## 3 Energy Harvesting  
The focus of this paper is kinetic energy harvesting. Therefore, this section looks at energy harvesting from the viewpoint of kinetic energy research. Energy harvesting is defined as converting kinetic energy--mainly mechanical energy from vibrations or applied pressure--into electrical energy by using piezoelectric materials [2]. While this definition emphasizes piezoelectric materials, other materials can also be used to capture energy from the human movement.  
[PERSON] et al. [14] emphasize the need for sustainable, high-performance solutions that can operate under harsh conditions, addressing the limits of traditional energy-harvesting methods that rely on mechanical inputs such as vibrations or pressure. A review by [PERSON] et al. [15] discusses six piezoelectric nanogenerators (PENGs), eight triboelectric pairs (TENGs), two electromagnetic generators (EMGs), and PVC coverings for footstep energy harvesting. They used a triple-hybrid design with a scattered layout of PENGs, TENGs, and EMGs across six foldable modules to allow easy transport and setup, aiming to measure how well these devices collect power from footsteps. However, the work of [PERSON] et al. [15] is more theoretical, examining how advances in material science can aid energy harvesting for Internet of Things (IoT) applications. They also discuss future uses of spin caloritronic technology and thermoelectric materials in energy conversion but provide less empirical data than other studies.  
This study focuses on footstep energy harvesting. Footsteps in crowded places often generate energy that goes unused. Because energy-harvesting systems are lacking, high-traffic areas have strong potential for footstep-based energy collection [5; 15; 16; 17]. Piezoelectric materials, for instance, can capture energy from foot traffic to power low-energy devices such as streetlights or signs [5]. [PERSON] et al. [18] developed a prototype with piezo  
Figure 1: Systematic literature review steps of this work.  
electric transducers that gather energy through piezoelectric tiles, convert it into electricity, and store it in a 12 V battery.  
[PERSON] and [PERSON] [19] explored a new piezoelectric energy-harvesting design that uses a bridge shear-force structure to transform high compressive forces into shear forces on piezoelectric discs. This approach efficiently converts mechanical stress into electrical potential along the shear axis. [PERSON] et al. [20] use advanced production methods, such as Fused Deposition Modelling (FDM) and Direct Ink Writing (DIW), with specialized materials (polymers, ceramics, and metal composites enhanced by graphene oxide, PVDF, and CNTs) to create precise biomimetic designs. In another system with magnetoelectric coupling, mechanical strain from a magnetic field or vibration triggers polarization in the piezoelectric layer, which generates electrical energy [21]. The cantilever design further improves energy output through resonance, revealing the potential for powering portable electronic devices [21].  
[PERSON] et al. [22] offer further insight into energy-harvesting techniques, highlighting hybrid systems that combine piezoelectric, triboelectric, and electromagnetic methods to capture mechanical energy from sources such as foot traffic. Such advanced materials have shown outstanding energy conversion efficiency and durability under repeated mechanical stress [22; 23]. Their high piezoelectric and triboelectric performance makes them suitable for harvesting energy from vibrations or pressure [22]. Because these materials are lightweight and flexible, they can be smoothly incorporated into a variety of applications, which favors practical and scalable deployment [11]. They also exhibit strong resistance to factors such as humidity and temperature changes, enabling long-term reliability [24]. Efforts to enhance scalability in manufacturing, as described by [PERSON] et al. [14] and others [22], pave the way for more widespread adoption of these systems.