This paper presents vibration analysis and structural optimization of a swimming–morphing structure. The swimming of the structure is achieved by utilization of piezoelectric patches to generate traveling waves. The third mode shape of the structure in the longitudinal direction resembles the body waveform of a swimming eel. After swimming to its destination, the morphing structure changes shape from an open box to a cube using shape memory alloys (SMAs). The SMAs used for the configuration change of the box robot cannot be used for swimming since they fail to operate at high frequencies. Piezoelectric patches are actuated at the third natural frequency of the structure. We optimize the thickness of the panels and the stiffness of the springs at the joints to generate swimming waveforms that most closely resemble the body waveform of an eel. The traveling wave is generated using two piezoelectric sets of patches bonded to the first and last segments of the beams in the longitudinal direction. Excitation of the piezoelectric results in coupled system dynamics equations that can be translated into the generation of waves. Theoretical analysis based on the distributed parameter model is conducted in this paper. A scalar measure of the traveling to standing wave ratio is introduced using a 2-dimensional Fourier transform (2D-FFT) of the body deformation waveform. An optimization algorithm based on tuning the flexural transverse wave is established to obtain a higher traveling to standing wave ratio. The results are then compared to common methods in the literature for assessment of standing to traveling wave ratios. The analytical models are verified by the close agreement between the traveling waves predicted by the model and those measured in the experiments.
The main drawback of energy harvesting using the piezoelectric direct effect is that the maximum electric power is generated at the fundamental resonance frequency. This can clearly be observed in the size and dimensions of the components of any particular energy harvester. In this paper, we are investigating a new proposed energy harvesting device that employs the Automatic Resonance Tuning (ART) technique to enhance the energy harvesting mechanism. The proposed harvester is composed of a cantilever beam and sliding masse with varying locations. ART automatically adjusts the energy harvester’s natural frequency according to the ambient vibration natural frequency. The ART energy harvester modifies the natural frequency of the harvester using the motion of the mobile (sliding) mass. An analytical model of the proposed model is presented. The investigation is conducted using the Finite Element Method (FEM). THE FEM COMSOL model is successfully validated using previously published experimental results. The results of the FEM were compared with the experimental and analytical results. The validated model is then used to demonstrate the displacement profile, the output voltage response, and the natural frequency for the harvester at different mass positions. The bandwidth of the ART harvester (17 Hz) is found to be 1130% larger compared to the fixed resonance energy harvester. It is observed that the proposed broadband design provides a high-power density of 0.05 mW mm−3. The piezoelectric dimensions and load resistance are also optimized to maximize the output voltage output power.
This work presents a model for energy harvesting characterization of a simply supported beam with a mass in the middle to be used for powering pacemakers from heartbeat vibrations. The required power for a typical pacemaker is about 1.0 microwatts. A uniform cross-section beam, bimorph structures, employing double piezoelectric layers is used. PSI-5H4E piezoelectric and brass substrate is used in this study. Different configurations are utilized to identify the optimal design for lightweight energy harvesting devices with low-power applications to tune the natural frequencies of the energy harvester towards the operating ambient vibration source. In this paper, the exact analytical solution of the piezoelectric beam energy harvester with Euler–Bernoulli beam assumptions is presented. The energy harvester is intended to generate power from heartbeat induced vibrations to power implantable cardiac devices. The base excitations are thus heartbeat induced tissue vibrations. The proposed configuration harvests energy from the reverberation of heartbeats and converts it to electricity and could generate about 0.22 microwatts of power. Using the Fourier transform, the frequency response function for the voltage; current and power of the harvester are obtained. The power output for a range of values for the resistive load connected to the bimorph PZT layers is investigated to determine the optimized value of the resistive load that gives the maximum power output for the corresponding configuration of the beam. Stress analysis is performed for the substrate and PZT layer to make sure that the stress are within the permissible values to avoid breaking or failing of the beam. Results show that the use of mid mass is capable of harvesting a significant power with the proposed configurations.
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