RF Harvesting Research Articles

Fully Polarized Wideband Omnidirectional RF Harvester with Highly Efficient DC Power Combination

In this work, an omnidirectional RF energy harvester with wideband coverage (1.5–2.7 GHz), all-polarization, and high-efficiency DC combining is proposed. The harvester integrates six microstrip rectenna elements with varying directions and polarizations. The harvester strategically combines six microstrip rectenna elements with different orientations and polarizations to enhance the stability of omnidirectional energy harvesting. The rectifier employs impedance compression matching techniques, incorporating open-circuited and short-circuited transmission lines to achieve a compact, broadband rectification. Experimental results show that the rectifier maintains an RF-to-DC conversion efficiency exceeding 50% within a bandwidth of 1.5 GHz to 2.7 GHz at an input power of 0 dBm, achieving a maximum efficiency of 62%. The maximum DC-combining efficiency of the rectifier array reaches 92%. These findings indicate that the harvester performs effectively with RF energy of all polarizations from various directions.

Hybridization of Cockcroft-Walton and Dickson Voltage Multipliers for Maximum Output Through Effective Frequency Dedication in Harvesting Radio Frequency Energy

Objective: This study investigates solutions to the challenges of limited RF energy harvesting by designing a hybridized voltage multiplier system aimed at optimizing output across a wide frequency range. Theoretical Framework: The research centers on the principles and comparative efficiencies of the Cockcroft-Walton and Dickson voltage multipliers, known for their applications in RF energy harvesting. These multipliers’ performance was analyzed theoretically to guide a hybrid design that could adaptively respond to input frequency variations. Method: Voltage multipliers were designed and simulated in Multisim, with further analysis in MATLAB. Both the Cockcroft-Walton and Dickson voltage multipliers were subjected to a constant input of 1V across frequencies from 50 Hz to 5 GHz to assess their respective efficiencies. Subsequently, a hybrid voltage multiplier system was developed, combining an 8-stage Cockcroft-Walton and an 8-stage Dickson multiplier. A fast Fourier transform (FFT) frequency-selective algorithm, implemented in MATLAB, dynamically directed input voltages to the optimal multiplier based on frequency. Results and Discussion: Results showed that the Dickson multiplier excelled in the lower frequency range (50 Hz to 1 MHz), achieving a maximum output of 14.763V at 5 kHz and 10 kHz. In contrast, the Cockcroft-Walton multiplier was more effective in the higher frequency range (1 MHz to 5 GHz), reaching a peak output of 6.671V at 5 GHz. The hybrid system demonstrated efficient, frequency-dependent voltage multiplication and aligned well with anticipated performance metrics, suggesting an improvement in RF energy harvesting across the tested frequency range. Research Implications: This work contributes to the field of RF energy harvesting by introducing a frequency-adaptive system that enhances voltage output through targeted frequency routing. The results underscore the potential for hybrid designs to overcome limitations associated with individual voltage multipliers, presenting a versatile approach to harvesting RF energy effectively across broad frequency spectra. Originality/Value: By implementing a hybrid approach with a frequency-selective algorithm, this study offers an innovative solution for frequency-dependent RF energy harvesting. The findings provide a foundation for future research into adaptable energy harvesting systems that optimize voltage output across diverse frequencies, with practical implications for RF-powered devices and wireless energy transfer applications.

Quad-Band Rectifier Circuit Design for IoT Applications

In this work, a novel quad-band rectifier circuit is introduced for RF energy harvesting and Internet of Things (IoT) applications. The proposed rectifier operates in the Wi-Fi frequency band and can supply low-power sensors and systems used in IoT services. The circuit operates at 2.4, 3.5, 5, and 5.8 GHz. The proposed RF-to-DC rectifier is designed based on Delon theory and Greinacher topology on an RT/Duroid 5880 substrate. The results show that our proposed circuit can harvest RF energy from the environment, providing maximum power conversion efficiency (PCE) greater than 81% when the output load is 0.511 kΩ and the input power is 12 dBm. In this work, we provide a comprehensive design framework for an affordable RF-to-DC rectifier. Our circuit performs better than similar designs in the literature. This rectifier could be integrated into an IoT node to harvest RF energy, thereby proving a green energy source. The IoT node can operate at various frequencies.

Ambient nano RF-Energy driven self-powered wearable multimodal real-time health monitoring

As the trend of population aging intensifies, the demand for continuous and efficient health monitoring for solitary elderly individuals and those with limited self-care capabilities is growing. Traditional wearable health monitoring devices primarily rely on battery power, which not only incurs high maintenance costs but also risks interruption of monitoring due to battery depletion. To address these issues, this paper introduces a self-powered flexible wearable monitoring device utilizing far-field Radio Frequency Energy Harvesting (RFEH) technology. This device powers integrated sensors and Bluetooth by harvesting RF energy from ambient Wi-Fi and other wireless signals, enabling real-time monitoring of the wearer's physical behaviour and health status with immediate feedback via mobile terminals. Under conditions of 100 cm distance and a power intensity of 0.8 dBm, the system can charge a 220 μF capacitor to 4.12 V within just 23.24 seconds, ensuring stable operation of the device. Moreover, the monitoring device is equipped with a low-power wireless sensor system capable of sampling up to 100 Hz, which accurately and promptly tracks and analyzes key health indicators such as walking, physiological activities, and respiratory status. This technology provides a reliable health monitoring solution for elderly individuals living alone and those with difficulties in self-care, significantly enhancing the effectiveness of remote medical services, improving their quality of life, and reducing the occurrence of emergency medical events. This research not only advances wearable device technology but also paves new paths for health management in an aging society.

Design and implementation of a hybrid piezoelectric, radio frequency, solar, and thermal energy‐harvesting system for portable medical devices

AbstractToday, energy harvesting has developed into a technique from which various aspects are still hidden. By extracting energies from the environment and even the human body, and converting them into electrical energy, we can supply power to low‐consumption electronic devices. Energy harvesting works by inhibiting small amounts of ambient energies; otherwise, it is wasted in other forms such as heat, vibration, and light. In this paper, we aim to eliminate or minimize the dependence of portable electronic devices to the batteries, which have limited life times, service costs, handling, and environmental problems. This is accomplished via incorporating the hybrid energy‐harvesting techniques and designed to power (bio)medical devices in order to measure vital signs. In this circuit, by simultaneously harvesting RF, light, thermal, and solar (natural and artificial) energies, we were able to increase the reliability of continuous supply of electrical energy in energy‐harvesting systems by generating and storing maximum power from the environment. Supercapacitors are used as the energy storage elements so that there is no energy waste, and each system is constantly storing the electrical energy with the aid of a diode block. In addition, with the help of supercapacitors, this device is able to transmit a maximum of 420 mW to the load and the total efficiency is equal to 74%.

A Battery-Free Crystal-Less BLE Transmitter Tag With Fully-Integrated RF Harvesting and Multitag TDD and FDD Broadcasting

A Battery-Free Crystal-Less BLE Transmitter Tag With Fully-Integrated RF Harvesting and Multitag TDD and FDD Broadcasting

A Study on Electrical Performance of SiC-based Self-switching Diode (SSD) as a High Voltage High Power Device

The Self-switching Diodes (SSDs) have been primarily researched and used in low-power device applications for RF detection and harvesting applications. In this paper, we explore the potential of SSDs in high-voltage applications with the usage of Silicon Carbide (SiC) as substrate materials which offers improved efficiency and reduced energy consumption. Optimization in terms of the variation in the interface charges, metal work function, and doping concentration values has been performed by means of a 2D TCAD device simulator. The results showed that the SSD can block up to 600 V of voltage with an optimum interface charge value of 1013 cm-2, making them suitable for higher voltage applications. Furthermore, it also found that the work function of the metal contact affected the forward voltage value, impacting the current flow in the device. Variation in doping concentrations also resulted in higher breakdown voltages and significantly increased forward current, leading to an increased power rating of 27 kW. In conclusion, the usage of 4H-SiC-based SSDs shows a usable potential for high-voltage applications with optimized parameters. The results from this research can facilitate the implementation of SSD in the development of high-power semiconductor devices for various industrial applications.

Computation Offloading and Beamforming Optimization for Energy Minimization in Wireless-Powered IRS-Assisted MEC

Intelligent reflecting surface (IRS) has been recently exploited as a symbiotic radio (SR) technology to improve energy-and spectral-efficiencies in wireless systems. In this paper, we consider a symbiotic IRS-assisted mobile edge computing (MEC) system that allows edge users to first harvest RF power from a hybrid access point (HAP) and then offload its computational workload to the MEC server associated with the HAP. We aim to minimize the HAP’s energy consumption by jointly optimizing the users’ offloading schemes, the HAP’s active beamforming, and the IRS’s passive beamforming strategies. We propose an optimization-driven hierarchical deep deterministic policy gradient (OH-DDPG) framework to decompose the energy minimization problem into the optimization and the learning sub-problems, respectively. The outer-loop DDPG learning method adapts the IRS’s passive beamforming strategy, while the inner-loop optimization deals with the other control variables with reduced dimensionality. Moreover, to improve the learning efficiency, we extend OH-DDPG to the multi-agent scenario. In particular, the HAP first estimates the users’ offloading strategy by the inner-loop optimization and shares it with all user agents. Then, each user agent refines its offloading decision using the DDPG algorithm independently. This can avoid signaling overhead among users and improve the multi-user learning efficiency. Simulation results show that the proposed OH-DDPG and the multi-user extension can achieve significant performance gains compared to the conventional model-free learning algorithms.

A multiband SSr diode RF rectifier with an improved frequency ratio for biomedical wireless applications

This paper described a four-band implantable RF rectifier with simplified circuit complexity. Each RF-rectifier cell is sequentially matched to the four operational frequencies to accomplish the proposed design. The proposed RF rectifier can harvest RF signals at 1.830, 2.100, and white space Wi-Fi bands between 2.38 to 2.68 GHz, respectively. At 2.100 GHz, the proposed RF harvester achieved a maximum (radio frequency direct current) RF-to-DC power conversion efficiency (PCE) of 73.00% and an output DC voltage V_{DC} of 1.61 V for an RF power of 2 dBm. The outdoor performance of the rectenna shows a V_{DC} of 0.440 V and drives a low-power bq25504-674 evaluation module (EVM) at 1.362 V. The dimension of the RF-rectifier on the FR-4 PCB board is 0.27lambda _{g}times 0.29lambda _{g}. The RF-rectifier demonstrates the capacity to effectively utilize the frequency domain by employing multi-band operation and exhibiting a good impedance bandwidth through a sequential matching technique. Thus, by effectively controlling the rectenna’s ambient performance, the proposed design holds the potential for powering a range of low-power biomedical implantable devices. (BIDs).

Performance analysis and optimization of multiple IIoT devices radio frequency energy harvesting NOMA mobile edge computing networks

In this day and age, the Industrial Internet of Things (IIoT) has been considered to revolutionize industrial manufacturing by capturing and accessing massive data sources with incredible speed and efficiency than before. Combined with it, Mobile Edge Computing (MEC) is a comprehensive Digital Transformation tendency to solve the problems Cloud computing faces. However, the fundamental challenges of energy and latency make deploying IIoT MEC networks difficult. Accordingly, this paper considers the efficient design of time allocation for successful computation probability (SCP) maximization for multiple energy-constrained mobile devices (MD) and multiple antennas access point (AP) in uplink radio frequency energy harvesting (RF EH) non-orthogonal multiple access (NOMA) IIoT network. Specifically, multiple MDs need to receive the energy and compute support of a MEC server placed in a multiple antenna wireless AP to complete the task immediately. Accordingly, a four-phase communication protocol is proposed to ensure system performance. The system follows the cluster head (CH) scheme based on the channel state information (CSI) to harvest RF energy from the AP. To ensure the highest system performance, we propose two algorithms for determining the optimal EH time for two CHs: SCPM-GSS and SCPM-GA. In addition, we derive the closed-form expressions for the SCP of the system and each CH. Monte Carlo simulations are used to verify the results of the analysis. The numerical results demonstrate the effects of crucial system parameters of our proposed NOMA scheme with those of conventional orthogonal multiple access (OMA) schemes. Furthermore, the proposed optimization algorithms allow the system to avoid outages like the random parameters setting approach and improve the SCP by 3 to 30% compared to the fixed parameters set when the transmit power is low and medium.

Fabrication and optimization of passive flexible ammonia sensor for aquatic supply chain monitoring based on adaptive parameter adjustment artificial neural network (APA-ANN)

Traditional rigid sensors and imperfect calibration methods are difficult to meet the demand of food quality and safety monitoring in aquatic products supply chain, which requires redesign and optimization. This paper designed and optimized a passive flexible ammonia sensor based on adaptive parameter adjustment artificial neural network (APA-ANN) for aquatic monitoring. The proposed sensor could acquire ammonia information and transmit to the wireless reader by radio frequency identification (RFID) with 13.56 MHz. Through the energy harvesting module, which has a harvesting efficiency of about 63.07%, the passive flexible ammonia sensor could harvest RF energy and supply continuous power for the normal operation of sensor without battery. Oysters and abalone were selected for the sensor output calibration and verification in waterless and watery environments, respectively. The sensor output had a good fitting effect in the sensing range (R2 > 0.99932) and the APA-ANN could improve and optimize the sensor output accuracy under the multiple interference and the impact of cross-sensitivity. The final result showed that all regression coefficients were>0.997 and the accuracy of the optimization model was higher than 89.5%, which proved the applicability of the passive flexible ammonia sensor and provided a optimization method for sustainable monitoring in agriculture.

Energizing Emergency Exit Signs with Wireless Energy Transfer

Emergency exit lights in public buildings are necessary for safety and evacuation. International safety standards require such lighting in many public places, like airports, schools, malls, hospitals, and other spaces, to prevent human casualties in emergencies. Emergency exit lights have become an essential part of casualty reduction projects. They can pose several application problems, including fire safety concerns. The issue of providing a safe way and operating emergency exit lights along one side of a long path arises during an emergency. Many studies in this field consider the case in which emergency exit lights’ battery or main power fails. Power failures in dangerous situations such as fires or terrorist attacks make it difficult for people to escape. The lighting in open areas and stairwells during an emergency should be at least 2 lux. This work proposes an innovative technique for wirelessly powering emergency lights using microwave energy. Specifically, the study designed and fabricated a new wirelessly powered emergency lighting prototype. This prototype’s wireless power transfer (WPT) base comprises an RF/DC converter circuit and an RF microwave transmitter station. The device can harvest RF microwave energy to energize the emergency light. This research aimed to develop a compact device that captures maximum RF strength to power emergency lights. As a prototype, the proposed device was designed to provide sufficient microwave energy to power an emergency light at 3 W over a 62 m distance.

Wideband RF rectifier circuit for low-powered IoT wireless sensor nodes

This paper proposed a broadband RF-rectifier circuit. The design is matched through a combination of a wideband resistance compression network (RCN) with a modified short-stub matching network (MN) for Terminal-1 (T1) and a Π-MN for Terminal-2 (T2). The RCN incorporates the two terminals using a transmission line (TL) of 50 Ω. The TL-MN parameters are analyzed and evaluated in the design using closed-form equations. The HSMS2850-based prototype model demonstrates that the peak RF-to-DC power conversion efficiencies (PCE) realized at 3 dBm input power (Pin) are (76.92%, 70.53%, 69.75%, 67.54%) for (1.82, 2.13, 2.45, and 2.67 GHz), respectively. The prototype is terminated with a 1 kΩ load terminal (RL) and attained a maximum average output DC voltage VDC of 2.52 V. The model is tested in the ambient environment and achieved a T1(T2) VDC of 0.350(0.230) V. This approach also mitigated the impact of impedance variations imposed by diode non-linearity. The RF harvester drive a low-power evaluation module (EVM) for T1(T2) at 0.600(0.470) V.

Design of high-efficiency circularly polarized wideband energy harvesting rectenna using characteristic mode analysis

This paper presents a compact wideband rectifier system for wireless energy harvesting. The presented rectifier system is completed in two stages. In the first stage, a crescent-shaped wideband circularly polarized antenna (CPA) is designed to receive and transmit RF signals using characteristic mode analysis (CMA). And the CPA consists of a monopole antenna at the top and a slot antenna at the bottom, which control the higher and lower operating bands, respectively. In the second stage, a wideband rectifier is designed using a HSMS-2860 Schottky diode and a three-stage matching network. The HSMS-2860 Schottky diodes improve rectification efficiency at medium-power density, and the three-stage matching network effectively increase the operating bandwidth, filter out the output RF signal, and cancel out and stabilizes the impedance. To validate the proposed rectifier system, a crescent-shaped CP receiving antenna and a rectifier operating in C-band are fabricated, and the rectification performance is measured. The measurement results indicate that the proposed rectifier system harvests RF signals on the broadside and backside of the CPA over a wide input power range (8–13 dBm input power).

Multiband Microstrip Rectenna Using ZnO-Based Planar Schottky Diode for RF Energy Harvesting Applications.

This paper presents a single-substrate microstrip rectenna for dedicated radio frequency energy harvesting applications. The proposed configuration of the rectenna circuit is composed of a clipart moon-shaped cut in order to improve the antenna impedance bandwidth. The curvature of the ground plane is modified with a simple U-shaped slot etched into it to improve the antenna bandwidth by changing the current distribution; therefore, this affects the inductance and capacitance embedded into the ground plane. The linear polarized ultra-wide bandwidth (UWB) antenna is achieved by using 50 Ω microstrip line and build on Roger 3003 substrate with an area of 32 × 31 mm2. The operating bandwidth of the proposed UWB antenna extended from 3 GHz to 25 GHz at -6 dB reflection coefficient (VSWR ≤ 3) and extended from both 3.5 to 12 GHz, from 16 up to 22 GHz at -10 dB impedance bandwidth (VSWR ≤ 2). This was used to harvest RF energy from most of the wireless communication bands. In addition, the proposed antenna integrates with the rectifier circuit to create the rectenna system. Moreover, to implement the shunt half-wave rectifier (SHWR) circuit, a planar Ag/ZnO Schottky diode uses a diode area of 1 × 1 mm2. The proposed diode is investigated and designed, and its S-parameter is measured for use in the circuit rectifier design. The proposed rectifier has a total area of 40 × 9 mm2 and operates at different resonant frequencies, namely 3.5 GHz, 6 GHz, 8 GHz, 10 GHz and 18 GHz, with a good agreement between simulation and measurement. The maximum measured output DC voltage of the rectenna circuit is 600 mV with a maximum measured efficiency of 25% at 3.5 GHz, with an input power level of 0 dBm at a rectifier load of 300 Ω.

UWB Microstrip Patch Antenna Design for Energy Harvesting Applications

RF energy harvesting systems, which are the receiver part of Wireless Power Transfer (WPT), have gained significant development in recent years. For maximum energy acquisition over a wide frequency range, such as to provide power to small handheld devices like cell phones, tablets, smart watches, and other smart devices, wideband and compact antennas are desired. RF systems are expected to cover different frequency bands, such as 2.4 GHz, 5.1 GHz, 5.8 GHz (Bluetooth/Wi-Fi), 2.3 GHz, 2.5 GHz, 3.5 GHz, 5 GHz (WiMAX), for energy harvesting. For such an RF harvesting system, the antenna is desired to have a wide bandwidth, good gain, and an omnidirectional radiation pattern. Energy harvesting devices refer to designs that integrate production and storage. For instance, radio frequency energy sources contain a large amount of electromagnetic energy in the environment, and with RF energy harvesting systems, a portion of this electromagnetic energy can be collected and converted into usable DC voltage. Microstrip patch antennas are very good alternatives for energy harvesting applications because they are cost-effective, compact in size and weight, flat in structure, and highly repeatable. This paper presents a microstrip patch antenna with a bandwidth of 3.9 GHz in the 3.4 to 7.3 GHz range for UWB applications. The antenna design has a gain value of 3.28dBi at the numerically calculated resonance frequency of 4.9 GHz and generally covers frequencies used for electronic device communication such as Wi-Fi 5 GHz and WiMAX. The proposed antenna design has gain values that are allowed to be used for RF energy harvesting applications.

A REVIEW OF INTEGRATED RADIO FREQUENCY ENERGY HARVESTING AND COGNITIVE RADIO FOR THE INTERNET OF THINGS

In recent decades, there has been significant growth in interconnected communication devices, with the Internet of Things (IoT) being one of the most intensively developed wireless communication appliances. This concept can be implemented in several areas, including smart cities, transportation, telemedicine, agriculture, and wearable applications. However, this increase in connectivity demand can lead to spectrum shortages in the future. In addition, in the development of future green communications, it is crucial to incorporate self-powered systems using energy harvesting technologies. In this review, it is shown that the integration of cognitive radio and radio frequency energy harvesting into IoT development can address the spectrum shortages and energy issues mentioned earlier. The findings indicate that the operating model works based on the slotted approach and state consideration, and the system’s performance metric can be optimised by adjusting parameters such as harvesting time, sensing time, transmit time, transmission power, interference level, and others. This review provides a comparative summary of several focus domains, such as RF harvesting, spectrum sensing and utilisation, operating models, and some open research issues for further work.

Customizable and upgradable design triple-band dual circular polarization rectenna for ambient RF energy harvesting

A Customizable and upgradable design of triple-band dual circular polarization (CP) rectenna is presented for ambient RF energy harvesting of available frequency bands (i.e., 1800, 2.15, 2.42) efficiently. A broadband dual CP receiving antenna is proposed with a broadband impedance matching bandwidth of 123% from 1 to 4.2 GHZ and axial-ratio (AR) bandwidth of 75% from 1.45 to 3.06 GHz with a maximum gain of 5.54 dBi to cover the selected frequency bands. Besides, the proposed triple-band rectifier with a multi-stub impedance matching network is feasible for RF harvesting with the new design method, and the non-dependence of the resonance frequencies on the distance between the stubs, the rectifier can be easily adjusted for other frequencies. The proposed rectenna’s measurement results show that the generated average dc output voltage and conversion efficiency are improved to 0.8 V and 60%, respectively, at a low RF input power density of −2 dBm for a load resistance of 1.5 kΩ.

Г-Shaped Asymmetrical Monopole Antenna on Truncated DGS For Multiband RF Energy Harvesting Applications

In today's world, through the advancement of technology, wireless communication has become an integral part of our lives with the utilization of versatile electronic devices such as cell phones, tablets, and computers that contain wireless communication modules. The idea of utilizing different frequencies and power of RF signals in the environment has led to the concept of harvesting RF signals to produce DC output voltage. In this paper, a printed multiband monopole antenna is presented. The proposed antenna is composed of two Г-shaped asymmetrically positioned feeding lines which are located on slotted truncated ground plane with three stubs loaded on both ground plane sides. The antenna design covers the frequently used frequencies for electronic device communication, such as GSM 1800, UMTS 2100, WLAN 2450 and LTE 2600 With the numerically computed gain values of 3.89dBi at 1.8GHz, 4.51dBi at 2.1GHz, 5.02dBi at 2.45GHz, and 5.03dBi at 2.6GHz, respectively. The proposed antenna design has permissible gain values to be used for RF energy harvesting applications.

Radio-Frequency Energy Harvesting Using Rapid 3D Plastronics Protoyping Approach: A Case Study

Harvesting of ambient radio-frequency energy is largely covered in the literature. The RF energy harvester is considered most of the time as a standalone board. There is an interest to add the RF harvesting function on an already-designed object. Polymer objects are considered here, manufactured through an additive process and the paper focuses on the rapid prototyping of the harvester using a plastronic approach. An array of four antennas is considered for circular polarization with high self-isolation. The RF circuit is obtained using an electroless copper metallization of the surface of a 3D substrate fabricated using stereolithography printing. The RF properties of the polymer resin are not optimal; thus, the interest of this work is to investigate the potential capabilities of such an implementation, particularly in terms of freedom of 3D design and ease of fabrication. The electromagnetic properties of the substrate are characterized over a band of 0.5–2.5 GHz applying the two-transmission-line method. A circular polarization antenna is experimented as a rapid prototyping vehicle and yields a gain of 1.26 dB. A lab-scale prototype of the rectifier and power management unit are experimented with discrete components. The cold start-up circuit accepts a minimum voltage of 180 mV. The main DC/DC converter operates under 1.4 V but is able to compensate losses for an input DC voltage as low as 100 mV (10 μW). The rectifier alone is capable of 3.5% efficiency at −30 dBm input RF power. The global system of circularly polarized antenna, rectifier, and voltage conversion features a global experimental efficiency of 14.7% at an input power of −13.5 dBm. The possible application of such results is discussed.