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Sensors and Materials, Vol. 32, No. 7 (2020) 2539–2549
MYU Tokyo
S & M 2281

Harvesting Energy Using Triboelectric Nanogenerator
Mounted inside Rolling Tire
Hiroshi Tani,1* Mutsuki Sugimoto,2 Kazuhisa Fushihara,2 Yukio Nakano,2Renguo Lu,1 Shinji Koganezawa,1 and Norio Tagawa1
1

Mechanical Engineering Department, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680, Japan
2
Sumitomo Rubber Industries, Ltd., 2-1-1 Tsutsui-cho, Chuo-ku, Kobe, Hyogo 651-0072, Japan(Received February 10, 2020; accepted March 9, 2020)

Keywords: triboelectric nanogenerator, triboelectrification, tire, energy harvesting

In this study, we developed a triboelectric nanogenerator (TENG) for intelligent tires.
This TENG was attached on the inner surface of a racing cart tire. First, we evaluated thedependences of the TENG output on the environmental temperature and relative humidity toensure that the proposed TENG can operate in a wide range of these parameters. Then, we
packaged the TENGs in aluminum laminate film and mounted them on the inner side of thetire. The charged voltage and output voltage of the TENGs were evaluated on a moving belt.
The output voltage signals were observed at the region of contact; the signals increased withrotational speed and load weight but decreased with tire pressure. The charged voltage in the
10 μF capacitor was found to be approximately 14 V, which corresponds to 1.0 mJ at the speedof 16 km/h after the tire rotated for 15 min. These results suggest that the proposed TENG can
operate as an energy harvester for the temperature and pressure sensors built into intelligent
tires.

1.

Introduction

The tread of a vehicle tire is the only component that interacts with the road surface. It
dictates the motion of the vehicle and is an important factor in the stability and control of thevehicle. Intelligent tires with tire condition monitoring systems (TCMSs) that can monitor
parameters such as the coefficient of friction between tires and the road surface, vehicle speed,tire pressure, and tire load are being developed by various companies. Tire pressure monitoring
systems (TPMSs) have already been installed to observe tire pressure. In the future, TCMSs
mounted on tires will play an important role in adaptively adjusting the vehicle stability. Power
components are a significant part of the TCMS. Therefore, TCMSs require an energy harvesterthat can operate in severe tire environments, which are already significantly harsh because
their range of operating temperature and humidity is −40 to 130 °C(1) and 0–100% relative
humidity (RH), respectively. Moreover, the acceleration in an energy harvester is very large.
Additionally, the energy harvester should be lightweight to ensure rotational balance in the tires.
*

Corresponding author: e-mail: hrstani@kansai-u.ac.jp
https://doi.org/10.18494/SAM.2020.2827
ISSN 0914-4935 © MYU K.K.
https://myukk.org/

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Sensors and Materials, Vol. 32, No. 7 (2020)

Several studies have been conducted to develop energy harvesters for TCMSs. Several
researchers have focused on the development of piezoelectric energy harvesters for TCMSs.
Keck developed an energy harvester using piezoelectric materials to provide power to thesensors embedded in a tire.(2) Their energy-harvesting device could generate an average
power of 40 μW over a velocity range of 30–180 km/h.  Zheng et al. proposed a piezoelectricenergy-harvesting device that should be installed on the wheel upside down. This device
works in the compression mode.(3)   Their energy-harvesting device could scavenge 47 μW at
approximately 80 km/h.  Tang et al. developed an energy-harvesting device with piezoelectric
cantilevers excited by magnetic repulsive force.(4) This device was mounted on the rim inside
the tire cavity and effectively generated an average power of 10 μW.  Lee and Choi developed apiezoelectric energy harvester that generated 380.2 μJ per revolution under a load of 500 kgf at
a velocity of 60 km/h.(5) They fabricated a self-powered wireless sensor system for applicationand tested it during driving of a vehicle.   The harvester generated a power of 1.37 μW/mm3.
Singh et al. proposed a novel artificial neural-network-based closed-loop system capable of
ensuring broadband operations to optimize the harvester performance with changing dominanttire vibration frequencies.(6)Electromagnetic energy harvesters have been considered viable devices for the TCMSs.(7)Inertial electromagnetic and relative displacement electromagnetic transducers are the twodifferent types of electromagnetic energy-harvesting devices in tires.   Wang et al. proposedan energy harvester to harvest power from a rotating wheel.(8) Their fabricated harvester
includes two springs along with a coil, a magnet, and an electrical circuit. Their device could
generate a power of 30–4200 μW for a range of speed between 200 and 900 rpm.  Wang et al.
also developed an energy harvester using a well-weighted pendulum to harvest energy froma rotating wheel by the electromagnetic induction technique.(9) Their device could generate
several milliwatts, which is sufficient for operating sensors inside a tire.   Wang et al. thenproposed a similar design using a weighted pendulum-type electromagnetic harvester
attached to a rotating wheel.(10) Their energy harvester could generate an electrical power of
200–300 μW at approximately 200–400 rpm.
Mao et al. utilized single-electrode triboelectric nanogenerators (TENGs) using triboelectrification to scavenge the friction energy from rolling tires.(11) They systematicallyanalyzed the potential of TENGs in tires.  Their fabricated device could generate a maximum
instantaneous power xof 1.79 mW at a load resistance of 10 MΩ.   Qian et al. proposed amagnetic TENG mounted on the wheel hub of a tire for self-powered TPMS application. TheirTENG could deliver a maximal output voltage of 316 V and power of 22.3 mW at a rotation
speed of 100 rpm and load of 3 MΩ, thereby enabling the self-powered sensor to monitor
the tire pressure.(12) Guo et al. demonstrated an array of compressible hexagonal TENGs for
harvesting the mechanical energy from a rolling tire. A combination of 8 units of TENGs
yielded a maximum instantaneous power of 1.9 mW at a weight load of 10 N and speed of
2.51 m/s; additionally, it was found to be stable and durable after 30 continuous working days
and could power a wireless tire pressure sensor once every 14 min at a rolling speed of 2.51 m/s
and load weight of 10 N.(13)   Wu et al. developed a smart green-energy tire by introducing
silica fillers and TENGs into natural rubber tires. This green-energy tire could serve as a self-Sensors and Materials, Vol. 32, No. 7 (2020)

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powered sensor to monitor subtle changes in the pressure and road condition from the TENG
output signal.(14)In contrast, the TENG output is affected by the environmental humidity because thecharged static electricity in the contact surfaces of the TENG escapes into the air owing to theenvironmental humidity. Shen et al. studied humidity-resistant TENGs for high-performance
biomechanical energy harvesting.(15) They applied electrospun nanofibrous membranes in
the TENG to eliminate the adverse effects of water vapor on the electrical output. Mule et al.
proposed a pouch‐type TENG to significantly reduce the effect of RH.(16)Generally, the TENG is mounted in the closed space of tires. It is used in a wide rangeof temperatures. Additionally, the humidity in tires varies from 0 to 100% RH. Thus, wedeveloped a TENG using a silicone-rubber base sheet with cylindrical protrusions that
contributed to the roughness of the surface.(17) Our TENG was mounted inside the rolling tire
and the TENG output signal was confirmed at different rolling speeds, tire pressures, and load
weights.(18)  We assert that our TENG is a suitable energy harvester for mounting on a rollingtire, because it was indeed easily mounted and the power was harvested from the deformationof TENG at the contact patch of the rolling tire, which was the portion of a vehicle’s tire thatwas in actual contact with the road surface. In addition, the cost and weight of our TENG
are considerably low. In this study, we designed a packaged TENG, mounted it in tires, andconfirmed its output at different rolling speeds, tire pressures, and load weights.

2.

Experimental Sample and Setup

2.1

Structure of TENG

The structure of the contact-type TENG is illustrated in Fig. 1.  When two different materials
come into contact, the transfer of electrons between the material surfaces causes contact
electrification. In this study, we used fluorinated ethylene propylene (FEP) and polyurethane(PU) films. After the silicone rubber surface underwent plasma etching, a conductive cloth
electrode was adhered to the silicone rubber.  An FEP film with a thickness of 12.5 μm and a

(a)

(b)

Fig. 1. (Color online) (a) Structure of TENG used in this study and (b) surface pattern of cylindrical protrusions
on silicone rubber.

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PU film with a thickness of 7 μm were adhered to the conductive cloth surfaces to make theupper and lower elements. The mechanical and electrical properties of these materials areshown in Table 1. The resistivities of the FEP and PU films are very high, and the hardnessof the silicone rubber is small. These elements were used as the TENG with the film surfaces
facing each other. Silicone rubber was used as the base material of the triboelectrification films
and the electrode to increase the deformation under pressure and the changes in contact areaand distance between the mean plane of film surfaces with pressure fluctuations. Furthermore,
the silicone rubber surface had cylindrical protrusions that enhanced the changes in contact
area and distance between mean planes.  The diameter and height of the protrusions were ϕ1.5
and 0.5 mm, respectively. The size of the silicone rubber was 50 × 50 mm2. Electric charge
was induced in the conductive cloth by the electrostatic charge on the film surface.  When the
distance between the mean planes of the film surfaces changed, the charge potential in the
conductive cloth changed, and the current could be extracted.
The TENG, as shown in Fig. 1, was packed using an aluminum laminate film with apolyethylene terephthalate/polyamide/aluminum/polyethylene structure to block the water
vapor. The TENG package is illustrated in Fig. 2.
2.2

Environmental evaluation of TENG

TENGs with and without packaging were evaluated to confirm the effect of environmental
temperature and humidity using an environmental chamber, as shown in Fig. 3. The TENG
was put on a shaker table that was preloaded with a weight of 42 N. The table was vibrated atTable 1
Mechanical and electrical characteristics of each material.
Material
Tensile strength (GPa)Hardness (°)
23.5–37.2—
FEP(19)PU——
Conductive cloth
9.8—
Silicone rubber
9.2
A 60

Fig. 2. (C o l o r o n l i n e) A l u m i n u m l a m i n a t e
packaging of TENG to block humidity.

Dielectric constant
2.6
6.5–7.1—
3–4

Resistivity (Ω cm)> 1016109 –1012< 0.05> 1014

Fig. 3. (Color online) Schematic of experimental
set up to evaluate the effect of environ mental
temperature and humidity on TENG.

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a frequency of 20 Hz and accelerated at 9.8 m/s2. The TENG output was monitored using anoscilloscope and the average output voltage was compared at different values of humidity (50–90%
RH at 25 °C) and temperature (0–80 °C at 50% RH).
2.3

Setup of tire rolling experiment

The packed TENGs were mounted on the back surface inside the tire using adhesive tape. A
racing cart tire (diameter: 210 mm, width: 105 mm) was used to evaluate the TENG, as shownin Fig. 4. The TENG output was connected to the wireless data transmitter and the voltage data
were received via the receiver. The tire was preloaded with a weight of 150–350 N and rotatedon the moving belt of a treadmill at a speed of 4–16 km/h as shown in Fig. 5. The tire pressure
was set to 100–250 kPa. The generated power was obtained from the voltage across a load
resistance of 10 MΩ.

Fig. 4.

(Color online) Mounting position of TENG inside the rotating racing kart tire of 210 mm diameter.

(a)

(b)

Fig. 5. (Color online) (a) Evaluation of TENG mounted inside rolling tire on treadmill and (b) schematic ofexperimental setup.

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Sensors and Materials, Vol. 32, No. 7 (2020)

3.

Results and Discussion

3.1

Dependence of TENG output on environmental temperature and humidity

The TENG output was measured at different temperatures and humidity environments. A
typical TENG output is shown in Fig. 6. The average output voltages, which changed at higher
humidity, are shown in Fig. 7. The output voltages of the TENG without an aluminum laminate
package decreased as the humidity and temperature increased.   However, approximately
constant voltage was observed in the packaged TENG despite the changes in external humidity
and temperature. Therefore, it was found that the output performance of TENG significantly
deteriorates owing to the formation of a water layer on the surface of the triboelectric materials,
which depletes the induced charges.(16) Even when the temperature increases, the TENG output
decreases owing to the same effect of humidity because the absolute humidity increases.  When
the TENG is encased in the aluminum laminate package, the output is not affected by thehumidity or temperature because the absolute humidity is constant in the package. Considering
this result, the proposed TENG element was packed using the aluminum laminate film for
mounting in tires.

(a)Fig. 6.

(b)(c)

Typical output of TENG at different values of environmental humidity, i.e., (a) 50, (b) 80, and (c) 90% RH.

(a)Fig. 7.

(b)(a) Humidity dependence of TENG output and (b) temperature dependence of TENG output.

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Output of TENG mounted inside rolling tire

The performance of the TENG mounted inside the rolling tire was monitored. The typical
outputs have been demonstrated in Fig. 8 at different rolling speeds of 8, 12, and 16 km/h. Two
positive peaks and two negative peaks per rotation of the tire were observed. These peaks
occurred at the point of contact between the TENG and the tire. To confirm that the output
waveform of the TENG is caused by the velocity changes along the radial direction when it
comes in contact with a patch of the tire, the radial acceleration component, measured using
an acceleration sensor, was compared with the TENG output obtained during the experimentusing an automobile tire at a speed of 20 km/h on a drum-type rolling resistance tester. The
measured TENG output and acceleration sensor output are shown in Fig. 9(a). The waveform ofacceleration at the region of contact was found to be similar to that in a previous study.(6) The
differential waveform of the TENG output was similar to the acceleration waveform, as shownin Fig. 9(b).   This approximation suggests that the output of TENG depends on the velocity
component in the radial direction when passing through the contact patch. The dependencesof the positive peak voltage of the TENG output on the tire rolling speed, load weight, and tire(a)Fig. 8.

(b)(Color online) Typical output of TENG mounted inside rolling tire at different speeds.

(a)Fig. 9.

(c)(b)(Color online) (a) Acceleration and TENG output. (b) Differential output of TENG and acceleration.

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Sensors and Materials, Vol. 32, No. 7 (2020)pressure are illustrated in Figs. 10(a)–10(c), respectively. The TENG output increases withthe tire rolling speed because the velocity of tire deformation along the radial direction at thecontact patch increases with rolling velocity. It increases with tire load weight because thedeformation at the region of contact increases with load weight. In contrast, the TENG output
decreases as the tire pressure increases. In this study, we used a racing cart tire with a bias tire
structure for the experiment.  Therefore, the deformation at the contact patch decreased because
the tire bent along the width and expanded.   However, it is predicted that automobile tires,
which are radial tires, do not expand much even when the tire pressure increases.  Because thespeed and load of automobile tires are larger than those of cart tires (used in this experiment), it
is estimated that the automobile tires exhibit higher voltage.  In fact, the positive voltage of theoutput from the TENG mounted inside the automobile tire at a rolling speed of 20 km/h wasapproximately 70 V0p, as shown in Fig. 9.
3.3

Output power of TENG mounted inside rolling tire

The charged voltage in the 10 μF capacitor was measured using the bridge rectifier.  Thesecharged voltages as a function of the rolling speed, rolling duration, load weight, and tire

(a)

(b)

(c)

Fig. 10. (Color online) (a) Rolling speed dependence, (b) load weight dependence, and (c) tire pressure dependence
for positive voltage of TENG output.

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pressure of 16 km/h, 10 min, 350 N, and 100 kPa, respectively, are shown in Figs. 11(a) and11(b).  The charged voltage, found to be approximately 12.5 V, was proportional to the speed.  
The voltage increased with rolling duration. The charged energy was obtained from the charged
voltage, as shown in Fig. 12. The charged energy proportionally increased with rolling duration
and became more than 1 mJ at 15 min. From the slope of the line fitted to the measured data,
the power generated by the TENG in the rolling tire under this condition was determined to beapproximately 1.0 μW.  If the harvested energy is proportional to the rolling speed, the obtainedenergy is estimated to be approximately 5.4 mJ for rolling at the speed of 40 km/h for 10 min
by extrapolating the line in Fig. 11(a).  In actual car tires, on the basis of the discussion in theprevious section, the output power of TENG will be larger than this estimation and it can beconcluded that TENG has the potential to be used as a power source for tire sensors.

(a)

(b)

Fig. 11. (Color online) (a) Charged voltage in capacitor of 10 µF as a function of tire rolling speed. (b) Charged
voltage in capacitor of 10 µF as a function of rolling duration at a rolling speed of 16 km/h.

Fig. 12. Energy charged to capacitor as a function of tire rolling duration.

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4.

Sensors and Materials, Vol. 32, No. 7 (2020)

Conclusions

In this study, we developed a TENG for intelligent tires. This TENG was attached to theinner surface of a racing cart tire.  We evaluated the dependences of the TENG output on theenvironmental temperature and RH to ensure that the proposed TENG can operate in a wide
range of temperature and RH. Then, we prepared TENGs packaged with aluminum laminate
film and mounted them on the inner side of the tires. The charged voltage and output voltageof the TENGs were evaluated on a moving belt. The output voltage signals were observed at
the region of the contact patch. The signals increased with rotational speed and load weight;
however, they decreased with tire pressure.   The charged voltage in the 10 μF capacitor was
found to be approximately 14 V, which corresponds to 1.0 mJ at the speed of 16 km/h after
15 min of tire rotation. These results suggest that the proposed TENG can be used as an energy
harvester for the temperature and pressure sensors built into intelligent tires.

Acknowledgments
This research is supported by the Feasibility Study of Adaptable and Seamless Technology
Transfer Program through Target-driven R&D (A-STEP) from the Japan Science andTechnology Agency (JST).

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About the Authors
Hiroshi Tani received his B.S. and M.S. degrees from Hiroshima University, Japan, in 1984
and 1986, respectively, and his Ph.D. degree from the University of Tokyo, Japan, in 2003.
From 1986 to 2008, he worked for Hitachi and Hitach GST. In 2008, he became an associate
professor in Kansai University, Japan. Since 2011, he has been a professor at Kansai University.
His research interests are in the domain of tribology and triboelectric nanogenerators.
(hrstani@kansai-u.ac.jp)
Mutsuki Sugimoto received his B.E. and M.E. degrees from Yamagata University, Japan, in
2000 and 2002, respectively. Since 2002, he has worked for Sumitomo Rubber Industry Co.
His research interests include intelligent tires. (m-sugimoto.az@srigroup.co.jp)
Kazuhisa Fushihara received his B.E. and M.E. degrees from Tohoku University, Japan, in
1991 and 1993, respectively. Since 1993, he has worked for Sumitomo Rubber Industry Co. His
research interests include intelligent tires. (k-fushihara.az@srigroup.co.jp)
Yukio Nakano received his B.E. and M.E. degrees from Kobe University, Japan, in 1980 and
1982, respectively. Since 1982, he has worked for Sumitomo Rubber Industry Co. His researchinterests are in intelligent tires. (y-nakano.az@srigroup.co.jp)
Renguo Lu received his Ph.D. degree from Iwate University, Japan, in 2009. Since 2015, he has
been an associate professor at Kansai University. His research interests include tribology.
(r_lu@kansai-u.ac.jp)
Shinji Koganezawa received his Ph.D. degree from Tokyo Institute of Technology, Japan, in
2004. Since 2016, he has been a professor at Kansai University. His research interests are in
the field of mechatronics. (skoga@kansai-u.ac.jp)
Norio Tagawa received his B.E. and M.E. degrees from Tohoku University, Japan, in 1975 and1977, respectively, and his Ph.D. degree from the University of Tokyo, Japan, in 1986. From1977 to 1997, he worked for NEC. Since 1997, he has been a professor in Kansai University,
Japan. His research interests are in the tribology of head-disk interfaces.
(tagawa@kansai-u.ac.jp)