A Wearable Power Generator for Sports Monitoring ApplicationsUrsula Leonard 08331502

Sports and Exercise Engineering, National University of Ireland, GalwaySupervisors: Dr. Maeve Duffy, Dr. Edward Jones

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.

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 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”.

IntroductionOver 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.

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.

Further workThe 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.

ConclusionMaximum 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.

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.

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.