frequency (hz)
DESCRIPTION
SF (south). Sausalito (north). 500 ft. Time plot, vertical sensors at L1-L5. Frequency plot, vertical sensors at L1-L5. 8. V2. 4200 ft. V2. V4. 1125 ft. 246 ft. 6. V13. V4. V7. V13. 4. 56 nodes. 10. 4. V9. V7. V9. 8 nodes. 2. Acceleration (mg). 0. abs(FFT(.)). 2. 10. - PowerPoint PPT PresentationTRANSCRIPT
0 2 4 6 8 10 12 14 16 18 2010
-2
100
102
104
Frequency (Hz)
abs(
FF
T(.
))
Frequency plot, vertical sensors at L1-L5
V2V4V13V7V9
0 1 2 3 4 5 6 7 8 9 10-8
-6
-4
-2
0
2
4
6
8
Time (sec)
Acc
eler
atio
n (
mg)
Time plot, vertical sensors at L1-L5
V2V4V13V7V9
Wireless Sensor Networks for Structural Health Monitoring
Overview• Ambient vibrations of the structure are monitored and used to determine the health status of the structure.• With a Wireless Sensor Network, low cost monitoring is possible without interfering with the operation of the structure.
Accelerometer Board
Challenges• High Fidelity Data• High Frequency Sampling with Low Jitter• Time Synchronized Sampling [FTSP]• Large-scale Multi-hop Network [Mint]• Reliable Command Dissemination [Broadcast]• Reliable Data Collection [Straw]
Silicon Designs 1221LADXL 202E
ADXL202E
Silicon Designs221L
Range -2G ~ 2G -0.1G ~ 0.1G
Systemnoise floor
200(μG/√Hz) 30(μG/√Hz)
Price $10 $150
• Two measurement axis each with two accelerometers• Thermometer, 16bit ADC, Low-pass filter• On-board Digital Signal processing• Calibration for manufacturing variation and temperature
-0.99
0.19-0.73
1.000.74
First Vertical Mode of Vibration
Estimated results match with a FE model of the bridge (SAP)
Deployment at the Footbridge
Berkeley SF Bay
mid-spanquarter-span
59
Base Station
260ft
16ft27 1
1310 38 4
121114
Sukun Kim*, Shamim Pakzad+, David Culler*, James Demmel*, Gregory Fenves+, Steve Glaser+, Martin Turon#
* EECS, UC Berkeley +CEE, UC Berkeley #Crossbow
Software Architecture
Best-effort Single-hop Communication
Broadcast MintRouteFTSP
Low-level FLASH
BufferedLogStraw
Sentri (Application Layer)
• When sampling, only necessary components are turned on to reduce jitter• Straw provides reliable data collection
• Selective-NACK is used – complexity is drawn from the sender (mote) to the receiver (PC)• Rate-based control• Pipelining increases channel utilization
Deployment at theGolden Gate Bridge
1st mode 2nd mode 3rd mode
Vertical Frequency (Hz) 1.35 1.79 11.47
Damping Ratio 0.055 0.02 0.043
Horizontal Frequency (Hz) 2.37 7.87 11.91
Damping Ratio 0.26 0.16 0.123
• Nodes on the main span and the south tower• Distance between nodes on the west span is either 100ft or 50ft• Exposed to strong and salty wind and fog
8 nodes
56 nodes
1125 ft 4200 ft
500 ft
246 ft
SF(south)
Sausalito(north)
Node, Battery, Antenna Rusting of C-clamp Base station in Tower
0 100 200 300 400 500 600-20
0
20
Time (sec)
Acc
el (
mg)
Time and Frequency plots, Vertical sensors, s284n62
45 50 55 60 65-5
0
5
Time (sec)
Acc
el (
mg)
0 5 10 15 20 25 30 35 40 45 500
1
2
frequency (HZ)
PS
D (
mg/
Hz)
0 0.5 1 1.5 2 2.50
1
2
frequency (HZ)
PS
D (
mg/
Hz)
0 100 200 300 400 500 600-50
0
50
Time (sec)
Acc
el (
mg)
Time and Frequency plots, Vertical sensors, s284n45
45 50 55 60 65-10
0
10
Time (sec)
Acc
el (
mg)
0 5 10 15 20 25 30 35 40 45 500
2
4
frequency (HZ)
PS
D (
mg/
Hz)
0 0.5 1 1.5 2 2.50
2
4
frequency (HZ)
PS
D (
mg/
Hz)
(a) Vertical, Quarter spanNorth of the South Tower
(b) Vertical, Quarter spanSouth of the North Tower
Bandwidth versus Hop Count
0
200
400
600
800
1000
1200
1400
0 10 20 30 40 50Hop Count
Bandw
idth
(B
/s)
Vibration Data from the Footbridge