A renewable low-frequency acoustic energy harvesting noise barrier for high-speed railways using a Helmholtz resonator and a PVDF film
Graphical abstract
Introduction
High-speed railways (HSR) are currently considered as one of the most significant transportation modes due to their large passenger volume and high efficiency [1]. Countries all over the world are developing high-speed railway transportation, which is an essential mode of transportation in modern society [2]. Railway networks have covered large areas [3]. However, the environmental costs cannot be ignored, especially the noise pollution, such as aerodynamic noise and rolling noise generated form high-speed trains, which has become a prominent environmental issue [4]. With energy harvesting becoming increasingly promising [5], a method to use noise energy to achieve noise reduction and power generation is an interesting topic in this research field. Presently, researches on reducing noise and harvesting acoustic energy mainly focus on three existing aspects.
First, noise barriers have become a widely used technical measure for noise reduction from road and railway transportation to mitigate potentially significant noise impacts. The sound absorption, insulation and reflection performances of a noise barrier were a studies concern. Reiter et al. determined the reflection characteristics of a noise barrier, and they analysed, compared and evaluated several methods to find a model for predicting the sound reflection index (RI) of a noise barrier [6]. With the environmental assessment process, Arenas et al. described the potential problems and effects of existing environmental noise barriers [7].
Second, with increasing global energy demand, a substantial change in energy systems is necessary [8]. Researchers have been studying on alternative energy resources over the past years, and studies on the conversion of sunlight, such as photovoltaics (PV), were rapidly developed over the past few years [9]. PV power systems are presently an indispensable technology [10], and noise barriers combined with PVs have been studied for many years. Recently, deep investigations and research been performed on PV module technology due to its many advantages like energy potential, and great research progress has been made on the construction of photovoltaic noise barriers (PVNBs) [11]. Many fundamental studies have verified the implementability of PVNBs. EllenDe Schepper investigated the feasibility of a PVNB, and the Monte Carlo method was used to analyse its cost benefit. Additionally, the results showed that PVNBs are a profitable project [12]. Faturrochman et al. built a prototype of a bifacial photovoltaic noise barrier and demonstrated, through experiments, that the measured power output results agree well with the simulated power output data [13]. Gu et al. proposed and installed a complete noise barrier with a 360 m PV array along a Chinese metro railway line. The proposed PVNB can achieve a power generation of approximately 5000 kWh annually, which will avoid the emission of some harmful gases to a certain extent [14].
Third, renewable, sustainable and non-pollution sources of energy have attracted much attention, and harvesting abundant environmental energy, such as sunlight, wind, water and sound have become an extremely important part of energy utilization and recovery. Many research efforts have been devoted to technologies focusing on alternative energy harvesting or energy conversion. Zhang et al. designed a kinetic energy harvesting system to harvest power wasted by vehicles passing through a road tunnel [15]. For use in extended range electric vehicles, Zhang et al. presented a novel shock absorber to collect the wasted suspension energy from the moving vehicles [16]. Technologies of energy harvesting will be a desirable solution to energy shortages [17]. Orrego et al. developed a novel wind energy harvester by self-sustained oscillations of a flexible piezoelectric membrane fixed in an inverted orientation [18]. Helios Vocca discussed a vibration harvesting method with bi-stable oscillators to model nonlinear piezoelectric harvesters, investigating the potential of the noise driven dynamics [19]. Zhang et al. developed a portable electro-magnetic energy harvesting design that converts vibrations of railroads into electricity through mechanical transmission, and the proposed energy harvester proved through tests to be effective with an efficiency of 55.5% [20]. The applications of piezoelectric designs are fully developed to convert vibrations to electrical energy and have captured much attention in recent years due to the superiorities of a high transduction efficiency, easy establishment and so on. An innovative energy harvesting pavement system is fully designed in [21] by Guo et al., in which the asphalt layers composed of piezoelectric materials become conductive to harvest the kinetic energy of vehicles. The maximum electric output can reach 300 mW. Roshani et al. verified the feasibility of harvesting mechanical energy of the strain and stress generated by the vehicles through the roadways. They conducted experiments to consider the potential of harvesting energy from asphalt pavements using piezoelectric materials [22]. Guan et al. proposed a piezoelectric system to harvest energy from rotational movement, such as generators integrated onto the inner surface of vehicle tires. During the rotation of the energy harvester, the repeated deformation of piezoelectric elements will be transferred to electricity, and an output energy of 83.5–825 μW is gained at rotating frequencies of 7–13.5 Hz [23]. Abdelmoula et al. evaluated low-frequency Zigzag energy harvester with torsion-bending properties, and the proposed torsion-dominant mode proved to provide a higher harvested power level, decreasing the operating frequency by 50% [24].
Although various energy resource harvesting technologies have been extensively investigated, there are neglected and wasted energies all around us. For instance, acoustic energy is a significant energy resources that is generated constantly but remains unused [25]. Sound waves are pressure vibrations that propagate in elastic media. Acoustic energy can be acquired in an environment. With autonomous micro-electromechanical systems (MEMS) rapidly, globally developing, acoustic energy harvesting (AEH) that converts environmental acoustic waves into electricity using a resonator or a transducer has become viable [26]. Zhou et al. presented an acoustic energy harvester in a bi-stable state with a flat plate that is excited to oscillate, and for a certain sound pressure level (SPL), a high voltage output was generated when reaching a coherence resonance [27]. Generally, an acoustic resonator is not only used to absorb an unexpected frequency component of a sound system but also to amplify the sound pressure in an acoustic field at a specific frequency band [26]. As an efficient device for noise control, Helmholtz resonators (HRs) are one of the most universally used acoustic resonators [28]. Liu et al. studied the progress of an acoustic energy harvesting device using an electro-mechanical Helmholtz resonator (EMHR), which mainly consists of a cavity, an orifice, and a diaphragm of piezoelectric materials. For an incident SPL of approximately 160 dB, the output power can be up to approximately 30 mW which is adequate to power many low power electronic devices [29]. Yuan et al. suggested a focus on increasing the output power of acoustic energy gathering due to the low sound intensity and proposed a special design for harvesting acoustic energy. The proposed high-performance system is mainly composed of a HR with an unfixed bottom, which is appropriate for low-frequency sound waves [30]. Kim et al. developed an acoustic energy scavenger to use large amplitude acoustic waves, which was developed in response to the air that flows across the opening of a HR [31]. Noh et al. proposed a piezoelectric cantilever integrated within a HR. To maximize the efficiency of energy harvesting, the mechanical resonance of the piezoelectric cantilever was in accordance with acoustic resonance of the HR [32].
Despite the existing approaches having partly covered the problems of noise pollution and noise energy waste, certain aspects of HSR noise have not been addressed yet. Two main facts about the technology still challenge researchers: (1) Noise insulation and absorption have been emphasized but harvesting noise energy to power small electronic equipment is neglected in HSR. (2) The popularity of HSR requires better performances of noise barriers on noise reduction, especially for low-frequency noise that mostly escape the existing noise barriers along HSR. To follow up and address the aforementioned problems we proposed, in this paper, a novel noise barrier that harvests alternative acoustic energy using a HR and a Polyvinylidene Fluoride (PVDF) film for HSRtransportation to both achieve noise reduction and electricity generation. Supercapacitors are used in the system for energy storage to power some small electronic devices and serve as standby power supplies along the HSR, such as railway monitors and maintenance.
The rest of this paper is generally structured as follows. In Section 2, the design of the noise barrier system is described, including the noise collection input module, the resonant pressure amplification module, the electricity generator module and the energy storage module. A description of the modelling and analysis of the system is presented in Section 3. Then, the experimental details are described in Section 4. In Section 5, results and discussion are presented to verify the feasibility of the system, and further applications are described. Finally, the conclusion is given in Section 6.
Section snippets
System design
The general architecture of the proposed novel acoustic energy harvesting noise barrier (AEHNB), as shown in Fig. 1, consists of four parts: the noise collection input module, the sound pressure amplification module, the electricity generation module and the power storage module. The noise along the HSR is collected through the honeycomb structure and is input into the noise barrier. This is called the noise collection module. Then, the noise enters the HR, which is called the sound pressure
Helmholtz resonator
The air in the neck part can be regarded as a mass vibrating with the incident sound waves, while the air in the container is expanded and shrunk due to the vibrations of the air through the neck. Then, it can be seen as a spring, and the HR is the same as a mass spring system, as shown as Fig. 8.
The basic resonance frequency of the HR in response to the incident sound pressure crossing the neck is given in [38].where is the basic resonance frequency of the HR, is
Experimental details
A prototype of the acoustic energy harvesting noise barrier was built. The overall experimental setup is shown in Fig. 12, and the experimental schematic model and details are shown in Fig. 12(a) and (b) respectively. As shown in Fig. 12, we used the speakers to simulate a certain frequency of noise to verify our proposed methods. The tests were conducted in the laboratory of thermal power and automotive engineering at Southwest Jiaotong University, and the overview of the experimental
Acoustic resonance in the AEHU
The characteristics of HR have been described. The HR is designed with the basic acoustic resonance frequency of 550 Hz.
In both the simulations and experiments, the incident sound is set as 100 dB SPL. To ensure that the resonators were excited resonantly, the incident sound frequency ranged widely from 100 Hz to 600 Hz in the simulations and 270 Hz to 600 Hz in the experiments. And both of the frequency ranges contain the resonance frequencies.
For the AEHU in the first model, without the noise
Conclusion
In this paper, a renewable low frequency acoustic energy harvesting noise barrier is reasonably, systematically and successfully developed for high-speed rails. The proposed system provides a practical method of energy supply for low power electronic devices along a high-speed rail. For the purposes of noise reduction and electricity generation, the proposed system converts sound energy to electricity using a Helmholtz resonator and a PVDF (Polyvinylidene Fluoride) film. The renewable energy
Acknowledgments
This work was supported by the National Natural Science Foundation of China under Grant No. 51675451, by the Science and Technology Projects of Sichuan and Chengdu under Grant Nos. 2016GZ0026, 2016CC0027, 2017RZ0056 and 18MZGC0272. The first three authors contributed equally to this work. The asterisk indicates the author to whom all correspondence should be directed.
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