Article 1 Development of Piezoelectric Harvesters with 2 Integrated Tuning Devices 3 Alberto Doria 1, *, Cristian Medè 2 , Giulio Fanti 3 , Daniele Desideri 4 , Alvise Maschio 5 , and 4 Federico Moro 6 5 1 Department of Industrial Engineering, University of Padova, Italy; alberto.doria@unipd.it 6 2 Department of Industrial Engineering, University of Padova, Italy; cristian.mede@unipd.it 7 3 Department of Industrial Engineering, University of Padova, Italy; giulio.fanti@unipd.it 8 4 Department of Industrial Engineering, University of Padova, Italy; daniele.desideri@unipd.it 9 5 Department of Industrial Engineering, University of Padova, Italy; alvise.maschio@unipd.it 10 6 Department of Industrial Engineering, University of Padova, Italy; federico.moro@unipd.it 11 * Correspondence: alberto.doria@unipd.it; Tel.: +39-049-827-6803 12 Featured Application: The research aims to lower the natural frequency and to widen the band 13 of operation of piezoelectric harvesters by means of tuning devices integrated with the 14 structural layer of the harvester. 15 Abstract: The possibility of improving the performance of a piezoelectric harvester by means of 16 novel tuning devices integrated with the harvester’s structure is investigated. Some prototypes of 17 harvesters with tuning devices are developed by mounting cantilever dynamic absorbers on 18 standard harvesters. A mathematical model is used for predicting the natural frequencies of the 19 coupled system. Tests on prototypes are carried out with an impulsive method. Experimental 20 results show that a small tuning device can lower the main resonance frequency of a piezoelectric 21 harvester of the same extent as a larger tip mass and moreover generates at high frequency a 22 second resonance peak. A multi-physics numerical model is developed for predicting the 23 generated power and for performing stress-strain analysis of harvesters equipped with Integrated 24 Tuning Devices (ITDs). The numerical model is validated on the basis of experimental results. 25 Several configurations of ITDs are conceived and studied. Numerical results show that harvesters 26 with ITDs are able to generate relevant power at two frequencies owing to the particular shape of 27 the modes of vibration. The stress in the harvesters with ITDs is smaller than the stress in the 28 harvester with a tip mass tuned to the same frequency. 29 Keywords: harvester; piezoelectric; dynamic vibration absorber; tuning. 30 31 1. Introduction 32 In recent years there has been a great development of energy harvesting techniques based on 33 piezoelectric devices. Piezoelectric harvesters have been successfully used for transforming ambient 34 vibration energy into electrical energy for feeding sensors, biomedical equipment and small 35 electronic devices [1-3]. The tuning of the harvester to the vibration source is essential to improve 36 the vibration-to-electric energy conversion. In the presence of harmonic vibrations optimum tuning 37 is achieved when the natural frequency of the harvester is set equal to vibration frequency [4-5]. 38 Usually cantilever harvesters are tuned by adding a tip mass [5-6], which increases the 39 excitation of the harvester, because the inertia force due to the lumped mass adds to the inertia 40 forces due to the distributed harvester mass. This phenomenon has a beneficial effect on the 41 generated voltage, but it increases the stress inside the harvester, which may be damaged. 42 The problem of harvester tuning becomes more complex when ambient vibrations are 43 characterized by a variable frequency or by a broadband spectrum. Several techniques have been 44 developed to cope with these working conditions. Some researchers have proposed self-tuning 45 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 17 January 2018 doi:10.20944/preprints201801.0159.v1 © 2018 by the author(s). Distributed under a Creative Commons CC BY license.