The Study On Output Characteristics Of Piezoelectric Cantilever Beams Array

As a kind of widespread energy in life and actual project, the vibration energy has a diversity of form. Gathering the energy of vibration source reasonably and efficiently provides the possibility for the self-power supplying of electronic equipment. Piezoelectric vibration energy collection becomes one focus of the researches on the vibration energy harvesting, because of its advantages like high electromechanical conversion coefficient, self-powered, suitability for MEMS. Due to the low vibration frequency, piezoelectric cantilever beam is suitable for collecting vibration energy that exist in the actual environment. So the piezoelectric cantilever beam gets some application in the field of low power consumption. But due to the instability of the environment vibration and only the condition of resonance can ensure the output power level of piezoelectric energy collection, a single piezoelectric beam of energy harvesting system can only meet the low power consumption of electronic equipment. In order to improve the power output and meet the demand of more power electronic devices, the study of piezoelectric energy harvesters array has a great significance.Based on the piezoelectric cantilever beam of energy harvester, this paper adopted the method of combining theoretical analysis and experimental verification to study the piezoelectric energy harvesters array for the purpose of increasing the output power and widening the operation frequency band.First of all, based on the the lumped equivalent circuit model of piezoelectric cantilever beam, this paper adopted the method of superposition theorem to conduct theory analysis and experimental verification for parallel, series and series-parallel mixed array, and then pointed out the mixed connection can satisfy the impedance matching when load changing. Secondly, the piezoelectric beams array with rectifiers was simulated, including the affect of connection before rectifying and rectifying before connection on the output power of array. In the end, the influence of the differences among resonance frequencies, output voltages amplitude of beams and the phase difference among excitation on output power of array was studied through simulation and experiments respectively.The simulation and experimental results showed that:(1) The array of N beams can generate the maximum output power at the optimal load when series, parallel or mixed connection. The maximum output power of array is N times that of a single beam. But the optimal load of serial beams and parallel beams is N and 1/N times of a single beam, respectively. However, the mixed connection can implement the load matching by changing the number of series and parallel connections and sequence of series and parallel. (2) Whether multiple rectifiers were applied or single rectifier was applied, the maximum output power is the same, but the former matching impedance is less than the latter matching impedance. (3) The piezoelectric beams with different resonant frequencies can be connected to widen the frequency band or improve the output power. But on the condition that the parameters of dimension and material are same with those of this paper and the bandwidth of beam is 3.5Hz, the most important premise is that the ratio △f/BW should be less than 0.657 for the beams in parallel and 2.571 for the beams in series. When the ratio △fr/BW exceeds the limits but closed to the boundaries of the limits or there exists phase difference, the beams can still be connected via separate rectifying circuits to load to widen the band. (4) The piezoelectric beams with different output voltages amplitude can still be connected to improve the output power. But the amplitude ratio of beams must be greater than 6.2/15.0 and less than 15.0/6.2 when beams in series or in parallel. In this condition, the output power of array will be higher than that of a single beam. (5) The piezoelectric beams with different phase of output voltages can still be connected to improve the output power. When the array consisted of 6 or 3 beams, the phase difference must be less than 27° and 54°, respectively, so that the output power of array will not be decreased by 50%.