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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 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.

Piezoelectric energy harvesting has gained attention owing to its effectiveness at harvesting electrical energy from various energy sources. Especially, with the increasing demand for smart highways, piezoelectric energy harvesting from road traffic has been increasingly studied. However, existing piezoelectric road-energy harvesters have limitations of low electrical output and low durability. A novel piezoelectric energy harvester was designed and fabricated to overcome these limitations. The proposed harvester had a maximum output power of 3.93 mW at a load resistance of 130 kΩ under an input displacement of 2.5 mm. The proposed harvester had 4.2 times more output power than the existing vibration-type road energy harvesters and was much less susceptible to destruction-in contrast to existing impact-type road-energy harvesters. The proposed road-energy harvester can be used as a power source for wireless sensor networks in smart highways.

In this study, a nonlinear piezoelectric energy harvester (PEH) with a ball tip mass was designed and fabricated for broadband energy harvesting. The proposed nonlinear PEH exhibits two resonant frequencies (5 and 15 Hz) and can harvest a considerable amount of electrical energy, whereas a conventional PEH with a rigid tip mass only exhibits one (15 Hz). The minimum acceleration that can induce nonlinearity in the proposed PEH was determined to be 3 m s –2 . In order to maximize the electrical output of the proposed PEH, 0.1 mm was selected as the optimal vibration amplitude of the ball among three options (0.1, 0.5, and 1.0 mm). The maximum output power of the proposed PEH was measured as 13.5 mW at 15 Hz and at a load resistance of 30 kΩ, which is the matching load resistance calculated and verified with the experimental result. The output power of the proposed PEH was measured to be 1.8 mW at 5 Hz and 45 kΩ, whereas that of the conventional PEH at 5 Hz was 0.03 mW, implying that the proposed PEH possesses one additional resonant frequency over the conventional PEH. In addition, the proposed PEH performs significantly better than the conventional PEH in terms of broadband energy harvesting. At a power level of 100 μW, the proposed PEH at 3 m s –2 provides a bandwidth of 20 Hz, which is more than 133% wider than the 15 Hz provided by the conventional PEH. By utilizing the nonlinearity with a ball tip mass, the PEH vibration is capable of harvesting considerable electrical energy from more than two resonant frequencies.

The purpose of this study is designing and examining impact-based piezoelectric road energy harvesters as power sources of a variety of sensors and smart highways. The impact-based piezoelectric road energy harvesters (15 × 15 × 9 cm3) developed in this research can convert the input energy efficiently into electrical power. The output power of the proposed harvester is significantly higher than that of the existing harvesters. Moreover, in previous studies, simple experiments were performed for measuring the output power of a road energy harvester, with no consideration for the practical road conditions. In this study, the output power is measured using machines that can simulate the practical road conditions. First, the output power of the harvester is measured using a universal testing machine (UTM) that can apply an axial load with a controlled loading frequency. Then, a third-scale mobile loading simulator (MMLS3) that can simulate practical traffic load on a lab scale is used. As a result, the maximum output power of the road energy harvester is 483 mW(21.47 W/m2).

We propose a smart pen piezoelectric energy harvester (SP-PEH) that simultaneously produces energy in both d31 and d33 modes during writing. Two piezoelectric devices were installed in SP-PEH, a cantilever type device and an impact type device. With preliminary Fast Fourier Transform analysis on the writing conditions, power generation tests were conducted. For cantilever type, the harvester generated instantaneous maximum power of 1.5 μW (3 MΩ) at a writing frequency of 3 Hz (most frequent value during actual writing) and a writing length of 12.5 mm. For impact type, it generated 2.6 μW at a load resistance of 5 MΩ. With those power generations, the stored energy in the two capacitors were 1 μJ (47 μF, cantilever type) and 0.05 μJ (220 μF, impact type) separately for 10 s, and a total energy of 3.1 μJ (about 3 times higher than sum of two types) was stored in an actual writing test because of movement in all directions rather than just a single direction. The proposed device successfully turned on a ZigBee wireless sensor after 10 s, which confirmed the possibility of the battery-less smart pen that harvests energy and collects and transmits environmental and biological data from writing.

We propose a pavement block piezoelectric energy harvester (PBPEH) that can be installed in an actual walkway. We developed an Internet of Things (IoT) system that can power the walkway signal indicator (delineator) and also collect environmental data (such as humidity and temperature) near the walkway utilizing the PBPEH, without a battery. A highly integrated module with 24 piezoelectric devices were fixed inside the PBPEH. Under maximum weight condition, that is, in case of a person weighing 100 kg passing over the module, an output voltage of 38.52 Vmax, current of 3.85 mAmax, and power of 148.3 mWmax (3.7 W/m2) were generated at a load resistance of 10 kΩ. Energy storage test as applied to realistic conditions, that is, when a 60 kg person (average weight condition) passes over the module 10 times it charged a capacitor (1000 μF) to 55.6 mJ. As a result, it successfully turned on a delineator installed on an actual walkway after 4.8 s and powered the IoT sensor system without an external energy source.

Many researches with regard to piezoelectric energy harvesting from pressure exerted by passing cars have been conducted. In this paper, an impact-based road energy harvester as buried-type is developed with the method that the piezoelectric device is deformed directly by the pressure due to passing cars. Based on this, the developed road energy harvester is made to the size of 30 × 30 × 9 cm3. The performance of this new road energy harvester is measured with UTM (Universal Testing Machine) and MMLS3 (Third-scale Model Mobile Load Simulator) which can apply loads similar to the actual traffic loads to the harvester in lab-scale. Finally, the buried harvester is experimented with APT (Accelerated Pavement Testing).