Airflow Energy Harvester Research Articles

Analysis of Output Performance of Airflow Energy Harvester Using Diamagnetic Levitation Based on Taguchi Method

Analysis of Output Performance of Airflow Energy Harvester Using Diamagnetic Levitation Based on Taguchi Method

Pulsed Airstream-Driven Hierarchical Micro-Nano Pore Structured Triboelectric Nanogenerator for Wireless Self-Powered Formaldehyde Sensing.

Formaldehyde (HCHO), as a common volatile organic compound, has a serious impact on human health in the daily lives and industrial production scenarios. Given the security issue of HCHO detection and danger warning, a ZIF-8/copper foam based pulsed airstream-driven triboelectric nanogenerator (ZCP-TENG) is designed to develop the self-powered HCHO sensors. By combining contact electrification and electrostatic induction, the ZCP-TENG can be utilized for airflow energy harvesting and HCHO concentration detection. The short-circuit current and output power of the ZCP-TENG can reach 2.0 µA and 81 µW (20 ppm). With the high surface area, abundant micro-nano pores, and excellent permeation flux, the ZCP-TENGs exhibit excellent HCHO sensing response (61.3% at 100 ppm), low detection limit (≈2 ppm), and rapid response/recovery time (14/15 s), which can be served as a highly sensitive and selective HCHO sensor. By connecting an intelligent wireless alarm, the ZCP-TENGs are designed to construct a self-powered warning system to monitor and remind the HCHO of exceedance situations. Moreover, by combining a support vector machine model, the difference concentrations can be quickly identified with an average prediction accuracy of 100%. This study illustrates that ZCP-TENGs have broad application prospects and provide guidance for HCHO monitoring and danger warnings.

Improvement of the Airflow Energy Harvester Based on the New Diamagnetic Levitation Structure.

This paper presents an improved solution for the airflow energy harvester based on the push-pull diamagnetic levitation structure. A four-notch rotor is adopted to eliminate the offset of the floating rotor and substantially increase the energy conversion rate. The new rotor is a centrally symmetrical-shaped magnet, which ensures that it is not subjected to cyclically varying unbalanced radial forces, thus avoiding the rotor's offset. Considering the output voltage and power of several types of rotors, the four-notch rotor was found to be optimal. Furthermore, with the four-notch rotor, the overall average increase in axial magnetic spring stiffness is 9.666% and the average increase in maximum monostable levitation space is 1.67%, but the horizontal recovery force is reduced by 3.97%. The experimental results show that at an airflow rate of 3000 sccm, the peak voltage and rotation speed of the four-notch rotor are 2.709 V and 21,367 rpm, respectively, which are 40.80% and 5.99% higher compared to the three-notch rotor. The experimental results were consistent with the analytical simulation. Based on the improvement, the energy conversion factor of the airflow energy harvester increased to 0.127 mV/rpm, the output power increased to 138.47 mW and the energy conversion rate increased to 58.14%, while the trend of the levitation characteristics also matched the simulation results. In summary, the solution proposed in this paper significantly improves the performance of the airflow energy harvester.

Airflow Energy Harvester Based on Diamagnetic Levitation Structure With Double Stabilizing Magnets

In this paper, an airflow energy harvester based on a push-pull diamagnetic levitation structure with double stabilizing magnets is proposed to explore its energy harvesting efficiency and environmental adaptability. The static and dynamic mechanical characteristics of the floating magnet are studied. Then, three structure parameters resulting in the change of energy conversion factor (ECF) are analyzed using COMSOL software. A platform was constructed to carry out experiments, and the results are as follows. Firstly, when the air flowrate from left nozzle ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q_NL</i> ) and the air flowrate from right nozzle ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q_NR</i> ) are both 3000 sccm, the average peak voltage (APV) is 1.924 V, the average power (AP) is 97.93 mW and the energy conversion ratio (ECR) is 41.12%. Secondly, when <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q_NL</i> is 3000 sccm and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q_NR</i> is 2000 sccm, the APV is 1.245 V, the AP is 41.01 mW and the ECR is 26.57%. Thirdly, when <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q_NL</i> is 3000 sccm and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q_NR</i> is 0 sccm, the APV is 0.666 V, the AP is 11.68 mW and the ECR is 9.82%. The experiment results show that it is feasible and performs well in a real-life situation, which is a major step toward the application as an energy harvester.

Optimal analysis on coil and rotor in a diamagnetically airflow energy harvester

In this paper, the proposed diamagnetic levitation structure was studied to explore its potential in energy harvesting. It is proved that the floating magnet rotor can be levitated stably under the joint action of two highly oriented pyrolytic graphite (HOPG) sheets and the lifting magnet. Simulation calculation was carried out to analyze the influence of different coil radius and wire diameter on peak voltage and average power in scheme A or scheme B, so as to obtain appropriate layout and wire diameter for the coils which was built the experimental platform. Subsequently, the center hole, notch radius and thickness of the floating rotor are analyzed by experiment. And the influence of different parameters on rotation speed of the rotor and peak output voltage of coils is obtained. Through experimental results, it is found that the notch radius of the floating rotor has the greatest influence on the rotation speed of the rotor. Based on the experiment, a new-type rotor was designed, with an outer shell to reduce the notch radius. Compared with the original floating rotor, there was 49.73% increase in voltage, 55.70% increase in rotation speed and 124.50% increase in power according to the experimental results. Test was performed with the optimization, the LED array of Zhengzhou University logo, which was composed of 60 LED lights, was lighting up. According to the oscilloscope measurement, the diamagnetic levitation energy harvester has an output voltage up to 1.294 V and average power of 60.67 mW under gas flow rate of 3000 sccm and nozzle exit velocity of 6.173 m/s. Obviously, the new-type rotor proposed in this paper could significantly increase the energy conversion efficiency, and make the future application of airflow energy harvester a step further.

Harvesting airflow energy from circular cylinder wake via a thin polyvinylidene fluoride film

To improve the characteristics of airflow energy harvesting, this paper presents a new piezoelectric wind energy harvester (PWEH), in which a polyvinylidene fluoride (PVDF) film was directly located in the wake of the circular cylinder. Four important parameters were independently varied for detailed experimental investigations: wind speed, spacing ratio for the distance between the center of the circular cylinder and the tip of the PVDF film to the circular cylinder diameter, diameter of the circular cylinder, and load resistance. The results indicated that the designed PWEH performed optimally with the occurrence of resonance, maintaining a relatively high output when significantly exceeding the resonance wind speed. The PVDF film inhibited the vortex shedding of the circular cylinder, which weakened with increasing spacing ratio. The optimum value of the spacing ratio should be approximately 2.5, which yields an effective coupling between the vortex and structure. The diameter of the circular cylinder played an important role in determining the output power. The match between the load resistance and PWEH also contributed to the high-level performance. Moreover, with an increase in the diameter of the circular cylinder, the increasing blockage ratio unexpectedly enhanced the vortex shedding frequency and decreased the theoretical resonance wind speed, which provided a new orientation for improving the performance of such PWEHs.

Analysis and experiment of an airflow energy harvester based on diamagnetic levitation

This paper proposes an energy harvesting structure that can effectively generate electrical power. Diamagnetic levitation mechanism is utilized, with a floating magnet rotor levitated between two pyrolytic graphite plates just using a lifting magnet and airflow. The magnet rotor could be stably suspended under joint action of magnetic forces and diamagnetic forces, being driven to rotate by airflow. Three magnet rotors, with 1.5 mm, 3 mm and 4.5 mm thickness respectively, were adopted in the study so as to investigate the influence of structural parameters of the magnet rotor on the performance of the harvester. Simulation and experiment were carried out for the three magnet rotors. Among the tree magnet rotors, the 1.5 mm-thick one has the best output performance, with the lowest dynamic stability. Therefore, the energy harvester is to find tradeoff between output characteristics and dynamics. In this work, it was discovered that the peak output voltage of the energy harvester increased with the square of flowrate. As the flowrate increased to 3000 sccm, the 1.5 mm-thick rotor was rotating at a speed of 19729 rpm under standard temperature and pressure, with 1.255 V output voltage and 49 mW power. The diamagnetic levitation structure is expected to be applied to sensing, energy harvesting and air bearing under actuation of airflow due to its advantages of low friction, high rotation speed and large levitation space.

Self-powered communicating wireless sensor with flexible aero-piezoelectric energy harvester

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 μW instead of 30 μW 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 (≈540 cm3), however the threshold wind speed to increase (>6 m/s). The harvested energy was then used to operate a wireless sensor.

Overview of environmental airflow energy harvesting technology based on piezoelectric effect

With the development of environmental energy harvesting technology, the research focus gradually develops from the energy harvester itself to the energy harvesting system of coupled environmental vibration sources, in which environmental airflow energy harvesting technology based on the piezoelectric effect is an important research direction. Here, the study status and development trend of piezoelectric energy harvesting were reviewed and summarized including rotation types, vortex-induced vibration types, flutter types and resonant types. It was found that the rotational multi-array energy harvesters are easy to scale, and the vortex-induced vibration and the flutter energy harvesters are poor adaptability for wide range of airflow velocity, and the resonant types can effectively improve excitation energy and output power. In order to improve power generation capacity and broaden the range of airflow velocity, energy harvesting with multiple frequency excitation and multi-piezoelectric array are future main development tendencies.

Airflow energy harvesting through diamagnetically levitated magnet rotor

An airflow energy harvester by using diamagnetic levitation technology to generate electricity is presented in this paper. The energy harvester consists of a lifting magnet, an upper pyrolytic graphite plate, a magnet rotor, two centrosymmetric nozzles, induction coils, and a lower pyrolytic graphite plate. The lifting magnet is used to exert an upward force on the magnet rotor, so the levitated magnet rotor can stably levitate. In order to study the output characteristics of the energy harvester, two streams of airflow are applied to the magnet rotor to form a force couple. The relationship between the induced voltage and the airflow rate was analyzed and tested by simulation and experiment. In this paper, the flow rate was controlled by the mass flow controller, and the output voltage under different airflow rates was recorded. It was found that the peak induced voltage of the coil could reach 2.8 V when the flowrate was 3000 sccm.

Enhancing Output Power of a Cantilever-Based Flapping Airflow Energy Harvester Using External Mechanical Interventions.

This paper presents a flapping airflow energy harvester based on oscillations of a horizontal cantilever beam facing the direction of airflow. A wing is attached to the free end of a cantilever beam and a bluff body is placed in front of the wing from where vortex falls off, producing vortices under the wing and driving it to oscillate. An electromagnetic transducer is integrated to convert the flow induced vibration into electrical energy. This flapping energy harvester, however, may stop oscillating or vibrate in the second mode under high electrical damping, and thus may be unable to achieve its optimum performance. Simple yet effective mechanical interventions can be applied to the harvester to enhance its power output, i.e., to increase flow velocity and to apply external magnetic interaction. The effect of airflow velocities on output power was investigated experimentally and the results show that the energy harvester scavenges more power in airflow at higher Reynolds numbers (higher flow velocity at < 24,000). The external magnetic excitation is achieved though placing one magnet to the wing and another one above the wing to induce a repelling force, aiding the beam to oscillate in high electrical damping. Experimental results show that the power output can be enhanced by 30% when the magnet interaction is properly integrated.

Damping Characteristic Analysis of an Airflow Energy Harvesting System

Abstract With the rapid development of electronic technology, the use of portable and wearable electronics hasbeen widely. In order to eliminate the dependency of low-power electronic devices on batteries and the associated requirement of periodic replacement, researchers have begun investigating methods of generating energy from ambient sources. An airflow energy harvester for human motion is typically composed of a spring-mass system with an air pump connected in parallel with a spring and a turbine. Recent studies have proposed some airflow energy harvesting devices. However, these studies are focused on structural design and little attention has been devoted to the energy conversion process. There are two processes for energy conversion: human motion to airflow energy, then airflow energy to electricity. Focus on the energy conversion, this paper proposes a way to evaluate the energy of the airflow from the perspective of damping at harmonic excitations. The model of an airflow energy harvester for human motion composed of a spring-mass system with an air pump connected in parallel with a spring and a turbine is built, and the balance force analysis is carried out. Comparing the mathematical models and the force analysis equations, the regular pattern of the damping change of the system during the vibration is defined. The simulation isperformed, the result indicates that the energy of the airflow which the vibration system provides is related to the damping of the system. This paper provides a new method toanalyzethe energy conversion process, which helps to measure the efficiency of the airflow energy harvester preferably.

An airflow energy harvester using diamagnetic levitation structure

Abstract This paper presents an airflow energy harvester based on diamagnetic levitation structure. A magnet rotor with three teeth evenly distributed on the edge was introduced into the energy harvester, which is freely levitated between highly oriented pyrolytic graphite (HOPG) sheets. A simple prototype of the airflow energy harvester was built, and the performance was tested in various airflow speeds. The experiment results show that the proposed harvester can work stably within an airflow speed range from 0.34 m/s to 9.2 m/s. When the airflow speed was 7.8 m/s, a maximum RMS induced voltage of 61.7 mV was measured and a maximum power output of 31.1 μW was achieved.

On the electrode segmentation for piezoelectric energy harvesting from nonlinear limit cycle oscillations in axial flow

Aeroelastic energy harvesters can be used for low-power electricity generation in various applications ranging from aircraft and rotorcraft to civil structures in high wind areas. Among the various alternative transduction mechanisms for airflow energy harvesting, piezoelectric energy harvesting from limit cycle oscillations of cantilever beams in axial flow has been pointed out as a geometrically scalable and simple option. The dynamic deformed shape of flexible beams during limit cycle oscillations involves more complex motions than simple standing waves and mode shapes. Such deformations yield moving strain nodes (inflection points), where the dynamic bending strain changes sign. As a result, the use of segmented piezoelectric layers to avoid charge cancellation is more involved as compared to modal vibration problems that have fixed strain nodes. To alleviate this issue without implementing complex optimization schemes, this work presents a criterion for segmentation of the piezoelectric layers to enhance the power extraction from aeroelastic limit cycle oscillations of a flexible cantilever in axial flow, based on a cyclic average of the strain node motion. A fluid–structure interaction model that couples the nonlinear governing equations of an electromechanically coupled beam with an unsteady aerodynamic model is implemented, and wind tunnel experiments are performed for validation. Theoretical predictions of the electromechanical response for a piezoelectric bimorph cantilever in axial flow are experimentally validated for both continuous and segmented configurations of the piezoelectric layers. More than 30% enhancement in the electrical power output is observed when piezoelectric layers are segmented based on the criterion given here.

A scalable, flexible and transparent GaN based heterojunction piezoelectric nanogenerator for bending, air-flow and vibration energy harvesting

Flexible functional devices are extremely suitable for malleable, sustainable, and portable applications such as smart clothing, flexible electronics and medical applications. Here, we present a scalable, transparent, and flexible piezoelectric nanogenerator (STF PNG) fabricated by forming a p-n NiO/GaN heterojunction using an electrochemical lift-off process to transfer GaN onto a flexible substrate. Several actuation sources such as air-flow, finger forces for bending, vibrations with a frequency of 20 Hz, and cyclic stretching-releasing agitation by a linear motor were applied to generate piezoelectric bias. Peak piezoelectric output voltage and current of 30 V and 1.43 µA, respectively, were measured. Such high piezoelectric bias was generated by suppressing free carrier screening and junction screening; the former was achieved due to removal of compressive stresses from GaN after the lift-off process, while the latter was achieved by the deposition of a highly resistive p-type NiO layer on transferred GaN and a sandwiched Polydimethylsiloxane resulting in a very high junction resistivity of the p-n NiO/GaN heterojunction STF PNG. As a result, our approach provides a new strategy for novel and highly efficient design of semiconductor-based flexible PNGs for a wide variety of applications.

Airflow energy harvester of piezoelectric thin-film bimorph using self-excited vibration

The airflow energy harvesters (AFEHs) of piezoelectric Pb(Zr,Ti)O3 (PZT) thin films were developed. Electric power was generated by self-excited vibration of the piezoelectric bimorph cantilevers induced by a continuous airflow. To enhance the vibration in low wind speed, we used very thin stainless-steel (SS) foils with thickness of 20μm as base substrates, and the PZT thin films were deposited on both surface of SS foils by radio-frequency (rf) magnetron sputtering. When the angle of attack (AOA) was 20° and above, stable self-excited vibration was generated at wind speeds larger than 4.5m/s. When the wind speed was 8m/s, the maximum output power reached 36.4μW at the AOA of 20°. From the evaluation of the thickness effect of the base cantilevers, it was confirmed that the thinner substrate reduced not only cut-in wind speed but also maximum output voltage.

Airflow energy harvesting with high wind velocities for industrial applications

An airflow energy harvester capable of harvesting energy from vortices at high speed is presented in this paper. The airflow energy harvester is implemented using a modified helical Savonius turbine and an electromagnetic generator. A power management module with maximum power point finding capability is used to manage the harvested energy and convert the low voltage magnitude from the generator to a usable level for wireless sensors. The airflow energy harvester is characterized using vortex generated by air hitting a plate in a wind tunnel. By using an aircraft environment with wind speed of 17 m/s as case study, the output power of the airflow energy harvester is measured to be 126 mW. The overall efficiency of the power management module is 45.76 to 61.2%, with maximum power point tracking efficiency of 94.21 to 99.72% for wind speed of 10 to 18 m/s, and has a quiescent current of 790 nA for the maximum power point tracking circuit.

A triboelectric wind turbine for small-scale energy harvesting

This paper deals with a rotational energy harvester including a Horizontal Axis Wind Turbine (HAWT), a cylindrical stator covered by several electrodes, and thin Teflon dielectric membranes hung on the rotor. The sliding contact of the Teflon membranes on the stator provides simultaneously large capacitance variations and a polarization source for the electrostatic converter by exploiting triboelectric phenomena. 1μW has been harvested at 4m/s; 130μW at 10m/s and 550μW at 20m/s with a 40mmØ device. In order to validate the energy harvesting chain, the airflow energy harvester has been connected to a power management circuit implementing Synchronous Electric Charge Extraction (SECE) to supply a wireless sensor node with temperature and acceleration measurements, transmitted to a computer at 868MHz.

Triboelectret-based aeroelastic flutter energy harvesters

This paper highlights some experimental results on several electrostatic membranes tested in a wind tunnel between 0 and 20m.s-1 for airflow energy harvesting. The main idea is to use the aeroelastic behavior of thin flexible films to induce simultaneously the capacitance variations and the polarization required by the triboelectric/electrostatic conversion. This technology provides thin and flexible devices and avoids the issue of electrets discharge. Our prototypes (<16cm2) allowed a quick startup (from 3ms-1), an electrical power-flux density from 0.1μW.cm-2 to 60μW.cm-2. In order to complete the energy harvesting chain, we have used a wireless sensor with temperature and acceleration measures coupled to a low power transmission (Bluetooth Low Energy) with reception on a smartphone.

A cm scale electret-based electrostatic wind turbine for low-speed energy harvesting applications

This paper presents a small-scale airflow energy harvester built on an axial turbine architecture and exploiting an electret-based electrostatic converter. When the airflow velocity is high enough, the windmill starts rotating and creates a periodic relative motion between a stator and a rotor which induces variations of capacitance. These ones are directly converted into electricity thanks to the use of Teflon electrets charged at −1400 V which polarize the variable capacitors. We focus our study on a 4-blade axial turbine with a diameter of D = 40 mm, a depth of W = 10 mm, for a total volume of 12.6 cm3. This windmill has been tested with various blade angles and different types of electrostatic converters and output powers up to 90 μW at 1.5 m s−1 (7.5 μW cm−3) and 1.8 mW at 10 m s−1 (111 μW cm−3) have been obtained so far. The coefficient of power reaches Cp = 5.8% and among the small-scale airflow energy harvesters previously reported, this one has the lowest cut-in speed (1.5 m s−1).