# Energy Harvester Based on a Rotational Pendulum Supported with FEM
###### Abstract  
The proposed energy harvesting system is based on a rotational pendulum-like electromagnetic device. Pendulum energy harvesting systems can be used to generate power for wearable devices such as smart watches and fitness trackers, by harnessing the energy from the human body motion. These systems can also be used to power low-energy-consuming sensors and monitoring devices in industrial settings where consistent ambient vibrations are present, enabling continuous operation without any need for frequent battery replacements. The pendulum-based energy harvester presented in this work was equipped with additional adjustable permanent magnets placed inside the induction coils, governing the movement of the pendulum. This research pioneers a novel electromagnetic energy harvester design that offers customizable potential configurations. Such a design was realized using the 3D printing method for enhanced precision, and analyzed using the finite element method (FEM). The reduced dynamic model was derived for a real-size device and FEM-based simulations were carried out to estimate the distribution and interaction of the magnetic field. Dynamic simulations were performed for the selected magnet configurations of the system. Power output analyses are presented for systems with and without the additional magnets inside the coils. The primary outcome of this research demonstrates the importance of optimization of geometric configuration. Such an optimization was exercised here by strategically choosing the size and positioning of the magnets, which significantly enhanced energy harvesting performance by facilitating easier passage of the pendulum through magnetic barriers. v 20  
conversion from ambient mechanical vibrations using a pendulum-like rotating body with modifications possible in the system's potential [7]. It is worth mentioning that energy harvesting systems that are based on ambient mechanical vibrations are generally divided into electromagnetic [8; 9], piezoelectric [10; 11], and electrostatic [12; 13] categories. In many scientific articles, they are called vibration energy harvesters (VEH) [14; 15]. VEH systems have gained popularity because they provide the simplest transduction mechanism and highest efficiency of energy transduction [16; 17]. Practical applications of VEH systems span diverse sectors. In the automotive industry, these systems can capture energy from vehicle vibrations to power tire pressure monitoring systems or onboard sensors [18]. Similarly, in structural health monitoring, they can be employed to generate power for sensors embedded in bridges or buildings while facilitating continuous monitoring. This eliminates the need for frequent battery replacements as well [19]. Furthermore, wearable devices [20] can utilize VEH system to extend battery life or even eliminate the need for batteries altogether, enhancing user convenience and sustainability. Being a linear dynamic system, a simple VEH responds well only when excited near its resonance frequency. This is a major disadvantage because the harvested power from the device drops when excited at other non-resonant operational frequencies resulting from uncertain ambient conditions [21]. However, to overcome this problem, many current research works are focusing on the broadband frequency-response effect to build a flexible system adjusting to the wider range of operational frequencies [22; 23; 24]. Compared to a linear system, the broadband frequency effect causes a reduction in the mechanical quality factor (Q-factor). The highest power output obtained under resonant conditions also reduces because a nonlinear system may exhibit multiple low- and high-amplitude solutions [25; 26; 27]. However, as the nonlinear systems exhibit better performance at non-resonant conditions, overall harvesting efficiency is improved due to the broadband response. Such nonlinear behavior has been obtained by using nonlinear mechanical and magnetic springs with softening or hardening effects [28].