# A Novel Piezoelectric Energy Harvester Using a Multi-Stepped Beam with Rectangular Cavities
## 1 Introduction  
In the last decade, researchers in all disciplines have evoked great interest in harvesting energy from ambient sources, which were otherwise unutilized. Among various sources such as vibration, solar, wind and thermal considered for energy harvesting, the most attractive source is vibration because of its availability in all environments. Vibration can be used to source wireless sensor systems and researchers across the world are working towards its possible use in industrial condition monitoring systems, medical implants, and smart clothing. Most energy harvesters based on vibration are linear generators that generate power efficiently only at their resonant frequency or near their resonant frequency. In practice, the use of linear generators is limited as they are inefficient at harvesting energy from the frequency-varying ambient vibrations. Hence, in recent years, to overcome this limitation, more focus has been given towards designing vibration-based energy harvesters having wider bandwidth and high output. The techniques to broaden the operating frequency range are reviewed and presented in References [1,2]. The harvester design presented in Reference [3] widened the bandwidth by appropriately connecting several piezoelectric bimorphs with different resonant frequencies. A special structure having a 'L' shaped beam was presented in Reference [4] featuring the first two natural frequencies that were closer to achieving broadband energy harvesting. In the harvester design reported in Reference [5], the wide bandwidth was achieved by elastically and electrically coupling two identical beams with adjustable and close resonant frequencies. A novel two-degrees-of-freedom(2 DOF) based harvester proposed in Reference [6] provided wider bandwidth compared to the typical Single-degree-of-freedom (SDOF). The harvester design had an outer primary beam and inner cut beam with tip mass. The tip mass was varied to achieve wider bandwidth. The harvester proposed in Reference [7] was designed with a clamped-clamped primary beam bonded with a piezoelectric composite and multiresonant secondary beams attached to one side of the primary beam. The multiresonant response of the secondary beams induced wide band output in the primary beam. The harvester design presented in Reference [8] consisted of a flexible rectangular frame with low Young's modulus in which a series of cantilevers were interdigitally bonded. It provided a multiresonant response and showed a larger bandwidth compared to a conventional cantilever beam. A harvester designed with a dual cantilever with tip mass was reported in Reference [9] in which the resonance frequency was widened by a sliding system having two slanting springs connected to the tip mass. The broadband energy harvester focusing on the dynamic compressive loading was presented in Reference [10]. The flexible slim beam and the applied non-linear axial magnetic force enhanced the output voltage and broadened the bandwidth. A stiffness tunable piezoelectric energy harvester was reported in Reference [11] to achieve high power in the broadband range. Subsequently, the energy harvester with tuning and coupling magnets proposed in Reference [12] could tune the natural frequency to the operating conditions. A new 2D tunable energy harvester based on vibration and featuring transverse and axial stiffness tuning capability was proposed in Reference [13]. The techniques proposed in [14; 15; 16; 17; 18; 19] focused on the increment of the output by shaping different cavities in the structure and splitting the beams of smaller size. Piezoelectric broadband energy harvesters having a propped cantilever beam with variable overhang length as host structure was proposed in References [20; 21; 22; 23] to get high output over a wide range of operating frequencies. The required bandwidth of the harvester was obtained by varying the support position.