Multi-physics phenomena influencing the performance of the car horn

Usually cars are equipped with disk horns. In these devices electromagnetic energy is converted into mechanical energy of two nuclei that vibrate and impact each other \u2013 the impacts excite the disk that radiates sound. This paper aims at understanding the results of acoustic tests carried out on horns with different excitation voltages and different mounting brackets. Since many non-linear phenomena are inherent in the vibrations of the nuclei, a detailed model of the electromechanical system is developed. Results show the dependence of operating frequency on the input voltage and the role played by the various mechanical and electrical parameters on the dynamics of the horn. Particular nonlinear effects, like sub-harmonic excitation, are presented and discussed. A general agreement between experimental results and numerical simulations is found

Development of piezoelectric harvesters with integrated trimming devices

Piezoelectric cantilever harvesters have a large power output at their natural frequency, but in some applications the frequency of ambient vibrations is different fromthe harvester\u2019s frequency and/or ambient vibrations are periodicwith some harmonic components. To copewith these operating conditions harvesters with integrated trimming devices (ITDs) are proposed. Some prototypes are developed with the aid of an analytical model and tested with an impulsive method. Results show that a small trimming device can lower the main resonance frequency of a piezoelectric harvester of the same extent as a larger tip mass and, moreover, it generates at high frequency a second resonance peak. A multi-physics numerical finite element (FE) model is developed for predicting the generated power and for performing a stress-strain analysis of harvesters with ITDs. The numerical model is validated on the basis of the experimental results. Several configurations of ITDs are conceived and studied. Numerical results show that the harvesters with ITDs are able to generate relevant power at two frequencies, owing to the particular shape of the modes of vibration. The stress in the harvesters with ITDs is smaller than the stress in the harvester with a tip mass trimmed to the same frequency

Improvement of harvesters for tires by means of multi-physics simulation

The specific working conditions of piezoelectric harvesters for scooter tires are analyzed. Calculated and experimental results show that the excitation of the harvester can be considered a series of separated impulses. Harvester response to an ideal impulse is analyzed with a single-mode model. An optimal ratio between impulse duration and natural period of the harvester that maximizes harvester excitation is found. A numerical finite element (FE) model of a bimorph cantilever harvester is developed in COMSOL and validated by means of experimental tests. The validated FE model is used for showing that an actual harvester excited by road impulses generates a large voltage only if there is a specific relation between impulse duration and natural period of the harvester. Starting from the validated FE model, small harvesters suited to tires are developed and analyzed. Also these harvesters show the best performance for a specific range of impulse durations, which corresponds to the highest speeds of the speed range of the scooter (50-80 km/h) and to high levels of acceleration

Tuning of a Piezoelectric Harvester by Means of a Cantilever Spring-Mass System

The possibility of improving the performance of a piezoelectric harvester by means of a cantilever dynamic vibration absorber (CDVA) is investigated. The CDVA cancels the original mode of vibration of the harvester and generates two new modes. Some prototypes are developed using a mathematical model for predicting the natural frequencies of the coupled system. Impulsive tests were performed on prototypes. Experimental results show that a small CDVA can lower the main resonance frequency of an harvester of the same extent as a larger tip mass. The measured voltage shows also an high frequency resonance peak, which can be exploited for collecting energy. A multi-physics numerical model is developed for performing modal analysis and stress analysis. Numerical results show that the stress inside the piezoelectric material of the harvester with CDVA results smaller than the stress inside the harvester with a tip mass tuned to the same frequency