Study On Low Frequency Piezoelectric Harvesters

The developments of new generation sensor technology rely significantly on the improvement of wireless power supply technology in microelectronic devices. In fact, energy to supply microelectronic devices can be scavenged directly from latent power source of environment. The device which picks up energy from environment is called"energy harvester". The piezoelectric energy harvester has the best performance among common energy harvesters (electrostatic energy harvesters, electromagnetic energy harvesters and piezoelectric energy harvesters etc.). Considering the previous research about piezoelectric energy harvesters concentrate on the piezoelectric structure's optimization, however the electric circuit's side is simplified to impedance or system damping; or concentrate on the electric circuit's optimization and the piezoelectric side is simplified to current source, treating like these neglect the coupling action between piezoelectric side and electric circuit side, so the high performance harvester can not be obtained.Specific contents as follows:(1) From three-dimension piezoelectric fundamental equation, we set up dynamic equations of piezoelectric structure with beam, plate and shell. It is useful to design and analyses on microelectronic device.(2) This paper builds up coupling action model of bimorph beam-type harvester and RLC power storage circuit. We study the nonlinear coupling law between harvesting process and store process by means of multiple time scale method, and analyze on mechanism of important structure parameters and circuit parameters of harvester on its performance. Base on this, we optimize on performance of whole energy harvester.(3) We propose a kind of low frequency piezoelectric energy harvester structure using spiral-shaped bimorph, and build a coupling counting model for the energy harvester by using transfer matrix method. Analyze and discuss the affection of harvester system parameters on its performance. Piezoelectric structure picks up energy to power microelectronics directly and no need to storage. This type of harvester suits to scavenge energy from ambient with high vibration level. This means that energy is no need to accumulate and enough to ensure microelectronic device keeps working effectively.(4) This paper brings forward to set up a self-adaptive energy harvester mode with lower working frequency, better performance and longer service life time. It has two important characteristic: firstly, through modulating duty cycle of circuit parameter, piezoelectric structure can be optimized even under situation of varied vibration amplitude; secondly, introduction of SSHI into piezoelectric part further elongates the close time of the rectifier, and can pick up much more energy from vibration environment. The piezoelectric structure and storage circuit are coupled into a whole, and set up a coupling action model between harvesting process and storing process. Comprehensive calculates on harvesting-storing coupling process by means of multiple time scale. According to the results, integral optimum design on the harvester. This kind of harvester has a good performance, and stores the harvesting energy effectively, even under the low level environmental vibration. This kind of harvester has a wide-rang to supply energy to microelectronic device.This paper has set up three types of low frequency harvester models. By utilizing multiple times scale method, we calculates and analyzes the coupling between the piezoelectric end and circuit end, and obtains a series of methods and conclusions which respectively suits to different kind of harvester model. These achievements have instructional significance to optimum design on harvesting structure and storage circuit, and performance of the harvester. At the same time, it has given an effective analytic method and provided examples to study on harvester.