12st10 final report (1)

Multi-Input Energy Harvesting System

A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT

FOR THE DEGREE OF

Master of Technology

In The

Faculty Of Engineering

Submitted By

Aditya Mitra

M S Chaitanya CH

Under The Guidance Of

T.V.Prabhakar

K.J.Vinoy

NVC Rao

June 2012

Contents

1 Introduction 1

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Functional Aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3 Characteristics and performance . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.4 User Aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5 Environment aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.6 Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.7 Reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.8 Wish Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Study 6

2.1 Market Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.2 Functional Aspect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2.1 Transducer Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2.2 Conditioning Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2.3 Boost Converter with Power Management . . . . . . . . . . . . . . . . . . 12

2.2.4 Switching Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2.5 Energy Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2.6 Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.3 Modular Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.3.1 Harvester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.3.2 Rectifiers And Doublers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.3.3 Boost Convertor Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.3.4 Energy Storage Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.3.5 Micro-Controller Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.4 Industrial Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

i

CONTENTS CONTENTS

3 Module Design 17

3.1 Transducer Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2 Rectifier Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.3 Doublers Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.4 Boost Converter Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.5 Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.6 Jennic Board Developement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.7 Jennic Board Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.8 Jennic Board Programming Interface and Software . . . . . . . . . . . . . . . . . 31

3.9 Jennic Board BOM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.10 Industrial Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4 Engineering And Fabrication 34

4.1 Product Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.2 Solar Harvester Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.2.1 Module Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.3 Pulsed RF Harvester Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.3.1 Doublers module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.3.2 Module Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.4 Thermal Harvester Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.4.1 Module Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.5 Ambient RF Harvester Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.5.1 Rectifier module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.5.2 Module Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.6 Harvester Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.6.1 Module testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.7 Component Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.8 Universal Harvester Board Characterization . . . . . . . . . . . . . . . . . . . . . 46

4.8.1 Performance Results of Boost Converter for Ambient RF . . . . . . . . . 46

4.8.2 Performance Results of Boost Converter for Thermal Gradient . . . . . . 47

5 Concluding Remarks 49

5.1 User instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.2 Suggestion for Future Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Aditya Mitra,M S Chaitanya CH ii/57 June 2012

CONTENTS CONTENTS

6 APPENDIX 50

6.1 PCB Layers OF Universal Harvester Board . . . . . . . . . . . . . . . . . . . . . 50

6.2 Design Status And Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . 52

7 Acknowledgements 56

8 Bibliography 57

Aditya Mitra,M S Chaitanya CH iii/57 June 2012

List of Figures

2.1 EH-Link Product . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 EH-Link Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3 Average Transmission Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.4 Cymbet Energy Processor Functional Block Diagram . . . . . . . . . . . . . . . . 9

2.5 Comparision of market products with present work . . . . . . . . . . . . . . . . . 10

2.6 Block Diagram of Multi-Input Energy Harvesting System . . . . . . . . . . . . . 11

2.7 Antenna Array in Series Connection . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.8 Harvesting Temperature Differential . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.9 Harvesting Body Temperature Differential . . . . . . . . . . . . . . . . . . . . . . 14

3.1 Bi-Quad antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2 Dimensions of Bi-Quad antenna . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.3 Harvesting set up for Pulsed RF Energy . . . . . . . . . . . . . . . . . . . . . . . 18

3.4 solar panel to collect indoor light energy . . . . . . . . . . . . . . . . . . . . . . . 19

3.5 Thermo-electric transducer for harvesting energy from thermal gradient . . . . . 19

3.6 Parameters of the substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.7 Circuit diagram of rectifier designed to match 50ohm antenna . . . . . . . . . . . 20

3.8 Layout of rectifier circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.9 Circuit diagram of voltage doubler designed to match 50ohm antenna . . . . . . 22

3.10 Layout of Volatge doubler circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.11 Fabricated Voltage doubler circuit . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.12 Circuit diagram of the boost converter for continuous operation . . . . . . . . . . 24

3.13 Circuit diagram of the boost converter for dis-continuous operation . . . . . . . . 24

3.14 Inductor Current waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.15 Experimental setup of boost converter . . . . . . . . . . . . . . . . . . . . . . . . 26

3.16 Efficiency at different input power levels . . . . . . . . . . . . . . . . . . . . . . . 27

iv

LIST OF FIGURES LIST OF FIGURES

3.17 Circuit diagram of boost converter in one-pulse method . . . . . . . . . . . . . . 27

3.18 Cascaded cell approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.19 Enerchip driving the micro-controller load . . . . . . . . . . . . . . . . . . . . . . 29

3.20 Jennic Board schematic 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29



3.23 JN1548 current vs time, deep sleep to active transmitting and back to deep sleep 31

3.24 Completed Jennic Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.25 Completed Jennic Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.1 Block Diagram Of Energy Harvesting System . . . . . . . . . . . . . . . . . . . . 34

4.2 Solar Harvester Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.3 Pulsed RF Harvester Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.4 Measuring S11 of doubler circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.5 Thermal Harvester Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.6 Input waveform of thermal harvester at 50 degree differential . . . . . . . . . . . 40

4.7 Pulsed RF Harvester Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . 40



4.10 Harvester Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.11 Component Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

4.12 Boost Converter efficiency for Ambient RF . . . . . . . . . . . . . . . . . . . . . 46

4.13 Efficiency vs Input Power level Plot for Ambient RF Harvestor . . . . . . . . . . 47

4.14 Boost Converter efficiency for Thermal gradient . . . . . . . . . . . . . . . . . . . 48

4.15 Efficiency vs Temperature Plot for Thermal Harvester . . . . . . . . . . . . . . . 48

6.1 Top layer Of Harvester Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

6.2 Bottom Layer Of harvester Board . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

6.3 Simulation result of rectifier circuit . . . . . . . . . . . . . . . . . . . . . . . . . . 52

6.4 Inductor Current waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

6.5 Simulation result of output capacitor charging . . . . . . . . . . . . . . . . . . . . 53

6.6 Efficiency with percentage change of ripple on input capacitor at 0.15V . . . . . 54

6.7 Efficiency with percentage change of ripple on input capacitor at 0.2V . . . . . . 54

6.8 Efficiency with percentage change of ripple on input capacitor at 0.3V . . . . . . 55

Aditya Mitra,M S Chaitanya CH v/57 June 2012

LIST OF FIGURES LIST OF FIGURES

6.9 Simulation result of voltage doubler circuit . . . . . . . . . . . . . . . . . . . . . 55

Aditya Mitra,M S Chaitanya CH vi/57 June 2012

Chapter 1

Introduction

1.1 Background

One of the major problem faced by applications like wireless sensor networks, medical implantsetc is the energy. When these applications are depleted of energy, they can no longer fulfilltheir role unless the source of energy is replenished. Therefore, it is generally accepted that theusefulness of these applications expires when the battery runs out. Much of the research forsuch applications has assumed the use of a portable and limited energy source, namely batteries,to power sensors and focused on extending the lifetime of the network by minimizing energyusage. The batteries will experience current leakages that drain the resource even when theyare not used. If such applications are not dependent on a limited power source, essentially theyenjoy infinite lifetime. This has motivated the search for an alternative source of energy topower such application especially for applications that require sensors to be installed for longduration (up to decades) or embedded in structures where battery replacement is impractical.We believe that at any place there is presence of more than one type of harvestable energysources, hence we can harvest more energy from other source. To make our power source morereliable and efficient, we recharge a battery. In this work, energy harvesting from low energysource such as ambient RF, pulsed RF, solar and temperature differential is being targeted. Wehave focused our work on scavenging energy from GSM 935 MHz to 960 MHz bands for ambientRF, Mobile phones for pulsed RF, indoor light for solar and low temperature differentials andthen storing this energy into battery. The level of power available for harvesting is typicallyin order of microwatts and the level of power required by the load is typically in order ofmilliwatts. Hence this forces us to use accumulate and use concept. The voltage developedby the energy transducers like ambient RF and TEGs at this power level is very small (in orderof millivolts) hence a boost convertor is required. The commercially available boost convertorsare inefficient for these input power levels for voltage magnification greater than 10 times.Moreover they are typically designed for continuous operation whereas ’accumulate and use’supports intermittent operation. Designing a boost convertor for such a load at this input powerlevel is very challenging. Also while using multiple sources, MPPT, design of sensing circuit,isolation of sources becomes very crucial. Achieving this with minimum possible hardware andenergy consumption by the system becomes very challenging. We have designed a system whichaccomplishes all the above mentioned design challenges. For practical demonstration a radiomodule was powered up.

1

1.2. Functional Aspect Chapter 1. Introduction

1.2 Functional Aspect

The primary function of our product is to harvest from solar, thermal gradient electromagneticenergy from the environment, mobile phones and make it to drive a practical load, the load neednot be an extremely low power device, it could be an LED, a microprocessor, a radio module,an LCD display etc, the technique which allows such wide variety of loads is the intermittentoperation, in essence the power is supplied to the load only when the desired amount of energyhas been accumulated, Apart from the loads requiring burst of energy, there is also a provisionfor connecting loads which require small continuous power in nano-watts, such applications caninclude for example, keeping a microprocessor in active sleep mode so that it can respond to awakeup event and retain the context, another application would be to drive a digital watch ,a sensor etc. Although multi-input energy harvesting is not an entirely new area of study, thetrend in the past has been towards designing for continuous mode of operation and assumes tohave equal power availability for all sources. Moreover the designs target high power levels atthe input. Recently a few low power systems have been reported in papers and other technicalliterature, In our market survey we found couple of product namely EH link 2.4 GHz EnergyHarvesting WIreless sensor node from Microstrain Inc. and Enerchip from Cymbet Corp. whichfalls into same league as ours , however an important difference to note is in the power levelsof the two systems, Our system is designed to work at almost 5 times lesser input power level.Also it works for temperature differential as low as 25 degree Celsius. Our product has alsoextra feature of pulsed RF/ High power input. We believe through numerous search for papersand patents that our work has produced certain novel circuit ideas.

1.3 Characteristics and performance

The input parameters to our system are

• Solar :

Illuminance Usually expressed in Lux

• Pulsed RF :

Input Power Usually expressed in dbm

Input frequency We have designed our system to operate in 900Mhz, the target beingthe GSM cellphones.

• Ambient RF :

Input Power Usually expressed in dbm

Input frequency We have designed our system to operate in 935 Mhz to 965 MHz, thetarget being the GSM cellphone towers.

• Thermal Gradient :

Temperature differential expressed in degree Celsius

Aditya Mitra,M S Chaitanya CH 2/57 June 2012

1.3. Characteristics and performance Chapter 1. Introduction

The output performance parameters to our system are

• Output Voltage : The system provides with output voltage of 3.5 to 4 V

• Peak Output Current : The peak current can be very high in range of 100’s of milliampere

• Energy Efficiency: The boost convertor has max efficiency of 65 percent

The variables which are likely to effect the performance of the product are

• Solar :

Illuminance Higher the illuminance higher the efficiency, but closed circuit input voltageshould not exceed rated battery voltage of 4V

• Pulsed RF :

Input Power It is designed to operate at high RF power, at the lower side the poweravailable to the output is offset by the voltage drop across the diode and the mosfet.

Input frequency We have designed our system to operate in 900Mhz, pushing beyondthese limits will lead to decrease in the efficiency.

• Ambient RF :

Input Power the system is designed to operate at an ultra low RF power, at the lowerside the power available to the output is offset by the minimum power required tokeep the system running, at the higher side the efficiency is reduced by the reflectionsin the matching network which leads to lesser transfer of energy.

Input frequency We have designed our system to operate in 935 Mhz to 965 MHz,pushing beyond these limits will lead to decrease in the efficiency.

• Thermal Gradient :

Heat Sink design If Heat sink should be designed such that the heat delivered by thehot side to the cold side is not accumulated on the cold side, failing to achieve thiscauses temperature differential to reduce and reduce the efficiency and eventuallycease to work.


1.4. User Aspect Chapter 1. Introduction

1.4 User Aspect

The user is not expected to be technically enlightened with the working of the product as thereis no external interface required from the user, user interaction would normally involve pressingcouple of button to activate or deactivate a harvesting source.

1.5 Environment aspects

• Ambient temperature range -20 degree Celsius to +60 degree Celsius, classification isbased on components used, no overall testing has been performed, the performance of thesystem is expected to degrade with increase in temperature as the leakage power for all thedevices will increase, however no thermal tests have been made in the scope of the projectand all the results obtained are at the room temperature with day to day variations nottaken into account.

• Humidity can degrade the performance of the system, it will make the FR4 board morelossy at high frequency, also capacitor dielectrics will absorb moisture and leakage willincrease , the system must be kept away from water and high humidity areas, vibrationand pressure are not expected to effect the performance although no tests have beenperformed.

• The compliance to any of the MIL-STD has not been proved.

1.6 Power Supply

The product does not need a external power supply in form of batteries as it scavenges energyfrom the environment. If however all input sources are not available for a considerable amountof time ( in order of few days ) the system will stop harvesting more energy, and cease to powerup the load. But when the power is available, it can self start provided at least one of the solaror pulsed RF is active.

1.7 Reliability

• Presence of multiple sources in parallel provides with the advantage that if one sourceis not available or one portion of the circuit breakdown then also circuit is capable ofharvesting.

• No degrading components except batteries. Care should be taken that the battery isnot excessively depleted. Since the the number of recharge cycles are high the system isexpected to live long.

• No moving mechanical parts

• Components work at an extremely low power levels, so less chance of burn outs and devicefailures


1.8. Wish Scope Chapter 1. Introduction

Detailed study of reliability using engineering techniques has not been performed as the projectwas investigative in nature focusing mainly on ”Techniques to improve efficiency at extremelylow input power level and integration of all sources”, however extremely good figures of meritrelating to reliability are expected for the above reasons.

1.8 Wish Scope

As mentioned before the idea of integrating multiple energy harvesting source is not a newone , however all the previous attempts barring few have been on much higher power levelsachieved through directed sources like huge solar panels, magnetron and Klystrons , temperaturedifferential near the furnace. The nearest competitor in today’s time does not work below -10dbm of RF power, or temperature differential of just 25 degree Celsius. Also the efficiencyof any such harvester is much less. Our aim in this project is to efficiently harvest multiplesources and integrate them into a multi-input harvester. Below are the wish specifications forour harvester board :

• Solar : Harvest from 200 lux at a solar panel of size less than 5x5 cm

• Pulsed RF : Harvest from 0 dbm continuous power

• Ambient RF : Harvest from -30 dbm input power to antenna

• Thermal Gradient : Harvest from temperature differential of 25 degree Celsius

• System efficiency greater than 50 percent

• Standard output load voltage 3.5V to 4V independent of the load and inputpower

• Wireless Sensor Network Micro controller Sleep Current ¡ 1uA

• Wireless Sensor Network Radio Programmable Transmit Power up to -30dBm

• Ultra Low Tx and Rx energy per bit 10nj/bit

• Board Size less than 5cm X 5cm


Chapter 2

Study

2.1 Market Survey

The products falling into the same league as ours and is available in the market are EH link 2.4GHz Energy Harvesting WIreless sensor node from Microstrain Inc. and Enerchip from CymbetCorp.

Micro Strain Inc. Product : EH-Link 2.4 GHz Energy harvesting wirelesssensor node

The EH-Link wireless node is a self powered sensor, harvesting energy from ambient energysources. EH-Link is compatible with a wide range of generator types, including piezoelectric,thermoelectric generators, EM field and high impedance AC or DC sources, in the range of 5.0 Vto 20 V. The ultralow voltage (ULV) input of the EH-Link allows powering from ThermoelectricGenerators (TEGs). This ULV input can power the EH-Link from as low as 0.02 V and up to0.6 V making the wireless sensor node operable from thermal gradients below 8C with TEGs.It will get the sufficient energy from high energy sources and continuously transmit the dataand from ultra low voltage sources, it will slowly accumulate the energy until enough poweris available to support transmission of sensor data. whenever the power drops, it will chargeback and then continue the data transmission. The Figures 2.[1] shows the EH-Link and thefunctional block diagram.

The EH-Link has 5 harvester input ports. The system can harvest energy from all ambientenergy sources ranging from high energy sources to ultra low voltage sources. It has an additionalfeature of on-board energy storage. The most commonly used harvester input is the Piezo input,an ultra-efficient switch mode converter. Figure 2.[2] clearly demonstrates the capability of theEH-Link versus different wireless transmit rates. Figure 2.[3] shows test results where theapplied voltage was 7.5V, a 1000 ohm Wheatstone bridge is being measured, and the transmitrate and packet payload size were varied. In this test the sample rate is fixed at one sample persecond. The number of measurements saved up for transmission was varied from 1 to 30, whereat 1 a single measurement was transmitted over the wireless link once per second. At 30 inthis test, 30 measurements are accumulated and transmitted every 30 seconds. This is done todemonstrate that much less power is used to sample than to transmit. It is important to notethat even at 30, the data sample timing is preserved and no data are missed in the received

6

2.1. Market Survey Chapter 2. Study

Figure 2.1: EH-Link Product

Figure 2.2: EH-Link Block Diagram

measurement stream.



Figure 2.3: Average Transmission Rate

Comparison of the proposed system with EH-Link

The EH-Link even though has a multi-input harvester support, it needs high voltages from theAC sources and EM fields. It has an ultra low voltage support, but that it for the dc sourceslike TEGs, it doesn’t have a support for very low power level ambient RF energy. Our target isto design a system which can harvest both from ac and dc sources which are at ultra low powerlevel.



Cymbet Corp Product : Enerchip Energy Processor Energy harvesting wire-less sensor node

The Cymbet Energy Processor Chip is an universal Harvesting Processor which harvests energyfrom ambient energy sources. It harvests energy from solar,thermoelectric generators, Vibrationand Electromagnetic radiations. It can harvest RF energy with voltage ranging from 0.4V to4V after rectification, energy from thermal gradient with minimum voltage of 0.4V and frompiezo-electric with voltage range 4-20V after rectification. The EnerChip EP uses an advancedMaximum Peak Power Tracking (MPPT) algorithm that constantly matches the EH transduceroutput impedance. The EnerChip EP operates in multiple modes and can communicate withmicrocontrollers. The EP manages all aspects of energy storage devices/peripherals and usesintelligent power management during the start-up initialization sequence. The key to designingenergy harvesting-based wireless sensors with high efficiency power conversion is to utilize theEnerChip EP along with EnerChip rechargeable energy storage devices. The EnerChip EP per-forms the high efficiency energy conversion, energy storage and power management.The fig.2.4shows the functional diagram of energy processor harvesting energy from thermal gradient.

Figure 2.4: Cymbet Energy Processor Functional Block Diagram

Comparison of the proposed system with Cymbet Enerchip

The Energy Processor from Cymbet even though it supports multi-input harvester, it supportsonly one input harvester at a time. Comparing with EH-Link it can harvest at low voltage andlow power levels but our universal harvester unit can harvest energy from munch lower levels.



Figure 2.5: Comparision of market products with present work


2.2. Functional Aspect Chapter 2. Study

2.2 Functional Aspect

Fig 2.5 illustrates the functional diagram of multi-input energy harvesting system , with amicro-controller and on-board radio module for WSN implementation

Figure 2.6: Block Diagram of Multi-Input Energy Harvesting System

The overall system can be divided into following functional blocks

2.2.1 Transducer Unit

The following blocks forms transducer unit :

• Antenna

• Thermo-Electric Generator

• Solar Panel

Antenna is required to capture RF signal, and provide necessary gain, the desirable propertiesof antenna for energy harvesting circuit are high gain, low substrate loss, impedance matchingwith the rectifier at desired frequency, and bandwidth sufficient to capture the power in thechannel. Thermo Electric Generator is required to capture temperature differential. Indoorsolar panel is required to capture diffused light in closed room.


2.2. Functional Aspect Chapter 2. Study

2.2.2 Conditioning Unit

The following blocks forms conditioning unit :

• Rectifier

• Doublers

The energy is stored in energy storage device as a DC voltage. Some sources like RF gives ACoutput. This requires rectification and bringing to a estimated voltage level where the boostconverter works efficiently. In case of RF it is specifically known as RF to DC converter. Alsoimpedance matching is required for efficient energy transfer. In case of other source doublermay be used, or it can be used directly.

2.2.3 Boost Converter with Power Management

As the commonly low-power loads need minimum of 3.2V for their operation and as the micro-level energy sources will not produce that much of voltage, so a Boost converter is needed tostep-up the voltage level. Also, power management circuitry is needed to reduce the leakagesand efficiently utilize the harvested energy.

2.2.4 Switching Circuit

This block is responsible for Isolation of different sources, comparing the available power andswitch to the source which has appropiate energy available.

2.2.5 Energy Storage

The harvested energy is temporarily stored on a super capacitor or a rechargeable battery. Thechoice of the type of storage is discussed in modular study

2.2.6 Load

The harvester module is used as Li thin film battery charger in our case. The battery powersup the sensor module and the harvester charges the battery during off cycle of this sensor node.


2.3. Modular Design Chapter 2. Study

2.3 Modular Design

The main modules of the design are

• Harvester

• Rectifiers and Doublers

• Starter Circuit

• Storage Device

• Volatage Boost Up Circuits

2.3.1 Harvester

Antenna

The desired features of the antenna are high gain, less size, 50 ohm impedance (for standardiza-tion). But achieving all simultaneously is not possible. For ambient RF the received power is inorder of - 25 to -30 dbm. Hence it becomes necessary to introduce a single high gain antenna atthe input stage. Whereas for pulsed RF the power level received is much higher hence relativelylesser gain antenna can be used to reduce the size. To achieve more output voltage antennashould be used in a array as shown in figure 2.6.

Figure 2.7: Antenna Array in Series Connection

Thermo Electric Generator

The desired feature of a TEG are low input impedance, should provide with higher voltage atoutput at temperature differential (eg. micropelts). An experiment was conducted as shown inthe Figure 2.7. 2 TEGs (Tellurex C2-30-1505) connected in parallel was placed between a hotmug and a heat sink. Temperature differential of around 50 degree Celsius was observed and200 mV output was observed after loading it with a capacitor.



Figure 2.8: Harvesting Temperature Differential

Solar Panel

The solar panel used should be designed to work at fluorescent light. It should have low inputimpedance and high open circuit voltage.

Figure 2.9: Harvesting Body Temperature Differential



2.3.2 Rectifiers And Doublers

RF Doublers

The limiting factor of a voltage doubler and rectifier is its Q factor. The antenna source,matching network and the rectifier makes a RLC series network. Such network has QualityFactor defined as ωL/R. Where ω is the frequency of operation, L is inductance and R is thesource resistance of antenna (which is typically 50Ω) As number of doubler stages increases thecapacitance of the doubler reduces. This in turn reduces the value of inductance required tomatch the capacitive load. As L reduces the quality factor reduces and the voltage developedacross the output also reduces. Also the RF diodes used should have extremely less forwardvoltage drop.

2.3.3 Boost Convertor Circuits

The voltage developed by low grade energy sources at the output of the transducers are typicallyin order of millivolts. Whereas the voltage required drive a typical low power radio module is2.5 V to 4 V. The commercially available boost convertor are designed for continuous operationwhich proves to be highly inefficient for intermittent mode for such level of voltage magnification.Also, power management circuitry is needed to reduce the leakages and efficiently utilize theharvested energy. Hence a custom made boost converter is needed. The boost converter can beoperated in either closed loop or open loop mode. There can be two basic topologies for a boostconverter design. One is either to boost-up the voltage to a required value independent of inputvoltage value. This can be done only in a closed loop. Another one making the output constantwith some battery at the output and transferring the energy harvested to that battery efficiently.Our aim is to design a boost converter with commercially available discrete components withminimum power requirements. So to get good efficiency an open-loop mode can be designed.

2.3.4 Energy Storage Device

The energy storage device should be a battery with large self discharge time and should havemany charge discharge cycles.

2.3.5 Micro-Controller Unit

The desired feature of micro-controller unit are ultra low energy consumption, time for onetransmitting cycle (i.e. from sleep to transmit to sleep) should be very less, transmitting currentshould also should be low, the minimum operating voltage should be low and have a high rangeof operation.


2.4. Industrial Design Chapter 2. Study

2.4 Industrial Design

The section should include the following

• The size of the whole system will be governed mainly by the size of the transducers,are they are comparatively big with respect to universal harvester board, therefore cir-cuit enclosure is separated from transducers except solar panel, and this would serve thepurposes:

Will allow different type of transducers can be connected.

Will allow different type of antenna to be connected for RF Harvesting Unit.

It will make the circuit part small and portable.

• The size of the Harvester Board will be less than 7cm X 7cm, Solar panel can be placedon board.

• Antenna array will be placed in separate box.

• The antennas and the doubler circuits for pulsed RF energy harvesting should be enclosedin a different enclosure.


Chapter 3

Module Design

3.1 Transducer Selection

The transducers are the first in the receiver chain. These transducers convert the energy in theenvironment into electrical energy. The energy sources we choose to harvest is solar, thermalgradient and ambient and pulsed RF.

Ambient RF

Ambient RF energy harvesting is targeted on the energy available GSM towers. Antenna isused to harvest RF energy. The amount of power received by the antenna is dependent on thegain of the antenna. We are harvesting RF power in two forms - pulsed and ambient power.Ambient RF is harvested from the GSM towers whose centre frequency is 945 MHz and has abandwidth of 25 MHz (GSM frequency band used in India). The antenna for this purpose ischosen to be the Bi-Quad antenna which provides with 11 dBi gain and is of fairly compactsize. The power received by this antenna is around -20 to -25 dBm at the hot spots.

The Bi-Quad antenna shown in Fig[3.1] is easy to build, and provides a reliable 11dBi gain,with a fairly wide beam-width. The element is made from a length of copper wire, bent intothe appropriate shape. Fig[3.2] shows the dimensions of the manufactured antenna.

Figure 3.1: Bi-Quad antenna

17

3.1. Transducer Selection Chapter 3. Module Design

Figure 3.2: Dimensions of Bi-Quad antenna

Pulsed RF

Pulsed RF energy harvesting is targeted on the power transmitted by a mobile to the basestation when a call is initiated and audio data is being transmitted or received by the mobile.The nature of the transmitted power is like a high powered pulse which exists for a very shortduration of time and the repetition rate of these pulses are proportional to the amount of audiodata is being sent. The peak power of the pulse was measured to be + 2 dbm with the Bi-Quadantenna centered at 900 MHz at the distance of 0.5 meter from the mobile.

Figure 3.3: Harvesting set up for Pulsed RF Energy


3.1. Transducer Selection Chapter 3. Module Design

Solar

The solar energy intended to be harvested falls in the range of indoor light intensity (200 to1000 lux). Hence the solar panel chosen for this should be chosen for indoor light (fluorescentand incandescent light). The solar panel should generate more than 3.3 volts on open circuitcondition. We have chosen SANYO AM-1801CA shown in Fig[3.4] which provides the requiredcharacteristics because of its small size.

Figure 3.4: solar panel to collect indoor light energy

Thermal Gradient

Thermal energy can be harvested using Thermo-Electric Generator. Temperature differentialavailable should be able to provide us with an output DC voltage of at least 200 mV. TellurexC2-30-1505 shown in Fig[3.5] is chosen for this purpose.

Figure 3.5: Thermo-electric transducer for harvesting energy from thermal gradient


3.2. Rectifier Design Chapter 3. Module Design

3.2 Rectifier Design

The output of the antenna (RF power) is given to rectifier for RF to DC conversion. For ambientRF energy harvesting, the power available is a high frequency AC with very small amplitude.Hence a high sensitivity RF diode is needed. Hence based on the above mentioned selectioncriteria HSMS 2852 is selected for the purpose of designing a rectifier.

The rectifier shows capacitive impedance and the voltage developed across is very less hencefor power matching and for passive amplification of the signal an inductive matching network isused. The series inductor and the shunt inductor (implemented by a short circuit stub) used inthe matching network rotates the impedance seen by the antenna to a 50ohm point achievingpower match.

The circuit and the layout are shown below and the simulation result is given in appendix.

Figure 3.6: Parameters of the substrate

Figure 3.7: Circuit diagram of rectifier designed to match 50ohm antenna


3.3. Doublers Design Chapter 3. Module Design

Figure 3.8: Layout of rectifier circuit

The circuit is fabricated on AD250 board and is fabricated and tested.

3.3 Doublers Design

In Pulsed RF energy harvesting, high instantaneous power is received for a very short duration.The power level received by this exceeds the limit of maximum input power of diodes HSMS2852. Hence a higher power rating diodes are used. High voltages can be developed across thestorage capacitor using doublers. This relaxes the need of boost converter which are inefficientfor intermittent operation. The design of RF doublers is similar to rectifier design.

The circuit and the layout are shown bellow and the simulation result is given in appendix.

The circuit is fabricated on AD250 board and is fabricated and tested.


3.4. Boost Converter Design Chapter 3. Module Design

Figure 3.9: Circuit diagram of voltage doubler designed to match 50ohm antenna

Figure 3.10: Layout of Volatge doubler circuit

3.4 Boost Converter Design

Boost type switching converters are used to step-up the voltage from low voltage sources to ahigher level. The boost converters available in the market is designed for continuous operation.



Figure 3.11: Fabricated Voltage doubler circuit

The internal circuit involves complex power consuming circuits for MPPT. Since we are usingthe boost converter in intermittent operation, the boost converter recognizes only capacitor asthe source. The effective input resistance seen is constant, hence we can conclude that thereis no need of MPPT and we can do away with the complex power consuming feedback circuitswhich implements MPPT. The removal of feedback circuit makes it work in open loop hence weloose the control over the output voltage. We fix this problem by putting battery as the load.Hence allowing only current to pass into the battery and hence charging it. This principle canbe applied to transfer energy from one source to another source. The boost converter designedis based on this.

Continuous Operation

The approach used here in designing the boost converter in open loop is based on resistoremulation. The converter is realized to act as a constant positive resistance at its input portwith less control circuitry while transferring energy to a battery. The basic circuit in open loopconfiguration is shown in fig[3.12]. The input is an ambient energy harvested source which willdirectly feed the converter. When the transistor is switched on, the energy is transferred to theinductor. When it is turned off, the magnitude of energy stored in the inductor is forced tobattery.

Discontinuous Method

For energy harvesting purposes the amount of ambient energy availability is limited. So, weneed to accumulate the energy on a capacitor (Cin) shown in fig[3.13] then it is boosted to a



Figure 3.12: Circuit diagram of the boost converter for continuous operation

required voltage. It means boost converter is not in continuous operation, it needs to be switchedwhenever sufficient energy is available at the input capacitor. In this mode of operation, thenormal boost converters which are meant for continuous operation will give less efficiency. Wedesigned a boost converter which is efficient for this kind of operation.

Figure 3.13: Circuit diagram of the boost converter for dis-continuous operation



The circuit shown in fig[3.13] is the basic boost converter circuit. When the MOSFET (M1) ison, the some of the energy in the capacitor is transferred to the inductor and next when it isoff, this energy along with some energy from capacitor is transferred to a battery. This is likea transfer of energy from a low voltage source to a high voltage source, without this switchingoperation this can’t happen. The inductor current wave form is shown in fig[3.14]. A diode (D1)is used to detect the inductor zero-crossings and also for uni-directional power flow from sourceto battery. The converter parameters are an inductor L, switching period of the MOSFET ’T’with on time of t1.

Figure 3.14: Inductor Current waveform

Instantaneous inductor current during M1-on

i(t) =VinLt (3.1)

Inductor Peak current

Ip =VinLt1 (3.2)

R.M.S. value of current during M1-on

ILrms1 = Ip√ t1

3T(3.3)

Instantaneous inductor current during M1-off

i(t) =Vin − Vo

Lt+ Ip (3.4)

Time, t2

t2 =Vin

Vo − Vint1 (3.5)

R.M.S. value of current during M1-off

ILrms2 = Ip√ t2

3T(3.6)



Average value of current during M1-off

ILavg2 = Ipt22T

(3.7)

The losses in the converter are

Ploss = Pcond + Psw + Pcontrol (3.8)

Conduction losses,

Pcond = Rl(I2Lrms1 + I2Lrms2) +RonI

2Lrms1 + VoILavg2 (3.9)

Switching losses,

Psw = (QgVo/2 + CjoV2in/2)

1

T(3.10)

Control losses,Pcontrol = Poscillator + Pcomparator (3.11)

Based on the above equations the converter parameters are varied to get high efficiency. Theoptimized values come out to be inductance (L) of 150uH, switching period (T) of 40usec withon-time (t1) of 20 usec. To switch the N-MOS with this frequency, an oscillator is needed. Oncethe boost converter parameters are designed, now it needs to get the value of capacitor (Cin)which is used for storing the energy at the input of the boost converter. A 100uF capacitor isgiving the good converter efficiency.

Figure 3.15: Experimental setup of boost converter

The boost converter efficiency was calculated for the above circuit for different power levelsavailable at the input. Fig[3.16] tabulates the results of the boost converter.

The selection of all the discrete components for designing the converter is mainly based onthe low power consumption and low operating losses. The N-MOS switch should have a lowon-resistance to have a low on drop, low gate charge and gate capacitance to have low switchinglosses. Si1563 will serve this purpose. The oscillator which is used to switch on the N-MOS



Figure 3.16: Efficiency at different input power levels

instead of having low power consumption it should have a low settle time during starting aswe are not operating the boost converter in continuous mode, so this is a primary constraint.LTC6906 will serve this purpose. HSMS2822 is selected because of its zero-bias and less forwarddrop.

One Pulse Method

The boost converter designed is based on operating the boost converter for just one pulse. In onepulse we can switch on the mosfet and cause high rate of current flowing through the inductorcausing high voltage to get developed. This high voltage directly comes across the capacitorwhen the mosfet is switched off. Hence a fraction of energy in the capacitor is now transferedto the capacitor which can now charge the battery with power management.

Figure 3.17: Circuit diagram of boost converter in one-pulse method

Cascaded Cell Method

We have proposed this approach to generate higher voltage by combining the rectenna’s inseries, In doing so we have exploited the fact that the output terminal of any rectenna is anRF ground due to high value capacitor being connected, hence if output terminal of the firstrectenna is connected to the ground plane of other rectenna then the net dc value will be sum


3.5. Storage Chapter 3. Module Design

of voltages across individual rectenna’s . N number of such rectenna’s can be connected togenerate voltage high enough to drive a microcontroler, It may also be noted that this schememay as well be used with the multistage inductive-antenna capacitive rectifier type rectenna,the number of units required in that case will be lesser.

Figure 3.18: Cascaded cell approach

3.5 Storage

The energy after being boosted up in voltage domain can be stored in either battery or supercapacitor. We choose rechargeable thin film battery because of its higher energy density andthe ability to provide with fixed voltage for long time even after few transmissions has beendone. Also the battery will power up the sensors, micro-controller and trans-receiver and ensureits reliable operation. The battery used is 4V, 300mAh rated rechargeable battery (MEC220)from THINEGY. It has several thousands of charge/discharge cycles. The recharge time to 80

General Description of battery

The THINERGY MEC220 is a solid-state, flexible, rechargeable, thin-film Micro-Energy Cell(MEC). This unique device substantially outperforms all other small form factor electrochemicalenergy storage technologies, including super capacitors, printed batteries, and other thin-filmbatteries. The device is fabricated on a metal foil substrate to achieve its flexibility, thin profile,broad operating temperature range, and long life. The active materials in the device include aLithium Cobalt Oxide (LiCoO2) cathode and a Li-metal anode. A solid-state electrolyte calledLiPON (Lithium Phosphorus Oxynitride), with its high Li-ion conductivity, is used to providesuperior power performance. Due to its low internal cell resistance, the MEC offers superiorcharge acceptance, making it an ideal energy storage device for applications where extremely lowcurrent recharge sources are available, including various ambient energy harvesting methods.Pulsed or continuous currents as low as 1 µA can be used to effectively recharge this device.The low self-discharge rate results in decades of shelf life. With its recharge cycle stability, thedevice offers tens of thousands of recharge cycles for many years of use with no memory effects.Its performance characteristics are shown in FIG 3.19


3.6. Jennic Board Developement Chapter 3. Module Design

Figure 3.19: Enerchip driving the micro-controller load

3.6 Jennic Board Developement

Figure 3.20: Jennic Board schematic 1


3.7. Jennic Board Features Chapter 3. Module Design



3.7 Jennic Board Features

The important features of the MCU board are:

Board:


3.8. Jennic Board Programming Interface and Software Chapter 3. Module Design

Figure 3.23: JN1548 current vs time, deep sleep to active transmitting and back to deep sleep

• All the peripherals are enabled using jumper pins, which would essentially bring down theleakage current when the peripheral is disabled.

• Reduction of the system cost of about 4x in comparison with the development kit providedby Jennic

• 2.4GHz IEEE802.15.4 compliant radio.

• Very low energy/bit consumption during transceiver operation.

Microcotroller:

• Extremely low sleep current of the order of few nA.

• 4 to 32 MHz configurable CPU clock.

• 128k internal ROM and RAM each support external Flash.

3.8 Jennic Board Programming Interface and Software

• USB to Serial Interface

• GNU-based toolchain-C compiler

• GUI and command line interface Flash programmer

• Eclipse IDE

3.9 Jennic Board BOM

• Jennic microcontroller JN5148

• 32KHz and 32MHz crystals


3.10. Industrial Design Chapter 3. Module Design

Figure 3.24: Completed Jennic Board

• LEDs

• On board Antenna

• Discrete components

3.10 Industrial Design

The section should include the following

• The harvester board is to be placed inside a watch. the screen will consist of solar panel.The harvester and the radio module is to be placed bellow the solar panel as shown infigure 3.25.

• The size of the whole system will be governed mainly by the size of the transducers,are they are comparatively big with respect to universal harvester board, therefore cir-cuit enclosure is separated from transducers except solar panel, and this would serve thepurposes:

Will allow different type of transducers can be connected.

Will allow different type of antenna to be connected for RF Harvesting Unit.

It will make the circuit part small and portable.

• The size of the Harvester Board will be less than 7cm X 7cm, Solar panel can be placedon board.

• Antenna array will be placed in separate box.

• The antennas and the doubler circuits for pulsed RF energy harvesting should be enclosedin a different enclosure.


3.10. Industrial Design Chapter 3. Module Design

Figure 3.25: Completed Jennic Board


Chapter 4

Engineering And Fabrication

4.1 Product Structure

The Block Diagram level representation of the Multi-Input Energy Harvesting system is asshown figure 4.1.

Figure 4.1: Block Diagram Of Energy Harvesting System

In this project Solar, Thermal and RF (ambient and pulsed) sources are targeted. The powerlevels of the inputs are well below the level of power required by the Trans-Receiver modulein active mode. Hence we choose to use the harvester in intermittent mode to recharge thebattery. The battery not only provides reliable supply for Trans-Receiver module but alsohelps in improving the performance of boost convertor present in harvester by eliminating theneed of feedback circuits to maintain the voltage and MPPT. Moreover the battery powers upthe sensing circuits in thermal and ambient RF harvester. Further detailed block diagram of

34

4.2. Solar Harvester Design Chapter 4. Engineering And Fabrication

each harvester is explained in the next section. The Trans-Receiver module is programmed tosense temperature and transmit the data to the receiving station. The Trans-Receiver used wasJENNIC 1548. At the receiver end the data is collected by the 15.04 standard JENNIC1548.The data is then sent to a Bluetooth 2.0 module via serial port. This Bluetooth module collectsthe data from the JENNIC module and makes it available for Bluetooth enabled devices whichhave the application running on it.

4.2 Solar Harvester Design

The targeted source for solar are incandescent light and diffused sunlight where the luminousintensity is less than 1000 lux. The block diagram of solar harvester is shown below. The solar

Figure 4.2: Solar Harvester Block Diagram

panel is providing us with a constant voltage and a current enough to recharge a battery. Henceno extra circuitry is needed for the processing. Isolation is needed for preventing back flow ofenergy and interaction with other harvesting sources.

4.2.1 Module Testing

Equipment Required

• High Impedance Multimeter

• Oscilloscope

Procedure

• Check Open Circuit Voltage

• Connect Solar Panel

• Check panel voltage waveform in oscilloscope

• Check panel current


4.3. Pulsed RF Harvester Design Chapter 4. Engineering And Fabrication

Results

• Open Circuit voltage 5.1 V

• Current flowing at 250 lux is 9 µA from a panel of size 2.5 X 3 cm

4.3 Pulsed RF Harvester Design

The targeted source is the mobile phones when communication is established between the basestation and the mobile phone when a call is initiated. Since the mobile communicates the basestation with burst of RF signals the instantaneous power is high but overall energy is low. Thisgives an advantage over ambient energy harvesting that even though the energy is low but thevoltage developed at the output is high. The block diagram of Pulsed RF harvester is shownbellow. The antenna used is the commercially available dipole antenna. The commercially

Figure 4.3: Pulsed RF Harvester Block Diagram

available dipole antennas are typically low gain antenna. To compensate for the low gain, anarray of antenna put in series can be used followed by a rectifier or voltage doublers after eachantenna. This energy is stored in a small capacitor. The sensing network draws power frominput, allowing it to be self starting. When the input voltage rises above the reference, theswitch is closed and energy stored capacitor is transferred to the battery. Isolation is requiredfor preventing back flow of energy and interaction with other harvesting sources.

4.3.1 Doublers module

• Physical Dimension : 5X4 cm

• Connectors : Edge mount SMA connector connects between the pad 1 and the GROUNDPLANE as shown. Connectors J1 100 mil pitch right hand bend female connectors,connect to the adjacent module (energy storage and management module) to be shownsubsequently.


4.3. Pulsed RF Harvester Design Chapter 4. Engineering And Fabrication

• Development details: Copper Thickness 35 um Substrate FR4 Board thickness 1.6 mm.Number of layers 2 Routing Layer TOP

• Assembly and mounting details: Reflow soldering of all SMD components. Manual sol-dering of all through hole components and the SMA connector.


Equipment Required

• Mobile Phones


• Oscilloscope

Procedure

• Check S11 of Rectifier/Doublers module

• Connect Rectifier/Doublers module to antenna array

• Check individual rectifier+antenna is working

• Check to see that polarity of each output capacitor is same

• Connect rectifier to the harvesting module

• Check input voltage waveform in oscilloscope for input voltage ripple

• Check current flowing into the battery

Results

• Open Circuit voltage 4.5 V at a distance of 10 cm

• Average Current flowing through battery was approximately 25 µA from 3 series connecteddoubler arrangement.


4.4. Thermal Harvester Design Chapter 4. Engineering And Fabrication

Figure 4.4: Measuring S11 of doubler circuit

4.4 Thermal Harvester Design

The targeted source is the temperature differential between any two surface. For purpose ofdemonstration, two Thermo-Electric Generators (Tellurex c2-1530) were connected in paralleland was sandwiched between a Hot Mug and a plain surface attached to heat sink. The blockdiagram of Thermal harvester is shown below. The voltage developed by the TEGs at the

Figure 4.5: Thermal Harvester Block Diagram

input were less compared to Solar and pulsed RF, hence a boost convertor is required. Acustom boost convertor was proposed and designed for intermittent operation. The designedboost convertor provides with higher efficiency than any commercially available boost convertor


4.4. Thermal Harvester Design Chapter 4. Engineering And Fabrication

which is naturally designed for continuous operation. The sensing circuit draws power from theoutput battery.


Equipment Required


• Oscilloscope

Procedure

• Check Open Circuit Voltage

• Connect Solar Panel

• Check panel voltage waveform in oscilloscope

• Check panel current

Results

• Open Circuit voltage 500 mV at a temperature differential of 50 degree Celsius

• Voltage waveform on the input capacitor is shown in fig

• Vinitial= 170mV

• Vfinal= 200mV

• Time of charging= 100msec.

• Temperature difference= 55deg.

• Average current into the battery = 9.25 u A

• Efficiency= 61


4.5. Ambient RF Harvester Design Chapter 4. Engineering And Fabrication

Figure 4.6: Input waveform of thermal harvester at 50 degree differential

4.5 Ambient RF Harvester Design

The targeted source is the power radiated GSM towers which are operating at 945 MHz inIndia. Unlike the pulsed RF, the instantaneous power is very less. Hence a very high gainantenna is used at the input. The antenna used is Bi-Quad antenna which has 11dBi gain.Output of antenna is AC in nature so it is given to a rectifier. The voltage developed by

Figure 4.7: Pulsed RF Harvester Block Diagram

the rectifier is less compared to Solar and pulsed RF; hence a boost convertor is required. Acustom boost convertor was proposed and designed for intermittent operation. The designedboost convertor provides with higher efficiency than any commercially available boost convertorwhich is naturally designed for continuous operation. The sensing circuit draws power from the



output battery. The block diagram of Ambient RF Harvester is shown below.

4.5.1 Rectifier module

• Physical Dimension : 5X4 cm

• Connectors : Edge mount SMA connector connects between the pad 1 and the GROUNDPLANE as shown. Connectors J1 100 mil pitch right hand bend female connectors,connect to the adjacent module (energy storage and management module) to be shownsubsequently.

• Development details: Copper Thickness 35 um Substrate FR4 Board thickness 1.6 mm.Number of layers 2 Routing Layer TOP

• Assembly and mounting details: Reflow soldering of all SMD components. Manual sol-dering of all through hole components and the SMA connector.


Equipment Required

• Portable Network Analyzer

• High Gain Transmitting Antenna (to simulate GSM tower)


• Oscilloscope

Procedure

• Check S11 of Rectifier module

• Connect Rectifier module to receiving antenna

• Check rectifier output

• Connect rectifier to the harvesting module

• Check input voltage waveform in oscilloscope for input voltage ripple

• Check current flowing into the battery

Results

• Open Circuit voltage 350 mV at a temperature differential of 50 degree Celsius

• Vinitial= 160mV

• Vfinal= 200mV



• Time of charging= 250 msec.

• Power level= -7 dBm

• Average current into the battery = 4.82 u A

• Efficiency= 59




4.6. Harvester Board Chapter 4. Engineering And Fabrication

4.6 Harvester Board

Fig[4.9] shows the entire harvester board (excluding the transducers)

Figure 4.10: Harvester Board

• Physical dimensions 2 inch X 3 inch Mount holes 2 Mount holes Drill size 110 mil Mounthole Pitch 1800 mil Connectors:Connector J4, J5. 100 mil pitch Right hand bend Maleconnectors, connect to the RF-DC module shown in the previous hardware module. A 12pin connector at the edge of the board provides an easy access to program and monitorcritical signals of the microcontroller. The mapping of the microcontroller signals to theconnector pins is shown in Fig[4.13]

• Development details: Copper Thickness 35 um Substrate FR4 Board thickness 1.6mm.Number of layers 2

• Assembly and mounting details: Reflow soldering of all SMD components except super-capacitor. Manual soldering of through hole components and the super-capacitor.


4.6. Harvester Board Chapter 4. Engineering And Fabrication

4.6.1 Module testing

Equipment Required

• All the energy transducers mentioned in previous sections

• Portable Network Analyzer and high Gain Antenna for simulating a indoor GSM tower

• Connectors and wires

• A gateway consisting of IEEE 15.04 standard Jennic receiver and a bluetooth module

• android mobile with a bluetooth application running on it

• Multimeter And Oscilloscope

Procedure

• For testing individual module follow the testing procedure mentioned in previous section

• Monitor all the voltage variations in the input side.

• Setup the gateway. to form a receiving section

• Connect the module to power up a Jennic transmitter

• Run bluetooth application on the android mobile to receive the data on the mobile

Software requirements for Jennic Module

• Eclipse: For source code compilation.

• Flash programmer: To fuse the code into the flash present on board.

• The entire software development tool kit can be downloaded from http://www.jennic.com/support/software

Testing procedure for Jennic MCU+Radio

• Ensure supply voltage of at least 2.5V.

• To set the microcontroller in programming mode

• Connect power and ground on pins 24 (VDD), 25 (GND) and 26 (VSSA).

• Ensure that pins 9 (SSZ) and 13 (SSM) are tied together. This enables the on board flash.

• To enter programming mode, pin 7 (MISO) must be held LOW at power up or reset andthen released.

• Fuse the code which activates the RF module and transmits data.

• Follow the same procedure and fuse a receiver code on another microcontroller.

• Once both are programmed, reset the devices. Monitor the receiver to verify reception ofdata packets.


4.7. Component Chart Chapter 4. Engineering And Fabrication

4.7 Component Chart

Figure 4.11: Component Chart


4.8. Universal Harvester Board Characterization Chapter 4. Engineering And Fabrication

4.8 Universal Harvester Board Characterization

4.8.1 Performance Results of Boost Converter for Ambient RF

Steps for characterization of boost convertor for ambient RF

• The rectifier module was directly connected to spectrum analyzer

• Input power level was set

• Input voltage ripple and charging time of capacitor, output average current, output voltageis noted

• The efficiency is calculated by :

Ein =1

2× C × (v22 − v21) (4.1)

Eout = VBat × IOavg × tcharge (4.2)

Efficiency =Eout

Ein(4.3)

• The efficiency is plotted against the input power. Figure shows the plotted results.

Figure 4.12: Boost Converter efficiency for Ambient RF



Figure 4.13: Efficiency vs Input Power level Plot for Ambient RF Harvestor

4.8.2 Performance Results of Boost Converter for Thermal Gradient

• The thermal harvester as shown in figure 2.8 was filled with hot water.

• Harvester output is given to the input of the board.

• Input voltage ripple and charging time of capacitor, output average current, output voltageis noted

• The efficiency is calculated by Equations 4.1 to 4.3

• The efficiency is plotted against the input power. Figure shows the plotted results.

Performance characterization of solar harvester cannot be evaluated since there is no powermanagement circuit in it and it is directly connected. Performance characterization of pulsedRF cannot be evaluated due to random nature of input RF pulse amplitude and time and alsodue to lack of equipment which can display time and duration of RF pulses.



Figure 4.14: Boost Converter efficiency for Thermal gradient

Figure 4.15: Efficiency vs Temperature Plot for Thermal Harvester


Chapter 5

Concluding Remarks

5.1 User instructions

Below are the specifications of the device.

• Minimum Ambient RF input power at which the circuit is functional = -18 dBm. RFfrequency = 930-960MHz

• Minimum Temperature difference at which the circuit is functional = 25 deg.

• Minimum Indoor light intensity at which the circuit is functional = 200 lux.

• High Power burst mode for quick charging.

• On board MCU operating voltage is 3V to 4.1V.

Other useful information of the device are listed below.

• Two push button switches are provided to connect the battery to the boost convertercircuit to power-up the comparator.

• The Matching circuit for RF is tuned to the frequency band 930Mhz - 960Mhz. At otherfrequency bands appropriate matching circuit has to be used.

• Other Energy harvesting transducers whose output voltage is dc can be connected to theany low voltage input terminals of the Harvester Board.

5.2 Suggestion for Future Generation

• Implementing a multi hop wireless sensor network

• Implementing on chip harvester with inductors and input capacitor as off chip components.

• Adding a wake up receiver circuit (which consumes less than 500nA) with the radio toreduce the energy consumption by the load during sleep period

49

Chapter 6

APPENDIX

6.1 PCB Layers OF Universal Harvester Board

Figure 8.1 and 8.2 shows the top and bottom layer of the Universal Harvester Board along withtop and bottom silkscreen layers

Figure 6.1: Top layer Of Harvester Board

50

6.1. PCB Layers OF Universal Harvester Board Chapter 6. APPENDIX

Figure 6.2: Bottom Layer Of harvester Board


6.2. Design Status And Simulation Results Chapter 6. APPENDIX

6.2 Design Status And Simulation Results

Figure 6.3: Simulation result of rectifier circuit



Figure 6.4: Inductor Current waveform

Figure 6.5: Simulation result of output capacitor charging



Figure 6.6: Efficiency with percentage change of ripple on input capacitor at 0.15V





Figure 6.9: Simulation result of voltage doubler circuit


Chapter 7

Acknowledgements

First of all, we would like to thank our advisors, Prabhakar T.V and Dr. K.J Vinoy, for theirencouragement and unfailing support throughout this ambitious project. Thanks also to ourIndustrial Design advisor Chalapati Rao N.V for his support, and Mr B.K.A.N Singh for guidingus in manufacturing issues. We also thank Mrs. Vasanta K B and Mr. Anthonisamy C forPCB manufacturing. We Would also like to thank our colleagues at IISC for all the intellectualdiscussions, especially I.Hiteshwar Rao (CEDT) for helping with the board assembly. We extendour sincere gratitude to the following organizations for their kind support in form of samples,technical support and reference designs. Wurth Electronics, Coilcraft for all the free samples ata very short notice. Linear Technologies for introducing a wonderful chip LTC3108 at just theright time, and samples.

56

Chapter 8

Bibliography

• Thurein Paing, Erez Falkenstein, Regan Zane, Zoya Popovic, ”Custom IC for Ultra-lowPower RF Energy Scavenging” in IEEE power electronics Letters, Nov 13, 2010.

• Triet Le, Karti Mayaram, ”Efficient Far-Filed Radio Frequency Energy Harvesting forPassively Powered Sensor Networks”, in IEEE Journal of Solid-State Circuits, vol 43,No.5, May 2008.

• Arseny Dolgov, Regan Zane, Zoya Popovic, ”Power Management System for Online LowPower RF Harvesing Optimization”, in IEEE Transactions on Circuits and Systems,vol.57, No.7, July 2010.

• Energy Harvesting Chip and the Chip Based Power Supply Development for a WirelessSensor Network. Sensors 2008, 8, 7690-7714.

• Christopher J. Love, Shuguang Zhang, Andreas Mershin ”Source of Sustained VoltageDifference between the Xylem of a Potted Ficus benjamina Tree and its Soil” PLoS ONE,Issue 8, vol 3, Aug 2008.

• T. S. Paing, J. Morroni, A. Dolgov, J. Shin, J. Brannan, R. A. Zane, and Z. B. Popovic,”Wirelessly-powered wireless sensor platform,” in Proc. IEEE 37th Eur. Microw. Conf.,Munich,Germany, Oct. 2007, pp. 1-4.

• Chao Shi, Brian Miller, Kartikeya Mayaram, and Terri Fiez,”A Multiple-Input BoostConverter for Low-Power Energy Harvesting,”in IEEE Trans. Circuits Syst. II, Exp.Briefs, vol. 58, no. 12, pp. 827-831, Dec. 2011.

• S. Dhople, J. Ehlmann, A. Davoudi, and P. Chapman, ”Multiple-input boost converterto minimize power losses due to partial shading in photovoltaic modules,” in Proc. IEEEEnergy Convers. Congr. Expo., Sep. 2010, pp. 2633-2636.

• Triet Le, Karti Mayaram, ”Efcient Far-Field Radio Frequency Energy Harvesting for Pas-sively Powered Sensor Networks” in IEEE JOURNAL OF SOLID STATE CIRCUITS,VOL.43, NO. 5, MAY 2008.

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12st10 final report (1)

Documents

thermal harvester design

solar harvester design

module design

solar harvester block

boost converter design

pulsed rf harvester

ambient rf harvester

jennic board schematic