Real-time ranging and angle measurements using radar and surface acoustic wave transponders

A system for tracking file position of each of a plurality of different objects in three dimensional space comprising, in combination,

• at least one transmitter for transmitting a sequence of electromagnetic interrogation signals each of which has a predetermined wave shape,
• a transducer attached to each of said objects comprising:
• a piezoelectric substrate,
• a receiving antenna for receiving said electromagnetic signals,
• a first set of conductive elements connected to said receiving antenna for converting one at least one of said interrogation signals into a surface acoustic wave,
• a second set of conductive elements positioned in a path of travel of said surface acoustic wave at a first distance from said first set of conductive elements to produce a response signal having detectable properties that identify said transducer, for transmission back to said one or more transmitting stations as an electromagnetic signal,
• a third set of conductive elements positioned in a path of travel of said surface being shorter than said first distance, such that said third set of conductive elements produces a control signal that occurs prior to the production of said response signal,
• a transmitting antenna,
• an amplifier having a signal input coupled to said second set of conductive elements and a signal output connected to said transmitting antenna for amplifying said response signal transmitted from said transmitting antenna as said electromagnetic response signal from said transducer,
• a switching circuit connected to said third set of conductive elements and responsive to said control signal for supplying an operating potential to said amplifier during the time when said response signal is produced by said second set of conductive elements, and
• at least one signal processor located remotely from said transducer for receiving said electromagnetic response signal to identify said transducer and estimate its position in three-dimensional space.

A surface acoustic wave transducer comprising, in combination:

• a receiving antenna for capturing electrical energy from an electromagnetic interrogation signal received from a remotely located transmitting station,
• a piezoelectric substrate,
• a first set of conductive elements coupled to said receiving antenna, said first pattern of conductive elements being positioned adjacent to the surface of said piezoelectric substrate at a first location for converting said electrical energy into surface acoustic waves that propagate across the surface of said piezoelectric substrate,
• a second set of conductive elements positioned adjacent to the surface of said piezoelectric substrate at a second location spaced from said first location by a first distance for converting surface acoustic waves received at said second location into a control signal,
• a third set of conductive elements positioned adjacent to the surface of said piezoelectric substrate at a third location spaced from said first location by a second distance that is greater than said first distance for converting surface acoustic waves received at said third location into a response signal,
• an amplification circuit having a signal input coupled to said third set of conductive elements for receiving said response signal, a control input responsive to said control signal for activating said amplification circuit, and a signal output for producing an amplified response signal when said amplification circuit is activated, and
• a transmitting antenna connected to said signal output for converting said amplified response signal into an electromagnetic response signal that is transmitted to one or more remotely located receiving stations.