This paper summarizes ongoing work on applying passive magneto-inductive (MI) waveguides as wireless sensor arrays
to monitor corrosion in infrastructure systems. The passive uniformly-spaced sensor array provides a low-cost and quick
method to detect the onset of corrosion in concrete structures using a noninvasive approach. The embedded sensors
communicate with neighboring sensors through inductive coupling. The corrosion information is interpreted based on
both frequency and time domain characteristics. Bandpass characteristics in the frequency domain and received reflected
time domain waves are investigated to locate the defects along the wireless sensor array. Using the relationship between
the relative positions of defects and MI waveguide performances, a new combined technique to determine location of
defects has been developed and proven to provide both improved sensitivity and defect location capability.
KEYWORDS: Sensors, Transceivers, Reflectometry, Directional couplers, Surveillance, Corrosion, Analog electronics, Signal analyzers, Signal generators, Magnetism
A reconfigurable and portable wireless reader has been designed for embedded passive Electronic Structural
Surveillance (ESS) sensors, used to monitor corrosion in infrastructure systems. The passive ESS sensors have been
developed and proven effective in monitoring localized defects in their environment. They are interrogated by
inductively coupled magnetic field of a reader coil. The input impedance of the reader coil is monitored to determine
whether a corrosion threshold has been reached. We have previously used an impedance analyzer to obtain the
impedance data. Such systems have good sensitivity and moderate speed but are bulky and heavy. The new reader
approach presented in this paper is designed addressing the need of portability, sensitivity and read range. The reader
electronics is implemented on a reconfigurable National Instruments (NI) modular transceiver platform, capable of
software defined radio. The design employs a reflectometer, which is implemented using a 3-port directional coupler and
a single coil as both the driver and reader, along with the transceiver. The NI transceiver is used to generate a swept
frequency input signal and analyze reflected signal from the reader, which is related to the input impedance of our ESS
sensor. The configuration of the reader coil is optimized for reader range and sensitivity. We have acquired analog data
using this design, showing that the real-time reader system facilitates especially fast detection and long read ranges for
threshold-only sensing.
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