# Simulation of Electromagnetic Generator as Biomechanical Energy Harvester
## 1 Introduction
This backpack mechanism uses its weight as a source to initiate the rotary system attached to it and apart from the weight the output is significantly influenced by the walking speed. A total of 7.4 W was generated from this  
Figure 1: Global energy-harvesting market. energy harvester backpack with 38 kg as the load. [PERSON] et al. [20] designed a knee energy-harvester device which is 1.6 kg. At a walking speed of 1.5 m/s, the device was able to generate 3.5 W.  
The lower extremity of the human is identified to be the anatomical part that exhibits higher motion during a walking gait cycle [21]. A lot of studies had been carried out to investigate the potential of energy harvesting via hip, knee, ankle, and heel strike. [PERSON] et al. [22] demonstrated two types of piezoelectric footwear harvesters with different piezoelectric stack quantities. This was designed to amplify the transferred heel strike force via force amplification frames. The average power generated at 4 km/h by the eight-stack piezoelectric is 6 mW/shoe and the six-stack piezoelectric produces 8 mW/shoe. [PERSON] et al. [23], established a piezoelectric patch by optimizing the placement around the knee by using the MEMS-based piezoelectric. During walking, the harvester generated RMS power of 6.2 \(\mu\)W and 12 \(\mu\)W while running. [PERSON] et al. [24] analyzed a microelectromagnetic energy harvester by converting vibration energy to electrical power. This harvester utilizes a planar copper spring mechanism and generates maximum power of 205.38 \(\mu\)W at 124 Hz resonance frequency. [PERSON] et al. [25] investigated a hybridized generator by incorporating a nonlinear electromagnetic generator and triboelectric nanogenerators. This hybridized harvester generated 131.4 mW as the maximum output power during horizontal handshaking. [PERSON] et al. [26] developed a flexible lower limb exoskeleton which is worn in parallel to assist walking gait while generating power. At the 5.1 km/h walking speed, the harvester generates a maximum power of 6.47 W. [PERSON] et al. [27] use a brushless DC motor as the generator by integrating a gear train with a 1:86 ratio. At 5211 RPM, the generator produces 8.43 W. [PERSON] et al. [28] investigated a knee-mounted harvester with a cable-pulley mechanism. This cable-pulley mechanism converts the flexion and extension gait cycle of the knee to electrical power. This harvester generates average power of 4.1 W.  
The discussed related work shows two main types of generator mechanisms which are the piezoelectric and electromagnetic generators. However, the generated power for piezoelectric ranged between 6.2 \(\mu\)W and 8 mW, and electromagnetic generators ranged between 205.38 \(\mu\)W and 8.43 W. This power is significantly lower, although [PERSON] et al. [27] has produced 8.43 W at 5211 RPM which is considered better than previous work. With these limitations, hence, in this paper, an electromagnetic generator for a biomechanical energy harvester for knee motion has been investigated and designed to produce a higher output power at lower RPM based on biomechanical motion. The proposed design is small-scale and lightweight to ensure minimal impact against the normal gait cycle of the user. As such, the proposed design is 40 mm in diameter and 10 mm in thickness. The designed small-scale generator is able to generate higher output power which is 14.95 W per device at 800 RPM with minimal effort from the user. The effort to actuate the generator is minimized by reducing the cogging torque of the generator by lowering the slot opening to slot pitch ratio. This is the major contribution of the research. The rest of the paper is organized as follows: Section 2 focuses on electromagnetic generator modelling. Section 3 shows the simulation results and discussions with results validation through two case studies. Finally, in Section 4, the conclusion is presented.