Office of Technology Transfer – University of Michigan

Wireless Sensor System for Structural Health Monitoring, Bridge Safety, Damage Detection

Technology #4756

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Bridges and buildings featuring wireless monitoring systemswireless sensor monitoring system inventor Jerome LynchFunctional elements of a wireless sensor for structural monitoring applicationshand-held wireless sensor prototype
Jerome Lynch
Managed By
Richard Greeley
A Summary Review of Wireless Sensors and Sensor Networks for Structural Health Monitoring
The Shock and Vibration Digest,
Sensor Nets Bridge Safety Gap
EE Times, 2007

As bridges and other structures such as buildings age, they naturally develop cracks, concrete deterioration, and steel corrosion that can impact the safety of the bridge or the structural integrity of the building. 

This wireless sensor system enables remote damage detection and structural health monitoring for bridges and other structures. The device for use in bridge monitoring. The wireless bridge inspection device, applied directly to bridge surfaces, measures electrical impedance to detect changes in the condition of the bridge, such as steel corrosion and concrete deterioration.

This structural health monitoring device consists of three components: a wireless transceiver, a direct digital synthesizer with a 32-channel multiplexed sensing interface, and a microcontroller that communicates between the transceiver and synthesizer — all mounted on circuit boards and contained within a portable housing. 

The device sends an electrical current through the material at set times each day, and the multi-channel impedance analyzer measures the material response over time and transmits data to the user via the wireless datalink, providing low cost, ongoing, automated structural health monitoring.  

Portable, Wireless Impedance Analyzer Uses Thin Films to Create ‘Smart Structures’

This wireless impedance analyzer can be incorporated into a variety of flexible fabrics, including multi-layer thin films and nano composite materials that create a type of “sensing skin” that can be applied to surfaces to provide direct spatial mapping of damage over a large area. 

This allows the wireless impedance analyzer to be used in a variety of “smart structures” capable of sensing and reacting to their environment. By contrast, traditional wired sensors can only measure behavior at one specific point.

Other impedance-based structural health monitoring platforms are large, bulky systems requiring numerous wires that transmit sensor data. This impedance measurement device operates at low power, runs off a battery pack, and fits within a portable carrying case. The wireless interface means that data can be acquired from the sensor without having to install wiring on the bridge. This simplifies the system, reduces the time and labor costs for installation, and makes installation on difficult-to-access bridges easier and more economical. 

Another key technical advantage is that this wireless multi-channel impedance analyzer’s sine wave generator, which is capable of generating regulated current signals with frequencies from near DC to 20 MHz, giving greater control over the amplitude, frequency, and phase of a regulated injected current. In addition, the use of a multiplexed sensing interface offers 32 addressable channels from which voltage measurements can be made.

Wireless Impedance Analyzer a Proven Tool for Material Characterization, Electrical Impedance Tomography and Spectroscopy 

The device was successfully used to measure electrical impedance tomography (EIT) and electrical impedance spectroscopy (EIS), and for material characterization. In these demonstrations, data collected from the device was compared to similar data obtained from an existing commercial impedance analyzer. The data from the new device showed slightly shifted values, but the overall trends perfectly matched the results from the commercial measuring instrument.

The wireless impedance analyzer was also successfully tested by using it to conduct electrical impedance tomography on a “sensing skin” thin film composite composed of a polyvinyl alcohol (PVA),  poly(sodium 4-styrene sulfonate) (PSS), and single-wall carbon nanotubes. Field testing is underway to test the performance of the device with sensing skins applied on actual bridges as automated structural health monitoring.


  • Wireless, automated impedance measurements for various applications including:

    • material characterization
    • structural health monitoring (SHM)
    • electrical impedance tomography
    • lectrical impedance spectroscopy
    • “sensing skin” thin film composite 
  • Detect steel corrosion and concrete deterioration

  • Bridge inspections and safety

  • Building SHM


  • Wireless device simplifies data acquisition system and does not lead to significant increase in associated labor and cost with increased numbers of installed sensors
  • Does not required wiring on the bridge or structure

  • Can be incorporated into a variety of flexible fabrics, including multi-layer thin films and nano composite materials to create a “sensing skin"

  • Measures multiple points of structure

  • Offers 32 addressable channels for voltage measurement

  • Sine wave generator’s broad frequency range gives greater control over amplitude, frequency, and phase of a regulated injected current

  • Operates at low power

  • Runs off a battery pack

  • Portable, fit in carrying case