1. Structural Health Monitoring
Sukun Kim, David Culler
James Demmel, Gregory Fenves, Steve Glaser, Shamim Pakzad
UC Berkeley
CENTS Retreat

2. Structure Monitoring Data Acquisition Data Collection
Data Processing & Feedback

3. Accelerometer Board Two accelerometers for two axis Thermometer
16bit ADC
ADXL 202E
Silicon Designs 1221L
Range
-2G ~ 2G
-0.1G ~ 0.1G
System noise floor
200(μG/√Hz)
30(μG/√Hz)
Price
$10
$150

4. Mint Route (Alec Woo, et al)
Hardware
Board
Accelerometers Comparison
Noise Floor (Vault Test)
Tilting Calibration
Temperature Calibration
Mote
Antenna
Options and Our Choice
Power
Power Consumption Profile
Power Source Options and Choice
Package
Software Architecture
Overall Structure
High Frequency Sampling
Jitter Test
Jitter Analysis
Multi-hop Communication
Time Synchronization
Reliable Command Dissemination
Reliable Data Collection
Data Analysis
Signal Processing
Hardware Low-pass Filter
Software High-pass Filter
Calibration Process
System Identification
Box-Jenkins Multi-input Multi-output Model
Mint Route (Alec Woo, et al)
The Flooding Time Synchronization Protocol
(Miklos Maroti, et al)
Drip (Gilman Tolle)

5. Why temperature calibration?
Accelerometer is sensitive to temperature change
In bridge environment, there exists significant variation in temperature (up to 45F, 40 mG)
We are looking at very subtle signal (down to 0.5 mG)
Signal to noise ratio becomes small under temperature change (down to 1%)

6. Temperature Calibration TestF C
81.1
27.3
67.1
19.5
53.0
11.7
Temperature
39.0
3.9 mG
27.5
Thanks to Crossbow
-27.5
Acceleration

7. Temperature Calibration
Suggestion to estimate instantaneous regression parameters by windowing the signals
a window of length 199 samples is considered and a linear regression model of the form
accel.count = a + b*temp.count + e
is fit to that windowed segment of the data
The following graphs are the estimated parameters. The parameters include a and b (as defined above) and the standard deviation of e, the error term in the regression model

8. However, concern for temperature hysteresis drives us to second runmG
2.75
0.92
Temperature change will not be as dramatic as in the test (with insulation)
However, concern for temperature hysteresis drives us to second run

9. Bridge Dimension 2
500 ft
1125 ft
2100 ft 4 8
246 ft 1
* Blue number presents rough ratio
Need to cover large bridge, so directional antenna is needed

10. Types of Antenna Dish Yagi Horn Patch Bigger Size Longer Range
Smaller Size
Shorter Range

11. How much gain do we need?
Golden gate bridge is 6,450 ft including main span and side spans
Assuming 20 hops along the span, each hop is 340 ft
433MHz Mica2 reached 100ft (84% success)
916MHz Mica2 will reach 50ft
916MHz with maximum radio power will reach 225ft (4.5X increase: 10dBm to -3dBm)
1.5X increase in range is needed
3.3 dBi antenna is needed

12. Antenna Candidates Bi-directional patches (2.4GHz) From Superpass
4.8”
4.4”
11.5”
4.5”
5.5 dBi
9 dBi

13. Performance of antenna
5.5dBi antenna with Telos
Maximum output power (0dBm)
0.5ft above the ground
in front of Soda Hall
3ft above the ground, success rate was close to 100%
9dBi antenna showed very similar behavior (0% above 0.5ft, >99% above 3ft)
The distance to the ground is more important than the gain of the antenna

14. Power Consumption Data
Board only: 26.7*
Idle: 39.8
One led on: 42.6
Erasing flash: 77.5 (with one led on)
Sampling: 42.6 (with one led on)
Transferring data: 46.0 (with one led on)
* unit is mA at 9V

15. Node Deployment Plan 10 nodes 30 nodes 10 nodes
* Nodes on both sides of span

16. Power Consumption
The most burdened node transfers data one third of time
Tadiran 5930: 3.6V, 19Ah, $17, D size
Usual 9V alkaline battery has 625mAh (12X)
Usual 1.5V D battery has 18Ah (2.5X)
3 of Tadiran 5930 costs $51, and lasts 23 days
3 weeks is good enough

17. Power Consumption (cont)
With optimal sleeping, 30 days
Board itself consumes significant amount of energy
Power source
Power source
Switch
Switch
Sensor
Mote
Mote
ADC
Sensor
ADC

18. Reliable Data CollectionPC

19. Footbridge & Location of Nodes
Quarter
Half
1/8
Quarter
260ft 7 2 4 6
16ft
Marina
Berkeley 8 1 3 5
Base Station

20. Data is from single-hop version

21. We will collect data for multi-hop version

22. Data Analysis
Characteristic vibration modes were observed

23. Conclusion Practical problems to solve
Interesting challenges and research topics (more efficient reliable transfer)
Future Work
Handling temperature hysteresis
Antenna
More efficient data collection (pipelining?)

24. Questions

30. Examples 433 MHz 916 MHz 2.4 GHz Dish N/A 18 dBi, 16 deg 47.2", 32 lbs
Yagi
8~14 dBi, 90~30 deg
15~43”, 2~4 lbs
$45~90, 4.5~18X
9~14 dBi, 60~30 deg
6x3~18x3”, 0.5~2 lbs
$36~53, 5.6~18X
Horn
10~12 dBi, 60~60 deg
2x4x5~4x6x7”, 1.5~2 lbs
7.1~11X
Patch
8 dBi, 70 deg
8.5x8.5", 1 lbs
$45, 4.5X
8~14 dBi, 75~30 deg
4.5x4.5~8.5x8.5”, 0.4~1 lbs
$23~34, 4.5~18X
Gain, angle, size, weight, (price), range compared to wire whip antenna

31. Comment on Availability
Availability of horn antenna is limited
Antenna for 433MHz can be found, but with some more work (probably from abroad)

32. Suggested Choice – Yagi, Patch
Dish is overkill
Yagi without shell
Enough gain
Long (15” for 916MHz) and narrow
Robust to strong wind
Horn has limited availability
Patch
With large surface (8.5X8.5” for 916MHz) and thin
Plate part can be a problem under strong wind

33. Bi-directional Patches
Manufacturer
Name
Gain
(dBi)
Angle
Size (")
Weight
(lbs)
Price
($)
3com
3CWE497 4
2.6x1.8x0.2
0.1364 90
SuperPass
SPPG11BD 6 65
4.5x4.4x1
0.5 29
SPPG24BD
9.5
65x22
11.5x4.8x1
1.5 45
Centurion
TERRACE 5
2.7x2.5x0.8
MaxRad
MHA2400
75x100
3x2.5x0.5
50~100
MHA890PT
6.5x3.9x2.3
109
TIL-TEK
TA-814
60x18
48x13x6 40

34. References (Antenna) Antenna vender Horn antenna Antenna in general
Horn antenna
Antenna in general
dBi, dBd
Golden Gate Bridge Facts

35. dBi, dBd
dBi (decibels-isotropic) – a unit of measuring how much better the antenna is compared to an isotropic radiator
dBd (decibels-dipole) – compared to a dipole antenna
Dipole antenna typically has a 2.4dBi gain
Wire whip antenna (used in mica2) would have 1.5dBi gain

40. One Base Station w/o Pipelining
If only one base station is located at kth place from the right, total transfer time is
2 * { (k-1)k/2 + (16+5-k)(16+5-k+1)/2 + 4(16-k) + 6} * (single one-hop transfer time)
Minimum 248 when k=12 or 13
When flash is full (6min data at 200Hz, 5 channels = 10min xfer), and with 800bytes/s bandwidth*  2.1 days of data collection
* Every data in this file is based on Mica2
Minimum positions

41. One Base Station w/ Pipelining
Assuming communication can occur 3 hops away, lower bound is 3 * 50 times of single one-hop transfer (10min)  25 hours
Bottleneck is speed of data arriving at the base station with space among them
With N base stations, time will become 25/N hours
Space preventing interference
Base Station

42. More thought on pipelining
As the network gets bigger, we can get more benefit (N versus N2)
However, in small network, path is not long enough for multiple transfers to happen
With 4 sinks, assuming perfect pipelining (can be unrealistic), it takes 4.2 hours (20min * 50 / 4)
Base Station

44. Preliminary BOM Item Price Mica2 $150 Board (including parts) $300
Enclosure of board
$100
Antenna
$50
Antenna mount
$10
Mount Bracket
Battery $5
Antenna connector, cable
Battery connector, cable
Miscellaneous (screw, etc)
Total
$645
Total without board
$345

46. 1. Radio with Mica2
19.2Kbps = 2400bytes/s = 66.7pkts/s
Media access control reduces this to 52pkts/s.
Single mote can achieve 42pkts/s. (probably due to processing overhead?)
2. UART
57.6Kbps = 7200bytes/s = 200pkts/s
3. TOSBase
In TOSBase with Mica2,
### 34pkts/s max in theory.
23pkts/s is a reliable upper bound.

47. Overall Process PC PC PC 1. Trigger Sampling 2. Transfer Metadata
3. Transfer Data
* PC has most of intelligence. Motes are almost stateless.