Wireless power supply for ambient assisted living

205 Pages·2016·25.24 MB·English

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UNIVERSITY OF SOUTHAMPTON

FACULTY OF PHYSICAL AND APPLIED SCIENCE

Department of Electronics and Computer Science

Wireless Power Supply for Ambient
Assisted Living

by

Yi Li

A thesis submitted in partial fulfilment for the degree of Doctor of Philosophy

February 2015
UNIVERSITY OF SOUTHAMPTON
ABSTRACT
FACULTY OF PHYSICAL AND APPLIED SCIENCE
Discipline (underlined)
Thesis for the degree of Doctor of Philosophy
Wireless Power Supply for Ambient Assisted Living
Yi Li

This thesis focuses on the development of the wireless applications for Ambient Assisted Living
(AAL) system, the energy harvesting technique for powering the passive sensors in the building
environment, and the flexible screen printed coils for Wireless Power Transfer (WPT) system to
provide the power for a body-area sensor network in an AAL system. The AAL provides safe
environments around assisted peoples and help them maintain independent living. The
applications in AAL include the fixed monitor sensor in building environment and the wearable
sensor on users body area. For supplying power for the applications of AAL wireless power
supply provides the power without cables while offers a more environmentally friendly solution.
Compared with energy harvesting technology, WPT is capable of supplying more power
without increasing the size of the device. In this work, a solar powered PIR sensor demonstrates
that the energy harvesting technique for a passive sensor application for the fixed monitor
sensor in building environment, which can work for up to 16 hours without ambient energy
input. For the on-body area application, the flexible coils are employed in the WPT system
because of the comfort requirement. The coils are printed on 65/35 polyester/cotton textile with
a Fabink-UV-IF1 interface layer coating. The interface layer provides a relatively flat and
smooth surface to prevent the permeation of the conductive paste into the textile and allows the
printing of finer profile coils, and the flexibility and breathability of textile can be remained.
The measured inductances of the printed flexible coils are 3.9 µH for single layer. The design of
the printed coil minimises the coil’s parasitic capacitance, which is less than 25 pF, and
consequently increase the self-resonant frequency of the printed coil. A 5 V 1.51 W DC output
has been achieved by a wireless power transfer system using the printed flexible coils with Qi
standard circuitry; a DC-DC efficiency of 38% has been measured. It has been compared with
the system employed with Qi standard wound copper coils which has the recorded 52% DC-DC
efficiency.
Acknowledgements
I would like to thank Prof. Steve Beeby and Dr Neil Grabham for all the guidance and support
they have kindly given me over the course of my PhD. This thesis would never have been
possible without all the work they put in to, include teaching me how to do a research and write
professionally. I would also like to thank Dr John Tudor for his help and advice.
Thanks to Dr Russel Torah, Dr Dibin Zhu, Dr Kai Yang, and Dr Alex Weddell for their time,
and for providing expertise on the chemistry and electronics in this thesis respectively. Thanks
also to Fan Pei for assisting in the investigation of wireless EMG system, and thanks to Wenhan
Jin for assisting in the fabrication and testing of the curvature-adjustable support.
odical><pages>215</pages><volume>20</volume><numor their kindly help and advice about
the general issues of daily life and study, and for their camaraderie. Thanks to fellow students in
Bay 4 and 5 for their friendliness and companionship. Thanks also to Zihao, Ahmed, Joseph,
Huihui, Nur, Marc, Komolafe, Ivo, Zhuo and everyone else who made the research group an
enjoyable place to work.
Thanks to Eric Cooke and David Oakley for offering me the opportunity to be a demonstrator
and teaching undergraduates in labs. Thanks to all the technic staff in the labs who made lab
equipment keeping work.
I would like to dedicate this thesis to the people closest to me. My gratitude and love to my
parents for everything they have done for me, I could never be in UK without their kindly help
and support. I am really lucky to have my wife Shuo Liu in my life, and great thanks to her for
making me happy.
Contents
ABSTRACT ...................................................................................................................... i
Acknowledgements ......................................................................................................... iii
Contents ........................................................................................................................... v
List of figures .................................................................................................................. ix
List of tables ................................................................................................................... xv
DECLARATION OF AUTHORSHIP ....................................................................... xix
Abbreviations ............................................................................................................... xxi
List of symbols ............................................................................................................ xxiii
1 Introduction ........................................................................................................... 1
1.1 Introduction . 1
1.1.1 Ambient Assisted Living System ........................................................................ 1
1.1.2 Wireless Power Transfer ..................................................................................... 2
1.2 Research Motivation and Aims ........................................................................... 2
1.3 Statement of Novelty ........................................................................................... 4
1.4 Publications arising from this work .................................................................... 4
1.5 Thesis Outline ..................................................................................................... 5
2 Background and Literature Review of Wireless Power Supply ........................ 7
2.1 Introduction . 7
2.2 Ambient Assisted Living ..................................................................................... 7
2.2.1 Building Environment . 9
2.2.2 Body Area Sensors and Network .......................................................................12
2.2.3 Energy Requirements .13
2.3 Power Suply .15
2.3.1 Wired and Battery Power Supplies ....................................................................15
2.3.2 Energy Harvesting Power Supplies ....................................................................16
2.3.3 Wireless Power Transfer ....................................................................................19
2.4 Inductive Coupled Wireless Power Transfer System .........................................22
2.4.1 System Structure .22
2.4.2 Safety of Wireless Power Transfer .....................................................................23
2.4.3 Driver and Receiver ...........................................................................................25
2.4.4 Characteristics of Coils ......................................................................................27
2.5 Scren Printing .27
2.5.1 Background of Screen Printing Technique ........................................................27
v
2.5.2 Screen Printing Paste ......................................................................................... 30
2.5.2.1 Surface Tension and Surface Energy ........................................................... 30
2.5.2.2 Sheet Resistivity of Conductive Paste ......................................................... 31
2.5.2.3 Permittivity of Dielectric Paste and Surrounding Material ......................... 32
2.5.3 Screen Printing Processing ................................................................................ 32
2.5.4 Curing Proces . 35
2.6 Summary ............................................................................................................ 36
3 A Solar Powered PIR Sensor for Fixed Node in Ambient Assisted Living
System ................................................................................................................... 39
3.1 Introduction ........................................................................................................ 39
3.2 Hardware Investigation . 41
3.2.1 Artificial illumination sources ........................................................................... 41
3.2.1.1 Static Characteristic of Different Light Sources .......................................... 42
3.2.1.2 Warm up time for CFL and LED ................................................................. 46
3.2.2 Solar Cells Investigated ..................................................................................... 47
3.2.2.1 Multicomp MC-SP0.8 . 48
3.2.2.2 Panasonic Amorton AM1815 and AM5608 ................................................ 49
3.2.2.3 G24i Indy 4050 ............................................................................................ 50
3.2.2.4 Output Testing of Solar Cells ...................................................................... 50
3.2.2.5 Performances under Different Types of Light Sources ............................... 53
3.2.2.6 Performances under Different Spectral Ranges ........................................... 59
3.2.2.7 Selection of solar cell .................................................................................. 62
3.2.3 Micro Controller and Radio Transceiver ........................................................... 63
3.2.4 PIR Sensor . 6
3.2.5 Summary ............................................................................................................ 67
3.3 A PIR Wireless Sensor ...................................................................................... 68
3.3.1 Hardware Design . 68
3.3.2 Embedded Software Design ............................................................................... 75
3.4 Practical System Testing .................................................................................... 79
3.4.1 Worst Case Scenario .......................................................................................... 79
3.4.2 Normal Scenario . 80
3.5 Conclusions . 81
4 Theory of Wireless Power Transfer ................................................................... 85
4.1 Introduction ........................................................................................................ 85
4.2 Inductively Coupled System for Wireless Power Transfer ................................ 85
4.2.1 Coupled-Mode Theory . 85
4.2.2 Transferring Power via Two Coupled Coils ...................................................... 86
4.3 Mathematical Circuit Modelling for Coil Inductor ............................................ 87
vi
4.3.1 Self-inductance .88
4.3.2 Resistance .89
4.3.3 Parasitic Capacitance .92
4.3.4 Self-Resonant Frequency .93
4.3.5 Unloaded Quality Factor ....................................................................................94
4.3.6 Mutual Inductance of Two Coils ........................................................................96
4.3.7 Coupling Factor between Two Coils ..................................................................97
4.4 Compensation Circuitry .98
4.5 Summary ..........................................................................................................100
5 Design of Printed Coils for Wireless Power Transfer .................................... 101
5.1 Introduction ......................................................................................................101
5.2 Substrate Selection .101
5.3 Materials for Screen Printed Coils ...................................................................103
5.3.1 Interface and Dielectric Material ......................................................................103
5.3.2 Conductive Material .103
5.4 Coils Design .104
5.4.1 Shape ................................................................................................................104
5.4.2 Diameter .105
5.4.3 Tracks ...............................................................................................................106
5.4.4 Number of Turns ..............................................................................................107
5.4.5 Minimising Parasitic Capacitance ....................................................................110
5.5 Circuitry Design for Flexible Coils ..................................................................112
5.6 Summary ..........................................................................................................115
6 Experimental Results of Flexible Printed Coils .............................................. 117
6.1 Introduction ......................................................................................................117
6.2 Screen Printed Fabrication ...............................................................................117
6.2.1 Interface Layer .117
6.2.2 Thermal Curing Duration of Conductive Layer ...............................................120
6.2.3 Bottom Conductive Layer ................................................................................123
6.2.4 Dielectric Layer .126
6.2.5 Top Conductive Layer ......................................................................................127
6.3 Screen Printed Coils .........................................................................................129
6.3.1 Electrical Characteristics of Printed Coils ........................................................129
6.3.1.1 DC Resistance .130
6.3.1.2 AC Resistance .132
6.3.1.3 Relative Permittivity of Interface Material in Dielectric Layer .................135
6.3.1.4 Inductance, Parasitic Capacitance and Self-Resonant Frequency ..............136
6.3.1.5 Unloaded Q Factor of Coils .......................................................................139
vi