Micro-scale Energy Harvesting Research Articles

Attachable piezoelectric nanogenerators using collision-induced strain of vertically grown hollow MoS2 nanoflakes

Piezoelectric materials convert external mechanical force into electrical energy, due to the breaking of the centrosymmetry of the atomic structure. Piezoelectricity-based nano-generators (PNGs) based on two-dimensional transition metal dichalcogenides (TMDs) can generate electrical energy stably by the piezoelectric effect at their nanoscale thickness. However, the commercialization of TMD-based PNGs is limited by their poor piezoelectric performance and microscale energy harvesting. Here, we present the first centimeter-scale PNGs based on molybdenum disulfide (MoS2) nanosheets with vertically grown hollow MoS2 nanoflakes (v-MoS2 NFs) obtained by chemical vapor deposition for energy harvesting from human motions. The collision of v-MoS2 NFs with a preferred odd-atomic-layer number and their 2H antiparallel phase leads to efficient electrical energy generation during the bending movement. Further, basal MoS2 films with v-MoS2 NFs are transferred onto flexible substrates via conventional polymer-assisted methods for the fabrication of attachable and wearable piezoelectric power generators.

Performance evaluation of a novel piezoelectric-based high-frequency surge-inducing synchronized switching strategy for micro-scale energy harvesting

Abstract Energy harvesting technology has recently received remarkable attention in line with progressive developments in low-power-consuming microsystems used in daily applications. In particular, piezoelectric elements have received considerable attention for promising energy harvesting systems because of their applicability and simplicity. In this study, a high-frequency surge-inducing synchronized switching (H-S3HI) strategy that exploits the full potential of the surge phenomenon is proposed to effectively improve the energy harvesting efficiency of piezoelectric harvesters. Moreover, this strategy can guarantee the useable energy harvesting performance even for micro-scale vibrations. The effectiveness of the proposed switching strategy was demonstrated by performing numerical simulations and experiments with a cantilever-type piezoelectric harvester under sinusoidal and random-vibration conditions.

Flow-induced vibration of a square cylinder and downstream flat plate associated with micro-scale energy harvester

The phenomenon of flow-induced vibration (FIV) over a square cylinder at Reynolds numbers, Re = (3.6–12.5 × 103) is numerically studied. This current study provides a detailed explanation of the behaviour of transverse motion of square cylinder with the mass damping ratio, mζ* = 2.48. The computation of FIV is conducted by numerical simulation based on the Unsteady Reynolds Navier-Stokes (URANS) flow field using OpenFOAM software. The first part of the numerical simulation consists of an isolated square cylinder to validate the solution with previous studies. The computation of FIV with a total number of cells, N = 101,662 have shown a comparable pattern of amplitude curve. The coexistence of vortex-induced vibration (VIV) and galloping is observed for a single isolated cylinder. A downstream flat plate is introduced in the second part of the work. Different gaps separation between the cylinder and flat plate (0.1 ⩽G/D ⩽ 3) are simulated. Based on the amplitude curve against reduced velocities 4 ⩽UR⩽ 20, four regimes are identified. According to the power estimation, the optimum gap separation is G/D = 0.1. The harnessed power is higher than a single isolated square cylinder while preserving the robustness for the remote harvesting purpose.

Micro Energy Harvester With Dual Electrets on Sandwich Structure Optimized by Air Damping Control for Wireless Sensor Network Application

In this paper, we have designed, fabricated, and characterized a micro-scale electrostatic energy harvester based on microelectromechanical system technology. Sandwich structure with dual electrets was utilized, which can be fully packaged with optimal pressure control to reduce the energy loss from squeeze air damping. With out-of-the-plane gap closing scheme, the energy harvester mainly consists of two variable capacitors, and the overall size of the micro device is about 1.3 cm $\times1.8$ cm $\times0.15$ cm. With dual electrets, the output power of the device can be increased to 1.5–2 times higher. With low damping effect at packaging pressure of 5 Pa, the normalized power density can be improved by about 2300 times. The device has been used to provide power supply for a battery-free wireless sensor network, and a temperature signal can be posted to internet every 265 s.

On the performance of a micro-scale Bach-type turbine as predicted by discrete-vortex simulations

The flow past a Bach-type vertical-axis wind or current turbine is simulated using a viscous Discrete-Vortex Method at a Reynolds number of 1500. The main purpose of the study is to evaluate the suitability of Bach-type turbines for use as micro-scale energy harvesters that can be applied to power, for example, sensor nodes of a wireless sensor network. The maximum power coefficient of the turbine operating at a prescribed constant tip-speed ratio is found to be 0.18, which is comparable to the performance of the same turbine at much higher Reynolds numbers, thus indicating only minimal performance penalty for miniaturization. The speed of the turbine has a strong influence on the evolution of vortical flow structures. A new wake-capturing mechanism that boosts the performance of the turbine is discovered from the simulations for a certain range of tip-speed ratios where the vortex shed by the advancing blade helps drive the returning blade. In addition to prescribed rotation, free rotation of a steel Bach-type turbine in water is also investigated. Significant fluctuation in angular velocity over one period of rotation is observed. This speed fluctuation is found to be detrimental to energy extraction, reducing the maximum power coefficient to approximately 0.16. The estimated power generating capacity of a micro-scale turbine indicates that it can significantly extend the life expectancy of a wireless sensor node or even maintain the node in a low-power state indefinitely.

Effects of Deposition Process on Poly-Si Microscale Energy Harvesting Systems: A Simulation Study

In this paper, the feasibility of a low-temperature polysilicon (LTPS) microscale energy harvester for a wireless sensor node is investigated. For that purpose, two device-level models for the LTPS solar cell and thin-film transistors are proposed and employed in system-level evaluation of an energy harvesting system. The results of our analysis indicate that: 1) the maximum power operating point for the solar cell is different when connected to a lossy power converter; 2) increasing the average grain size of the LTPS film can reduce the circuit area by 20 times, while increasing the output power by 6%; and 3) the proposed bottom–up approach enables the designers to identify system bottlenecks and improve the performance accordingly.

Modeling and experimental verification of a fan-folded vibration energy harvester for leadless pacemakers

This paper studies energy harvesting from heartbeat vibrations for powering leadless pacemakers. Unlike traditional pacemakers, leadless pacemakers are implanted inside the heart and the pacemaker is in direct contact with the myocardium. A leadless pacemaker is in the shape of a cylinder. Thus, in order to utilize the available 3-dimensional space for the energy harvester, we choose a fan-folded 3D energy harvester. The proposed device consists of several piezoelectric beams stacked on top of each other. The volume of the energy harvester is 1 cm3 and its dimensions are 2 cm × 0.5 cm × 1 cm. Although high natural frequency is generally a major concern with micro-scale energy harvesters, by utilizing the fan-folded geometry and adding tip mass and link mass to the configuration, we reduced the natural frequency to the desired range. This fan-folded design makes it possible to generate more than 10 μW of power per cubic centimeter. The proposed device is compatible with Magnetic Resonance Imaging. Although the proposed device is a linear energy harvester, it is relatively insensitive to the heart rate. The natural frequencies and the mode shapes of the device are calculated analytically. The accuracy of the analytical model is verified by experimental investigations. We use a closed loop shaker system to precisely replicate heartbeat vibrations in vitro.

A Novel Tunable Multi-Frequency Hybrid Vibration Energy Harvester Using Piezoelectric and Electromagnetic Conversion Mechanisms

This paper presents a novel tunable multi-frequency hybrid energy harvester (HEH). It consists of a piezoelectric energy harvester (PEH) and an electromagnetic energy harvester (EMEH), which are coupled with magnetic interaction. An electromechanical coupling model was developed and numerically simulated. The effects of magnetic force, mass ratio, stiffness ratio, and mechanical damping ratios on the output power were investigated. A prototype was fabricated and characterized by experiments. The measured first peak power increases by 16.7% and 833.3% compared with that of the multi-frequency EMEH and the multi-frequency PEH, respectively. It is 2.36 times more than the combined output power of the linear PEH and linear EMEH at 22.6 Hz. The half-power bandwidth for the first peak power is also broadened. Numerical results agree well with the experimental data. It is indicated that magnetic interaction can tune the resonant frequencies. Both magnetic coupling configuration and hybrid conversion mechanism contribute to enhancing the output power and widening the operation bandwidth. The magnitude and direction of magnetic force have significant effects on the performance of the HEH. This proposed HEH is an effective approach to improve the generating performance of the micro-scale energy harvesting devices in low-frequency range.

A REVIEW ON THE POTENTIAL OF SILICON NANOWIRES (SINWS) IN THERMOELECTRIC ENERGY HARVESTERS

There are various types of micro-scale energy harvesters (EH) that have been reported by many researchers around the world such as photovoltaic cells, piezoelectric transducers, electromagnetic transducers, thermoelectric and others. Energy harvester that harvest ambient energy which exists naturally or produced by mankind or machines, are able to be an alternative source for low-power devices such as mobile phone, laptop, health implant and many more. Thermoelectric is an energy harvester that converts heat waste from any sources such as vehicle engines, laptops or human body into electricity. Numerous kind of thermoelectric materials including metals and semiconductors have been investigated by researchers that produce different performances and efficiencies. Recently, researchers are looking forward to nanostructured semiconductors such as nanoribbons, nanotubes, nanowires and quantum dots as a potential to increase the figure of merit (ZT) and efficiency of thermoelectric EH. This paper reviews on silicon as the second most abundant element on earth and commonly used in electronic components is possible to be used as thermoelectric material. Silicon in bulk has high thermal conductivity which is less desirable for thermoelectric application. However, many studies regarding nanostructured silicon such as silicon nanowires have been carried out with promising results in reducing thermal conductivity.

Applications of energy harvesting for ultralow power technology

Ultra-low-power (ULP) technology is enabling a wide range of new applications that harvest ambient energy in very small amounts and need little or no maintenance – self-sustaining devices that are capable of perpetual or nearly perpetual operation. These new systems, which are now appearing in industrial and consumer electronics, also promise great changes in medicine and health. Until recently, the idea of micro-scale energy harvesting, and collecting miniscule amounts of ambient energy to power electronic systems, was still limited to research proposals and laboratory experiments.Today an increasing number of systems are appearing that take advantage of light, vibrations and other forms of previously wasted environmental energy for applications where providing line power or maintaining batteries is inconvenient. In the industrial world, where sensors gather information from remote equipment and hazardous processes; in consumer electronics, where mobility and convenience are served; and in medical systems, with unique requirements for prosthetics and non-invasive monitoring, energy harvesting is rapidly expanding into new applications.This paper serves as a survey for applications of energy harvesting for ultra low power technology based on various technical papers available in the public domain.

Micropower Clock Generator Circuit Using an Optimized Band-Gap Reference for Energy Harvesting Charge Pumps

In recent years, a lot of research and effort have been developed in micro-scale energy harvesting (EHV) for Wireless Sensor Networks (WSN) because of their viable and promising approach for self powering low voltage circuit. The key element in such an application is the charge pump circuit as a power converter. A charge pump (CP) driven by tow pumping clocks, is introduced to generate voltages beyond the supply voltage range. In this paper, a clock circuit for a charge pump was proposed. This circuit was achieved using tow components: a Voltage Control Ring Oscillator (VCOR) as a clock generator and a Band-Gap Reference (BGR) as a voltage reference. The circuit was implemented using 0.35 µm CMOS process, and was generated the desired pumping clocks signals at tens of Mhz under just 9.6 µW for a power supply of only 1V.

Power management circuits for self-powered systems based on micro-scale solar energy harvesting

In this paper, two types of power management circuits for self-powered systems based on micro-scale solar energy harvesting are proposed. First, if a solar cell outputs a very low voltage, less than 0.5 V, as in miniature solar cells or monolithic integrated solar cells, such that it cannot directly power the load, a voltage booster is employed to step up the solar cell’s output voltage, and then a power management unit (PMU) delivers the boosted voltage to the load. Second, if the output voltage of a solar cell is enough to drive the load, the PMU directly supplies the load with solar energy. The proposed power management systems are designed and fabricated in a 0.18-μm complementary metal–oxide–semiconductor process, and their performances are compared and analysed through measurements.

Maximum Power Point Tracking for the Micro-Scale Photovoltaic Power System

In this paper, we give a comprehensive consideration on the maximum power point tracking (MPPT) algorithm for micro-scale solar energy harvesting system. Basing on the comparison analysis the MPPT algorithm of fractional open circuit voltage (FOCV) is certificated to be the simplest method among all the algorithms focus on small size photovoltaic devices. As a validation, an example is given to demonstrate the effectiveness of the proposed idea.

Experimental Study of a Piezoelectric Rain Energy Harvester

Over the past few decades there has been significant advancement in the development of microelectronics. This has attracted attention of micro-scale energy harvester systems that could harvest energy from the operating environment of the microsystem. In this paper, rain energy harvesting using piezoelectric beam is tested. This paper seeks to create an experimentally validated proof of concept piezoelectric rain energy harvester using a piezoelectric beam. A rain simulator consists of six solenoid valves is designed to simulate different rain types. The effect of multiple water droplets impinging different positions on the piezoelectric beam is studied in this paper. Results show that a 4.5 ± 0.2 mm diameter water droplet falling at height of 0.82 m impinging the piezoelectric energy harvester is capable of generating a peak power of 0.16 mW.

Ultra-wide frequency broadening mechanism for micro-scale electromagnetic energy harvester

This work proposed a hybrid frequency broadening (HFB) mechanism in micro-scale for vibration energy harvesting with ultra-wide bandwidth. A strong HFB behavior is induced by the Duffing stiffening of the clamped-clamped beam stretching and further stimulated continuously by three distributed resonances including out-of-plane mode I at 62.9 Hz, torsion mode II at 82.1 Hz, and twist mode III at 150 Hz. At the acceleration of 1.0g, the microfabricated device with a small area of 6 × 6 mm2 is able to broaden the operating bandwidth from 62.9 Hz to be as wide as 383.7 Hz. This design methodology can be implemented for efficient electromagnetic energy harvesting.

Design Methodology of a Micro-Scale 2-DOF Energy Harvesting Device for Low Frequency and Wide Bandwidth

A detailed design methodology of a micro-scale 2-DOF energy harvesting device that can harvest human motion energy of low frequency and wide bandwidth is developed. Based on the concept of the 2-DOF vibration absorber, device parameters are selected to harvest energy at low frequency of 1-10 Hz and wide bandwidth with ±20% of the mean frequency, which matches the human motion. The device dimensions are limited to 40 × 30 × 10 mm3 to fit with the human wrist size. Then, a finite element model is developed to investigate the system performance with the selected parameters. When subjected to harmonic excitation of 1 g, the proposed 2-DOF device is able to provide a power of at least 10 μW in between the two close resonant peaks of 4 Hz and 6 Hz, which is the target frequency range. The device shows very high power per square frequency compared with the reported harvesters.

A Batteryless low Input Voltage micro-scale Thermoelectric Based Energy Harvesting Interface Circuit with 100mV Start-up Voltage

A Batteryless low input voltage micro-scale thermo electric based energy harvesting interface circuit with 0.1V start-up voltage presents in this paper. The active technique and its components have been chosen such as MOSFET and thyristor to design the proposed DC-DC boost converter with low input voltage (i.e., 0.1V) for energy harvesting interface circuit. The minimum working voltage as low as 0.1V an input the equivalent voltage of thermoelectric transducer has been proposed to design the boost converter. This paper presents techniques for the systematic modeling, analysis, and design of interface circuitry used in the equivalent voltage of the micro-scale thermoelectric energy harvesting systems. In the development of active-based circuits, the DC-DC step-up (boost) converter with thyristor have been designed instead of mainly diode and other components because the forward voltage of diode is (0.7V) higher than the incoming input voltage (0.1V). Finally, the complete proposed energy harvester circuit have been designed and simulated using the PSPICE software. The proposed circuit is capable to step-up regulated DC voltage up to 3.75V. The efficiency of the proposed circuit is greater than 65% following the simulation results. This work has focused on the application of micro-devices Wireless Sensor Network (WSN) device can be operated without battery. Streszczenie. W artykule opisano oszczednościowe źrodlo napiecia wykorzystujące jedynie sile temoelektryczną. Uklad elektroniczny startuje juz przy napieciu zasilania 0.1V i potrafi wytworzyc wyjściowe napiecie o poziomie blisko 4 V. Jako zastosowanie ukladu przewiduje sie mozliwośc zasilania czujnikow bezprzewodowych jedynie z baterii slonecznej. (Bezbateryjny przeksztaltnik napiecia termoelektrycznego o poziomie 0.1V na sygnal napieciowy o poziomie kilku woltow)

Triboelectric nanogenerators as new energy technology and self-powered sensors - principles, problems and perspectives.

Triboelectrification is one of the most common effects in our daily life, but it is usually taken as a negative effect with very limited positive applications. Here, we invented a triboelectric nanogenerator (TENG) based on organic materials that is used to convert mechanical energy into electricity. The TENG is based on the conjunction of triboelectrification and electrostatic induction, and it utilizes the most common materials available in our daily life, such as papers, fabrics, PTFE, PDMS, Al, PVC etc. In this short review, we first introduce the four most fundamental modes of TENG, based on which a range of applications have been demonstrated. The area power density reaches 1200 W m(-2), volume density reaches 490 kW m(-3), and an energy conversion efficiency of ∼50-85% has been demonstrated. The TENG can be applied to harvest all kinds of mechanical energy that is available in our daily life, such as human motion, walking, vibration, mechanical triggering, rotation energy, wind, a moving automobile, flowing water, rain drops, tide and ocean waves. Therefore, it is a new paradigm for energy harvesting. Furthermore, TENG can be a sensor that directly converts a mechanical triggering into a self-generated electric signal for detection of motion, vibration, mechanical stimuli, physical touching, and biological movement. After a summary of TENG for micro-scale energy harvesting, mega-scale energy harvesting, and self-powered systems, we will present a set of questions that need to be discussed and explored for applications of the TENG. Lastly, since the energy conversion efficiencies for each mode can be different although the materials are the same, depending on the triggering conditions and design geometry. But one common factor that determines the performance of all the TENGs is the charge density on the two surfaces, the saturation value of which may independent of the triggering configurations of the TENG. Therefore, the triboelectric charge density or the relative charge density in reference to a standard material (such as polytetrafluoroethylene (PTFE)) can be taken as a measuring matrix for characterizing the performance of the material for the TENG.

새로운 MPPT 제어기능을 갖는 마이크로 빛에너지 하베스팅 회로

In this paper micro-scale solar energy harvesting system with a new MPPT control are proposed. In conventional solar energy harvesting systems, continuous perturbation techniques of the clock frequency or duty cycle of a power converter have been used to implement MPPT(Maximum Power Point Tracking) control. In this paper, we propose a new MPPT technique to control the duty cycle of a power switch powering a power converter. The proposed circuit is designed in CMOS process, and the designed chip area including pads is .

Enhanced Performance of Dispenser Printed MA n-type Bi2Te3 Composite Thermoelectric Generators

This work presents performance advancements of dispenser printed composite thermoelectric materials and devices. Dispenser printed thick films allow for low-cost and scalable manufacturing of microscale energy harvesting devices. A maximum ZT value of 0.31 has been achieved for mechanically alloyed (MA) n-type Bi₂Te₃-epoxy composite films with 1 wt % Se cured at 350 °C. The enhancement of ZT is a result of increase in the electrical conductivity through the addition of Se, which ultimately lowers the sintering temperature (350 °C). A 62 single-leg thermoelectric generator (TEG) prototype with 5 mm ×700 μm × 120 μm printed element dimensions was fabricated on a custom designed polyimide substrate with thick metal contacts. The prototype device produced a power output of 25 μW at 0.23 mA current and 109 mV voltage for a temperature difference of 20 °C, which is sufficient for low power generation for autonomous microsystem applications.