Funding is provided by the National Institute on Disability and Rehabilitation Research under the US Department of Education, Grant # H133E040019.University of Colorado at Denver & Health Sciences Center,

School of Medicine, Department of Physical Medicine & Rehabilitation

• Power converter provides maximum energy harvesting from rectenna and delivers usable energy to the load

• Boost power converter emulatesa positive resistance to optimallyload rectenna input source

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

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

System OverviewRF Power

Sensor Prototype

Power Converter

Applications

Wireless switch for improved accessibility

Power wireless devices

indefinitely

Eliminates need to replace batteries in countless devices

Maintenance-free implanted biomedical

devices

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• 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.

• Custom IC design realized in 0.35 m CMOS to support operation down to 10W input power

• Developing algorithms for auto-tuning to the input source and thin-film battery

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RF Power Transmitter Energy Harvester & Wireless Sensor

Data Receiving Station

Picture courtesy of: http://www.23art.com/images/Archviz_Pic_L5.jpg

43’

25’RF power

• 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

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• 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%)

Single rectenna for dual-polarized waves (~5cmx5cm) receives up to 10 mW at 2.4GHz (unlicensed band)

Arrays of rectennas for broadband (multi-band) power reception and rectification (~2x2cm and ~6x6cm) operate over all wireless bands

Measured rectified power from small patch

• 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

RF Power Transmitter20 µW/cm2

Typical Exposures provided by the World Health Organization (WHO)

TV/Radio Transmitters10 mW/cm2

Radars20 mW/cm2

MicrowaveOven

50 mW/cm2

Cell Phone50 mW/cm2

Is it SAFE?

• 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

PCB Antenna

Accelerometer

MCU

Transceiver

GSRContacts

Power Circuitry

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Time (ms)

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rre

nt

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MCU, Radio Power Up

X, Y, Z

Radio Settling

Accelerometer Settling

Sampling

Temp GSR

Assemble PacketCalculate CRC

Transmit

ResumeSleep

Experimental results showing total instantaneous sensor current consumption during one sample-and-transmit cycle and associated operating modes of the sensor electronics

Operating Current

2.93.13.3

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Average Power

Lifetime

Average Power

Average power required by the sensor as a function of sample period, demonstrating an average power of less than 5 W when sampling once every ten seconds.

Output (Harvested) Power

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