Transcript Slide 1

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
• 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
14.0
Transmit
12.0
Power
wireless
devices
indefinitely
Current (mA)
10.0
Eliminates need to
replace batteries in
countless devices
Assemble Packet
Calculate CRC
MCU, Radio
Power Up
8.0
Radio Settling
6.0
Sampling
4.0
Resume
Sleep
Accelerometer Settling
X, Y, Z
Temp
GSR
2.0
30
30
26.4
0
Maintenance-free
implanted biomedical
devices
0.5
1
1.5
2
2.5
3
3.5
4
4.5
21
20
Experimental results showing total instantaneous sensor
current consumption during one sample-and-transmit cycle
and associated operating modes of the sensor electronics
10.2 10
10
10
7
4.5
3.3
3.1
5
2.9
0
0
20
25
30
35
Q2
L
gatep
V in
4.2”
RF power
15
VL
iL
Data Receiving Station
43’
25’
10
Power Converter
Energy Harvester
& Wireless Sensor
• 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
5
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.
Transceiver
Measured rectified power
from small patch
Arrays of rectennas for
broadband (multi-band)
power reception and
rectification (~2x2cm and
~6x6cm) operate over all
wireless bands
3.7
0
PCB
Antenna
GSR
Contacts
Typical Exposures provided by the World Health Organization (WHO)
Single rectenna for
dual-polarized waves
(~5cmx5cm) receives
up to 10 mW at 2.4GHz
(unlicensed band)
7.0
5
Accelerometer
Radars
20 mW/cm2
• 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%)
15
Lifetime
MCU
• 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
+
–
gaten
C1
Q1
C2
Vo
energy storage
element
• Power converter provides maximum energy harvesting
from rectenna and delivers usable energy to the load
• Boost power converter emulates
2  L  Thf  M  1 
a positive resistance to optimally Remulated  2


t1  k  M 
load rectenna input source
• 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.
Output
(Harvested)
Power
Power Delivered
to Load vs. Incident Power
Density
800
Power Delievered to Load
(μW)
RF Power Transmitter
RF Power Transmitter
20 µW/cm2
Average Power
15
15
Voc
TV/Radio
Transmitters
10 mW/cm2
20
18
Sample Period (s)
System Overview
RF Power
Microwave
Cell Phone
Oven
2
50 mW/cm2 50 mW/cm
25
22
Power
Circuitry
Time (ms)
Is it SAFE?
24
25
3
0.0
Wireless switch for
improved accessibility
Average Power
Lifespan (years)
Operating Current
Average Power (uW)
Applications
700
600
500
400
300
200
100
0
0
20
40
60
80
Incident Power Density (μW/cm2)
100
120
• 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
Picture courtesy of: http://www.23art.com/images/Archviz_Pic_L5.jpg
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