Wireless Power Harvesting Research Articles

A Self-Adaptive Dual-ILRO Clock-Recovery Technique for Two-Tone Battery-Free Crystal-Free Neural-Recording SoC.

Wireless implantable devices are widely used in medical treatment, which should meet clinical constraints such as longevity, miniaturization, and reliable communication. Wireless power transfer (WPT) can eliminate the battery to reduce system size and prolong device life, while it's challenging to generate a reliable clock without a crystal. In this work, we propose a self-adaptive dual-injection-locked-ring-oscillator (dual-ILRO) clock-recovery technique based on two-tone WPT and integrate it into a battery-free neural-recording SoC. The 2[Formula: see text]-order inter-modulation (IM2) component of the two WPT tones is extracted as a low-frequency reference for battery-free SoC, and the proposed self-adaptive dual-ILRO technique extends the lock range to ensure an anti-interference PVT-robust clock generation. The neural-recording SoC includes a low-noise signal acquisition unit, a power management unit, and a backscatter circuit to perform neural signal recording, wireless power harvesting, and neural data transmission. Benefiting from the 6.4 μW low power of the clock recovery circuit, the overall SoC power is cut down to 49.8 μW. In addition, the proposed clock-recovery technique enables both signal acquisition and uplink communication to perform as well as that synchronized by an ideal clock, i.e., an effective number of 9.6 bits and a bit error rate (BER) less than 4.8 × 10-7 in chip measurement. The SoC takes a die area of 2.05 mm 2, and an animal test is conducted in a Sprague-Dawley rat to validate the wireless neural-recording performance, compared to a crystal-synchronized commercial chip.

Fascicle-Selective Ultrasound-Powered Bidirectional Wireless Peripheral Nerve Interface IC.

This paper presents an innovative, minimally invasive, battery-free, wireless, peripheral nervous system (PNS) neural interface, which seamlessly integrates a millimeter-scale, fascicle-selective integrated circuit (IC) with extraneural recording and stimulating channels. The system also incorporates a wearable interrogator equipped with integrated machine-learning capabilities. This PNS interface is specifically tailored for adaptive neuromodulation therapy, targeting individuals with paralysis, amputation, or chronic medical conditions. By employing a neural pathway classifier and temporal interference stimulation, the proposed interface achieves precise deep fascicle selectivity for recording and stimulation without the need for nerve penetration or compression. Ultrasonic energy harvesters facilitate wireless power harvesting and data reception, enhancing the usability of the system. Key circuit performance metrics encompass a 2.2 μVrms input-referred noise, 14-bit ENOB, and a 173 dB Schreier figure of merit (FOM) for the neural analog-to-digital converter (ADC). Additionally, the ultra-low-power radio-frequency (RF) transmitter boasts a remarkable 1.38 pJ/bit energy efficiency. In vivo experiments conducted on rat sciatic nerves provide compelling evidence of the interface's ability to selectively stimulate and record neural fascicles. The proposed PNS neural interface offers alternative treatment options for diagnosing and treating neurological disorders, as well as restoring or repairing neural functions, improving the quality of life for patients with neurological and sensory deficits.

A wireless, battery-free device enables oxygen generation and immune protection of therapeutic xenotransplants in vivo

The immune isolation of cells within devices has the potential to enable long-term protein replacement and functional cures for a range of diseases, without requiring immune suppressive therapy. However, a lack of vasculature and the formation of fibrotic capsules around cell immune-isolating devices limits oxygen availability, leading to hypoxia and cell death in vivo. This is particularly problematic for pancreatic islet cells that have high O2 requirements. Here, we combine bioelectronics with encapsulated cell therapies to develop the first wireless, battery-free oxygen-generating immune-isolating device (O2-Macrodevice) for the oxygenation and immune isolation of cells in vivo. The system relies on electrochemical water splitting based on a water-vapor reactant feed, sustained by wireless power harvesting based on a flexible resonant inductive coupling circuit. As such, the device does not require pumping, refilling, or ports for recharging and does not generate potentially toxic side products. Through systematic in vitro studies with primary cell lines and cell lines engineered to secrete protein, we demonstrate device performance in preventing hypoxia in ambient oxygen concentrations as low as 0.5%. Importantly, this device has shown the potential to enable subcutaneous (SC) survival of encapsulated islet cells, in vivo in awake, freely moving, immune-competent animals. Islet transplantation in Type I Diabetes represents an important application space, and 1-mo studies in immune-competent animals with SC implants show that the O2-Macrodevice allows for survival and function of islets at high densities (~1,000 islets/cm2) in vivo without immune suppression and induces normoglycemia in diabetic animals.

Far-field wireless power harvesting for inaccessible area wireless monitoring

Far-field wireless power solutions are essential for wireless monitoring of inaccessible industrial areas. However, the intuitive nature of RF power is to degrade with distance square law. Due to this attribute, the wireless power solution in a far-field zone has not been practically conceptualized for industrial deployments. To identify a feasible wireless power solution, a 5×10 rectenna panel has been designed and developed in this work. The panel has been designed with a staggered row arrangement to investigate different rectenna arrangement patterns. With experimentation, an optimized rectenna arrangement pattern has been selected for demonstration of its applicability for network sustenance. This work emphasises that smart charging of storage capacitors plays a vital role in extending the wireless power range. The power demand for resource-constrained devices is on a microwatt scale, which can be easily delivered through wireless power in seconds.

Composite Right/Left-Handed Transmission Line Metamaterial-Inspired Small Antenna Design: Topologies, reconfigurability, and applications

With the development of modern wireless communication systems, the demand for high-performance, multifunctional, low-cost, and compact antennas has been increasing substantially. The greatest challenge when designing this type of antennas is the tradeoff between complexity and performance. More design freedom is therefore highly desired. As an important subtype of metamaterials, composite right/left-handed transmission line (CRLH-TL) metamaterials have paved the way to achieve this compromise. In this review article, first, the possible CRLH-TL topologies that can be used in antenna design are discussed, involving structures based on not only Cartesian but also polar coordinates and 2D CRLH-TLs. The reconfigurability of the CRLH-TLs in terms of operating mechanisms, reconfigurability methods, and control techniques is then reviewed. By applying these structures to electrically small antenna design, considerable extra design freedom can be obtained. In the literature, a whole range of novel antennas with remarkable performances have been reported, holding great potential for various applications, such as wireless body area networks (WBANs), multiple-input, multiple-output (MIMO), radio-frequency identification devices (RFIDs), wireless power harvesting, and so on. All of these applications are briefly discussed.

SEAL-RF: Secure Adiabatic Logic for Wirelessly Powered IoT Devices

Wireless power harvesting has become popular for various Internet-of-Things (IoT)-based devices, such as wireless sensors, radio frequency identification (RFID)-based systems, and implantable devices for healthcare. Since these ubiquitous computing devices are likely to handle confidential information, ensuring their security is critical. In this work, a secure adiabatic logic family, referred to as SEAL-RF, is developed, specifically for RF-powered IoT devices. SEAL-RF is highly energy efficient and resistant against power-based side-channel attacks. Specifically, at the gate-level, the normalized energy deviation (NED) of SEAL-RF is up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$180\times $ </tex-math></inline-formula> lower than conventional (unprotected) adiabatic logic, while consuming up to 39% less average energy per transition. Furthermore, the NED of SEAL-RF is up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.5\times $ </tex-math></inline-formula> lower than an existing secure adiabatic logic, while consuming up to 32% less average energy per transition. A lightweight encryption core based on SIMON algorithm is also designed with the proposed SEAL-RF and conventional adiabatic logic. A correlation power analysis (CPA)-based side-channel attack is mounted on both designs. The secret key for the unprotected SIMON core is retrieved with less than 800 traces whereas the secret key for the SEAL-RF-based SIMON core cannot be retrieved with more than 40K traces. Furthermore, the average power and energy per encryption of the SEAL-RF-based SIMON core is 15.6% lower than the conventional adiabatic logic-based SIMON.

Self-excitation of radio waves in the metal–insulator–metal structure doped with metal nanowires

The effect of self-excitation of radio waves in the metal–insulator–metal structure doped with metal nanowires is predicted and its theory is developed. Both the transient stage of self-excitation and the steady-state regime of self-oscillation are analyzed in a fully analytical form. The numerical estimates demonstrate that this effect can be used for diverse practical purposes, in particular, for radio frequency wireless power harvesting. These findings extend the approach developed in nano-optics to the field of electrical engineering.

An Ultrawideband High-Efficiency Rectifier Based on Harmonic Feedback Topology

With the rapid and extensive development of wireless communication and low power electronics, electromagnetic wireless power harvesting (WPH) draws more and more attention. As the core component for RF-to-DC power conversion, its characteristics determine the performance of the overall WPH system. To obtain as much dc energy as possible, ambient electromagnetic energy with various frequencies should be efficiently rectified. Therefore, it is important to widen the operating bandwidth of the rectifier. According to the theoretical analysis of the Schottky diode, it can be found that if the harmonic components generated by the diode can be fed back through a specific approach for rectifying, the bandwidth of the rectifier will be effectively improved. Therefore, a broadband rectifier has been proposed based on the previous principle. For validation, a wideband rectifier based on Schottky diode SMS7630 had been designed, fabricated and measured. When the input power level is 0 dBm, the conversion efficiency of the implemented rectifier is larger than 40% from 0.4 to 2.6 GHz within a relative bandwidth of 146.67%, exhibiting an ultrawide bandwidth compared with existing state-of-the-art configurations.

SEE‐MAC: Spectrum and energy efficient‐medium access control protocol for Internet of Things

SummaryIn this paper, we have devised a method for spectrum‐and energy‐efficient wireless communication systems for the Internet of Things (IoT) devices that require continuous uninterrupted power for their operation. However, the potential application of the proposed scheme is vast and is relevant to any wireless communication systems deployed for the next generation connected systems that face challenges in spectrum availability and battery charging of the devices. To fulfill the demand of wireless devices, such as sensor nodes deployed in the IoT, we have proposed a spectral‐and energy‐efficient‐medium access control (SEE‐MAC) protocol with a radio‐frequency energy harvesting (EH) facility. The proposed protocol has integrated wireless power harvesting with cognitive sensor nodes to provide both the energy‐ and spectrum‐efficient wireless communication system. In the proposed SEE‐MAC, the cognitive sensor nodes take the advantage of both the idle and active licensed channels of the primary network for data transmission and EH. The proposed system identifies the active licensed channel of the network to be allotted to each cognitive sensor node for EH and idle channel recognition for data transmission. The mathematical analysis has also been performed representing allocation of primary user channels for the EH and data transmission. The closed‐form expressions obtained along with simulation results have illustrated the amount of harvested energy, throughput, and energy efficiency achieved by the cognitive sensor nodes of the network.

Wireless power transfer and energy harvesting in distributed sensor networks: Survey, opportunities, and challenges

Distributed sensor networks have emerged as part of the advancements in sensing and wireless technologies and currently support several applications, including continuous environmental monitoring, surveillance, tracking, and so on which are running in wireless sensor network environments, and large-scale wireless sensor network multimedia applications that require large amounts of data transmission to an access point. However, these applications are often hampered because sensor nodes are energy-constrained, low-powered, with limited operational lifetime and low processing and limited power-storage capabilities. Current research shows that sensors deployed for distributed sensor network applications are low-power and low-cost devices characterized with multifunctional abilities. This contributes to their quick battery drainage, if they are to operate for long time durations. Owing to the associated cost implications and mode of deployments of the sensor nodes, battery recharging/replacements have significant disadvantages. Energy harvesting and wireless power transfer have therefore become very critical for applications running for longer time durations. This survey focuses on presenting a comprehensive review of the current literature on several wireless power transfer and energy harvesting technologies and highlights their opportunities and challenges in distributed sensor networks. This review highlights updated studies which are specific to wireless power transfer and energy harvesting technologies, including their opportunities, potential applications, limitations and challenges, classifications and comparisons. The final section presents some practical considerations and real-time implementation of a radio frequency–based energy harvesting wireless power transfer technique using Powercast™ power harvesters, and performance analysis of the two radio frequency–based power harvesters is discussed. Experimental results show both short-range and long-range applications of the two radio frequency–based energy harvesters with high power transfer efficiency.

Far-Field Wireless Power Harvesting: Nonlinear Modeling, Rectenna Design, and Emerging Applications

Continuous advances in ultralow-power electronics are a fundamental driving force of developing far-field wireless power harvesting techniques, which generally harnesses low/ambient energy in free space or dedicated wireless power from a power base station. This article reviews recent developments and technology trends in far-field (radiative) wireless power harvesting, including modeling of rectification process inside nonlinear devices, insights into rectenna system design, and demonstrations of emerging applications. The rectification process inside nonlinear devices will be explored, upon which a device selection guideline is provided to help quickly identify suitable devices. Then, the optimization of rectenna design is discussed to realize efficiency enhancement at a limited input power level. Since far-field wireless power harvesting has become a critical enabling technology for battery-free Internet of Things, a series of promising applications is demonstrated in this article to highlight the challenges and opportunities in the field.

Secure Wirelessly Powered Networks at the Physical Layer: Challenges, Countermeasures, and Road Ahead

Harvesting wireless power to energize miniature devices has been envisioned as a promising solution to sustain future-generation energy-sensitive networks, e.g., Internet-of-Things systems. However, due to the limited computing and communication capabilities, wirelessly powered networks (WPNs) may be incapable of employing complex security practices, e.g., encryption, which may incur considerable computation and communication overheads. This challenge makes securing energy harvesting communications an arduous task and, thus, limits the use of WPNs in many high-security applications. In this context, security at the physical layer (PHY) that exploits the intrinsic properties of the wireless medium to achieve secure communication has emerged as an alternative paradigm. This article first introduces the fundamental principles of primary PHY attacks, covering jamming, eavesdropping, and detection of covert, and then presents an overview of the prevalent countermeasures to secure both active and passive communications in WPNs. Furthermore, a number of open research issues are identified to inspire possible future research.

Compact and High-Efficiency Rectenna for Wireless Power-Harvesting Applications

A compact, single-layer microstrip rectenna for dedicated far-field RF wireless power-harvesting applications is presented. The proposed rectenna circuit configurations including multiband triple L-Arms patch antenna with diamond slot ground are designed to resonate at 10, 13, 17, and 26 GHz with 10 dB impedance bandwidths of 0.67, 0.8, 2.45, and 4.3 GHz, respectively. Two rectifier designs have been fabricated and compared, a half wave rectifier with a shunted Schottky diode and a voltage doubler rectifier. The measured and simulated maximum conversion efficiencies of the rectifier using the shunted diode half-wave rectifier are 41%, and 34%, respectively, for 300 Ω load resistance, whereas they amount to 50% and 43%, respectively, for voltage doubler rectifier with 650 Ω load resistance. Compared to the shunted rectifier circuit, it is significant to note that the voltage doubler rectifier circuit has higher efficiency. Both rectifier’s circuits presented are tuned for a center frequency of 10 GHz and implemented using 0.81 mm thick Rogers (RO4003c) substrate. The overall size of the antenna is 16.5 × 16.5 mm2, and the shunted rectifier is only 13.3 × 8.2 mm2 and 19.7 × 7.4 mm2 for the voltage doubler rectifier. The antenna is designed and simulated using the CST Microwave Studio Suite (Computer Simulation Technology), while the complete rectenna is simulated using Agilent’s ADS tool with good agreement for both simulation and measurements.

Performance analysis of wireless power harvesting over signal to interference plus noise channel for full‐duplex services in LTE MIMO system

SummaryThe evolution of wireless communication systems and its strive to provide 5G services accompanied with the expanded use of communication devices with greedy applications have strained the device's battery power. In its quest to provide a solution to this problem, wireless communication systems proposed wireless energy harvesting. Communication channel time shall be split between sending and receiving data as well as energy harvesting. Maximizing spectral efficiency and minimizing power consumption are aims of 5G technology. In the literature, the time split was analyzed without considering LTE resource blocks or interference from adjacent devices and objects. In this second paper, we first pay special attention to interference and its impact on the system, as well as the mathematical equations derived for time split protocol while considering two main types of internet traffic services: VoIP and FTP. Second, the attention will be directed towards reasonable and logical analysis of LTE MIMO systems considering different internet traffic profiles.

Wireless Communication and Power Harvesting in Wearable Contact Lens Sensors

The human eye contains multiple biomarkers related to various diseases, making electronic contact lens an ideal non-invasive platform for their diagnosis and treatment. Recent advances in technology have enabled the monitoring and diagnosis of glaucoma from Intraocular Pressure (IOP) detection, diabetes from glucose concentration detections, and other biosensors for pH and temperature sensing. Different sensor designs have led to distinct power transfer techniques, among which inductively coupled power transfer is considered most favourable for electronic contact lenses power delivery applications. Therefore, loop antenna, spiral shape antenna, and antenna with nanomaterials such as graphene and hybrid silver nanofibers have been explored under Industrial, Scientific, and Medical (ISM) frequency bands for both Wireless Power Transfer (WPT) and data communication. Notably, spiral antennas are also considered as the component of IOP sensing using capacitive sensors to detect the changes in frequency caused by pressure. This article reviews the state-of-the-art technologies in electronic contact lens sensors and their power delivery techniques. Herein, diverse sensing methods, materials, and power transfer techniques and the promising future trends and challenges in electronic contact lenses have been presented.

Wireless Power and Energy Harvesting Control in IoD by Deep Reinforcement Learning

Internet of Drones (IoD), which deploys several drones in the air to collect ground information and send them to the IoD gateway for further processing, can be applied in traffic surveillance and disaster rescue. The performance of IoD is greatly affected by drones' battery capacities. We hence utilize the energy harvesting technology to charge the batteries and the wireless power control to adjust the drone wireless transmission power in order to address this challenge. In our work, we investigate the joint optimization of power control and energy harvesting control to determine each drone's transmission power and the transmitted energy from the charging station in time-varying IoD networks. Our objective is to minimize the long-term average system energy cost constrained by the drones' battery capacities and quality of service (QoS) requirements. A Markov Decision Process (MDP) is formulated to characterize the power and energy harvesting control process in time-varying IoD networks. A modified actor-critic reinforcement learning algorithm is then proposed to tackle our problem and its performance is demonstrated via extensive simulations.

Microscale Optoelectronic Devices for Biomedical Sensing

Conventional bioelectrical sensors and systems integrate multiple power harvesting, signal amplification and data transmission components for wireless biological signal detection. Here we report that the real-time biophysical and biochemical activities can be optically captured using a microscale light-emitting diode (micro-LED), eliminating the need for complicated sensing circuit. Such a thin-film diode based device simultaneously absorbs and emits photons, enabling wireless power harvesting and signal transmission. Additionally, owing to its strong photon-recycling effects, the micro-LED’s photoluminescence (PL) emission exhibits a superlinear dependence on the external conductance. Taking advantage of these unique mechanisms, instantaneous biophysical signals including galvanic skin response, pressure and temperature, and biochemical signals like ascorbic acid concentration, can be optically monitored, and it demonstrates that such an optoelectronic sensing technique outperforms a traditional tethered, electrically based sensing circuit, in terms of its footprint, accuracy and sensitivity. This presented optoelectronic sensing approach could establish promising routes to advanced biological sensors.

Implantable platinum nanotree microelectrode with a battery-free electrochemical patch for peritoneal carcinomatosis monitoring

As a severe stage of cancers, peritoneal carcinomatosis should be frequently monitored by means of ascites analysis. Nevertheless, the analysis process is traumatic and time-consuming in clinical practice. In this study, an implantable platinum nanotree microelectrode with a wireless, battery-free and flexible electrochemical patch was developed for in vivo and real-time peritoneal glucose detection to monitor peritoneal carcinomatosis. As the core of implantable microelectrode, platinum trees were synthesized by one-step electrodeposition method and highly sensitive to glucose detection. The platinum nanotree microelectrode was implantable in peritoneal cavity in minimally invasive way. A flexible circuit patch could execute electrochemical test and realize wireless power harvesting and data interaction with a near field communication (NFC)-enabled smartphone. The whole system could detect glucose dynamics in vivo in rat peritoneal cavity. Furthermore, the accuracy of this system was validated in ascites of patients. In this way, the system could offer hassle-free, rapid and minimally invasive opportunities toward peritoneal carcinomatosis monitoring.

An Optically Transparent Near-Field Focusing Metasurface

We propose a novel optically transparent reflection-type metasurface based on indium tin oxide (ITO) material for simultaneously achieving high transmission of visible light and near-field focusing (NNF) of microwave, demonstrating its potential for wireless power transfer (WPT) and harvesting applications. By achieving high impedance of the metasurface, this work overcomes the main challenge in designing metasurface with lossy metal materials, i.e., optimizing the tradeoff between phase shift characteristics and efficiency loss. We propose a new element with two degrees of freedom to ensure that the phase shift range can reach 350° while keeping |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | less than -2.5 dB. In addition, we adopt the grid ground (GND) instead of the complete GND plane to further improve the light transmittance. Based on the above considerations, we design two types of metasurfaces for deployments in ambient wireless energy harvesting (plane-wave feeding) and WPT (horn feeding), respectively. Its NNF transfer efficiency can reach more than 60% of the metasurface based on good conductor materials. The relative bandwidth with 50% transfer efficiency can reach 34.5% (4.9-6.9 GHz). We fabricate an ITO-based prototype of the metasurface with the dimension of 342 ×342 ×4.4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ( 6.6 ×6.6 ×0.08λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) with the sheet impedance of 1 Ω/sq and a light transmittance of 60%. We also perform near-field scanning measurements to verify that the focusing position is accurate. Finally, through WPT and harvesting tests, we achieve a WPT and receiving efficiency (from power source to receiving antenna) of 12.6% and a rectification efficiency of 55%, confirming the practicability and effectiveness of the proposed work.

Optoelectronic sensing of biophysical and biochemical signals based on photon recycling of a micro-LED

Conventional bioelectrical sensors and systems integrate multiple power harvesting, signal amplification and data transmission components for wireless biological signal detection. This paper reports the real-time biophysical and biochemical activities can be optically captured using a microscale light-emitting diode (micro-LED), eliminating the need for complicated sensing circuit. Such a thin-film diode based device simultaneously absorbs and emits photons, enabling wireless power harvesting and signal transmission. Additionally, owing to its strong photon-recycling effects, the micro-LED’s photoluminescence (PL) emission exhibits a superlinear dependence on the external conductance. Taking advantage of these unique mechanisms, instantaneous biophysical signals including galvanic skin response, pressure and temperature, and biochemical signals like ascorbic acid concentration, can be optically monitored, and it demonstrates that such an optoelectronic sensing technique outperforms a traditional tethered, electrically based sensing circuit, in terms of its footprint, accuracy and sensitivity. This presented optoelectronic sensing approach could establish promising routes to advanced biological sensors.