MICRO-LEVEL ENERGY HARVESTING Prakash Hiremath. M 1DA06EC061

 Introduction  Energy harvesting mechanisms  Power management  Energy harvesting application OVERVIEW

INTRODUCTION Definition : Energy harvesting is defined as extracting energy from the environment to power the electrical and electronic devices. Energy harvesting Macro-level Micro-level

MOTIVATION Low-cost embedded intelligent systems Complexity of wiring and wiring costs Increasing popularity of wireless networks Limitations of batteries Limitations of power management techniques

BLOCK DIAGRAM Energy harvesting system/sensor Rectifier Battery charge controller Voltage regulator Battery eg:Li-ion To circuit

TRADE-OFFS Strict power budget Dependent on availability Higher upfront cost Less mature technology No power wires Less maintenance Environment friendly Higher uptime ADVANTAGES DISADVANTAGES

Radiation sources Pyroelectric Photovoltaic Piezoelectric Electrostatic Electromagnetic Thermoelectric Magnetostrictive ENERGY HARVESTING MECHANISMS

BATTERY TECHNOLOGY Li-ion battery  also called Li polymer cell  obsolete for today’s requirements Thin film battery  flexible packaging options  broad temperature range  superior cycle life Supercapacitor  to buffer transient energy  no aging & rate-capacity issues  limited energy capacity

Li-ionThin film rechargeableSuper capacitor Recharge cycles100s5k-10kmillions Self dischargemoderateNegligiblehigh Charge timehoursminutessec-minutes SMT & reflowPoor-nonegoodpoor Physical sizelargesmallmedium Capacity mAhr12-700uAhr10-100uAhr Environmental impacthighminimal

POWER MANAGEMENT To design an efficient energy harvesting system, following trade-offs need to be understood in-depth: characteristics of harvesting transducers chemistry & capacities of batteries(if used) power supply requirements & power management features of the system application behaviour

Performance parameters : Conversion efficiency – one form of energy to other Transfer efficiency – from source to supply Buffering efficiency – after harvesting is done Consumption efficiency – amount of useful work Energy harvesting embedded systems Environmentally embedded Wireless energy transfer Wearable or implantable

System design issues : 1) Voltage & current : Need voltage conversion to a controllable level Linear regulators – lower efficiency Switching regulators – higher efficiency Overall conversion efficiency is dependent on operating range also Power fragmentation problem can be solved by using boost regulators Dynamic voltage range can be increased by choosing alternative cap compositions.

2) Maximum power point tracking : drawing power from energy harvesting source at the level that maximizes power output Conversion losses of 65%-90% are common MPPT controllers can be implemented both in hardware & software 3) Power defragmentation : Problem Solution Dynamic power range Power fragmentation Add more power sources Power matching switches

Energy neutrality : Energy neutrality can be achieved by: i. Average power generated by harvesting device ii. Capacity of energy storage device iii. Design choices by system architect Non-idealities like round-trip efficiency & self- discharge need to be considered. Other power management techniques : Node level power management Network level power management

APPLICATIONS Automotive applications Industrial applications Building & home automation Environment monitoring applications Military & aerospace applications Medical applications Consumer electronics applications

STATUS IN DIFFERENT APPLICATION FIELDS Research & Development Development/ Small production In production Environment Medical Consumer electronics Automotive Industrial Military & aerospace Building & home automation

TREE ENERGY HARVESTING The sensor system produces enough electricity to allow the trees’ temperature & humidity sensors to regularly & wirelessly transmit signals.

WIRELESS SENSOR NETWORKS A WSN monitors physical space or objects. It has limited resources viz, memory & processing power. WSN challenges are, - Task assignment - Data collection - Security - Reliability

Wireless sensing node(WSN) Sensor inputs Sensor signal conditioning Multiplexer, PG instrumentation amplifier Micro-power voltage regulator with energy harvesting power source A/D convertor (16bit resolution) RF transmitter or transceiver 8-bit low-power microcontroller Flash EEPROM for sensor logging RF power control

STRUCTURAL HEALTH MONITORING SHM consists of an integrated paradigm of sensing, data interrogation & statistical modeling to assess the performance conditions of a structure. Sensor nodes can harvest for monitoring, Solar energy Thermal energy Mechanical vibrations Galvanic corrosion