- Email: [email protected]
Piezoelectric device operating as sensor and harvester to drive switching circuit in LED shoes
Accepted Manuscript Piezoelectric device operating as sensor and harvester to drive switching circuit in LED shoes Se Yeong Jeong, Won Seop Hwang, Jae Yong Cho, Jae Chul Jeong, Jung Hwan Ahn, Kyung Bum Kim, Seong Do Hong, Gyeong Ju Song, Deok Hwan Jeon, Tae Hyun Sung PII:
S0360-5442(19)30684-X
DOI:
https://doi.org/10.1016/j.energy.2019.04.061
Reference:
EGY 15090
To appear in:
Energy
Received Date: 29 November 2018 Revised Date:
8 April 2019
Accepted Date: 9 April 2019
Please cite this article as: Jeong SY, Hwang WS, Cho JY, Jeong JC, Ahn JH, Kim KB, Hong SD, Song GJ, Jeon DH, Sung TH, Piezoelectric device operating as sensor and harvester to drive switching circuit in LED shoes, Energy (2019), doi: https://doi.org/10.1016/j.energy.2019.04.061. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Piezoelectric device operating as sensor and harvester to drive
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switching circuit in LED shoes
Se Yeong Jeonga, Won Seop Hwanga, Jae Yong Choa, Jae Chul Jeongb, Jung Hwan Ahna, Kyung Bum Kima,
Department of Electrical Engineering, Hanyang University, Wangsimni-ro, Seongdong-gu, Seoul, Republic of Korea
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Seong Do Honga, Gyeong Ju Songa, Deok Hwan Jeona, and Tae Hyun Sunga*
Department of Clothing & Textiles, Hanyang University, Wangsimni-ro, Seongdong-gu, Seoul, Republic of Korea
*Corresponding author; [email protected]
ABSTRACT
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The power generated by the designed piezoelectric energy harvester replaces the standby power that is constantly used in sensors and driving circuits in commercial LED shoes; the harvester thus reduces battery consumption. LED shoes incorporating a piezoelectric energy harvester are designed for night workers who work near roads. The piezoelectric energy harvester, composed of
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a piezoelectric device (PZT ceramic), which is inserted under the insoles of shoes, converts mechanical energy generated by motion of user into electrical energy. The designed harvester has
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an area of 6 × 4 mm and height of 3 mm (pressed state); it weighs 14 g. Because of its small size and light weight, device is suitable for real workers’ shoes. This piezoelectric energy harvester produces 800 μW at a resistive matching point of 400 kΩ; it is used as a sensor to control an LED switching circuit, allowing the LEDs to blink based on user movements. By applying the piezoelectric energy harvester to LED shoes, battery usage time can be doubled compared to LED shoes that are turned on continuously.
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Keywords— Piezoelectric materials; piezoelectric sensor; energy harvesting; wearable device; shoe energy generator.
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1. Introduction We live in a society in which daily activities are inseparable from electronic devices. Numerous electronic devices have already made human life more convenient, and additional devices are being
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developed for convenience, safety, and security. When studying such devices, safety issues related to human life should be most important. There are numerous ways to use electronic devices to
on roads at night from traffic accidents.
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reduce risks of accidents. One method that we have found is a device to protect workers who work
Due to reduced visibility at night, more traffic accidents occur at night than during the day [1]. For this reason, many devices using LED technology have been developed to increase the visibility of workers at night; however, these products have so far all used single-use or rechargeable
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batteries. When batteries are completely discharged, it is troublesome to replace or recharge them. In addition, if a battery is fully discharged during work time, the worker will be exposed to a hazardous situation. To increase device usage time, research into low-power devices is being
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conducted [2]. Furthermore, energy-harvesting technologies are being actively studied to solve these energy problems.
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Energy-harvesting technology can serve as a power source, independent of batteries, to operate devices such as wireless sensor networks [3] and water meter systems [4]. There are many ways to harvest electrical energy from the surrounding environment, including photovoltaic [5], thermal [6], tribo [7], electromagnetic [8], and piezoelectric [9] technologies. Brogan et al. [10] applied solar and thermal energy harvesters to a jacket. Sixteen photovoltaic (PV) cells and twelve thermoelectric generators (TEGs) were attached on both the inside and outside of the jacket to charge one AAA battery. Seung et al. [11] fabricated a flexible nanopatterned textile-based wearable triboelectric nanogenerator and inserted it into a jacket sleeve. The electrical energy 2
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harvested powered commercial LCDs and LEDs attached to the jacket. Fan et al. [12] attached an electromagnetic energy harvester to a human subject’s arms and legs. The authors carried out a study to power an LED and operate a pedometer utilizing energy generated when the subject was
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walking. Wang et al. [13], by attaching a piezoelectric harvester to a subject’s leg, measured power levels generated according to different motion speeds and resistances. Attaching harvesters to a
human body, however, can cause discomfort, and such devices are therefore difficult to apply to
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workers. In addition, when a harvester is inserted into a garment, there is a space between the human body and the garment, and so energy harvesting is in actual practice very difficult.
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In attempts to make energy harvesting less inconvenient for users, many researchers have applied harvesters to shoes. In addition, since the foot is the area where the weight of the human body is most concentrated, it can supply more mechanical energy than other parts of the human body, and so that more power can be generated. Moro and Benasciutti [14] applied a bimorph piezoelectric beam as a cantilever with a tip mass to the inside of a shoe and compared results of
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numerical simulations and experimental measurements. Turkmen and Celik [15] made a piezoelectric energy harvester of cymbal type using PZT-5H and PZT-8 piezoelectric ceramics and placed it in the heel of a shoe. Deformation and power generated by the harvester were analyzed
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according to the applied load. Youngsu Cha and Jiyeon Seo [16] applied a piezoelectric energy transducer to a slipper, and studied energy harvesting methods that used the bending of the slipper
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rather than the striking of the heel on the ground. J. G. Rocha et al. [17] attached two electroactive β-polyvinylidene fluoride piezoelectric polymer films as a piezoelectric generator above the sole of a shoe; they also applied an electrostatic generator under the sole. Jingjing Zhao et al. [18] used flexible and stable polyvinylidene difluoride (PVDF) to fabricate energy harvesters; they also made a power management circuit to allow the harvesters to be put in shoes. PVDF is not only light but also thin, so it can be easily applied to shoes. This study, however, only mentions the possibility of replacing a battery with a harvester as a wearable power supply; no actual application is performed, as has been the case for most previous studies, which have only calculated energy that can be 3
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harvested. Most prior studies have focused on storing harvested energy in a battery or using it directly for a device. The power generated by the subject’s movement serves as a limit to the continuous operation of an electronic device. Also, powering LEDs directly or charging a battery
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with a mass capacity is difficult to achieve with an energy harvester. In this study, we utilize a piezoelectric device consisting of lead-zirconate-titanate (PZT)
[19,20] as a sensor that can detect stepping movement while generating electrical energy. Our
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research focus is on how to efficiently drive the circuit. Instead of directly powering LEDs or
extending battery life, the electrical energy from the piezoelectric device replaces the energy that is
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constantly being used in sensors and driving circuits in conventional commercial products. In addition, when the sensor senses stepping movement and the piezoelectric device is active, the battery current flows to the LEDs and turns them on. System reduces battery consumption by turning off the LEDs when stepping movement is not detected. In addition, when inserted into the shoe, the thin and light energy harvester that we designed does not cause any inconvenience to
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workers. It is designed to be suitable for real environments and to perform effectively, contributing to solving the social problem of poor worker visibility at night.
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2. Theory
The fundamental constitutive equations for linear piezoelectricity, shown below, illustrate the
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relationship between the exerted mechanical energy and the output electrical energy.
D = S
T , E
(1)
where D is the electric displacement, S is the strain, d is the piezoelectric coefficient, ε is the dielectric permittivity, s is the elastic compliance, T is the stress, and E is the electric field. Equation (1) clearly shows that when there is no electric field change, the output electrical energy
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remains at zero. As has been shown in other studies [21,22], an electric potential difference V is induced when there is a stress change, as shown below. ∙ T,
(2)
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V= where t is the thickness of the PZT plate.
3.1. Piezoelectric energy harvester structure design
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3. Experimental section
The piezoelectric device consists of PZT ceramic and substrate, as shown in Fig. 1a. The
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substrate helps the PZT ceramic to bend effectively. There are holes in one side of the device, allowing it to be riveted to a base frame. The characteristics of the piezoelectric device are shown in Table 1. The piezoelectric device and its characteristics were provided by Tocean (South Korea). Fig. 1b shows the piezoelectric energy harvester (PEH), which is inserted under the insole of a shoe
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to generate power when a user moves. A spring was inserted between the piezoelectric device and the base frame. In the initial state of the PEH, the piezoelectric device is bent because of the restoring force of the spring and the rivets that fix one end of the device to the base frame. When no external force is applied to the PEH, the spring is released. In the initial state, the height of the
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PEH is 7 mm (Fig. 1c(i)). When a force is applied to the PEH, the spring is compressed and the
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height is reduced to 3 mm (Fig. 1c(ii)). When user takes one step, the harvester generates electrical energy twice, with pressing and release. Fig. 1d shows the generating sequences for the PEH according to the stepping movement. The area of this harvester is 40 × 60 mm and the height is 3 mm (pressed state); device weighs only 14 g. Therefore, when applied to shoes, this harvester does not cause any discomfort to user.
Table 1. Material properties of piezoelectric device. Material Parameter
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Steel Substrate
7.6 2300.0 450.0 22.1 62.4 13.8 11.8 193.0 8.0
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Piezoelectric Ceramic
Density (g/cm3) eT33/e0 d33 (10-12 mV) g33 (10-3 V·m/N) Kp (%) E S11 (×10-12 m2/N) S11E (×10-12 m2/N) Young’s Modulus (GPa) Density (g/cm3)
Fig 1. Schematics of (a) piezoelectric device; (b) PEH; (c) lateral face of PEH; (d) generating
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sequences.
3.2. Periodic voltage analysis PEH periodic open-circuit voltage when a user walks normally is presented in Fig. 2. There are positive and negative cycles within one period. When the PEH is compressed, it generates positive voltage. When the PEH is released, it generates negative voltage. The voltage of the piezoelectric device is approximately 30 V. The voltage states of the PEH can be divided into four states, T1–T4. When the heel of the shoe touches the ground, the PEH is pressed by the pressure of the foot, 6
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generating electricity. At this time, the voltage rises dramatically (T1). When the heel is completely in contact with the floor and the PEH is completely contracted (T2), no further deformation can occur. The PEH then stops generating electricity and the charge stored in the inner capacitor of the
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piezoelectric device is discharged to the measurement equipment (Oscilloscope, DPO 4054B, Tektronix, USA), so the graph shows a voltage drop. When the foot is lifted from the ground, the pressure between the shoe and foot is reduced and the PEH is released by the elasticity of the
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spring (T3). At this time, electricity is produced with an opposite polarity. When the shoe is
completely lifted from the ground (T4), the PEH no longer generates electricity and the charge
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stored in the inner capacitor is discharged in the same state as that in T2. The polarities of voltage generation upon pressing and releasing are different because the PEH bends in opposite directions
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when pressed and released.
Fig. 2. PEH voltage waveform during walking.
4. Results and discussion
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The piezoelectric device can be described as an equivalent circuit with a resistor and capacitor at a non-resonant frequencies [23]. Fig. 3a shows the equivalent circuit for the piezoelectric device, the full bridge rectifier, and the LED switching circuit. Because the voltage waveform is AC, the
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full bridge rectifier (bas3007) must be used to rectify the voltage generated from the PEH, as shown in Fig. 2. The voltage of the PEH is rectified and connected through a resistor (309 Ω) to the gate pin of a MOSFET (2N7002). When the PEH is pressed, it generates voltage. If the voltage
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increases over 1.5 V, which is the threshold voltage (Vth) for the MOSFET gate pin, the MOSFET turns on. Fig. 3b shows the operating modes of the LED switching circuit according to the user’s
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footsteps. The current (IBAT) from the battery (lithium polymer) flows from the drain pin to the source pin and the LED turns on (Mode 1, T1 in Fig. 2). If the gate pin’s voltage is lower than Vth, the MOSFET remains off and the drain and source pins are disconnected. Therefore, IBAT cannot flow from the drain to the source and the LED turns off (Mode 2, T2 in Fig. 2). When the PEH releases, it generates a voltage opposite to that in Mode 1. Although the current (Ip) direction from
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the PEH is different from that of Mode 1, the operating principle is the same and the LED turns on (Mode 3, T3 in Fig. 2). Finally, the LED turns off when the voltage drops below 1.5 V (Mode 4, T4 in Fig. 2). Fig. 3c shows the voltage waveforms of the gate pin of the MOSFET and the LED input
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voltages. Because of the loading effect that occurs with connection to the MOSFET, the maximum voltage decreases from the open-circuit voltage (30 V) to approximately 12 V. The current from
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the piezoelectric device flows into the MOSFET and the voltage decreases. Furthermore, this voltage has only a positive cycle because it was rectified using a rectifier consisting of four diodes. When the piezoelectric device is pressed, the maximum voltage level is approximately 12 V. When device is released, the maximum voltage level is approximately 8−9 V. When the piezoelectric device generates voltage, the MOSFET turns on and a battery voltage of 3.2 V is transferred to the LEDs. If the maximum value of the gate pin voltage is 1.5 V(Vth), the MOSFET will turn on, but its on-time will be reduced and the LED on-time will decrease. To turn the LED on for a sufficient time for it to be recognised by drivers, the maximum value of the voltage generated by the 8
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piezoelectric device must be much higher. When a user walks at normal speed, the LED on-time during one step is approximately half of one period. As a result, the battery life can be more than doubled as long as the LED is always on because the current of the battery is cut off during LED
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off-time.
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Fig. 3. (a) Schematics of LED switching circuit. (b) Operating modes of LED switching circuit. (c)
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Gate pin and LED input voltages.
Fig. 4a shows the voltage, current, and power of PEH with resistive matching load of 400 kΩ. The matching resistance value is the value at which the open-circuit voltage is halved [24]. At this point, maximum power is transferred based on load. When PEH is pressed, the output power of the
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rectifier is 800 µW. Since a value of 950 µW was measured as the input power of the rectifier, the efficiency of the rectifier is 84%. When PEH is released, its power output is 600 µW. Fig. 4b
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shows the voltage charge in a 100-µF capacitor when the PEH is pressed 30 times. At this time, the voltage is 4.1 V and the energy is 840 µJ, as calculated using Equation (3), where E is the energy, in joules; C is the capacitance in farads; and V is the voltage, in volts. Figs. 4c and (d) are graphs representing different types of movement, namely (A) slow walking, (B) normal walking, (C) running, and (D) jumping. As speed increases, the acceleration and force applied to the harvester
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increase, thereby increasing the current and the voltage.
E = × C × V
(3)
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Fig. 4. Graphs generated by PEH: (a) voltage, current, and power of PEH. (b) Capacitor charge over 30 presses on PEH. (c) Voltage and (d) current trends with different types of movement. The sole of the shoe has some space (Fig. 5a) for a battery and a small PCB (Fig. 5b). This
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space eliminates user inconvenience. There is a battery charger connector inside the shoe that allows device to charge. The on/off connector is located near the shoelaces and, when the
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connector is disconnected, the battery is also disconnected. This connecter can also be used to turn off the LEDs according to user intention or during daytime. All components of shoes are presented in Fig. 5c. The actual appearance of the LED shoe lighting each time user walks is shown in Fig. 5d−g. The shoes are expected to be useful for workers working at night near streets, to make them visible to motorists. Additionally, this technology can be applied as a wearable device to smart shoes.
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Fig. 5. (a) Space inside shoes including battery and circuit. (b) PCB next to 1-euro coin. (c) LED
5. Conclusion
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shoe components. (d)−(g) LED lights up in the direction of stepping movement.
For workers working on roads, the incidence of traffic accidents tends to increase at night. To
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ensure that workers are visible to motorists, workers must wear garments with LED devices applied. Since these electronic devices have limitations of battery usage, it is essential to apply
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energy harvesting technology. We fabricated a small (area: 4 × 6 mm, weight: 3 mm (pressed)), lightweight (14 g) PEH with PZT ceramics and an LED switching circuit and inserted it into the sole of a shoe. The PEH was used as a sensor to detect user’s walking; at the same time, it converted mechanical energy generated by human motion into electric energy. It was found that power generated by the PEH can be used to replace battery power continuously supplied to sensors and driving circuits of commercial products. The LED switching circuit was driven by electrical energy generated by PEH and, when user motion was not detected, the battery current was cut off.
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As a result, we were able to reduce unnecessary battery usage and more than double battery usage time as compared to shoes with LEDs that are continuously lit. One limitation of this system is that this device may not meet the Rohs (Restriction of the use of Hazardous Substances in EEE)
limitation by replacing PZT with a lead-free material.
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References
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standard because it contains lead (Pb). For commercialization, it will be necessary to overcome this
Plainis S. Road traffic casualties: understanding the night-time death toll. Inj Prev 2006;12:125–38. doi:10.1136/ip.2005.011056.
[2]
Cheng X, Zhang Y, Xie G, Yang Y, Zhang Z. An ultra-low power output capacitor-less low-dropout regulator with slew-rate-enhanced circuit. J Semicond 2018;39:035002. doi:10.1088/1674-4926/39/3/035002.
[3]
Jung HJ, Song Y, Hong SK, Yang CH, Hwang SJ, Jeong SY, et al. Design and optimization of piezoelectric impact-based micro wind energy harvester for wireless sensor network. Sensors Actuators A Phys 2015;222:314–21. doi:10.1016/j.sna.2014.12.010.
[4]
Cho JY, Choi JY, Jeong SW, Ahn JH, Hwang WS, Yoo HH, et al. Design of hydro electromagnetic and piezoelectric energy harvesters for a smart water meter system. Sensors Actuators A Phys 2017;261:261–7. doi:10.1016/j.sna.2017.05.018.
[5]
Karthick A, Kalidasa Murugavel K, Kalaivani L. Performance analysis of semitransparent photovoltaic module for skylights. Energy 2018;162:798–812. doi:10.1016/j.energy.2018.08.043.
[6]
McKay IS, Wang EN. Thermal pulse energy harvesting. Energy 2013;57:632–40. doi:10.1016/j.energy.2013.05.045.
[7]
Mule AR, Dudem B, Yu JS. High-performance and cost-effective triboelectric nanogenerators by sandpaper-assisted micropatterned polytetrafluoroethylene. Energy 2018;165:677–84. doi:10.1016/j.energy.2018.09.122.
TE D
EP
AC C
[8]
M AN U
[1]
Gui P, Deng F, Liang Z, Cai Y, Chen J. Micro linear generator for harvesting mechanical energy from the human gait. Energy 2018;154:365–73. doi:10.1016/j.energy.2018.04.123.
[9]
Kim K-B, Cho JY, Jeon DH, Ahn JH, Hong S Do, Jeong Y-H, et al. Enhanced flexible piezoelectric generating performance via high energy composite for wireless sensor network. Energy 2018;159:196–202. doi:10.1016/j.energy.2018.06.048.
[10]
Brogan Q, O’Connor T, Ha DS. Solar and thermal energy harvesting with a wearable jacket. Circuits Syst. (ISCAS), 2014 IEEE Int. Symp., IEEE; 2014, p. 1412–5.
13
ACCEPTED MANUSCRIPT
Seung W, Gupta MK, Lee KY, Shin KS, Lee JH, Kim TY, et al. Nanopatterned textilebased wearable triboelectric nanogenerator. ACS Nano 2015;9:3501–9. doi:10.1021/nn507221f.
[12]
Fan K, Cai M, Liu H, Zhang Y. Capturing energy from ultra-low frequency vibrations and human motion through a monostable electromagnetic energy harvester. Energy J 2019;169:356–68. doi:S0360544218324198.
[13]
Wang W, Cao J, Bowen CR, Zhou S, Lin J. Optimum resistance analysis and experimental verification of nonlinear piezoelectric energy harvesting from human motions. Energy 2017;118:221–30. doi:10.1016/j.energy.2016.12.035.
[14]
Moro L, Benasciutti. D. Harvested power and sensitivity analysis of vibrating shoe-mounted piezoelectric cantilevers. Smart Mater Struct 2010;19. doi:10.1088/09641726/19/11/115011.
[15]
Turkmen AC, Celik C. Energy harvesting with the piezoelectric material integrated shoe. Energy 2018;150:556–64. doi:10.1016/j.energy.2017.12.159.
[16]
Cha Y, Seo J. Energy harvesting from a piezoelectric slipper during walking. J Intell Mater Syst Struct 2018;29:1456–63. doi:10.1177/1045389X17740962.
[17]
Rocha JG, Gonçalves LM, Rocha PF, Silva MP, Lanceros-Méndez S. Energy harvesting from piezoelectric materials fully integrated in footwear. IEEE Trans Ind Electron 2010;57:813–9. doi:10.1109/TIE.2009.2028360.
[18]
Zhao J, You Z. A shoe-embedded piezoelectric energy harvester for wearable sensors. Sensors (Switzerland) 2014;14:12497–510. doi:10.3390/s140712497.
[19]
Hu Y, Yi Z, Dong X, Mou F, Tian Y, Yang Q, et al. High power density energy harvester with non-uniform cantilever structure due to high average strain distribution. Energy 2019;169:294–304. doi:10.1016/j.energy.2018.11.085.
[20]
Su X, Bai G, Jia Y, Wang Z, Wu W, Yan X, et al. Flash sintering of lead zirconate titanate (PZT) ceramics: Influence of electrical field and current limit on densification and grain growth. J Eur Ceram Soc 2018;38:3489–97. doi:10.1016/j.jeurceramsoc.2018.04.007.
[21]
Woo MS, Hong SK, Jung HJ, Yang CH, Song D, Sung TH. Study on the strain effect of a piezoelectric energy harvesting module. Ferroelectrics 2013;449:33–41. doi:10.1080/00150193.2013.822765.
AC C
EP
TE D
M AN U
SC
RI PT
[11]
[22]
Guan MJ, Liao WH. On the equivalent circuit models of piezoelectric ceramics. Ferroelectrics 2009;386:77–87. doi:10.1080/00150190902961439.
[23]
Jabbar H, Hong S Do, Hong SK, Yang CH, Jeong SY, Sung TH. Sustainable micro-power circuit for piezoelectric energy harvesting tile. Integr Ferroelectr 2017;183:193–209. doi:10.1080/10584587.2017.1376964.
[24]
Das P. Maximum Power Tracking Based Open Circuit Voltage Method for PV System. Energy Procedia 2015;90:2–13. doi:10.1016/j.egypro.2016.11.165.
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Acknowledgements This research was supported by Research Program To Solve Social Issues of the National Research Foundation of Korea(NRF) funded by the Ministry of Science and ICT. (NRF-
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2015M3C8A8050335)
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Highlights Designed piezoelectric energy harvester has an area of 6 × 4 mm and height of 3 mm.
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Piezoelectric energy harvester produces 800 µW at a resistive matching point of 400 kΩ.
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Harvester works as a sensor to drive an LED switching circuit in LED shoes.
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The proposed LED shoes enhance the visibility of night workers in dark areas.
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Battery usage time can be doubled compared to LED shoes.
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•
1
S0360-5442(19)30684-X
DOI:
https://doi.org/10.1016/j.energy.2019.04.061
Reference:
EGY 15090
To appear in:
Energy
Received Date: 29 November 2018 Revised Date:
8 April 2019
Accepted Date: 9 April 2019
Please cite this article as: Jeong SY, Hwang WS, Cho JY, Jeong JC, Ahn JH, Kim KB, Hong SD, Song GJ, Jeon DH, Sung TH, Piezoelectric device operating as sensor and harvester to drive switching circuit in LED shoes, Energy (2019), doi: https://doi.org/10.1016/j.energy.2019.04.061. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Piezoelectric device operating as sensor and harvester to drive
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switching circuit in LED shoes
Se Yeong Jeonga, Won Seop Hwanga, Jae Yong Choa, Jae Chul Jeongb, Jung Hwan Ahna, Kyung Bum Kima,
Department of Electrical Engineering, Hanyang University, Wangsimni-ro, Seongdong-gu, Seoul, Republic of Korea
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a
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Seong Do Honga, Gyeong Ju Songa, Deok Hwan Jeona, and Tae Hyun Sunga*
Department of Clothing & Textiles, Hanyang University, Wangsimni-ro, Seongdong-gu, Seoul, Republic of Korea
*Corresponding author; [email protected]
ABSTRACT
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The power generated by the designed piezoelectric energy harvester replaces the standby power that is constantly used in sensors and driving circuits in commercial LED shoes; the harvester thus reduces battery consumption. LED shoes incorporating a piezoelectric energy harvester are designed for night workers who work near roads. The piezoelectric energy harvester, composed of
EP
a piezoelectric device (PZT ceramic), which is inserted under the insoles of shoes, converts mechanical energy generated by motion of user into electrical energy. The designed harvester has
AC C
an area of 6 × 4 mm and height of 3 mm (pressed state); it weighs 14 g. Because of its small size and light weight, device is suitable for real workers’ shoes. This piezoelectric energy harvester produces 800 μW at a resistive matching point of 400 kΩ; it is used as a sensor to control an LED switching circuit, allowing the LEDs to blink based on user movements. By applying the piezoelectric energy harvester to LED shoes, battery usage time can be doubled compared to LED shoes that are turned on continuously.
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Keywords— Piezoelectric materials; piezoelectric sensor; energy harvesting; wearable device; shoe energy generator.
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1. Introduction We live in a society in which daily activities are inseparable from electronic devices. Numerous electronic devices have already made human life more convenient, and additional devices are being
SC
developed for convenience, safety, and security. When studying such devices, safety issues related to human life should be most important. There are numerous ways to use electronic devices to
on roads at night from traffic accidents.
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reduce risks of accidents. One method that we have found is a device to protect workers who work
Due to reduced visibility at night, more traffic accidents occur at night than during the day [1]. For this reason, many devices using LED technology have been developed to increase the visibility of workers at night; however, these products have so far all used single-use or rechargeable
TE D
batteries. When batteries are completely discharged, it is troublesome to replace or recharge them. In addition, if a battery is fully discharged during work time, the worker will be exposed to a hazardous situation. To increase device usage time, research into low-power devices is being
EP
conducted [2]. Furthermore, energy-harvesting technologies are being actively studied to solve these energy problems.
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Energy-harvesting technology can serve as a power source, independent of batteries, to operate devices such as wireless sensor networks [3] and water meter systems [4]. There are many ways to harvest electrical energy from the surrounding environment, including photovoltaic [5], thermal [6], tribo [7], electromagnetic [8], and piezoelectric [9] technologies. Brogan et al. [10] applied solar and thermal energy harvesters to a jacket. Sixteen photovoltaic (PV) cells and twelve thermoelectric generators (TEGs) were attached on both the inside and outside of the jacket to charge one AAA battery. Seung et al. [11] fabricated a flexible nanopatterned textile-based wearable triboelectric nanogenerator and inserted it into a jacket sleeve. The electrical energy 2
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harvested powered commercial LCDs and LEDs attached to the jacket. Fan et al. [12] attached an electromagnetic energy harvester to a human subject’s arms and legs. The authors carried out a study to power an LED and operate a pedometer utilizing energy generated when the subject was
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walking. Wang et al. [13], by attaching a piezoelectric harvester to a subject’s leg, measured power levels generated according to different motion speeds and resistances. Attaching harvesters to a
human body, however, can cause discomfort, and such devices are therefore difficult to apply to
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workers. In addition, when a harvester is inserted into a garment, there is a space between the human body and the garment, and so energy harvesting is in actual practice very difficult.
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In attempts to make energy harvesting less inconvenient for users, many researchers have applied harvesters to shoes. In addition, since the foot is the area where the weight of the human body is most concentrated, it can supply more mechanical energy than other parts of the human body, and so that more power can be generated. Moro and Benasciutti [14] applied a bimorph piezoelectric beam as a cantilever with a tip mass to the inside of a shoe and compared results of
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numerical simulations and experimental measurements. Turkmen and Celik [15] made a piezoelectric energy harvester of cymbal type using PZT-5H and PZT-8 piezoelectric ceramics and placed it in the heel of a shoe. Deformation and power generated by the harvester were analyzed
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according to the applied load. Youngsu Cha and Jiyeon Seo [16] applied a piezoelectric energy transducer to a slipper, and studied energy harvesting methods that used the bending of the slipper
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rather than the striking of the heel on the ground. J. G. Rocha et al. [17] attached two electroactive β-polyvinylidene fluoride piezoelectric polymer films as a piezoelectric generator above the sole of a shoe; they also applied an electrostatic generator under the sole. Jingjing Zhao et al. [18] used flexible and stable polyvinylidene difluoride (PVDF) to fabricate energy harvesters; they also made a power management circuit to allow the harvesters to be put in shoes. PVDF is not only light but also thin, so it can be easily applied to shoes. This study, however, only mentions the possibility of replacing a battery with a harvester as a wearable power supply; no actual application is performed, as has been the case for most previous studies, which have only calculated energy that can be 3
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harvested. Most prior studies have focused on storing harvested energy in a battery or using it directly for a device. The power generated by the subject’s movement serves as a limit to the continuous operation of an electronic device. Also, powering LEDs directly or charging a battery
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with a mass capacity is difficult to achieve with an energy harvester. In this study, we utilize a piezoelectric device consisting of lead-zirconate-titanate (PZT)
[19,20] as a sensor that can detect stepping movement while generating electrical energy. Our
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research focus is on how to efficiently drive the circuit. Instead of directly powering LEDs or
extending battery life, the electrical energy from the piezoelectric device replaces the energy that is
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constantly being used in sensors and driving circuits in conventional commercial products. In addition, when the sensor senses stepping movement and the piezoelectric device is active, the battery current flows to the LEDs and turns them on. System reduces battery consumption by turning off the LEDs when stepping movement is not detected. In addition, when inserted into the shoe, the thin and light energy harvester that we designed does not cause any inconvenience to
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workers. It is designed to be suitable for real environments and to perform effectively, contributing to solving the social problem of poor worker visibility at night.
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2. Theory
The fundamental constitutive equations for linear piezoelectricity, shown below, illustrate the
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relationship between the exerted mechanical energy and the output electrical energy.
D = S
T , E
(1)
where D is the electric displacement, S is the strain, d is the piezoelectric coefficient, ε is the dielectric permittivity, s is the elastic compliance, T is the stress, and E is the electric field. Equation (1) clearly shows that when there is no electric field change, the output electrical energy
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remains at zero. As has been shown in other studies [21,22], an electric potential difference V is induced when there is a stress change, as shown below. ∙ T,
(2)
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V= where t is the thickness of the PZT plate.
3.1. Piezoelectric energy harvester structure design
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3. Experimental section
The piezoelectric device consists of PZT ceramic and substrate, as shown in Fig. 1a. The
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substrate helps the PZT ceramic to bend effectively. There are holes in one side of the device, allowing it to be riveted to a base frame. The characteristics of the piezoelectric device are shown in Table 1. The piezoelectric device and its characteristics were provided by Tocean (South Korea). Fig. 1b shows the piezoelectric energy harvester (PEH), which is inserted under the insole of a shoe
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to generate power when a user moves. A spring was inserted between the piezoelectric device and the base frame. In the initial state of the PEH, the piezoelectric device is bent because of the restoring force of the spring and the rivets that fix one end of the device to the base frame. When no external force is applied to the PEH, the spring is released. In the initial state, the height of the
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PEH is 7 mm (Fig. 1c(i)). When a force is applied to the PEH, the spring is compressed and the
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height is reduced to 3 mm (Fig. 1c(ii)). When user takes one step, the harvester generates electrical energy twice, with pressing and release. Fig. 1d shows the generating sequences for the PEH according to the stepping movement. The area of this harvester is 40 × 60 mm and the height is 3 mm (pressed state); device weighs only 14 g. Therefore, when applied to shoes, this harvester does not cause any discomfort to user.
Table 1. Material properties of piezoelectric device. Material Parameter
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Steel Substrate
7.6 2300.0 450.0 22.1 62.4 13.8 11.8 193.0 8.0
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Piezoelectric Ceramic
Density (g/cm3) eT33/e0 d33 (10-12 mV) g33 (10-3 V·m/N) Kp (%) E S11 (×10-12 m2/N) S11E (×10-12 m2/N) Young’s Modulus (GPa) Density (g/cm3)
Fig 1. Schematics of (a) piezoelectric device; (b) PEH; (c) lateral face of PEH; (d) generating
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sequences.
3.2. Periodic voltage analysis PEH periodic open-circuit voltage when a user walks normally is presented in Fig. 2. There are positive and negative cycles within one period. When the PEH is compressed, it generates positive voltage. When the PEH is released, it generates negative voltage. The voltage of the piezoelectric device is approximately 30 V. The voltage states of the PEH can be divided into four states, T1–T4. When the heel of the shoe touches the ground, the PEH is pressed by the pressure of the foot, 6
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generating electricity. At this time, the voltage rises dramatically (T1). When the heel is completely in contact with the floor and the PEH is completely contracted (T2), no further deformation can occur. The PEH then stops generating electricity and the charge stored in the inner capacitor of the
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piezoelectric device is discharged to the measurement equipment (Oscilloscope, DPO 4054B, Tektronix, USA), so the graph shows a voltage drop. When the foot is lifted from the ground, the pressure between the shoe and foot is reduced and the PEH is released by the elasticity of the
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spring (T3). At this time, electricity is produced with an opposite polarity. When the shoe is
completely lifted from the ground (T4), the PEH no longer generates electricity and the charge
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stored in the inner capacitor is discharged in the same state as that in T2. The polarities of voltage generation upon pressing and releasing are different because the PEH bends in opposite directions
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when pressed and released.
Fig. 2. PEH voltage waveform during walking.
4. Results and discussion
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The piezoelectric device can be described as an equivalent circuit with a resistor and capacitor at a non-resonant frequencies [23]. Fig. 3a shows the equivalent circuit for the piezoelectric device, the full bridge rectifier, and the LED switching circuit. Because the voltage waveform is AC, the
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full bridge rectifier (bas3007) must be used to rectify the voltage generated from the PEH, as shown in Fig. 2. The voltage of the PEH is rectified and connected through a resistor (309 Ω) to the gate pin of a MOSFET (2N7002). When the PEH is pressed, it generates voltage. If the voltage
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increases over 1.5 V, which is the threshold voltage (Vth) for the MOSFET gate pin, the MOSFET turns on. Fig. 3b shows the operating modes of the LED switching circuit according to the user’s
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footsteps. The current (IBAT) from the battery (lithium polymer) flows from the drain pin to the source pin and the LED turns on (Mode 1, T1 in Fig. 2). If the gate pin’s voltage is lower than Vth, the MOSFET remains off and the drain and source pins are disconnected. Therefore, IBAT cannot flow from the drain to the source and the LED turns off (Mode 2, T2 in Fig. 2). When the PEH releases, it generates a voltage opposite to that in Mode 1. Although the current (Ip) direction from
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the PEH is different from that of Mode 1, the operating principle is the same and the LED turns on (Mode 3, T3 in Fig. 2). Finally, the LED turns off when the voltage drops below 1.5 V (Mode 4, T4 in Fig. 2). Fig. 3c shows the voltage waveforms of the gate pin of the MOSFET and the LED input
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voltages. Because of the loading effect that occurs with connection to the MOSFET, the maximum voltage decreases from the open-circuit voltage (30 V) to approximately 12 V. The current from
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the piezoelectric device flows into the MOSFET and the voltage decreases. Furthermore, this voltage has only a positive cycle because it was rectified using a rectifier consisting of four diodes. When the piezoelectric device is pressed, the maximum voltage level is approximately 12 V. When device is released, the maximum voltage level is approximately 8−9 V. When the piezoelectric device generates voltage, the MOSFET turns on and a battery voltage of 3.2 V is transferred to the LEDs. If the maximum value of the gate pin voltage is 1.5 V(Vth), the MOSFET will turn on, but its on-time will be reduced and the LED on-time will decrease. To turn the LED on for a sufficient time for it to be recognised by drivers, the maximum value of the voltage generated by the 8
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piezoelectric device must be much higher. When a user walks at normal speed, the LED on-time during one step is approximately half of one period. As a result, the battery life can be more than doubled as long as the LED is always on because the current of the battery is cut off during LED
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off-time.
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Fig. 3. (a) Schematics of LED switching circuit. (b) Operating modes of LED switching circuit. (c)
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Gate pin and LED input voltages.
Fig. 4a shows the voltage, current, and power of PEH with resistive matching load of 400 kΩ. The matching resistance value is the value at which the open-circuit voltage is halved [24]. At this point, maximum power is transferred based on load. When PEH is pressed, the output power of the
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rectifier is 800 µW. Since a value of 950 µW was measured as the input power of the rectifier, the efficiency of the rectifier is 84%. When PEH is released, its power output is 600 µW. Fig. 4b
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shows the voltage charge in a 100-µF capacitor when the PEH is pressed 30 times. At this time, the voltage is 4.1 V and the energy is 840 µJ, as calculated using Equation (3), where E is the energy, in joules; C is the capacitance in farads; and V is the voltage, in volts. Figs. 4c and (d) are graphs representing different types of movement, namely (A) slow walking, (B) normal walking, (C) running, and (D) jumping. As speed increases, the acceleration and force applied to the harvester
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increase, thereby increasing the current and the voltage.
E = × C × V
(3)
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Fig. 4. Graphs generated by PEH: (a) voltage, current, and power of PEH. (b) Capacitor charge over 30 presses on PEH. (c) Voltage and (d) current trends with different types of movement. The sole of the shoe has some space (Fig. 5a) for a battery and a small PCB (Fig. 5b). This
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space eliminates user inconvenience. There is a battery charger connector inside the shoe that allows device to charge. The on/off connector is located near the shoelaces and, when the
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connector is disconnected, the battery is also disconnected. This connecter can also be used to turn off the LEDs according to user intention or during daytime. All components of shoes are presented in Fig. 5c. The actual appearance of the LED shoe lighting each time user walks is shown in Fig. 5d−g. The shoes are expected to be useful for workers working at night near streets, to make them visible to motorists. Additionally, this technology can be applied as a wearable device to smart shoes.
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Fig. 5. (a) Space inside shoes including battery and circuit. (b) PCB next to 1-euro coin. (c) LED
5. Conclusion
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shoe components. (d)−(g) LED lights up in the direction of stepping movement.
For workers working on roads, the incidence of traffic accidents tends to increase at night. To
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ensure that workers are visible to motorists, workers must wear garments with LED devices applied. Since these electronic devices have limitations of battery usage, it is essential to apply
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energy harvesting technology. We fabricated a small (area: 4 × 6 mm, weight: 3 mm (pressed)), lightweight (14 g) PEH with PZT ceramics and an LED switching circuit and inserted it into the sole of a shoe. The PEH was used as a sensor to detect user’s walking; at the same time, it converted mechanical energy generated by human motion into electric energy. It was found that power generated by the PEH can be used to replace battery power continuously supplied to sensors and driving circuits of commercial products. The LED switching circuit was driven by electrical energy generated by PEH and, when user motion was not detected, the battery current was cut off.
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As a result, we were able to reduce unnecessary battery usage and more than double battery usage time as compared to shoes with LEDs that are continuously lit. One limitation of this system is that this device may not meet the Rohs (Restriction of the use of Hazardous Substances in EEE)
limitation by replacing PZT with a lead-free material.
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References
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standard because it contains lead (Pb). For commercialization, it will be necessary to overcome this
Plainis S. Road traffic casualties: understanding the night-time death toll. Inj Prev 2006;12:125–38. doi:10.1136/ip.2005.011056.
[2]
Cheng X, Zhang Y, Xie G, Yang Y, Zhang Z. An ultra-low power output capacitor-less low-dropout regulator with slew-rate-enhanced circuit. J Semicond 2018;39:035002. doi:10.1088/1674-4926/39/3/035002.
[3]
Jung HJ, Song Y, Hong SK, Yang CH, Hwang SJ, Jeong SY, et al. Design and optimization of piezoelectric impact-based micro wind energy harvester for wireless sensor network. Sensors Actuators A Phys 2015;222:314–21. doi:10.1016/j.sna.2014.12.010.
[4]
Cho JY, Choi JY, Jeong SW, Ahn JH, Hwang WS, Yoo HH, et al. Design of hydro electromagnetic and piezoelectric energy harvesters for a smart water meter system. Sensors Actuators A Phys 2017;261:261–7. doi:10.1016/j.sna.2017.05.018.
[5]
Karthick A, Kalidasa Murugavel K, Kalaivani L. Performance analysis of semitransparent photovoltaic module for skylights. Energy 2018;162:798–812. doi:10.1016/j.energy.2018.08.043.
[6]
McKay IS, Wang EN. Thermal pulse energy harvesting. Energy 2013;57:632–40. doi:10.1016/j.energy.2013.05.045.
[7]
Mule AR, Dudem B, Yu JS. High-performance and cost-effective triboelectric nanogenerators by sandpaper-assisted micropatterned polytetrafluoroethylene. Energy 2018;165:677–84. doi:10.1016/j.energy.2018.09.122.
TE D
EP
AC C
[8]
M AN U
[1]
Gui P, Deng F, Liang Z, Cai Y, Chen J. Micro linear generator for harvesting mechanical energy from the human gait. Energy 2018;154:365–73. doi:10.1016/j.energy.2018.04.123.
[9]
Kim K-B, Cho JY, Jeon DH, Ahn JH, Hong S Do, Jeong Y-H, et al. Enhanced flexible piezoelectric generating performance via high energy composite for wireless sensor network. Energy 2018;159:196–202. doi:10.1016/j.energy.2018.06.048.
[10]
Brogan Q, O’Connor T, Ha DS. Solar and thermal energy harvesting with a wearable jacket. Circuits Syst. (ISCAS), 2014 IEEE Int. Symp., IEEE; 2014, p. 1412–5.
13
ACCEPTED MANUSCRIPT
Seung W, Gupta MK, Lee KY, Shin KS, Lee JH, Kim TY, et al. Nanopatterned textilebased wearable triboelectric nanogenerator. ACS Nano 2015;9:3501–9. doi:10.1021/nn507221f.
[12]
Fan K, Cai M, Liu H, Zhang Y. Capturing energy from ultra-low frequency vibrations and human motion through a monostable electromagnetic energy harvester. Energy J 2019;169:356–68. doi:S0360544218324198.
[13]
Wang W, Cao J, Bowen CR, Zhou S, Lin J. Optimum resistance analysis and experimental verification of nonlinear piezoelectric energy harvesting from human motions. Energy 2017;118:221–30. doi:10.1016/j.energy.2016.12.035.
[14]
Moro L, Benasciutti. D. Harvested power and sensitivity analysis of vibrating shoe-mounted piezoelectric cantilevers. Smart Mater Struct 2010;19. doi:10.1088/09641726/19/11/115011.
[15]
Turkmen AC, Celik C. Energy harvesting with the piezoelectric material integrated shoe. Energy 2018;150:556–64. doi:10.1016/j.energy.2017.12.159.
[16]
Cha Y, Seo J. Energy harvesting from a piezoelectric slipper during walking. J Intell Mater Syst Struct 2018;29:1456–63. doi:10.1177/1045389X17740962.
[17]
Rocha JG, Gonçalves LM, Rocha PF, Silva MP, Lanceros-Méndez S. Energy harvesting from piezoelectric materials fully integrated in footwear. IEEE Trans Ind Electron 2010;57:813–9. doi:10.1109/TIE.2009.2028360.
[18]
Zhao J, You Z. A shoe-embedded piezoelectric energy harvester for wearable sensors. Sensors (Switzerland) 2014;14:12497–510. doi:10.3390/s140712497.
[19]
Hu Y, Yi Z, Dong X, Mou F, Tian Y, Yang Q, et al. High power density energy harvester with non-uniform cantilever structure due to high average strain distribution. Energy 2019;169:294–304. doi:10.1016/j.energy.2018.11.085.
[20]
Su X, Bai G, Jia Y, Wang Z, Wu W, Yan X, et al. Flash sintering of lead zirconate titanate (PZT) ceramics: Influence of electrical field and current limit on densification and grain growth. J Eur Ceram Soc 2018;38:3489–97. doi:10.1016/j.jeurceramsoc.2018.04.007.
[21]
Woo MS, Hong SK, Jung HJ, Yang CH, Song D, Sung TH. Study on the strain effect of a piezoelectric energy harvesting module. Ferroelectrics 2013;449:33–41. doi:10.1080/00150193.2013.822765.
AC C
EP
TE D
M AN U
SC
RI PT
[11]
[22]
Guan MJ, Liao WH. On the equivalent circuit models of piezoelectric ceramics. Ferroelectrics 2009;386:77–87. doi:10.1080/00150190902961439.
[23]
Jabbar H, Hong S Do, Hong SK, Yang CH, Jeong SY, Sung TH. Sustainable micro-power circuit for piezoelectric energy harvesting tile. Integr Ferroelectr 2017;183:193–209. doi:10.1080/10584587.2017.1376964.
[24]
Das P. Maximum Power Tracking Based Open Circuit Voltage Method for PV System. Energy Procedia 2015;90:2–13. doi:10.1016/j.egypro.2016.11.165.
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Acknowledgements This research was supported by Research Program To Solve Social Issues of the National Research Foundation of Korea(NRF) funded by the Ministry of Science and ICT. (NRF-
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2015M3C8A8050335)
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Highlights Designed piezoelectric energy harvester has an area of 6 × 4 mm and height of 3 mm.
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Piezoelectric energy harvester produces 800 µW at a resistive matching point of 400 kΩ.
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Harvester works as a sensor to drive an LED switching circuit in LED shoes.
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The proposed LED shoes enhance the visibility of night workers in dark areas.
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Battery usage time can be doubled compared to LED shoes.
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