Sensors 2014, 14, 12497-12510; doi10.3390s140712497 s.docx

Sensors 2014, 14, 12497-12510; doi:10.3390/s140712497
sensors
ISSN 1424-8220
www.mdpi.com/journal/sensors
Article
A Shoe-Embedded Piezoelectric Energy Harvester for
Wearable Sensors
Jingjing Zhao 1,2,3 and Zheng You 1,2,3,*
1 Collaborative Innovation Center for Micro/Nano Fabrication,
Device and System,
Tsinghua University, Beijing 100084, China
2 State Key Laboratory of Precision Measurement Technology
and Instrument, Tsinghua University,
Beijing 100084, China
3 Department of Precision Instrument, Tsinghua University,
Beijing 100084, China;
E-Mail: [email protected]
* Author to whom correspondence should be addressed; E-Mail:
[email protected];
Tel./Fax: +86-10-6277-6000.

Received: 1 June 2014; in revised form: 28 June 2014 /
Accepted: 7 July 2014 /
Published: 11 July 2014
Abstract: Harvesting mechanical energy from human motion is
an attractive approach for
obtaining clean and sustainable electric energy to power
wearable sensors, which are
widely used for health monitoring, activity recognition, gait
analysis and so on. This paper
studies a piezoelectric energy harvester for the parasitic
mechanical energy in shoes
originated from human motion. The harvester is based on a
specially designed sandwich
structure with a thin thickness, which makes it readily
compatible with a shoe. Besides,
consideration is given to both high performance and excellent
durability. The harvester
provides an average output power of 1 mW during a walk at a
frequency of roughly 1 Hz.
Furthermore, a direct current (DC) power supply is built
through integrating the harvester
with a power management circuit. The DC power supply is
tested by driving a simulated

wireless transmitter, which can be activated once every 2–3
steps with an active period
lasting 5 ms and a mean power of 50 mW. This work
demonstrates the feasibility of
applying piezoelectric energy harvesters to power wearable
sensors.
Keywords: energy harvester; wearable sensors; power supply;
wearable energy harvester
OPEN ACCESS
Sensors 2014, 14 12498
1. Introduction
Wearable sensors are becoming smaller and increasingly widely
used, resulting in an increasing
need for independent and compact power supplies.
Electrochemical batteries, the most common power
supplies for wearable sensors, cannot meet the need because of
their limited energy storage capacity
and potential environmental and health risks, emerging as a
critical bottleneck for wearable sensors.

This has driven the development of wearable energy harvesters,
which harvest the mechanical energy
dissipated in human motion to provide renewable and clean
energy [1]. Several concepts of wearable
energy harvesters based on different mechanisms have been
studied, such as electromagnetic [2–5],
electrostatic [6], thermoelectric [7], nano-triboelectric [8] and
piezoelectric [9–13]. Piezoelectric
energy harvesters and nano-triboelectric generators can convert
mechanical energy into electric energy
directly, thus their structures are more compact and simpler in
comparison to those of other types. The
materials for nano-triboelectric generators are generally not
accessible in the market, hence this work
focuses on piezoelectric energy harvesters. Lead zirconate
titanate (PZT) and polyvinylidene difluoride
(PVDF) are the two most important piezoelectric materials for
energy harvesting, owing to their high
piezoelectric performance. PZT is rigid, brittle, and heavy,
bringing limitations in wearable
applications where flexibility is necessary. PVDF has
considerable flexibility, good stability, and is
easy to handle and shape [14]. Taking into account the human
motion characteristics of high amplitude

and low frequency, PVDF is more appropriate for wearable
applications than PZT. PVDF has been
used in wearable energy harvesters that are implemented in
shoes [15,16], bags [17,18], and
clothing [19–21]. Kymissis, et al. [16] developed an insole
made of eight-layer stacks of 28 μm PVDF
sheets with a central 2 mm flexible plastic substrate. It
harnessed the parasitic energy in shoes and the
average power reached 1.1 mW at 1 Hz. Granstrom, et al. [17]
utilized PVDF straps as backpack
shoulder straps to collect mechanical energy produced by the
backpack, with an average power of
45.6 mW during a walking of 0.9–1.3 m/s. Yang and Yun [21]
fabricated a PVDF shell structure
generating an output power of 0.87 mW at a folding angle of
80° and a folding-and-unfolding
frequency of 3.3 Hz, which could be worn on the elbow joint to
harvest energy from human motion.
The mechanical energy dissipated in shoes can even power a
computer, serving as an attractive
energy source for wearable harvesters [1]. This paper develops
a shoe-embedded piezoelectric energy
harvester, which can be integrated in a shoe readily for energy
harvesting from human locomotion with

little discomfort for the wearers. The harvester is based on a
specially designed sandwich structure,
resulting in a thin geometrical form, a high performance and an
excellent durability. Two harvester
prototypes are made and tested. The first one is made up of a
multilayer PVDF film and a structure of
engineering plastics, which is placed under the heel. The second
one is designed as an insole shape and
used as a normal insole, consisting of a structure of flexible
silicone rubber and two multilayer PVDF
films. More power can be generated by the former prototype,
while the other one has an advantage of
remarkable comfort. In order to store the harvested energy and
provide a constant DC output voltage, a
power management circuit is designed. A series of experiments
are performed to characterize the
harvester prototypes, proving that the harvester can serve as a
wearable power supply for low power
wearable sensors and potentially provide a valuable alternative
to the use of batteries.
Sensors 2014, 14 12499

2. Harvester Design
The main structure of the harvester is a sandwich structure,
where a multilayer PVDF film is
sandwiched between two wavy surfaces of a movable upper
plate and a lower plate, as shown in
Figure 1a. The multilayer PVDF film (Figure 1b) is fixed on the
lower plate, and composed of several
PVDF layers which are wired in parallel for a high output
current. When the upper plate is subject to a
compressive force produced by foot, the upper plate moves
down and the PVDF film is stretched along
1-axis simultaneously, as presented in Figure 1c. This leads to a
piezoelectric field created inside every
PVDF layer, driving the free electrons in the external circuit to
accumulate on the upper and lower
3-axis surfaces (electrodes) of every PVDF layer to screen the
piezo-potential. When the force is lifted,
the upper plate moves up and the PVDF film is relaxed,
therefore the piezo-potential diminishes,
resulting in releasing the accumulated electrons. A dynamic
force Ffoot applied by foot on the upper
plate drives the electrons in the external circuit to flow back
and forth with an alternating current (AC)

output. The sandwich structure is characterized by the inner
wavy surfaces, where arc-shaped grooves
and arc-shaped ribs exist. The specially designed surfaces
enable the PVDF film to generate a large
longitudinal deformation and reduce the harvester thickness,
which enhances the harvesting
performance and makes it possible to integrate the harvester
into a shoe whose inner space is limited.
The design parameters are defined in Table 1 and presented in
Figure 1d.
Figure 1. (a) The sandwich structure of the harvester; (b) The
multilayer PVDF film;
(c) The force applied by foot drive the upper plate to move up
and down circularly; (d) The
design parameters.
(a) (b)
(c) (d)
An optimization method is utilized to design the harvester, and
the objective function, constraint
conditions and value ranges of parameters will be established.
When the upper plate moves down to
the lowest position, both the tension of the multilayer PVDF
film F1 and the resistive force F3 against

the upper plate produced by the PVDF film reach maximum.
The tension F1 can be expressed by:
Sensors 2014, 14 12500
sin sin i
NT
s
I
n
L L
l L l l l L l l
(3)
where σ1 is the normal stress, ε1 is the normal strain. For
simplicity of description, the frictions

between the PVDF film and the two wavy surfaces are ignored,
and the resistive force F3 (Figure 2)
can be given in Equation (4).
Nwhl
F l L F l L F Y
L
Table 1. Design parameters.
Parameter Name Descriptions
l PVDF layer length (along 1-axis)
w PVDF layer width (along 2-axis)
h PVDF layer thickness
A1 (= wh) Cross-sectional area of one PVDF layer
A3 (= wl) 3-axis surface area of one PVDF layer
N The number of PVDF layers
L Chord length of an arc-shaped groove/ rib
2α Intersection angle of an arc-shaped groove/rib
n (=INT(l/L)) Number of arc-shaped grooves/ribs
Figure 2. The resistive force F3 against the upper plate is
produced by the PVDF film.
The quantity of charges produced by the PVDF film during the

period that the upper plate moves
down to the lowest position is equal to the quantity of charges
generated during the period that the
upper plate moves up to the initial position. According to the
piezoelectric effect, the charge quantity
|Q| is written below, and d31 is the piezoelectric constant:
31 1 1 31 3 1
sin
l
Q N d A d NA Y
h
(5)
|Q| is the key parameter to describe the energy harvesting
performance of the piezoelectric
harvester, and the larger |Q| the better. Hence, Equation (5) is
the objective function for the design
optimization. In Equations (3)–(5), INT(l/L) is approximated as
l/L, leading to the approximate

expressions of ε1, F3, and |Q|. At the cost of accuracy, these
expressions reduce calculation cost and are
Sensors 2014, 14 12501
deemed sufficient for the harvester design where high precision
is not required. In order to improve the
durability of the multilayer PVDF film, the wavy surfaces must
be carefully designed to keep the
PVDF film from experiencing plastic deformation. Moreover,
another two factors need taking into
account when designing the harvester. The first is that the
resistive force F3 should be lower than the
driving force Ffoot. The second is that the harvester thickness
should be less than a set value Tm for a
thin geometrical form of the harvester. Therefore, the constraint
conditions for the design are presented
in the equation below:
1
3
1

sin
2 sin
1- cos
2 tan
2 sin 2
e
foot
S m
Nwhl
F Y F
L
L
T Nh Nh L T

(6)
where εe is the elastic limit of the PVDF film, TS is the sum of
the thicknesses of the multilayer PVDF
film and a groove and a rib. The value ranges of the above
design parameters can be determined by the
application requirements of a specific design.
3. Fabrication
Two prototypes of the harvester are fabricated for two different
purposes. Prototype 1 is made up of
a multilayer PVDF film and a structure of rigid engineering
plastics, for a high output power.
Prototype 2 is designed as an insole shape, consisting of a
structure of flexible silicone rubber and two
multilayer PVDF films, with an advantage of excellent comfort.
The multilayer PVDF film is composed of
a stack of several PVDF layers connected in parallel. The
properties of the PVDF layers are listed in

Table 2. In order to provide a DC source for electronics, a
power management circuit is utilized.
Table 2. Properties of the PVDF layer.
Material Property Symbol Value
Relative permittivity εr 9.5 ± 1
Piezoelectric constant d31 17 × 10
−12 C/N
Elastic modulus Y 2500 MPa
PVDF layer thickness h 30 μm
Yield strength σs 45~55 MPa
3.1. Fabrication of Prototype 1
Prototype 1 is designed to exploit the high pressure exerted in
heel strikes. The schematic of
Prototype 1 is shown in Figure 3a. The upper plate and the
lower plate are made of engineering plastics
whose stiffness is far greater than that of the PVDF film. The
multilayer PVDF film is bolted to the
lower plate, as presented in Figure 3b. According to Table 2,
the elastic region of the PVDF layer is
about 0%–2%. Hence, the normal strain ε1 should be no more
than 2%. The dynamic foot pressure
distribution is studied in reference [22], showing that the peak
force of a heel strike is about 400 N.

Sensors 2014, 14 12502
Thus the resistive force F3 is better no more than 400 N. The
total thicknesses TS is set to not exceed 3 mm.
Equation (6) indicates that α reaches the maximum value of
19.7° when ε1 equals to 2%. The value
ranges of N, L and α are defined in Equation (7). Besides, the
PVDF film length l is 80 mm and the
width w is 50 mm for a normal heel size. The harvester is
designed by using optimization method. In
conjunction with Matlab built-in optimization routines, several
solutions are obtained. Among them, it
is found that the solution of L = 10 mm, N = 8 as well as α =
19.7° is the optimal solution, which is
selected for Prototype 1:
1 8
15 20
5 mm 20 mm
N
L

(7)
Figure 3. (a) The schematic of Prototype 1; (b) Prototype 1
without the movable upper plate.
(a) (b)
3.2. Fabrication of Prototype 2
Prototype 2 is designed as an insole shape, as illustrated in
Figure 4a, which can be divided into
three parts. Part 1 and Part 2 are the sandwich structures for
harvesting energy with two 8-layer PVDF
films. Similar to the rigid energy harvester, Part 1 is applied to
harness the energy from heel strikes.
Part 2 is used to tap the energy dissipated in bending of the
shoe. Part 3 is under foot arch where foot
pressure is low, which is a chamber offering vacant space to
accommodate circuits and energy storage
devices. The upper plate and the lower plate are made of
silicone rubber (by injecting modeling

process) whose stiffness is far less than that of the engineering
plastics used in Prototype 1. Therefore,
the practical PVDF film deformation is lower than the
theoretical maximum value calculated by
Equation (3). In order to reduce this adverse influence caused
by the flexible material, the angle α is
increased to 27.7°, resulting in a theoretical maximum normal
strain ε1 of 4%. The chord length L is
assigned 10 mm. The upper plate, the lower plate and two
multilayer PVDF films are fixed together by
bolts, and the finished Prototype 2 is shown in Figure 4b.
Sensors 2014, 14 12503
Figure 4. (a) The schematic of flexible energy harvester; (b)
The finished Prototype 2.
(a) (b)
3.3. Power Circuit
The PVDF film generates AC power with high voltage and low
current, which cannot meet the need
of commercial electronics that are practically driven by a
uniform DC power. Furthermore, if wearable

sensors are not in operation, the harvested energy needs storing
in a storage device. Based on the above
the two considerations, a power management circuit is designed,
as diagrammed in Figure 5, mainly
consisting of two full bridge rectifiers, a buck converter, two
button batteries (optional) and some
capacitors. The buck converter and one rectifier are contained
in the chip LTC 3588-1. Two rectifiers
can simultaneously rectify two AC currents of different phases
respectively, which is useful for
Prototype 2. The harvested energy accumulates on the input
capacitor Cin, and then transferred by the
buck converter to the output capacitor Cout. The target value of
the output voltage Vout (the voltage
across output capacitor Cout) is set to 3.6 V. When Vout
reaches the target value, a logic high is
produced on the PGOOG pin. If the load shuts off or the input
power is more than the output power,
there exists unused energy, which will be stored in the batteries.
On the contrary, if the harvester
cannot generate enough power to meet the load demand, the
batteries will be discharged to offer
supplemental power.

Figure 5. Schematic and physical photograph of the power
management circuit.
Sensors 2014, 14 12504
4. Experiments and Results
Prototype 1 and Prototype 2 were implemented in shoes to
harness the parasitic energy during
walking, as shown in Figure 6. A series of experiments were
carried out to evaluate the performance of
the prototypes. In the first experiment, the prototype was
terminated with a matched resistor(s), hence
yielded maximum power transfer. In the second experiment, the
quantities of the charge produced by
the prototypes during one step (QS) were measured. In the third
and fourth experiment, the prototypes
were connected with the power management circuit (without
using batteries) to form DC power supply
systems. The start-up time of the systems were measured.
Besides, the power supply systems were
tested to power a simulated transmitter load.

Figure 6. (a) Prototype 1 with an 8-layer PVDF film was
mounted on the inner sole and
gathered energy under the heel; (b) Prototype 2 with two 8-layer
PVDF films was used as a
normal insole in a shoe.
(a) (b)
4.1. Performance of Prototype 1
Prototype 1 with an 8-layer PVDF film (the capacitance of the
PVDF film was 126 nF) was
mounted on the inner sole and harnessed energy under the heel.
Firstly, Prototype 1 was tested during a
brisk walk at roughly 1 Hz [23], and terminated with a 1.268
MΩ resistor. Figure 7 shows the voltages
across the resistor and the resulting power delivered to the
resistor. The peak-to-peak values of the
voltage were about 136 V. The peak power was roughly 4 mW,
and the mean power was much lower
with a value of about 1 mW, meaning that the average net
energy transfer was about 1 mJ per step. It
demonstrates that the harvester is an attractive alternative for
powering some low wearable sensors,
such as activity trackers, blood pressure sensors, and sensors
for healthcare [24].

Secondly, QS was measured by using an energy storage circuit
shown in Figure 8. During one step [25],
the increment of the voltage on the storage capacitor CS was
ΔUS. About 30 μC charge was produced per
step. If two button batteries (GMB301009 for example) with a
capacity of 2 × 8 mAh are charged by
Prototype 1, as shown in Figure 5, they can completely charge
from empty in 1.92 million steps (about 200
days with 10,000 steps per day, 2 × 8 mA × 3600 s ÷ 30 μC/step
= 1,920,000 steps ≈ 10,000 step/day ×
200 day). Although it is not an optimal way to charge batteries,
the battery lifetime can be prolonged
owing to the harvester.
Sensors 2014, 14 12505
Figure 7. The voltage across the resistor load and the resulting
power delivered to the resistor.
Figure 8. The voltage across the storage capacitor CS.
Thirdly, the start-up time of DC power supply system,
consisting of Prototype 1 and the power

management circuit, was measured. Figure 9 shows two
measured voltages on Cin and Cout. The
voltage on Cin increased during every step, and when it
surpassed the threshold of about 4.8 V, the
energy would be transferred to Cout. Meanwhile, Cin
discharged and its voltage declined rapidly with an
increment of the voltage on Cout. It indicates that after 13 steps
the voltages across Cout (the output
voltage Vout) reached the set value 3.6 V. Hence, the setup time
of the system was about 13 s during a
walk of 1 Hz, which was not a long waiting time for wearers.
Sensors 2014, 14 12506
Figure 9. The two measured voltages across Cin and Cout, and
after 13 steps the output
voltage reached the set value 3.6 V.
Figure 10. Performance of the power supply system.
Fourthly, the complete DC power supply system was tested by
powering a simulated wireless

transmitter [26], as shown in Figure 10. The simulated load was
modeled as a 180 Ω resistor load Rload
which was controllable by pulse-width modulated (PWM) signal
with a duty cycle of 0.5% and a
frequency of 1 Hz. When the output voltage of the power supply
system was ready (PGOOD at logic
high), the supply rails to the simulated load was activated and
energy was consumed. Prototype 1 was
driven at roughly 2 Hz. Figure 10 shows the representative
signals from the complete power supply
system when powering the simulated load. The red trace is the
output voltage Vout and the black trace
is the voltage across the resistor load (VR-load). The simulated
transmitter load was activated once every
Sensors 2014, 14 12507
2–3 steps. Because the load dissipated power faster than the
harvester generated power, Vout and VR-load fell
when the simulated load was active. During the active period of
5 ms, VR-load declined from 3.4 V to
2.7 V, and the calculated values of the mean load power and the
mean load current were 50 mW and

16 mA respectively. The power output could certainly be used
to power some low-power wireless
transmitters, such as transmitters based on Bluetooth Low
Energy (BLE) or ANT+.
4.2. Performance of Prototype 2
The insole-shaped Prototype 2 with two 8-layer PVDF films was
placed in a shoe, and tested during
a walk at about 1 Hz. The capacitances of the PVDF film placed
under forefoot and the PVDF film
placed under heel were 250 nF and 110 nF respectively. The
four experiments executed above were
also done for Prototype 2.
Figure 11. The voltages across RH and RF as well as the
resulting power delivered to
the resistors.
In the first experiment, the forefoot-placed PVDF film was
connected with a 660 kΩ resistor RF,
and the heel-placed PVDF film was terminated with a 1.682 MΩ
resistor RH. The voltages across the
resistors and the powers were presented in Figure 11.
Obviously, the two output voltages had different
phases. The heel-placed PVDF film produced peak-to-peak

voltages of roughly 30 V, while the
forefoot-placed PVDF film gave lower response with peak-to-
peak values approaching 22 V. The
mean powers were 30 μW for the heel-placed PVDF film and 90
μW for the forefoot-placed PVDF
film. In total, about 0.12 mJ per step could be supplied, which
was significantly lower than the energy
of 1 mJ per step provided by Prototype 1. That was because the
PVDF film deformations in Prototype 2
was smaller than those in Prototype 1. In the second
experiment, about 5 μC charges could be
generated by the heel-placed PVDF film during one step, and 11
μC for the forefoot-placed PVDF
film, as shown in Figure 12. In the third experiment, the two
PVDF films were wired with the two
rectifiers of the power management circuit respectively, and the
harvester served as a DC power
Sensors 2014, 14 12508
supply system. The output voltage reached the set value 3.6 V
after 25 steps. In the fourth experiment,
the power supply system could activate the simulated load once

every 6–8 steps. In conclusion, Prototype 2
offers more comfort for users compared to Prototype 1, at a cost
of generating performance.
Figure 12. The voltages across the storage capacitors of 25 μF,
the red trace for the
forefoot-placed PVDF film, the black trace for the heel-placed
PVDF film.
5. Discussion
Compared with other reported shoe-embedded PVDF energy
harvesters, the harvester proposed
here has advantages of a thin geometrical form, high
performance and an excellent durability,
benefitting from its specially designed sandwich structure. The
deformation of the multilayer PVDF
film is kept elastic and the maximum deformation is close to
PVDF elastic limit, thus there is a tradeoff
between performance and durability. The average power of the
harvester is up to 1 mW (at 1 Hz), which
approximates the power of 1.1 mW (at 1 Hz) of the PVDF insole
in reference [15]. While more
comfort and durability can be provided by our design. By
combining the merits of Prototype 1 and
Prototype 2, a better harvester can be developed in the future

work. The arc-shaped grooves and ribs
on the wavy surfaces will be made of some harder material,
polyurethane for example, to improve the
PVDF film deformation for more energy produced, and the other
parts of the plates are made of
flexible material to keep users comfortable. In addition,
increasing the number of PVDF layers serves
as another approach to improving generating performance.
6. Conclusions
A shoe-embedded piezoelectric energy harvester is developed in
this paper, and it can be integrated
in a shoe readily for energy harvesting from human locomotion.
Two prototypes with different
characteristics are fabricated and tested. One prototype
produces more energy, while the other one is
more comfortable without creating any inconvenience or
discomfort for wearers. The DC power
Sensors 2014, 14 12509
supply system, including the harvester and a power management
circuit, is used to collect the

mechanical energy dissipated in shoes and power some low-
power wearable sensors, such as activity
trackers. Even though the harvester is unlikely to replace
completely the batteries in all wearable
sensors, it is a significant role in reducing the problems related
to the use of batteries. The work
presents a successful attempt in harnessing the parasitic energy
expended during person’s everyday
actions to produce power for wearable sensors.
Author Contributions
The paper was completed in collaboration between the two
authors. Zheng You proposed the
research theme and idea. Jingjing Zhao completed the design,
fabrication, and characterization of the
harvesters. Both authors have read and approved the final
manuscript.
Conflicts of Interest
The authors declare no conflict of interest.
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harvesting for bio-MEMS applications.
In Proceedings of the SPIE’s 8th Annual International
Symposium on Smart Structures and Materials,
International Society for Optics and Photonics. Newport Beach,
CA, USA, 4–8 March 2001;
pp. 429–438.
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wearable energy harvesters for
effective power generation at low-frequency movement. Sens.
Actuators A Phys. 2012, 188, 427–433.
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undergraduates jog. J. Clin. Rehabil. Tissue

Eng. Res. 2009, 13, 9109–9112.
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human soleus H reflex during walking
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871 | P a g e
MOBILE PHONE CHARGING USING WALKING
MOVEMENT
Prof. S. S.Bhandare
1
, Mr. Akshay J.Bavkar
2
, Mr. Shankar R.Chavan
3
,
Ms. Sukhada S. Parab
4
, Mr. Mayur P.Sawant
5
1
Asst.Prof.
2,3,4,5
UG Student , Electronics & Telecommunication Engineering
Department ,
RMCET, (India)

ABSTRACT
In today’s hectic lifestyle, health has been seriously hampered
due to sedentary work. Our project represents an
idea of walking based wearable piezoelectric device that
provides an alternate means for powering mobile
phone batteries. Since, the mechanism of the device is based on
walking; the device promotes human
metabolism as well as physical fitness. Hence, it can be seen as
an e-health gadget that encourages walking
exercise as a means to charge mobile phone batteries. Walking
is the best and common activity in day to day
life. As per the study of biomechanics, we came to realize that
ground reaction force (GRF) exerted from the
foot, when converted into voltage gives enough power supply to
run a device. While walking the person loses
some energy from foot in the form of vibrations which are
sensed and converted into electric form. Piezoelectric
crystal does the work of generating output out of foot moment.
Piezoelectric materials have the capability of
absorbing mechanical energy from surroundings, especially
vibrations and transform it into electric energy that
can be used as power supply in real time to other appliances
like mobile phones, power banks, various small
handy biomedical instruments etc.

Keywords: Piezoelectric disc, Energy harvesting, DC
conversion circuit, Alternate energy source.
I. INTRODUCTION
The busy lifestyle of today‟s world has made people neglect
their health. As people are working very hard, and
have a sedentary lifestyle, they are falling prey to many health
and coronary problems. Researchers have shown
that walking is one of the most important and health enhancing
exercise. Development of technology has made
us lazier and physically unfit. Here we propose a walking based
mobile phone charging device that enhances
physical exercise from the user and also provide for alternate
source of energy. Also, mobile phones have
become an integral part of one‟s life. Charging mobile phone is
a time consuming process. It requires user
constraints in charging mobile phones. The increase in energy
consumption in mobile phones is in alarming rate.
A problem arises when such an enormous use of mobile phones
is not completely supported by their fast
discharging batteries. Charging mobile phone requires user
attention, it requires appropriate socket and electrical

connectivity. Particularly for tourists, mountaineers and
villages, it provides specific constraints in charging
mobile phones. These difficulties are encountered in charging
mobile phone from time to time.
872 | P a g e
II. LITERATURE SURVEY
International journal of Innovation Research in Science,
Engineering and Technology, “Real Time Battery
Charging System by Human Walking”,2 Feb 2015.Piezoelectric
Disc is used which converts vibrations of feet
into electrical signals. Signal is in AC which is converted into
DC and then boosted by using DC to DC boost
convertor. For storing the electrical signal, „Lithium Batteries‟
are used.
III. PRINCIPLE
The basic principle involved is the conversion of human
mechanical power into electrical signals. This
mechanical power comes from human walk. Now, this
mechanical energy in terms of vibrations is fed to the

piezoelectric disc that transforms these vibrations into useful
electric power. This output of the transducer is
rectified and regulated to a value sufficient enough to charge a
mobile phone battery. The input energy is purely
a mechanical one that comes from user‟s motion and gets
converted into the required signals via piezoelectric
harvesting system. The charging time of the mobile phone
depend on the frequency and amplitude of vibration
provided to the transducer. So, if the speed of user‟s motion is
increased the output of the device can be
enhanced. For measuring this output we have develop an
Android app which gives information about the input
of solar and piezoelectric transducer and the output of battery.
IV. DESIGN
The circuit of the device mainly consist of a piezoelectric
harvesting system, Solar cell , regulating IC. A
apacitor (1000 uF) is used to store the electric charge so that
when the person is not in motion the power is
continually supplied. The piezoelectric disc is equipped in the
interface between the bottom and upper part of
the sole. The whole circuit is made on a small chip and is fitted
at the back part of the shoe. Different connectors

for charging mobile phone batteries can be taken out from the
shoe. A switch is also provided in the circuit for
the user to decide whether he wants to charge his mobile phone.
V. BLOCK DIAGRAM
Fig. Block diagram
5.1 Piezoelectric disc:-
Piezoelectric disc is a transducer which converts the vibrational
pressure into electricity.
873 | P a g e
We have connected three piezoelectric discs in parallel. Each
generates an output of maximum 8-9V.
Fig. Piezoelectric disc
5.2 Solar Panel:-
A Solar panel turns the suns light into electricity. One solar
panel consists of many small solar cells. Each of
these solar cells uses light to make electrons move which
generates electricity.

In our Project we are using three solar panel of 4v and 100mA
current which are connected in parallel with the
piezoelectric disc. We get a total output of 4V and 300mA
current which is sufficient to charge a battery of 4V.
The Coin is given only to compare the size of solar panel.
Fig. Solar Panel
5.3 Battery:
For storing the charge, we are using a Lead Acid Rechargeable
DC Battery of 4V 1A. It is a maintenance free
sealed battery used as a Power bank in our project.
Fig. Storage Device
5.4 Bluetooth Module:
HC-05 module is an easy to use Bluetooth SPP (Serial Port
Protocol) module, designed for transparent wireless
serial connection setup.
874 | P a g e
Serial port Bluetooth module is fully qualified Bluetooth

V2.0+EDR (Enhanced Data Rate) 3Mbps Modulation
with complete 2.4GHz radio transceiver and baseband. It uses
CSR Bluecore 04-External single chip Bluetooth
system with CMOS technology and with AFH(Adaptive
Frequency Hopping Feature). It has the footprint as
small as 12.7mmx27mm. Hope it will simplify your overall
design/development cycle.
Fig. Bluetooth Module
5.5 ATmega 328 microcontroller:-
TheATmega48A/48PA/88A/88PA/168A/168PA/328/328P is a
low-power CMOS 8-bit microcontroller
based on the AVR enhanced RISC architecture. By executing
powerful instructions in a single clock cycle, the
ATmega48A/48PA/88A/88PA/168A/168PA/328/328P achieves
throughputs approaching 1 MIPS per MHz
allowing the system designed to optimize power consumption
versus processing speed.
We are using Pin no. 23 ADC0 as Input of Battery and Pin no.
24 ADC1 as input of solar and piezoelectric
transducer and RXD and TXD, Pin no.2 and 3 for serial
communication with Bluetooth Module.

Fig. Pin Diagram of Atmega328
5.6 DC to DC converter:-
The output from the battery is further feed to DC to DC booster
which functions as Step-up booster. If the
voltage level is above 1.5V which is its threshold level, it will
give a constant output of 5V which is given
through the USB port to the Mobile Phone.
875 | P a g e
Fig. DC Step-Up Boost Module with USB Port
VI.COMPONENT LIST
Components Specifications
Piezoelectric metal type disc 10hz
Solar Panel 4V 100mA
Atmega328 8-bit microcontroller
Storage Unit Lead Acid Battery (4V)
Diode(1n4148) 0.4V

Crystal oscillator 16Mhz
Capacitor 22uf
Resistor 100k
Led 5V
Bluetooth Module HC-05
DC Step-up boost module with USB Port 5V 600mA
VII. PROJECT PROTOTYP
VIII. REAL TIME APPLICATION
1. Mobile Phones
2. Electronic Torch
876 | P a g e
3. Cell Charger
IX. ADVANTAGES
1. Can be used anywhere.

2. Portable charging.
3. No side effect on Human Body.
4. Can be used in different shoe.
5. Gives the power supply in real time.
6. The extra power generated can be stored and used for further
purpose.
X. CONCLUSION
When we connect the piezoelectric disc in parallel instead of
series for better results, we obtain more current
instead of voltage which is desirable for charging the battery. ,
Thus in all we conclude that with this process,
we can extract the energy from the human feet, convert it into
electric energy and use it in real time application
of charging the devices.
XI. RESULT
The output of piezoelectric disc is up to 8-9V and that of solar
is 4V and 100mA. The input given to the
battery is up to 3.8V using solar and piezoelectric disc. By
using piezoelectric disc the time required to charge
1000mAh battery is 2 hours while walking and same while

running is 1.40 hours. By using Piezoelectric and
solar together time required is 1.30 hrs.
XI.ACKNOWLEDGMENTS
We have opportunity to say thank to all who have helped us
directly or indirectly to make the project successful
which is “MOBILE PHONE CHARGING USING WALKING
MOVEMENT”.
Many guides have contributed to the successful completion of
the project. We would like to place on record my
grateful thanks to each one of them who help me in this project.
We would like to thank our parents & friends for giving us full
feedback when we were in trouble. We are
sincerely thankful to Prof S.S.Bhandare (Internal Guide) and
the whole staff of EXTC department of
„Rajendra Mane College of Engineering and Technology‟ ,
their extensive help and for providing valuable
information, suggestions, and inputs at various stages of work.
They helped us to understand the whole project
and conceptualized the idea of the project.
REFERENCES

[1] Harsh pandey, Ishan khan, Arpan gupta Department of
Mechanical Engineering Graphic Era University
Dehradun, India, “Walking based wearable mobile phone
charger and lightening system”,2014.
[2] International journal of Innovation Research in Science,
Engineering and Technology, "Real Time Battery
Charging System by Human Walking”,2 Feb 2015.
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Walking based wearable mobile phone charger
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DOI: 10.13140/2.1.5058.6409
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Walking based wearable mobile phone charger and
lightening system
Harsh pandey, Ishan khan, Arpan gupta
Department of Mechanical Engineering
Graphic Era University
Dehradun, India
[email protected], [email protected], [email protected]
Abstract — In today’s hectic lifestyle, health has been

seriously hampered due to sedentary work. This paper
represents
an idea of walking based wearable piezoelectric device that
provides an alternate means for powering mobile phone
batteries. Moreover, it simultaneously serves another purpose of
providing an emergency torch. Since, the mechanism of the
device is based on walking; the device promotes human
metabolism as well as physical fitness. Hence, it can be seen as
an
e-health gadget that encourages walking exercise as a means to
power emergency torch and mobile phone batteries. The
portable
device comprises of a piezoelectric power generator, connectors
for charging different mobile phone batteries and a Light
Emitting Diode (LED) embedded in shoe for providing
emergency torch. Piezoelectric circuit harvests energy from
user’s trotter movement. This energy is amplified, rectified by
using a DC convertor and then regulated to 4.2 volts which is
required by a Li ion mobile battery. By using this device, a man
weighing 60 Kg can charge a 800mAh capacity battery in 2.6
hours by normal walking.
Keywords—piezoelectric disc; LED, energy harvesting, DC
conversion circuit, alternate energy source.
I. INTRODUCTION
The busy lifestyle of today’s world has made people
neglect their health. As people are working very hard, and
have a sedentary lifestyle, they are falling prey to many health
and coronary problems[1]. Numerous diseases such as back
ache, indigestion, head ace, obesity, high blood pressure etc.,
are consequence of lack of physical exercise in the body [2].
Researchers have shown that walking is one of the most
important and health enhancing exercise [3]. Development of
technology has made us lazier and physically unfit. Here we

propose a walking based mobile phone charging device that
enhances physical exercise from the user and also provide for
alternate source of energy.
Also, mobile phones have become an integral part of one’s
life. Charging mobile phone is a time consuming process. It
requires user attention, appropriate socket (country specific)
and electrical connectivity which are some constraints in
charging mobile phones. The increase in energy consumption
in mobile phones is in alarming rate. A recent study at the
“Global conference Wikimedia 2014 London” says out of 100
citizens in the world 97 are the mobile phone users[4]. A
problem arises when such an enormous use of mobile phones
is not completely supported by their fast discharging batteries.
Charging mobile phone requires user attention, it requires
appropriate socket and electrical connectivity. Particularly for
tourists, mountaineers and villages, it provides specific
constraints in charging mobile phones. These difficulties are
encountered in charging mobile phone from time to time.
In recent years, a lot of alternate means have been
proposed to provide emergency power for charging mobile
phones. The means with renewable and sustainable features
has attracted as increasing interest in last few years. One such
means is the extraction of human power using piezoelectric
harvester. In past years, many human powered generator and
human powered harvesting system has been proposed [5][6].
Harvesting kinetic energy is promising because of abundant
motion and vibration in the ankle which produces moderate
power. Solar power extraction is a useful and efficient
technique but it is a dependent source. In recent years, lot have
research have been made for generating power from
vibrational energy [7]. A Li-ion battery which is discharged to
3.2 volt can be charged up to 3.6 volt through 2 hours when a

human whose weight is 60 kg walk with the speed of 23
steps/sec [8]. Though, the speed is difficult to achieve during
walking. Alternate power has also been achieved using
thermal gradients, internal lightning and radio frequency
waves [9]. But the power available by these methods is lower
than their kinetic counter parts. Also using piezoelectric
polymer transducer energy is harvested from human walk
without affecting user’s gate. The obtained energy is rectified
with 65% efficiency and regulated to 4V [10]. But, it serves
only a single purpose of charging mobile phone with a lesser
efficiency. Also in some past work, miniaturized mobile
electronic system such as biomedical drug delivery implants
[11], acceleration and pressure monitoring sensors
[12],[13]have been suggested. But they have short operational
lives due to the deficiency of storage space.
This utility model comprises of a piezoelectric transducer,
amplification and rectification circuit, light emitting diode
(LED) and connectors. A switch is provided to operate the
emergency torch. The user can easily charge their mobile
2014 International Conference on Medical Imaging, m-Health
and Emerging Communication Systems (MedCom)
978-1-4799-5097-3/14/$31.00 ©2014 IEEE 407
https://www.researchgate.net/publication/9609409_The_Relatio
nship_of_Reported_Coronary_Heart_Disease_Mortality_to_Phy
sical_Activity_of_Work?el=1_x_8&enrichId=rgreq-
dbac0a80714a73ce7c7979ba7d2e1244-
xOTY2MTk1OTgzNDAxMDZAMTQyMzg4OTE3MzQ1MA==
https://www.researchgate.net/publication/222513144_A_Study_
of_Low_Level_Vibrations_as_a_Power_Source_for_Wireless_S
ensor_Nodes?el=1_x_8&enrichId=rgreq-
dbac0a80714a73ce7c7979ba7d2e1244-

phone by normal walking. Moreover, he can use it as an
emergency torch by simply pressing the switch provided in his
shoe. According to the study made in this paper, a man
weighing 60 Kg can charge 800mAh capacity battery in 2.6
hours by normal walking. Further, the charging time can be
reduced to 1.8 hours in running at the rate of 10 – 12 Km per
hour.
II. DESIGN AND DEVELOPMENT OF DUAL WORKING
GADGET
A. Principle
The basic principle involved is the conversion of human
mechanical power into electrical signals. This mechanical
power comes from human walk. Now , this mechanical energy
in terms of vibrations is fed to the piezoelectric disc (Fig. 1)
that transforms these vibrations into useful electric power.
This output of the transducer is amplified, rectified and
regulated to a value sufficient enough to charge a mobile
phone battery and provide emergency light. The input energy
is purely a mechanical one that comes from user’s motion and
gets converted into the required signals via piezoelectric
harvesting system. The charging time of the mobile phone and
the intensity of torch light depend on the frequency and
amplitude of vibration provided to the transducer. So, if the
speed of user’s motion is increased the output of the device
can be enhanced.
Figure 1 Piezoelectric disc.

B. Design
The circuit of the device mainly consist of a piezoelectric
harvesting system, Darlington transistor (Fig. 2), an amplifier
(dual op-amp) (Fig. 3), rectifier circuit (Fig. 4), regulating IC,
LED and a switch. A capacitor (1000 F) is used to store the
electric charge so that when the person is not in motion the
power is continually supplied. The piezoelectric disc is
equipped in the interface between the bottom and upper part of
the sole. LED is fitted at the front part of the shoe which
behaves as an emergency torch. The whole circuit is made on
a small chip and is fitted at the back part of the shoe. Different
connectors for charging mobile phone batteries can be taken
out from the shoe. A switch is also provided in the circuit for
the user to decide whether he wants to charge his mobile
phone or to operate the emergency light.
Figure 2 Darlington transistor
Figure 3 Voltage amplification circuit.
Figure 4 Rectification circuit.
C. Working
The working of the gadget is totally based on human
power. As a person walks, mechanical stresses are induced in
his feet which are transmitted to the piezoelectric disc which is
embedded in the shoe. This vibrational energy is converted
into electrical energy by the transducer. The output of the

transducer is fed into the harvesting circuit that consists of
three main parts namely, voltage amplification, rectification
(DC conversion), and current amplification. In normal walking
condition for a 60 Kg man the disc produces a voltage of
1.5V-2V. This voltage is amplified up to 10V by using a
suitable resistance arrangement of 8 and 2 . By using this
arrangement, a voltage gain of 5 times can be achieved. The
output from the amplifier is now fed to the rectifier circuit for
converting it into DC signals in pure continuous form. After
the rectification, current can be amplified using the Darlington
transistor and lastly voltage is regulated to 4.2V by using a
regulating IC 7805. The output after regulation is sufficient
enough to charge the mobile phone and to power the small
electronic devices. The whole circuit arrangement is shown in
Fig. 5 below.
408
Figure 5 Mobile phone charging circuit.
III. EQUATIONS
The voltage produced by a single piezoelectric disc is
given by-
StPV ××= (1)
Where, P = pressure applied,

t = thickness of the disc,
S = rating of the piezoelectric material.
The voltage gain factor of the amplification circuit is based
on the choice of 2 resistances and is given by
1+=
i
f
R
R
Gain (2)
Where, Rf = resistance connected in parallel,
Ri = resistance connected in series.
IV. EXPERIMENT
The experiment is performed by giving actuation to the
piezoelectric disc as shown in Fig. 7, 8. The walking and
running conditions are modeled by different excitation to the
piezoelectric disc by different intuitive vibration excitation
given to the disc. An 800mAh capacity Li-ion battery is used
for the experiment. In the experiment, the percentage charging
of the battery is done for different intervals and the
corresponding time is recorded with the help of stopwatch. For
normal excitation it takes 2.6 hours to get fully charge the
battery. Further, for excitation at faster rate (high frequency)
the charging time gets reduced to 1.8 hours. The results for
charging mobile phone are shown in table below.

Table 1 Charging time for walking condition with normal
excitation.
Percentage charged (in
%)
Time taken (in minutes)
10-11 1.50
11-12 1.52
12-13 1.52
13-14 1.54
14-15 1.53
15-16 1.56
16-17 1.54
17-18 1.58
18-19 1.55
19-20 1.6
Figure 6 Figure showing comparison of charging time
using the designed device for excitation corresponding to
walking and running.
Table 2 Charging time for running condition with
excitation at high frequency.
Percentage charged (in
%)

Time taken (in minutes)
10-11 0.8
11-12 0.9
12-13 1.1
13-14 1
14-15 1.2
15-16 1.1
16-17 1.2
17-18 1.3
18-19 1
19-20 1.2
Table 3 Charging time for walking condition with normal
excitation for extended charging.
Percentage charged (in %) Time taken (in
minutes)
10-15 7.4
15-20 7.8
20-25 7.7
25-30 7.2
30-35 7.5
35-40 7.6
40-45 8.1
45-50 8.3
50-55 8.5
55-60 8.5
409

Table 4 Charging time for running condition with
excitation at high frequency for extended charging.
Percentage charged(in %) Time taken (in min)
10 - 15 4.9
15 - 20 5.1
20 - 25 5.2
25 - 30 5.2
30 - 35 5.5
35 - 40 5.4
40 - 45 5.5
45 - 50 5.6
50 - 55 5.4
55 - 60 5.7
When the gadget was used as an emergency torch by pressing
the switch, the LED was lighten up. It was observed, for
normal excitation of piezoelectric disc for 10 minutes, LED
glows for 10-12 minutes. At higher speed the LED glows for
15 -16 minutes.

V. RESULTS
The experiment performed over the designed gadget gives
the following results - when the excitation corresponds to a
person walking at normal speed of 3-4Km/hr the time taken by
the utility model to charge an 800mAh Li-ion battery was 2.6
hours. Moreover, at higher excitation corresponding to
running at 10-12 Km/hr the time taken by the same battery to
get charged was 1.8 hour. When the experiment was studied
for the function of emergency torch (LED), it was seen that in
normal walking for 10 minutes the torch was glown up to 10-
12 minutes. In the same way, when jogging was performed for
10 minutes, torch gave light for 15-16 minutes. So, the study
shows the intensity of torch light as well as the power for
battery both are directly proportional to the speed of the user.
Figure 7 Device powering the emergency torch.
Figure 8 Mobile shows charging.
VI. CONCLUSION
In this paper, a dual working piezoelectric based gadget is
developed and studied for the first time. The utility gadget
based on walking, experimentally evaluated and presented in
this paper gives a voltage sufficient to charge a Li-ion battery.
Moreover, the piezoelectric walking based gadget can perform
dual functions, one for powering the mobile phone battery and
other for providing an emergency torch. It was seen that when
the excitation vibration corresponding to a person walking at a
slow speed, the time taken by the gadget to charge the mobile

phone was higher. Further, when the data was recorded for his
running condition, the time taken to charge the mobile phone
got reduced tremendously. So, it is concluded that the
effectiveness of the device depends on user’s walking activity,
i.e. how well he is in performing his morning walk or jog.
Therefore, the device is indirectly proving to be an asset for
human health by encouraging a renowned fitness activity
termed as walking. This can be the most beneficial and healthy
input, an e-gadget can ever take making it a health promoting
device. Hence, people can easily charge their mobile phone
battery and use emergency torch daily by just walking more
and more.
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