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A pedestrian floor tile energy harvesting system (PFEH) capable of accommodating harvesters of variable widths (20, 30, and 40 mm) is designed for operating Internet of Things (IoT) sensors. The electrical characteristics of the piezoelectric energy harvesters (PEHs) were measured using an impedance analyzer. The PEHs in the PFEH are displaced following a cantilever mechanism, over a distance of 4 mm. Finite element simulations using the ANSYS tool reveal similar stress distributions for various widths at the same displacement (d = 4 mm). The 40 mm PEH group (six 40 mm wide PEHs) produced the highest output power of 1.01 mWmax under identical impedance conditions (RL = 105 kΩ). The PFEH containing the 40 mm PEH group turns on a small LED display board (comprising 30 LEDs) for 2 s through an undervoltage-lockout (UVLO) module. The proposed pedestrian floor tile energy harvesting system can be employed as a power source for IoT sensors.

While there is a demand for energy harvesting in environments with water, such as rivers, lakes seas, it has been difficult to use energy harvesting, especially piezoelectricity, because of the waterproof problem and the low output scale. Here, we report a propeller-based underwater piezoelectric energy harvester consisting of a propeller, hitting sticks and a piezoelectric module. The hitting sticks spin with a rotating axis connected to a propeller rotated by water flow and hit a piezoelectric cantilever beam. Unlike previous tip mass method, a newly applied technique makes it possible to match a frequency by easily controlling the bending length of a piezoelectric module using an acrylic plate to find the maximum output power. For reliability, we performed an experiment at 1.2 m/s, which is the actual water flow rate of the Han River in South Korea, and a frequency of 24.5 Hz occurred with four hitting sticks. The frequency-matched bending length was 80 mm (acrylic plate length: 10 mm). Then, impedance matching was carried out: At a resistance of 10.8 kΩ, an output power of 17 mWrms and a power density of 57.4 mW/cm3 were obtained. This result is one of the highest results in a field of similar piezoelectric energy harvesting devices considering challenging conditions that occur in real environments. Finally, the system was applied to an LED light system, one of applications under water, and succeeded in operating a total of 972 LEDs with only one piezoelectric device. This research proves the potential and the feasibility of applying a piezoelectric energy harvesting system to a real underwater environment.

We propose a piezoelectric energy harvesting technology installed in a roadway speed bump. We have installed a module that can charge mobile phones utilizing a speed bump piezoelectric harvester (SBPH), which is easy to apply to roads. A highly integrated module with 40 piezo-generators was fixed and installed at the center of the speed bump. When a medium-sized vehicle passed the module at a speed of 30 km/h, an output voltage of 144 Vmax, output current of 45.2 mAmax, and output power of 4086.08 mWmax (6.81 W/m2) were measured at a load resistance of 2 kΩ. When the vehicle passed over the SBPH nine times, it charged a capacitor (10,000 μF) to provide 6 V for about 200 s, and the charged electrical energy was enough to operate a cellphone. The self-controlled battery charging system via electricity generated by the piezoelectric module could be applied to a speed bump installed on an actual road.

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 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 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.

Piezoelectric energy harvesting technology can be used for a wide range of purposes through the design of road energy harvesting devices. For the roadway piezoelectric energy harvester (RPEH) developed here, a piezoelectric energy harvester (PEH) is fixed at both ends to increase the tolerable load and a module durable against harsh highway environments were developed using aluminum plates, steel plates, and polypropylene bars. A maximum voltage of 66 V, maximum current of 30.37 mA and maximum output power of 830 mW were measured with 2 mm of displacement at 15 Hz using the RPEH (50 cm × 20 cm) with 80 PEH units connected in parallel. On an actual high-speed road, measurements from a medium-sized vehicle which passes the RPEH at a speed of 90 km/h record an output voltage of 46.52 Vmax, output current of 93.04 mAmax, and power of 4.3 Wmax (power density: 43.0 W/m2) at a load resistance level of 0.5 kΩ. In an actual roadway environment, the electrical energy generated by the RPEH is sufficient to operate a temperature sensor and to transmit data wirelessly.

The purpose of this research was to demonstrate a road-compatible piezoelectric energy harvester (RPEH) that uses the energy to power self-powered sensors and vehicle indicators. The demonstrated RPEH (20 × 50 × 10 cm3) with 80 piezoelectric devices can efficiently convert mechanical energy stemming from the small vertical displacement (1.45 mm) from vehicles into electrical power. The maximum voltage is 113.5 V, the maximum current is 25.71 mA, and the maximum power is 661 mW (6.61 W/m2) at an impedance resistance level of 0.9 kΩ under a z-axial load. The high-power RPEH was initially installed at a highway rest area. The measured output performances of the installed module on the actual roadway in the test setup area were a maximum voltage of 196 V and output power of 2080 mW (20.79 W/m2) at a vehicle speed of 30 km/h. Tests of the RPEH module demonstrate its ability to measure temperature, strain, and leakage values in real time and the generated energy provides sufficient power to illuminate LED indicators. It was also found that the z-axial loaded piezoelectric devices with a two-end fixed beam provide high output power with low levels of vertical displacement, making it highly efficient and durable for actual highway energy-harvesting applications.

For the development and application of wearable electronics, a transparent and flexible piezoelectric sensor (TFPS) system is an important component considering the physical motion energy of the human body. This work newly proposes a transparent and biocompatible boron nitride nanosheet (BNNS) material with a TFPS device. The TFPS device is based on BNNS as a piezoelectric active component and PDMS as a flexible element. The device is able to generate electrical energy from mechanical push force and human movement; it has an output voltage of 22 V, output current of 75 nA, output power of 40 µW (power density: 106 μW/cm3), and energy conversion efficiency of 12.6%. In addition, the TFPS device based on BNNS (1.0 wt%) is proposed as a significant step toward devices which are self-powered by the biomechanical movement of the human foot, neck, wrist, and knee, converted into electric energy in various signal forms. It will be deployed as a body-movement sensor.

A self-powered energy harvester for real roads to predict and detect black ice formation and pinpoint dangerous road sections was developed. An open-type piezoelectric device was developed for a high-efficiency module to achieve uniform stress distribution for enhanced energy harvesting performance by free-fixed-end type central strike mechanism. The output performance of the open-type device was 80% higher than that of the closed-type device. A uniform stress distribution road piezoelectric generator (URPG) with 120 open-type devices was installed on real roads. The URPG showed output power performance of up to 2.38 mW/cm3 when a vehicle passed once under the condition of being buried 2.5 cm below the road surface. The URPG can operate a wireless temperature sensor monitoring system for 83 s and charge a cellphone battery for 53 s. The developed self-powered energy harvesters can be used to reduce accidents caused by black ice on real roads.

To meet the increasing demand for electric vehicles, this paper presents a novel concept to enhance the energy generation performance of piezoelectric energy harvesters used as charging stations on roads. A lever-type piezoelectric energy harvester with a deformation-guiding mechanism was designed and fabricated to overcome the existing limitations of low electrical output and low durability of piezoelectricity under extremely low road displacement conditions of 1 mm. The proposed harvester achieved a maximum output power of 60.3 mW at a load resistance of 50 kΩ under an input displacement of 1 mm. Thus, the module’s electrical performance was significantly higher than that obtained in previous similar studies. The proposed harvester had 467% higher output power than the previously proposed vibration type road energy harvester. For the energy storage test, a 0.08 F supercapacitor was charged up to 5.09 V (1 J) in 170 min. The results prove that the energy generated by the proposed harvester can be potentially used as a power source for electric vehicles on smart roads beyond the power supply of various sensor systems on the road.