Vibration energy harvesting is a promising solution for powering battery-free IoT systems; however, the instability of ambient vibrations presents significant challenges, such as limited harvested energy, intermittent power supply, and poor adaptability to various applications. To address these challenges, this paper proposes ViPSN2.0, a modular and reconfigurable IoT platform that supports multiple vibration energy harvesters (piezoelectric, electromagnetic, and triboelectric) and accommodates sensing tasks with varying application requirements through standardized hot-swappable interfaces. ViPSN 2.0 incorporates an energyindication power management framework tailored to various application demands, including light-duty discrete sampling, heavyduty high-power sensing, and complex-duty streaming tasks, thereby effectively managing fluctuating energy availability. The platform’s versatility and robustness are validated through three representative applications: ViPSN-Beacon, using an ultra-lowcost structural PZT (ϕ35 mm, <0.002 $) to enable a BLE advertisement from a single transient fingertip press with 100 m line of sight; ViPSN-LoRa, supporting wireless communication powered by wave vibrations in actual marine environments (Bohai Bay) with per-uplink task energy compatible with kilometer-scale field links; and ViPSN-Cam, enabling intermittent image capture and wireless transfer, delivering one frame approximately every 15 s under typical conditions. Experimental results demonstrate that ViPSN 2.0 can reliably meet a wide range of requirements in practical battery-free IoT deployments under energy-constrained conditions.

Human-motion energy harvesting is emerging as a promising solution for wearable electronics and devices, offering a sustainable power source that extends operational longevity and enhances durability. However, current techniques and prototypes have yet to achieve fully interactive, battery-free functionality. This paper presents a battery-free interactive gaming system powered by energy harvested from transient fingertip motion. To ensure the reactivity, interactivity, and stability of the fingertip motion harvester (FMH), we employ a multistable structure. The FMH unit provides a reliable energy solution by utilizing precharged potential energy within dynamically varying potential wells. Additionally, the integration of a bistable screen design facilitates seamless gaming experiences, decouples game logic from user interface mechanics, and ensures rapid system recovery after power interruptions. Beyond advancing fundamental research, this work pioneers a practical battery-free interaction paradigm based on fingertip motion, with potential for broader battery-free user interfaces and low-power interactive systems.

An increasing number of emerging Internet of Things (IoT) devices are transforming our daily lives in various fields, such as transportation, manufacturing, and home automation. The smart sensing floor offers solutions for tracking and analyzing user movements while maintaining acceptable privacy levels in both public and private spaces. Considering the large number of networked IoT devices on the ground, addressing power supply issues is crucial for efficient installation and convenient maintenance. This paper presents a self-powered and self-sensing smart floor design, with a particular application emphasis on fall detection. The design integrates energy harvesting and information collection, eliminating the reliance on traditional sensors. Each wireless floor tile serves as an integrated self-powered Bluetooth transmitter. It utilizes multiple piezoelectric patches for energy harvesting, a customized energy management circuit to accumulate the generated energy, and a low-power, low-cost system on chip (SoC) for wireless transmission. The signal packets from all tiles are collected and processed through an edge gateway to detect abnormal actions, like falls. A co-design of the piezoelectric array, power management, and transmission circuitry ensures that each step or fall can generate sufficient energy for three rounds of Bluetooth low-energy (BLE) beacon transmission. By receiving immediate data packets from all tiles and conducting specific analyses, the system can effectively identify accidental falls and send timely notifications. A prototype floor composed of 28 tiles and a gateway receiver has been developed. Experiments to test the performance of individual tiles and field tests with the multi-tile floor demonstrate that the system can detect falls reliably.

With the development of the Internet of Things (IoT), wireless pushbuttons are being increasingly used to control devices such as lights, fans, and air conditioners in smart homes and offices. In contrast to conventional systems, self-powered pushbuttons eliminate the inconvenience of cable arrangement and the cost of battery replacement. However, existing self-powered wireless pushbuttons can only send commands unidirectionally and lack an instant feedback mechanism. This limitation reduces system reliability and impairs the user experience. To tackle this issue, we propose ViPSN-button, a motion-powered wireless pushbutton that offers instant feedback. When the ViPSN-button is pressed, it can deliver instant feedback to the user. This feedback mechanism enables the user to confirm whether the host unit has successfully acknowledged their command. ViPSN-button is powered by a quasi-static-toggling energy harvester (QST harvester). The entire communication process of the ViPSN-button includes three steps: sending commands, receiving acknowledgments (ACK), and displaying an indication. All of these actions are carried out solely by utilizing the energy generated from a single press action. Experiments demonstrate that the ViPSN-button can achieve low-power, fast, private, and reliable bidirectional communication under the Enhanced ShockBurst (ESB) communication protocol. Field tests have been conducted, showing that the ViPSN-button can achieve reliable communication at a distance of 50 meters. ViPSN-button offers an innovative design concept for self-powered sensing nodes, facilitating bidirectional communication between host units and sensing nodes. This feature renders it highly suitable for a wide range of applications, including smart homes, smart offices, smart cities, and industrial IoT.

In the energy internet era, distributed energy storage systems will be widely used in various industrial, commercial, and residential scenarios. However, the modeling of energy flow and the digital flow of information operate on different temporal and spatial scales in traditional energy storage systems, lacking deep integration between energy flow and information flow. This prevents it from completely addressing the complex battery cell balancing and low safety issues in current distributed energy storage systems. The proposal of software-defined energy storage provides a new approach to solve the inherent problems in the battery industry by introducing the idea of internet shielding terminal differences into energy storage system. We proposed a software-defined reconfiguration battery system (SRBS) in this paper, which can manage different types of energy storage media to adapt to varying loads and operating conditions. Energy-type batteries, power-type batteries, and supercapacitors are integrated together to form an efficient and safe energy storage and power supply system. The hardware architecture and software control method of SRBS are described in detail. Finally, a real-world prototype is charged and discharged to show the successful coexistence and operation of different energy storage media within a single system.

Synchronous switch (SS) technique has been extensively studied in piezoelectric energy harvesting (PEH). The SS circuits can significantly enhance the output power under the same vibration excitation. Some SS solutions have also been developed for an inductive electromagnetic (EM) source by referring to its capacitive PEH counterpart and taking a complementary design. This paper proposes a synchronized current inversion and energy extraction (SCIEE) circuit for EM energy harvesting (EMEH). SCIEE utilizes two switched capacitive branches to carry out the synchronized current inversion at the electromotive voltage negative-to-positive zero-crossing instants and energy extraction at the voltage positive-to-negative zero-crossing instants. Theoretical analysis shows that the proposed circuit is suitable to be used with an EM transducer, whose quality factor is relatively large. Experiments show that, under the same mechanical excitation, SCIEE can harvest 25% more power compared with the cutting-edge synchronized switch energy extraction (SSEE) circuit for EMEH.

As the number of Internet of Things (IoT) nodes exponentially increases, replacing or recharging batteries for these end devices limits the working lifetime and space span of ubiquitous IoT. This paper introduces a battery-free IoT tag for indoor light illuminance estimation and evaluation. Utilizing the relationship between the light intensity and the interval between transmitted Bluetooth low energy (BLE) packets, the proposed system assesses the current indoor lighting conditions without using an additional sensor. Owing to their battery-free characteristics, these maintenance-free tags can be easily installed in a very wide range. The cost of this proposed tag is low, only a few discrete components enable the energy to slowly buffer and rapidly release after fully charged. The on/off voltage thresholds can be handily reconfigured. The compact prototype, whose size and cost are only 32x20 mm2and US$1, respectively, is fabricated and tested. It is capable of grading light levels above 30 lux. Field tests prove the feasibility and performance of this design. It gives a new insight into the future of pervasive sensing.

Vibration energy harvesters have been widely investigated to supply sustainable power for devices in the Internet of Things (IoT). Despite the advances in vibration energy harvesters, there still remain challenges in the design and optimization of energy harvesters to meet the increasing power demand of long-range IoT applications. In this article, an auxetic piezoelectric energy harvester with tapered thickness (TAEH) is proposed to improve the efficiency of energy harvesting by achieving the uniform stress and high average stress. Compared with traditional auxetic piezoelectric energy harvester with uniform thickness (UAEH), the stress distribution with tapered thickness is more uniform, which can contribute to a higher power output with lower maximum stress. Furthermore, the multiobjective optimization is used to further improve the average stress values without increasing the maximum stress, thus increasing the energy output. Finite element analysis is performed to validate the performance of the energy harvesters. In the experimental validation, it is found that with the tapered thickness introduced to the auxetic energy harvester, the maximum power output and power density of TAEH can be increased by 212.84% and 279.08%, respectively, compared with UAEH. After the optimization, these two indices of the optimized TAEH (OTAEH) are further increased by 24.32% and 27.59%, respectively. Specifically, a high power density of 0.148 mW/g is achieved in the OTAEH, indicating its high vibration energy harvesting performance with lightweight. Finally, it is demonstrated that the OTAEH can generate more than 40.94 mJ within 27.6 s to successfully power an IoT device for temperature sensing and long-range data transmission.

With the rapid advance of the Internet of Things (IoT), more and more wearable devices are being developed for real-time monitoring. Most of these existing monitors are powered by chemical batteries. Replacing and disposing batteries for an exponentially increasing number of IoT nodes prohibitively results in labor-intensive maintenance. It is also environmentally unfriendly. Gls EH, reclaiming the wasted ambient energy, is a promising technology for battery-free IoT. This article presents a novel motion-powered real-time human activity recognition (HAR) system called motion-powered HAR system (MP-HAR), where the harvester works as both an energy source and sensor. MP-HAR emphasizes low-power as well as low-cost characteristics, encompassing four necessary units: 1) energy transduction unit (ETU); 2) energy management unit (EMU); 3) energy user unit (EUU); and 4) edge computing unit (ECU). In particular, the unique intermittent operation based on the reconfigurable on/off threshold voltages given by the well-rounded energy-aware circuit has been discussed in detail. The balance between energy supply and information demand in MP-HAR has been achieved by using a handy design. Utilizing the unique correspondence between human arm swing frequency and harvested energy, the information flows with energy inside the system. By knowing the interval between transmitted packets, MP-HAR has realized HAR in real time. Moreover, an all-in-one prototype has been fabricated to validate the performance of the proposed system. Lab and field tests have demonstrated that MP-HAR can reliably recognize different human activities, such as standing, walking, jogging, and running. As a cyber-electro-mechanical co-design, MP-HAR has brought a promising solution for pervasive HAR and ubiquitous IoT.

Energy harvesting (EH) provides a promising solution for powering distributed Internet of Things (IoT) devices. Due to the low-level and sporadic ambient energy supply, an EH-powered device should operate in an intermittent and energy-driven mode. Commercial voltage supervisors were not optimized for the EH scenario, making it difficult to satisfy all new demands. The conventional energy management (EM) circuit has a risk of locking up during the turn-ON transient; therefore, it might fail to power the IoT load device. Previous technologies have used a relatively large circuit to solve this problem. In this article, a concise discrete three-transistor EM (3T-EM) circuit is proposed. It can track stored energy, switch ON/OFF to the load device, and provide a regulated voltage output. These key functions are realized by utilizing a minimum number of components; therefore, power consumption and manufacturing cost are largely cut. The voltage thresholds and minimum input current are theoretically derived. In experiments, the ON/OFF thresholds can be adjusted accurately, as predicted by the theory. The 3T-EM circuit can ensure the correct operation when the input current is as low as$0.4~ \mu \text{A}$. Control experiments also prove the effectiveness and performance of the 3T-EM circuit. The proposed 3T-EM circuit shows the characteristics of low cost, low power, inherent regulation, high voltage rating, and good predictability. It is a good candidate to perform the EM task in widely distributed EH-powered IoT devices.

Synchronous switch (SS) technique has been extensively studied in piezoelectric energy harvesting (PEH). The SS circuits can significantly enhance the output power under the same vibration excitation. Some SS solutions have also been developed for an inductive electromagnetic (EM) source by referring to its capacitive PEH counterpart and taking a reciprocal design. This paper proposes a synchronized current inversion and energy extraction (SCIEE) circuit for EM energy harvesting (EMEH). SCIEE utilizes two switched capacitive branches to carry out the synchronized current inversion at the electromotive voltage negative-to-positive zero-crossing instants and energy extraction at the voltage positive-to-negative zero-crossing instants. By inverting the transducer current, SCIEE increases the torque/force inside the transducer to extract more energy from the relative movement between magnets and coils. Theoretical analysis shows that the proposed circuit is suitable for use with an EM transducer, whose quality factor is relatively large. Experiments compared the output power of three harvesting schemes: SCIEE, synchronized switch energy extraction (SSEE), and conventional pulse-width modulation (PWM)-based harvesting scheme. When using the same prototyped EM harvester under the same mechanical excitation, SCIEE can harvest 38% more power, compared with the cutting-edge SSEE circuit for EMEH; and 900% more power, compared with the PWM-based harvesting scheme.

The literature on piezoelectric energy harvesting (PEH) systems underscores the role of circuit advancements in enhancing energy harvesting capability in resonance. Recent studies using phase-variable (PV) synchronized switch technologies have also shown potential in broadband PEH, thereby improving off-resonance energy harvesting. However, the electrically induced dynamics by existing interface circuits lack a comprehensive definition and demonstration, hampering the performance comparisons across different circuits. Regarding these gaps, this paper presents an impedance-based analysis and comparison of electromechanical joint dynamics in PEH systems employing various interface circuits. The focus is on their contributions to enhancing harvesting bandwidth. By introducing resonance tunability into the conventional ideal PEH model, this paper proposes a more generic impedance model. It reveals that the achievable dynamic ranges of practical interface circuits are subsets of the ideal arbitrarily tunable scenario. A detailed quantitative study on the attainable ranges of the PV synchronized switch circuit solutions is provided after the introduction of the ideal target. Simulation and experimental data from different interface circuits align well with theoretical findings. The paper concludes that resonance tunability hinges on the extent of the achievable reactive (imaginary) part of the equivalent impedance. Electromechanical coupling conditions and dielectric loss may further impact resonance tunability. The general ideal model and quantitative impedance analysis provided in this paper help guide the future design effort toward high-capability and broadband PEH systems.

The increasing number of distributed Internet of Things (IoT) devices makes the power supply a prominent issue, which limits the extent and lifetime of ubiquitous IoT networks. Mechanical energy harvesting (MEH) technology transforms the local mechanical energy into useful electricity. It provides a solution for the realization of self-sustainable motion-powered IoT applications. Given the volatile feature of most ambient vibrations, energy management methods are necessary for matching the unstable energy supply from the MEH sources and the energy demand of timely IoT tasks. This paper summarizes and analyzes two energy buffer-release mechanisms (EBRM) from mechanical and electrical aspects, respectively, for ensuring the robust operation of motion-powered IoT systems. Rather than emphasizing harvesting more energy from vibrations, as most of the previous studies did, we focus on energy neutrality among the mechanical, electrical, and cyber ingredients. A preset energy release threshold realized in either a mechanical or electrical way ensures the completion of every fundamental atomic task. The necessity of EBRM is demonstrated in three controlled experiments. Only those systems with a mechanical or electrical buffer-release mechanism can operate correctly.

Nowadays, the Industrial Internet of Things (IIoT) plays a more and more significant role in smart manufacturing. Predictive Maintenance (PdM) is one of the essential applications, recognizing the current status of the machine and preventing disastrous breakdowns. End-point sensors for such monitoring systems are powered mainly by batteries. As IIoT grows, constantly replacing batteries across thousands of devices is cost-prohibitive. In addition, tremendous original sensing data are wirelessly transmitted to the server for data analysis, causing colossal energy consumption. In this paper, we propose the first self-powered on-device PdM system based on piezoelectric energy harvesting and tiny machine learning (Tiny ML). A trained TinyML model is deployed on the low-cost microcontroller (MCU) for on-device inferring; only the diagnosis result is transmitted. With an emphasis on ultra-low-power demands, a piezoelectric energy harvester is utilized as an energy source and self-powered sensor (SPS) simultaneously. The energy-aware circuit provides reconfigurable on/off threshold voltages for efficient and robust intermittent operation. The balance between energy supply and demand in the battery-free system has been achieved by a handy design. A rich SPS dataset has been collected in a simulated vibration environment and analyzed by five well-known machine-learning models. Random forest stands out given ultra-small data length and sampling rate with accuracy up to 99% for four-class similar vibration diagnosis. Lab test validates the feasibility and performance. As a cyber-electro-mechanical co-design, the system provides a promising solution to the ubiquitous artificial intelligence of things (AIoT).

Owing to the advancement of vibration energy harvesting technology, many motion-powered battery-free Internet of things (IoT) applications have been reported in recent years. Since the ambient energy is usually weak, these IoT devices (a) mostly operate in intermittent or burst mode. The operation of these devices heavily depends on the level of stored energy. Conventional energy-aware solutions are carried out based on discrete general-purpose comparators or analog-to-digital converters (ADC) inside the system on chip (SoC) to monitor the storage level. Their power consumption is considerable in a low-power system. This paper presents a new energy-aware circuit, which can wake up or turn off the IoT devices according to the stored energy. Its standby quiescent current is at the sub-$\mu$A level. The proposed circuit also provides a regulated output voltage for IoT applications. This design is built with discrete analog components. It is low cost and has high feasibility. It is compatible with different kinds of micro-power generators.

This paper presents a triple-output piezoelectric energy harvesting (PEH) system with parallel synchronized switch harvesting on capacitors (P-SSHC) rectifier based on shared capacitors. By analyzing the principle of the P-SSHC rectifier, this paper supports the rationality of using shared capacitors to construct the multi-voltage conversion ratio (VCR) switch capacitor (SC) DC-DC converters. In addition, the adoption of a parallel structure in the multi-output SC DC-DC converters reduces the cross-regulation. Simulation results show that the proposed system not only has good input power adaptability (1/3X,1X,2X) but can also provide triple voltage (0.5V, 1V, 2V) with less cross-regulation. The maximum output power is 14.4μW when peak-to-peak open circuit voltage is 1.7V.

Wireless sensor network (WSN) enables the continuous monitoring of environmental conditions. These systems are usually powered by batteries. Given that there might be tremendous distributed sensor nodes in a network, battery maintenance must become one of the major challenges for their massive deployment. Energy harvesting technology, by which energy is extracted from the ambient environment, is developed for powering the ubiquitous Internet of Things (IoT) devices using different types of local energy, such as solar, vibration, and wind. In this paper, based on the vibration energy harvesting technology, we introduce a battery-free pavement roughness estimation system (BF-PRES), which provides road roughness information by linking the driving vibration and wireless packet count. Instead of harvesting energy to power an off-the-shelf commercial accelerometer and implementing some algorithms for vibration estimation, BF-PRES simply sends out a BLE Beacon packet, when the accumulated energy arrives at a sufficient level. Given that larger vibration intensity gives higher harvested power, the packet count within a constant time interval should be positively related to the road roughness. Lab testing shows the feasibility of the proposed design. In addition, this study also provides a new design scheme and easy implementation of battery-free or energy-constrained IoT systems.

Synchronized switch harvesting on inductor (SSHI) is an efficient active rectifier to extract energy generated from piezoelectric transducer in piezoelectric energy harvesting system. Unlike passive rectifiers, SSHI rectifiers require a power supply to drive synchronized switches. Unfortunately, there is no stable supply when the system starts from the cold state. Most designs let the system work as a passive full bridge rectifier (FBR) to charge power capacitor until a supply is available. However, a FBR requires high open-circuit voltage (VOC) and the FBR’s output voltage cannot go over VOC. This prevents the system from starting the SSHI rectifier if VOCis low. This paper proposes a new transducer reconfiguration design to lower the required VOCby 4 $\times$ to start up the SSHI system from the cold state. The proposed system is designed in a 0.18$-\mu$m BCD process and post-layout simulations show that the successful cold-startup under low VOCvoltage.

Energy harvesting technology enables the battery-free realization of some sensing, computing, and connectivity functions. However, its promotion in battery-free human-computer interaction is relatively slow in comparison. There is a critical energy gap around interactive devices which are screen-focused and usually power-hungry. This energy gap can be narrowed down and filled up by selecting a proper display and taking a sophisticated hardware and software co-design. Motion-powered gameboy, the first robust personal mobile gaming device, is manufactured by combining the features of a bistable E-ink display and a quasi-static toggling motion energy harvester. With the hardware-software co-design, the amount of energy generated by the player's pinch action can adequately guarantee successful user interaction and preferable user experience. The design methodology of the motion-powered game-boy provides a valuable example for the development of motion-powered human-computer interactive devices.

The emerging energy harvesting technology facilitates the development of ubiquitous and everlasting battery-free motion detectors. This article introduces a robust design of the transient-motion-powered motion detector, which is called ViPSN-pluck. “ViPSN” is the acronym for the 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 precharging 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 radio-frequency (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-electromechanical 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 Internet of Things devices.

Efficient simulation of switched-mode power conversion circuits is necessary for the analysis and optimization of power electronics. This paper introduces the extended impedance method (EIM) to the simulation and analysis of general switched-mode power converter circuits. By using the EIM method, the conventional impedance concept can be extended to involve more linear time-variant (LTV) and nonlinear devices, such as MOSFET switches and diodes, which are commonly used in switched-mode power conversion circuits. EIM models a circuit network from the component level in the frequency domain, rather than from the system-level constitutive differential equation in the time domain. Compared with the conventional averaging method, EIM can reveal more high-frequency features of a switched-mode converter circuit, in particular, those around the switching instants. A buck converter is taken as a representative example to validate the EIM based analysis. Both the simulation and experimental results prove that EIM provides precise numerical results, which match the real waveform, as the commercial simulators, e.g. PSpice and ADS, do. Moreover, it largely reduces the computational complexity towards more efficient and more flexible steady-state analysis of switched-mode power electronics.

A well-performed capacitive power transfer (CPT) system highly depends on its compensation to achieve load-independent (LI) output and zero phase angle (ZPA) operation. It is particularly meaningful to maintain these objectives under various misalignments. This paper is devoted to a general and comprehensive method to study and explore all the potential high-order compensations. The coupler parameter variation is evaluated under different types of misalignment, and misalignment-insensitive (MI) parameters are properly designed for MI resonance. A general and straightforward decomposition and synthesis method is then proposed to generate the high-order resonant tanks. With the help of inverse ABCD parameters, all tank candidates are further judged by their capability for LI output and ZPA operation. Finally, two example CPT systems are built to verify the LI output and ZPA operation under misalignment.

In piezoelectric energy harvesting (PEH), utilizing the synchronized switch interface circuits can significantly enhance the energy harvesting capability. Vibration sensing and synchronization are necessary functions for carrying out the synchronized switching actions. Those functions were usually implemented with an external displacement sensor in the early designs, which is not friendly for self-contained applications. This paper proposes a compact time-sharing solution for energy harvesting and vibration sensing by making full use of a modified buck-boost design. The circuit works in a strong discontinuous conduction mode (DCM). It is based on the principle that, under DCM operation, the voltage levels of the piezoelectric source side and the storage side are proportional to the actively switch- on and passively freewheeling intervals, respectively. Compared with the other self-powered synchronized switch PEH solutions, which rely on analog peak detectors, this self-sensing solution not only provides synchronized triggering signals for carrying out the switching actions but also tells more information about the driven vibration, such as its frequency and displacement magnitude. With the detailed vibration information, such a time-sharing solution offers more design convenience towards future multi-functional battery-free IoT applications.

The development of Internet of Things (IoT) has placed a strong demand on human motion detection technologies. Motion detectors acts an essential role in many civil applications, such as home security, occupancy and activity monitoring, retail analysis, etc. Emerging energy harvesting technologies provide promising solutions towards the ubiquitous and everlasting deployments of motion detectors. However, most existing battery-free solutions require special environmental conditions and suffer from frequent energy outages. Therefore, their applications are still very limited. This live demonstration exhibits a transient-motion-powered motion detector, named ViPSN-E, where "ViPSN" stands for vibration-powered sensor node [1]; "E" stands for an energy-mode device. ViPSN-E can carry out maintenance-free motion detection and wireless communication by making good use of the energy harvested from an instantaneous motion. The prototype of ViPSN-E is shown in Fig. 1. The system is developed based on ViPSN [1], an open-source development platform specified for vibration- powered IoT devices. ViPSN-E is composed of four parts: a piezo-magneto-elastic structure as energy harvester, a self- powered synchronized switch harvesting on inductor (SP- SSHI) interface circuit [2], an enhanced energy management unit, and a Bluetooth low energy (BLE) unit. The piezo- magneto-elastic harvester is composed of a low-cost piezoelectric cantilever and a pair of magnets, which are used to induce a plucking excitation in a transient and one-way movement.

Full-wave bridge rectifiers are widely used in power electronics for ac-dc conversion. In most of the conventional rectifier analysis, the diodes were modeled as unidirectional ideal switches with a constant threshold voltage. Prior knowledge was needed for specifying the on/off state of a diode in different phases, as well as whether the circuit works under continuous or discontinuous condition modes (CCM or DCM). However, under high-frequency operation, whose frequency might be up to several MHz, the influence of parasitic components, such as the junction capacitor, is more significant. Such a simple ideal switch model and preliminary on/off assignment are not accurate enough to describe the actual switching dynamics. Given this insufficiency, this paper proposes an equivalent impedance analysis and compensation study of full-wave bridge rectifiers based on the extended impedance method (EIM). EIM provides an efficient frequency-domain numeric solution for nonlinear circuit analysis. The steady-state characteristics of a rectifier circuit can be easily and efficiently simulated with EIM, no matter it operates in CCM or DCM, under low or high frequencies. Taking the bridge rectifier in the secondary side of a 6.78MHz wireless power transfer (WPT) system, for example, we demonstrate that EIM can model its dynamics very well. The efficient numeric method is further utilized to optimize the rectifier circuit through impedance compensation towards zero phase angle (ZPA) operation. Both the commercial simulator PSpice and experiment results validate the feasibility of this EIM based analysis and optimization.

To increase the energy extraction capability and thus improve the power efficiency, it is critical to reduce the energy loss of interface circuit in the energy harvesting (EH) system. The synchronized multiple bias-flip (SMBF) control has been proposed and proved to be highly effective to increase the output power in piezoelectric EH systems. However, many existing designs based on bias-flip suffer from the limitations in real application as the external control or supply are required. Moreover, the control algorithm is often only suitable for a designated transducer and inductor. In this paper, an integrated piezoelectric EH interface circuit with synchronized triple bias-flip (S3BF) has been proposed to flip the voltage across the parasitic capacitor of piezoelectric transducer during the zero-crossing. Meanwhile, the adaptive control of the flipping signal has also been adopted to meet the requirement of different configurations of transducers and inductors. The proposed interface circuit has been designed in 0.18-μm CMOS technology. Without any external control circuit or power supply, it can achieve cold start-up when the external inductances vary from 33 μH to 500 μH. When the external inductance is 50 μH, the simulated flip efficiency is 87.2 %, and the maximum output power is 17.4 μW, which is 3.4 times of the full-bridge rectifier.

In this article, we introduce a vibration-powered sensing node (ViPSN), a programmable Internet-of-Things (IoT) platform for the development of vibration-powered or motion-powered sensing and transmitting systems. It leverages the exploitation and utilization of ambient vibration energy by using a piezoelectric transducer. The roles and relations of six necessary modules, including energy generation unit (EGU), energy transduction unit (ETU), energy enhancement unit (EEU), energy management unit (EMU), energy user unit (EUU), and edge demonstration unit (EDU) are discussed in detail. In particular, an enhanced EMU is proposed by making necessary complements to an extensively used off-the-shelf integrated circuit (IC) solution for piezoelectric transducers. It provides more comprehensive energy storage indicating signals, such that the sensing, computing, and transmitting tasks can be carried out more robustly by keeping a good awareness of the remaining energy. Owing to the enhanced EMU design, vibration energy in various forms, such as intermittent and transient ones, can be more effectively harvested and utilized. The performance of ViPSN is evaluated, in terms of its lifetime and Quality of Service (QoS), under different vibration scenarios. The inclusive design and affiliated opensource project of ViPSN help build a new ecosystem for the research and development of vibration- or motion-powered IoT systems.

This work presents the novel integration of a reconfigurable piezoelectric energy harvester array (RPA) with a parallel synchronized switch harvesting on inductor (P-SSHI) rectifier. The proposed design realizes maximum power point tracking (MPPT) by adjusting RPA with changes in vibration amplitude. Compared with the traditional interface systems based on monolithic piezoelectric energy harvester (PEH), this design can operate in a wider range of input voltage, removing the need for a DC-DC converter, essential in the traditional design. This adaptability eliminates the need for extra-passive components and reduces switching loss. RPA can be also configured in series to reduce the inherent capacitance of PEHs, effectively improving the extraction efficiency of P-SSHI rectifier. Simulations of this system show that the efficiency of the RPA/P-SSHI combined system can be kept above 66% within an input voltage range from 0.03V to 4.39V.

In piezoelectric energy harvesting (PEH), synchronous electric charge extraction (SECE) has the benefit of load independence. To reduce the energy dissipation on parasitic resistance, multi-shot SECE (MCE) was implemented to split the charge extraction process. In this paper, a multiple charge extraction with bias-flip (MCEBF) interface circuit is proposed. It not only reduces the dissipation in charge extraction but also enlarges the extractable energy of piezoelectric structure by adding a bias-flip action. MCEBF can also generate positive and negative voltage rails via buck-boost topology to supply power for double-rail devices. The analytical and experimental comparison among SECE, MCE, and MCEBF under different controls are also provided. In experiments, MCEBF offers a 57.3% improvement over SECE and 24% over MCE, in terms of harvested power.

This paper presents a piezoelectric energy harvesting (PEH) interface circuit, which integrates an adaptive synchronized switch harvesting on inductor (SSHI) circuit and an active rectifier. The proposed adaptive SSHI circuit utilizes the signal of the active rectifier to control the synchronized switch so that the external control is not needed and the proposed PEH circuit can be effective for varies inductance. The active rectifier circuit and the switch control circuit of this paper are directly powered by the storage capacitor, which avoids the auxiliary power supply. As a result, the PEH interface circuit is self-powered. The proposed circuit has been designed in 0.18-μm CMOS technology, and the simulated power consumption of the control part is 0.178 μW. The simulation result shows the output power is 4.6 times of that in the ideal full-bridge rectifier. Moreover, without any external power supply, it is capable of cold startup to provide a stable output voltage.

This paper introduces the series synchronized triple bias-flip (S-S3BF) interface circuit for piezoelectric energy harvesting (PEH) enhancement. The S-S3BF topology is derived from its parallel counterpart (P-S3BF), which was proved to offer the maximum energy harvesting capability when three bias-flip actions are implemented. The S-S3BF is a little bit less capable than P-S3BF. However, it eliminates the circuit components by removing the bridge rectifier connected in parallel, such that can use only one capacitor to realize the bias voltages and energy storage simultaneously. Compared to the other single capacitor designs, the S-S3BF makes the best energy harvesting capability so far. Moreover, S-S3BF can automatically shift among single, double, and triple bias-flip operations under heavy, medium, and light load conditions, respectively. Therefore, it is more adaptive than previous designs. Theoretical and experimental results show that the harvested power can always follow the envelope (best case) of the single, double, and triple bias-flip operations during an entire charging process.

This paper introduces a new phase-variable switch control for the parallel synchronized triple bias-flip (P-S3BF) interface circuit, towards the broadband and high-capability piezoelectric energy harvesting (PEH) systems. By using the phase-variable P-S3BF (PV-P-S3BF), both the electrically induced damping and electrically induced mass/stiffness can be tuned to a certain extent in operation, such that to simultaneously make the dual tasks of broadband and high-capability in PEH. The joint dynamics and harvested power of the PEH systems using the PV-P-S3BF circuits are thoroughly discussed based on the harmonic analysis and impedance modeling. The available range of PV-P-S3BF is rationally shown in the complex impedance plane. The experimental results obtained with a PCB-level prototyped circuit show agreement with the analytical results. The new PV-P-S3BF circuit opens a promising future towards the electrically in-situ tunable broadband and high-capability PEH systems.

Literature has shown that the interface circuit plays an important role in a piezoelectric energy harvesting (PEH) system. By referring to the general model of synchronized multiple bias-flip (SMBF) and the recent implementation of parallel synchronized triple bias-flip (P-S3BF), this paper introduces a new implementation called parallel synchronized septuple bias-flip (P-S7BF) for further enhancing the PEH performance. By sophisticatedly designing the current steering network, P-S7BF realizes seven self-adaptive voltage bias-flip actions at every synchronized instant, such that it can further increase the net harvested power under the compromise of larger power extraction and smaller dissipation in power conditioning. The steady-state operation of P-S7BF is discussed in detail. Experiments are carried out on a prototyped piezoelectric structure under the same harmonic base vibration. The experimental results show that the ratios among the maximum harvested powers by using P-S7BF, P-S3BF, P-SSHI (parallel synchronized switch harvesting on inductor), and SEH (standard energy harvesting bridge rectifier) are 1.75 : 1.56 : 1.45 : 1.0, which validate the advantage of P-S7BF over the state-of-the-art solutions.

The energy harvesting technologies are going to replace the chemical batteries by providing an ever-lasting power solution for future dispersive devices in the Internet of Things (IoT), in particular, wireless sensor networks (WSN) and wearable electronics. The power conditioning circuit plays an crucial role for enhancing the energy harvesting capability [1]. This live demonstration shows a vibration-powered Bluetooth wireless sensor node with an emphasis on its running power factor correction (PFC) power conditioning design. The concurrent full paper has been submitted to the regular ISCAS track [2]. The self-powered sensor node is composed of three modules: the piezoelectric transducer, the self-powered synchronized switch harvesting on inductor (SP-SSHI) circuit for the running PFC power conditioning, and the Bluetooth module. These modules are enclosed by a 3D-printed frame. The sensor node assembly and disassembly are shown in Fig. 1(a) and (b).

The kinetic energy harvesting technologies have attracted extensive research interests with the purpose to enable more distributed and wearable electronics to be powered by their surrounding mechanical vibrations or motions. The power conditioning circuit is of importance for harvesting more energy from the vibration source and better managing the energy storage and power users. This paper introduces the design and implementation of a vibration-powered Bluetooth wireless sensor node, whose power is acquired by a low-cost piezoelectric transducer and processed by a self-powered synchronized switch power conditioning circuit. Given the capacitive feature of the piezoelectric transducers and the irregular feature of most vibration sources, the power conditioning circuit realizes the running power factor correction (PFC), making the piezoelectric voltage in phase with the equivalent current source at every current zero-crossing. As a result, it can significantly enhance the energy harvesting capability. Detailed analysis on the power consumption shows the feasibility of this design.

It has been shown in the previous study that the class-E power amplifier (PA) circuit can be efficiently simulated and optimized in the frequency domain by modeling the whole circuit with the extended impedance method (EIM). This paper reports a breakthrough in the EIM based class-E PA design by taking the nonlinear components into consideration. In analysis, the effect of the two state-dependent nonlinear components in a practical MOSFET switch, i.e., the parasitic drain-to-source junction capacitance and the body diode, is turned into the time-dependent characteristics by carrying out the states-to-time mapping. Iterative computation is necessary for obtaining the steady-state waveforms in view of the nonlinear components. Yet, given the high efficiency of EIM, it is proved that the EIM based optimization runs much faster than the state-of-the-art numerical class-E PA optimization.

This article introduces a novel perspective to the study of Class-E power amplifier by extending the scope of electrical impedance. Owing to this extension, the electrical property of the active switch in a Class-E circuit is taken as a special kind of impedance. Consequently, it is possible to regard a whole Class-E circuit as combination of impedances, whose total impedance is obtainable according to the existing circuit laws. When subjected to a DC supply voltage, the steady-state response of the total impedance can be directly obtained with the Ohm's law, regardless of the transient state. In addition, based on the formulation, regarding maximum power conversion efficiency as its design objective, Class-E optimization is also carried out. Since no waveform equation is required for both simulation and optimization, these simulation and optimization are more concise and efficient than those in all of the previous studies.