| With the rapid development of new information technologies such as the Internet of Things and Artificial Intelligence,the issue of power supply for low-power electronic devices has become a major limiting factor for their large-scale and special environment applications.Therefore,finding a convenient and reliable solution has become an urgent problem to be solved.Piezoelectric energy harvesters are devices that can convert rich mechanical energy in the environment into electricity,enabling low-power electronic devices to be self-powered.Due to its simple structural design and high energy density,piezoelectric energy harvesters have been widely studied.Currently,research on piezoelectric energy harvesters mainly focuses on improving output performance,widening frequency response width,and increasing environmental adaptability,which are the main challenges faced by the development of piezoelectric energy harvesters.This paper starts with finite element simulation and experimental research methods,proposing a trapezoidal beam structure to improve the output voltage and power of the energy harvester.Secondly,a multi-modal structure and frequency conversion mechanism are introduced to lower the working frequency of the energy harvester,making it more adaptable to low-frequency environments and thus expanding its application scenarios.In addition,we also improved the working temperature of the energy harvester by using high-temperature piezoelectric ceramics instead of traditional lead zirconate titanate ceramics,to adapt to special high-temperature vibration environments such as automotive,aerospace,and geological exploration.The main contents are as follows:(1)The use of a trapezoidal beam structure improved the output performance of the piezoelectric energy harvester in low-frequency vibration environments.The simulation results indicate that the stress distribution of the rectangular cantilever beam is extremely uneven,with the highest stress occurring at the fixed end of the cantilever beam and sharply decreasing along the length direction of the beam.The trapezoidal beam structure can reduce the area of the small stress area inside the cantilever beam to improve stress utilization and thus enhance the output performance of the energy harvester.In the experiment,a trapezoidal beam piezoelectric energy harvester with a total thickness of 100 μm was obtained by mechanical thinning.The mechanical thinning reduced the structural stiffness of the energy harvester,thereby lowering its operating frequency.The experimental results showed that the trapezoidal beam piezoelectric energy harvester can generate an open-circuit voltage of 5.4 V and an output power of 0.2 mW under lowfrequency(35.2 Hz)and small excitation acceleration(5m/s2)vibration excitation,which can directly light up four light-emitting diodes in real-time and serve as a power supply device for wireless sensor networks in low-frequency mechanical vibration environments.(2)A multi-modal piezoelectric energy harvester composed of a main beam and two novel L-shaped wing beams was designed.The effects of the wing beam shape and mass block configuration on the number of resonance frequencies and output voltage of the energy harvester were studied through finite element simulation and experimental testing.The experimental results show that the introduction of L-shaped wing beams not only lowers the operating frequency of the energy harvester,but also widens its frequency response bandwidth,allowing three resonance peaks to appear in the lower frequency range of 9 to 20 Hz.The multi-modal harvester generated output voltages of 9.2 V,4.5 V,and 3.0 V at the resonant frequencies of 9.2 Hz,14.3 Hz,and 18.3 Hz,respectively.The multi-modal energy harvester has the potential to work in a wide frequency band,low frequency,and low amplitude vibration environments.(3)This paper proposes a magnetically excited rotational piezoelectric energy harvester based on a trapezoidal cantilever beam in order to further reduce the operating frequency of the piezoelectric energy harvester.The trapezoidal beam rotational piezoelectric energy harvester can generate a voltage greater than 2 V within a low frequency range of 5 to 13 Hz,with a maximum output voltage of 4.1 V,which is about 1.4 times higher than that of the rectangular beam rotational piezoelectric energy harvester.The maximum output power is 152μW,which is 1.6 times higher than that of the rectangular beam rotational piezoelectric energy harvester.By using the trapezoidal cantilever beam magnetically excited rotational piezoelectric energy harvester to harvest wind energy,the harvester was able to generate an average output power of 0.64 mW/cm2 and continuously light up a commercial LED,verifying the feasibility of the trapezoidal beam rotational energy harvester for self-powering low-power electronic devices.(4)A piezoelectric ceramic material with a composition of 0.34BiScO3-0.61PbTiO30.05Pb(Sn1/3Nb2/3)O3(PSN-BS-PT)was prepared using the solid-state reaction method.This ceramic material has the advantages of high Curie temperature(380℃)and high piezoelectric constant(d33 value of 726 pC/N at a temperature of 200℃).This paper investigated the electrical output performance of an energy harvester based on the PSNBS-PT piezoelectric ceramic at room temperature and high temperature.Even at a high temperature of 200℃,the cantilever-type energy harvester made of PSN-BS-PT ceramic can generate an open-circuit voltage of 9.0 V and an output power of 75.6 μW under 2.5 m/s2 acceleration.To reduce its operating frequency,a mechanical impact piezoelectric energy harvester based on PSN-BS-PT piezoelectric ceramic was also designed in this paper.The resonance frequency of this mechanical impact energy harvester is 16 Hz,which is one-fourth of the natural frequency of the cantilever-type energy harvester.Under vibration excitation with a frequency of 16 Hz and acceleration of 3 m/s2,this energy harvester can output an open-circuit voltage of 15 V and an output power of 168μW.The results show that the energy harvester based on PSN-BS-PT piezoelectric ceramic has good frequency response to low-frequency vibration sources(vibration source frequency<20 Hz)in a higher temperature range(100℃ to 250℃),and has the potential to power small portable devices and wireless sensor nodes.(5)To further explore the working conditions of piezoelectric energy harvesters at high temperatures,this paper investigates the electrical output characteristics of a cantilever-beam high-temperature vibration energy harvester based on chromium iondoped Bi3TiTaO9 piezoelectric ceramics(Bi3Ti0.98Cr0.02TaO9)within the high-temperature range of room temperature to 400℃.It is found that the output voltage of the energy harvester rapidly decreases when the ambient temperature exceeds 250℃.To address this issue,this paper further designs an energy harvester based on tungsten ion-modified Bi3TiTaO9 piezoelectric ceramics(Bi3Ti0.97W0.03TaO9).Experimental results show that the high-temperature energy harvester based on tungsten ion-modified Bi3TiTaO9 can output a stable voltage signal within the temperature range of room temperature to 300 ℃.Even at an ambient temperature of 400℃,the output voltage of the energy harvester can still reach 6.0 V. |
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