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Wire
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2015
Taimur Aftab
DIELECTRIC RESONATORS: A NEW FRONTIER
IN WIRELESS PASSIVE SENSING
Laboratory of Electrical Instrumentation, IMTEK, University of Freiburg,
Germany
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Outline
Laboratory for Electrical Instrumentation
– Power supply for wireless sensing
Wireless passive sensing
Dielectric resonators as wireless passive sensors
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Chair for Electrical Instrumentation
2000 – 2003 Prof. Dr. Walter Kuntz
Since 2003 Prof. Dr. Leonhard Reindl
Currently 65 Researchers
– 34 graduate researchers (PhD students, Engineers)
– 25 undergraduate research assistants
– 21 external PhD students
Equipment:
– RF-measurements: network analyzers, impedance analyzers,
noise measurement equipment, synthesizers, spectrum analyzers,
oscilloscopes
– RF on wafer measurement equipment with thermo chuck
– Laboratory with 15 measurement working places
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Wireless sensing
Wireless networking
Low power WSNIndoor
Localization
Energy harvesting
Photovoltaic Thermo-Electric RF
Near field coupling
Inductive Coupling
Implant power management
Chiplesssensing
Acoustic Electromagnetic
Outline of Research
Page 5
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Wireless sensing
Wireless networking
Low power WSNIndoor
Localization
Energy harvesting
Photovoltaic Thermo-Electric RF
Near field coupling
Inductive Coupling
Implant power management
Chiplesssensing
Acoustic Electromagnetic
Outline of Research
Page 6
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Energy consumption of a sensor node
1
10
100
Cu
rre
nt
co
ns
um
pti
on
/ m
A
Radio
(CC1101) Sensor
interface Micro
Controller
(MSP 430)
17 mA
30 mA IDLE Mode / Sleep Mode
Active
transmit receive
500 nA
300 mA
200 nA
10 mA 2 mA
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Wake up receiver
868 MHz or 2.4 GHz standard bands
Addressable wake-up with 125 kHz
Wake up distance 50 … 100 m
Real-time wake-up @ 10 µW power
consumption
Network protocols for wake-up and multi-
hop networks
UHF carrier with 125°kHz
ASK wake up signal
UHF communication
Basis Station
or
other Node
µC
Antenna
switch
UHF
radio
125 kHz
wake up
receiver
Impedance matching Rectifier Low pass filter
mC
Switch
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Neckartalbridge Weitingen – WSN
Intended installation of a multi-hop wireless sensor network
with sensors, wireless repeater and one master node.
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Network Topology for Bridge Monitoring
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2015
SE Monitoring Portal SE Master SE Sensor
Start-up Company Smart Exergy
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Wireless sensing
Wireless networking
Low power WSNIndoor
Localization
Energy harvesting
Photovoltaic Thermo-Electric RF
Near field coupling
Inductive Coupling
Implant power management
Chiplesssensing
Acoustic Electromagnetic
Outline of Research
Page 12
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2015
Energy Harvesting: Indoor Solar Power
Solar cell characterization using photoluminescence
Optimization of solar cells for low intensity applications
Low cost metal-insulator-semiconductor (MIS) solar cells
0,1 1 10 100
1
10
100
1000
10000
31mW/cm²
optimized a-Si Solar cell (clean room)
optimized c-Si Solar cell (industrial scale)
optimized c-Si Solar cell (clean room)
Standard c-Si Al-BSF Solar cell
Pow
er
outp
ut [µ
w/c
m²]
Intensity [mW/cm²]
15mW/cm²
Rühle et al., Energy Procedia 2012
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Simualtion : Optimizing Photovoltaic Cells
Jph
J01 J02
Rsh
Rs
10-4
10-3
10-2
10-1
0
4
8
12
16
20
24
Standard
Effic
ien
cy (
%)
Intensity (W/cm²)
Cell efficiency collapses indoor light intensities ~ 0,01 - 1 mW/cm2
Can a solar cell be optimized to improve cell efficiency at indoor lighting
conditions?
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Simualtion : Optimizing Photovoltaic Cells
Jph
J01 J02
Rsh
Rs
10-4
10-3
10-2
10-1
0
4
8
12
16
20
24
Effic
ien
cy (
%)
Intensity (W/cm²)
Standard
improved Rsh
improved J02
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10-4
10-3
10-2
10-1
0
4
8
12
16
20
24
Effic
ien
cy (
%)
Intensity (W/cm²)
Standard
improved Rsh
improved J02
improved J01
but worse Rs
Simualtion : Optimizing Photovoltaic Cells
Jph
J01 J02
Rsh
Rs
Is this technologically achievable?
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Wireless sensing
Wireless networking
Low power WSNIndoor
Localization
Energy harvesting
Photovoltaic Thermo-Electric RF
Near field coupling
Inductive Coupling
Implant power management
Chiplesssensing
Acoustic Electromagnetic
Outline of Research
Page 17
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2015
Thermoelectric Generators (TEG)
Mikro Peltier coolers © FhG-IPMand MicroPelt, Freiburg
Micro-TEG from Seiko (1994) and
„Seiko ThermicTM“ (small series
production in 1998, ceased)
400 µm
P
heat sourceelectrical power
heat sink
typical power parameters:
10 μA, 30 μW @ ∆T = 5 K
25 μA, 135 μW @ ∆T = 10 K
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2015 heat source
T1
heat sink
T0
p n
load resistor
Tg=Th-Tc
qh
qcKc
Kh
Heat
flow
Electrical Circuit
0 1 2 3 40
100
200
300
400
K [K/W]
Pm
ax/
T2
[mW
/K2]
Thermo-electric Harvesting of Day – Night
Cycle using a thermos flask
Thermoelectric Harvesting
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7thA
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Wireless sensing
Wireless networking
Low power WSNIndoor
Localization
Energy harvesting
Photovoltaic Thermo-Electric RF
Near field coupling
Inductive Coupling
Implant power management
Chiplesssensing
Acoustic Electromagnetic
Outline of Research
Page 20
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A
B C
Power distribution system via
intermediate coil
● Efficient power transfer to multiple
receiver devices
● More flexible positioning
● Smaller antennas: inside and outside
● Higher power efficiency / higher data
rates on power interface
High data rate communication
●1st approach: off-the-shelf components
868 MHz / 250 kbps / MSK
●2nd approach: power link
Similar to RFID / 13.56 MHz / 1Mbps
1 cm
1 cm
Brain Link Brain Tools-”MakeITReaL”
Power distribution system using multi resonators
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Brain Link Brain Tools-”SEAM-WiT”
Efficient Wireless Powering of Biomedical Implants
Challenges
• high efficiency and small size required
• variations in coil positioning and
power consumption (M12 and RL change)
varying optimum load RL,opt and
link input impedance Rin
Developed reader unit featuring the class E
amplifier and communication circuitry, the ferrite
shielding and the primary coil.
Results
• Coil optimization
• Adaptive electronics
Intelligent power transmitter
Dynamic impedance matching on
implant side
Prototype circuit for dynamic
implant side impedance
matching.
Schematic representation of the adaptive class E amplifier.
f = 13.56 MHz
rcoil,implant = 5 mm
rcoil,reader = 15 mm
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Wireless sensing
Wireless networking
Low power WSNIndoor
Localization
Energy harvesting
Photovoltaic Thermo-Electric RF
Near field coupling
Inductive Coupling
Implant power management
Chiplesssensing
Acoustic Electromagnetic
Outline of Research
Page 23
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2015
Sensor Motes vs Passive Sensors
Battery powered system
– Complex, ‘smart’ sensor node
– Simple reader
Wireless passive system
– Simple, ‘dumb’ sensor node
– More complex reader unit.
Display ProcessingRF
transceiver Processing/
ADCSensor
Battery
Digital
Display Processing SDR
Sensor
Analog
RF front
end
RF
transceiver
Page 24
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2015 Short range interrogation of high-Q resonators
Wireless sensing principle
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2015 Very high Q resonator needed (Q > 500)
Time domain gating for S11 NWA signals
Quality factor and resonance frequency estimation
Received signal analysis
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Recent resonant wireless sensors
Acoustic wave resonators: SAW, BAW
Metamaterial based devices: CSRRs
Cavity resonators
– Coaxial
– Evanescent mode
Dielectric resonators
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EM Resonators – Basic distinctions
Confined
– Cavity
– Coaxial
Evanescent
– Microstrip/stripline
– Dielectric
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Parallel plate dielectric resonators
Very high Q resonator
Used traditionally to characterize DR
Adjustable resonance frequency
Operating in the fundamental TE01δ mode
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Quality factor considerations
Three sources of energy loss
– Dielectric loss
– Lossy conductor
– Radiation
Q-factor: metric for loss
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Force Sensor concept
Evanescent open ended waveguide antenna.
Loaded with a dielectric resonator
Cantilever beam spring.
Force → Displacement → Frequency shift
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2015 Electromagnetic force actuator
Readings at 1 m.
Poor reference sensor performance.
Experimental sensor characterisation
Page 32
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2015 Using commercial saw resonator interrogation unit.
< 1 ppm frequency tracking @ 1 k samp/sec, 2.46 GHz
5 m range in noisy environment.
2 dBi antenna gain.
Far field sensor performance
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Torque Sensor concept
The PPDR loaded onto a shaft
Clamps transfer torsional strain into linear displacement
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Torque Sensor characterization
Easy to install torque sensor
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Torque measurement
Self calibration using analytical models
Saint-Venant
torsion model
Inverse Itoh’s
PPDR solver
Zero airgap
Embedded processor
Shaft
material
and
geometry
Human operator
Resonance
Frequency
SDR + RF-frontend
Sensor
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Torque Sensor characterization
Good experimental, analytical fit.
High sensitivity: 5 orders of magnitude, for Aluminum shaft.
0 10 20 30 40-5000
-4000
-3000
-2000
-1000
0
Torque load (Nm)
Res
on
ance
fre
qu
ency
sh
ift
(pp
m)
Experimental data
Experimental least squares fit
OnePoint algo. estimate
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Cross sensitivity analysis
Torque sensor in climatic chamber
Applied pressure on sensor element.
0
20
40
60
80
100
120
Fre
qu
ency
sen
siti
vit
y (
pp
m)
Parameters perturbing frequency
Torque (1 Nm)
Temperature (1 K)
Pressure (1 bar)
Humidity (1 %)
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PPDR Temperature sensor
PPDR connected to a wideband antenna.
Antenna
Micro-strip
transmission line PPDR
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Multiple modes detected
Several modes
Various Q factors
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Mode Table
Modes under investigation
Mode ID Scientific name Frequency (GHz)
1 TE01δ 2.40
2 HEM22δ 3.62
3 TE01(δ+1) 3.73
4 HEM31δ 3.78
5 TE02δ 4.00
6 HEM32δ 4.33
7 HEM41δ 4.47
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Temperature sensitivity
Modes behave differently
TE01(δ+1) and HEM31δ modes
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Temperature sensitivity
Normalized frequency shift
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Isolated dielectric radiator
Metal free resonating reflector
Only a few modes couple well
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- 44 -
1.0
6 m
Inner view of the oven at 700 °C with a dielectric resonator placed inside
Complete measurement setupReading distance: 1.20 m
reader
PC+Labvie
w
oven
17 dBi patch antenna
0 100 200 300 400 500 600 700-5000
-4000
-3000
-2000
-1000
0
1000
Temperature [°C]
Re
so
na
nc
e f
req
ue
nc
y s
hif
t [p
pm
]
Tracked resonance frequency shift
Maximum frequency shift of -4500 ppm
Metallization free Dielectric Resonator based high temperature sensing
J.-M. Boccard, T. Aftab, J. Hoppe, A. Yousaf, R. Hütter, L. M. Reindl,Far- Field passive temperature sensing up to 700 °C using a dielectric resonator 2014 IEEE
International Conference on Wireless for Space and Extreme Environments, Wisee, European Space Agency, ESTEC,
Isolated dielectric radiator
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Isolated dielectric radiator
HEM21δ+1, HEM13δ+1 and HEM23δ+1 modes
Good Q, SNR
Low mode independence
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Isolated dielectric radiator
HEM21δ+1, HEM13δ+1 and HEM23δ+1 modes
Good Q, SNR
Low mode independence
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Thank you!
TE01δHEM12δ
