An Impulsive Method for the Analysis of Piezoelectric Energy Harvesters for Intelligent Tires

Piezoelectric harvesters used for feeding the sensors of intelligent tires experience impulse excitation when the harvester enters the contact patch of the tire. The design, development and set up of advanced harvesters characterized by new materials, optimized shape and specific solutions for tuning require the possibility of testing prototypes in the laboratory simulating the actual working conditions and in particular impulsive events. The aims of tests are manifold: verification of mechanical and electrical performance, comparison with numerical models and updating, identification of parameters of the harvester that are difficult to measure directly. In this paper a testing method based on hammer excitation of an harvester mounted on a specific testing rig is presented. The testing rig is simple and low cost. It makes possible the measurement of the frequency response function (FRF) between output voltage and input acceleration. Design requirements for the testing rig are reported and a validation of the realized system is presented. A multimodal mathematical model is developed in MATLAB to simulate the impulse response of the harvester and in particular to stress the effect of higher order modes. Results show the dominance of the fundamental mode in the response of the tested harvesters. Calculated and experimental results are in good agreement.