RF Energy Harvesting

By Y.G.SAI RAGHU(124576)

Under the guidance ofDr. P. SREE HARI RAO

INDEXIntroductionRequirements of Energy HarvestingSources of Energy HarvestingNeed for the RF based HarvestingOrigin of RF Energy HarvestingChallenges with RF Energy HarvestingArchitecture of RF Energy Harvesting system

Energy HarvestingEH is the process by which energy is derived

from the external sources; captured and stored

Hydro electricity generation

Why do we need EH

Sufficient power as/when needed

Adequate life time-no/low maintaince

Easy low cost installation

Flexibility

Sources of EnergyPhotovoltaic solar cells

Vibrations Piezoelectric Capacitive Inductive

Radio-Frequency (RF)

Thermoelectric conversion

Wind/air flow

Why RF based wireless PowerIndustrial Minimizes Operating Costs Eliminates cost to hard wire or replace batteries – e.g.

wireless sensors. Eliminates service downtime caused by depleted batteries. Reduces battery handling and disposal.End-Users Convenience and Usability Placement flexibility – no charging mats or charging

stations. Transparent charging – no user action required. In some deployments, owing to the sensor location, battery

replacement may be both practically and economically infeasible.

OriginThe Wireless electricity transmission system pioneered by

Dr Nikola Tesla has the potential to meet our future global energy needs

RF Energy is every where

Sources of RF Energy for harvestingFM Radio systems ( 88 – 108 MHz, tens of KW )

TV Transmission ( 180 – 220 MHz, tens of KW )

Cell Tower Transmission ( 800 – 1800 MHz, 10 – 20 W per carrier)

AM Transmission ( 540 – 1600 KHz, few hundred W)

Mobile phones ( 1W to 2W )

Out of which cell towers can be considered as renewable source as they transmit whole 24 hours of the day.

Power Sources Categories

Architecture Of RF Energy Harvesting System

Receive the power from RF Source and rectify the AC voltage in to DC through rectification circuit.

Stepping up of the voltage level of the rectified output through dc – dc converter.

Feeding the stepped voltage to charge a battery through the charging circuit.

Challenges with RF Energy HarvestingAvailable input power to the rectifier is low

and there is no external bias voltage applied. Non-linear dependence of the rectifier

impedance on the frequency and power, broadband impedance matching network is essential for maximum power transfer.

High efficiency of RF-DC conversion and low power DC-DC converter is required.

The rectifier should have minimum power loss to increase the overall efficiency.

Matching circuitThe matching circuit is composed of

inductive and capacitive elements ensure smooth deliver to the load.

A slight change in the matching circuit parameters alters significantly the frequency range in which efficiency of energy conversion is maximum.

Rectification using Schottky diodesRF EH is able to operate even for the low RF

power. As the peak voltage of the a.c signal is very smaller than the diode thershold. These diodes must operate with low thershold and high frequency.

A voltage doubler is designed with silicon based Schottky diode having threshold voltage of 230mV and diode capacitance of .26pF.(HSMS-2852,HSMS-2822).

At microwave frequency, the non-linear capacitance of the diode governs the maximum power transfer to the load and amplitude of the rectified output as input impedance of the rectifier changes with the frequency.

CMOS Rectifier circuitThe operation of the four-transistor cell is

easily understood if Vp and Vp are assumed to be large enough to turn the transistors on and off.

Thus, a dc voltage is developed across a load connected

between VH and VL . In general,ѴH-VL=2*Vref-Vo

Dc-Dc converterA DC-to-DC converter is an electronic

circuit which converts a source of direct current (DC) from one voltage level to another.

When the switch is closed inductor will charge and at that time charge stored in the capacitor delivers voltage to the load.

When switch is open inductor discharges to load and capacitor.

VOLTAGE MULTIPLIERSingle stage voltage doublers is used generally

for doubling the voltage that from the rectifier.Number of voltage multiplier stages can be

increased to have more voltage, but by increasing the number of stages the current will be decreased resulting in the increase of the delay.

single stage voltage doublers

Microstrip antenna designThe main challenge faced in harvesting RF

energy is the free space path loss of transmitted signal with distance.

Pr=PtGrGt(λ⁄4∏R)² Proposed antenna for RF Energy Harvesting is

broadband electromagnetically coupled Square microstrip antenna.

In India cell towers transmit in the frequency range of 869- 890 MHz in CDMA, 935-960MHz in GSM 900 and 1810-1880MHz in GSM 1800 bands.

A single patch antenna provides a maximum directive gain of around 6-9 dBi.

Effect of Input power

EH circuit consists of diodes, which are non-linear devices, the circuit itself exhibits non-linear.

The impedence of EH circuit varies by the amount of power received from the antenna.

RF EH from the multiple antennasThe use of multiple antenna in addition to the

existing circuits the amount of EH can be increased depending on the number of antennas implimented.

By using this mode does not increase the efficiency of the circuit.

Applications: Bulk Trickle Charging

Freedom of placement

Eliminate wires and connectors

Automatic/transparent charging

Multiple battery types/chemistry

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future for energy harvesting?

System integration

Low power electronics

Falling costs

ConclusionsHarvesters must supply sufficient power from

immediately available energy sources and meet the full operating condition requirements .

A RF Energy Harvesting system is designed with a high gain electromagnetically coupled antenna is developed.

Because of the development of low power circuits made possible to use the RF as power source.

References N. Kumar and G. Kumar, Biological Effects of Cell Tower

Radiation on Human Body, IEEE Conf. ISMOT, pp.1365-1368, Aug. 2012.

Z. W. Sim, R. Shuttleworth, and B. Grieve Investigation of PCB Microstrip patch receiving antenna for outdoor RF energy harvesting in wireless sensor networks, IEEE Conf. Antenna and Propagation Conference, Loughborough, pp.129-132, Feb. 2012

A.C. Patel, et al, Power Harvesting for Low Power Wireless Sensor Networks. IEEE Conf. Antenna and Propagation Conference, Loughborough, pp.633-636, Nov. 2009

V.Rizzoli, et al, CAD Multi-Resonator rectenna for micro power generation. Proc. of 4th European Microwave Conference, pp.1684-168, Sep. 2009.