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

Structure Monitoring Data Acquisition Data Collection Data Processing & Feedback

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

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)

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%)

Temperature Calibration Test F 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

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

However, concern for temperature hysteresis drives us to second run mG 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

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

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

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

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

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

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

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

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

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

Reliable Data Collection PC

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

Data is from single-hop version

We will collect data for multi-hop version

Data Analysis Characteristic vibration modes were observed

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?)

Questions

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

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

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

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

References (Antenna) Antenna vender Horn antenna Antenna in general http://www.hyperlinktech.com http://www.antennafactory.com http://www.antennafactor.com http://www.antennasystems.com Horn antenna http://www.phazar.com Antenna in general https://ewhdbks.mugu.navy.mil/ANTENNAS.HTM dBi, dBd http://www.tmeg.com/tutorials/antennas/antennas.htm Golden Gate Bridge Facts http://www.thoma.com/thoma/ggbfactsX.html

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

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

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

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

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

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.

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