System for sensing backscatter tag communications from retrodirective antenna arrays

Abstract

A system for using thin and energy-autonomous backscatter tags and corresponding sensing nodes may operate with 24 GHz backscatter reflectarray tags having low power consumption. A digital beam steering, frequency-modulated continuous wave (FMCW) radar may be used for detection, localization, identification and communications. The tags may include environmental sensors that are used to modulate backscatter waves for data communications directed to a reader or may digitally modulate the backscatter transmissions without sensor data for independent localization of each tag in a network.

1 - 25 . (canceled) 
     
     
         26 . A tag device, comprising:
 a sensor adapted to sense environmental data;   an oscillator generating a signal having a frequency response corresponding to the environmental data sensed by the sensor; and   an antenna array:
 receiving an incident wave; 
 receiving the signal generated by the oscillator; 
 modulating the incident wave with the signal to generate a backscatter wave; and 
 transmitting the backscatter wave. 
   
     
     
         27 . The tag device of  claim 26 , wherein the antenna array comprises:
 a first port to receive the incident wave;   a second port to receive the signal from the oscillator; and   a third port to transmit the backscatter wave.   
     
     
         28 . The tag device of  claim 27 , wherein the first port is a serial port of a first antenna, wherein the third port is a parallel port of a second antenna, wherein the second port is coupled to the first antenna as a serial feed, and wherein the second port is coupled to the third port as a parallel feed. 
     
     
         29 . The tag device of  claim 27 , wherein the second port is coupled to a switch controlled by the signal from the oscillator. 
     
     
         30 . The tag device of  claim 29 , wherein, responsive to receiving the signal in a first state, the switch induces the backscatter wave to be transmitted in a same polarization as the incident wave, and, responsive to receiving the signal in a second state, the switch induces the backscatter wave to be transmitted in an opposite polarization of the incident wave. 
     
     
         31 . The tag device of  claim 26 , wherein the sensor comprises a resistometric device with a resistance that varies based on the environmental data. 
     
     
         32 . The tag device of  claim 26 , further comprising an energy storage device operatively coupled to the sensor, the oscillator, and the antenna array, the energy storage device providing power to the sensor, the oscillator, and the antenna array. 
     
     
         33 . The tag device of  claim 26 , wherein the antenna array transmits the backscatter wave at maximum gain in a direction of a reader that transmitted the incident wave. 
     
     
         34 . A method, comprising:
 receiving an incident wave;   sensing environmental data;   generating, by the tag device, a signal having a frequency response corresponding to the sensed environmental data;   modulating the incident wave with the signal to generate a backscatter wave; and   transmitting the backscatter wave.   
     
     
         35 . The method of  claim 34 , further comprising transmitting the backscatter wave in a cross-polarized state. 
     
     
         36 . The method of  claim 34 , further comprising:
 responsive to receiving the signal in a first state, transmitting the backscatter wave in a same polarization as the incident wave; and   responsive to receiving the signal in a second state, transmitting the backscatter wave in an opposite polarization of the incident wave.   
     
     
         37 . The method of  claim 34 , further comprising generating the signal proportional to a resistance that varies based on the environmental data. 
     
     
         38 . The method of claim  349 , further comprising:
 harvesting or storing energy; and   using the energy to generate and transmit the backscatter wave.   
     
     
         39 . The method of  claim 34 , further comprising transmitting the backscatter wave at maximum gain in a direction of a reader that transmitted the incident wave. 
     
     
         40 . The method of  claim 34 , further comprising shifting a frequency of a tone in the incident wave to generate the backscatter wave. 
     
     
         41 . The method of  claim 34 , further comprising transmitting the backscatter wave at a frequency of at least 24 GHz.