Low-frequency Energy Harvester Research Articles

Flexible and ferroelectric electrospun PVDF- non-stoichiometric PZT nanogenerators (PENGs) membranes for low-frequency acoustic energy harvesting

Acoustic energy harvesting (AEH) at low-frequency has been exposed to serious problems such as low energy of input sound and lack of efficient materials to absorb the sound and convert it to electrical power. This study focused on the enhancement of the AEH performance of polyvinylidene fluoride (PVDF) membrane via the incorporation of non-stoichiometric PZT (nsPZT) nanoneedles as piezoelectric nanogenerators (PENG). The nanofibrous membranes with different amounts of PENG (x = 0, 2.5, 5, and 10 wt %) were synthesized by the electrospinning method. The nsPZT was provided via Nd3+ and Nb5+ co-doping as a novel approach. The microstructures revealed that the PENG was embedded well inside the fibers (x = 2.5), while the agglomerates were formed at higher amounts (x = 10). Also, the fiber diameters and porosity of membranes were changed. It was found that the maximum crystallization of the β-phase of PVDF has occurred at x = 2.5 (71 %). The dielectric of the PVDF membrane decreased with increasing the x factor due to the formation of further pores. In contrast, the ferromagnetic properties, piezoelectric sensitivity, and electrical conductivity were improved by adding the PENG. The maximum coercivity of 750 Oe, piezoelectric sensitivity of 1.959 V N−1, and minimum sheet resistance of 1.2 kΩ.sq−1 were achieved by x = 2.5. The noise reduction coefficient (NRC) of the PVDF membrane was enhanced drastically (53–163 %) by adding the PENG. The AEH performance was also enhanced by adding the PENG. The highest power density was achieved 0.0822 W g−1 (56.23 W m−2) by the PVDF-PENG membrane (x = 2.5) under 90 dB sound pressure at 2000 Hz frequency. These findings suggest the high potential of nanofibrous PVDF-PENG membrane for use in low-frequency AEH systems.

Rainbow trapping and concentration of surface waves on broad waveguide

Abstract In recent years, topological insulators have been widely designed to manipulate various types of classical waves. The topological edge states characterized by defect and backscattering immunity show great application potential in energy harvesting. This work reports a spin-locked topological surface wave channel, which consists of concrete-filled steel tubes (CFST) placed on foundation soil. Here, the distance between the lattice and the center of the CFST controls the hopping strength between adjacent atoms, determining the topological phase transition. Introducing the surface wave crystal with Dirac cones in the interface, then the robust broad waveguide modes of phononic heterostructure are explored. Notably, incorporating the rainbow effect allows for precise regulation and reliable concentration within the broad waveguide. The proposed broad waveguide surpasses traditional waveguides by simultaneously focusing and segregating energy, enabling applications in low-frequency energy harvesting, sensing, and logic gates. Our work will provide an efficient recovery platform for daily vibration energy, especially for vehicle loads.

High-performance triboelectric nanogenerator based on biocompatible electrospun polycaprolactone nanofiber and counter convex PDMS for low-frequency mechanical energy harvesting

High-performance triboelectric nanogenerator based on biocompatible electrospun polycaprolactone nanofiber and counter convex PDMS for low-frequency mechanical energy harvesting

Bio-inspired mechanical metamaterial with ultrahigh load-bearing capacity for energy dissipation

Mechanical metamaterials with energy-dissipating properties can provide impact mitigation in the field of engineering. However, current energy-dissipating metamaterials frequently face a tradeoff between energy-dissipation performance and load-bearing capability, severely limiting their practicality in high-intensity impact scenarios. Here, inspired by mushroom gills, we propose a mechanism for the snap-through buckling induced by geometric frustration, and we construct a snap-through metamaterial (STM) to address this problem. By analyzing the bifurcation buckling phenomenon, the STM is improved with higher energy-dissipation efficiency. Experiments demonstrate that the STM adaptively dissipates energy and mitigates impacts, achieving up to 33% reduction, in a reusable, self-recoverable, and rate-independent manner, leading to comprehensive performance. Employing a preloading strategy further enhances its impact mitigation capability as required. Notably, the STM exhibits a remarkable load-bearing capacity of up to 55 times higher than those of previous designs. The proposed design strategy of STMs paves the way for the development of interaction-based metamaterials, enabling applications in advanced dampers, mechanical waveguides, soft robotics, and low-frequency energy harvesters.

A false trigger pulse elimination circuit for low-frequency energy harvesting active rectifiers

Abstract In this article, a false trigger pulse elimination circuit is proposed to be used for a low-frequency energy harvesting active rectifier. It is divided into two-stage circuits, each stage almost including a switching signal generation circuit, a switching inverter, and an inverter to eliminate false triggering pulses on the rising edge and falling edge respectively. There is an edge detection circuit in each switching signal generation circuit, generating a switching signal that controls the switching inverter’s on-off behavior. This allows the inverter to achieve inverter output voltage clamping by turning off its inverter function and turning it into a switch that is only turned on at the high or low level. At the same time, a thyristor delay element is used to determine and adjust the effective level time of the switching signal, which can reach over 150 μs, completely covering the rising or falling edge false trigger pulse so that no GΩ-level resistors are needed in the low-frequency field. The results show that the low-frequency false trigger pulse elimination circuit proposed in this article can better eliminate false trigger pulses on both rising and falling edges. It can also achieve on-chip integration, reduce the power consumption of the self-adaptive delay compensation loop, and enhance the stability of the circuit.

Experimental and simulation of a tension-like nonlinear piezoelectric energy harvester

This article proposes a low-frequency and efficient tension-like nonlinear piezoelectric energy harvester, which increases the harvesting performance of the harvester by swinging the support frame. Firstly, design the structure of the harvester and draw a physical model. Secondly, finite element models are used to simulate and analyze the structure’s dynamic characteristics. Finally, make an experimental prototype of the harvester and explore the power generation characteristics of the device through experiments. The results indicate that the harvester has two natural frequencies under low-frequency conditions. The energy harvester has the optimal external resistance to achieve peak output power. The greater the excitation acceleration, the greater the total output power value of the energy harvester. When the mass of the mass block is 3.7 g and the excitation acceleration is 0.4 g, the total output power value of the energy harvester is 3.88 mW, and the harvesting frequency band is wide, indicating excellent output performance of the harvester. The experimental results of the energy harvester device are consistent with the simulation results, fully verifying the correctness of the experiment and simulation. This piezoelectric energy harvester can efficiently harvest vibration energy at low frequencies, providing a good prospect for supplying power to microelectronic devices.

A compact self-powered inductor-less piezoelectric energy harvesting circuit using gyrator

In traditional low-frequency energy harvesting circuits, a large matched inductor with a large size is unavoidable. To reduce the size of the circuit, this paper proposes a compact self-powered inductor-less high-efficiency piezoelectric energy harvesting circuit using a low-power-consumption gyrator. A self-powered floating gyrator inductor is used in place of an inductor in the proposed circuit, and the required phasor response is acquired by using its voltage–current (V–I) relationship. The proposed circuit offers easy adjustability and performance benefits in small integrated circuits packages. The proposed circuit can be cost-effective and provide reduced area advantages in autonomous self-powered Internet-of-Things and wireless sensor nodes applications. Regarding harvested energy, the proposed circuit with a storage capacitor of 0.24 F can obtain 320% improved performance than standard energy harvesting along with the lowest power consumption of 0.25 µW in self-powered operation. The proposed technique can also be applied to similar piezoelectric energy harvesting strategies with large inductors.

Enhancement of acoustic properties of carbon fibrous membrane (CFM) by in-situ crystallization of PZT nanogenerators (PENGs) inside the fibers for a low-frequency acoustic energy harvesting

Acoustic energy harvesting (AEH) by a nanostructured membrane has recently gained increasing attention. This study focused on a novel approach for in-situ crystallization of Pb(Zr0.58Ti0.42)O3 (PZT) as a piezoelectric nanogenerator (PENG) inside the carbon fibrous membranes (CFM). The electrospinning process and post-heat treatment were applied to synthesize the CFM-embedded PENG, which benefits from both the flexibility of carbon fibers and the piezoelectric properties of the crystallized PZT. The results indicated that the carbon fibers kept their microstructure over the heat treatment at 250 and 350 °C while the crystallization fraction of PZT increased. The XPS analysis revealed that the CFM embedded by in-situ crystallized PENG had a higher diversity of tetragonal and rhombohedral in comparison with the CFM embedded by the pre-crystallized PENGs. Furthermore, the electrical conductivity, dielectric constant, and ferromagnetic properties of CFM were improved with the incorporation of the in-situ crystallized PENGs. The acoustic studies in the range of 250–2000 Hz under sound pressure of 90 dB revealed that sound absorption performance of CFM was increased by about +35 %. Also, the ability of CFM in the AEH process was enhanced drastically by embedding the PENGs inside the carbon fibers. The maximum harvested electricity at 500 Hz was 5.9 and 13.9 W m−2 by CFM embedded by in-situ crystallized and pre-crystallized PENGs, respectively. The above results exhibit the great potential for the CFM-embedded PENGs to be used in low-frequency AEH applications.

High-sensitivity wearable multi-signal sensor based on self-powered MXene hydrogels

Developing high-performance wearable sensors with multi-sensing capabilities for different signals such as temperature, human motion and physiological signals remains a challenge. In this report, a novel catechol functionalization of PVA-CA/Poly(N-acryloyl glycinamide)/MXene hydrogels(PcNA-M) was fabricated by combining the thermosensitivity of Poly(N-acryloyl glycinamide)(PNAGA) hydrogel and the self-powered properties of the catechol functionalization of PVA(Pc)/MXene hydrogels. The mixing ratio of PNAGA and Pc was adjusted to impart the resulting PcNA-M with good tensile, compression, rebound properties, rapid self-healing and temperature sensing properties. In addition, the conductivity of the hydrogel was found to have contributions from ionic and electrical conductivity. To produce different forms of electrical signals for different signal sources, the PcNA-M sensor was utilized to monitor the resistive and voltage signals during body movements, switching temperature and handwriting motion. The PcNA-M sensor exhibits high sensitivity, identifiability, and reliability in applications of self-powered wearable sensors, and demonstrates great prospects in the field of low-frequency mechanical energy harvesting. This study opens a new possibility for wearable self-powered multi-signal sensors to monitor different signals related to human motion.

A vortex-induced vibration device based on MG-TENG and research of its application in ocean current energy harvesting

In recent years, with the extensive research on the application of triboelectric nanogenerators (TENGs) by scholars all over the world, the development of TENGs in harvesting and utilization of ocean energy has attracted more and more attention according to the advantages of TENGs in low-frequency energy harvesting. As a kind of ocean energy, the development and utilization of ocean current energy is of great significance to the diversification of energy sources, the promotion of sustainable energy development, the protection of ecological environment and the response to climate change. In this work, a novel device based on the combination of vortex-induced vibration (VIV) and multi-grating TENG (MG-TENG) is proposed for energy harvesting in low-speed ocean currents. The device consists of an up and down moving float driving the TENG to convert kinetic energy into electrical energy. The result shows that the system has a maximum average output power of nearly 20 μW under the condition of 8 grating TENG. This work demonstrates the ability of devices based on the combination of VIV and MG-TENG to drive low-power electronic components, demonstrating future applications for sensing, positioning, and more.

Improving the performance of low-frequency magnetic energy harvesters using an internal magnetic-coupled mechanism

In this study, we present a novel low-frequency magnetic field energy harvester (EH) employing beryllium bronze/Pb(Zr,Ti)O3 ceramic composited dual-beam structures with tip magnets attached to the inner and outer beams. This design incorporates the internal magnetic-coupled (IMC) effect, resulting in significantly enhanced coupling ability and a wide bandwidth. The validity of the IMC mechanism is confirmed through theoretical formulas and numerical simulations. By leveraging the IMC condition, the EH achieves an expanded bandwidth, which increases from 22 to 43 Hz. Moreover, the total output voltages at the inherent resonance and internal resonance are boosted by 15.4% and 32%, respectively. The performance of the IMC-EH can be further improved by increasing the number of the endmost magnets. Experimental investigations reveal that the IMC-EH generates a maximum RMS output power density of 56.25 μW Oe−2 cm−3, surpassing existing magnetically coupled piezoelectric energy harvesters. Remarkably, even under an ambient magnetic field as low as 1 Oe, the proposed IMC-EH still yields a total output power of 185 μW, sufficient to continuously power 26 LEDs in real time. This demonstrates its potential as a promising solution for low-power consumption small electronics. Furthermore, the implications of this work extend beyond its immediate benefits, as it inspires the design of future self-powered wireless sensor networks in the context of the Internet of Things.

Nonlinear double-mass pendulum for vibration-based energy harvesting

To enhance the performance of a vibration-based energy harvester, typical approaches employ frequency-matching strategies by either using nonlinear broadband or frequency-tunable harvesters. This study systematically analyzes the nonlinear dynamics and energy harvesting performance of a recently emerging tunable low-frequency vibration-based energy harvester, namely, a double-mass pendulum (DMP) energy harvester. This energy harvester can, to some extent, eliminate frequency dependence on pendulum length but exhibit vibration-amplitude-dependent softening nonlinearity. The natural frequency of the DMP structure is theoretically derived, showing several unique characteristics compared with the typical simple pendulum. The DMP energy harvester exhibits alternate single-period, multiple-period, and chaotic vibration behaviors with increase in excitation amplitudes. The analysis of gross output power indicates that the rotating motion, regardless of chaotic or periodic rolling motions, improves the energy harvesting performance in terms of power leap and broader bandwidth. Based on the parameter space analysis, the rotating motions usually occur at the shift-left locations of frequency ratios 1 and 2; a smaller damping ratio corresponds to a lower on-demand excitation amplitude for the rotating-motion occurrence. Numerical results confirm that the DMP is suitable for low-frequency energy harvesting scenarios, suggesting the realization of rotating motion for improving energy harvesting performance. Moreover, a shake table test was performed, and the experimental results validated the accuracy and effectiveness of the DMP modeling analysis. Practical issues related to DMP energy harvesters under different types of excitations are finally discussed. Although the analysis is for the DMP, the corresponding conclusions may shed light on other pendulum-type energy harvesters.

Repulsive magnetic levitation-based electromagnetic energy harvesting of a low-frequency ocean wave

In this study, an electromagnetic energy harvester for a low-frequency ocean wave was developed in a compact 3D-printed structure. Ocean wave energy conversion technologies exist, but maintaining them in the harsh marine environment is crucial for business. Friction increases maintenance costs. Therefore, magnetic levitation, being friction-free, is used for cost-effective, low-maintenance electromagnetic energy harvesting applications. Low-frequency oscillating energy is captured using repulsive magnetic levitation with a buoy and generating electricity using a permanent magnet and copper coil. A levitating magnet is repelled by a fixed one, inducing electricity as it passes through a coil. Experiments with a 0.1 Hz sine wave mimic the average frequency of ocean waves, showing successful voltage peaks at intervals. The output voltage and measured power from the harvester exhibit variations influenced by multiple parameters. The maximum output voltage observed was 3.4 V and an average of 99 mW of power was calculated. The experiment demonstrates the feasibility of using repulsive magnetic levitation for low-frequency wave energy harvesting and also encompasses various harvester configurations, including transfer magnet forces and top magnets.

Integrated acoustic metamaterial triboelectric nanogenerator for joint low-frequency acoustic insulation and energy harvesting

In this study, we present a new device designed to manipulate low-frequency sound waves. The device utilizes the principles of acoustic metamaterials to achieve high-performance sound insulation, while also possessing the capability to convert sound energy into electrical energy. Unlike previous studies on membrane acoustic metamaterials, this device incorporates a membrane component but eliminates the need for precise tension force. The structural parameters of the device are frequency-dependent, allowing for a lightweight design while maintaining satisfactory low-frequency sound insulation performance. At the sound insulation peak frequency, the IAM-TENG exhibits an impressive sound insulation capability of over 30 dB. Moreover, when subjected to bandlimited white noise excitation in the frequency range of 50 Hz-500 Hz, the IAM-TENG showcases a substantial enhancement of nearly 10 dB in sound insulation performance in comparison to a sample of the same weight and size. Additionally, the device achieves a uniform displacement distribution, with large amplitude displacement occurring around the sound transmission dip frequency. Exploiting this property, we have designed a triboelectric nanogenerator (TENG) that can convert incident acoustic energy into electrical energy. This nanogenerator structure utilizes multi-walled carbon nanotubes (MWCNTs) and FEP (Fluorinated Ethylene Propylene) membrane as the triboelectric layers. With an acoustic excitation level of 100 dB at the optimal frequency, the harvested electrical power reaches 0.93 mW. The device has a surface mass density of only 2kg/m2, yet it provides remarkable acoustic insulation performance and can power small-scale electronic devices. These innovative properties have the potential to accelerate the development of self-powered, smart, and multifunctional structures in the Internet of Things era.

Orange peel-like triboelectric nanogenerators with multiscale micro-nano structure for energy harvesting and touch sensing applications

With the continuous advancements in technology, triboelectric nanogenerators (TENGs) have gained significant traction as efficient harnessers of low-frequency mechanical energy to meet the escalating energy demands. Notably, employing solid polymer electrolyte (SPE) as a contact layer or optimizing the microstructural composition of the surface material represents a prevalent strategy for augmenting the output performance of TENGs. However, the fabrication of numerous microstructures poses significant challenges, particularly in terms of incorporating environmentally harmful materials. Moreover, the utilization of triboelectric nanogenerators is further constrained by limitations associated with electrode materials. Although various techniques are available for producing transparent and stretchable electrodes for such generators, these procedures can be intricate and necessitate the use of hazardous chemicals. In this study, we exploit Poly(vinyl alcohol) (PVA) and natural bacterial cellulose (BC) nanofibers to fabricate contact layers with OP structures characterized by micron-scale domes and nanoscale microcracks. The electrodes were fabricated using BC hydrogel and ionic liquids(ILs). Under the action of hydrogen bond topological network, a multi-scale structure is formed comprising of a molecular-scale interlacing network of hydrogen bonds and a nanoscale fiber skeleton, which synergistically confer the ionic gel with remarkable tensile strength and high ionic conductivity (up to 83.51mS/cm). The resulting OP-TENG exhibited an output open-circuit voltage of 280 V, a short-circuit current of 24μA, and a maximum power density of 5.6 W m−2, enabling it to illuminate up to 303 LEDs. A SSEM-TENG was devised by stacking two single electrode mode TENGs on top of each other using a single wire. This innovative design holds great potential for applications in wearable motion monitoring, high-precision writing stroke recognition, and low-frequency mechanical energy harvesting.

A methodology for low-frequency rotational energy harvesting with synergistic effects of centrifugal softening and passive adaptive barrier reduction

Energy harvesting in rotating environments is significant to realize the condition monitoring of mechanical equipment. In this paper, to accommodate the low-frequency rotating environment, a piezoelectric energy harvester with two magnetic coupled cantilevers perpendicular to each other is designed. The harvester exhibits the magnet-induced nonlinearity, centrifugal softening effect and passive adaptive barrier reduction effect. The influences of these characteristics on the dynamic performance are investigated comprehensively by establishing the electromechanical coupling equations in a rotational coordinate system through the extended Hamiltonian principle. The correctness of the mathematical model and simulation analysis is verified by experiments. Compared with single cantilever based harvester, the system output voltage is boosted by more than 10.56 times over the whole test frequency band (0.6–4 Hz). The significant enhancement of the energy scavenging capability proves its potential for low-frequency rotating applications.

Droplet energy harvesting system based on MXene/SiO2 modified triboelectric nanogenerators

Raindrops are an abundant micromechanical renewable energy source in nature, and raindrop energy harvesting has always been a research hotspot. Traditional hydropower generation is not suitable for low-frequency energy harvesting, and it is difficult to realize distributed energy harvesting. The development of triboelectric nanogenerator (TENG) is a promising strategy for converting raindrop energy in the environment into electrical energy. Polydimethylsiloxane (PDMS) composite has received much attention due to its excellent chemical stability and insulating properties for TENG. However, the deficiency of the low output performance and insufficient hydrophobicity of PDMS limits the application of PDMS in droplet energy capture. Modification of PDMS can improve the droplet energy collection capability of the liquid–solid contact triboelectric (LS-TENG). In this work, a new approach to modifying polydimethylsiloxane (PDMS) as a hydrophobic negative triboelectric material using a high dielectric constant MXene and a hydrophobic nano-SiO2 was reported. The as-prepared composites′ permittivity and triboelectric performance were remarkably promoted as compared to composites without interfacial modification. In addition, the use of composites for TENG assembly improved the open-circuit voltage and short-circuit current by a factor of 47.5 and 25.21, respectively, compared to pure PDMS. Application of the composite to the assembled TENG was employed as energy harvester to light up LEDs and charge a capacitor. In addition, a cathodic protection system was designed to demonstrate its potential application in the field of electrochemistry. This provides guidance for the practical implementation of TENGs in the field of electrochemical cathodic protection.

Reversal in Output Current Direction of 4H-SiC/Cu Tribovoltaic Nanogenerator as Controlled by Relative Humidity.

Tribovoltaic nanogenerators (TVNG) represent a fantastic opportunity for developing low-frequency energy harvesting and self-powered sensing, by exploiting their real-time direct-current (DC) output. Here, a thorough study of the effect of relative humidity (RH) on a TVNG consisting of 4H-SiC (n-type) and metallic copper foil (SM-TVNG) is presented. The SM-TVNG shows a remarkable sensitivity to RH and an abnormal RH dependence. When RH increases from ambient humidity up to 80%, an increasing electrical output is observed. However, when RH rises from 80% to 98%, the signal output not only decreases, but its direction reverses as it crosses 90% RH. This behavior differs greatly from that of a Si-based TVNG, whose output constantly increases with RH. The behavior of the SM-TVNG might result from the competition between the built-in electric field induced by metal-semiconductor contact and a strong triboelectric electric field induced by solid-liquid triboelectrification under high RH. The authors also demonstrated that both SM-TVNG and Si-based TVNG can work effectively as-is even fully submerged in deionized water. This mechanism can affect other devices and be applied to design self-powered sensors working under high RH or underwater.

Bio-inspired quad-stable piezoelectric energy harvester for low-frequency vibration scavenging

Due to the unique and diverse nonlinear characteristics, bionic structures can effectively broaden the acquisition bandwidth and improve the performance of harvesters. Inspired by dipteran flight motion, a novel bionic quad-stable piezoelectric energy harvester (BQPEH) is designed to collect low-frequency ambient vibration. The novelty of this bionic energy harvester lies in the combination of the “click” mechanism and “snap-through” motion, thus broadening the application scenarios and improving adaptability for the harvesters. A mass block and a post-buckled piezoelectric beam are connected by a rigid bar to create quadruple-well potentials. The static bifurcation analysis is performed to identify the quad-stable region in the parameter space. The dynamic responses of the system are investigated theoretically and numerically under constant and swept-frequency excitations and then verified experimentally. Broadband low-frequency and high-power energy harvesting are obtained through the inter-well motion induced by the combined nonlinearity of the BQPEH. The results indicate the potential of the bionic strategy for powering wireless devices in low-frequency environments and provide a novel concept for the innovative development of energy harvesters.

(Invited) bionic Composite Films for Biomechanical Energy Harvesting and Self-Powered Sensing Applications

Triboelectric nanogenerators (TENGs) are novel and sustainable devices for harvesting ambient energy for many technological-based applications. However, extreme friction wear of triboelectric layers severely limits their long-term electrical stability and mechanical reliability, restricting the applicability of TENGs for low-frequency mechanical energy harvesting. Herein, we report novel bionic composite (BC) films, inspired by the structures and compositions of bioskins, as wear-resistant triboelectric contact layers for TENGs. We demonstrated that the proposed BC films has superior charge transfer capability, high wear resistance, and maintained long-term stable outputs compared to commercially available films. These works provide an effective strategy to reduce material abrasion by exploiting unique characteristics of the bionic materials, and lays a foundation for effective environmental energy harvesting toward practical applications. Figure 1