1. Radiofrequency Energy Harvesting System based on a Rectenna Array in the Urban Environment of Brasilia, Brazil
EMS Research Group – Fraunhofer IIS and TU Ilmenau Wireless Distribution Systems / Digital Broadcasting LASP – UnB Laboratory of Array Signal Processing
Jayme Milanezi Junior, João Paulo C. Lustosa da Costa, Edison Pignaton de Freitas, Giovanni del Galdo, Wolfgang Felber, Ronaldo S. Ferreira Júnior and Ricardo Kerhle Miranda
Uzbekistan, November 2016
Fachgebiet Hochfrequenz- und Mikrowellentechnik

2. Outline DVT Motivation State of the art and candidate solutions
Feasability evaluation via measurements
Simulation results
Conclusions
EMT

3. Outline DVT Motivation State of the art and candidate solutions
Feasability evaluation via measurements
Simulation results
Conclusions
EMT

4. Motivation Energy recycling
Increase of the energetic needs versus limited natural sources
Exploitation of the produced energy
Examples of energy harvesting in the literature:
Small piezoelectric generator (shoes movement): 330 μW/cm3
Thermoelectric generator 10 ̊ C gradient: 40 μW/cm3
Acoustic noise generator (100 dB): less than 1 μW/cm3
Radio frequency (RF) energy recycling: transmitted information is not relevant.
Signals captured by the antenna are converted into energy.
Exploitation of the part of the available hardware
Dependence of the ubiquity and intensity of the RF signal in a given location

5. Motivation RF energy harvesting for Wireless Sensor Networks (WSN)
Sensor nodes: low energy consumption of the order of hundreds of mW per unit
Changing the batteries of the sensor nodes not feasible in several applications: huge forests and catastrophe areas
RF harvesting to extend the life time of the sensors impacting the life time of the whole WSN
Multi hop communications
Recharging the sensor nodes of the WSN as well as portable electronic devices, such as cell phones
Amount of typically harvested power in the order of few microwatts for RF harvesting systems
Antenna array based RF harvesting
Currently used in 4G wireless communication systems: increased data throughput
In case of energy harvesting:
Adaptive systems: higher power consumption, lowering the final net power to be harvested

6. Motivation Antenna array based RF harvesting Contributions
Non-adaptive systems: dependence on the direction of arrival of the line-of-sight (LOS) component
5G wireless communications system
Massive MIMO systems, where transmitters and receivers are equipped with hundreds of antennas
Contributions
Proposal of a rectenna array system inspired by antenna array based solutions in telecommunications
Feasibility of the RF energy harvesting in real urban scenarios via measurement
Measurement performed in Brasília
Comparison between rectenna array systems and non-adaptive antenna array based systems for LOS scenarios and for only non-LOS scenarios

7. Outline DVT Motivation State of the art and candidate solutions
Feasability evaluation via measurements
Simulation results
Conclusions
EMT

8. State of the art and candidate solutions
Rectenna for energy harvesting
The output of a rectenna is often connected to a battery.

9. State of the art and candidate solutions
Adaptive antenna array systems spend more power.

10. State of the art and candidate solutions
Non-adaptive antenna array systems
Overall power depends on the direction of arrival (DOA).

11. State of the art and candidate solutions
Connecting rectennas in series
No influence of the DOA of the RF incident waves on the overall power

12. Outline DVT Motivation State of the art and candidate solutions
Feasability evaluation via measurements
Simulation results
Conclusions
EMT

13. Feasibility evaluation via measurements
RF measurements in four different places in Brasília, Brazil
Place 3, near TV Tower, provided the best incident power

14. Feasibility evaluation via measurements
A more complete measurement campaign performed in place 3
Higher dBm values than
places 1, 2 and 4
Variation of the amount of
antennas
Antennas fixed onto the roof
of the car

15. Feasibility evaluation via measurements
Measurements comprised arrays with 1, 2, 3 and 4 antennas
Spectrum analsysis with 4 antennas
93.7 MHz
12.45 dBm (17.59 mW)
91.7 MHz
11.34 dBm (13.61 mW)

16. Feasibility evaluation via measurements
Values of incident dBm according to the amount of employed antennas in place 3

17. Feasibility evaluation via measurements
By performing measurements in specific frequency ranges and with an antenna array with 4 elements
an average incidence power: +11 dBm
Given the global efficiency of 18 % for RF wave converters, the total power is equivalent to 2.27 mW.
In a period of 24 hours, the total harvested energy of mWh
Given that the consumption of a sensor node consumes is more than 10 mW to transmit a packet over a wireless link, 5 rectennas are needed.

18. Outline DVT Motivation State of the art and candidate solutions
Feasability evaluation via measurements
Simulation results
Conclusions
EMT

19. Simulation results
By means of simulations, we compare the performance of a rectenna array and an antenna array in the presence of multipath components
Prec: power produced by a rectenna array
Pant: power produced by an antenna array
Kt: coefficient for the LOS component varying between 0, 0.3, 0.6 and 1 to represent the presence of shadowing.
K: Zero mean Gaussian generated with variance 1.
In some generated scenarios: K > Kt

20. Simulation results
Only NLOS scenarios (Kt = 0) and 11 rectennas/antennas: Prec > 2 Pant

21. Outline DVT Motivation State of the art and candidate solutions
Feasability evaluation via measurements
Simulation results
Conclusions
EMT

22. Conclusions
The usage of such amount of energy is mainly applicable to:
sensor nodes
low power consumption electronic devices
For a sensor node consumption of more than 10 mW, 5 rectennas are needed. Less rectennas can be necessary, since only dozens microwatts in sleep mode.
Usage of rectenna arrays as well as antenna arrays in buildings close to the TV tower due to the high power electromagnetic waves on the area
Antenna arrays without adaptive system: TX and RX are static.
Massive antenna systems for 5G
mmWave systems (up to 60 GHz) have a high attenuation.
Transmitters and receivers in massive MIMO are equipped with hundreds antennas. Such antennas can be exploited in a RF harversting system.
Pratical value: approx. 50 antennas to load a cell phone

23. Thank you for your attention!
João Paulo C. L. Da Costa
Uzbekistan, November 2016
Fachgebiet Hochfrequenz- und Mikrowellentechnik