Multiple frequency tag

A method of making a multiple frequency composite security tag comprising the steps of:

• (a) providing a first security tag having a first resonant circuit including a first inductor coil, the first resonant circuit having a first predetermined resonant frequency;
• (b) providing a second security tag having a second resonant circuit including a second inductor coil, the second resonant circuit having a second predetermined resonant frequency;
• and
• (c) positioning the first and second security tags with respect to each other so that the first inductor coil partially overlies the second inductor coil in a manner which minimizes magnetic coupling between the first and second coils.

A method of detecting the presence within a surveilled area of a security tag having multiple resonant circuits which resonate at different frequencies within a detection frequency range, the method comprising the steps of:

• establishing an electromagnetic field within the surveilled area, the frequency of the electromagnetic field varying within the detection frequency range;
• detecting disturbances within the surveilled area caused by resonances within the electromagnetic field;
• comparing the frequencies of the detected disturbances with the predetermined resonant frequencies of the security tag;
• and
• confirming the presence of a security tag within the surveilled area only if a disturbance is detected at each predetermined resonant frequency of the security tag, wherein each resonant circuit of the security tag partially overlies at least one other resonant circuit of the security tag in a manner which minimizes magnetic coupling between said overlying circuits.