Battery-free Antenna Sensors for Strain and Crack Monitoring of Bridge Structures (SN-2)

Universities: Georgia Institute of Technology
                           Missouri University of Science and Technology

Principal Investigator: Dr. Yang Wang, Georgia Institute of Technology

PI Contact Information: Phone: (404) 894-1851  |  Email:

Co-Principal Investigators: Dr. Reza Zoughi, Missouri University of Science and Technology
                                                        Dr. Genda Chen, Missouri University of Science and Technology

Funding Sources and Amounts Provided:
Georgia Institute of Technology: $74,624
INSPIRE UTC: $128,663

Total Project Cost: $203,287

Match Agencies ID or Contract Number:
Georgia Department of Transportation: TBD
Georgia Institute of Technology: In-Kind Match
INSPIRE UTC:  00055082-02A

INSPIRE Grant Award Number: 69A3551747126

Start Date: March 1, 2017
End Date:  June 30, 2020

Brief Description of Research Project:

Fatigue cracks need to be monitored in fracture critical elements. Previous research by the PI produced an RFID (radiofrequency identification) sensor prototype that can accurately measure tens of micro-strains in laboratory. The antenna sensor was made on a glass microfiber-reinforced polymer substrate. Although accurate for strain measurement and detection of fatigue cracks in laboratory testing, the sensor performs less satisfactorily in field conditions since the substrate material (RT/duroid® 5880) is susceptible to thermal effect.

Approach and Methodology: An innovative, battery-free, wireless strain/crack sensor is proposed for bridge monitoring. Unlike conventional smart sensors with wireless transmission of digitized data, the proposed sensor makes use of the strain-dependent (transducer-like) behavior of electromagnetic (EM) waves in an antenna. Upon illumination by a wireless reader that is carried by a human inspector or an aerial robot, the antenna sensor scatters an EM signal back to the reader. The radiation parameters of the antenna sensor, such as resonant frequency and backscattered power level, can be wirelessly interrogated by the reader. When bonded to a base structure to be monitored, a thin planar antenna sensor is deformed as the structure is loaded or experiences cracking. The deformation in a properly designed antenna can cause a significant and observable change of antenna radiation parameters.

Overall Objectives: This project aims to develop and validate a new antenna sensor prototype that has significantly improved thermal stability than previous versions.  In addition, an integrated dual-mode prototype will be developed to allow the sensor operation to benefit from battery power, when available, in active mode. A small circuit with a credit-card size solar panel and a rechargeable coin cell battery will be designed. If the battery is charged by solar power, the sensor operates in the active mode, providing stronger response to the reader.  When the battery is drained up, the sensor automatically falls back to the passive mode, i.e. receiving operational energy completely from reader interrogation.

Scope of Work in Year 1: (1) Select a new substrate material that provides steady performance under temperature changes, (2) Redesign an RFID antenna sensor and characterize its performance in temperature chamber, and (3) Validate the sensor performance in both tensile, compressive, and crack tests.

Scope of Work in Year 2: (1) Test the performance of the new antenna sensor in application settings and compare it with the pervious sensor prototypes and metal foil gauges, (2) Extend the wireless interrogation distance by an integrated dual mode sensor design, and (3) Characterize the strain sensing performance of the dual-mode sensor with tensile tests.

Describe Implementation of Research Outcomes:

Building on current research, recommendations on applying patch antenna sensors on strain/crack sensing are listed as follows:

The temperature effect on resonance frequency of patch antenna sensors should be taken into consideration in measurements. Using thermally-stable substrate material can greatly reduce the resonance frequency change due to dielectric constant variation. However, this thermal effect cannot be perfectly eliminated. Calibration according to environmental temperature can lead to more accurate measurement results.

Sensing consistency, particularly between compressive and tensile testing scenarios, needs further study. Detailed modelling and extensive experiments should prove helpful for investigating the difference between strain sensitivity of the antenna sensor in compressive and tensile tests.

Impacts/Benefits of Implementation:
Harnessing the latest wireless and energy harvesting technologies, the research team has developed RFID-based patch antenna sensors demonstrated with potential in strain and crack sensing.  Fabricated on thermally stable substrate, the antenna sensors operate at more steady resonance frequencies under temperature fluctuation. Equipped with a power management system, a dual-mode patch antenna sensor can achieve long interrogation distance in active mode, while maintaining the capability of strain sensing in passive mode when external power supply is not available. The designed patch antenna sensors enable a low-cost solution for large scale heath monitoring of engineering structures.

Project Website:
Progress Reports: