Study On Characteristics Of A Mechanical Frequency Up-converted Piezoelectric Wave Energy Converter

Piezoelectric-based wave power generation is a new solution for the continuous power supply of transducers. Therefore, the research and development of piezoelectric-based wave power generation device has a very good application prospect, and will become one of the developing directions in continuous power supply for marine monitoring instruments. A novel piezoelectric wave energy converter with proprietary intellectual property rights is investigated in this paper. This converter, through a frequency up-conversion method, transforms irregular and slow wave motions into high-speed and stable mechanical oscillations which are subsequently converted into electrical energy utilizing piezoelectric effects. Mechanisms underlying the transformation from wave energy to electrical energy is investigated both numerically and experimentally, focusing on interactions among waves, buoy, piezoelectric vibrators and electrical loads.A nonlinear three-dimension wave-buoy-vibrator coupled model is first established in the paper, based on the potential theory and Euler-Bernoulli beam theory. The model is then verified by experiments. And effects of Young’s modulus, vibrator number as well as wave parameters on the wave-buoy-vibrator transformation are numerically probed based on the validated model. It is found that the vibrating frequency of the vibrator changes little with the incident wave period whereas it could be tuned to a high preset frequency by modifying the physical parameters of the vibrator such as Young’s modulus. As the Young’s modulus and number of the vibrator increase, the rebound ratio which represents the wave-buoy-vibrator transformation state increases. When the Young’s modulus and number of the vibrator individually exceed a threshold, the “translation + release”mechanism for the frequency up-conversion fails, and interaction between the buoy and vibrators turns “cushion + rebound”.The piezoelectric vibrator(with piezoelectric membranes adhered to top and bottom surfaces of the vibrator) is an element in the system which generates electricity. Coupling between the vibrator and electrical loads has an important influence on the output power and transformation efficiency of the piezoelectric vibrator. The dimensionless electromechanical coupling coefficient is a key factor which represents damping suffered by the piezoelectric vibrator induced from the electrical power take-off. And it determines the electromechanical transformation efficiency of the piezoelectric vibrator. Influences of the physical and geometrical parameters of the piezoelectric membrane and substructure on the electromechanical transformation of the piezoelectric vibrator are thoroughly investigated. It is found that piezoelectric vibrator with unequal piezoelectrics and substructure length has a better electromechanical coupling compared to the equal one. And for most cases, the optimal piezoelectrics-to-substructure length ratio ranges between0.55 and 0.75.Characteristics of a mechanical frequency up-converted piezoelectric wave energy device is experimentally studied, and variations of the buoy motion and output voltage with time are recorded under different wave periods. A nonlinear coupled model with the consideration of interaction among wave, buoy, piezoelectric vibrators and electrical loads is proposed to simulate energy transformation from wave to electrical energy. And the variations of output power with electrical resistance, piezoelectric vibrator number,piezoelectric length, overlapping length between piezoelectric vibrator and plectrum, as well as wave characteristics are systematically studied. It is found that augmenting the piezoelectric vibrator number appropriately not only increases the output power, but also broadens the bandwidth of the device.