodes to provide a fully integrated circuits. A detailed analytical model that supports the improved circuit model is given. The measurement results of both rectifier circuits show good agreement with the simulation results. The fabricated rectifiers’ start to operate at −17.5-dBm input power. The tested frequency of operation of the rectifier circuits is 953 MHz (GSM900 band), however, other frequency bands such as 2.4 GHz (Bluetooth/WLAN) could be covered with proper impedance matching. The measured peak power conversion efficiency (PCE) of the implemented rectifiers are 84.37% and 56.16% at input power levels of −12.5 and −15 dBm, respectively. To the best of our knowledge, this is the highest achieved PCE for the class of rectifiers at such low input power level in the literature. High sensitivity and excellent PCE of the presented rectifiers are ideal for utilization in wireless sensor network, Internet of Things, energy harvesting, and biomedical applications.

2.45-GHz wideband harmonic rejection rectenna for wireless power transfer

In this paper, a 2.45-GHz wideband harmonic rejection rectenna for wireless power transfer is proposed. The rectenna comprises a microstrip-fed circular ring slot antenna (CRSA) and a series-parallel rectifier (SPR). A compact micro strip resonant cell is inserted into the CRSA so that the harmonic suppression over a wide bandwidth (3–8 GHz) can be obtained. The radio-frequency (RF)–DC conversion efficiency of the SPR is improved effectively by loading a proper compensating inductance, especially under the low input power levels. Furthermore, the proposed rectenna can easily achieve large-scale rectenna arrays using its simple structure. The adopted rectenna fabricated on a low cost Taconic RF-35 substrate has been measured. By up to 3rd-order harmonic rejection, the efficiency of the rectenna can achieve 70.2% with the optimum load resistance 1 kΩ. Good agreement among the calculated, simulated, and measured rectenna is observed.

Differential Rectifier Using Resistance Compression Network for Improving Efficiency Over Extended Input Power Range

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.