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Analysis of methods and MEMS for Acoustic Energy Harvesting with Application in Railway Noise Reduction

The Romanian Review Precision Mechanics, Optics & Mechatronics, 2011, No. 40 123

ANALYSIS OF METHODS AND MEMS FOR ACOUSTIC ENERGY HARVESTING WITH APPLICATION IN RAILWAY

NOISE REDUCTION

I. Kralov, S. Terzieva, I. Ignatov Technical University of Sofia,

“Kliment Ohridski” blvd. № 8 E-mail: [email protected], [email protected], [email protected]

Abstract – A short state of the art survey of acoustic energy harvesting methods and MEMS is realized in this paper. Comparison between the basic functional parameters is carried out of the standard solutions for receiving, converting and storing the energy from the noise sources. The goal is to study the possibility of applying MEMS for acoustic energy harvesting in a new construction for railway noise reduction. For this purpose experimental tests are made. On the base of the analysis of the results conclusions about effectiveness of the solution are done. Keywords: Energy harvesting, Micro-electro-mechanical systems, Railway noise reduction, Noise absorbers.

1. Introduction The railway transport is the only alternative to the fast industry and population growth with its unlimited opportunites for development. New railway projects around the world plus upgrading/expanding existing railway lines caused orders in virtually all market segments to surge. According to studies, the total annual world market for the rail supply industry in 2007 is estimated at more than €120 billion, out of which €85 billion is accessible. As for the annual growth rate, it is considered to be between 2,0% and 2,5% over the next nine years. Railway operational noise originates from a number of sources. These include the engines and cooling fans of locomotives, the under-floor engines of “diesel multiple units” (self-propelled sets of railway coaches), gears, aerodynamic effects at higher speeds, and the interaction of wheels and rails. The latter source tends to have an influence on overall noise levels at speeds above 50 km/h and is normally predominant at speeds above around 100 km/h. Wheel/rail noise, or “rolling noise”, results from the vibration–excitation of the wheels and track as the wheel rolls on the rail. The excitation is provided by the combined surface roughness at the interface, or “contact patch”, between the wheel and the rail. Because the entire wheel and track system is excited by the combined roughness at the interface, it is this combined value that determines the level of rolling noise rather than the individual rail and wheel

roughness components [1, 2, 3, 4]. The noise from wheel/rail contact has negative effect on the surroundings, and there are many methods for its description and abatement. But in the past few years a topic for ambient energy harvesting is drawing more and more attention, and in this sense a question for noise energy harvesting takes place. Surveys show that there are many ideas, as well as number of successful constructions of MEMS for acoustic energy harvesting exists [5]. The goal of this paper is to present the methods for noise abatement, short review of state of the art MEMS for acoustic energy harvesting, and express the prerequisites for applying the MEMS technology for acoustic energy harvesting into the noise absorbers construction [5, 6]. 2. Classical methods for railway noise reduction, patent reviewed Many years of research and engineering have led to package of solutions for noise reduction. Some of them are summarized in the table 1 [7], and particular realisations are shown on figure 1 [8, 9]. In this particular paper a new construction is presented. The invention is a method for noise absorbtion of the noise generated by the wheel rail contact of rail-bounded transport (figure 2-a). The invention is proper for noise absorber (figure 2-b) and finds its application in railroad construction, in railway stations, metro stations (figure2-d) and rail tunnels (figure 2–c).



Table 1. Methods for noise reduction

Noise reduction method

Overall reduction potential

Noise reduction

effect Comment/ status

1 Retrofitting

with K-blocks

8-10 dB Network wide

K-blocks are homologated however require adaptation of the braking system

2

Retrofitting with LL-

brake blocks

8-10 dB Network wide

LL-brake blocks are only provisionally homologated

3 Wheel absorber 1-3 dB Network

s wide

Effect strongly depend on local conditions. Wheel maintenance difficulties may occur

4 Track absorbers 1-3 dB Local

Track maintenance difficulties may occur, effect strongly depends on local conditions, not homologated in many countries

5 Acoustic

rail grinding

1-3 dB Local

Effect strongly depends on local rail roughness conditions, smooth wheels are precondition for effect

6 Operational Variable Local

Negative effect on the operations and railway capacity. The method hinders railway traffic therefore not in line with efforts to promote sustainable transport

7 Noise barriers 5-15 dB Local

Effect depends on height and local geography, negative effect on the landscape, influence on railway maintenance procedures

8 Noise

insulated windows

10-30 dB Local Effect is only achieved only when windows are closed

The idea of the invention is to suggest method for noise abatement and reduction, of noise propagated from wheel/rail contact of railway vehicles, by capturing and absorbing the radiated sound in small volumes near the track. The essence of the method is to install fixed, noise absorbing tube-like materials parallel to the track trajectory. The material is

situated according figure 2-b near the track.

2

4

3

7

Figure 1: Some examples of noise abatement

according to table 1.

b

c d

a

Figure 2: Application of the noise abatement

construction

3. Experimental setup, results and discussion

On figure 3 it is shown the testing procedure of the absorber introduced in section 2. The noise levels in a discrete frequency spectre from 500 to 8000 Hz, compared to noise A level (Lp(A)), are presented on figure 4. On graphic 4-a the results are without the absorber, on graphic 4-b the results are according the test procedure and on graphic 4-c the results with and without the absorber are compared. The comparison shows noise level reduction of 17,75 dB at frequency 4000 Hz, as in the investigated range the total reduction is averaged 11,12 dB. All the results are collected according to the standards and legislations concerning calibration and testing procedures, as well as measurement error evaluation. These results indicate very promising opportunity for application of acoustic energy harvesting technology, especially in railway transport, in order to turn the passive absorption into active one. The advantages could be more valuable with applying advanced nanopiezotronic technology. It would give new opportunity for development of self sufficient energy system for lighting purposes in passenger car



or train, and in the same time providing better comfort with its ability on noise absorption performance.

Noise generator

LV

Noise Source

Noise absorber Measuring equipment

Test chamber

Figure 3: Noise absorber testing procedure.

Figure 4: Results obtained with the noise absorber

4. MEMS analysis

4.1. Electromagnetic sound pressure harvesters The electromagnetic energy sources are widespread and the energy available could be harvested in inaccessible environment. The energy density of the electromagnetic sources is small (in order of 1

2μW/cm ). That requires the use of highly efficient amplifiers and transducers. In that case the control circuit is designed to harvest energy in longer periods, longer than 10 min, while in cycles shorter than 1s, by producing amplified output energy flow.

The structure of composite transducer, presented on figure 5, consists of piezoelectric PZT fixed to Be-bronze horn – magnetostrictive Terfenol-D plate (produced by Gansu Tianxing Rare Earth Functional Materials Co., Ltd.) with dimensions 12 x 6 x 1 mm is longitudinal symmetrically located at the mechanical anchor of the ultrasonic horn where the displacement is zero [10]. Designed in this order the system aims to enhance the energy density and obtain convergence while transferring the wave trough larger cross sections to less cross sections. The experimental general design is shown on figure 5. The three piezo-plates are longitudinal orientated and fixed, and their dimensions are 12 x 2 x 0.8 mm. They are glued to the ultrasonic horn by acrylic adhesive. The prototype of the Terfenol-D/PZT/Be–bronze composite transducers is used to harvest electromagnetic energy and supplies power for aWSN. In the experiment, through the proposed supply management circuit, the low-power (20 W) energy harvester can drive the wireless sensor nodes with a higher power consumption (75 mW) at transmitting and 1mW at receiving, at a communication distance of 60 m, and an operation cycle of 620 ms [10].

a

b

Figure 5: Experimental apparatus photo of magnetoelectric transducer

4.2. Piezoelectric sound pressure harvesters Most common and used piezo-materials in MEMS are ZnO (zinc oxide), AlN (aluminum nitride), PZT (lead zirconate titanate). The material is selected depending on various factors, some of them are: difficulties in producing it, ensuring certain parameters, compatibility with integrated circuits, etc.

b



The adoption of piezoelectric elements (plates, produced in specific way), for mechanical energy transducing (sound pressure in this particular case) is based on the direct piezoelectric effect – during mechanical deformation on the both surfaces of the plate opposite electrical charges occurred, i.e. voltage proportional to the deformation occurs. It could be assumed that in sinusoidal changing over time sound wave, on the plates output will be obtained sinusoidal voltage with the same frequency as the sound wave [11, 12, 13, 14, 15, 16, 17]. The most common piezo-transducer of sound pressure is the Helmholtz resonator with piezoelectric composite backplate. It consists of cavity, connected to the surrounding environment through narrow neck, as shown on figure 5. Here V indicats the cavity’s volume, 2S a is the cross section area of the neck, l its length and a its radius, 1P is the pressure of the surrounding environment,

2P - the pressure of the cavity. The resonator is presented as acoustic oscillating system with lumped parameters, which could be presented by equivalent mechanical oscillating system. The air transferred through the neck has finite mass and could induce dissipative losses. In the cavity, the air is compressible and it could be modeled as compliance. Moreover, based on electroacoustic analogy the model is transformed into equivalent electric circuit, which is presented by series RLC – circuit (figure 6). There are three acoustic elements:

AL – mass, AR - active resistance,

AC - compliance. They correspond to the electrical ones - coil with inductance, resistor with active resistance and capacitor respectively with certain capacity. The relevant equations according to [5] are:

a

b Figure 6: Graphic showing the mechanical equivalent of the Helmholtz resonator and

equivalent electrical circuit of the Helmholtz resonator

02 2 43( )A

V kgLa m

;

2 4

8A

l kgRS m s

;

3

20 0

AV mCc Pa

(1)

where 0 is the mean density of the air, -

dynamic viscosity of the air, 0c - sound velocity. Preliminary energy harvesting experiments indicate a power density of 0.34µW/cm2 for acoustic input of 149 dB. Furthemore calculations indicate a potentially achievebale power density of 252 µW/cm2 at 149 dB with same design but improved fabrication conditions of teh module. 4.3. Acoustic energy harvesting using resonant cavity of a sonic crystal The propagation of acoustic or elastic waves in sonic crystals have been the subject of intense investigation in the past few years. The sonic crystals have attracted a lot of attention in some possible applications, such as, acoustic filters, vibrationless environments for high-precision mechanical systems, and transducers. Furthermore, the point defect is created by removing a rod from a perfect sonic crystal and can act as a resonant cavity. The acoustic wave can be localized in the cavity of the sonic crystal as the incident acoustic wave is at the resonant frequency. By means of this phenomenon, piezoelectric material into the cavity of the sonic crystal can be placed to convert the acoustic energy to electric energy at the resonant frequency of the cavity. The two-dimensional square sonic crystal, consisting of polymethyl methacrylate (PMMA) cylinders in the air background, is studied, where density of PMMA and air is 1190 and 1,2 kgm3, respectively, and wave velocity of PMMA and air is 2694 and 343 m/s, respectively. The radius of each cylinder is r0=17,5 mm. The lattice constant is a0=49 mm, and the filling fraction of the cylinder in the unit cell, f =πr0

2 /a02, is 40% [18].

The inset of figure 7 shows the schematic of the experimental setup and the position of the PVDF (polyvi-nylidene fluoride) film in the cavity of the sonic crystal. Figure 6 shows the frequency response of the PVDF film voltage output in the cavity of the 5x5 sonic crystal. The frequency of the peak indicated by the arrow is 4,2 kHz and it is very close to the resonant frequency of the cavity without PVDF film. The maximum voltage output of the PVDF film occurs as the frequency of incident acoustic wave is near the resonant frequency of the cavity. It shows that the acoustic waves can be localized in the cavity of the sonic crystal at the resonant frequency, and then the voltage output of the PVDF film is excited by the resonance of the cavity. The power harvesting efficiency without the sonic crystal η is the ratio of the output power to



input power and can be expressed as: η= WOut/WIn, Figure 7 also shows the output voltage with and without the sonic crystal. The voltage variation is a sinusoidal function of time. The solid line represents the output voltage as the PVDF film is put in the cavity of 5x5 sonic crystal and the frequency of the incident acoustic wave is 4,2 kHz. The dotted line represents the output voltage of the PVDF film without sonic crystal. At 4,2 kHz, the output voltage with the 5x5 sonic crystal is 25 times larger than that without the sonic crystal. In summary, an acoustic energy harvesting generator based on the sonic crystal and the piezoelectric material are realized and modeled The larger voltage output of the piezoelectric material is associated with the larger pressure in the cavity of the sonic crystal. When the frequency of the incident acoustic wave is at 4,2 kHz, a maximum power is generated under a load resistance 3,9 kΩ. The output power is dependent on the input level of the source. If the source is a turbofan engine, we think that the large output power will be produced. To improve the output power, the higher piezoelectric constant of piezoelectric materials should be selected. In addition, the piezoelectric beam can be designed to have the resonant frequency, which is the same as the resonant cavity and incident wave. The larger output should be reached. By using properties of band gaps and wave localizations of the sonic crystal, the noise control and energy harvesting can be achieved simultaneously. 5. Conclusion and further work In the recent years, energy producing and harvesting from the surrounding environment becomes significant scientific area having practical application, and its development continues rapidly. The increased number of publications confirms it. The developments in the micro-electro-mechanical (MEMS) have wide application, for example: - Wireless receivers and life – supporting equipment supply; - Battery recharging; - Vehicles tire pressure monitoring used in the automotive industry; - Remote control of security devices, etc.

Figure 7: Frequency response of PVDF film voltage output in the cavity of 5x5 sonic crystal and output voltage from the piezoelectric material of the sonic

crystal cavity. Survey done by IDTechEx in 22 countries and 200 organizations in Europe, North America, East Asia and other countries indicates the between 2009 – 2019 the design and production of MEMS shall be speeded up. The expanding publicity of problems, concerning the environment protection, could rise the energy harvesting technology (in this particular case sound pressure is used) using MEMS to a promising method for low voltage system supply. This will avoid the use of disposable batteries and the need of recycling. The increase and development of portable electric devices having smaller and smaller mass, extends the necessity of highly effective energy sources to supply them. With the creation of technology and devices, which will be able to convert and store the energy from the surrounding environment, the question for excluding batteries as a main source supplying low power consuming devices arises [19]. A volume of 1 3cm lithium batteries consists of 2800 J , which is enough for supplying consumer with average power of 100 W nearly a year, but systems having higher energy consumption the battery replacement have to be made in a shorter periods. The most common systems convert solar, thermal energy and energy from mechanical oscillations in electrical. The main energy harvesting from mechanical oscillations approaches are three, namely: electromagnetic (inductive), electrostatic (capacitive) and piezoelectric. The long range of applications of MEMS for energy harvesting and in this particular case for acoustic energy harvesting, and the rapid development of this technology as well as the results from the absorber testing from section 3 indicate a promissing opportunity for possible combination. Investigation on the possible combination between sound absorbing and harvesting has a very promising future. It will open a new prospect for eco-friendly life style, as well as solution to some



noise problems. According [20] such combined constructions are implemented. 6. Acknowledgments This research is realised with the support of the “Centre of Excellence - Technical University of Sofia”, “DUNK 01” contract. 7. Bibliography [1] Hardey AEJ and Jones RRK., “Rail and wheel roughness -implications for noise mapping based on the Calculation of Railway Noise procedure, AEA Technology Rail, Issue 1, March 2004. [2] Thompson D. J. and Jones C. J. C., A review of the modelling of wheel/rail noise generation, Journal of Sound and Vibration, 231(3), 519-536, 2000. [3] Hubner Peter, Reducing railway noise, strategic challenges and state of the art, Forum Acusticum, 1243-1248, 2005. [4] A. Van Beek et al., Task 1.2.1, State of the art, Technical Report, SNCF, 2002. [5] Horovitz, St., Development of a MEMS-based Acoustic Energy Harvester, University of Florida, PhD Thesis, 2005. [6] Trevor J. Cox and Peter D’Antonio, Acoustic Absorbers and Diffusers, Taylor & Francis, 2009. [7] Oertly Jakob and Hubner Peter, UIC, Railway noise in Europe. A 2010 report, state of the art. [8] Jansen Erwin, Acoustic measurement on rolling stock retrofitted with composite brake blocks, IPG Rail seminar, December 2008. [9] D. Benton et al., Reducing Railway Noise in Urban Areas, Silence Seminar, Paris, 2008. [10] Li, P., A Magnetoelectric Energy Harvester and Management Circuit for Wireless Sensor Network, Elsevier, vol. 157, 100-106, 2009.

[11] Morris j. Dylan, Need Ryan, F. Anderson, Michael J., Bhr, David F., Enhanced actuation and acoustic transduction by pressurization of micromachined piezoelectric diaphragms, Sensors and Actuators, [12] Ramadass, Y., A. Chandrakasan, An Efficient Piezoelectric Energy Harvesting Interface Circuit Using a Bias-Flip Rectifier and Shared Inductor, IEEE Journal of Solid-State Circuits, Vol. 45, №. 1, 189-192, January 2010. [13] Yong Zhu, Reza Moheimani, Mehmet Yuce, A 2-DOF MEMS Ultrasonic Energy Harvester, IEEE Sensor Journal, Vol. 11, No. 1, January 2011. [14] Adhikari, S., M. I. Friswell and D. J. Inman, Piezoelectric Energy Harvesting from Broadband Random Vibrations, Smart Materials and Structures, Vol. 18, 115005, 2009. [15] J. Smoker, M. Nouh, O. Aldraihem, A. Baz, Energy Harvesting from a Standing Wave Thermo-Acoustic-Piezoelectric Resonator, American Institute of Aeronautics and Astronautics, 2010. [16] Triet T. Le, Efficient Power Conversion Interface Circuits for Energy Harvesting Applications, Oregon State University, PHD Thesis, 2008. [17] Joseph Paradiso A. and Thad Starner, Energy Scavenging for mobile and wireless electronics, Pervasive computing, 2005. [18] Liang-Yu Wu, Lien-Wen Chen, and Chia-Ming Liu, “Acoustic energy harvesting using resonant cavity of a sonic crystal”, Applied Physics Letters’95, 2009. [19] http://www.computescotland.com/energy-harvesting-devices-2103.php [20] Iwan Yahia, iARG Advance in Power Generating Sound Absorber, Proceedings of Acoustics & Geophysics Cluster Meeting, March 2011.

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