ELEC-E4740 Antennas Workshop 1.Research on RF-powered devices at the Department of Radio Science and Engineering 2.IEEE AP-S Student Design Contest 3.RF-energy harvesting 11 Sept. 2015

Future Huge amount of radio waves in air! CAGR = Compound annual growth rate ~ average growth / year

J. G. Koomey, S. Berard, M. Sanchez, and H. Wong, "Implications of Historical Trends in the Electrical Efficiency of Computing," IEEE Annals of the History of Computing, vol.33, no.3, pp.46-54, Mar Less and less energy needed for one binary operation!

Future vision – RF-Powered Ubiquitous Sensing and Computing Ambient RF energy Used to power up wireless devices Used for communication (ambient back or re- scattering communication principle)

Needed features in antennas

RF power scavenger project and contest

Contest in brief Goal: Design and build a power-harvesting device that can convert RF emissions into DC power Specs: Antenna + rectifier + energy storage device Total production cost less than 1500 USD Device size 50 x 50 x 50 cm^3, frequency 300 kHz – 60 GHz Teams: 2-5 students (>50 % undergraduate) + mentor Team Aalto ELEC: 2 students from Antennas Workshop course, 2-3 from Elektroniikkapaja or Sähköpaja courses Possible to complete ”ELEC-E Special assignment in radio science and engineering” by participating in the contest

Contest in brief 1.Preliminary design by November 2, 2015 A detailed description of the system to be built The steps that will be taken to ensure the accuracy of the system A bill of materials (up to 1500 USD) 2.Six semi-finalists selected by November 16, 2015 –Each receive 1500 USD for building the system 3.Three finalists selected –Team receives a stipend of 2500 USD to travel to and attend the IEEE AP-S Symposium (San Juan, Puerto Rico, USA, summer 2016) –1st prize 1500 USD, 2nd 750 USD, 3rd 250 USD

Contest in brief Assessment criteria (equally weighted): 1.Available input power and DC power delivered to the load (net efficiency) 2.Bandwidth of the power-harvesting antenna, measured with a network analyzer (300 kHz – 60 GHz) 3.Size and mass of the overall solution 4.Energy storage device

IEEE AP-S Student Design Contest 2014 – 2 nd Prize RFID-based book finder RFID tag RFID reader Team Aalto ELEC Mentors: Kimmo Silvonen, Jari Holopainen, Ville Viikari IEEE AP-S Student Design Contest 2015 – 3 rd Prize System for monitoring respiration during Yoga exercise

Simplified antenna + rectifier + load Diode or transistor is used for rectification Highest rectification efficiency obtained when all the RF power is delivered to the diode Diode is often zero-biased

Impedances of some diodes at 1 and 2 GHz Highly reactive load

Bode-Fano criterion Theory for the largest possible impedance bandwidth Assumes a lossless matching network with an infinite amount of inductors and capacitors Tells the trade-off between matching level and bandwidth

Rectification at small power levels I-V-curve of a Schottky- diode: DC-current under small- signal conditions: DC-power: Rectification efficiency:

Commercial wireless power transfer solution P2110 Powerharvester Receiver (long range) Low RF input for longer range operation RF harvesting range down to -11dBm input power Frequency range from MHz

Student design made in RF and Microwave Engineering course: dBm P2110 Powerharvester Receiver