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Sakamuri, Vandana

Electrical Engineering

2012

M.S.

This work presents the design, development and test of a mobile interrogator for a new class of wireless sensors. The sensors are entirely passive and are intended for deeply embedded structural health monitoring. The interrogator must both transmit a signal'to elicit a response from the sensor and be able to monitor that response. The interrogator considered transmits in the 2.40-2.48 GHz ISM band and monitors the 2nd harmonic response created by the rectenna-based sensing device. The interrogator is designed to either sweep across the transmit band or to transmit at a fixed frequency within the band depending on whether the sensed parameter is static or dynamic, respectively, in nature. The received signal lies in the 4.80-4.96 GHz band and is downconverted to a constant frequency (70 MHz). The approach is novel in that two digitally controlled phase-lock loop synthesizers are used to create both the interrogation signal and a reference signal for the interrogator.
The performance of the interrogator-sensor system under favorable and multi-path fading scenarios are evaluated. The interrogator-sensor system was tested with the sensor in an anechoic chamber and a multi-path chamber. Alternative methods for interrogation are also presented.