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

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

6 Applications Biomedically implanted devices such as stimulator and drug deliverer The unchangeable power source decreases the patient s risk of death.

8 Energy Harvesting Solar Vibration Radio Frequency 100mW/cm 2 (Under sunlight) Big area High power density 100 mw/cm 2 1 mw/cm 2 Cont. vibration is needed Easy to apply on Biomedical Technology Low power density Easy to get from ambient 6%~20% >95% 50%~70%

RF Energy Harvester 9

Vibration Sensor Vibration Energy Harvester Application Circuit Frequency 75Hz Peak Efficiency ~90% Output Voltage 3~5V Output Power > 1mW 10

Solar Energy Harvester Solar Energy Harvester High Input Energy No Need Rectifier Low Efficiency Large Area Output Voltage 4V Peak Efficiency ~20% Output Power > 1W 11 11

12 Thermoelectric Energy Harvester Thermoelectric Sensor Application Circuit Output Voltage Peak Efficiency Output Power 3V ~20% ~ 2mW

14 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.

The Limits and Current Practice (I) Power Sources The limits of received power in current practices: Frequency Distance Transmitted power Received Power Efficiency [3] 677 MHz 4.1 km 960 kw 60 mw 16.3 % [4] Digital TV 6.6 km N/A 15-23 mw N/A Power Conversion Efficiency(PCE) of the Rectifier PCE P P out in P out Pout P loss P out Pout P diode [5] [6] [7] [8] [9] Technology 0.3 mm 0.35 mm 0.5 mm 0.25 mm 0.18 mm Max. PCE 33% 24% 28% 60% 67.5% Sensitivity -14 dbm -10 dbm -17.8 dbm -22.6 dbm N/A

The Limits and Current Practice (II) Broad-Band Matching Broad-band matching means low Q resonant V in V 2 ant 1 Q matching 2 Low V in will degrade the efficiency of Rectifier

17 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].

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

19 Architecture Single-Band (900MHz) RF Energy Harvesting System

Rectifier s V out @ Max. Eff. Rectenna Efficiency 20 Principle of the Circuit We are able to approach the max. rectifier s efficiency by adjusting the effective Z in of the DC-DC converter across different P IN and maintaining the rectifier s output at ~0.5V. This is achieved with the auto-z in -adjust circuit * *matching network cause the efficiency gliding, not the rectifier

21 High efficiency rectifier The rectifier s efficiency fast degrades with P in due to impedance mismatching. Auto-Z in -circuit Max. efficiency is maintained with P in > -18dBm P IN

Auto-Z in -Adjust circuit Adjusts the length of T off and therefore the effective Z in of the DC-DC converter to maintain the rectifier s efficiency If V d > V out Z in is too high the counter will count down To decrease T off, increase average load cur., and decrease effective R L If V d < V out Z in is too low the counter will count up To increase T off, decrease average load cur., and increase effective R L

23 T off Tuning Circuit Frequency divider with 6-bit configuration T off can be 3x~320x the clock period 3-bit Selector 2 4 8 16 32

24 T n,t p generator T n generator:3x of clock period T p generator :1x of clock period

25 Performance Calculation Eff _totsl = Eff matching Eff rectifier Eff DC_DC = 54% Pin_rectifier Eff matching = = 87% Pin_matching Pout_DC_DC -Pconsumption Eff rectifier = = 83% Pin_DC_DC Pin_DC_DC Eff DC_DC = = 74% P in_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.

26 Startup Circuit During startup phase, there is no load current. With enough Pin (-15dBm at TT corner 27 o C), 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.

S 11 (db) Antenna a. 28 Frequency 500 MHz~900 MHz Size 190 15 mm 2 Max. Gain > 2dB DTV 470~840 GSM 900 Frequency (GHz)

S 11 (db) Frequency GSM/GPS/Wi-Fi Size 90 50 mm 2 Max. Gain > 2dB Antenna b. DCS1800, GSM1900, WiMAX2350, WLAN2400 29 GSM900 GPS1575 Frequency (GHz)

S 11 (db) Frequency (GHz) Frequency 3 GHz~10 GHz Size 30 30 mm 2 Max. Gain > 4dB Antenna c. 30 802.11a

Size Comparison Antenna 31 [13] a b c [13]

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 Max. Output Power Matching Eff. Rectifier Eff. DC-DC Eff. Max.Total Eff. -18dBm N/A -18dBm -22.6dBm 113mW @ - 5dBm* 87.8% @ -15dBm 83% @ -15dBm 74.4% @ -15dBm 54.2% @ -15dBm 140mW 9mW N/A N/A 56.8% N/A 65% 16% @ -15dBm 60% @ - 7dBm 75% N/A N/A N/A N/A 60% @ - 7dBm Output Voltage 2V 1.2V 1.2V @ R L =1M 1.4V @ R L =1.32M *The total Eff is 36% @-5dBm 33

35 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 f f1 of DC-DC converter to change the loading for each Z Hout of different harvesters

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. Solid- State 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

38 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

39 Reference (III) [15] G. Papotto, F. Carrara, and G. Palmisano, A 90-nm CMOS Threshold- Compensated 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