Patent ID: 9574966
Date: 2017-02-21
CPC Classifications: G01M

Claim:
1. A method of monitoring a condition of a structure, comprising: transmitting, at a first time, an interrogation signal to a passive wireless antenna sensor mounted on the structure, wherein the interrogation signal includes frequencies in a frequency range, wherein the frequency range includes a resonant frequency of the passive wireless antenna sensor, wherein the passive wireless antenna sensor is configured such that a change in the condition of the structure will change the resonant frequency; receiving a first backscattered signal, wherein the first backscattered signal comprises an antenna backscattered signal from the passive wireless antenna sensor and a structure backscattered signal from the structure, wherein the antenna backscattered signal is modulated by the passive wireless antenna sensor at a modulated frequency; detecting a first envelope of the first backscattered signal; normalizing the first envelope; selecting a reference amplitude; determining a first frequency of the first envelope that is associated with the reference amplitude; transmitting, at a second time, the interrogation signal to the passive wireless antenna sensor mounted on the structure; receiving a second backscattered signal, wherein the second backscattered signal comprises an antenna backscattered signal from the passive wireless antenna sensor and a structure backscattered signal from the structure, wherein the antenna backscattered signal is modulated by the passive wireless antenna sensor at a modulated frequency; detecting a second envelope of the second backscattered signal; normalizing the second envelope; determining a second frequency of the second envelope that is associated with the reference amplitude; determining a frequency shift based on a difference between the first frequency and the second frequency; and determining the condition of the structure based on the frequency shift.