A Wearable Power Generator for Sports Monitoring Applications

1. A Wearable Power Generator for Sports Monitoring Applications Ursula Leonard 08331502Sports and Exercise Engineering, National University of Ireland, Galway Supervisors: Dr. Maeve Duffy, Dr. Edward Jones Introduction Over the past number of years, the number of portable electronic devices we use in everyday life has steadily increased. With the advantage of portability comes one crucial limitation; they are all inherently dependant on batteries to meet their energy requirements. By prolonging the life of batteries or eliminating them completely, we are confident the results would be life changing; for example, detection of problems earlier with monitoring applications, less interaction with your physician and a decrease in the number of operations performed yearly replacing batteries. • Project Objectives • Design and test of a wearable generator to provide maximum output AC power in the space available in a typical “smart” running shoe. • Design, modelling and testing of an optimised AC/DC converter stage for connecting between the generator output and a load device. • Investigate possible low power consuming applications in the field of sports and exercise and incorporate into system. • Comprehensive system testing for different combinations of user activity levels and identification of limits in generator performance. Method In previous studies it has been calculated that up to 67W of power are available from heel strike while walking[1]. By electromagnetic induction, this wasted energy is captured and used. Faraday’s law states that the induced voltage in any closed circuit is equal to the rate of change of magnetic flux. The magnetic flux is directly proportional to the magnetic field, so as the magnitude increases, the magnetic flux increases. The magnitude of the voltage is proportional to the speed at which the conductor cuts the flux and the number of turns in the conductor. Materials To achieve the movement of a magnetic field through a conductor, the generator utilises copper coils and small neodymium magnets. Placed at the ankle, the generator takes advantage of the repetitive pendulum motion of the feet during normal gait. By allowing the magnet to slide freely up and down through the coil, a voltage is induced. Using Psim simulation software, possible conversion circuits were analysed and a doubler circuit was chosen as the converter stage. A network of schottky diodes and capacitors implements this circuit outputting constant DC power. Figure 2 A schematic of the coversion circuit drawn in Psim is presented with a picture of the choosen circuit built on a small board. The graphs show predicted DC output and measured DC output from generator. Figure 1 The table lists energy levels available form the body[2]. The optimised generator structure shown outputs max AC voltage. The green waveform (generator shaken) and the yellow waveform (running on a treadmill) are examples of generator output. Conclusion Maximum energy is available for capture during fast walking and fast running. In the transition from walking to running, there is a dip in available power. This is because, while walking there is always at least one foot on the ground, but while running both feet are off the ground for a period of time. The reduced swinging causes a dip in generator performance. Gender or weight has no effect on generator performance . All testing was completed indoor on a treadmill. Further work The emphasis can now be on developing a load device and possibly a storage unit. Further optimization of the generator structure would be encouraged, to improve the power output levels and perhaps make the structure even smaller. At present the generator is placed at the ankle; incorporation into an altered shoe and a better hardware system would help during the texting phase. Figure 3 shows two graphs; possible load devices and the relationship between generator output and speed. The images are possible load devices. References [1] T. Starner, “Human-Powered Wearable Computing”; [2]E. Romero, R. O. Warrington, and M. R. Neuman “Body Motion for Powering Biomedical Devices”. Acknowledgments The author would like to thank Maeve Duffy, Edward Jones, Myles Meehan and Martin Burke for their continued help and guidance throughout the course of the project.