A Reflectometer-Based Reader for Passive Wireless Structural Surveillance Sensors

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.