Sound Energy Harvesting Research Articles

Synchronous Sound Recognition and Energy Harvesting by Flexible Piezoelectric PLLA/VB2 Composites.

In the present study, poling-free PLLA/VB2 piezoelectric composites are fabricated to achieve synchronous sound recognition and energy harvesting. The addition of VB2 can interact with PLLA by intermolecular hydrogen bonding, inducing the dipole orientation of C=O in PLLA. Meanwhile, VB2 can promote crystallization of PLLA through heterogeneous nucleation. The combination of the two strategies significantly improves the piezoelectric performance of PLLA/VB2 composites. The PLLA/VB2 can detect the sound frequency with an accuracy of 0.1% in the range of 0-20 kHz to recognize characteristic sounds from a specific source. PLLA/VB2 can also convert sound into electrical energy synchronously with an energy density of 0.2 W/cm-3 to power up LEDs. Therefore, PLLA/VB2 shows great potential in the field of information and energy synchronous collection.

Reflective vortex focusing for acoustic contact-free object rotation

The use of acoustic vortex waves with angular momentum is a promising means of transferring mechanical torque to an object without making any physical contact. However, the existing passive-conversion vortex lenses are unable to produce strong acoustic radiation torque. To address this issue, we propose a flat reflector sculpted by spiral grooves. It reflects and converts incident waves into vortex-focusing waves that generate radiation torque. Compared with a transmission-type lens, a reflection-type vortex focusing plate exhibits superior functionality in converging sound waves and creating a stronger circular intensity flow. In this work, we analyze the vortex-focusing sound by Rayleigh-Sommerfeld integral theory and boundary element simulation, confirmed by experiments. The number, depth and direction of spiral grooves determine the topological charge, focusing intensity and torque direction, respectively. We evaluate the local and total acoustic radiation forces and torques, acting on small and large fixed spherical targets in the vortex-focusing beam. As a result, spinning a centimeter-size origami pinwheel several times larger than the wavelength at 40 kHz is realized without direct contact, by utilizing the enhanced acoustic radiation torque converged by the reflector. This technology enables efficient convergence of acoustic waves and simultaneous contactless transfer of mechanical torque to an object, thereby presenting potential applications in sound energy harvesting and wireless power supplies.

Energy harvesting and inter-floor impact noise control using an optimally tuned hybrid damping system

Impact-loaded floor structures radiate undesired sound waves into adjacent rooms, compromising the acoustic comfort. On the other hand, substantial structural vibrations caused by the impact loading offer a promising energy source for harvesting. Nevertheless, a systematic analytical or numerical investigation of simultaneous inter-floor impact sound transmission control and energy harvesting appears to be missing. Current study describes the conceptual development of a fully coupled 3D analytical model of a dual-functional double-plate floor structure optimized for hybrid regenerative control of inter-floor impact sound transmission. Leveraging multi-mode shunted piezoelectric and Electromagnetic Damper (EMD) energy transduction mechanisms, the model structure is composed of two PZT sandwich plates, which are interlinked through a Nonlinear Vibration Absorber (NVA)-based EMD. The finite Fourier cosine transform and standard normal mode approach are employed to treat the governing acousto-elastic equations. Non-dominated Sorting Genetic Algorithm II is applied to tune the system parameters along Pareto frontiers to target maximum pressure mitigation, maximum energy harvesting, or dual-objective optimization, which hires advantageous features from both configurations for an optimal trade-off between them. Simulations reveal that elasto-acoustic response suppression and energy extraction of the employed stand-alone PZT-based conversion mechanism can be remarkably improved with the adopted optimized hybrid PZT/NVA/EMD-equipped system.

Acoustic energy harvesting using an array of piezoelectric cantilever plates for railways and highways environmental noise

This paper introduces a model of sound energy harvesting that operates at a low frequency of less than 200 Hz. This investigation focuses on the produced outcomes when the vibrations of sound energy are converted into electricity. Sound vibrations are received from outside sources and pass through a piezoelectric barrier (wall) equipped with 4*3 array of energy harvesting elements of lead zirconate titanate (PZT-5H) cantilever plates which are constructed to harvest noise in the form of sound from passing trains and vehicles on roads. This paper covers how sound vibrations change into electrical energy at two sound pressure levels (85 dB and 100 dB for environmental noise of road vehicles and railways, respectively). Furthermore, the effects of changing the pressure level on the generated voltage for the intended model have been studied as well as the effects of increasing the piezoelectric plate number on the voltage generated for the 85 dB pressure level. The simulation is conducted numerically using the Finite Element Method FEM (COMSOL). An analytical model of a literature paper is used and simulated using MATLAB to be compared with the FEM results and found to be completely converged. Afterward, to figure out the relationship between voltage and sound pressure level, an equation is derived analytically. According to simulation results, 15 V and 18.2 V are produced for an incoming acoustic pressure level of 85 dB and 100 dB, respectively. Two models are compared, an array of beams with similar dimensions and a single beam with a volume that equals the dimensions of all array beams; it is observed that the array of beams produced 33.9 % more voltage than a single beam with the same volume. The comparison of the proposed model results with experimental literature results is conducted and exhibited an excellent convergence.

Near-Zero Quiescent Power Sound Wake-Up and Identification System Based on a Triboelectric Nanogenerator.

Sound monitoring has been widely used in the field of the Internet of Things (IoT), in which the sensors are mainly powered by batteries with high power consumption and limited life. Here, a near-zero quiescent power sound wake-up and identification system based on a triboelectric nanogenerator (TENG) is proposed, in which the sound TENG (S-TENG) is used for ambient sound energy harvesting and system activation. Once the sound intensity is higher than 65 dB, the converted and stored electric energy by the S-TENG can wake up the system within 0.5 s. By integrating a deep learning technique, the system is used for identifying sound sources, such as drilling, child playing, dog barking, and street music. In the active mode, the sound signals are recorded by a microelectromechanical systems (MEMS) microphone and then sent to a remote computer for sound recognition through a wireless transmitter within 2.8 s. In the standby mode, the ambient sound is not enough to wake up the system, and the quiescent power consumption is only 55 nW. This work provides a triboelectric sensor-based ultralow quiescent power sound wake-up system, which has shown excellent application prospects in smart homes, unmanned monitoring, and the Internet of Things.

Studi Eksperimental Performa Sound Energy Harvesting Device Menggunakan Variasi Rangkaian Piezoelektrik

High ound vibration is very noisy even though they are harmful to human hearing have the potential to be used as a source of micro-electrical energy. This is also supported by the many places that have the potential to produce noise, such as airports and industrial manufacturing plants. However, currently there is no optimal utilization of the sound noise. Whereas sound noise can be converted into electrical energy using electromagnetic, piezoelectric or electrostatic mechanisms. One of the electrical energy harvesting media that is very easy to use today is piezoelectric material which has an element of Lead-zirconate-titanate (PZT). However, if only use one piezoelectric, the electricity generated is very small. Therefore, the purpose of this study is to determine the effect of variations in piezoelectric circuits and variations in sound noise levels in producing electrical energy for sound energy harvesting devices. The method used in this research is an experimental method with a quantitative approach. There are two independent variables used, consist of (1) variations in piezoelectric circuits (single, double series, double parallel, quad series, and quad parallel), and (2) variations in sound noise levels (80 dB, 90 dB, and 100dB). The tests carried out are testing the electric voltage, the electric current, and the calculation of the electric power. Based on the test results, the higher the intensity of the sound will increase the value of voltage, electric current, and electric power. The best circuit in electrical voltage testing is the A2B3 circuit which uses a double-series that can produce an electrical voltage of 2,030 AC V. Meanwhile, in testing the electric current and calculating power, the double parallel circuit (A3B3) is the best circuit capable of producing strong electric current of 0.261 AC mA and 0.278 AC mW of electrical power. Thus, the double parallel circuit is the most appropriate circuit used in sound energy harvesting devices. Keywords: Harvesting Device, Piezoelectric, Sound Noise

Acoustic-electric conversion and triboelectric properties of nature-driven CF-CNT based triboelectric nanogenerator for mechanical and sound energy harvesting

Currently, the world is facing severe environmental challenges such as water pollution, rising temperatures beyond the tolerable range, and air pollution. Moreover, improper waste disposal is becoming a serious concern that enhances global warming. Among the waste materials, plastic waste and cigarette butts (CBs) or cigarette filters (CFs) are causing major environmental problems. Therefore, treating these waste materials has become a critical issue. In this scenario, converting waste to energy is considered to be the most effective disposal process for discarded materials. Furthermore, integrating waste matters with nanomaterials can lead to novel technological aspects. Herein, we utilized discarded CFs and plastic waste as positive and negative tribo materials, respectively, to fabricate a triboelectric nanogenerator (TENG) device. The energy harvesting performance of the developed TENG device was investigated by adding a small amount (0.1 wt %) of carbon nanotubes (CNTs). The CNTs incorporated TENG device exhibited exceptional energy harvesting performance by generating 60 V output voltage, 1805 nA current, and 110.6 mW/m2 power density under 10 N applied force. The energy harvested by the fabricated device can efficiently light 50 green LEDs and power the LCD of a portable timer clock. The developed CF-CNT TENG device exhibited robust electrical performances under various compressive forces and showed long-term stability. Moreover, the fabricated device can be used as a sound-driven TENG device that can work effectively in broad bandwidths ranging from 100 Hz to 400 Hz. Thus reducing sound pollution and simultaneously generating green and clean energy. Therefore, we anticipate that the present study will pave the way for green energy generation and environmental remediation.

Low-frequency enhancement of acoustic black holes via negative stiffness supporting

Acoustic black holes (ABHs) attract increasing attention in the field of vibration suppression, sound radiation control and energy harvesting. Though the ABH effect usually works well in the mid-high frequency range, it cannot be triggered below the cut-on frequency. Thus, enhancing the vibration reduction at low frequencies is an urgent task. Inspired by the impressive low-frequency performance of the negative stiffness, we propose a novel idea that combines an ABH beam with a negative stiffness element (NS-ABH beam). To characterize such a system, a semi-analytical model is developed based on the Gaussian expansion method (GEM) in the framework of the Rayleigh–Ritz method. The modal loss factors (MLFs) and mean square velocity (MSV) are calculated to estimate the damping performance. The results show that the proposed NS-ABH beam can achieve remarkable vibration reduction below the cut-on frequency without sacrificing the ABH effect at higher frequency. The coupling mechanism between negative stiffness and ABH beam and the reduction mechanism behind are studied based on the modal projection method to better understand the observed phenomena. Finally, experiments have been implemented to validate the theoretical model and the NS-ABH performance.

Sound Energy Harvesting and Converting Electricity (SEHCE)

The research study “Sound Energy Harvesting and Converting Electricity (SEHCE)” aims to create a better and easier way of producing another source of clean and renewable energy through sound. The study did not aim to be compared to other proven sources of electricity such as heat, wind, solar and hydroelectric, instead, it was created to find and explore new ways of producing an alternative source of energy. The project will undergo several processes such as designing, construction, testing, and evaluation. Through this, the researcher will be able to find out that sound energy can be converted to electricity.

Metamaterial based piezoelectric acoustic energy harvesting: Electromechanical coupled modeling and experimental validation

Piezoelectric energy harvesting technology utilizing acoustic metamaterials investigated by experiment and simulation improves the sound energy density and conversion efficiency. A fully coupled electromechanical model in both the mechanical and electric domains is crucial for accurate prediction and optimization of acoustic metamaterial based on sound energy harvesting. Based on the Kirchhoff thin plate theory, constitutive laws of isotropic aluminum substrate and transversely isotropic piezoelectric bimorph, the electromechanical coupled governing equation in the mechanical domain is deduced for a two-dimensional acoustic metamaterial based piezoelectric energy harvester. Each piezoelectric layer is represented as a current source in series with its internal capacitance for derivation of the electromechanical coupled governing equation in the electrical domain via Gauss’s law and Kirchhoff’s laws. With generalized boundary conditions, modal analysis is performed using the Galerkin method and Kelvin-Kirchhoff condition. The general transient response and frequency response functions are obtained under the excitation of sound waves and the reaction forces of the silicone rubbers. The time-history, power spectrum and phase portrait of the measured harvested voltage at 90 fixed frequencies agree well with the model predictions. The theoretical maximal harvested power is 3.09 mW, with the optimal resistance of 28180 Ω and inductance of 0.28H connected in parallel. Near the resonant frequency, the utilization rate of converting sound energy into electrical power is maximized. The proposed electromechanical coupled model can be used as a basis for further topology design and optimization and underlying physics for experimental study.

Experimental realization of boundary-obstructed topological insulators using acoustic two-dimensional Su–Schrieffer–Heeger network

Topological insulators that can host special symmetry-protected boundary states and corner states have attracted increasing intention in acoustic engineering. Recently, the concept of the boundary-obstructed topological (BOT) phases has defined a class of topological phases without bulk energy band closing around zero energy, which greatly broadens the applications of the topological states. In this work, based on the two-dimensional Su–Schrieffer–Heeger network, we show that the band degeneracies around zero energy can be removed to open a complete bandgap by judiciously tuning the hopping terms to break C4v symmetry down to C2v symmetry but with the topological phase invariant, which can be directly characterized by the BOT phase. Furthermore, we experimentally propose a rigorous acoustic sample to visualize the hierarchy of the in-gap higher-order topological states exactly. Crucially, by designedly connecting the lattice with outside environment, we show that these spectrally isolated states still response to the specific frequencies robustly. Our results are expected to be helpful for manipulating wave propagation and sound energy harvesting.

Broadband Sound Absorption and Energy Harvesting by a Graded Array of Helmholtz Resonators

In both experiment and simulation, we demonstrate a graded array of Helmholtz resonators (HRs) with cross-linked polypropylene (IXPP) ferroelectret films on the inner walls of cavities, which can realize both sound absorption and energy harvesting within 300–800 Hz. This dual-function graded array contains nine HRs with different sizes, which can offer a broadband working frequency and absorb part of acoustic energy. The unique ability of IXPP ferroelectret films can be used to efficiently harvest sound energy during resonant performances. An electric circuit is designed for collecting electrical signals of each branch individually. The average values of sound absorption coefficient and output power are about 0.81 and 1.43 nW in the range of 300–800 Hz with an input sound pressure level (SPL) of 100 dB in experiment, respectively. Our results enrich the fundamental techniques of both sound absorption and acoustic energy harvesting (AEH), which can pave a way for designing acoustic device in the field of sound absorption and energy conversion for future engineering application.

Multi-Tube Helmholtz Resonator Based Triboelectric Nanogenerator for Broadband Acoustic Energy Harvesting

Acoustic energy, especially broadband low-frequency sound energy is part of the environmental mechanical energy acquisition cannot be ignored. Herein, a multi-tube parallel Helmholtz resonator-based triboelectric nanogenerator (MH-TENG) is investigated to reap sound energy in low-frequency noise environments. The designed MH-TENG consists of a modified Helmholtz resonator and a thin-film TENG transducer. The core materials of the TENG transducer are aluminum, FEP film, and carbon. To further clarify the influence of the modified Helmholtz resonator on the conversion performance of MH-TENG, the acoustic characteristics of the improved resonators are systematically studied. A series of experiments show that the multi-tube parallel Helmholtz resonator structure has a better sound wave collection effect. Meanwhile, the flexible film TENG can reduce the optimal output frequency of the device. The power generation performance and the bandwidth of the MH-TENG are significantly improved by adopting a multi-tube Helmholtz resonator. Within the frequency bandwidth range of 230 Hz, MH-TENG can effectively improve the efficiency of acoustic energy harvesting. 110 LEDs and an electronic thermometer can be powered by the sound-driven MH-TENG. In addition, the MH-TENG has a good capacitor charging performance, which is conducive to its application in ambient sound energy harvesting.

Band-gap dynamics and programming for low-frequency broadband elastic metamaterial

Local resonant elastic metamaterials are broadly studied as sound barriers, vibration isolators and energy harvesting walls. For real applications of these devices in the environment with low frequency and broadband sound waves, band-gap frequency and width of the elastic metamaterial should be programmed. This paper proposes an effective dynamic method to estimate the band-gap edge frequencies of the local resonant elastic metamaterials with four representative resonators. Particularly, uniform resonator, tapered resonator, double-decked resonator and necked resonator are examined. According to Bloch’s theorem, periodic boundary conditions are introduced to transform vibration study of the elastic metamaterial into vibration analysis of its unit cell. Wave equations of the axial vibrations of the unit cells are established. The frequency functions are deduced for predicting the lower and upper edge frequencies of the band-gap. Finite element analyses with Bloch periodic conditions are performed, and the band structures and eigenmodes of the four configurations verify the mathematical model and frequency functions. The resonator dimension is programmed for realizing the maximum normalized band-gap width with respect to the lower edge frequency and unit cell volume considering space limitation. The elastic metamaterial with the necked resonators is demonstrated to have the most superior low-frequency and broadband performances.

Integrated piezo-tribo hybrid acoustic-driven nanogenerator based on porous MWCNTs/PVDF-TrFE aerogel bulk with embedded PDMS tympanum structure for broadband sound energy harvesting

In this work, a novel type of acoustic-driven nanogenerator (ANG) that integrates piezoelectric and triboelectric effects is reported for broadband sound energy harvesting. With an internal structure combining beam-like porous multi-walled carbon nanotubes/polyvinylidene fluoride-trifluoroethylene (MWCNTs/PVDF-TrFE) aerogel and polydimethylsiloxane (PDMS) tympanum, the integrated MWCNTs/PVDF-TrFE/PDMS (MCPP) ANG achieves efficient collection of acoustic energy through the enhanced vibration and friction generated internally. Besides, by eliminating the need for a contact separation structure or an external resonator cavity, this design greatly simplifies the structure and contributes to the flexibility and durability of the device. The MCPP ANG, with 20 wt% sodium carboxymethyl cellulose (SCMC), 2 wt% MWCNTs and 5% w/v PDMS, reaches an optimal output of 34.4 V and 1.74 μA under 150 Hz and 115 dB sound stimulation, corresponding to an areal power density of 11.62 mW/m2. It possesses a broad working bandwidth from 110 Hz to 400 Hz, and can directly illuminate 7 light-emitting diodes (LEDs) in series. Employing a novel, simple and effective structural design, the ANG proposed here achieves flexible and stable acoustic collection, offering a promising path toward sound spectrum analysis, noise detection and power supply for various low-power sensors.

Observing localization and delocalization of the flat-band states in an acoustic cubic lattice

Over the past decades, wave localization and a wide variety of related phenomena have come to the forefront of research. Here, we theoretically and experimentally investigate the localization and delocalization of the flat-band states in an acoustic cubic lattice. Under evanescent couplings, the band structure of the designed cubic lattice has two dispersive bands and two degenerate flat bands. According to the analyses, we find that the constructions of flat-band states only depend on the excitation pressures and the coupling coefficients, which are frequency independent. With the flat-band state excitation, the acoustic wave can be either localized or delocalized in the lattice, which is determined by the excitation frequency. When the excitation frequency is close to the flat-band frequency of the lattice, the flat-band state can spread into the whole cubic lattice due to the resonance energy transfer among primitive cells. On the other hand, when the excitation frequency deviates from the flat-band frequency, the flat-band state can be localized in any primitive cell of the designed lattice. This work lays the groundwork for exploring the high-dimensional bound states in acoustic systems and has potential impacts on the applications of acoustic sensing and sound energy harvesting.

Multi-frequency sound energy harvesting using Helmholtz resonators with irradiated cross-linked polypropylene ferroelectret films

Harvesting multi-frequency sound energy from environmental noise is a meaningful topic to supply energy for potential devices. In this work, we constructed an array of Helmholtz resonators (HRs) with cross-linked polypropylene (IXPP) ferroelectret films on the inner walls of HR cavities, whose resonant frequencies range from 300 to 800 Hz and quasi-static piezoelectric coefficient d33 is 230 pC/N. The energy harvesting performance of IXPP films is investigated, both theoretically and experimentally, in a single HR with various sizes, showing the high energy conversion capability close to the resonant frequencies of HRs, e.g., 337, 375, 445, 522, 588, 661, 739, 782, and 795 Hz, in the experiment. By putting one, two, three, and four samples of nine different sized HRs in series connection in order, we measured the average output power of 3.16, 5.31, 7.36, and 8.66 nW at the resonant frequencies. It shows that the output power of IXPP films has been significantly improved at multiple frequencies by series connection of IXPP films. In parallel, the optimal electrical resistance increases in a quasilinear way compared to the number of HRs. These results are helpful for designing efficient sound energy harvesters in the broadband frequency range.

Subwavelength higher-order topological insulator based on stereo acoustic networks

Recently, the concept of a higher-order topological insulator has prompted increasing scientific interest in achieving the lower-dimensional boundary states. Among them, the zero-dimensional topological corner states in 2D/3D stereo acoustic systems are sustained in the second-/third-order topological insulators. However, the wavelength-scale unit size limits the application potential of corner states in acoustics, and the acoustic third-order topological insulator with a subwavelength unit cell is in urgent need to be proposed. Here, we use sub-wavelength acoustic waveguide networks to construct sonic lattices and configure the waveguide size to modulate the coupling strength in both 2D and 3D systems. The topological corner mode of second-/third-order topological insulators appears when the intra-cell coupling strength is weaker than the inter-cell one. Through calculating the eigenfrequencies and simulating the intensity response, the existence of a topological 2D surface, 1D hinge, and 0D corner states is ascertained. We demonstrate that the proposed topological acoustic corner mode may have potential applications in realizing the sound confinement and energy harvesting in both 2D and 3D systems.

Sound energy harvesting by leveraging a 3D-printed phononic crystal lens

We investigate the harvesting of sound waves by exploiting a 3D-printed gradient-index phononic crystal lens. The concept is demonstrated numerically and experimentally for focusing audio frequency range acoustic waves in air to enhance sound energy harvesting. A finite-element model is developed to design the unit cell dispersion properties and to construct the 3D lens for wave field simulations. Numerical simulations are presented to confirm the focusing of incident plane waves and to study the sensitivity of the refractive index profile to the direction of wave propagation. The theoretical predictions are validated experimentally using a scanning microphone setup under speaker excitation, and a very good agreement is observed between the experimental and numerical wave fields. A circular piezoelectric unimorph harvester is placed at the focal position of the lens, and its performance is characterized with a resistor sweep in the absence and presence of the lens, resulting in more than an order of magnitude enhancement in the harvested power with the lens. The 3D-printed lens presented here substantially enhances the intensity of sound energy via focusing, yielding micro-Watt level power output, which can find applications for wireless sensors and other low-power electronic components.

Sound energy enhancement via impedance-matched anisotropic metamaterial

Sound energy enhancement realized by electronic circuit designs plays a vital part in many fields, including acoustic communication, medical imaging, acoustic positioning and sound energy harvesting. The same effect, actually, can be achieved based on anisotropic acoustic meta-structures without electronic components, which has rarely been studied before. Fabricated by 3D printing technology, a two-way spiral-shaped metamaterial and its two-dimensional array are designed in the study, which is capable to realize sound energy enhancement. Due to the impedance matching design, the meta-structure shows almost opposite transmission behaviors in orthogonal directions. The sound wave compression and resonance effects come from the high-refractive-index medium, leading to enlarged acoustic signals inside the waveguide. For the array with an inside point sound source, an energy enhancement phenomenon occurs in the wave emission area outside the structure. Through experimental results and numerical simulations, it is revealed that the sound intensity of the emission wave can be increased more than fifteen-fold compared with the insulation condition in the range of 4.8–5.8 kHz, when the anisotropic metamaterial array is applied. The flexibility of the anisotropic meta-structure and corresponding array designs enables versatile applications demanding excellent sound signal and broadband performance.