The polymer crystallization process, promoting the formation of ferroelectric β-phase, is essential for developing polyvinylidene fluoride (PVDF)-based high-performance piezoelectric energy harvesters. However, traditional high-temperature annealing is unsuitable for the manufacture of flexible piezoelectric devices due to the thermal damage to plastic components that occurs during the long processing times. In this study, we investigated the feasibility of introducing a flash lamp annealing that can rapidly induce the β-phase in the PVDF layer while avoiding device damage through selective heating. The flash lightirradiated PVDF films achieved a maximum β-phase content of 76.52% under an applied voltage of 300 V and an on-time of 1.5 ms, a higher fraction than that obtained through thermal annealing. The PVDF-based piezoelectric energy harvester with the optimized irradiation condition generates a stable output voltage of 0.23 V and a current of 102 nA under repeated bendings. These results demonstrate that flash lamp annealing can be an effective process for realizing the mass production of PVDF-based flexible electronics.

In the 4^th industrial age, electronic devices are becoming smaller and lighter with a low power consumption to overcome spatial limitation. The piezoelectric energy harvesters can convert mechanical kinetic energy into electric energy; thus, enabling the operation of small electronic devices. Recently, various piezoelectric harvesters have been reported and the electric output from these harvesters could be anticipated by theoretical analysis methods. For example, COMSOL Multiphysics software provides a theoretical simulation of piezoelectric effect with a combination of mechanical and electrical phenomena in the piezoelectric materials. This article introduces a brief modeling of piezoelectric harvester to investigate mechanical stress and electrical output of harvesting devices by the COMSOL Multiphysics software.

The piezoelectric properties of 0.65Pb(Zr_1-xTi_x)O₃-0.35Pb(Zn_1/6Ni_1/6Nb_2/3)O₃ (PZT_x-PZNN) ceramics with 0.530≤ x≤0.555 were investigated for application to piezoelectric energy harvesters. Although a morphotropic phase boundary (MPB) was found at approximately x＝0.545, the ceramic with the highest figure of merit (FOM) (d₃₃×g₃₃) was observed at a composition of x＝0.540. Values of this figure of merit, d₃₃×g₃₃, of 19.6 pm²/N and 20.2 pm²/N were obtained from PZT_0.540-PZNN ceramics sintered at 920℃ and 950℃, respectively. A high output power of 937 μW and a high power density of 3.3 mW/cm³ were obtained from unimorph-type piezoelectric energy harvesters fabricated using PZT_0.540-PZNN ceramic sintered at 920℃ for 4h.

A unimorph piezoelectric cantilever generator with an interdigitated electrode (IDE) was developed for vibration energy harvester applications driven in the longitudinal mode. Hard lead zirconate titanate (PZT) ceramic with a high Q_m of 1,280 was used as the piezoelectric active material. Ten PZT sheets produced by tape casting were laminated and co-fired with an Ag/Pd IDE at 1,050℃ for 2 h. The approximately 280 μm-thick co-fired PZT laminate with the IDE was attached to a stainless steel substrate with an adhesive epoxy for the fabrication of an IDE unimorph cantilever. Its energy harvesting characteristics were evaluated: an output power of 1.1 μW at 120 Hz across the resistive load of 700 k□ was obtained, corresponding to a normalized power factor of 4.1 μW/(G²·cm³).

A piezoelectric cantilever energy harvester (PCEH) driven in longitudinal (3-3) vibration mode was fabricated, and its electrical properties were evaluated by varying the resistive load. A commercial PZT piezoelectric ceramic with a high piezoelectric charge constant (d₃₃) of 520 pC/N and the interdigitated (IDT) electrode pattern was used to fabricate the PCEH driven in longitudinal vibration. The IDT Ag electrode embedded piezoelectric laminates were co-fired at 850℃ for 2 h. The 3-3 mode PCEH was successfully fabricated by attaching the piezoelectric laminates to a SUS304 elastic substrate. The PCEH exhibited a high output power of 3.8 mW across the resistive load of 100 kΩ at 100 Hz and 1.5 G. This corresponds to a power density of 10.3 mW/cm³ and a normalized global power factor of 4.56 mW/g²·cm³. Given the other PCEH driven in transverse (3-1) vibration mode, the 3-3 mode PCEH could be better for vibration energy harvesting applications.

Recently, energy harvesting technology is increasing due to the fossil fuel shortages. To compensate problem of low generating power than other energy harvesters, many researchers have studied about piezoelectric harvester for obtaining high output. In this paper, four kinds of unimorph based piezoelectric harvesters were proposed and its generating characteristics were studied. Each of the piezoelectric harvesters has three, four, and six unimorph arms, respectively, and the arms are symmetrically arranged from one central point. The centrosymmetric structure of the harvesters guarantees more stable and multiplied generation than a cantilever-type harvester since the arms of the harvester resonate at same frequency. Resonance frequency, output voltage, displacement, and stress characteristics of the generator were analyzed by using a FEM (finite element method) program. Harvesters were fabricated on the basis of analysis results. Experimental results were compared with simulated results.

Piezoelectric thick films of a soft Pb(Zr,Ti)O₃ (PZT) based commercial material were produced by a conventional tape casting method. Thereafter, the interdigitated (IDT) Ag-Pd electrode pattern was printed on the 25 ㎛ thick piezoelectric film at room temperature. Co-firing of the 10-layer laminated piezoelectric thick films was conducted at 1,100℃ and 1,150℃ for 1 h, respectively. Piezoelectric cantilever energy harvesters were successfully fabricated using the IDT electrode pattern embedded piezoelectric laminates for 3-3 operation mode. Their energy harvesting characteristics were investigated with an excitation of 120 Hz and 1 g under various resistive loads (ranging from 10 kΩ to 200 kΩ). A parabolic increase of voltage and a linear decrease of current were shown with an increase of resistive load for all the energy harvesters. In particular, a high output power of 3.64 mW at 100 kΩ was obtained from the energy harvester (sintered at 1,150℃).

We present the results of a study of a piezoelectric generator that generates electricity by the application of tension to an element. A device is named “EYE-type generator”. The EYE-type generator consists of a rectangular ceramic and two elastic body plates that are attached to upper and lower surfaces of a ceramic. If tension is applied to both ends of the elastic body, that tension is transformed to pressure on the ceramic through a change in the form of the elastic body, causing a piezoelectric effect whereby electricity is generated by the ceramic. This generator is relatively durable because a forces are not applied directly to the ceramic. We examined dependencies of the generator’s output characteristics on the size of the ceramic and elastic body. A resonance and output characteristics were analyzed by using a finite element method. The generator was fabricated based on results of the analysis, and this was attached to a frequency-controllable vibrator to measure the output characteristics. The measured results were compared with results of the simulation, and the results pointed to the practicality of the design.

Recently, energy harvesting technology is increasing due to the fossil fuel shortages. Energy harvesting is generating electrical energy from wasted energies as sunlight, wind, waves, pressure, and vibration etc. Energy harvesting is one of the alternatives of fossil fuel. One of the energy harvesting technologies, the piezoelectric energy harvesting has been actively studied. Piezoelectric generating uses a positive piezoelectric effect which produces electrical energy when mechanical vibration is applied to the piezoelectric device. Piezoelectric energy harvesting has an advantage in that it is relatively not affected by weather, area and place. Also, stable and sustainable energy generation is possible. However, the output power is relatively low, so in this paper, newly designed honeycomb shaped piezoelectric energy harvesting device for increasing a generating efficiency. The output characteristics of the piezoelectric harvesting device were analyzed according to the change of parameters by using the finite element method analysis program. One model which has high output voltage was selected and a prototype of the honeycomb shaped piezoelectric harvesting device was fabricated. Experimental results from the fabricated device were compared to the analyzed results. After the AC-DC converting, the power of one honeycomb shaped piezoelectric energy harvesting device was measured 2.3[mW] at road resistance 5.1[KΩ]. And output power was increased the number of harvesting device when piezoelectric energy harvesting device were connected in series and parallel.

In this paper, we designed and fabricated electromagnetic induction based scaffold type energy harvester. For energy harvesting, mechanical energy of vertical motion is transferred to rotational energy using rack gear and multiplying gear was used to maximize energy transfer. To optimize design parameters, physical structure of energy harvester was modeled using finite element method. The effect of multiplying gear ratio and frequency levels of applied mechanical energy on energy generation efficiency are analyzed by computer simulation and experimental test. Experimental results showed that maximum 25.36 W of electric power can be achieved at the frequency of 2 Hz and 1:77 of gear ratio with only 5 mm of vertical changes on scaffold structure.

Recently, energy harvesting technologies are considered as the great alternatives to reduce the dependency on secondary batteries. In this paper, we proposed PCB type energy harvester which can be directly integrated with other electronic components on same board. To form the three dimensional coil structure, two PCBs with patterned metal lines are solder bonded. For magnetic induction, inside of coil structure was filled with magnetic substance and rotary motioned external magnets are applied to near the harvester. The effects of metal wire width on PCB, thickness of magnetic substance, and frequency of rotary motion on energy harvesting performance are analyzed by computer simulation and experiments. Experimental results showed 29.89 ㎼ of power generation performance at the frequency of 5.2 Hz and it is shown that designed harvester can be effectively applied on vibration environment with very limited frequency.

In this study, KNbO3-substituted (Li,Na,K)(Nb,Sb,Ta)O3 ceramics were investigated to develop Pb-free composition ceramics for multilayer actuator and energy harvester applications. The X-ray diffraction analysis indicated that all samples were pure perovskite phase and no secondary phase was found. A tetragonality as a function of KNbO3 substitution showed the maximum value at 1.5 mol% KNbO3 and then decreased. The SEM image analysis showed the maximum grain size of 3.14 ㎛ at 1.5mol% KNbO3. In the composition ceramics with 1.5 mol% KNbO3 sintered at 1,100℃, excellent properties of density= 4.75 g/cm3, electromechanical coupling factor (kp)= 0.50 and piezoelectric constant(d33)= 290 pC/N were obtained, respectively, suitable for piezoelectric actuator and energy harvester applications.

Spring supported piezoelectric cantilever structures (SPCS) were fabricated for vibration-based energy harvester application. We selected four elastic springs (A, B, C, and D type) as cantilever`s supporter, each elastic spring has a different spring constant (S). The C type of SPCS (SC: 4,649 N/m) showed a extremely low resonance frequency of 81 Hz along with the highest power output of 38.5 mW while the A type of SPCS (SA: 40,629 N/m) didn`t show a resonance frequency while. Therefore, it is considered that the lower spring constant lead to a lower resonance frequency of the SPCS. In addition, a tip mass (18 g) at one end of the SPCS could further reduce the resonance frequency without heavy degradation of power output.

Owing to the rapid growth of mobile and electronic equipment miniaturization technology, the supply of micro mobile computing machine has been fast raised. Accordingly they have performed many researches on energy harvesting technology to provide promising power supply equipment to substitute existing batteries. In this paper, in order to have low resonance frequency for piezoelectric energy harvester, we have tried to make it larger than before by adopting nickel that has much higher density than silicon. We have applied it for our energy harvesting actuator instead of the existing silicon based actuator. Through such new concept and approach, we have designed energy harvesting device and made it personally by making with micromachining process. The energy harvester structure has a cantilever type and has a dimension of 10×2.5×0.1 mm3 for length, width and thickness respectively. Its electrode type is formed by using Au/Ti of interdigitate d33 mode. The pattern size and gap size is 50 μm. Based on the measurement of the nickel-based piezoelectric energy harvester, it is found to have 778 Hz for a resonant frequency with no proof mass. In that resonance frequency we could get a maximum output power of 76 μW at 4.8 MΩ being applied with 1 g acceleration.

Nowadays, the increasing demands upon mobile devices such as wireless sensor networks and the recent advent of low power electrical devices such as MEMS make such renewable power sources attractive. A vibration-driven MEMS lead zirconate titanate Pb(Zr,Ti)O3 (PZT) cantilever device is developed for energy harvesting application. This paper presents a piezoelectric based energy harvester which is suitable for power generating from conventional vibration and has in providing energy for low power electronic devices. The PZT cantilever is used d33 mode to get the electrical power. The PZT cantilever based energy harvester with the dimension of 7 mm×3 mm×0.03 mm is fabricated using micromachining technologies. This PZT cantilever has the mechanical resonance frequency with a 900 Hz. With these conditions, we get experimentally the 37 uW output power from this device with the application of 1g acceleration using the 900 Hz vibration. From this study, we show the feasibility of one of energy harvesting candidates using PZT based structure. This PZT energy harvester could be used for various applications such a batteryless micro sensors and micro power generators.