Dynamics identification of a piezoelectric vibrational energy harvester by image analysis with a high speed camera q Piotr Wolszczak a,⇑ , Krystian Lygas a , Grzegorz Litak a,b a Department of Automation, Lublin University of Technology, Nadbystrzycka 36, PL-20-618 Lublin, Poland b Department of Process Control, AGH University of Science and Technology, Mickiewicza 30, PL-30-059 Krakow, Poland article info Article history: Received 8 August 2017 Received in revised form 20 November 2017 Accepted 15 January 2018 Available online 2 February 2018 Keywords: Broadband energy harvesting Nonlinear vibration Hilbert-Huang transform Piezoelectric High seed camera signal abstract This study investigates dynamic responses of a nonlinear vibration energy harvester. The nonlinear mechanical resonator consists of a flexible beam moving like an inverted pendu- lum between amplitude limiters. It is coupled with a piezoelectric converter, and excited kinematically. Consequently, the mechanical energy input is converted into the electrical power output on the loading resistor included in an electric circuit attached to the piezo- electric electrodes. The curvature of beam mode shapes as well as deflection of the whole beam are examined using a high speed camera. The visual identification results are com- pared with the voltage output generated by the piezoelectric element for corresponding frequency sweeps and analyzed by the Hilbert transform. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction Power supply networks for sensors and data transmission are widely used in industrial processes and structural health monitoring. In the conventional approach, wire connections to power supply or battery exchange are required. Since all mea- suring points must be wired, this approach is expensive. New developments in the field of monitoring include minimization of the number of wires and addressing devices as well as reduction of power consumption [1,2]. An additional difficulty is to maintain connections, which may require the use of an additional equipment. In this context, the use of ambient vibration energy can allow for powering autonomous measuring devices. The source of vibration can be natural processes such as wind and sea level movement; vibration can also be generated by vibrating parts of machines, vehicles and other technical objects. New methods for monitoring conditions in an urbanized environment (industrial processes, road and rail transport) [2] offer a great potential thanks to the implementation of self-powered sensors. One way to obtain fairly high-density energy converted from the environment is to use piezoelectric elements attached to the elements of deformable continuous objects such as cantilever beams [3]. Other solutions based on electrostatic, electro- magnetic or magnetostrictive laws are also considered and tested [3–5]. The performance of piezoelectric harvesters depends on the operating conditions such as the frequency and amplitude of deformation and their mode shapes. Recent studies point to the role of nonlinearities [4,6–8] as a cause of frequency broadening in the vicinity of harvester resonance [9,10]. This phenomenon is forced by inherent variable working ambient conditions (excitation conditions) that are fre- quently determined as periodic excitations with a modulated frequency and/or amplitude or even random character https://doi.org/10.1016/j.ymssp.2018.01.024 0888-3270/Ó 2018 Elsevier Ltd. All rights reserved. q This paper belongs to the Special issue ‘‘Oulu Workshop”. ⇑ Corresponding author. E-mail address: p.wolszczak@pollub.pl (P. Wolszczak). Mechanical Systems and Signal Processing 107 (2018) 43–52 Contents lists available at ScienceDirect Mechanical Systems and Signal Processing journal homepage: www.elsevier.com/locate/ymssp