Design and Testing of a Self-Powered Wireless Hydrogen Sensing Platform University of Florida Jerry...
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Transcript of Design and Testing of a Self-Powered Wireless Hydrogen Sensing Platform University of Florida Jerry...
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
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.
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
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
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)
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
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
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
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
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.
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
Fabricated Pt-ZnO Nano-Rod for Use in Differential Detection
CircuitZnO with increase Pt catalyst
1400142014401460148015001520154015601580
time(min)
Resis
tan
ce(o
hm
s)
Fabricated Differential Detection Circuit
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
)
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
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
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
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
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
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)
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
Full System Integration and Testing
Schematic of Hydrogen Chamber
Schematic of Hydrogen Chamber
or
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
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
• 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
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
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.