Received RF Power Research Articles

Real-Time In-Process Evaluation of Spatter Area and Depth of Aluminium Surface in a Pulsed Laser Ablation Process Using Received Radio Frequency Power from Plasma Plumes

During the pulsed laser ablation of metals, as well as other materials, the development of a plasma plume close to the ablated surface leads to the emission of radio frequency energy. In this paper, we describe a process for analysing the received radio frequency power (RFP) for an aluminium (Al) surface ablation process in atmosphere using picosecond laser pulses at a wavelength of 1064 nm. The analysis of the RFP was carried out on two sets of experiments, where two parameters of the laser (repetition rate of laser (RRL) and power of laser (PL)) were varied while other parameters remained constant. In addition to the RFP measurement during the laser processing, the spatter area (SA), which is defined in this paper, and the depth of the ablated hole were measured post-process using a 3D microscope. It was observed that there is a direct relationship between (RFP)2 and SA. Accordingly, an appropriate RF calibration was performed, which leads to the definition of a quantity called the RF regulation % (RFR%). By comparing the RFR and PL/RRL variations, to which the laser beam fluence is proportional in these experiments, a diagnostic process (i.e., flowchart) for real-time depth evaluation was proposed and experimentally confirmed. This diagnostic process can indicate if the depth of the laser ablated crater is less than or exceeds a predetermined depth, which in this study was set to 15 µm. It is also demonstrated that the SA variation can be estimated in real-time by analysing the received RF power and, secondly, the depth of ablation can be measured in real time using a combination of information from the received RF power and laser parameters.

A Comprehensive Review on High-efficiency RF-DC Converter for Energy Harvesting Applications

The design of radiofrequency energy harvesting (RFRH) circuit for wearable devices, wireless sensor networks, and IoT applications can be classified mainly into radio frequency to direct current (RF-DC) converter, a transmitter and receiver antenna, an impedance matching network, and a storage device or a load. By scavenging RF energy from the ambient environment, this developing technology allows low-power wireless devices to be self-sustaining and environment friendly. To eliminate the need for batteries, RFEH technology has become a dependable and promising alternative for extending the lifetime of power-constrained wireless networks. This paper mainly focused on the input and output power, Power conversion efficiency (PCE), and sensitivity. Due to the weak and limited signal strength of received RF power, high-efficiency state-of-the-art RF energy harvesters must be designed to provide sufficient DC supply voltage to wireless networks. We provide in-depth information on the system’s parameters. Optimum efficiency and maximum output power are the main concerns of an RFEH system. Therefore, RF Energy harvesting system review, antenna design, impedance matching, and RF-DC converter are presented in this paper to provide a deep insight into the design of the RFEH system. This article may help in identifying new research in the field of RF Energy Harvesting.

Highly-Isolated RF Power and Information Receiving System Based on Dual-Band Dual-Circular-Polarized Shared-Aperture Antenna

A highly integrated RF power and information receiving system is proposed in this paper. The system consists of an antenna, a rectifier, and an information receiving module. The information receiving module acts as part of the dc load. To realize high integration, a dual-band, dual-circular-polarized shared- aperture antenna is implemented. The antenna consists of a left-circular-polarized element operating at 2.4-GHz band, and a high-gain, right-circular-polarized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> array operating at 5.8-GHz band. The lower-frequency antenna is for communication, while the higher-frequency one is for power transmission. All the elements share the same aperture, and the radiator of lower- frequency antenna acts as the reflector of higher-frequency elements. Accordingly, a class-F rectifier that matches the higher- frequency array is designed and verified, and a system-level demonstration is implemented. Owing to the high isolation on frequency splitting and polarization diversity, the baseband signal can be successfully demodulated under a 30-dB input-power-level difference at two frequency bands. The base-band information can be displayed by an ink screen. The received RF power can be effectively rectified and power the data-processing modules.

MODIFIED DESIGN STRUCTURE OF A METAMATERIAL MICROSTRIP PATCH ARRAY ANTENNA FOR RF ENERGY OPTIMIZATION

We propose a modified design of a microstrip patch array antenna for RF energy optimization over 2.45 GHz WLAN communication applications. Initially, a one-patch and a two-patch array antennas were developed and considered as the base for the construction of a four-patch array antenna in the GSM 1800 frequency range. The energy usage by the WLAN application model includes a radiofrequency WLAN supply, a wireless connection, the proposed array antenna, impedance network matching, a voltage rectifier and a storage circuit that achieves higher efficiency. The proposed antenna design is utilized to examine the distance effect on the received RF power and it achieves the maximum efficiency of 47 % at 2.45 GHz at a 1-meter distance from the source. Improved gain is acquired at the expense of a greater array-antenna size with a -26 dB return loss, proving that it is much more efficient than other structures. Moreover, when experimentally analysed with HFSS, it delivers sufficient energy over WLAN applications.

Sidelobe Suppression Beamforming Using Tapered Amplitude Distribution for a Microwave Power Transfer System with a Planar Array Antenna

This paper proposes a sidelobe suppression beamforming scheme using tapered amplitude distribution for microwave power transfer (MPT) with a two-dimensional planar array antenna (PAA). To overcome the undesirable effects of sidelobes, the magnitude of the sidelobes can be lowered by manipulating the amplitude distribution of the PAA. By analyzing the array factor of the PAA, we expressed the amplitude distribution as the product of two one-dimensional vectors. Moreover, we developed a method for obtaining these vectors from an expected sidelobe level (SLL). We used the Chebyshev taper, which has a higher directivity than other distributions given an expected SLL, for the amplitude distribution. To verify the proposed method, we designed and implemented a digital beamforming system with a 4 × 4 transmitter (Tx) array and a receiver (Rx) at 5.8 GHz. Compared with a uniform amplitude distribution, the proposed method reduced the SLL by 7.5 dB but the received RF power by only 0.6 dB. We compared the performance of the proposed MPT system with the results of previous studies.

Design of a Highly Efficient N-Stage Harmonic Terminated Voltage Multiplier for Wireless Power Transfer

This paper proposes a 5.8 GHz highly efficient rectifier design using harmonic termination for wireless power transfer. The diode used to convert the received RF power to DC is a non-linear device, and a harmonic component is generated, which causes performance degradation. Therefore, in this paper, we designed a band stop filter for harmonic termination and proposed the N-stage harmonic terminated voltage multiplier (N-stage HTVM). The number of stages N can be designed differently to operate with high efficiency at various input powers for the proposed rectifier. In the proposed rectifier circuit, mathematical analysis of output DC voltage, power loss of the diode, and the power conversion efficiency (PCE) were evaluated through voltage/current waveform analysis of the diode. The design method of the filter for terminating harmonics is presented. Furthermore, the change of PCE according to the increase in the number of stages was analyzed using the equivalent model of the proposed circuit and verified through measurement. The maximum PCE of one-stage HTVM was 68% when 18 dBm of input power was applied. The DC output voltage was measured to 11.6 V. When the RF input power was 25 dBm and the load was 1500 Ω, the maximum PCE of the two-stage HTVM was 71% and the maximum DC output voltage was measured as 15.8 V. The measured performance of three-stage HTVM had a PCE of 67% and DC output voltage of 19.8 V when the input power was 30 dBm.

RF energy harvesting using a compact rectenna with an antenna array at 2.45 GHz for IoT applications

Abstract This work addresses the design, fabrication, and implementation of an RF energy harvester 2.45 GHz using a compact rectenna. Our proposed rectenna focuses on development of an antenna array and rectifier circuit. The proposed rectenna is fabricated using FR4 substrate with its overall size of 12.24 cm × 18.17 cm with a thickness of 1.6 mm. The measured results show that a 10 dB bandwidth covering in 2374-2549 MHz (175 MHz) with center frequency 2415 MHz at S 11 of −18.2 dB. There is a bandwidth enhancement of 57.6% compared to the single antenna. Gaining of the antenna array is 6 dB that is double a single antenna gain. Spatial diversity technique in antenna array yields a bigger antenna gain thereby increasing the received power level. Experimental measurements are carried out that the rectenna is placed indoor (LOS) at 5 m and outdoor (NLOS) at 15 m. Furthermore, we also explore the rectifier circuit that to maximize the output voltage. The received RF power that transmitted from WiFi router is −55 dBm (0.15 nW/cm2) at 5 m and −59 dBm (0.06 nW/cm2) at 15 m, respectively. The output voltages are achieved that 1092.5 mV at a distance of 5 m (LOS) and 5.48 mV at a distance of 15 m (NLOS). The highest RF-DC conversion efficiency of our proposed rectenna reaches 77.6%. The rectenna potentially meets all requirements to power up the IoT applications.

Dual-Band Compact Rectenna for UHF and ISM Wireless Power Transfer Systems

A dual-band UHF/industrial, scientific and medical (ISM) compact rectenna with wideband UHF matching (855-935 MHz) covering all, EU, U.S., and Chinese UHF radio frequency identification (RFID), standards is presented. The proposed design consists of a compact single-port, dual-band antenna, a three-port dual-branch matching network, and two voltage doubler rectifiers implemented with Schottky diodes and terminated with a common 10 kΩ load. For each band, the measured RF-to-dc efficiency is around 60% for a -5 dBm unmodulated signal. The wideband behavior of the rectenna supports harvesting of multitone signals. The use of a six-tone signal increases the maximum RF-to-dc efficiency of the dual-band rectifier, from approximately 60% for a single-tone UHF signal (890 MHz) to 80% for a six-tone signal for a received RF power of -5 dBm in both cases. A signal generator is used to generate a six-tone signal of equally weighted and equally spaced (10 MHz separation) monochromatic tones, with a total bandwidth of 50 MHz. The measurement results demonstrate that the dc voltages rectified from the two separate RF signals are effectively superimposed on the load, providing a clear advantage compared to single-band rectennas. The single-layer, compact design with a size of 80×45 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with a high RF-to-dc efficiency, is an excellent candidate for wirelessly powered RFID tags.

Efficient Rectifier for Wireless Power Transmission Systems

This article describes a full-bridge rectifier and a receiving antenna array for operation within an innovative wireless power transmission (WPT) system. A high-power transmitter using circularly polarized free-space waves and based on a retrodirective antenna array technology is also employed to boost the overall received RF power at the input of the rectenna. To the best of our knowledge, the proposed rectifier circuit and active antenna configuration are the first demonstration of a high-power beam tracking system for WPT scenarios, being different from previously reported near-field coupling and other lower power harvesting schemes. The main focus of this article is the rectifier design, its bench-top measurements, and operation in such a retrodirective, self-tracking microwave system. A novel approach based on in-phase multitone input signals is also developed to improve rectifier efficiency. The rectifier size is 4.5 cm by 2 cm and can offer more than 86% and 75% RF-to-dc rectification efficiency at 27 dBm for an input signal at 1.7 and 2.4 GHz, respectively. This rectifier circuit component can also be employed in other communication applications or WPT systems, for example, to convert to dc received RF signals or power in the radiating near- and far-field in order to wirelessly charge the batteries of home electronics, such as smartphones, tablets, or Internet of Things (IoT) devices.

Simultaneous wireless information and power transfer in heterogeneous cellular networks with underlay D2D communication

Device to device (D2D) communication that provides high data rate proximity based direct communication between users, along with simultaneous wireless information and power transfer (SWIPT) that extracts energy from the received RF power, can achieve high energy and spectral efficiencies together with low latency communication. Heterogeneous networks, that employ efficient frequency reuse, provide high gains in the coverage and capacity of the cellular networks. SWIPT helps in converting the harmful interference, incurred by the frequency reuse of D2D tier underlaying the Hetnet, into energy that can be stored for the future. This work presents a resource allocation and power control scheme for SWIPT enabled underlay D2D networks, designed to improve the energy efficiency and the amount of energy harvested while ensuring the minimum required data rates for the users. Resource allocation is performed using a stable many-to-one matching game model inspired from Gale-Shapley algorithm. Two techniques of SWIPT, namely power splitting SWIPT and time splitting SWIPT, are considered and the resource allocation schemes are designed for both. Simulation results demonstrate the superior performance of the proposed algorithm compared to an existing work in single tier network with power splitting SWIPT. The work is extended to a typical 5G HetNet scenario, and extensive simulations are done to compare the performance of the two SWIPT architectures in the HetNet scenario.

Solar Energy Harvesting from Solar Power Satellite

Nowadays electronic circuits are widely used which in turn increased the demand for power in future. Solar energy, which is non-renewable energy can be used. But only 1/100th part of total solar energy is received on the earth. There are many satellites which are being used for many applications. A Satellite with a specific application for generating power from solar energy is proposed which can be used to transmit the stored energy to the earth station in the form of microwaves (RF signal). This kind of satellites are called as solar power satellites (SPS) and these are placed in LEO/MEO so that they would be able to face the sun 99% of the time. These Solar Power Satellites collect energy from the sun and convert them to DC power and stores in a battery reserve. This DC power from the battery reserve can be converted into RF energy of required frequency using a device called Magnetron and the converted power is transmitted to the earth station antenna which is coupled to an array of Rectifier circuit so that the received RF power is then converted to DC energy. The motive behind the Solar power satellites is environmental pollution due to carbon dioxide emissions from thermal power plants and global warming.

A Dual-Mode RF Power Harvesting System With an On-Chip Coil in 180-nm SOI CMOS for Millimeter-Sized Biomedical Implants

In this paper, we present a dual-mode power harvesting system for millimeter-sized biomedical implants that are immune to the variation of wireless link parameters and loading. The design includes a multistage full-wave voltage rectifier, a power management unit, and a low dropout voltage regulator. Depending on the received RF power level and the required power by the load, power delivery is conducted in a continuous or duty-cycled mode. The system is fabricated in 180-nm silicon on insulator (SOI) CMOS technology with an active area of 2.56 mm2 including an on-chip coil. RF power is transferred to the chip from a $2\times 2$ cm2 coil through 10 mm of air at 434 MHz. The efficiency of the designed wireless link, which is the power transfer efficiency from the external coil to the on-chip coil, reaches up to 0.68% (−21.7 dB) at 10-mm separation through air. Keeping the transmitted RF power below 24 dBm, the system can provide a 1.08-V dc voltage for resistive loads larger than 20 $\text{k}\Omega $ continuously over time. When the harvested power is not enough to drive the load continuously, the system operates in the duty-cycled mode. Measurement results show that the system can drive a 1- $\text{k}\Omega $ load in the duty-cycled mode when the transmitted power level is 15 dBm.

Multipath Scintillation Statistics Obtained From RF Measurements Near the Earth’s Surface

We report on 1.78 GHz RF near-horizontal multipath propagation measurements, in both California and New Hampshire, taken over various links where there is no direct clear line of sight. This report deals specifically with the time-dependent fluctuations of the RF signal, which were observed in the time history of the received signals at various sites. We characterize and discuss the general statistical features of multipath scintillation and discuss the differences between the orders of magnitude enhanced scintillation index (SI) (defined as the variance of the received RF power divided by the square of the mean of the RF power) observed for multipath and that obtained for clear line-of-sight paths. To the best of our knowledge, for the first time reported in the literature, we have observed and statistically quantified multipath scintillation conditions where the SI is both of the order and greater than unity. The observed probability distributions of multipath scintillation are compared with several candidate distributions, and the Nakagami-m and the gamma–gamma distribution emerge as the preferred distributions for weak-to-moderate and moderate-to-strong scintillation conditions, respectively. The observed level crossing statistics of the multipath signal is compared with theory, where good agreement is obtained for all cases of concern.

The design of radio frequency energy harvesting and radio frequency-based wireless power transfer system for battery-less self-sustaining applications

In this paper, the RF energy harvesting system and RF-based wireless power transfer system are proposed and designed for battery-less self-sustaining application. For energy harvesting, the designed antenna array improves the received RF power effectively and also can harvest RF energy in multi-frequency bands. For wireless power transfer, the proposed helical antenna realizes the system design in miniaturization. Subsequently, the T shape LC matching network are designed between the antenna and the rectifying circuit to obtain more power transmission. The measured results show that the proposed Wi-Fi rectifier and 433 MHz rectifier offer a maximum conversion efficiency of 66.8% and 76% in case of the input power is −3 dBm and 0 dBm, respectively. Finally, the performance of the RF-based wireless power transfer system and RF energy harvesting system are attested by experimentally measurement, the measured results indicate that these systems can be used to power electronic.

Design of a Bidirectional Antenna inside a Vehicle and Measurement of Power Link for Vehicle-to-Vehicle Communication at 5.8 GHz

Communication between moving vehicles is very important for safety. In this paper, a bidirectional antenna that can be installed inside a vehicle is proposed and tested in a real vehicular environment at 5.8 GHz. The forward link and backward link seated by two persons and three persons were compared in terms of received RF power and the peak-to-average power ratio (PAR). It was found that, even with three persons, the power link fulfilled the communication requirements using the proposed antenna.

Matching Network Elimination in Broadband Rectennas for High-Efficiency Wireless Power Transfer and Energy Harvesting

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.

A 2.45-GHz Energy-Autonomous Wireless Power Relay Node

This paper describes the design and experimental characterization of a battery-less bidirectional 2.45-GHz circuit operating in oscillator mode as a wireless power transmitter or in rectifier mode as an energy harvester, with a measured efficiency greater than 50% in both operating states. The dc voltage harvested in rectifier mode provides the drain bias for the oscillator. The FET-gate self-bias mechanism is exploited in both functionalities, thus eliminating external gate bias. Bi-directionality is based on the time-reversal properties of a transistor oscillator. Energy autonomy is possible at received RF power levels as low as ${-}4$ dBm, by means of a bias-assisting feedback loop, consisting of a single matched low-power diode in shunt configuration. A hybrid prototype is demonstrated with the ability to operate as an energy-autonomous power relay node by switching between transmit and receive power modes.

A Passive Wake-Up Circuit for Event Driven Wireless Sensor Network Applications

The lifetime of battery operated sensor nodes is a critical issue. In the case of event driven applications where events take place infrequently, most of the energy is wasted in idle listening by the sensor nodes. The sensor node in continuous idle listening mode drains the batteries approximately in two days. This paper describes a passive wake-up circuit (PWUC), designed for 2.45 GHz ISM band, to suppress the idle listening by waking-up the sensor nodes asynchronously. The proposed PWUC consists of receiving antenna, RF rectifier and matching network. The impedance and number of stages of the RF rectifier have been optimized to yield the maximum sensitivity and conversion efficiency. The lumped component based external matching network has also been proposed to boost-up the received input voltage through antenna. The purpose behind the use of external matching network is to reduce the fabrication cost of RF rectifier. Very few realizations of passive wake-up circuits are reported in the literature and none of them presents the sensitivity and global conversion efficiency above -11 dBm and 30–40%, respectively. The designed PWUC gives an output voltage of 1.8 V for a -23 dBm received RF power and a 1 MΩ load, which translates to 69% global power conversion efficiency (GPCE). RF rectifier is designed in UMC 180-nm 1P6M CMOS standard process.

Power fading elimination and linearization for a dispersive optical true time delay using carrier phase shifting and optical sideband processing

A dispersive optical true time delay (OTTD) free from received RF power fading effect and third-order intermodulation distortion (IMD3) is proposed and investigated. In the transmitter, the carrier phase shifting (CPS) technique with optical double-sideband (ODSB) signal is used to eliminate the RF power fading by employing an integrated modulator. The output of the integrated modulator is an ODSB signal that the optical carrier (OC) can be shifted separately. In the receiver, the optical sideband processing technique is used to eliminate the IMD3 by employing a compensator. The two major origins of the IMD3 have identical intensity and opposite phase through the modulation of the compensator. Simulation results show that, the received RF power has no fading effect when the phase of carrier is optimized, and the IMD3 is efficiently suppressed and the fundamental to IMD3 ratio (FIR) can be improved more than 45dB when the optical sideband processing technique is used.

2.4-GHz High-Efficiency Rectenna Using an In-Phase Partially Reflective Surface and High-Order Harmonic Reject Bandpass Filter

A high-efficiency rectenna is designed at 2.4 GHz. In general, a rectenna consists of an antenna, a band-pass filter, a rectifying diode, and a low-pass filter. In this article, to increase transmission efficiency, a high-directional antenna is developed using partially reflective surfaces. In addition, the harmonic rejecting band-pass filter is designed to suppress the second and third harmonic signal from the nonlinear diode, resulting in high conversion efficiency. It is experimentally demonstrated that the proposed rectenna achieves an RF to DC conversion efficiency of 72.17% when the received RF power is 63.09 mW at 2.4 GHz.