Among the various alternative energy sources, harvesting energy from the movement of the human body has emerged as a promising technology. The interaction between the energy harvesting structure and the power conditioning circuit is nonlinear in nature, which makes selecting the appropriate design parameters a complex task. In this work, we present an electromagnetic energy harvesting system suitable for recovering energy from the movement of the lower limb joints during walking. The system under study is modeled and simulated, considering three different scenarios in which the energy source is the hip, knee, and ankle joint. The power generated by the energy harvester is estimated from kinematic data collected from an experimental gait study on a selected participant. State-space representation and Recurrence plots (RPs) are used to study the dynamical system’s behavior resulting from the interaction between the electromagnetic structure and the power conditioning circuit. The maximum power obtained through the simulation considering a constant walking speed of 4.5 km/h lays in the range of 1.4 mW (ankle joint) to 90 mW (knee joint) without implementing a multiplier gear.

The existing clearance in the mechanical joints plays a crucial role in the assembly of mechanical systems, allowing the mobility of its components. However, few studies have explored models that consider joint clearance in the case of electromechanical energy harvesting systems. This paper examines the effect of existing clearance in an electromagnetic energy harvester attached to the human lower limb. The dynamic response of the system and an estimate of its generated power are obtained by developing a lumped model, in which clearance is included by adding a dead band and assigning a stiffness coefficient during contact between elements. The natural motion of the lower limb is the input to the formulated model, which takes into account the nonlinear interaction of the electromagnetic device and the power conditioning circuit. Central composite design is used to study the influence of two selected factors on the dynamics of the system; joint clearance size and contact stiffness. The results suggest that the presence of clearance between the clamping mechanism and the human body positively affects the performance of the analyzed electromagnetic energy harvesting system. It was revealed that an increase of around 27% of output power could be intentionally achieved by adding larger clearance sizes.

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Over time, many researchers have focused on creating models to mathematically represent movements performed by human lower limbs, such as walking, running, and jumping. These models provide a non-invasive method to estimate kinematic and kinetic parameters under different conditions. This article reviews the main lower limb models used to study human walking and compares their performance with a 3D model consisting of seven links created using the simulation environment Simscape Multibody. A description of each model is presented, highlighting its main characteristics and the assumptions that led to its formulation. We execute numerical simulations based on the first-order Euler method to solve the differential equations resulting from the models’ implementation.