Patent ID: 7782209

Claim:
An RFID transponder detector comprising: a first LC pair including a first inductance coil and a first tuning capacitor; a second LC pair including a second inductance coil and a second tuning capacitor, wherein said first LC pair is coupled to said second LC pair; an antenna coupled to said first and second LC pair; a controller coupled to said first and second LC pairs for applying first pulses and second pulses to said first and second LC pairs, thereby resonating said first and second LC pairs to produce a sequence of first and second detection signals, wherein said first detection signal has a first detection frequency and said second detection signal has a second detection frequency different from said first detection frequency, further wherein transmitting said sequence of detection signals from said antenna results in corresponding first and second response signals having said first and second detection frequencies, respectively, on said antenna; a detection and response signal measurement circuit coupled to said antenna and said controller for receiving said first and second detection signals and said corresponding first and second response signals and measuring values of a preselected detection parameter for each of said detection signals and each of said response signals, wherein said controller or detection and response signal measurement circuit is configured to compare said values for said detection signals to said values for said response signals and determine if a transponder having a transponder resonant frequency corresponding to said first or second detection frequency is present in a proximal space of said transponder detector based on comparison of said values; and a coupling capacitor, wherein said first LC pair is coupled to said second LC pair across said coupling capacitor.