Piezoelectric beam generator based on MFC as a self-powered vibration sensor

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A piezoelectric generator is a device used to convert mechanical energy into electrical energy. The basic element of the generator is made from piezoelectric material in which electrical energy is created as a result of deformations caused by reactions of mechanical structure of the generator. The generators, in which the main element is a cantilever beam constructed from basic material and from piezoelectric material, are one of structures, which are used to the energy harvesting from the mechanical vibrations. The piezoelectric generator are used as a part of self-powered wireless sensor in many scientific research. Such self-powered sensor consists of a sensor measuring selected parameter, a radio transmitter, and aforementioned piezoelectric beam generator. However, the piezoelectric beam generator has a limited application in supply a sensor, because the amount of electric energy generated by such generator does not exceed a few mili Watts and is achieved only if the vibration frequency of mechanical energy source equals the resonant frequency of a cantilever beam of piezoelectric generator. This problem is mainly tried to solve by modifications of the generator beam structure or by introducing additional elements with geometry adapted to the source of mechanical vibration. In contrast to these approaches, the article presents the experimental investigation on the action of self-powered wireless sensor in which a decrease of consumed energy amount was achieved through an using of piezoelectric beam generator, which power the radio transmitter, as a vibration sensor. The piezoelectric beam generator should product an amount of electric energy which is enough to supply only the radio transmitter. Such self-powered wireless sensor is dedicated to a vibration monitoring, in which the basic purpose is a detection of an appearance of the dangerous for building structure vibration. The presented self-powered vibration sensor based on a piezoelectric beam generator equipped with a standard energy harvesting circuit, a radio transmitter and a system of energy transfer control enabling power of a radio transmitter for established level of stored energy in capacitor allows a detection of dangerous vibrations for building structure, monitored by this sensor. In laboratory stand vibration amplitudes of the free end of piezoelectric generator were obtained by changes of vibration frequency and vibration amplitudes of its fixed end. In laboratory experiments the time among radio signal was measured for selected values of capacitor capacity and for changed vibration amplitude of free end of piezoelectric generator beam. On the basis of this experiments it was found that full robustness of tested self-powered sensor was achieved for the capacitor capacity equal to 440μF. The sending of a full package of data by such sensor can be realized only above a minimum value of the capacity of applied capacitor equals 220μF. The capacity of capacitor in piezoelectric self-powered vibration sensor should be selected between minimum value for which full packages of data are sending, in tested sensor it equals 220μF, and maximum values for which full robustness to disturbances is achieved. It was found that an increase of the capacitor capacity caused an improvement of data sending robustness to disturbances in radio transmission. The full robustness manifested the sending of every package of data. On the other hand, an increase of capacitor capacity led to the decrease of detection sensitivity of appearance of short-lived vibrations with the big amplitudes due to longer time of capacitor charging. It was noted that the increase of capacitor capacity did not improve the acting of such sensor in case of appearance of long-lived vibrations.