1. Design and Testing of a Self-Powered Wireless Hydrogen Sensing Platform
Jerry Chun-Pai Jun, Jenshan Lin, Hung-Tan Wang Fan Ren, Stephen Pearton and Toshikazu Nishida
University of Florida

2. 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.

3. 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

4. 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 V 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

5. Energy Harvesting Techniques cont.
Solar Energy Harvesting
Vibration Energy Harvesting
IXOLAR XOD17-04B Solar Cell
Four mounted PSI D220-A4-203YB Double Quick Mounted Y-Pole Bender (a) Direct Charging Circuit (b)
Pulse Resonant Power Converter Functional Block Diagram (a) Bare die photo (b)

6. 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
Schematic of Multiple ZnO Nano-Rods
Close-Up of Packaged ZnO Nano-Rod Sensor

7. 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

8. Comparison of ZnO Nano-Rods Coated with Different Metals
Relative Resistance Change for Various Metal-coated ZnO Nano-Rods

9. 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

10. Instrumentation Amplifier
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.

11. 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

12. Fabricated Pt-ZnO Nano-Rod for Use in Differential Detection Circuit

13. Fabricated Differential Detection Circuit

14. Fabricated Differential Detection Circuit

15. Microcontroller Selection
REQUIREMENTS
Type of Program Memory
Flash
Program Memory
8 kB
RAM
256 Bytes
I/O Pins
22 pins
ADC
10-bit SAR ( successive approximation register )
Interface
1 Hardware SPI or UART, Timer UART
Supply Voltage Range
1.8 V – 3.6 V
Active Mode
1 MHz, 2.2 Vsupply
Standby Mode
0.7 uA
# of Power Saving Modes 5
Low-Voltage
Low-Active Current
Low-Sleep Current
Onboard Memory
Onboard ADC
Serial Output
Reprogrammable
Features of Texas Instruments’ MSP430F1232IPW

16. Microcontroller Operation
Level Monitoring State Machine
Data Transmission State Machine
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

17. Selection of a Modulation Technique
MODULATION REQUIREMENTS
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
Comparison of Complexity between π/4- DQPSK and OOK

18. Selection of RF Transmitter (1)
300 MHz Ming TX-99
Onboard antenna
OOK Modulation
Low Part Count
Low Complexity
Tunable Frequency
Colpitts Oscillator
Ming TX-99 Transmitter in OOK Mode
Ming TX-99 Transmitter

19. 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

20. Distance Measurements
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

21. 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
Moving Average Filter Example
Labview Block Diagram Code and Labview Front Panel Gui

22. Full System Integration and Testingor
Schematic of Hydrogen Chamber
Schematic of Hydrogen Chamber

23. 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
System Level Architecture for RXM-315-LR
Pin-Out of RXM-315-LR receiver, and receiver test board, shown with SPLATCH antenna

24. 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

25. Future Work: Minimum Redundancy Minimum Energy Coding
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 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.
Proposed Source Coding Technique

26. Minimum Redundancy Minimum Energy Coding (cont.)

27. 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.