WI-PIE: ENERGY HARVESTING IN MOBILE ELECTRONIC DEVICES

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1 WI-PIE: ENERGY HARVESTING IN MOBILE ELECTRONIC DEVICES Courtesy: Texas Instruments Project Team: Guru Karthik Balasubraminan Shivaraman Shankar Aditya Subramanyan College/University: Mentor and Guide: SRM University Mrs. A. Petrishia, SRM University, Ramapuram

2 ABSTRACT A recent study puts the number of mobile phones in use around the world at an astonishing 5 billion and these numbers are growing rapidly. This increases the energy consumption of mobile phones in the world by an alarming level. Wi-Pie or Wireless-Piezoelectric technique combines Piezoelectric Energy harvesting and RF Energy scavenging technologies to provide an alternative method of powering mobile electronic devices. By placing piezoelectric crystals beneath the keypad of a mobile phone, we intend to generate a small voltage with every key press which could be stored in a secondary storage device like a thin film battery. The charge accumulated in the device can then be transferred to the primary storage or the battery so that the use of external chargers can be minimized. Additional power management circuitry is used to intercept the known and the unknown sources of ambient RF radiations. The received RF power is converted to DC and conditioned before it s delivered to the load. Although the RF energy levels are low, a combination of the harvesting and scavenging techniques will provide a significant source of power. INTRODUCTION With the growth of technology and the advent of next generation wireless standards the reach of mobile communication is expected to grow over 90% in the coming years. With as many mobile phones as the world population the overall energy consumption increases as it becomes necessary that they be charged regularly. As the world is moving towards an energy crisis, finding an alternate method to power these mobile electronic devices is the need of the hour. Therefore, building an environment friendly system that could harvest energy from the surroundings will solve the problem. Preventing mobile phones going dry on remote locations, charging the device during power failure, minimizing the use of external chargers thereby reducing e-waste and eventually making these devices charger-free are some of the potential advantages of this method. The concept of harvesting energy from ambient vibrations is not new. It has been around since the invention of piezoelectric materials. The world at present communicates at an astonishing pace where the total number of SMS sent globally stands at a staggering 6.1 trillion. The process of texting in mobile phones and PDAs could well be harvested in to useful power by using the compressive property of piezoelectric ceramics. Our intention is to identify the average energy generated during every key press and then utilize it by storing in a secondary storage device. By placing piezoelectric crystals beneath the keys of a mobile phone, we hope to harvest the energy generated from the pressure of a key-press. Additional power circuitry could also be included to harvest the ambient RF energy in the environment.

3 ENERGY HARVESTING MODEL The energy generated and the amount of energy harvested in this process depends on the type of piezoelectric element chosen and the successful modeling of the harvester circuit. In this project we analyze the properties of various piezoelectric materials based on frequency and output efficiency. A piezoelectric generator, AC-DC conditioning circuit, regulator and a secondary storage device are the essential components of this model. An interface circuit is designed between the generator and the storage device. The circuit focuses on conditioning the output from the piezoelectric generator and providing a seamless input for the secondary device. Also, a comparison between a capacitor and a thin film battery would be drawn out on their choice as the secondary storage device. Although the power generated by this process wouldn t be sufficient to make the device totally battery-free, it will certainly reduce the number of times the device needs to be recharged. A harvester circuit that can improve the power output efficiency of the generator to run a mobile phone is still under study. From the size perspective, this model might not seem feasible for a mobile phone. But, with the advancement of MEMS technology and micro-sensor applications this could be developed in to an efficient control and interface circuit model to improve the power harvested from ambient vibrations. BLOCK DIAGRAM

4 SCHEMATIC OF THE HARVESTER CIRCUIT (FIRST STAGE): STEPS TO BE IMPLEMENTED IN THE SECOND STAGE 1. Testing the implemented circuit essentially with different configuration. 2. Trying different piezoelectric materials of different sizes and shapes. 3. Secondary storage such as capacitor and a Li-Ion battery cell has to be tested. 4. Implementing RF energy scavenging circuit and the related testing. ESTIMATED COST FOR FIRST STAGE 1. Piezoelectric material INR Harvesting circuit and RF scavenging circuit INR Secondary storage battery INR 500 TOTAL FUNDING REQUIRED FOR INITIAL PROGRESS: INR 2000 CHEQUE TO BE SENT TO THE PROJECT GUIDE In favour of: A.Petrishia

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