RF-DC Power Conversion Efficiency Research Articles

Microwave Energy Harvesting With No Extra Receiving Antenna

This paper addresses different cases of radio frequency harvesting using different antenna types as 
 transmitting antenna but using just the lead of the capacitor as the wire antenna at the receiving end 
 with a voltage rectifier circuit. Different antennas were used in the input and with two different 
 rectification circuits the conversion efficiencies were studied accordingly. For a source of log periodic 
 antenna, without any antenna, 27.31% RF-DC power conversion efficiency value was obtained at the 
 far-field. For a source of half wavelength dipole antenna, at the near-field, 50.53% RF-DC power 
 conversion efficiency value was obtained. For a source of helical antenna, up to 5 cm distance about 
 14.78% RF-DC power conversion efficiency was observed. For the Yagi-Uda antenna used as a source, 
 RF-DC power conversion efficiency that was obtained at the far was 28.89% without any receiving 
 antenna..

Two-Port Five-Band Rectenna for Ultralow Ambient RF Energy Harvesting

A two-port rectenna is proposed to harvest the ambient RF power from five commercial bands, including 1.8 GHz, 2.1 GHz, 2.4 GHz, 2.65 and 3.5 GHz for GSM, LTE, WLAN and 5G, respectively. The novel rectenna comprises a hybrid half-wave rectifier and two back-to-back slot antennas. The rectifier consists of a series rectifier branch and a parallel rectifier branch to extend its multi-band coverage, only sharing one diode. With this design strategy, its RF-DC power conversion efficiency (PCE) can reach 23.1% at 1.8 GHz, 26.4% at 2.1 GHz, 27.2% at 2.4 GHz, 20.7% at 2.66 GHz and 19.1% at 3.47 GHz with -20 dBm input power level. Notably, once a five-tone signal is input simultaneously with the identical power level of -20 dBm, the PCE of rectifying circuit can be improved to 43.7%, breaking the existing record to our best knowledge. The designed slot antennas can also receive omnidirectional RF power at five corresponding frequencies. The experimental results demonstrate that our proposed rectenna is competitive in band coverage and PCE with ultra-low input power, indicating enormous potential for RF energy harvesting and powering sensors, wearables, and other low-power scenarios.

A Low-Profile Compact Broadband CP DRA for RF Energy Harvesting Applications

In this letter, a low-profile circularly polarized (CP) chamfered rectangular dielectric resonator antenna (RDRA) is designed and investigated for radio frequency energy harvesting (RFEH) applications. The proposed modified RDRA comprises of dielectric resonator (DR) made up of Alumina material (ε r = 9.9) mounted on the PEC ground plane. Dual unequal triangular-shaped vertical slits are engraved on the rectangular DR for generating the orthogonal modes with CP characteristics. The optimized antenna offers an impedance bandwidth (IBW) of 51.4% (2.25–3.81 GHz) and axial ratio bandwidth (ARBW) of 14.8% (3.25–3.77 GHz), respectively. The peak realized gain and maximum radiation efficiency are 7.18 dBi and 97.8% in desired frequency bands. Due to the wide impedance and AR bandwidths with realized gain and radiation efficiency, the optimized antenna is suitable for integration with a rectifier circuit for RF energy harvesting applications. A rectifier circuit with a single shunt diode topology is also designed for rectification purposes. The rectifier achieved 67.16% RF-DC power conversion efficiency (PCE) at 3.5 GHz and 5dBm input power. At 0dBm input power, the rectifier achieved 60.26% PCE. The effective input power range, during which the PCE maintains above 50%, is calculated to be 15.2 dBm from −3.5 to 11.7 dBm.

Temperature Analysis of Schottky Diodes Rectifiers for Low-Power RF Energy Harvesting Applications

This article aims to contribute for the improvement of low-power Radio Frequency Energy Harvesting (RFEH) designs based on Schottky Barrier Diode (SBD) rectifiers, presenting a study of the relationship between RF-DC Power Conversion Efficiency (PCE) and circuit temperature, which is directly related to the non-linear behavior of the metal-semiconductor junction of SBDs. For this purpose, SPICE diode models were revisited, evaluating the temperature dependence and its effects on forward and reverse conduction modes. The SBDs SMS7621 and SMS7630 temperature dependent characteristics are evaluated according the proposal, and their use is explored through analytical modeling and simulation analyzes of an RFEH system for temperatures ranging from 240 to 360 K. Hence, after an initial formulation of the optimum operation in terms of PCE, two series RF rectifiers are designed based on the mentioned diodes, aiming at an efficient operation over different temperature ranges according to each component optimum PCE, at 300 K for the SMS7630 and over 340 K for the SMS7621. For the SMS7630 prototype, the maximum measured PCE is 25.33% around 293 K, but decreases to 3.65% around 353 K, and for the SMS7621 the measured PCE goes from 11.56% to 16.34% in the same temperature range, considering −20 dBm as Input Power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{in}$ </tex-math></inline-formula> ) due to the low-power RFEH premise. The results leads to a higher PCE stability for the SMS7621 through the whole analyzed range, despite the overall PCE that is limited by the matching network losses intrinsic to the design.

Single Band EBG Antenna for Wireless Power Transfer Applications

This work demonstrates the design of a single band Electromagnetic Band Gap (EBG) antenna by employing an open stub EBG microstrip of a patch antenna for better achievements in terms of its performance to be utilized in a reconfigurable harvester to operate over a wide input power range. The EBG antenna has been used to gather RF energy and a FET-transistor has been obtainable to determine and control the power flow with the intention to operate at the same time for a different level of input power. The measured data of the EBG antenna shows a directivity of 8.52 dBi, a gain of 7.18 dBi, a return loss of −27 dB with a radiation efficiency of 84.3%, showing a clear enhancement in directivity, peak realized gain, and radiation efficiency by 41.76%, 25.61%, and 17.12% respectively compared with a regular reference antenna; without utilized the EBG structure. Moreover, the harvester design accomplishes 40% of RF-DC power conversion efficiency over a wide dynamic input power range from −15 to 27 dBm, and its peak is around 78%. The harvester is designed to work at the ISM band for 915 MHz and is suitable for Wireless Power Transfer (WPT) uses.

Efficient and Compact Tri-Band Rectifier With Large Frequency Ratio for WPT

In this letter, an efficient and compact tri-band rectifier with large frequency ratio is proposed, which adopts a novel low-cost direct current (dc)-pass filter structure in the design. Three large frequency ratio rectifiers are combined together by using diode arrays with a frequency-selective topology without additional impedance matching networks. The dc-pass filter is composed of microstrip line structures cascaded low-cost lumped components, which can effectively suppress the high-order harmonics at high- and low-frequency points while reducing the circuit size and costs of large frequency ratio. For validation, the proposed rectifier working at 0.915, 2.45, and 5.8 GHz is fabricated with the dimensions of 29.5 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times21.3$ </tex-math></inline-formula> mm. The measured results show that the RF-dc power conversion efficiency (PCE) reaches 72.6%, 71.8%, and 73.5% at 0.915, 2.45, and 5.8 GHz, respectively, when the input power is 19 dBm. Compared with traditional multiband rectifiers, the proposed topology exhibits merits of compact size, high efficiency, and large frequency ratio.

Fast and Accurate Approach to RF-DC Conversion Efficiency Estimation for Multi-Tone Signals.

The paper presents a computationally efficient and accurate numerical approach to evaluating RF–DC power conversion efficiency (PCE) for energy harvesting circuits in the case of multi-tone power-carrying signal with periodic envelopes. This type of signal has recently received considerable attention in the literature. It has been shown that their use may result in a higher PCE than the conventional sine wave signal for low to medium input power levels. This reason motivated the authors to develop a fast and accurate two-frequency harmonic balance method (2F-HB), as fast PCE calculation might appreciably expedite the converter circuit optimization process. In order to demonstrate the computational efficiency of the 2F-HB, a comparative study is performed. The results of this study show that the 2F-HB significantly outperforms such extensively used methods as the transient analysis (TA), the harmonic balance method (HB), and the multidimensional harmonic balance method (MHB). The method also outperforms the commercially available non-linear circuit simulator Keysight ADS employing both HB and MHB. Furthermore, the proposed method can be readily integrated into commonly used commercially available non-linear circuit simulation software, including the Keysight ADS, Ansys HFSS, just to name a few—minor modifications are required. In addition, to increase the correctness and reliability of the proposed method, the influence of PCB is considered by calculating Y parameters of its 3D model. The widely employed voltage doubler-based RF–DC converter for energy harvesting and wireless power transfer (WPT) in sub-GHz diapason is chosen to validate the proposed method experimentally. This RF–DC converter is chosen for its simplicity and capability to provide sufficiently high PCE. The measurements of the PCE for a voltage doubler prototype employing different multi-tone waveform signals were performed in laboratory conditions. Various combinations of the matching circuit element values were considered to find the optimal one in both—theoretical model and experimental prototype. The measured PCE is in very good agreement with the PCE calculated numerically, which attests to the validity of the proposed approach. The proposed PCE estimation method is not limited to one selected RF–DC conversion circuit and can also be applied to other circuits and frequency bands. The comparison of the PCE obtained by means of the proposed approach and the measured one shows very good agreement between them. The PCE estimation error reaches as low as 0.37%, and the maximal estimation error is 32.65%.

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.

Compact Rectifiers With Ultra-wide Input Power Range Based on Nonlinear Impedance Characteristics of Schottky Diodes

Two high-efficiency radio-frequency (RF) rectifiers with extended input power range are proposed by taking the advantage of nonlinear impedance characteristics of diodes. Each rectifier consists of two subrectifiers that operates at high- and low-power levels, respectively. A nonlinear power division strategy is applied to the input power level without any power dividers or couplers. A λ/8 transmission line is introduced to compensate the imaginary part of diode impedance. A λ/4 transmission line is applied to reverse the diode impedance variation with respect to the input power. Two rectifiers operating at 2.45 GHz are fabricated and measured. Rectifier I shows a RF-dc power conversion efficiency exceeding 50% over an input power range of 23.3 dB (from 6.5 to 29.8 dBm), with maximum efficiency 74.5% at 27 dBm input power. Rectifier II shows an input power range exceeding 50% over 31 dB (-1 to 30 dBm) with maximum efficiency of 68.5% at 28 dBm.

A −20 dBm Passive UHF RFID Tag IC With MTP NVM in 0.13-μm Standard CMOS Process

A fully integrated passive ultrahigh-frequency (UHF) RF identification (RFID) tag integrated circuit (IC) based on Chinese UHF RFID standard (GJB 7377.1) is proposed. An optimized voltage multiplier with threshold compensation and leakage current suppression is designed to improve the RF-DC power conversion efficiency, which is more than 58% for different load current. A system clock constraint condition and proposed digital baseband (BB) algorithm instead of clock calibration is introduced to ensure correct demodulation of the forward link from reader to tag and back link frequency (BLF) tolerance from tag to reader. Moreover, a 2Kb multi-time programmable (MTP) non-volatile memory (NVM) in standard CMOS process without any additional masks and process modification is designed and implemented to significantly save the manufacture cost of the chip. The proposed RFID tag IC is fabricated using a $0.13-\mu \text{m}$ one-poly-five-metal (1P5M) standard CMOS process with an area of $620\times 660\,\,\mu \text{m}^{2}$ and a power consumption of 4.8 $\mu \text{W}$ and 11.5 $\mu \text{W}$ for reading and writing operations, respectively. The tag with antenna gain of 2 dBi shows successful reading detection at distances up to 17 m in the case of 4 W Equivalent Isotropically Radiated Power (EIRP) from reader.

A Wide Dynamic Range Rectifier Array Based on Automatic Input Power Distribution Technique

In this letter, a microwave rectifier array using an automatic input power distribution technique (AIPDT) is proposed to achieve high conversion efficiency over a wide dynamic input power range. The rectifier array employs two rectifier cells operating at low- and high-power levels, respectively, and utilizes AIPDT to distribute the RF input power between them according to the input power level. In this way, a high RF-dc power conversion efficiency (PCE) and a low reflection coefficient over a wide input power range are achieved. For validation, the proposed rectifier array at 2.4 GHz was designed, fabricated, and characterized. The experimental results show that the PCE maintains over 50% when the input power ranges from 2.2 to 26.5 dBm, and the input power range for PCE >30% is from −7 to 30 dBm. Besides, the reflection coefficient remains less than −10 dB over a 40-dB dynamic range (−10 to 30 dBm).

Compact High-Efficiency Broadband Rectifier With Multi-Stage-Transmission-Line Matching

This brief proposes a compact high-efficiency broadband microwave rectifier for energy harvesting. The proposed rectifier is designed to operate over a broad bandwidth spanning from 2 to 3 GHz and an input power dynamic range from 0 dBm to 10 dBm. In the proposed structure, a compact broadband low-loss matching network and a dc-pass filter with a broad stopband were designed, leading to a high conversion efficiency in a wide frequency range with compactness. For the matching network, low loss and compact size were achieved by strategically choosing and designing three transmission line segments. Moreover, the proposed dc-pass filter is compact and can effectively block broadband RF signal and its in-band high order harmonics. Theoretical analysis and simulations of the proposed structure were carried out. A prototype was fabricated, which demonstrates a broadband bandwidth of 41.5% (2.0–3.05 GHz) where the RF-dc power conversion efficiency is higher than 70% at an input power of 10 dBm. The measured efficiency remains over 45% within 1.9–3.05 GHz when the input power decreases to 0 dBm. The maximum measured efficiency is 75.8% at an input power of 14 dBm.

High-Efficient Rectifier With Extended Input Power Range Based on Self-Tuning Impedance Matching

In this letter, a microwave rectifier with a wide input power range is presented by proposing a self-tuning impedance matching (STIM). The STIM consists of a varactor reversely biased by the output voltage of the rectifier to compensate the variation of the input impedance caused by the input power, so that impedance matching is obtained over a wider input power range. For validation, the proposed rectifier at 2.4 GHz was designed and implemented. The experimental results show that the RF-dc power conversion efficiency maintains over 50% and 70% within the input power ranges of 2.5–25.5 dBm and 11–24.5 dBm, respectively. Compared with the counterpart without the STIM, an improvement of 7.2 dB in terms of the input power range when the reflection coefficient is less than −10 dB was successfully demonstrated.

One Octave Bandwidth Rectifier With a Frequency Selective Diode Array

In this paper, a high-efficiency rectifier with one octave bandwidth is proposed by proposing a diode array with a frequency selective topology. With the frequency selective topology, the low-and high-band rectifiers are combined together without extra matching circuit at the input leading to a high-efficiency broadband design. For validation, a prototype rectifier was fabricated and characterized. The measured results show that the RF-dc power conversion efficiency (PCE) maintains above 70% from 1.75 to 3.55 GHz at an input power of 10 dBm. The measured PCE remains more than 50% within 1.4–3.7 GHz and the $|S_{\textrm {11}}|$ is lower than −10 dB from 1.7 to 3.6 GHz.

High Efficiency Harmonic Harvester Rectenna for Energy Storage Application

This work presents harmonic harvester Rectenna integrated power management circuitry for improving RF-DC power conversion efficiency. The circuitry is developed for battery charging or energy storage application; resistance emulation method is used to realize a matching load resistance at output terminals. The proposed technique is useful for harvesting near maximum output power from the dual rectifiers (fundamental and harmonics) independently. Also, it delivers the combined maximal power to the energy storage cell. The power management module based on dual input buck-boost converter with simple open loop control is utilized.