In this paper, a high efficiency multi-piezoelectric harvesting circuit based on synchronous charge extraction (EM-SECE) is presented. The proposed circuit utilizes an improved positive and negative peak detection structure so that the phase difference between the peak voltage of the piezoelectric transducer and the switching action is reduced, and then the energy harvesting efficiency of the single piezoelectric transducer is improved. Further, using time division multiplexing of single inductor, multi-piezoelectric energy harvesting is achieved. The proposed circuit is of self-powered characteristic with no rectifying bridge structure. The experimental results show that under the same experimental condition, the harvesting power of the EM-SECE circuit for single piezoelectric transducer is 3.09 times than the maximum power of the standard energy harvesting circuit; with only one inductor, the harvesting power of the EM-SECE circuit with double piezoelectric transducers is 0.97 times of the harvesting power sum of two piezoelectric transducers.

The change of fixed mode of piezoelectric energy harvester(PEH) will directly affect its power generation performance, while the traditional cantilever beam fixed mode(CBFM) has a narrow frequency range and poor power generation performance. In order to maximize the power generation performance of the PEH, an intermediate beam fixed mode(IBFM) suitable for piezoelectric plates of any size is proposed. Meanwhile, the power generation performance of the two fixed modes of the CBFM and IBFM after adding different mass blocks has been studied through simulation and experiment methods. The results show that compared with the CBFM, the maximum open circuit voltage and maximum generated power of the PEH under unit acceleration are increased by 95.19% and 205.88%, respectively at the intersection frequency band. In addition, the electromechanical coupling coefficient(EMCC) is increased by 11.60% on average. Therefore, the proposed method can provide guidance for the selection of fixed mode of the PEH at different frequency bands.

In order to harvest the acoustic energy in the environment efficiently, an acoustic energy harvesting system is proposed with piezoelectric transducer array, straight tube resonator and energy harvesting circuit. When the acoustic wave transmits into the straight tube resonator, the resonance standing wave is generated in the tube, and excites the piezoelectric transducers; then the acoustic energy is converted into electrical energy. An energy harvesting circuit is designed and analyzed theoretically with simulation. The relationship between the number of piezoelectric chips, the frequency of acoustic waves, the acoustic pressure level and the output voltage is studied with experiments. The output voltage and power are analyzed with the change of load resistance. Experimental results show that the proposed system can harvest the acoustic energy in different frequencies, and the harvested power achieve the maximum at the sound frequency of 96Hz. Without using the energy harvesting circuit, the maximum output AC voltage effective value is 12.9V and the maximum output AC power is 799μW at the incident acoustic pressure level of 110dB. When the proposed energy harvesting circuit is applied, the maximum output DC voltage is 64.2V and the maximum output DC power is 473μW. The acoustic energy harvesting system can not only harvest acoustic energy, but also can power the micro electronic systems such as wireless sensor nodes.

Due to the large size, environmental pollution and requirement of periodically replacement, the classic batteries are no longer suitable for field work nowadays. Micro-wind energy harvesting by vortex-induced vibration can harvest the wind energy, and power the micro electric equipment such as wireless sensor nodes. Derived from the Buck-Boost circuit, a new energy interface circuit is designed for the micro-wind energy harvesting device. After theoretical analysis and simulation, there is an optimal duty cycle in the proposed circuit, which corresponds to the maximum output power. A control algorithm is developed with LabVIEW platform. Experimental results show that the proposed circuit and control algorithm can achieve the optimal duty circle, and keep the micro-wind energy harvesting outputs at its maximum power.

The length of the cantilever beam electrode is one of the important factors affecting the characteristics of piezoelectric vibration energy harvesting. The energy distribution function was proposed to describe the relationship between electric field energy and electrode ratio during the vibration energy harvesting, and the nature of the effect of electrode ratio on electrical characteristics was also explored. It is pointed out that the optimal electrode ratio of the rectangular and triangular cantilever beams to obtain the maximum power is between 50%~60%. In addition, the charge is redistributed with energy loss during vibration energy harvesting,  and the energy loss is lowest at the optimal electrode and greater when the electrode ratio reaches 100%. Both the simulation and experiment results show that the optimal electrode ratio of the rectangular and triangular cantilever beams is in accordance with the optimal value obtained by the energy distribution function, and it is feasible to increase the output power by optimizing the electrode-length.

According to the one-dimensional equivalent circuit of piezoelectric thickness-mode transducer,transmission line theory and ultrasonic propagation theory,a PSPICE equivalent circuit model was proposed.The model can model and simulate the mechanical loss process of piezoelectric transducer by using lossy transmission line.By using this method,the PSPICE equivalent circuit modeling and simulation of the electro-acoustic conversion channel of the ultrasonic wireless transmission system was carried out.The fast and reliable calculation results were obtained,and the circuit design process of the ultrasonic wireless energy transmission system was simplified.This method provides an effective and reliable theoretical and technical basis for the study of ultrasonic wireless transmission system.