D4. RF Energy Harvesting An Enabling Technology for Maintenance-Free Wireless Devices

1. Power Circuitry MCU Accelerometer PCB Antenna GSR Contacts Transceiver 4.2” 4.2” 2” CAD to Prototype D4. RF Energy Harvesting An Enabling Technology for Maintenance-Free Wireless Devices Principal Investigator:R. Zane; A. Dolgov, E. Falkenstein, J. Shin, T. Paing, Z. Popovic, Colorado Power Electronics Center, Electrical & Computer Engineering Dept, University of Colorado at Boulder Sensor Prototype Applications Operating Current Average Power • Module acquires the following data: • Motion from 3-axis accelerometer • Skin resistance from GSR sensor • Body temperature • Sensor module is controlled by an onboard microcontroller unit (MCU) optimized for low-power operation Eliminates need to replace batteries in countless devices Power wireless devices indefinitely Experimental results showing total instantaneous sensor current consumption during one sample-and-transmit cycle and associated operating modes of the sensor electronics Average power required by the sensor as a function of sample period, demonstrating an average power of less than 5 mW when sampling once every ten seconds. Maintenance-free implanted biomedical devices Wireless switch for improved accessibility Power Converter RF Power System Overview RF Power Transmitter Energy Harvester & Wireless Sensor Is it SAFE? Cell Phone 50 mW/cm2 Microwave Oven 50 mW/cm2 Radars 20 mW/cm2 • Power converter provides maximum energy harvesting from rectenna and delivers usable energy to the load • Boost power converter emulates • a positive resistance to optimally • load rectenna input source Measured rectified power from small patch RF Power Transmitter 20 µW/cm2 TV/Radio Transmitters 10 mW/cm2 Typical Exposures provided by the World Health Organization (WHO) • Power is delivered by one or more low-power radio waves, at one or more frequencies, well within FCC power density requirements (e.g. cell phones) • Power is received by an antenna (or array of antennas) integrated with a rectifier – RECTENNA • More power is received with a larger rectenna, and the efficiency is larger when the incident power density increases (as high as 50%) • RF power transmitter provides • wireless power to the sensor board • Energy harvester receives incident RF power and delivers maximum power to energy storage and load • Sensor data is received wirelessly and displayed on remote computer connected to data receiver board • Converter parameters are selected in order to minimize converter power losses. • Prototype design using discrete commercial components delivers more than 10x power required by the sensor at the lowest incident power level of 20 µW/cm2. Data Receiving Station 43’ • Wireless devices trickle charge when placed in RF powered areas (5’ radius) • Greater RF power coverage can be achieved with additional transmitters without increasing power density • Sensor transmits data to receiving station when in use anywhere in the living area (range of 30’) • Wireless device remains powered for hours when not in RF power areas Output (Harvested) Power • Custom IC design realized in 0.35 mm CMOS to support operation down to 10mW input power • Developing algorithms for auto-tuning to the input source and thin-film battery Arrays of rectennas for broadband (multi-band) power reception and rectification (~2x2cm and ~6x6cm) operate over all wireless bands Single rectenna for dual-polarized waves (~5cmx5cm) receives up to 10 mW at 2.4GHz (unlicensed band) 25’ RF power Picture courtesy of: http://www.23art.com/images/Archviz_Pic_L5.jpg