Impedance matching coil assembly for an inductively coupled transponder

A method for matching the impedance coupling between a transponder and an electromagnetic field generated proximate the transponder, the transponder including an integrated identification circuit device in electrical communication with a coil assembly having a central core and primary and secondary coils each disposed in winding relation around the core, the coil assembly being operative to transfer power derived from the electromagnetic field to the circuit device, comprising the steps of:

• receiving said electromagnetic field with a first length of conductive wire having open-circuited ends and forming said primary coil;
• converting the energy in said electromagnetic field into an induction power field having a first impedance level;
• receiving said power field with a second length of conductive wire forming said secondary coil and having its ends coupled to said circuit device;
• converting said power field into an electrical power signal having a second impedance level which substantially matches the impedance level of said electromagnetic field;
• and
• transferring said power signal to said circuit device, whereby the quantity of energy transferred from said electromagnetic field to said circuit device is maximized by matching said second impedance level with said first impedance level.

An electronic identification system for transmitting a high intensity electromagnetic field within the proximity of a transponder coil assembly inductively coupled to the high intensity field, the transponder coil assembly being operative to transfer power derived from the high intensity field to an integrated circuit device in electrical communication with the coil assembly and to retransmit a low intensity electromagnetic field which is detected by the identification system, comprising:

• a transmission and detection apparatus for transmitting said high intensity field and detecting the presence of said low intensity field emanating from said transponder coil assembly despite the presence of said high intensity field;
• and
• a transponder coil assembly, including:
• a core;
• first transponder coil means including a first length of wire disposed in winding relation around said core and with its ends open-circuited, and operative to receive said high intensity field and to convert the energy within said high intensity field into an induction power field having a first impedance level;
• and
• second transponder coil means disposed in winding relation around said core and operative to receive said power field, to convert the energy is said power field into an electrical power signal having a second impedance level, and to output said power signal to said integrated circuit device, whereby the power transferred to said circuit device is at said second impedance level and is sufficient to induce said circuit device to produce an identification signal for retransmission by said transponder coil assembly to said transmission and detection apparatus.

A transponder device for receiving transmitted electromagnetic energy and transmitting a responsive signal, comprising:

• a nonconductive substrate forming a support member for various components of said transponder device;
• means forming a transponder circuit affixed to said substrate;
• a magnetic core affixed to said substrate;
• first coil means disposed in winding relation about said core and including a first number of turns, the ends of said first coil means being open-circuited;
• and
• second coil means disposed in winding relation about said core and being electrically connected to said transponder circuit, said second coil means including a second number of turns substantially fewer in number than said first number of turns, said first and second coil means being inductively coupled together and operative to collect said transmitted electromagnetic energy and provide electric power to said transponder circuit.