Passive Wireless Surface Acoustic Wave Sensors for Corrosion Monitoring of Steel in Concrete Structures

Abstract The monitoring of corrosion in steel-reinforced concrete structures utilizing embedded sensors requires that the sensors have an operating life time of decades. Today’s common corrosion sensors use embedded probes within the concrete structure requiring an outside electrical power source. Power is provided to the probes through electrical wires that run to the probe from the outside world. These cable runs could damage the integrity of concrete structures. Other typical sensors may require the use of electrochemical electrodes which have several drawbacks (e.g. short lifespan and a recalibration requirement). However, wireless and powerless Surface Acoustic Wave (SAW) sensors have been developed to address some of the shortcomings of today’s existing corrosion monitoring sensors. To date, the testing of SAW sensors in a controlled environment includes the use of electrodes to accelerate the corrosion process in an attempt to correlate corrosion damage to SAW sensor Radio Frequency (RF) echo responses. Additionally, the testing has included long duration exposure to the concrete environment. These SAW corrosion sensors were first characterized in terms of the RF signal propagation through concrete in both a laboratory setting and actual concrete structures. This paper provides measured RF signal responses through concrete which has been immersed in sea water in a laboratory setting. The sea water immersion tank was used as a test bed for the accelerated corrosion process. Measured data collected from the accelerated corrosion test bed over a five month period will be presented.