RF Energy Harvesting
Principle and Research
Outline
Introduction and Motivation
Energy Harvesting Techniques
• RF Energy
• Vibration Energy
• Solar Energy
Energy Harvesting Architecture
• System Evaluation
• Circuit Simulation
• Antenna Design
Performance Summary
Future Work and Prospect
2
Outline
Introduction and Motivation
Energy Harvesting Techniques
• RF Energy
• Vibration Energy
• Solar Energy
Energy Harvesting Architecture
• System Evaluation
• Circuit Simulation
• Antenna Design
Performance Summary
Future Work and Prospect
3
Introduction and Motivation
The size and power supply has been drastically
decreased for many devices in decades.
Produce enough power to recharge the battery or
directly supply the electronics.
Solve the problem that the devices is at inaccessible
places.
4
Applications
WSN in environment, agriculture, and structures
applications requires continuously available power
source with long lifetimes.
Self-powering with energy harvesting
Satellite
Monitoring
Station
Existing weather station
5
Applications
Biomedically implanted devices such as stimulator
and drug deliverer
The unchangeable power source decreases the
patient’s risk of death.
6
Outline
Introduction and Motivation
Energy Harvesting Techniques
• RF Energy
• Vibration Energy
• Solar Energy
Energy Harvesting Architecture
• System Evaluation
• Circuit Simulation
• Antenna Design
Performance Summary
Future Work and Prospect
7
Energy Harvesting
Solar
Vibration
Radio Frequency
100mW/cm2
(Under sunlight)
100 mW/cm2
1 mW/cm2
Big area
Cont. vibration
is needed
Low power density
High power density
Easy to apply on
Biomedical Technology
Easy to get from
ambient
6%~20%
>95%
50%~70%
8
RF Energy Harvester
9
Vibration Energy Harvester
Vibration Sensor
Application Circuit
Frequency
75Hz
Peak Efficiency
~90%
Output Voltage
3~5V
Output Power
> 1mW
10
Solar Energy Harvester
Solar Energy Harvester
 High Input Energy
× Low Efficiency
 No Need Rectifier
× Large Area
Output
Voltage
4V
Peak
Efficiency
~20%
Output
Power
> 1W
11
11
Thermoelectric Energy Harvester
Thermoelectric Sensor
Application Circuit
Output
Voltage
3V
Peak
Efficiency
~20%
Output
Power
~ 2mW
12
Outline
Introduction and Motivation
Energy Harvesting Techniques
• RF Energy
• Vibration Energy
• Solar Energy
Energy Harvesting Architecture
• System Evaluation
• Circuit Simulation
• Antenna Design
Performance Summary
Future Work and Prospect
13
RF Energy Harvesting Process
• Wide-Band Antenna
500 MHz ~ 2.4 GHz
• Rectifier
Output Voltage: 0.2~0.5 V
• DC-DC Converter
Transfer the original DC voltage (0.2~0.5 V) to a
higher usable level (e.g., 2 V)
• Digital Controller
Control the input impedance of DC-DC converter
to deliver a maximum power to the output.
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The Limits and Current Practice (I)
Power Sources
The limits of received power in current practices:
[3]
[4]
Frequency
Distance
Transmitted power
677 MHz
Digital TV
4.1 km
6.6 km
960 kW
N/A
Received
Power
60 mW
15-23 mW
Efficiency
16.3 %
N/A
Power Conversion Efficiency(PCE) of the Rectifier
Pout
Pout
Pout
PCE 


Pin Pout  Ploss Pout  Pdiode
Technology
Max. PCE
Sensitivity
[5]
0.3 mm
33%
-14 dBm
[6]
0.35 mm
24%
-10 dBm
[7]
0.5 mm
28%
-17.8 dBm
[8]
0.25 mm
60%
-22.6 dBm
[9]
0.18 mm
67.5%
N/A
The Limits and Current Practice (II)
Broad-Band Matching
Broad-band matching means low Q resonant
Vant
2
Vin 
× 1  Qmatching
2
Low Vin will degrade the efficiency of Rectifier
The Limits and Current Practice (III)
Power Manager: DC-DC converter, control circuit.
• The limits of current practices: 80%
Hard to surpass.
We optimized the architectures mentioned in
[10]~[12].
17
Outline
Introduction and Motivation
Energy Harvesting Techniques
• RF Energy Harvesting
• Vibration Energy Harvesting
• Solar Energy Harvesting
Energy Harvesting Architecture
• System Evaluation
• Circuit Simulation
• Antenna Design
Performance Summary
Future Work and Prospect
18
Architecture
Single-Band (900MHz) RF Energy Harvesting System
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Principle of the Circuit
Rectenna Efficiency
Rectifier’s Vout @ Max. Eff.
We are able to approach the max. rectifier’s
efficiency by adjusting the effective Zin of the DC-DC
converter across different PIN and maintaining the
rectifier’s output at ~0.5V.
This is achieved with the auto-Zin-adjust circuit
*
*matching network
cause the efficiency
gliding, not the rectifier
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High efficiency rectifier
The rectifier’s efficiency fast degrades with Pin due to
impedance mismatching.
Auto-Zin-circuit
• Max. efficiency is maintained with Pin > -18dBm
PIN
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Auto-Zin-Adjust circuit
Adjusts the length of Toff and therefore the effective Zin
of the DC-DC converter to maintain the rectifier’s
efficiency
• If Vd > Vout  Zin is too high  the counter will count
down
To decrease Toff, increase average load cur., and
decrease effective RL
• If Vd < Vout  Zin is too low  the counter will count up
To increase Toff, decrease average load cur., and
increase effective RL
Toff Tuning Circuit
Frequency divider with 6-bit configuration
Toff can be 3x~320x the clock period
3-bit Selector
÷2
÷4
÷8
÷16
÷32
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Tn,Tp generator
Tn generator:3x of clock period
Tp generator :1x of clock period
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Performance Calculation
Eff_totsl = Effmatching × Effrectifier × EffDC_DC = 54%
• Effmatching =
Pin_rectifier
= 87%
Pin_matching
Pout_DC_DC - Pconsumption
• Effrectifier =
= 83%
Pin_DC_DC
Pin_DC_DC
• EffDC_DC =
= 74%
Pin_rectifier
Power Summary: estimated by Friis equation
Outdoor (GSM/TV base station): 490 mW
Indoor (Cell Phone and WLAN): 202.5 mW
Received power at least 100 mW.
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Startup Circuit
During startup phase, there is no load current. With
enough Pin (-15dBm at TT corner 27oC), the
rectifier’s output can reach > 0.6V.
• Using an oscillator that is able to oscillate with its
supply voltage less than 0.6V to control the DC-DC
converter, the output voltage can be boosted to 1.2V
• This zero startup circuit work with AC sources (ex.
RF or vibration) without precharge.
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Outline
Introduction and Motivation
Energy Harvesting Techniques
• RF Energy Harvesting
• Vibration Energy Harvesting
• Solar Energy Harvesting
Energy Harvesting Architecture
• System Evaluation
• Circuit Simulation
• Antenna Design
Performance Summary
Future Work and Prospect
27
Antenna a.
28
• Frequency
500 MHz~900 MHz
• Size
190×15 mm2
• Max. Gain
S11 (dB)
> 2dB
DTV 470~840
Frequency (GHz)
GSM 900
Antenna b.
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• Frequency
GSM/GPS/Wi-Fi
• Size
90×50 mm2
• Max. Gain
> 2dB
S11 (dB)
DCS1800, GSM1900,
WiMAX2350, WLAN2400
GSM900
GPS1575
Frequency (GHz)
Antenna c.
30
• Frequency
3 GHz~10 GHz
• Size
30×30 mm2
• Max. Gain
S11 (dB)
> 4dB
802.11a
Frequency (GHz)
Antenna
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Size Comparison
[13]
a
[13]
b
c
Outline
Introduction and Motivation
Energy Harvesting Techniques
• RF Energy Harvesting
• Vibration Energy Harvesting
• Solar Energy Harvesting
Energy Harvesting Architecture
• System Evaluation
• Circuit Simulation
• Antenna Design
Performance Summary
Future Work and Prospect
32
State-of-the-Art (RF)
The performance is much better than others.
This Work
RF[14]
RF[15]
RF[16]
Process
0.18mm
130nm
90nm
250nm
Frequency
890-920MHz
915MHz/1GHz
915MHz
906MHz
Min. Input
Power
-18dBm
N/A
-18dBm
-22.6dBm
Max. Output
Power
113mW
140mW
9mW
N/A
N/A
56.8%
N/A
16%
60%
Matching Eff.
Rectifier Eff.
DC-DC Eff.
Max.Total Eff.
@ － 5dBm*
87.8%
@ －15dBm
83%
@ －15dBm
74.4%
@ －15dBm
54.2%
@ －15dBm
Output Voltage
2V
65%
@ -15dBm
@ - 7dBm
75%
N/A
N/A
N/A
N/A
@ - 7dBm
1.2V
1.2V @ RL=1M
1.4V @ RL=1.32M
60%
*The total Eff is 36% @－5dBm
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Outline
Introduction and Motivation
Energy Harvesting Techniques
• RF Energy Harvesting
• Vibration Energy Harvesting
• Solar Energy Harvesting
Energy Harvesting Architecture
• System Evaluation
• Circuit Simulation
• Antenna Design
Performance Summary
Future Work and Prospect
34
Future Work
Construct an over-1mW energy harvesting system by
combining multi-harvester.
• Intelligent frequency-hopping RF energy harvesting
system
Analyze trade-off between efficiency and wideband
matching, targeting max. power transfer
Use power sensor to search for band with max.
energy and dynamically tune the matching network
• Multi-sources energy harvesting power manager
Adjust ff1 of DC-DC converter to change the
loading for each ZHout of different harvesters
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Milestones
1st Year
• Fully study all possible solutions, and finish the
energy harvesting circuit designs for the RF power.
2nd Year
• Use power sensor to search for band with max.
energy and dynamically tune the matching network
• By sensing the frequency band with the most sufficient
power, we will switch the corresponding rectenna to
a single DC-DC converter.
3rd Year
• Survey other energy solutions for researching
multi-sources energy harvesting power manager
• An mW-level (>1mW) energy harvester prototype will
be presented.
36
Reference (I)
[1] Federal Communications Commission (FCC) Codes of Regulation, U.S., Part 15,
Low Power Broadcasting, available at < www.fcc.gov>.
[2] U. Bergqvist et al., “Mobile telecommunication base stations-exposure to
electromagnetic fields, Report of a short term mission within COST-244bis,”
COST-244bis short term mission on base station exposure, 2000.
[3] Alanson Sample and Joshua R. Smith, “Experimental results with two wireless
power transfer systems,” Proceedings of the 4th international conference on
Radio and wireless symposium, pp. 16-18, Jan. 2009.
[4] H. Nishimoto, Y, Kawahara, and T. Asami ,“Prototype implementation of
wireless sensor network using TV broadcast RF energy harvesting,”
Proceedings of the 12th ACM international conference adjunct papers on
Ubiquitous computing, pp. 355-356, Sept. 2010.
[5] T. Umeda, H. Yoshida, S. Sekine, Y. Fujita, T. Suzuki, and S. Otaka, “A 950-MHz
rectifier circuit for sensor network tags with 10-m distance,” IEEE J. Solid-State
Circuits, vol. 41, no. 1, pp. 35-41, Jan. 2006.
[6] H. Nakamoto, D. Yamazaki, T. Yamamoto, H. Kurata, S. Yamada, K. Mukaida, T.
Ninomiya, T. Ohkawa, S. Masui, and K. Gotoh, “A passive UHF RF identification
CMOS tag IC using ferroelectric RAM in 0.35- um technology,” IEEE J. SolidState Circuits, vol. 42, no. 1, pp. 101-110, Jan. 2007.
[7] U. Karthaus and M. Fischer,“Fully integrated passive UHF RFID transponder IC
with 16.7- W minimum RF input power,”IEEE J. Solid-State Circuits, vol. 38,
no. 10, pp. 1602-1608, Oct. 2003.
37
Reference (II)
[8] T. Le, K. Mayaram, and T. Fiez, “Efficient Far-Field Radio Frequency Energy
Harvesting for Passively Powered Sensor Networks,” IEEE J. Solid-State
Circuits, vol. 43, no. 5, pp. 1287-1302, May 2008.
[9] Koji Kotani, Atsushi Sasaki, and Takashi Ito, “High-Efficiency Differential-Drive
CMOS Rectifier for UHF RFIDs,” IEEE J. Solid-State Circuits, vol.44, no.11, pp.
3011-3018, Nov. 2009.
[10] E. Carlson, K. Strunz, B. Otis, “20mV Input Boost Converter for Thermoelectric
Energy Harvesting,” Digest of Symposium on VLSI Circuits, pp.162-163, June
2009.
[11] I. Doms, P. Merken, C. Van Hoof, and M. C. Schneider, “Comparison of DC-DC
converter architectures of power management circuits for thermoelectric
generators,” EPE, pp. 1-5, Sept. 2007.
[12] I. Doms, P. Merken, R. P. Mertens, and C. Van Hoof, “Capacitive powermanagement circuit for micropower thermoelectric generators with a 2.1mW
controller,” ISSCC Dig. Tech. Papers, pp. 300-615, Feb. 2008.
[13] P. Li, X. Jiang, X. Liu, H. Shi, and X. Lu,” Research on the relation between
Printed Log-Periodic Antenna's feed and bandwidth,” IEEE Signals Systems
and Electronics, vol. 2, pp. 1-3, 2010.
[14] S. O’Driscoll, S. A. Poon, and T. H. Meng, “A mm-sized implantable power
receiver with adaptive link compensation,” IEEE ISSCC Dig. Tech. Papers,
pp.294–295, Feb. 2009
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Reference (III)
[15] G. Papotto, F. Carrara, and G. Palmisano, “A 90-nm CMOS ThresholdCompensated RF Energy Harvester,” IEEE J. Solid-State Circuits, vol. 46, no. 9,
pp. 1958-1997, Sept. 2011.
[16] T. Le, K. Mayaram, and T. Fiez, “Efficient far-field radio frequency energy
harvesting for passively powered sensor networks,” IEEE J. Solid-State Circuits,
vol. 43, no. 5, pp. 1287–1302, May 2008
39