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This works presents the design of wireless power transfer systems that can transfer power through materials such as stainless steel, aluminum, carbon fiber, and fiberglass. Wireless power transfer research has been limited to through-air applications, focusing on short distances and high efficiencies. However, complex scenarios require specific design criteria to provide the advantages of wireless power transfer for critical applications. Taking this into consideration, this work presents the extensive research towards enabling wireless power transfer systems for unconventional barriers. In the first chapter a new approach is taken towards the design of compact and embedded wireless power transfer solutions. A miniature coil is designed to transfer power through a 1 mm thick aluminum metal plate. The results are unprecedented, P_rx=100 mW, considering that through metal power transfer had only being demonstrated using large diameter coils. In addition to that, the metal barrier used is aluminum, a high conductivity material. This is important because traditional research focused on less conductive material such as stainless steel or tin. In the next chapter, we demonstrated a wireless power and data transfer system that uses a miniature coil with a size of 15 mm × 13 mm × 6 mm. Our system demonstrated that not only power but data could be transferred through an aluminum barrier using the same coil for power and data transmission. The maximum coil-to-coil power transfer efficiency is 2.4%, and the maximum harvested power is 440 mW operating at 2 kHz. Additionally, our system demonstrated that power can be harvested in variety of materials of different thicknesses. The next chapter presents a breakthrough in the field of wireless power transfer through metal by enabling long distance wireless power transfer. A large portion of the technologies for wireless power transfer are limited to short operation distances, distances around 1-10 millimeters to less than 20 cm. The operation distances are even shorter for the case of through metal wireless power transfer. For through metal wireless power transfer, the high losses from the metal barrier require short operation distances less than 1 mm, in order to transfer some energy through the metal barrier. On the contrary, our system uses a custom designed coil to transfer energy to a receiving coil enclosed in a 1-mm thick aluminum metal box up to a distance of 1m. The maximum AC harvested power was 231 μW when the transmitted power is only 6.16 W. The next chapter presents a long range through metal wireless power transfer and communication system. The system demonstrated that power can be harvested inside a metal box, and that data can be transferred bidirectionally between the nodes. Operating at 103 kHz, a maximum harvested power of 408 μW AC and 96 μW DC is achieved, with bidirectional communication at a rate of 1.2 kbps. The last chapter presents the design of a wireless power transfer systems that can operate through composite materials. The work analyses the effect of different materials and presents a system that can operate wirelessly through carbon fiber and fiberglass. Finally, conclusions present the results of this research and the future perspectives in the field.

Any problem becomes tractable with enough power. Since the inception of wireless sensornetworks, researchers have searched for ways to do more with less. Integrated circuits andsensors have continued to shrink in size, cost, and active and quiescent power. This hasresulted in sensors with increasing computational power and longer lifetimes. By comparison,however, the options for and quantity of power available for a wireless sensor has stagnated.The energy density of non-rechargeable batteries as well as photovoltaic efficiency haveapproached a plateau. As a result, wireless sensors are constrained in either lifetime or power.Technology improvements like integrated circuits that perform efficient maximum powertracking and voltage boosting, near-threshold computing, the advent of non-volatile memorytechnologies, and the rapid improvement of supercapacitor technology has enabled thedevelopment of sensors that can operate entirely on harvested power without batteries,and without a finite lifetime. But the lack of a reliable power source necessarily results ina system that is fundamentally unreliable. Despite this significant flaw, researchers havepursued this design archetype tirelessly, producing an impressive corpus of methods, systems,and solutions that attempt to improve batteryless design. Proponents of batteryless systemsare convinced that batteries are a threat to the future of wireless sensing, and that batterylesssensing is the only way forward. Despite this, batteryless sensing has not seen widespreadadoption by industry. There is a rift of design understanding between those who valuereliability, and those who do not.The core argument of this dissertation is that there is not a single design dogma, be itbatteryless or battery-powered, that can provide a solution for all applications. Instead,the correct design process must involve a balancing act of the inclusion and sizing of energyharvesting, rechargeable, and non-rechargeable energy storage to meet the goals of theapplication. This design space is large and difficult to navigate, resulting in many systemdesigners defaulting to following a predetermined design template archetype instead of fullyreasoning about their application and its requirements. In this dissertation, we develop adesign framework for energy harvesting systems that provides reasoned guidance for theinclusion and sizing of various power supply elements. In particular, we develop analyticaland simulation tools to size rechargeable energy capacity in a more reasoned way than currentheuristics and arbitrary methods.To develop this design framework, this dissertation explores previous wireless sensor applications, identifying the appropriateness of different approaches qualitatively and quantitatively.We explore the system-level effects of harvester size and rechargeable and non-rechargeableenergy capacity on wireless sensor application performance. To determine rechargeable energycapacity selection and sizing, we develop a novel heuristic for determining the minimumsufficient capacity for a sensor workload and expected energy income. We verify this heuristic through the use of a custom wireless sensor energy state simulator to estimate energyutilization and system performance. To identify technology options for energy capacity, wequantitatively compare energy buffer types and reevaluate the many qualitative claims madeagainst rechargeable batteries by batteryless proponents, concluding that many of them arewithout merit. Finally, we utilize the design framework developed within this dissertation,including the heuristics and simulation tool, to design and implement wireless sensor systems to address two real indoor sensing applications that achieve long-lived operation withconsistent and reliable sensing

Battery power has been a popular choice of delivering DC power to many portable RF systems including wireless sensor nodes/internet of Everything (IoE). An autonomously powered RF system of the orders of 100’s of µwatts is becoming increasingly popular in recent times because of integrated solutions in energy harvesting. The minimum sensitivity of an RF energy harvester and the targeted deliverable output voltage for a specific load resistance are dictated by threshold voltage of transistors used and reverse leakage of such transistors. A detailed look into the architectures of rectifiers can help tackle design problems in the RF-DC conversion process. So in this work we focused on the design of integrated RF energy harvesting by studying four important architectures of RF-DC converters. To achieve a fair comparison between these architectures, a matching network operating at 0.8 MHz is designed and applied for simulation. All of these converters are tested in LT-SPICE XVII using the same designed matching network and the rectifiers are implemented in 180 nm CMOS technology.

Wireless system-on-chip devices are emerging as the most promising solution for future wireless sensing with applications in medical implants and the Internet of Things (IoT). On one side, energy extraction from ambient sources facilitates permanent powering techniques required for long-term operation. On the other side, the high integration capability of commercial CMOS technology opens the opportunity for high-resolution sensing and data communication with a compact form-factor. In this dissertation, My research builds a foundation for joint wireless power delivery, low-power sensing, and wireless communication in such highly integrated systems yielding a paradigm shift in the design and development of future ubiquitous low-power wireless systems.This thesis presents the design, implementation, and experimental evaluation of integrated wirelessly powered solutions for next-generation medical implants and IoT devices. To this end, First, I leverage the high integration capabilities of CMOS technology and try to develop integrated systems for power delivery, environmental sensing, and wireless data communication. The small power budget available for an integrated solution severely limits its functionality and operating range. Hence, individual wirelessly powered solutions may not be able to satisfy the application requirements of future medical implants and IoT devices. To address this problem, I leverage another important feature of a commercial CMOS technology that is the low fabrication cost. I show how complex tasks such as localization and be realized using a swarm of millimeter-sized integrated chips.In this dissertation, I introduce the challenges of wireless power transmission to fully integrated systems on CMOS technology and present two types of RF power receiver systems for near-field and far-field electromagnetic region. I propose a comprehensive optimization algorithm for maximizing the power transfer efficiency and choosing the optimum frequency for wireless power transmission.Next, I present the world's most power-efficient wireless transceiver with an integrated wireless power delivery system. I demonstrate a fully on-chip operation and utilize two sets of loop and dipole antenna for wireless power delivery and data communication, respectively. I will explain how we achieve a 150 Mbps uplink communication data rate under a stringent power budget by introducing a power management technique.I will then, discuss the opportunities offered by this platform to enhance next-generation IoT and medical devices. In particular, we tackle the limited operating range by forming a synchronized distributed sensor network built from fully on-chip integrated systems. Also, we address the power scarcity challenges in biomedical/environmental sensing by adopting extensive low-power design techniques.This interdisciplinary research direction incorporates advancements such as applied physics, machine learning, healthcare, and wireless networking.

Internet of Things (IoT) is becoming pervasive in our daily lives. Wearable technologies will expand the connectivity of IoT and will increase the interaction between technology and human body. Micro Electro-Mechanical Systems (MEMS) microfabrication techniques that involve bulk Si micromachining and thin film processing have allowed us to develop electronic systems that are based on Si and other advanced materials that are flexible, wearable, and implantable. Wearable and implantable electronics equipped with sensors enable us to perform real-time health monitoring from above and below the skin, respectively, and can replace conventional bulky electrophysiological monitoring devices and systems. Research efforts in wearables and implantables have intensified in the last decade tackling several aspects of the sensor technology, embedded signal processing and conditioning, energy harvesting, connectorization, functionality, longevity and reliability. However, there are still technical challenges that impose restrictions for their widespread adoption. On top of these challenges is the power source for the wearable or implantable device. Energy harvesting is expected to replace conventional battery systems that power wearables and implantables. In this dissertation, we focus on solar energy as an energy source for self-powered electronics. In Chapter 1, the motivation of the dissertation together with a brief survey of state of the art in flexible and wearable electronics with energy harvesting system and implantable medical devices are discussed. In Chapter 2, we disclose our parametric studies on solar cells with different microwire surface and array morphologies to understand the effect of surface passivation, surface crystal orientation on surface recombination and carrier collection on SiMW solar cells with radial p-n junctions as well as their emitter series resistances with an overall goal of maximizing their power conversion efficiencies. In Chapter 3, we present an approach for self-powered wearable electronics by means of the monolithic integration of SiMW solar cells with Si MOSFETs on a Silicon on Insulator (SOI) wafer that is subsequently transferred to flexible substrates. The fabrication details and its application to a voltage-controlled oscillator and electrophysiological monitoring are discussed. In Chapter 4, we discuss the details of the novel fabrication processes for the development of a stylet guided depth/laminar probe and of a surface electrocorticography (ECoG) grid that is fabricated with bio-compatible polymers (Polyimide and Parylene C) including their electrochemical characterization and their use in vivo for electrophysiological recordings in rats.

Animal tracking tags are a useful tool in the study of wild animals and ecological systems, but the process of tagging an animal is costly and often traumatic for the animal. For many types of tags, the lifetime of the tag is determined by battery life. The Energy Scavenging Collar for Animal Physiology and Ecology (ESCAPE) project investigates several methods for reducing overall power consumption in wildlife tracking tags. This work develops and tests several algorithms for reducing GPS uptime in these tags, using Extended Kalman Filters to guide uncertainty-suppression GPS scheduling. These algorithms use less costly sensors such as accelerometers, magnetometers, and gyrometers to augment GPS in estimating locations during tracking. We implement and test these algorithms in tests on human subjects. This work also includes analysis of several proposed techniques for scavenging energy in the field, such as harvesting excess kinetic and thermal energy from the animal. Our analyses provide upper bounds on expected power returns from these strategies, providing useful metrics for determining whether such strategies are viable regions of the tag design space. The findings of the ESCAPE project contribute to future tag research and development by highlighting strategies with potential for improving tag lifetimes, and discouraging other strategies.

Piezoelectric energy harvester (PEH) arrays are promising in many application scenarios. However, few interface circuits have been developed to manage the multiple AC inputs from PEHs. This paper proposes an extensible P-SSHI (parallel synchronized switch harvesting on inductor) array interface scheme to realize a multi-input conversion from PEH arrays. We develop a split-inductor-capacitor topology that can extract electrical energy from multiple PEHs. The proposed circuit topology effectively handles the inductor access conflict in the cases of PEHs with close, identical, and opposite vibration phases, insensitive to AC input phase changes. For demonstrating the capability of dealing with multiple AC inputs from PEHs and the enhancement effect on power output, we construct and test a self-powered three-channel array circuit with the passive peak detection function. Excited by sinusoidal vibrations, our circuit effectively avoids the energy return and efficiently achieves the power combination of the three PEHs. Compared with the classic full-bridge circuit, the proposed circuit helps increase the power output by 4.8 times. Also, to show the universality of the circuit, the circuits operation under various excitations is tested and analyzed.

This paper proposes digitally controlled power management circuit (PMC) for vibration energy harvesting in vehicle suspension system. The PMC is tested with a mechanical motion rectifier based electromagnetic energy harvester that converts from bi-directional vibration to unidirectional rotation, with improved energy harvesting performance and efficiency. Topology of one-stage DC-DC converter is adapted, and it is digitally controlled while considering the uncertainty of vibration sources. In order to efficiently transfer the harvested power to the electrical load, the algorithm of digital controller is designed to have four operation modes, which are impedance matching mode, voltage regulation mode, generator protection mode, and low power mode, for increasing the PMC efficiency while reducing the power consumption of controller. Experimental results show that proposed circuit can successfully operate and switch between the four operation modes. In the evaluation of PMC performance with 2mm and 2Hz excitation, the efficiency of proposed one-stage power converter is 86%. The total power consumption of controller in active mode and low power mode are 109 mW and 2.52 mW respectively while harvesting about 3W vibration energy.

As wearable microelectronics become more ubiquitous, and the size and power requirements of such devices decrease, there is increasing research interest in harnessing power from ambient environmental sources through embedded systems as alternative to battery replacements. Accordingly, a multimodal hybrid piezo-electromagnetic insole energy harvester (PEM-IEH) has been presented in this paper as a means to reclaim the biomechanical energy wasted in the surroundings during daily walking. The hybrid device consists of two piezo-ceramic wafer plates, two magnets, and two wound coils. The designed harvester has been simulated, fabricated and experimentally validated. From the frequency response, the hybrid harvester exhibits four resonant frequencies concentrated around 8, 25, 50, and 51 Hz. A maximum combined power of 1400 µW is generated across the optimal load resistances of upper and lower electromagnetic generators at first resonant frequency (8 Hz) under 0.5 g base acceleration, and a 269 µW peak power is obtained across the optimum load resistances of the upper and lower piezoelectric generators at 4th resonance (51 Hz) under 0.5 g. The miniature (46.8 cm3) and lightweight (43.3 g) harvester was incorporated into the sole of an adult-sized commercial shoe, and has been shown to be able to charge a 100 µF capacitor, up to 2.4 Volt within approximately 10 min of slow jogging. The capacitor charging performance presents a remarkable potential application of the harvester in development of micro-power monitoring sensors and wearable microelectronic gadgets where batteries pose a practical bottleneck.

Inspired by hand push whisk blenders that are widely used in the kitchen, we here propose an energy harvester that enables conversion of low-frequency translational vibration to high-speed rotations and further generates electricity via the electromagnetic effect. The whisk-inspired energy harvester (W-EH) is composed of an internal thread sleeve, an external thread driving shaft, a spring, and a buoy. Compared with transmission approaches used by electromagnetic power generators, the proposed design has the superiority of low cost, ultra-low operation frequency (lower than 1 Hz), and high power output. Tests in water indicate that the normalized power density is 300% higher than the state of the art. Excited by mimicking ocean waves at 1.5 Hz, the W-EH prototype generates a maximum power of 64.4 milliwatts and succeeds in lighting up 115 LEDs simultaneously, which power is enough for continuous operations of most wireless sensors.

Owing to the shorter wavelength in the millimeter-wave (mmWave) spectrum, miniaturized antennas can receive power with a higher efficiency than UHF bands, promising sustainable mmWave-powered Internet of Things (IoT) devices. Nevertheless, the performance of a mmWave power receiver has not been compared, numerically or experimentally, to its sub-6 GHz counterpart. In this paper, the performance of mmWave-powered receivers is evaluated based on a novel wearable textile-based higher-order mode microstrip antenna, showing the benefits of wireless power transmission (WPT). Firstly, a broadband antenna is proposed maintaining a stable wearable measured bandwidth from 24.9 to 31.1 GHz, over three-fold improvement compared to a conventional patch. The proposed antenna has a measured 8.2 dBi co-polarized gain with the highest thickness-normalized efficiency of a wearable antenna. When evaluated for compact power receivers, the measured path gain shows that WPT at 26 GHz outperforms 2.4 GHz by 11 dB. A rectenna array based on the proposed antenna is then evaluated analytically showing the potential for up to 6.3x higher power reception compared to a UHF patch, based on the proposed antenna's gain and an empirical path-loss model. Both use cases demonstrate that mmWave-powered rectennas are suitable for area-constrained and large-area wearable IoT applications.

An energy harvesting system requires a power converter with its compact size and high power efficiency. Following the trend, this study suggests a new switched capacitor converter (SCC). The proposed converter is designed by a parallel- and cross-connecting two Fibonacci topologies. This connection leads the proposed SCC to generate its multilevel outputs as well. The proposed SCC has the lowest output resistors under five times conversion ratios from the theoretical analysis and comparison of two different SCC topologies. Simulation results confirm that the proposed SCC can be operated over 90% power efficiencies under 100 mW.

Vibration energy harvesting using multiple piezoelectric transducers (multi-PZTs) can increase its output power and environmental adaptability. At present, there are still few researches on multi-input interface circuits for multi-PZTs, especially those using the parallel synchronized switching harvesting on inductor (PSSHI) technique. Therefore, this article presents a self-powered dual-inductor MI-PSSHI-VDR interface circuit. It can process multi-PZT voltages with arbitrary phases input. The measurements demonstrate that the prototyped MI-PSSHI-VDR circuit can extract a peak power of 1.93 mW from four PZTs under an excitation of 1.5 g and 75.5 Hz. The energy integration efficiency and energy extraction efficiency of the prototyped circuit are 93.2% and 75.1%. Compared with a multi-input full-bridge rectifier, the proposed circuit can achieve 3.22 power improvement and 3.58 voltage improvement, which grasps a good balance between the indexes of peak output power and load voltage range. Additionally, the MI-PSSHI-VDR circuit is easy to implement and shows a good scalability, which can be an alternative solution for multi-PZTs energy harvest

In this paper, a single-stage rectifier-less boost converter circuit (SSRBC) for piezoelectric energy harvesting from ambient vibration was proposed. The proposed rectifier-less circuit acted as a boost converter to extract energy from a piezoelectric device (PD). It combined the conventional boost, buck-boost methods using two split inductors and single filter capacitor. The proposed integrated circuit topology functioned in both positive and negative half cycles generated by the PD. In the proposed topology, inductors were invigorated by being enveloped with the current, which was produced by the PD through the switches. This facilitated active rectification of ultra-low AC (amplitude < 0.5 VP). Theoretical analysis, control strategies, simulation and experimental study, were presented. The proposed circuit was capable of converting a low amplitude AC voltage of 0.5 VP into 5.1 Vdc. The highest output power extracted by the proposed circuit was 281.1 µW, which outperformed existing circuits. It could potentially facilitate the advancement of vibration-based energy harvesting system for low power demand applications such as sensors, quartz watches and portable charging devices.

The emerging energy harvesting technology facilitates the development of ubiquitous and everlasting battery-free motion detectors. This paper introduces a robust design of the transient-motion-powered motion detector, which is called ViPSN-pluck. “ViPSN” is the acronym for vibration-powered sensing node while “pluck” stands for the plucking-motion energy harvester. By using a piezo-magneto-elastic structure, ViPSN-pluck can efficiently harvest energy from a transient motion. By properly making good use of this tiny harvested energy, ViPSN-pluck can effectively carry out motion detection and Bluetooth low-energy (BLE) wireless communication. Given the concurrency of mechanical potential energy pre-charging and motion detection, the transient-motion plucking energy harvester used in ViPSN-pluck has the merit of high energy reliability. This unique feature is unprecedented in the solar and RF energy harvesting cases, which might suffer from energy outages under fluctuating irradiance or RF signal strength, respectively. The working principle of ViPSN-pluck, in particular, the dynamic characteristics of the plucking energy harvester and the energy matching between generation and utilization, are discussed in detail to demonstrate the robustness in operation. The cyber-electro-mechanical synergy among the mechanical dynamics, power conditioning circuit, and low-power embedded system is highlighted. The design methodology of ViPSN-pluck provides a valuable reference for the developments of future motion-powered IoT devices.

We propose a battery-free temperature monitoring device that can be fitted inside the ear for an accurate body temperature measurement of a subject. The proposed application consists of two primary systems: 1) a battery-free temperature sensing ultra-high-frequency radio frequency identification sensory tag and 2) an auxiliary energy harvesting system, which enhances the sensing device's measurement accuracy and precision. The system can record changes in the localized body temperature of authenticated users with an average latency of 501 ms. The assembly demonstrated a temperature average accuracy of ± 0.14 °C operating at 866 MHz. The system performance demonstrated high stability and repeatability of reported temperature measurements. The device's dimension is a form factor that can easily fit in a front shirt pocket, with a wire tethered earbud temperature sensor. The system is developed to make sensor measurements without requiring a battery for the device. Measurements are made remotely as users pass by checkpoints installed throughout a building. The device is a cost-effective solution for monitoring body temperature in work environments.

Backscatter communication is an emerging paradigm for pervasive connectivity of low-power communication devices. Wirelessly powered backscattering wireless sensor networks (WSNs) become particularly important to meet the upcoming era of the Internet of Things (IoT), which requires the massive deployment of self-sustainable and maintenance-free low-cost sensing and communication devices. This article will introduce the state-of-the-art antenna design and radio frequency (RF) system integration for wirelessly powered backscatter communications, covering both the node and the base unit. We capture the latest development in ultralow-power RF front ends and coding schemes for μW-level backscatter modulators, as well as the latest progress in wireless power transfer (WPT) and energy harvesting (EH) techniques. Newly emerged rectenna system, waveform design, and channel optimization are reviewed in light of the opportunities for adaptively optimizing the WPT/EH efficiency for low-power signals with varying conditions. In addition, advanced device packaging and integration technologies in, e.g., additively manufactured RF components and modules for microwave and millimeter-wave ubiquitous sensing and backscattering energy-autonomous RF structures are reported. Inkjet printing for the sustainable and ultralow-cost fabrication of flexible RF devices and sensors will be reviewed to provide a prospective insight into the future packaging of backscatter communications from the chip-level design to complete system integration. Finally, this article will also address the challenges in fully wireless powered backscatter radio networks and discuss the future directions of backscatter communication in terms of ``Green IoT'' and ``Low Carbon'' smart home, smart city, smart skin, and machine-to-machine (M2M) applications.

International audience; This paper presents an ultra-flexible piezoelectric air flow energy harvester capable of powering a wireless sensor. The method to easily adapt the aero-electric generator to the wind is presented. In the wind tunnel, different configurations have been tested to determine the best one for energy harvesting at low wind speed. In particular, the galloping configuration, with the addition of a bluff body at the free end of the cantilever which allows to improve the performance of the micro-generator by coupling the vibrations induced by the vortices and the galloping phenomena. In this study, we also present a method to optimize the energy harvesting without increasing the volume of the device. The effects of mechanical and electrical coupling of several generators on the performance of energy harvesting are presented. Thus, with the electrical parallel coupling of four generators, we obtained a maximum power of 60 mW instead of 30 mW with two generators for a wind speed of about 6 m/s. The mechanical coupling of the micro-generators allowed the device to keep the same volume (z540 cm3), however the threshold wind speed to increase (>6 m/s). The harvested energy was then used to operate a wireless sensor.

A backpack energy harvester converts mechanical energy associated with the oscillation of the backpack during human walking, into electric energy. It can be a very promising solution for supplying portable devices, especially in outdoor activities, disaster relief, and military applications. In this article, a backpack energy harvesting system that is able to self-adapt its operating condition to maximize the extracted power while supplying a dc load is presented and studied, analytically and experimentally. It is based on a mechanical motion rectifier that converts the up-and-down oscillation of the backpack into a unidirectional rotation of a dc generator. The generator output voltage is regulated by a power electronic interface implementing a maximum power point tracking technique to maximize the extracted power. Experimental results confirm the tracking ability of the proposed system and show the advantages with respect to other wearable energy harvesting systems published in the literature.

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.

The design of an ambient radio frequency (RF) energy harvesting system is introduced to replace the battery of the mass Internet-of-Things devices. This system can achieve high sensitivity with high efficiency over a wide input power range by optimizing the differential-drive cross-coupled (DDCC) rectifier and the load. The impedance of the dual-band four-port loop antenna array is directly conjugated to match with the rectifier, which reduces insertion loss of the matching network to improve efficiency. At 915 and 945 MHz for ISM and GSM bands, the rectenna can achieve high sensitivity of -30 dBm with 22% and 24% efficiency, high efficiency of 65% and 48% with -20-dBm input power, and a wide input power range from -30 to -18 dBm with 22-65% and 24-48% efficiency. The dual-band design explores the frequency diversity to harvest more RF energy from the environment, while the cross-shaped antenna array utilizes the space diversity to harvest RF energy from different directions with a compact size of 0.15λ x 0.15λ per antenna element (where λ is the free space wavelength at 915 MHz). This new harvesting system can provide output dc power of 21.4 and 2.95 μW in real-world outdoor and indoor ambient environments, respectively.

Harvesting the pervasive ultralow-frequency (

Concurrent high force detection accuracy and extended battery lifetime are strongly expected in wearable gait monitoring systems, which are essential for many Internet of Health Things (IoHT) applications. In this article, a piezoelectric insole device and a rectifying circuitry-based technique is presented to achieve these two ultimate goals. Here, walking induced positive and negative charges are separated for plantar stress detecting and energy harvesting, respectively; these two functions are realized concurrently. Experimental results demonstrate that first, the high detection sensitivity of 55 mN and responsivity of 231 mV/N are achieved, satisfying the need for diagnosing various diseases; second, the electric energy of 9.6 pJ (2.67×10-15 W·hr) is stored during a walking cycle, showing the potential of extending the battery lifetime. The developed technique enhances the development of gait monitoring in IoHT.

The self-sustainable Wireless Sensor Networks (WSNs) face a major challenge in terms of energy efficiency as they have to operate without replacement of batteries. The benefits of renewable and green energy are taken into consideration for sensing and charging the battery in recent literatures using Energy Harvesting (EH) techniques. The sensors are provided with a reliable energy source through Wireless Charging (WC) techniques. Several challenges in WSN are addressed by combining these technologies. However, it is essential to consider the deployment cost in these systems. This paper presents a self-sustainable energy efficient WSN based model for Mobile Charger (MC) and Energy Harvesting Base Station (EHBS) while considering the cost of deployment. This system can also be used for low-cost microelectronic devices and low-cost Micro-Energy Harvesting (MEH) system-based applications. While considering the deployment cost, the network lifetime is maximized and an extensive comparison of simulation with various existing models is presented to emphasize the validity of the proposed model.

Piezoelectric transducers provide a bidirectional channel for converting energy from mechanical form to electrical or in the opposite direction. Various applications were developed with either of these two energy-flow processes. For example, energy harvesters take advantage of the energy flow from mechanical to electrical domains, while vibration exciters utilize that from electrical to mechanical domains. However, few designs have integrated the bidirectional energy-flow processes in a single device in the past. Such an integration is beneficial to some multifunctional applications. The key obstacle of integrated bidirectional design results from the interface circuit design, rather than the transducer. This article makes a breakthrough by proposing a bidirectional energy conversion circuit (BECC) solution for the time-sharing energy harvesting and vibration exciting purpose. It is realized by developing a new control strategy on the synchronized triple bias-flip (S3BF) piezoelectric interface circuit, which was formerly used for energy harvesting enhancement. The control logic for energy harvesting and vibration exciting modes are discussed in detail. The time-sharing multi-functional ability is validated in experiments. It is the first time to realize a compact and integrated self-excitable energy harvester by using a single interface circuit. Experiments are carried out for validating the feasibility of the BECC toward future versatile engineering designs.

A photovoltaic (PV) energy harvesting chip with novel multiplier-based perturb and observe (P&O) maximum power point tracking (MPPT) circuit for Internet - of-Things applications is proposed, and it can be powered by only a small PV module. The proposed P&O MPPT circuit can accurately detect the maximum power point of the PV module without using a power-hungry microcontroller or inaccurate analog multiplier. Instead, a high-accuracy pulse-based multiplier is proposed. Its input signals are analog, while its output signal is digital. Moreover, a new MPPT controller based on the proposed multiplier is also presented. The chip was fabricated using a 0.18 μ m 1P6M mixed-signal CMOS process. According to the measured results, the available power from the chosen PV module is 0.1–3 mW, the maximum tracking efficiency of the proposed MPPT circuit is 99.3%, and the maximum total efficiency of the proposed harvesting chip is 94.7%.

Wireless transmission of sensor node signal at minimum power consumption and on-site charging of batteries is the key to the success of Wireless Structural Health Monitoring (WSHM) technology. In structures like bridges, vibration-based piezoelectric energy harvesters are generally employed to convert the ambient vibrations available in the bridges into usable electrical energy. Achieving a lower resonance frequency in a compact micromachined structure is the main goal of this work. It is attempted by optimizing various parameters, including the choice of piezoelectric material used, harvester structural configuration, and conditioning of the output of the energy harvesting circuitry. The authors propose to maximize the induced stress and therefore harvested power by proposing a sectioned cantilever with gradually decreasing widths. Such a design analyzed using the analytical model developed in this work and industrial standard MEMS design tools show that two section beams employed harvesters induce more power and it is 22.8% higher than the power induced in conventional uniform section cantilever beam harvesters. With three sections it is found that it can be further improved by 42.47%. This significant improvement without compromising miniaturization is the key contribution of this work.

There has been a significant increase in the number of total knee replacement (TKR) surgeries over the past few years, particularly among active young and elderly people suffering from knee pain. Continuous and optimal monitoring of the load on the knee is highly desirable for designing more reliable knee implants. This paper focuses on designing a smart knee implant consisting of a triboelectric energy harvester and a frontend electronic system to process the harvested signal for monitoring the knee load. The harvester produces an AC signal with peak voltages ranging from 10 V to 150 V at different values of knee cyclic loads. This paper demonstrates the measurement results of a PCB prototype of the frontend electronic system fabricated to verify the functionality and feasibility of the proposed approach for a small range of cycling load. The frontend electronic system consists of a voltage processing unit to attenuate high peak voltages, a rectifier and a regulator to convert the input AC signal into a stabilized DC signal. The DC voltage signal provides biasing for the delta-sigma analog-to-digital converter (ADC). Thus, the output of the triboelectric harvester acts as both the power signal that is rectified/regulated and data signal that is digitized. The power consumption of the proposed PCB design is approximately $5.35~\mu \text{W}$ . Next, the frontend sensor circuitry is improved to accommodate a wider range of cyclic load. These results demonstrate that triboelectric energy harvesting is a promising technique for self-monitoring the load inside knee implants.

It is a common power supply method in the power distribution system that energy extracted from the bus current supplies power to the intelligent monitoring devices. The ability to extract energy is directly related with the dimension of the core and the parameters design of the energy harvester. The present literatures only consider the case where the core works on unsaturated region, which rarely consider the case where the core works on saturated region. In this paper, the effects of the core saturation, the voltage ripple of the load, voltage drop of the rectifier diode, winding resistance and the number of turns are fully considered, and the output voltage theoretical model of energy harvester is established. The validity and accuracy of the output voltage theoretical model analysis is verified by experiment and simulation. To maximize the output characteristics of the energy harvester, the capacitance compensation circuit is proposed. When the core is not saturated, the capacitor plays a role of resonance. When the core is saturated, the capacitor provides some negative volt-second product to lift the output voltage. The output voltage theoretical model provides a more complete and effective approach for the optimal design of the energy harvesting current transformer parameters.

Estimating the state-of-charge of a lead-acid battery at remote seismic nodes is a key factor in managing the available power. Optimal management enables the continuous acquisition of seismic data of an area. This paper presents the management of lead-acid batteries at remote seismic nodes, using the Neural Network model's historical data to estimate the battery's state-of-charge. Powersim (PSIM) simulation tool was used to implement photovoltaic energy harvesting system with a buck mode converter and maximum power point tracking algorithm to acquire historical data. A backpropagation neural network technique for training the historical dataset of hourly points in 500 days on the Matlab platform is adopted, and a feedforward neural network is employed due to the irregularities of the input data. The neural network model's hidden layer contains the transfer function of the Tansig Function to produce the model output of state-of-charge estimations. Besides, this paper is based on the management of estimating the state-of-charge of the lead-acid battery near-realtime instead of relying on the vendor's lifecycle information. The simulated results show the simplicity and optimal estimations of state-of-charge of the lead-acid battery with RMSE of 0.023%.

This article presents a power-efficient hybrid energy-harvesting system that scavenges energy from solar, vibration, and radio frequency (RF) energy sources and converts into regulated output dc voltage courtesy buck–boost dc–dc converter. The proposed architecture incorporates tetra-paths for maintaining high power conversion efficiency (PCE) over extended input power range (−10 to 30 dBm). A time-domain maximum power point tracking technique is proposed for solar energy harvester. A high-efficiency full wave rectifier is designed for triboelectric rectifier. A 5.8-GHz RF-dc converter with adaptive matching is proposed to increase dynamic range of the input power. The chip is implemented in 0.18-µm bipolar-CMOS-DMOS process. The die area of the chip is 2.8 mm × 5.0 mm, including the pads. The solar and triboelectric energy harvesters achieve a measured peak efficiencies of 75.4% and 92.3%, respectively. The high-power 5.8-GHz RF-dc converter achieves measured PCE of 76% at 30 dBm input power. The low-power dual-band RF-dc converter operating at 900 MHz and 2.4 GHz obtains measured peak efficiencies of 73% and 71.9% at 0 dBm input, respectively. The buck–boost dc–dc converter employed in the proposed hybrid energy harvesting system achieves a measured peak PCE of 94.5%.

This article presents a textile antenna for dual-band simultaneous wireless information and power transfer (SWIPT). The antenna operates as a 2.4 GHz off-body communications antenna and a sub-1 GHz (785–875 MHz) broad-beam rectenna. Incorporated within the broadside microstrip antenna is a high-impedance rectenna for sub-1 GHz power harvesting. Utilizing antenna-rectifier co-design, the rectenna eliminates the rectifier matching network. The textile antenna is fabricated on a felt substrate and utilizes conductive fabrics for the antenna. At 2.4 GHz, the antenna achieves a realized gain of 7.2 dBi on a body phantom and a minimum radiation efficiency of 63%, with and without the rectifier. The rectenna achieves a best-in-class RF to dc efficiency of 62% from 0.8 $\mu \text{W}$ /cm2, representing over 25% improvement over state-of-the-art textile rectennas and demonstrating that SWIPT does not detrimentally affect the energy harvesting or communications performance. The antenna/rectenna occupies an electrically small area of $0.213\times 0.19\,\,\lambda ^{2}_{0}$ . This antenna is the first dual-band, dual-mode antenna demonstrated on textiles for SWIPT applications and the first dual-band matching network-free SWIPT rectenna.

This article presents a fully energy-autonomous temperature-to-time converter (TTC), entirely powered up by a triboelectric nanogenerator (TENG) for biomedical applications. Existing sensing systems either consume too much power to be sustained by energy harvesting or have poor accuracy. Also, the harvesting of low-frequency energy input has been challenging due to high reverse leakage of a rectifier. The proposed dynamic leakage suppression full-bridge rectifier (DLS-FBR) reduces the reverse leakage current by more than 1000 $\times $ , enabling harvesting from sparse and sporadic energy sources; this enables the TTC to function with a TENG as the sole power source operating at $\mu \text{m}$ 1P6M CMOS technology, consuming 0.14 pJ/conversion with 0.014-ms conversion time.

In this letter, we present Hermes – a novel, low-cost, wireless, batteryless, energy harvesting system for aerial vehicles for sensing wind speed and Angle of Attack (AoA) concurrently. Hermes comprises a set of piezoelectric films which flutter due to incoming wind and the characteristics of this aeroelastic flutter are utilized for determining the wind speed and AoA of the head-wind. Note that in our work we restrict the notion of flutter to high frequency oscillations due to incoming air flow. Hermes consists of five piezoelectric flags that are mounted on rigid clamps specifically placed at different angles. We designed Hermes to maximize the sensing performance and energy harvesting capability simultaneously, without compromising either accuracy or harvesting efficiency. Our current prototype can harvest the power of 440 $\mu$ W on average. Over a wide range AoA from $-10^{\circ }$ to $30^{\circ }$ , the estimation of the wind speed is within 0.7 km/h error with 90% probability, and AoA error is within $1.2^{\circ }$ with 90% probability. Since Hermes necessitates no wires and batteries and is a low-cost sensor, it is well suited for a range of UAVs, gliders, and aircraft, which require flexible sensor placement and do not require new wiring, which is often complex in aircraft. Hermes is the first of its kind that exploits piezoelectric energy harvesting to simultaneously sense AoA and wind speed. This work is expected to open up new avenues for interdisciplinary research on embedded computing devices for aerospace applications.

El presente artículo desarrolla una la revisión literaria sobre las arquitecturas de sistemas de captación de energía, identificando parámetros como: frecuencia, tipo de antena, arquitectura (elementos), entre otros. La metodología tiene cuatro etapas: a) búsqueda de documentación en la que se obtuvieron 10 sistemas, los cuales fueron denominados con la letra “S” acompañada del número de artículo; b) lectura de los documentos científicos; c) extracción de información y arquitectura de los sistemas en se detallan las etapas de cada sistema (las cuales varían de 2 a 4), las frecuencias de trabajo (300 KHz hasta 3.43 GHz, siendo la de 2.45 GHz la más empleada en sistemas para recolección de energía de radiofrecuencia). Además de utilizar, en ciertos sistemas, circuitos multiplicadores y rectificadores en diferentes configuraciones: media onda y onda completa, para posteriormente ser almacenadas en baterías o directamente aplicadas en dispositivos; d) documentación de la información extraída. Finalmente, completada la revisión literaria, se observó que en la mayoría de los artículos los sistemas tienen 3 etapas: antena, acoplamiento y rectificación, que el sistema transforma la energía recibida (corriente alterna) en corriente continua y que su funcionamiento varía en intervalos de frecuencia de 1.8 a 2.4 GHz, dependiendo de la configuración de cada sistema. Así también, el producto obtenido es una APP de consulta con un menú de selección de las diferentes arquitecturas investigadas, lo cual es un aporte muy beneficioso para los investigadores que deseen trabajar en esta área.

A novel ultrahigh frequency (UHF)/ultrawideband (UWB) hybrid radio frequency identification (RFID) tag is reported for object-specific remote vital-sign monitoring application. The tag achieves a record energy-harvesting sensitivity at the UHF band by codesigning a meander dipole antenna and a passive rectifier. The especially high quality-factor makes the frontend sensitive to near-field motions such as heartbeats and respiration in a wearable setting. The custom CMOS integrated circuit (IC) of approximately 1- $\mu \text{W}$ power consumption builds around a low-power UWB transmitter and converts the variations in the supply voltage to the impulse repetition rate. The tag consisting of the IC and UHF/UWB antennas requires no other discrete components and features a size of 4.2 cm $\times2.9$ cm and a weight of 0.93 g. A long-distance experiment verifies that the tag can be wirelessly powered up at 51 m from a 4-W effective-isotropic-radiation-power UHF transmitter. Remote vital-sign monitoring is validated on a human subject, in which the UHF power source is placed 2 m away from the subject with a power emission of less than 20 dBm. This work proposes a first-of-its-kind remote vital-sign monitoring solution based on a passively powered noncontact wearable tag. The design of the far-field energy-harvesting frontend with a record sensitivity serves as a reference for future works on battery-free remote sensors.

Unmanned aerial vehicle (UAV) could wirelessly transfer power to the devices on ground, thus recharging their batteries conveniently. Nevertheless, the efficiency of this wireless power transfer from UAV to ground remains unclear. This paper aims to answer this question from the theoretical perspective. We need two models for this purpose: an energy harnessing model and a UAV-to-ground wireless channel model. In the literature, a model of harnessing radio frequency (RF) energy and turning it into DC power is available. Our goal is to quantify the theoretical efficiency of RF-to-DC power conversion, and the amount of DC power gained as a result. Following this nonlinear energy harvesting circuit model, the signal level fluctuations caused by channel fading actually enhance the power conversion. To model the wireless channel gain from the UAV to the ground, we use the modified Loo’s channel model. Connecting it to the RF-to-DC power conversion model, we can determine the theoretical amount of DC power attainable from UAV’s transmission, in addition to its power conversion efficiency. Our finding shows that a heavy shadowing condition can enhance the RF-to-DC power conversion of a nonlinear energy harvesting circuit. For example, certain heavy shadowing condition may yield a conversion efficiency that is 7 dB higher than when shadowing is absent. This concurs with the previous finding that signal attenuation and fluctuation actually made the energy easier to be captured and harnessed by the nonlinear rectenna circuitry. Our finding confirms that high RF-to-DC conversion efficiency is attainable even under shadowing conditions.

Energy harvesting and power transmission is a significant challenge for the self-powered technologies towards mobile electronic devices. Here, we propose a hybridized energy harvester to complement each other’s strengths for simultaneously scavenging multiple types of energy and then wirelessly transmit the power. The harvester consists of electromagnetic-triboelectric nanogenerator units for collecting rotational energy and a commercial water-proof flexible solar cell. At a rotation rate of 500 rpm, the output current of electromagnetic-triboelectric nanogenerator units can reach about 630 mA through energy management. Moreover, the power harvested by hybridized energy harvester can be wirelessly transmitted up to a distance of about 100 cm in real time to charge mobile phone, anemometer, and hygrometer based on self-resonant coils. The hybridized energy harvester with wireless power transmission has potential applications in large-scale energy collection, long-distance wireless power transmission and sustainably driving mobile electronic devices.

This article proposes a continuously scalable-conversion-ratio (CSCR) switched-capacitor (SC) energy harvesting interface that extracts power from a thermoelectric generator (TEG), regulates a 0.75-V output load, and manages a 1.2–1.45-V battery. The structure employs the proposed CSCR SC converter to improve the power conversion efficiency up to 7.9% higher than that of the conventional converter. Moreover, the structure utilizes a proposed SC-based pulse frequency modulation (PFM) maximum power point tracking (MPPT) method to extract power from a TEG with an MPPT efficiency above 98.15%. In addition, the proposed interface adopts a flying capacitor sharing scheme for the dual-mode operation of the SC interface to increase both the peak end-to-end efficiency and maximum output power. With a 180-nm CMOS process, the proposed interface achieves a peak end-to-end efficiency of 85.4% and maximum output power of 20.8 mW.