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Study on harvesting energy from pavement based on piezoelectric effects

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 Journal of Wuhan University of Technology-Mater. Sci. Ed. Oct. 2014 933

DOI 10.1007/s11595-014-1023-3

Harvesting Energy from Asphalt Pavement

by Piezoelectric Generator

ZHAO Hongduo, TAO Yujie, NIU Yanliang, LING Jianming

(Key Laboratory of Road and Traffic Engineering of Ministry of Education, Tongji University, Shanghai 201804, China)

Abstract: This paper presents the way to harvest mechanical energy from asphalt pavement
by piezoelectric generator. Results show that the potential energy in asphalt pavement can be up to
150 kW/h per lane per kilometre. Part of the mechanical energy can be harvested by piezoelectric transducers.
The performance of seven typical transducers is examined through finite element analysis. Results show
that PZT piles and multilayer, cymbal and bridge can work in asphalt pavement environment. PZT piles and
multilayer have higher energy converting rate. However, the total harvested energy is small if these transducers
are embedded directly in pavement. A prototype pavement generator is developed using PZT piles to increase
the harvested energy. The generator can harvest more than 50 kW/h energy from the pavement under heavy
traffic. 8-16 PZT piles are recommended for one generator. Round shape is suggested for the PZT piles to reduce
the concentration of stress. And multilayer structure is recommended for PZT piles to decrease the electric
potential of generator. The generator can be extended as sensor in the asphalt pavement, which can be used to
monitor the traffic, pavement stress and temperature.
Key words: asphalt pavement; energy harvesting; piezoelectric generator; finite element analysis

1 Introduction 2009 showing the possibility of harvesting energy from

asphalt pavement. However, few technique details of
The asphalt pavements will endure millions of the study are reported publicly.
vehicle passes in its service life. The moving vehicles In this paper, the potential level of mechanical
cause stress, strain, deformation and vibration in energy in asphalt pavement is discussed. Various
pavement. At the same time, the pavement obtains piezoelectric transducers are compared for harvesting
strain and kinetic energies from the work of vehicle energy from the pavement. Then a pavement generator
load. However, these energies are dissipated in the with high energy converting efficiency is developed,
pavement as wasted thermal energy, which leads which can couple with the asphalt pavement as well.
to more risk of pavement damage. In recent years,
researchers began to seek new technology for 2 Potential energy in asphalt
harvesting those mechanical energies. Piezoelectric pavement
technology is the most potential one because of its
ability to convert stress into electricity. Innowattech, The mechanical energy in the asphalt pavement
an Israel based company announced that they have originates from the work of vehicle loads. The vehicle
developed a series of piezoelectric energy harvesting load and its displacement on the asphalt pavement
devices (IPEG TM ) for road, railroad, airport and can estimate the amount of energy. We consider two
pedestrian[1]. And a pilot project was constructed in types of truck: with one rear axle and 6 tires in total
(1+1 type) and with two rear axles and 10 tires in total
(1+2 type) as shown in Table 1. The contact stress
©Wuhan University of Technology and SpringerVerlag Berlin Heidelberg 2014 between tire and asphalt pavement is simplified as
(Received: Aug. 19, 2013; Accepted: June 18, 2014) uniform distribution in a circle area, which equals 0.7
ZHAO Hongduo(赵鸿铎): Prof.; Ph D; E-mail: hdzhao@ MPa. Assuming that the asphalt pavement is an elastic
tongji.edu.cn multilayer system, typical structure parameters are listed
Funded in Part by the National Natural Science Foundation in Table 2. Then the stress, strain and displacement can
of China (No.50908177); the National High-tech Research and
be analysed by software, such as BISAR, Openpave,
Development Program of China (863 Program)(No.2012AA112506)
or finite element analysis. The surface displacements
934 Vol.29 No.5 ZHAO Hongduo et al: Harvesting Energy from Asphalt Pavement by Piezoe...

under the centre of tire are shown in Fig.1. tires of truck.

The amount of potential mechanical energy
in the asphalt pavement equals to the work done by 3 Piezoelectric effects
the vehicle tires, which can be estimated by Eq.(1).
The sizable pavement mechanical energy
can be harvested using piezoelectric material. The
piezoelectric material has the ability to convert the
stress to electric charge. A piezoelectric material with
electric neutrality can be polarized by adding a strong
electric field. After the electric field is removed, there
will remain large strength of polarization. In order to
maintain the electric neutrality of the material, free
charges will be absorbed on the polarization surface.
When a force is applying on the material, the strength
of the polarization will be changed by the deformation
of the material, thus some free charge will be released
to keep the electric neutrality. If an electric route is
connecting to it, the changing of polarization will cause
the movement of charges in the route, which generates
the current.
PZT (lead zirconate titanate) is the most popular
material that has piezoelectric effects. The piezoelectric
effects of PZT can be analysed by piezoelectric
equation as Eq.(2)[2]. For more popular application, the
PZT materials are assembled into transducers.

(2)
where i, j=1, 2, 3… 6; m, k=1, 2, 3; Ti is the stress
in i direction; E k is the external electric fields in k
direction; Dm is the charge displacement on the surface
of m direction; dmi is piezoelectric strain constant; εTmk
(permittivity) is dielectric constant measure at constant
Ti condition.
For pavement energy harvesting, the external Ek
=0. Then the energy produced by the external stress can
be calculated by Eq.(3)[3].

(3)

where U E is the electric energy storage in the

piezoelectric device; P is the polarization caused by
the load; E is the inner electric field; Vo is the electric
Considering 1 lane of 1 km highway, if the truck potential in open circuit; A is the area of PZT; t is the
volume is 600 v/h, the potential energy in each lane thickness of PZT; εr is the relative dielectric constant of
produced by the truck reaches up to 150 kW in one PZT; ε0 is the dielectric constant in vacuum.
hour as shown in Fig.2. This amount of energy is
sizable for harvesting. 4 Piezoelecttic transducer comparison
PZT based piezoelectric transducers are used
(1)
widely in industry. Many of those transducers can be
used for harvesting energy from the ambient, such as
where W is the potential energy in asphalt pavement
the Multilayer[4,5], Moonie[6], Cymbal[6], RAINBOW
(J); Fi is the load for each tire (N); Di is the maximum
(Reduced and Internally Biased Oxide Wafer) [7] ,
displacement under each tire (m); n is the number of
 Journal of Wuhan University of Technology-Mater. Sci. Ed. Oct. 2014 935

THUNDER (Thin Layer Unimorph Ferroelectric where UE is the energy harvested from the pavement
Driver and Sensor)[8], Bimorph[9], MFC (Macro-Fiber for single PZT; T3 is the stress on the top of PZT; A is
Composite) [10] etc. However, none of them is designed the area of PZT, t is the thickness of PZT.
for asphalt pavement.

From Eq.(4), we know that larger U E will be

obtained from larger stress. In order to magnify
the stress on the PZT, a structure shown as Fig.4
is designed. The stress on those PZT piles can be
calculated by Eq. (5) and Eq. (6).

(5)

(6)
We put those transducers into pavement directly
as shown in Fig.3. The performance of transducers
where Ac is the effective load area for calculation as
can be evaluated by finite element analysis. Under
shown in Fig.5; σ is the vertical stress in the pavement;
the uniform tire stress, which equals 0.7 MPa, the
n is the number of PZT piles used in one generator; h is
efficiencies of the transducers are evaluated by the
the embedding depth of generator; d is the diameter of
electromechanical coupling factor k and the energy
one tire print.
transmission coefficient λ max. At the same time, the
coupling performance with asphalt pavement is
also considered. The comparing results are listed in
Table 3[11]. They show that PZT pile and Multilayer
have the highest k and λmax, which indicates that they
have high ability to convert stress to electric energy and
output the energy. Cymbal and Bridge are also suitable
for their reasonable k, λ max and medium stiffness.
However, the energy level of those transducers is very
low. They should be improved for further application.

5 PZT based pavement genera-

tor design
5.1 Prototype structure
The PZT pile is chosen for further design for
its excellent energy conversion efficiency. In the
pavement, the stress is mainly from the vertical vehicle
load. So the vertical stress is considered as the major
external stress for the PZT. Assuming the 3rd axle for
PZT is in vertical direction, then for pavement energy
harvesting, Eq.(3) can be rewritten as Eq.(4).

(4) In Eq. (5) and (6), σ and Ac can be determined

by the tire load and the location where the generator
936 Vol.29 No.5 ZHAO Hongduo et al: Harvesting Energy from Asphalt Pavement by Piezoe...

is embedded. So for the same location and load, the

harvested energy depends on the total area of PZT in
vertical direction. Assuming Ac=0.04 m2, t=0.1 m, the
generator is embedded in 4 cm depth (under the surface
layer) side by side. PZT 5H is used in this paper to get
more energy. Considering 1 lane 1 km highway, whose
1+1 type truck volume is 600 V/h per lane, the energy
these generators can be harvested from the pavement
is shown in Fig.6. It can be concluded that the energy
increases with the decreases of PZT area. However,
the stability and strength of generator decreases with
the area. Considering the energy level and coupling
performance with the pavement, the total PZT area at
4 cm2 is used in the following analysis. 5.3 Shape of PZT piles
5.2 Number of PZT piles Three shapes, which are square, round and
The stress and displacement for the generator hexagon, of PZT piles are compared through FEA. The
with various number of PZT piles are analysed maximum stresses in PZT are listed in Table 4. It shows
through finite element analysis. The total area of PZT that the PZT with round shape has less concentrated
piles is 4 cm2. The maximum tensile, compressive and stress. This shape is suggested for PZT piles of
shear stresses in the PZT are shown in Fig.7. It shows pavement generator.
that all stresses decrease with increasing PZT piles
number. The similar relation is also explored for the
displacement shown in Fig.8 and Fig.9. From these
figures, more than 4 PZT piles are suggested to get
less stress and displacement. However, the more PZT
piles lead to smaller single PZT pile area, which needs
higher fabrication costs. At the same time, if the PZT 5.4 Multilayer structure
pile is too thin, the generator is easy to lose stability
under the dynamic vehicle load. Considering the
stress, displacement, costs and stability of structure,
piles number of 8-16 is suggested for one pavement
generator.

From Eq.(2), it can be delivered that the electric

potential between two polarization surfaces increases
linearly with the thickness of PZT and external stress.
The electric potentials of PZT with different thickness
at various T are listed in Table 5. It can be concluded
that, huge electric potential will be produced for the
thicker PZT under larger external stress. However,
it is difficult to deal with large electric potential
for pavement energy harvesting and outputting. So
the external stress and thickness of PZT should be
 Journal of Wuhan University of Technology-Mater. Sci. Ed. Oct. 2014 937

balanced. A multilayer structure is suggested for appreciate Dr. Jeremy Lea providing Openpave for
pavement energy harvesting, as shown in Fig.10, which free.
has reasonable size and very thin single layer(less
than 0.1 mm). The multilayer structure has the same References
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potential (less than 200 V). Generator (IPEG™)[EB/OL]. http://www.innowattech.co.il/index.

aspx, 2008/2012
V=g33T3t (7)
[2] D Song, M Xiao. Piezoelectric Effects and Application[M]. Beijing:

Popular Science Press, 1987

6 Conclusions [3] H Zhao, J Yu, and J Ling. Finite Element Analysis of Cymbal

Piezoelectric Transducers for Harvesting Energy from Asphalt

a) For 1+2 type truck, the potential mechanical
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piles have excellent energy harvesting efficiency and Germany, 2002
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[6] A Dogan. Flextensional “Moonie and Cymbal” Actuators [D].
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are embedded in the pavement directly; Pennsylvania: The Pennsylvania State University, 1994

c) A prototype structure of pavement generator is [7] G H Haertling. Compositional Study of PLZT RAINBOW Ceramics for
designed. It is based on the PZT piles, and can magnify Piezo Actuators [C]. Proceedings of the Ninth International Symposium
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It is estimated that more than 50 kW energy can be
[8] K Mossi, G Selby, and R Bryant. Thin-Layer Composite Unimorph
harvested from one lane asphalt pavement;
Ferroelectric Driver and Sensor Properties[J]. Mater. Lett., 1998, 35:
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8-16 PZT piles are recommended for 0.04 m2 pavement [9] S J Roundy. Energy Scavenging for Wireless Sensor Nodes with a Focus
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Based on Piezoelectric Effects[J]. Journal of Shanghai Jiaotong

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