RESUMO
Piezoelectric nanogenerators can convert energy from ambient vibrations into electrical energy. In the future, these nanogenerators could substitute conventional electrochemical batteries to supply electrical energy to consumer electronics. The optimal design of nanogenerators is fundamental in order to achieve their best electromechanical behavior. We present the analytical electromechanical modeling of a vibration-based piezoelectric nanogenerator composed of a double-clamped beam with five multilayered cross-sections. This nanogenerator design has a central seismic mass (910 µm thickness) and substrate (125 µm thickness) of polyethylene terephthalate (PET) as well as a zinc oxide film (100 nm thickness) at the bottom of each end. The zinc oxide (ZnO) films have two aluminum electrodes (100 nm thickness) through which the generated electrical energy is extracted. The analytical electromechanical modeling is based on the Rayleigh method, Euler-Bernoulli beam theory and Macaulay method. In addition, finite element method (FEM) models are developed to estimate the electromechanical behavior of the nanogenerator. These FEM models consider air damping at atmospheric pressure and optimum load resistance. The analytical modeling results agree well with respect to those of FEM models. For applications under accelerations in y-direction of 2.50 m/s2 and an optimal load resistance of 32,458 Ω, the maximum output power and output power density of the nanogenerator at resonance (119.9 Hz) are 50.44 µW and 82.36 W/m3, respectively. This nanogenerator could be used to convert the ambient mechanical vibrations into electrical energy and supply low-power consumption devices.
RESUMO
Piezoelectric vibration energy harvesting (pVEH) microdevices can convert the mechanical vibrations to electrical voltages. In the future, these microdevices can provide an alternative to replace the electrochemical batteries, which cause contamination due to their toxic materials. We present the electromechanical modeling of a pVEH microdevice with a novel resonant structure for air conditioning vents at office buildings. This electromechanical modeling includes different multilayers and cross-sections of the microdevice resonator as well as the air damping. This microdevice uses a flexible substrate and it does not include toxics materials. The microdevice has a resonant structure formed by multilayer beams and U-shape proof mass of UV-resin (730 µm thickness). The multilayer beams contain flexible substrates (160 µm thickness) of polyethylene terephthalate (PET), two aluminum electrodes (100 nm thickness), and a ZnO layer (2 µm thickness). An analytical model is developed to predict the first bending resonant frequency and deflections of the microdevice. This model considers the Rayleigh and Macaulay methods, and the Euler-Bernoulli beam theory. In addition, the electromechanical behavior of the microdevice is determined through the finite element method (FEM) models. In these FEM models, the output power of the microdevice is obtained using different sinusoidal accelerations. The microdevice has a resonant frequency of 60.3 Hz, a maximum deflection of 2.485 mm considering an acceleration of 1.5 m/s², an output voltage of 2.854 V and generated power of 37.45 µW with a load resistance of 217.5 kΩ. An array of pVEH microdevices connected in series could be used to convert the displacements of air conditioning vents at office buildings into voltages for electronic devices and sensors.
RESUMO
Multilayered microresonators commonly use sensitive coating or piezoelectric layers for detection of mass and gas. Most of these microresonators have a variable cross-section that complicates the prediction of their fundamental resonant frequency (generally of the bending mode) through conventional analytical models. In this paper, we present an analytical model to estimate the first resonant frequency and deflection curve of single-clamped multilayered microresonators with variable cross-section. The analytical model is obtained using the Rayleigh and Macaulay methods, as well as the Euler-Bernoulli beam theory. Our model is applied to two multilayered microresonators with piezoelectric excitation reported in the literature. Both microresonators are composed by layers of seven different materials. The results of our analytical model agree very well with those obtained from finite element models (FEMs) and experimental data. Our analytical model can be used to determine the suitable dimensions of the microresonator's layers in order to obtain a microresonator that operates at a resonant frequency necessary for a particular application.