Activatable/deactivatable security tag for use with an electronic security system

Claim 2

A security tag for use with an electronic security system for a controlled area, the security system including transmitter means for transmitting into the controlled area electromagnetic energy within a predetermined detection frequency range and receiver means for detecting within the controlled area the presence of a security tag (10) resonating, in response to the electromagnetic energy, the tag (10) comprising: circuitry means for initially establishing a resonant circuit (14) having a first resonating frequency (f1) within a first frequency range which is outside of the detection frequency range; first means (C2, C4) for changing the resonating frequency of the resonant circuit to a second frequency (f2), within the detection frequency range, when the resonant circuit (14) is exposed to electromagnetic energy within the first frequency range of at least a predetermined minimum power level; and second means (C1, C3) for changing the resonating frequency of the resonant circuit (14') to a third frequency (f3) within a third frequency range which is outside of the detection frequency range when the resonant circuit (14') is exposed to electromagnetic energy within the detection frequency range of at least a predetermined minimum power level.

Claim 3

The security tag as recited in claim 1 wherein the circuitry means initially comprises: an inductance (L); a first capacitance branch (24) connected in parallel with the inductance (L), the first capacitance branch (24) including a first capacitor (C1) connected in series with a second capacitor (C2); and a second capacitance branch (26) connected in parallel with the inductance (L) and the first capacitance branch (24), the second capacitance branch (26) including a third capacitor (C3) connected in series with a fourth capacitor (C4).

Claim 4

The security tag as recited in claim 2 wherein the first means comprises one of the second and fourth capacitors (C2, C4) and wherein the second means comprises the other of the second and fourth capacitor (C2, C4), the second and fourth capacitors (C2, C4) each including fusing means (38) for short-circuiting one of said second and fourth capacitors (C2, C4) upon exposure to said electromagnetic energy within the first frequency range for changing the resonating frequency of the resonant circuit (14) from said first frequency (f1) to said second frequency (f2) and for short-circuiting the other of said second and fourth capacitors (C2, C4) upon to exposure to said electromagnetic energy within the detection frequency range for changing the resonating frequency of the resonant circuit from said second frequency (f2) to said third frequency (f3).

Claim 5

The security tag as recited in claim 3 wherein the first and third capacitors (C1, C3) are generally of the same capacitance and wherein the second and fourth capacitors (C2, C4) are generally of the same capacitance.

Claim 6

The security tag as recited in claim 1 wherein the first frequency range is higher than the detection frequency range and the third frequency range is lower than the detection frequency range.

Claim 7

A security tag for use with an electronic security system for a controlled area, the security system including transmitter means for transmitting into the controlled area electromagnetic energy within a predetermined detection frequency range and receiver means for detecting within the controlled area the presence of a tag (10) resonating, in response to the electromagnetic energy, the tag (10) comprising: a resonant circuit (14) having a first resonating frequency within a first frequency range which is outside of the detection frequency range, the circuit comprising an inductance (L), a first capacitance branch (24) connected in parallel with the inductance (L), the first capacitance branch (24) including a first capacitor (C1) connected in series with a second capacitor (C2), and a second capacitance branch (26) connected in parallel with the inductance (L) and the first capacitance branch (24), the second capacitance branch (26) including a third capacitor (C3) connected in series with a fourth capacitor (C4); the capacitance of the first and third capacitors (C1, C3) being generally the same and the capacitance of the second and fourth capacitors (C2, C4) being generally the same, the second and fourth capacitors each including a fusing means (38) for selectively short circuiting said second and fourth capacitors (C2, C4) whereby when the resonant circuit (14) is exposed to electromagnetic energy within the first frequency range of at least a predetermined minimum power level, one of the second and fourth capacitors (C2, C4) is short circuited to change the resonating frequency (f1) of the resonant circuit (14) to a second frequency (f2) within the detection frequency range and when the resonant circuit (14') is thereafter exposed to electromagnetic energy within the detection frequency range of at least a predetermined minimum power level, the other of the second and fourth capacitors (C2, C4) is short circuited to change the resonating frequency (f2) of the resonant circuit (14') to a third frequency (f3) within a third frequency range which is outside of the detection frequency range.

Claim 8

A security tag for use with an electronic security system for a controlled area, the security system including transmitter means for transmitting into the controlled area electromagnetic energy within a predetermined detection frequency range and receiver means for detecting within the controlled area the presence of a tag (10) resonating, in response to the electromagnetic energy, the tag (10) comprising: a resonant circuit (14) having a first resonating frequency within a first frequency range which is outside of the detection frequency range, the circuit comprising an inductance (L), a first capacitance branch (24) connected in parallel with the inductance (L), the first capacitance branch (24) including a first capacitor (C1) connected in series with a second capacitor (C2), and a second capacitance branch (26) connected in parallel with the inductance (L) and the first capacitance branch (24), the second capacitance branch (26) including a third capacitor (C3) connected in series with a fourth capacitor (C4); the capacitance of the first and third capacitors (C1, C3) being generally the same and the capacitance of the second and fourth capacitors (C2, C4) being generally the same, the second and fourth capacitors each including a fusing means (38) for selectively short circuiting said second and fourth capacitors (C2, C4) whereby when the resonant circuit (14) is exposed to electromagnetic energy within the first frequency range of at least a predetermined minimum power level, one of the second and fourth capacitors (C2, C4) is short circuited to change the resonating frequency (f1) of the resonant circuit (14) to a second frequency (f2) within the detection frequency range and when the resonant circuit (14') is thereafter exposed to electromagnetic energy within the detection frequency range of at least a predetermined minimum power level, the other of the second and fourth capacitors (C2, C4) is short circuited to change the resonating frequency (f2) of the resonant circuit (14') to a third frequency (f3) within a third frequency range which is outside of the detection frequency range.

Claim 9

The security tag as recited in claim 6 wherein the first frequency range is higher than the detection frequency range and the third frequency range is lower than the detection frequency range.

Claim 10

A security tag for use with an electronic security system for a controlled area, the security system including transmitter means for transmitting into the controlled area electromagnetic energy within a predetermined detection frequency range and receiver means for detecting within the controlled area the presence of a tag (10) resonating, in response to the electromagnetic energy, the tag (10) comprising: circuitry means for initially establishing a resonant circuit (14') having a first resonating frequency (f1) within the detection frequency range; and means (C2, C4) for changing the resonating frequency (f2) of the resonant circuit (14') to a frequency (f3) outside of the detection frequency range when the resonant circuit (14') is exposed to electromagnetic energy within the detection frequency range of at least a predetermined minimum power level.

Claim 11

A security tag for use with an electronic security system for a controlled area, the security system including transmitter means for transmitting into the controlled area electromagnetic energy within a predetermined detection frequency range and receiver means for detecting within the controlled area the presence of a tag (10) resonating, in response to the electromagnetic energy, the tag (10) comprising: circuitry means for initially establishing a resonant circuit (14') having a first resonating frequency (f1) within the detection frequency range; and means (C2, C4) for changing the resonating frequency (f2) of the resonant circuit (14') to a frequency (f3) outside of the detection frequency range when the resonant circuit (14') is exposed to electromagnetic energy within the detection frequency range of at least a predetermined minimum power level.

Claim 12

The security tag as recited in claim 8 wherein the circuitry means comprises: an inductance (L); a capacitance branch (24) connected in parallel with the inductance (L), the capacitance branch (24) including first and second capacitors (C1, C3) connected in series, one of said first and second capacitors (C1, C3) including fusing means (38) for selectively short circuiting said one capacitor when the resonant circuit (14') is exposed to said electromagnetic energy within the detection frequency range of at least said predetermined minimum power level.

Claim 15

The method as recited in claim 10 further comprising the step of: determining that the tag has been deactivated by confirming that the resonating frequency of the resonant circuit is within the third frequency range.