1. Self-Powered Plant Sensor Node for Scatter Radio 1/40
Self-Powered Plant Sensor Node for Scatter
Radio
Christos
Konstantopoulos
M.Sc. Diploma defense
School of Electrical and Computer Engineering
Technical University of Crete
March 2015

2. Self-Powered Plant Sensor Node for Scatter Radio 2/40
Exploitation of biological sensors and energy sources
Outline
1 Exploitation of biological sensors and energy sources
Precision agriculture
Plant electrical signals
Biological sources of energy
Our approach
2 Plant Signal Acquisition Network
3 Energy harvesting from plants
4 Receiver Design
5 Experimental Results

3. Self-Powered Plant Sensor Node for Scatter Radio 3/40
Exploitation of biological sensors and energy sources
Precision agriculture
Precision agriculture
A need of large scale, low cost
environmental sensing & early
plant stress detection.
WSNs contribute to
monitoring of remote crop
fields
Sensing of environmental
variables
Optimal resource
management

4. Self-Powered Plant Sensor Node for Scatter Radio 4/40
Exploitation of biological sensors and energy sources
Plant electrical signals
Plant electrical signals
Correlation between
plant’s electrical signals
and external stimuli:
pollination
watering
wounding
temperature change
Common ECG electrodes
are used
No scalable
measurement
architectures so far
Cooling
response
Cooling
stimuli
50mV
5 s
12 s
70mV
Cutting
response
Cutting stimuli
leaf petioleb)
a)
Electrical signaling in Mimosa pudica: a) after
spontaneous cooling, b) stimulated by cutting
(J. Fromm and S. Lautner, Electrical signals and their
physiological significance in plants, Plant Cell and
Environment, 2006)

5. Self-Powered Plant Sensor Node for Scatter Radio 5/40
Exploitation of biological sensors and energy sources
Biological sources of energy
Harvesting energy from biological sources
Biological sources:
Endocochlear
potential
Microbial fuel cell
Plant electrical
potential
Common practice:
Anode electrode collect
electrons from the
oxidation of organic matter
Cathode electrode act as a
sink for electrons
8H+
8H+
8e–
8e–
8e–
8e–
Selectivemembrane
4O2
4H2O
8H+
edohtaCedonA
10H+
2CO2
2CH3COO–
e–
e–
e–
HO
O
HO
2H2O OH
OH
OH
e–
Example of microbial fuel cell producing electricity through a mechanism of
electron transfer to the anode (Derek R. Lovley, Bug juice: harvesting
electricity with microorganisms, Nature Reviews Microbiology, 2006)

6. Self-Powered Plant Sensor Node for Scatter Radio 6/40
Exploitation of biological sensors and energy sources
Our approach
Self-powered plant sensor node
Our approach:
Treat plants as biological
sensors and energy
sources
Scatter radio nodes that
sense and harvest the
plant electrical signals
A large scale network of
plants
Massive acquisition of
plant electrical signals

7. Self-Powered Plant Sensor Node for Scatter Radio 7/40
Plant Signal Acquisition Network
Outline
1 Exploitation of biological sensors and energy sources
2 Plant Signal Acquisition Network
Network of Plants
WSN node
Plant signal acquisition
FM modulation
3 Energy harvesting from plants
4 Receiver Design
5 Experimental Results

8. Self-Powered Plant Sensor Node for Scatter Radio 8/40
Plant Signal Acquisition Network
Network of Plants
Plant Signal Acquisition Network
One WSN node per
plant
Low cost
Scalability
Ultra low
consumption
Plant signal
sensing
Sensor node #N
Emitter
Reader
Sensor node #2
Sensor node #1
Sensor node #1

9. Self-Powered Plant Sensor Node for Scatter Radio 9/40
Plant Signal Acquisition Network
WSN node
Scatter Radio Sensor Node
FM modulation:
Plant signal amplitude to frequency conversion
Semi-passive
Scatter Radio
architecture
Mixed signal
design
Energy
Sustainable
Design
Harvests and
interfaces the
electrical signals
V-
V+
Plant sensor node
+
-
Antenna
Voltage
Controlled
Oscillator
Signal
Conditioner
VDD
Vplant
Vcond RF
choke

10. Self-Powered Plant Sensor Node for Scatter Radio 10/40
Plant Signal Acquisition Network
Plant signal acquisition
Signal Conditioning
Signal Conditioner
• Triple op-amp
instrumentation
amplifier
architecture
Long term
measurement
stability
• Ag pin electrodes
Desensitization from
environmental noise
• Braid shield
driven by the Vref
V-
V+
Vplant
+
-
Ag pins
Signal
Conditioner
VDD
Vref
Vcond
Shield
Braid

11. Self-Powered Plant Sensor Node for Scatter Radio 11/40
Plant Signal Acquisition Network
FM modulation
MAC networking
Frequency Division Multiple Access modulation
The same guard-band among the nodes
Same spectrum band allocated at every node
F#1 F#2
Flower
Fupper
BW#1
BandGuard Node#1
3rd
Harmonic
Carrier
Fcarrier F#3 F#N

12. Self-Powered Plant Sensor Node for Scatter Radio 12/40
Plant Signal Acquisition Network
FM modulation
WSN Frequency allocation
VCO characteristic:
F#N =
−Fswmax
Vcondmax
∗ Vcond + Fswmax (1)
Fsw
F#1
#2
F#3
..
F#N
Vcond
0 Vref#1
Vref#2
Vref#3
.. Vref#N
Fswmax
Vcond
Vrange
BW#1
F
BandGuard
Fupper
F
max
lower
Vcond = G ∗ Vplant + Vref#N
(2)
#Nodes =
Fupper − Flower
BW#N + BandGuard
(3)
BandWSN =
N
i=1
(BW#i + BandGuard) (4)

13. Self-Powered Plant Sensor Node for Scatter Radio 13/40
Energy harvesting from plants
Outline
1 Exploitation of biological sensors and energy sources
2 Plant Signal Acquisition Network
3 Energy harvesting from plants
Signal Acquisition and Energy Harvesting
Power Management Unit
4 Receiver Design
5 Experimental Results

14. Self-Powered Plant Sensor Node for Scatter Radio 14/40
Energy harvesting from plants
Signal Acquisition and Energy Harvesting
Electrodes setup
Plant signal measurement
electrodes
Ag pins
Plant signal harvesting
electrodes
Anode (Mg or Zinc alloy)
Cathode (Cu alloy)
Electrodes setup that reassure
measurement integrity
Vharvest
Vcm
Ag pins
Mg or Zinc alloy foil Vplant
Cu foil
V-
V+
branch
stem

15. Self-Powered Plant Sensor Node for Scatter Radio 15/40
Energy harvesting from plants
Signal Acquisition and Energy Harvesting
Plant Power-Voltage characteristics
P-V Measurements
across the day
Correlation related to
temperature and solar
irradiation
MPPs range across
the day: 0.5-0.8 V
0 0.2 0.4 0.6 0.8 1 1.2 1.4
0
200
400
600
800
1000
1200
1400 12:00 680 W/m2
22.3 o
C
14:00 450 W/m2
21.0 o
C
16:00 100 W/m2
19.5 o
C
18:00 0 W/m2
16.1 o
C
20:00 0 W/m2
15.7 o
C
MPP
Vharvest
(V)
Pharvest
(nW)

16. Self-Powered Plant Sensor Node for Scatter Radio 16/40
Energy harvesting from plants
Power Management Unit
Energy harvesting scheme
Harvest the low power plant signals (hundreds of nW)
One way approach:
Duty cycle operation
Static operational voltage levels
Power management
unit:
Energy storage
capacitance
Voltage Detector
Self-oscillating
DC-DC converter
Linear regulator
Self-powered plant sensor node
+
-
Voltage
Controlled
Oscillator
Signal
Conditioner
Vplant
Vcond
Power distribution
RF reflective
switch
Antenna
Power Management Unit
Voltage level
detector
Self-oscillating
DC/DC converter
Linear regulator
Cin
Iharvest
Vharvest RF
front-end
V+
V-

17. Self-Powered Plant Sensor Node for Scatter Radio 17/40
Energy harvesting from plants
Power Management Unit
Duty cycle operation
Linear regulator
V-
V+
Self-powered plant sensor node
+
-
Voltage
Controlled
Oscillator
Signal
Conditioner
Vplant
Vcond
Power distribution
RF reflective
switch
Antenna
Power Management Unit
Voltage level
detector
Self-oscillating
DC/DC converterCin
Vharvest RF
front-end
VL
VH
toff
0
VL
VH
0
Vharvest
Pharvest
Vharvest
Wait until Csto is charged towards the VH voltage level
System on state OFF

18. Self-Powered Plant Sensor Node for Scatter Radio 18/40
Energy harvesting from plants
Power Management Unit
Duty cycle operation
Linear regulator
V-
V+
Self-powered plant sensor node
+
-
Voltage
Controlled
Oscillator
Signal
Conditioner
Vplant
Vcond
Power distribution
RF reflective
switch
Antenna
Power Management Unit
Voltage level
detector
Self-oscillating
DC/DC converterCin
Vharvest RF
front-end
VL
VH
toff
0
Vharvest
VL
VH
0
Vharvest
Pharvest
Voltage Detector triggers when the VH level is reached
System remains on OFF state

19. Self-Powered Plant Sensor Node for Scatter Radio 19/40
Energy harvesting from plants
Power Management Unit
Duty cycle operation
Linear regulator
V-
V+
Self-powered plant sensor node
+
-
Voltage
Controlled
Oscillator
Signal
Conditioner
Vplant
Vcond
Power distribution
RF reflective
switch
Antenna
Power Management Unit
Voltage level
detector
Self-oscillating
DC/DC converterCin
Vharvest RF
front-end
VL
VH
toff
ton
0
Vharvest
Input capacitance Cin discharges towards VL voltage level
Signal Conditioner, VCO and RF switch units on ON state

20. Self-Powered Plant Sensor Node for Scatter Radio 20/40
Energy harvesting from plants
Power Management Unit
Voltage Level Detector
High impedance input for
harvesting
tens of MOhm input
impedance
Schmitt trigger
architecture
Bistable circuit
Temperature
compensation
NTC Thermistor (Rth)
Voltage level
detector
p
Cf
L2
L1
Ct Rt
Cout
Rd
n
Positive
feedback
control
Hysteresis
loop
R1
R2
Rf
Rth
Power Management Unit
Linear regulator
Cin
I harv
Vharvest
Self-oscillating DC/DC
power converter
VDD

21. Self-Powered Plant Sensor Node for Scatter Radio 21/40
Energy harvesting from plants
Power Management Unit
Self-oscillating DC-DC power converter
Cold start-up operation
Oscillation driven power
converter
Tuned for efficient
operation close to plant
MPPs
Efficient operation
0.5-0.7 V Vharvest input
Step-up voltage
conversion 0.58 V to 1.6
V
Planar core-less PCB
transformer
Voltage level
detector
p
Cf
L2
L1
Ct Rt
Cout
Rd
n
Positive
feedback
control
Hysteresis
loop
R1
R2
Rf
Rth
Power Management Unit
Linear regulator
Cin
I harv
Vharvest
Self-oscillating DC/DC
power converter
VDD

22. Self-Powered Plant Sensor Node for Scatter Radio 22/40
Receiver Design
Outline
1 Exploitation of biological sensors and energy sources
2 Plant Signal Acquisition Network
3 Energy harvesting from plants
4 Receiver Design
Duty cycle handler
5 Experimental Results

23. Self-Powered Plant Sensor Node for Scatter Radio 23/40
Receiver Design
Duty cycle handler
Duty cycle handler
FDMA implementation on
Software Defined Radio
Noise Floor Estimation
Carrier Frequency
Offset estimation &
correction
Signal power detection
Node
Detected?
Store
Yes
No
Noise floor
estimation
CFO
estimation
Band pass
filtering
Node Frequency
Calculation
CFO
estimation
Packet
acquisition
Packet
acquisition

24. Self-Powered Plant Sensor Node for Scatter Radio 24/40
Experimental Results
Outline
1 Exploitation of biological sensors and energy sources
2 Plant Signal Acquisition Network
3 Energy harvesting from plants
4 Receiver Design
5 Experimental Results
Prototypes
Self-powered node
Calibration
Plant Measurements

25. Self-Powered Plant Sensor Node for Scatter Radio 25/40
Experimental Results
Prototypes
Self-powered scatter radio sensor
Plant signal harvester
Mixed signal design
10 uW Comm. and
Signal Processing
consumption
Vplant range
−600 mV to +600 mV
Sensitivity 56.5 Hz/10
mV (BW 6.7 kHz).
Current
Implementation
capable of 10 Nodes
BOM at 8.70e(1 piece)
Signal
Conditioning
Unit
Voltage
Controlled
Oscillator
120 mm
71 mm

26. Self-Powered Plant Sensor Node for Scatter Radio 26/40
Experimental Results
Prototypes
Self-powered scatter radio sensor
Plant signal harvester
Mixed signal design
10 uW Comm. and
Signal Processing
consumption
Vplant range
−600 mV to +600 mV
Sensitivity 56.5 Hz/10
mV (BW 6.7 kHz).
Current
Implementation
capable of 10 Nodes
BOM at 8.70e(1 piece)

27. Self-Powered Plant Sensor Node for Scatter Radio 27/40
Experimental Results
Prototypes
Battery-assisted scatter radio sensor
Sensitivity 40 Hz/ 5 mV
(BW 4.5 kHz)
Measurement range
−250 mV to +250 mV
40uW power consumption
Current Implementation
capable to 43 Nodes
Signal
Conditioning
Unit
Voltage
Controlled
Oscillator
DGND
AGND
53 mm
47 mm

28. Self-Powered Plant Sensor Node for Scatter Radio 28/40
Experimental Results
Prototypes
Backscatter operation
Sub-carriers for 2 self-powered
nodes
867.98 867.99 868.00 868.01 868.02 868.03
−110
−100
−90
−80
−70
−60
−50
−40
−30
−20
Vplant =−600mV
Vplant = 600mV
Node 1 Node 2
sub-carriers
ReceivedPower(dBm)
Frequency (MHz)
Emitter’s
carrier
Sub-carriers of 8
battery-assisted nodes
867.99
868.03
868.07
868.11
868.15
868.19
868.23
868.27
−120
−110
−100
−90
−80
−70
−60
−50
−40
−30
−20
Frequency (MHz)
ReceivedPower(dBm)
Emitter’s
carrier sub-carriers
8 Nodes

29. Self-Powered Plant Sensor Node for Scatter Radio 29/40
Experimental Results
Self-powered node
PMU Operation
PMU signals during
operation
Cf
L2
L1
Ct Rt
Cout
Rd
n
Vcon
Vdrain Vout
Vharvest
Linear regulator
VDD
Voltage
Level
Detector
Cin
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4
−1.0
−0.5
0.0
0.5
1.0
1.5
2.0
2.5
0
x10-6
Time (s)
V
Vcon
Vdrain
PMU Efficiency for different
input (Vharvest) voltage levels
Vharvest(V) 0.826 0.784 0.647
ηPMU % 0.64 0.80 2.1

30. Self-Powered Plant Sensor Node for Scatter Radio 30/40
Experimental Results
Self-powered node
PMU Operation
DC-DC converter operation with unregulated output
0
100
200
300
400
500
600
700
800
900
1000
1.00
1.25
1. 50
1.75
2.00
2.25
2.50
Vout
(V)
Pout
(uW)
0
100
200
300
400
500
600
700
800
900
1000
0
5
10
15
20
25
30
35
40
45
Pout
(uW)
ηDC/DC(%)
583 mV
659 mV
716 mV
812 mV
Voltage output (Vout) and conversion efficiency for various loads
and different Vharvest input levels.

31. Self-Powered Plant Sensor Node for Scatter Radio 31/40
Experimental Results
Self-powered node
Example of duty cycle operation
tcold−start = 1130 s
ton = 176 ms
toff = 450 s
Duty cycle = 3.80 ∗ 10−4
ηeff−ener = 1.3%
Cin (uF) 2350 2820 3350 3820 4350
ton (ms) 176 194 247 266 274
Table: Transmission time for various input
capacitance
Vout
(V)
Time (s)
ton
0.2 0.3 0.4 0.5 0.6
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 0.1
0.401
0.456
0.513
0.568
0.624
0.680
0.737
0.794
0.849
Vharvest
(V)
toff
Vharvest
(V)
0 300 600 900 1200 1500 1800 2100
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Time (s)
tcold-start

32. Self-Powered Plant Sensor Node for Scatter Radio 32/40
Experimental Results
Self-powered node
Range Measurements
Signal to Noise Ratio, Mean Absolute Error and Root Mean
Square Error for two alternative bi-static configurations
Distance d
Reader Carrier
Emitter
Self-powered
WSN Node
r-n
dn-e
Error
Topology
Configuration
SNR (dB) RMS (mV) MAE (mV)
dr−n = 14.6 m & dn−e = 27.9 m 25.57 16.04 14.58
dr−n = 19.3 m & dn−e = 35.7 m 23.80 25.40 25.35

33. Self-Powered Plant Sensor Node for Scatter Radio 33/40
Experimental Results
Calibration
Calibration setup
VCO sensitivity according to temperature change
Calibration with
varying differential
input for different
environmental
conditions.
Emulation of energy
source in case of the
self-powered WSN
node.
V-
V+
Self-powered plant sensor node
+
-
Voltage
Controlled
Oscillator
Signal
Conditioner
Vplant
Vcond
Power distribution
RF reflective
switch
Antenna
Power Management Unit
Voltage level
detector
Self-oscillating
DC/DC converter
Linear regulator
Cin
Iharvest
Vharvest RF
front-end
+
-

34. Self-Powered Plant Sensor Node for Scatter Radio 34/40
Experimental Results
Calibration
Least Squares polynomial fitting
Temperature
desensitization
Accord.
RMS to Scale %
Nodes (mV) (500 mV)
#1 6.01 1.2
#2 14.39 2.8
#3 10.06 2.0
#4 14.05 2.8
#5 6.57 1.3
#6 26.99 5.3
#7 17.57 3.5
#8 22.80 4.5
Self-
powered
17.00
1.4
(Scale 1.2 V)
Table: Calibration Error

35. Self-Powered Plant Sensor Node for Scatter Radio 35/40
Experimental Results
Plant Measurements
Measurements from the self-powered node
Measurement of plant
signals across the day
Evidence of correlation
with environmental
variables
28/9 29/9 30/9 1/10 2/10 3/10 4/10
0
20
40
60
80
100
0
200
400
600
800
1000
15
20
25
30
−50
0
50
100
150
200
250
300
23:59 23:59 23:59 23:59 23:59 23:59 23:59
5/10
23:59
175
180
185
190
195
200
205
190
195
200
205
210
215
220
Node
mV
Temperature
oC
Solar
Irradiance
W/m2
Humidity
%RH
Irrigation Events
Days

36. Self-Powered Plant Sensor Node for Scatter Radio 36/40
Experimental Results
Plant Measurements
Measurements from the battery-assisted WSN nodes
Measurement of plant
signals across the day
Evidence of correlation
with environmental
variables
0
400
800
20
25
30
35
40
−250
0
250
−250
0
250
−250
0
250
−250
0
250
−250
0
250
−250
0
250
−250
0
250
−250
0
250
21/7
00:00 00:00 00:00 00:00 00:00
29/7
00:0000:00
22/7 23/7 26/7 28/7
00:00
27/7
Node 1
Node 2
Node 3
Node 4
Node 5
Node 6
Node 7
Node 8
mV
Days
Temperature
oC
Solar
Irradiance
W/m2

37. Self-Powered Plant Sensor Node for Scatter Radio 37/40
Experimental Results
Plant Measurements
Battery-assisted plant Sensor
Left -Battery-assisted WSN node
Right -Plant signal acquisition test-bed

38. Self-Powered Plant Sensor Node for Scatter Radio 38/40
Experimental Results
Plant Measurements
Self-powered plant sensor
Vharvest GND
V+
V-
Left -Self-powered WSN node
Right -Electrodes setup

39. Self-Powered Plant Sensor Node for Scatter Radio 39/40
Publications
Journal publications related to this work
Konstantopoulos C., Koutroulis E., Mitianoudis N. and
Bletsas A., "Converting a Plant to a Battery and Wireless
Sensor with Scatter Radio and Ultra Low-Cost”, IEEE
Sensors, Submitted
Kampianakis E. ,Kimionis J. ,Tountas K. ,Konstantopoulos
C. ,Koutroulis E. ,Bletsas A. "Wireless Environmental
Sensor Networking with Analog Scatter Radio and Timer
Principles", Special Issue of IEEE Sensors, Volume:14 ,
Issue: 10

40. Self-Powered Plant Sensor Node for Scatter Radio 40/40
Thank you for you attention!
Questions?
This work was supported by the ERC-04-BLASE project, executed in the context of the Education & Lifelong
Learning Program of General Secretariat for Research & Technology (GSRT) and funded through European Union -
European Social Fund and national funds