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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.

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.

Piezoelectric energy harvesting generally demonstrates low output power because its output current is low compared to its high output voltage. The low current and high impedance limit the applications of piezoelectric energy harvesting systems. Thus, it is necessary to increase the output current and reduce the internal impedance. This study presents the fabrication of multilayer piezoelectric thick films with high output currents. Single-layer and five-layer piezoelectric devices are prepared using the tape-casting process. The material properties of each lead zirconate titanate (PZT) ceramic are measured using an impedance analyzer and a d33 meter. The electrical properties of the piezoelectric devices were evaluated by a controllable strain module using vibration exciter. The capacitance of the single-layer device was 7.33 nF and that of the five-layer device was 241.04 nF, which was 32.88 times higher than that of the single-layer device. The open circuit voltage of the five-layer device decreased 6.09 times compared to the single-layer, but the short circuit current increased 5.30 times. The impedance matching load of the five layer device for maximum power transfer was averagely 34.05 times smaller than that of single-layer. Under maximum power transfer conditions, the current of the five-layer PZT device was 6.61 times larger than the single-layer, even though the output power of both devices was similar. Because of this capacitance and current increase, the energy stored in the 220 μF capacitor for 10 s using the five-layer device was 920% larger compared to the energy stored using a single-layer.

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.

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.

Piezoelectric devices previously studied usually generated a single voltage to power an electronic device. However, depending on the user’s purpose, the electronic device may need dual power supply. Here, we report a self-powered bipolar voltage generator using a piezoelectric energy harvester with two piezoelectric devices. When a force is applied to the piezoelectric energy harvester, the two piezoelectric devices separately supply positive and negative voltages to the operational amplifier that requires dual power supply to amplify an AC signal that have positive and negative polarity. At the same time, the harvester supplies additional power to an electronic device through a DC-to-DC converter with an output voltage of 3.3 V. This technique proves the feasibility of applying the piezoelectric energy harvester to operational amplifying systems in the field of sound, earthquake, and sonar that require both bipolar and single voltages without external power sources.