RF tagging system including RF tags with variable frequency resonant circuits

An RF tag comprising:

• resonant circuit means for being resonant at any one of a plurality of different frequencies within a frequency range;
• receiver means for receiving an interrogation signal;
• and
• control means responsive to receipt of an interrogation signal by said receiver means for causing said resonant circuit means to be resonant at selected ones of said different frequencies in a predetermined time sequence.

An RF tag comprising:

• a plurality of resonant circuits, each said resonant circuit being resonant within a respective different frequency range and at any one of a plurality of different frequencies within mid range;
• receiver means for receiving an interrogation signal;
• and
• control means responsive to receipt of said interrogation signal by said receiver means for causing each of said resonant circuits to be resonant at selected ones of said different frequencies in a predetermined time sequence.

An RF tag comprising:

• a plurality of resonant circuits, each said resonant circuit being resonant at a different frequency;
• receiver means for receiving an interrogation signal;
• and
• control means responsive to receipt of said interrogation signal by said receiver means for causing said resonant circuits to be resonant at selected frequencies in a predetermined time sequence.