This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. JOURNAL OF MICROELECTROMECHANICAL SYSTEMS 1 Evaluation of Vibrational PiezoMEMS Harvester That Scavenges Energy From a Magnetic Field Surrounding an AC Current-Carrying Wire Oskar Z. Olszewski, Ruth Houlihan, Alan Blake, Alan Mathewson, Senior Member, IEEE, and Nathan Jackson, Senior Member, IEEE Abstract—This paper reports on a low-frequency vibrational piezoelectric energy harvester that scavenges energy from a wire carrying an ac current. The harvester is described, fab- ricated, and characterized. The device consists of a silicon cantilever with an integrated piezoelectric capacitor and a proof- mass that incorporates a permanent magnet. When brought close to an ac current carrying wire, the magnet couples to the ac magnetic field from a wire, causing the cantilever to vibrate and generate power. The device was fabricated from a silicon-on-insulator substrate using microelectromechanical sys- tems (MEMS) technology. The charge generating capacitor uses a CMOS compatible aluminum nitride piezoelectric material and fabrication process. The device uses a commercial neodymium iron boron permanent magnet that is post-fabrication assembled with the device. The measured average power dissipated across an optimal load of 2 M was 1.5 μW. This was obtained by exciting the device into mechanical resonance with a peak displacement of 3 mm using the electro-magnetic field from a 2-A source current. The measurements also reveal that the device’s electrical response is nonlinear due to mechanical nonlin- earity of the device. In addition, bandwidth broadening by 250% is demonstrated by means of vibro-impact approach. [2016-0263] Index Terms—Energy, harvester, Internet of Things (IoT), microelectromechanical systems (MEMS), magnet, nonlinear, piezoelectric. I. I NTRODUCTION I N RECENT years, much attention has been placed on the Internet of Things (IoT) [1]. The IoT refers to a large number of nodes, also called “things” that exchange the data wirelessly across the network. The individual nodes are typi- cally powered by batteries with limited lifetime and currently the IoT urges for development of energy-autonomous nodes and energy harvesting is a key technology addressing such a demand [2], [3]. Multiple energy sources are available within the environment e.g. light, mechanical vibrations, electromag- netic fields, temperature gradients, and these can be converted into useable electrical power by means of various transduction Manuscript received October 28, 2016; revised May 16, 2017; accepted July 16, 2017. This work was supported by the Enterprise Ireland’s Innovation Partnership Program IP2013/0213 and Analog Devices, and in part by the Science Foundation Ireland (SFI) through the European Regional Develop- ment Fund under Grant 13/RC/2077. Subject Editor R. Pratap. (Corresponding author: Oskar Z. Olszewski.) The authors are with Tyndall National Institute, University College Cork, Cork, Ireland (e-mail: zbigniew.olszewski@tyndall.ie). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JMEMS.2017.2731400 methods, including photovoltaic, thermoelectric, electrostatic, and piezoelectric. Because of their numerous advantageous, vibrational piezoelectric harvesters have received much atten- tion [2], [4]–[9]. This is, because mechanical vibrations are ubiquitous in most applications, e.g. transport, human motion, household machines, and because piezoelectric harvesters have a simple structure and high conversion efficiency. Further- more, advances in thin piezoelectric films such as Aluminium Nitride (AlN) offer high-volume, wafer scale fabrication and integration capabilities [10]. A key challenge of vibrational harvesters, including piezo- electric technologies, is that the devices typically resonate with a high Q-factor or, in other words, have a narrow frequency bandwidth. Away from the resonance frequency the power generation drops significantly. This is a major problem because the frequency of the vibration source may vary over time and, as a result, no usable power may be generated. The frequency can also vary significantly between different vibration sources so this would require devices with different resonant frequency to be developed for individual applications. A number of solutions to broaden the operation bandwidth of vibrational harvesters have been proposed. The bandwidth can be broad- ened by mechanical tuning of the device stiffness affecting the device resonance frequency [11], cascading of multiple devices with different resonance frequencies that individually respond to distributed source frequencies [12], [13], introduc- ing a nonlinearity to the device behavior [14] by magnetic fields [15], [16], mechanical stops [17], rolling mass [18], or stress-stiffening effect [19], [20] whereby nonlinear compo- nent of stiffness comes into a play and broadens the device response. An alternative approach to bandwidth broadening is to select an application that provides a stable source of frequency [21]–[23]. One such source is the AC magnetic field surrounding an AC current-carrying wire such as the power mains of electrical equipment. Previously the excitation capability of the method for a piezoelectric MEMS AC current sensor was demonstrated [24], [25]. In this paper, we report on a piezoelectric harvester that scavenges energy from an AC current-carrying wire. In pre- vious work [21]–[23] a similar concept was demonstrated using a macro-scale assembled device with a volume in the order of cm 3 , which enabled a low frequency operation (≈50 – 60 Hz). This paper focuses on the development of a piezoelectric MEMS device (volume of the order of mm 3 ) 1057-7157 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.