Patent ID: 8594961

Claim:
A monitoring apparatus for determining a condition of a structure using a passive wireless antenna (PWA), comprising: a remote interrogation system that is configured to remotely interrogate a passive wireless antenna (PWA) that is mounted on the structure, the remote interrogation system comprising: a pulse generator that is configured to remotely activate a switching circuit associated with the PWA; a transceiver that is configured to: transmit to the PWA a series of radio frequency (RF) signals with sweeping frequencies around a known resonant frequency of the PWA; receive a first state response signal reflected by the PWA in a first state prior to activating the switching circuit; and receive a second state response signal reflected by the PWA in a second state after the switching circuit has been activated; and a signal analyzer that is configured to determine a measured resonant frequency of the PWA based at least in part on a normalized antenna mode component obtained using a mathematical difference between the first state response signal and the second state response signal, wherein a difference between the measured resonant frequency of the PWA and the known resonant frequency of the PWA is indicative of the condition of the structure.