design and testing of a self-powered wireless hydrogen sensing platform university of florida jerry...
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![Page 1: Design and Testing of a Self-Powered Wireless Hydrogen Sensing Platform University of Florida Jerry Chun-Pai Jun, Jenshan Lin, Hung-Tan Wang Fan Ren, Stephen](https://reader035.vdocument.in/reader035/viewer/2022070415/56649cc15503460f94989578/html5/thumbnails/1.jpg)
Design and Testing of a Self-Powered Wireless Hydrogen Sensing Platform
University of Florida
Jerry Chun-Pai Jun, Jenshan Lin, Hung-Tan Wang Fan Ren, Stephen Pearton and Toshikazu Nishida
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Motivation Behind a Self-Powered Wireless Hydrogen Sensing Platform
• Popular topic due to need of inexpensive sensor devices requiring minimal maintenance to monitor harsh and dangerous environs.
• Growing interest in hydrogen as a fuel cell, which is dangerous if not properly contained.
• Combustion gas detection in Spacecrafts and Proton-Exchange Membrane (PEM) Fuel Cells
• Greater than 4% of hydrogen concentrations are explosive.
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Limitations Of Sensor Development
• Limitations of Energy Harvesting Devices
• Limitations of Low-Power and Low- Voltage Commercial Components
• Limitations of a Wireless System
– Wireless Channel Estimation
– FCC Regulations
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Energy Harvesting Techniques
Solar Energy Harvesting• Solar Cells are a mature
commercial Product• Dependent upon real-
time lighting and temperature conditions
• Pulse Resonant Power Converter– Self-powered and self
controlled– Convert input voltage of
0.8-1.2V to steady 2V output
Vibration Energy Harvesting• Collection of energy
proportional to volume of device
• Limited to magnitude and frequency of vibrations
• For Proof of Concept– PSI D220-A4-203YB Double
Quick Mounted Y-Pole PZT Device
– Direct Charging Circuit
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Energy Harvesting Techniques cont.
Solar Energy Harvesting Vibration Energy Harvesting
Pulse Resonant Power Converter Functional Block Diagram (a) Bare die
photo (b)
IXOLAR XOD17-04B Solar Cell
Four mounted PSI D220-A4-203YB Double Quick Mounted Y-Pole
Bender (a) Direct Charging Circuit (b)
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ZnO Nano-Rods as a Sensing Mechanism
• ZnO currently used for detection of humidity, UV light and gas detection
• Easy to synthesize on a plethora of substrates
• Bio-safe characteristics• Large chemically sensitive
surface to volume ratio• If coated with Pt or Pd, can
increase device’s sensitivity to hydrogen
• High compatibility to microelectronic devices
S D
ZnO M-NRs
Al2O3 Substrate
Al/Pt/Au
a) b)
S D
ZnO M-NRs
Al2O3 Substrate
Al/Pt/Au
a) b)
Schematic of Multiple ZnO Nano-Rods
Close-Up of Packaged ZnO Nano-Rod Sensor
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Pt-ZnO Nano-Rod Sensors• Sputtered with Pt coatings of
approximately 10 Å in thickness• Show no response to the
presence of O2 and N2 at room temperature
• Pt increases conductivity of Nano-Rods
• Up to 8% change in resistance after 10 min. exposure to 500 PPM of hydrogen
• Greater than 2% change in resistance after 10 min exposure to 10 PPM of hydrogen
• 90% recovery within 20 seconds upon removal of hydrogen from the ambient
Pt-coated ZnO Nano-Rod - Relative Resistance Change for Various
Hydrogen Concentrations
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Comparison of ZnO Nano-Rods Coated with Different Metals
0 5 10 15 20 25 30
0
2
4
6
8500ppm H
2 Air
Time(min)
|ΔR
|/R (
%)
Pt Pd Au Ag Ti Ni
Relative Resistance Change for Various Metal-coated ZnO Nano-Rods
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Differential Measurement
• Wheatstone Resistive Bridge– Can limit current
consumption of resistive bridge
– Best way to detect changes in resistance
• Difference Amplifier– Using differential
architecture of operational amplifier to subtract difference at input, and apply gain
– Form of differential measurement
R3
R3
R2
R2
R3
R3
R2
R2
V2
V1
R3R1
R4R2
VgVs V2
V1
R3R1
R4R2
VgVs
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Instrumentation Amplifier
R3
R3
R2
R2
R1
R1
Rg
V1
V2
V3
V4
VOUT
R3
R3
R2
R2
R1
R1
Rg
V1
V2
V3
V4
VOUT
1 32 1
2
2( ) 1OUT
g
R RV V V
R R
• Provides High Impedance Input Buffers isolate V1 and V2 from resistive network of difference amplifier
• Buffers and provides gain before difference amplifier
• Gain can be easily adjusted by varying a single resistor, Rg.
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Differential Detection Circuit• Since Pt-ZnO Nano-Rod devices
react to both hydrogen and temperature, the use of a passivated ZnO as a reference resistor can mitigate the temperature dependency of the differential Detection Circuit.
• Rbias used to limit current flowing into both legs of resistive bridge
• Maintains concept of a differential measurement
• Instrumentation Amplifier helps balance input offset voltages, while providing gain, and conditioning signal for ADC
+
-
-
+
-
+
VDD
GNDGNDE
xpos
ed Z
nO
Pas
siva
ted
ZnO
R B
ias
R B
ias
R1
R1
RG
R2
R2
R3
R3
VOUT
+
-
-
+
-
+
VDD
GNDGNDE
xpos
ed Z
nO
Pas
siva
ted
ZnO
R B
ias
R B
ias
R1
R1
RG
R2
R2
R3
R3
VOUT
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Fabricated Pt-ZnO Nano-Rod for Use in Differential Detection
CircuitZnO with increase Pt catalyst
1400142014401460148015001520154015601580
time(min)
Resis
tan
ce(o
hm
s)
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Fabricated Differential Detection Circuit
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Fabricated Differential Detection Circuit
Output voltage vs sweep of exposed Pt-ZnO Nominal Resistance
0
100
200
300
400
1460 1480 1500 1520 1540 1560
Nominal Resistance (Ohms)
Ou
tpu
t V
olt
ag
e
(mV
)
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Microcontroller Selection
• Low-Voltage• Low-Active Current• Low-Sleep Current• Onboard Memory• Onboard ADC• Serial Output• Reprogrammable
Type of Program Memory
Flash
Program Memory 8 kB
RAM 256 Bytes
I/O Pins 22 pins
ADC
10-bit SAR ( successive
approximation register )
Interface1 Hardware SPI or
UART, Timer UART
Supply Voltage Range
1.8 V – 3.6 V
Active Mode200uA @ 1 MHz, 2.2
Vsupply
Standby Mode 0.7 uA
# of Power Saving Modes
5
REQUIREMENTS
Features of Texas Instruments’ MSP430F1232IPW
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Microcontroller Operation
• Runs through state until a discernable presence of hydrogen is detected.
• Once hydrogen is detected, microcontroller forces RF front-end to transmit an emergency pulse to the central monitoring station before returning back to an idle mode.
• Hydrogen threshold level is at far less than dangerous levels
• Runs through states until a discernable presence of hydrogen is detected.
• Once threshold is detected, the data from the ADC is queued onto the serial output port of the microcontroller to be transmitted.
• Once transmitted, state is reset to sleep
• For constant tracking of hydrogen levels
Data Transmission State Machine Level Monitoring State Machine
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Selection of a Modulation Technique
• RF Power Amplifiers and Oscillators have efficiencies of 50% at best
• Low parts count• Low Duty-Cycle, Low
Data Rate.• Expend energy only for
transmission of Data• Low complexity
4
-DQPSK
OOK
4
-DQPSK
OOK
4
4
-DQPSK
OOK
-DQPSK
OOK
Comparison of Complexity between π/4- DQPSK and OOK
MODULATION REQUIREMENTS
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Selection of RF Transmitter (1)
300 MHz Ming TX-99• Onboard antenna• OOK Modulation• Low Part Count• Low Complexity• Tunable Frequency• Colpitts Oscillator
VDD
GND
VDD
GND
Ming TX-99 Transmitter in OOK Mode
Ming TX-99 Transmitter
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Selection of RF Receiver (1)
300 MHz Ming RE-99• Onboard antenna• External Antenna Tap• Low Part Count• Low Complexity• Tunable Frequency• Envelope Detection• Little Documentation
Ming RE-99 Receiver Schematic
Ming RE-99 Receiver
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Distance Measurements
Received Power at 1m
Test Setup
Layout of Testing Room Maximum Transmission Distances
Received Power at 8m
19.4 mTransmitter & Receiver
16.8 mTransmitter Only
14.5 mReceiver Only
Maximum DistanceAntenna Locations
19.4 mTransmitter & Receiver
16.8 mTransmitter Only
14.5 mReceiver Only
Maximum DistanceAntenna Locations
AtriumHallway HallwayAtrium
3.5 m 10 m 20 m0 m
Tra
nsm
itte
r
0.4
5 m
0.5
5 m
Distance (m)
Transmitter
Receiver
Received Power vs. Distance With
Reference to Room Shape • Shape of room resulted in a wave-guide effect at 10
meters• Last successful data transfer occurred at 19.4 m• Received power at this distance was approximately -70
dBm• Can assume Ming RE-99 Receiver sensitivity is
approximately -70 dBm
-75
-65
-55
-45
-35
0 5 10 15 20
Distance (m)
Rec
eive
d Po
wer
(dB
m)
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Central Monitoring Station
• At the time, used Ming RE-99 Receiver
• NI USB-6008 DAQ device for power to Receiver, and ADC to capture data
• Powered from HP Laptop’s USB Port Running LabVIEW 7.1
• Moving Average Filter to differentiate data “pulse” from noise
Labview Block Diagram Code and Labview Front Panel Gui
Moving Average Filter Example
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Full System Integration and Testing
Schematic of Hydrogen Chamber
Schematic of Hydrogen Chamber
or
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Future Work: New Receiver
Linx Technologies RXM-315-LR
• Replacement for Ming RE-99 since Rayming Corp. went out of business
• OOK Modulation• Low Part Count• Low Complexity• RSSI/PDN• -112 dBm Sensitivity
Pin-Out of RXM-315-LR receiver, and receiver test board, shown with
SPLATCH antenna
System Level Architecture for RXM-315-LR
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Future Work: Low-Profile Antenna
• Linx Technologies ANT-315-SP ‘SPLATCH’ Style Antenna
• Grounded Line, Microstrip Monopole Antenna
• After matching, -9dB gain, trade off for low-profile antenna
• 5 MHz -10 dB BW, Center Frequency = 315 MHz
‘SPLATCH’ dimensions, matched S-parameters
Antenna Test Board w/ Matching Circuit
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• Mapping (n) source bits to message with a maximum of 2, or 3 “high” bits
– Example: 6 source bits 6 source bits = 64 messages (symbols)Find Codeword of length (m) that allow for 64 symbols, with a maximum of 3 high bits.
– 64 = mC3 + mC2 + mC1 + mC0 ; m = 7• Power Reduction
– Assumptions: for now, all source code symbols have equal probability of occurrences, and power is only consumed with the transmission of a high bit.
– So, Power Consumption Reduction is:
• By using a minimum energy coding technique, we can expect to reduce the power required to transmit an un-coded message by 20 to 40 percent.
# #
#
| |% 100
avgsourcehighbits avgcodedhighbitsReduced
avgsourcehighbitsPower
g
Future Work: Minimum Redundancy Minimum Energy Coding
1100011000000000000001111
10100010100000000000001110
011000010010000000000001101
0011000010001000000000001100
10010000010000100000000001011
100010000010000010000000001010
0100100000010000001000000001001
01000000000010000000100000001000
010100000000010000000010000000111
0010100000000010000000001000000110
00011000000000010000000000100000101
001000000000000010000000000010000100
0100000000000000010000000000001000011
00010000000000000010000000000000100010
000010000000000000010000000000000010001
000000000000000000000000000000000000000
CODED -2 “high”
CODED – 1“high-delay”
CODED – 1 “high”(Previous Work)
Source
1100011000000000000001111
10100010100000000000001110
011000010010000000000001101
0011000010001000000000001100
10010000010000100000000001011
100010000010000010000000001010
0100100000010000001000000001001
01000000000010000000100000001000
010100000000010000000010000000111
0010100000000010000000001000000110
00011000000000010000000000100000101
001000000000000010000000000010000100
0100000000000000010000000000001000011
00010000000000000010000000000000100010
000010000000000000010000000000000010001
000000000000000000000000000000000000000
CODED -2 “high”
CODED – 1“high-delay”
CODED – 1 “high”(Previous Work)
Source
Proposed Source Coding Technique
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Minimum Redundancy Minimum Energy Coding (cont.)
Power Consumption Reduction per Additional Redundant Bit
0
10
20
30
40
50
60
70
80
90
3 4 5 6 7 8 9 10
Original Source Bit Length
Pe
rce
nta
ge
of
Po
we
r R
ed
uc
ed
p
er
ad
dit
ion
al R
ed
un
da
nt
Bit
3 high
2 high
1 high
1 delay
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Conclusions
• Successfully designed a low-power sensor interface for the Pt-ZnO Nano-Rod hydrogen sensing mechanism
• In conjunction with the microcontroller, RF transmitter, and separate energy harvesting techniques, were successful in detecting and reporting the presence of 500 PPM of H2 in N2. (.05%) using Pt-ZnO Nano-rods as our sensing mechanism
• Energy harvesting techniques include solar and vibration energy devices.