Exploratory Advanced Research . . . Next Generation Transportation Solutions

the structure. There are a number of tools and 

technologies currently in use to locate fatigue 

cracks in steel bridge members; however, 

current sensing systems often require lengthy 

cables, are limited in coverage, or require 

manual control. These factors make such 

systems impractical for continual operation 

and large-scale deployment.

Detecting Cracks

To detect cracks at an early stage, this project 

explores a real-time, rugged, low-cost, and 

autonomous wireless-sensing system based on 

state-of-the-art wireless and nano technologies. 

The sensing network that forms the core of this 

project is capable of quantifying multiple small 

cracks using either passive or active millimeterwave antennas as sensors. 

The individual sensing elements that form 

the network can be constructed by printing 

conductive inks on a flexible material, using 

inkjet printers, to form a conductive thin film. 

The printed antenna and supporting circuits 

result in a wireless radio-frequency sensor able 

to monitor cracks in real time. The low cost 

offered by this inkjet printing technique also 

offers potential for large-scale monitoring at a 

reasonable cost. 

These antennas can be distributed over 

areas of a bridge that are known to be 

vulnerable to fatigue and cracking. The sensor 

network can then be periodically interrogated 

using a solar-powered radio frequency 

identification reader. When a small crack 

develops, antennas in the immediate area can 

measure the crack length based on the 

frequency shift caused by the deformation. As 

the crack length increases, the loss of signal 

power of the antenna covering that crack will 

increase until the antenna can no longer radiate 

a signal and is considered damaged. At this 

point the rest of the sensing network can 

continue to function normally and provide 

additional information on the orientation and 

length of the developing crack. 

The Exploratory Advanced Research Program Fact Sheet

Addressing Fatigue

According to the American Society of Civil 

Engineers’ 2009 Report Card for America’s 

Infrastructure, eliminating all bridge deficiencies 

in the United States within the next 50 years 

would require an investment of over $17 billion 

each year.1

 The development of effective rating 

tools to prioritize bridge projects and maximize 

efficiency is therefore a high priority for Federal 

and State agencies.

Metal fatigue in bridges begins with tiny 

fatigue cracks caused by the constant movement 

of car and truck traffic. These cracks usually 

initiate at the fatigue prone areas of the bridge 

and grow under repetitive loads until they can 

reach a critical size and eventually cause 

structural failure. To tackle this problem, 

engineers require the ability to determine the 

presence of fatigue cracks, calculate the rate of 

growth, and identify at what stage of fatigue is 

1 See http://www.infrastructurereportcard.org/fact-sheet/

bridges

With steel bridges representing 

approximately 34 percent of the 

nearly 600,000 highway bridges in the 

United States, continual monitoring and 

early detection of deterioration in these 

structures is vital to prevent expensive 

repairs or catastrophic failures. 

Developing a solution for autonomous 

crack monitoring is the goal of “LowCost Self-Powered Wireless Nanosensors 

for Real-Time Structural Integrity

Monitoring of Steel Bridges,” an 

Exploratory Advanced Research (EAR) 

Program project launched by the Federal 

Highway Administration (FHWA) in 2009 

and conducted by the Georgia Institute 

of Technology.

Real-Time Bridge Monitoring 

Developing Wireless Nanosensors to Monitor Structural Integrity
Material Challenges 

One of the challenges faced by this project is 

ensuring the environmental protection of the 

antenna and successfully incorporating all the 

required materials into the electrical modeling—a 

key requirement for the design process. The 

surface roughness of the weld connections on 

the bridge beam will also be a challenge because 

conventional operation of the antennas requires 

minimal surface roughness to correctly detect 

cracks underneath.

New materials will also need to be investigated 

for efficient power sourcing and antenna 

radiation. Solar cells are one option that has 

been identified for further investigation. 

Although nanomaterials have already been 

developed in other studies for piezoelectric 

generators, it is necessary to align nanowires in 

a specific way that is not currently possible with 

inkjet printing. Furthermore, various inkjet 

printing procedures are being investigated to 

optimize conductivity of the printed thin film, 

which is essential for antenna radiation 

efficiency. 

Improving Bridge Maintenance and 

Repair

The project aims to overcome the technical and 

cost obstacles to measuring in-situ bridge 

conditions and deliver a product with far greater 

ease than any current technique. It is expected 

that the system will ultimately improve the 

efficiency of bridge maintenance and repair, 

providing substantial savings in operations and 

increase in safety. In time this technology has 

the potential to transform the inspection and 

maintenance process for steel bridges and 

eventually expand into other classes of key 

infrastructure components.

Learn More

For more information on this project, contact 

Hamid Ghasemi, FHWA Office of Infrastructure 

Research and Development, at 202-493-3042 

(email: hamid.ghasemi@dot.gov).

What Is the Exploratory 

Advanced Research Program?

FHWA’s Exploratory Advanced Research 

(EAR) Program focuses on long-term, highrisk research with a high payoff potential. 

The program addresses underlying gaps 

faced by applied highway research 

programs, anticipates emerging issues 

with national implications, and reflects 

broad transportation industry goals and 

objectives. 

To learn more about the EAR Program, 

visit the Exploratory Advanced Research 

Web site at www.fhwa.dot.gov/

advancedresearch. The site features 

information on research solicitations, 

updates on ongoing research, links to 

published materials, summaries of past 

EAR Program events, and details on 

upcoming events. For additional 

information, contact David Kuehn at FHWA, 

202-493-3414 (email: david.kuehn@dot.gov), 

or Terry Halkyard at FHWA, 202-493-3467 

(email: terry.halkyard@dot.gov). 

Publication No. FHWA-HRT-13-057

HRTM-30/3-13(1M)E

Real-Time Bridge Monitoring

Developing Wireless Nanosensors to Monitor Structural Integrity

Image other side: 

www.istockphoto.com/ 

Sam Sefton