An efficient design of polymer based piezoelectric energy harvesting for wearable electronics
Date of Issue2014
School of Electrical and Electronic Engineering
Piezoelectricity remains an area which is being currently explored for dealing with our energy demands through ambient energy harvesting. Prototypes like shoes, door mats and road bumps have been developed throughout the world to generate electricity through piezoelectricity. The objective of this dissertation project is to explore newer prototypes for consumer usage and seeing its performance under various conditions. The prototype discussed has the potential to get integrated as a wearable power generation device for consumers. In this project, the prototype made is a bag fitted with flexible piezoelectric films. Through experiments and observations, points on the bag were identified where maximum impacts are observed due to human walking and running actions. Two strips of piezoelectric polymers were attached to the points identified. After this, the bag was subjected to different human locomotion environments to study the change in power generation. A commercially available piezoelectric energy harvesting circuit was then used to manage the generated power. The design of the prototype has been made such that while power gets generated during motion of the person, power also gets generated if the bag is being subjected to any kind of vibrations like while being carried on a car or a bike. While designing the bag, it was observed that the maximum impacts were on the straps of the bag and also at the back of the bag. These points were then used to extract energy. Each point identified was fitted with an energy harvester and two piezoelectric films connected in series. In addition to this, cantilever mode of operation was also explored. In the end, a prototype was conceived capable of generating electricity out of human locomotion. The output power generated through multiple experiments was found to be 0.87 m W after a jog of 110seconds at 9Kmph. The entire prototype is built around human gait. An analysis is done in the thesis using the inverted pendulum representation of human gait. Also, this inverted pendulum approach is further explored in conjunction with our application and the effect of this model on power generation in the prototype built. Apart from technical considerations, a great thought has also been spent to keep the application user friendly and opaque to the consumer using the application. While experiments, interesting revelations and unexpected results came out which forced some tweaks in the prototype. The readings were taken in a controlled and standardized environment by using a treadmill. These results revealed the effect of human gait on power generation. In the first prototype, the PVDF was used underneath the strap of the bag just above the shoulders. This yielded a power of 81.40 nW in one minute at a speed of 9 Kmph corresponding to a voltage of 337 mV. In the other prototype, the PVDF was used as a cantilever with tip mass. This yielded a power of 34.82 nW in one minute at a speed of 9 Kmph corresponding to a voltage of 220 mV. Thus the prior prototype is found to yield much more power in our application. The significance of this prototype is that in the era of electronics where power consumption is being hammered down to a bare minimum, we can omit the use of batteries altogether by a miser approach. This is exactly what the prototype has been shown to do in the thesis. If we use sufficient amount of PVDF, enough power can be generated to power up phones, tablets and even portable chargers. Also unlike solar power, vibrational energy is present all the time. A significant work has been done in firstly brainstorming, designing and redesigning of the prototype by keeping human gait into mind. The result is a simple yet effective prototype which can be used in our everyday lives. Practically, the power generated can be stored in an onboard portable battery which can then later be tapped using a USB port for mobile devices.