System and method for electronic article surveillance

• US 7,755,485 B2
• Filed: 03/08/2005
• Issued: 07/13/2010
• Est. Priority Date: 03/08/2005
• Status: Expired due to Fees

• Current Assignee: InPoint Systems, Inc.
• Original Assignee: InPoint Systems, Inc.
• Inventors: Howard, Richard E., Fenson, Eitan M.
• Primary Examiner(s): Pham; Toan N
• Assistant Examiner(s): MCNALLY, KERRI L
• Application Number:
  US11/076,576
• Publication Number:
  US 20060203838A1
• Time in Patent Office: 1,953 Days
• Field of Search: 340/568.1, 340/571, 340/572.1, 340/10.1, 340/442, 342/42, 455/39
• US Class Current: 340/572.1
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• CPC Class Codes: G08B 13/2482 EAS methods, e.g. description of flow chart of the detection procedure
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

An EAS tag polling system includes a plurality of EAS tags and a base station, wherein each of the tags transmits an acknowledgement to the base station. The base acknowledgments may be sent passively or actively in response to a request from the base station. The base station discriminates between each acknowledgment received and associates it to the tag from which it had been transmitted. From each acknowledgement received, the base station indicates that a positive response is associated with each of the tags from which the acknowledgement is received and a negative response is associated with each of the tags from which the acknowledgement is not received.

Claims

1. A system for electronic article surveillance, the system comprising:

a base station and a plurality of active RF tags being operable to attach to articles under surveillance,

wherein each of said RF tags being operative to repeatedly initiate, independently from other tags and the base station, an unsolicited radio transmission of a signal having a unique identifying characteristic of said RF tag; and

wherein the base station comprises

a receiver operative to receive a radio transmission from a RF tag,

a memory operative to store a lookup table containing a plurality of key entries corresponding to each of the plurality of RF tags, and

a processor operably coupled to the receiver and to the memory, the processor being operative to obtain from the received radio transmission an identifying characteristic of an RF tag and to determine whether said identifying characteristic corresponds to one of the key entries in the lookup table, wherein, in the event said identifying characteristic corresponds to one of said key entries, the processor sets a flag associated with said one of said key entries, said flag being an indication that a positive response is associated with the RF tag from which said radio transmission is received.

2. The system as set forth in claim 1 further comprising at least one repeater operationally interposed at least one of said tags and said base station such that a transmission range of said at least one of said tags is extended to said base station.

3. The system as set forth in claim 2 further comprising at least one further repeater operationally interposed said at least one repeater and said base station such that said transmission range of said at least one of said tags is further extended to said base station.

4. The system as set forth in claim 1 wherein each of said tags is further operative to transmit said signal with a preselected temporality.

5. The system as set forth in claim 4 wherein each of said tags is operative to transmit said signal with a continuous temporality.

6. The system as set forth in claim 4 wherein each of said tags is operative to transmit said signal with a periodic temporality.

7. The system as set forth in claim 4 wherein each of said tags is operative to transmit said signal with an intermittent temporality.

8. The system as set forth in claim 4 wherein each of said tags is operative to transmit said signal with a random temporality.

9. The system as set forth in claim 8 wherein said base station is operative to discriminate between said signal transmitted from each one of said tags using a time slot of each transmitted signal.

10. The system as set forth in claim 4 wherein said temporality differs between a first group of said tags and a second group of said tags.

11. The system as set forth in claim 1 wherein said positive response is minimally indicative that each of said tags with which said positive response is associated is present and operable within said system.

12. The system as set forth in claim 11 wherein said signal transmitted from each of said tags is a frequency pulse.

13. The system as set forth in claim 1 wherein the processor being further operative to set a second flag associated with one of said key entries for which no radio transmission has been received by the base station from a RF tag associated with said one of said key entries, wherein said second flag being an indication that a negative response is associated with the RF tag associated with said one of said key entries.

14. The system as set forth in claim 1 wherein said identifying characteristic is a unique pattern of one or more codes for said signal transmitted from each respective one of said tags.

15. The system is set forth in claim 14 wherein said base station is operative to discriminate between said signal transmitted from each one of said tags using the unique pattern of one or more codes in one or more transmitted signals.

16. The system as set forth in claim 1 wherein said identifying characteristic is a different frequency for each signal transmitted from each respective one of said tags.

17. The system as set forth in claim 16 wherein said base station is operative to discriminate between said signal transmitted from each one of said tags using the frequency of each transmitted signal.

18. The system as set forth in claim 1 wherein said identifying characteristic is a different time slot for each signal transmitted from each respective one of said tags.

19. The system as set forth in claim 1 wherein said identifying characteristic is a key uniquely identifying each respective one of said tags placed in said signal transmitted from each respective one of said tags.

20. The system as set forth in claim 19 wherein each of said tags includes a memory, said key being stored in said memory.

21. The system as set forth in claim 20 wherein said memory is nonvolatile.

22. The system as set forth in claim 20 wherein said memory is flash memory.

23. The system as set forth in claim 20 wherein each of said tags further includes a tag transmitter, said key being applied to said tag transmitter in each of said tags, said tag transmitter in each of said tags being operative to transmit said signal from each of said tags.

24. The system as set forth in claim 23 wherein said signal transmitted from each of said tags is minimally said key unique to each of said tags.

25. The system as set forth in claim 1 wherein each of said tags is further operative to develop a timing pulse, said signal being transmitted from each of said tags in response to said timing pulse.

26. The system as set forth in claim 25 wherein each of said tags includes the tag transmitter and a clock counter to provide a binary count of a number of clock pulses applied thereto, said clock counter having a plurality of output bits, said timing pulse being developed in response to a selected one of said output bits transitioning from a first binary state to a second binary state, said tag transmitter transmitting said signal in response to said timing pulse.

27. The system as set forth in claim 26 wherein said timing pulse is developed in response to a logical combination of selected ones of said output bits transitioning from said first binary state to said second binary state.

28. The system as set forth in claim 26 wherein said selected one of said output bits is the same in each of said tags.

29. The system as set forth in claim 26 wherein said selected one of said output bits is different in each of said tags.

30. The system as set forth in claim 26 wherein said selected one of said output bits is the same in one group of said tags but different from said selected one of said output bits in another group of said tags.

31. The system as set forth in claim 26 wherein each of said tags further includes a clock to develop said clock pulses.

32. The system as set forth in claim 26 wherein said base station includes a clock to develop said clock pulses and a base station transmitter to which said clock pulses are applied and wherein each of said tags further includes a tag receiver, said base station transmitter transmitting said clock pulses, said tag receiver receiving said clock pulses and applying said clock pulses to said clock counter.

33. The system as set forth in claim 32 wherein said tag receiver further converts RF energy of the carrier of said clock pulses to DC power.

34. The system as set forth in claim 1 wherein for one of said tags with which said positive response has been associated, said base station is further operative to determine that a negative response is to be associated with said one of said tags in the event said signal ceases to be received from said one of said tags.

35. The system as set forth in claim 34 wherein said negative response is associated with said one of said tags upon expiration of a selected time duration from last receipt of said signal received from said one of said tags.

36. The system as set forth in claim 35 wherein said one of said tags is operative to transmit said signal there from with a preselected temporality, said selected time duration being commensurate with said temporality.

37. The system as set forth in claim 36 wherein each of said tags is operative to transmit periodically said signal, said selected time duration being commensurate with a periodicity of said signal.

38. The system as set forth in claim 34 wherein said base station is further operative to transmit a request to said one of said tags from which said signal is not received prior to said negative response being associated with said one of said tags, said one of said tags being further operative in response to said request to retransmit said signal, said base station being further operative to indicate that said positive response is associated with said one of said tags in the event said retransmitted signal is received by said base station and said negative response is associated with said one of said tags in the event said retransmitted signal is not received by said base station.

39. The system as set forth in claim 38 wherein said request includes an identifying characteristic of one of said tags, said one of said tags being further operative to verify that said identifying characteristic of said request corresponds to said identifying characteristic of said signal transmitted from said one of said tags such that upon verification said one of said tags is operative to retransmit said signal.

40. The system as set forth in claim 39 wherein said identifying characteristic in each of said request and said signal transmitted from said one of said tags is a key uniquely identifying said one of said tags.

41. The system as set forth in claim 34 wherein said base station includes a processor and a clock counter to which a plurality of clock pulses are applied, said clock counter having a reset input and a plurality of output bits at which a count of said clock pulses is developed, said processor applying a reset pulse to said reset input upon said processor setting a flag to indicate that said positive response has been associated with said one of said tags, said negative response to be associated with said one of said tags upon a selected one of said output bits transitioning from a first binary state to a second binary state.

42. The system as set forth in claim 41 wherein said processor removes said flag in response to said selected one of said output bits transitioning from said first binary state to said second binary state.

43. A system for electronic article surveillance, the system comprising:

a wireless base station comprising a clock counter that provides a binary count of a number of clock pulses applied thereto, said clock counter having a plurality of output bits, and a transmitter operable to generate a sync pulse in response to a selected one of said output bits transitioning from a first binary state to a second binary state; and

a plurality of active RF tags being operable to attach to articles under surveillance, wherein each of said RF tags being operative to repeatedly initiate, independently from other RF tags an unsolicited radio transmission of a signal having a unique identifying characteristic of said RF tag and wherein each of said tags being responsive to said sync pulse from the base station to adjust the timing of the repetitive radio transmissions.

44. The system as set forth in claim 43 wherein said sync pulse is developed in response to a logical combination of selected ones of said output bits transitioning from said first binary state to said second binary state.

45. The system as set forth in claim 43 wherein said base station further includes a clock to develop said clock pulses.

46. The system as set forth in claim 43 wherein each of said tags is operative to transmit said signal after a selected time delay from receipt of said sync pulse wherein said time delay for each of said tags is selected such that said signal transmitted from each of said tags is received in succession at said base station.

47. The system as set forth in claim 46 wherein each of said tags includes a tag receiver, a clock counter to provide a binary count of a number of clock pulses applied thereto, said clock counter having a reset input and the plurality of output bits, said sync pulse being received by said tag receiver and said tag receiver applying said sync pulse to said reset input, said tag transmitter transmitting said signal in response to a timing pulse developed upon said selected one of said output bits changing state.

48. The system as set forth in claim 47 wherein said selected one of said output bits is different in each one of said tags.

49. A system for electronic article surveillance, the system comprising:

a base station and a plurality of active RF tags being operable to attach to articles under surveillance,

wherein each of said RF tags being operative to repeatedly initiate, independently from other tags and the base station, an unsolicited radio transmission of a signal containing a data content, wherein the data content for each of said RF tags is variant in accordance with a function that implements an algorithm and wherein said data content for each of said RF tags is developed in accordance with said function from a seed value used by said algorithm wherein said seed value is stored in each of said tags; and

wherein the base station being operative to receive a radio transmission from an RF tag and obtain data content from the received radio transmission, wherein said base station being knowledgeable of said function to verify said data content obtained from the radio transmission from said RF tag such that when verified said data content is valid and a positive response is associated with said RF tag and when not verified said data content is invalid and a negative response is associated with said RF tag.

50. The system as set forth in claim 49 wherein said data content is identical for two or more of said tags.

51. The system as set forth in claim 49 wherein said data content is different for each of said tags.

52. The system as set forth in claim 49 wherein said data content for each of said tags is a preselected bit string.

53. The system as set forth in claim 52 wherein said data content is a bit pattern of said preselected bit string, said base station recognizing said bit pattern to verify said data content.

54. The system as set forth in claim 49 wherein said data content for each of said tags is variant as a function of time.

55. The system as set forth in claim 49 wherein said data content for each one of said tags is variant as a function of a number of instances said signal is transmitted from a same one of said tags.

56. The system as set forth in claim 49 wherein said seed value is identical in each of said tags.

57. The system as set forth in claim 49 wherein said seed value is different in each of said tags.

58. The system as set forth in claim 49 wherein said seed value is an initialized bit string.

59. The system as set forth in claim 49 wherein said base station is further knowledgeable of said seed value stored in each of said tags to develop expected data content with which to verify said data content in said signal received from each of said tags.

60. The system as set forth in claim 59 wherein said base station is further operative to compare said expected data content to said data content in said signal received from each of said tags wherein said positive response is associated with each of said tags for which the comparison is positive and said negative response is associated with each of said tags for which the comparison is negative.

61. The system as set forth in claim 49 wherein each one of said tags includes a memory in which said seed is stored, a tag clock counter to which a succession of clock pulses is applied and having a plurality of output bits at which a count of said clock pulses is developed, a logic circuit to which each of said seed and at least one of said output bits of said count are applied to develop an output bit string applied to said transmitter, said transmitter being operative to transmit said signal wherein said output bit string is said data content in said signal.

62. The system as set forth in claim 61 wherein each of said tags further includes a register into which said output bit string is serially clocked and further wherein contents of said register is applied to said transmitter in response to a timing pulse.

63. The system as set forth in claim 62 wherein a current value of said at least one of said output bits of said clock counter is added to the contents of said register upon said timing pulse being developed such that said data content contains said at least one of said output bits and the contents of said register.

64. The system as set forth in claim 63 wherein a current value of said output bits is added to the contents of said register.

65. The system as set forth in claim 62 wherein said timing pulse is developed in response to a selected one of said output bits of said clock counter transitioning from a first binary state to a second binary state.

66. The system as set forth in claim 61 wherein each of said tags further includes a clock to develop said succession of clock pulses.

67. The system as set forth in claim 61 wherein said base station includes a processor, a lookup table containing said seed associated with each of said tags, a clock to develop said succession of clock pulses, a base station clock counter having a plurality of output bits at which a count of said clock pulses is developed and a transmitter operative to transmit said clock pulses to each of said tags, each of said tags further including a receiver to receive said clock pulses and to apply said clock pulses to said tag clock counter, said base station clock counter developing a value at least one of said output bits of said base station clock counter in lockstep with said at least one of said output bits of said tag clock counter, said processor developing expected data content from each of said seed in said lookup table associated with said one of said tags and said at least one of said output bits of said base station, clock counter in accordance with said algorithm as implemented by said logic circuit, said processor verifying said data content in said signal received from each of said tags to said expected data content developed for each of said tags.

68. The system as set forth in claim 67 wherein said processor is further operative to develop a sync pulse to reset each of said base station clock counter and said tag clock counter in each of said tags, each of said tags being responsive to said sync pulse to reset said counter.

69. The system as set forth in claim 68 wherein said base station further includes a transmitter to transmit said sync pulse to each of said tags and wherein each of said tags operative to receive using the receiver said sync pulse and to apply said sync pulse to said counter.

70. The system as set forth in claim 49 wherein each respective one of said tags includes a memory in which said seed is stored, an instance counter having a plurality of output bits at which a count of a number of instances of said signal has been transmitted from said respective one of said tags, a logic circuit to which each of said seed and said count are applied and operative to develop an output bit string, and a transmitter to which said output bit string is applied, said transmitter being operative to transmit said signal.

71. The system as set forth in claim 70 wherein each of said tags further includes a register into which said output bit string is serially clocked and further wherein contents of said register is applied to said transmitter in response to a timing pulse.

72. The system as set forth in claim 71 wherein said instance counter is incremented in response to said timing pulse.

73. The system is set forth in claim 71 wherein each respective one of said tags further includes a clock counter to which a succession of clock pulses is applied to develop a binary count of said clock pulses, said clock counter having a selected output bit, said timing pulse being developed in response to said selected output bit transitioning from a first binary state to a second binary state.

74. The system as set forth in claim 73 wherein each of said tags further includes a clock to develop said succession of clock pulses.

75. The system as set forth in claim 73 wherein said base station includes a clock to develop said succession of clock pulses and a transmitter operative to transmit said clock pulses to each of said tags, each of said tags further including a receiver to receive said clock pulses and to apply said clock pulses to said clock counter.

76. The system as set forth in claim 70 wherein said base station is further operative to develop a sync pulse, each of said tags being responsive to said sync pulse to reset said instance counter.

77. The system as set forth in claim 76 wherein each of said tags further includes a receiver operative to receive said sync pulse and to apply said sync pulse to said instance counter.

78. The system as set forth in claim 49 wherein each of said tags includes:

a n-bit wide shift register having a plurality of cascaded gates, said seed being applied as a bit string to said shift register, each of said gates having a Q and a Q output; and

a logic circuit having a plurality of inputs and an output, each of said inputs being connected to a selected one of said Q and said Q output of a corresponding one of said gates, said data content of said signal being an output bit string developed at said output.

79. The system as set forth in claim 78 wherein each of said tags further includes a memory to store said seed.

80. The system as set forth in claim 78 wherein said seed is transmitted to each of said tags by said base station.

81. The system as set forth in claim 78 wherein a number, of said inputs is less than a number of said gates.

82. The system as set forth in claim 78 wherein each of said gates further has a D input, said D input being selectively connected to one of said Q output and said Q output of an immediately preceding one of said gates.

83. The system as set forth in claim 78 further comprising a standard gate to which said seed and an output bit of a selected one of said Q output and said Q output of a least significant one of said gates are applied.

84. The system as set forth in claim 78 wherein each of said tags further includes:

a buffer containing said output bit string from said output;

a counter containing a count of a selected one of clock pulses applied to said counter and each instance of said signal being transmitted from each respective one of said tags, said counter having a plurality of output bits; and

a second logic circuit operative to combine logically said output bit string in said buffer with at least one of said output bits of said counter whereby said data content for signal for each respective one of said tags is developed.

85. The system as set forth in claim 78 wherein said seed is bitwise clocked into said shift register such that each bit of said output bit string is developed as each bit of said seed is applied to said shift register.

86. The system as set forth in claim 85 wherein each of said tags further includes a tag transmitter, said output bit string being bitwise applied to said transmitter.

87. The system as set forth in claim 78 wherein said base station is further knowledgeable of said seed value stored in each of said tags to develop expected data content with which to verify said data content in said signal received from each of said tags.

88. The system as set forth in claim 87 wherein said base station is further operative to compare said expected data content to said data content in said signal received from each of said tags wherein said positive response is associated with each of said tag for which the comparison is positive and said negative response is associated with each of said tags for which the comparison is negative.

89. The system as set forth in claim 88 wherein said base station includes a receiver to receive said signal from each one of said tags and a processor operative to read said data content in said signal from each one of said tags and compare said data content to said expected data for each one of said tags.

90. The system as set forth in claim 87 wherein said processor is further operative to generate contemporaneously said expected data for each one of said tags.

91. A method for electronic article surveillance, the method comprising:

receiving, at a base station, an unsolicited radio transmission of a signal from at least one of a plurality of active RF tags attached to articles under surveillance, the radio transmission being initiated by said at least one RF tag independent of the base station and of other of the plurality of RF tags, wherein said signal having a unique identifying characteristic of said at least one RF tag;

accessing, in a memory of the base station, a lookup table containing a plurality of key entries corresponding to each of the plurality of RF tags;

determine whether the identifying characteristic of said at least one RF tag corresponds to one of the key entries in the lookup table; and

in the event said identifying characteristic corresponds to one of said key entries, setting a flag associated with said one of said key entries, wherein said flag being an indication that a positive response is associated with said at least one RF tag.

92. The method as set forth in claim 91 further comprising providing at least one repeater operationally interposed at least one of said tags and said base station such that a transmission range of said at least one of said tags is extended to said base station.

93. The method as set forth in claim 92 further comprising providing at least one further repeater operationally interposed said at least one repeater and said base station such that said transmission range of said at least one of said tags is further extended to said base station.

94. The method as set forth in claim 93 wherein each of said tags is further operative to transmit said signal with a preselected temporality.

95. The method as set forth in claim 94 wherein each of said tags is operative to transmit said signal with a continuous temporality.

96. The method as set forth in claim 94 wherein each of said tags is operative to transmit said signal with a periodic temporality.

97. The method as set forth in claim 94 wherein each of said tags is operative to transmit said signal with an intermittent temporality.

98. The method as set forth in claim 94 wherein each of said tags is operative to transmit said signal with a random temporality.

99. The method as set forth in claim 94 wherein said signal temporality differs between a first group of said tags and a second group of said tags.

100. The method as set forth in claim 91 wherein said positive response is minimally indicative that each of said tags with which said positive response is associated is present and operable within said system.

101. The method as set forth in claim 100 wherein said signal transmitted from each of said tags is a frequency pulse.

102. The method as set forth in claim 91 wherein said signal transmitted from each of said tags further includes an informational characteristic, said base station being further knowledgeable of and operative to verify said informational characteristic in said signal transmitted from each of said tags such that a negative response is associated with anyone of said tags for which said informational characteristic in said transmitted therefrom fails verification.

103. The method as set forth in claim 91 wherein said identifying characteristic is a unique pattern of one or more codes for said signal transmitted from each respective one of said tags.

104. The method as set forth in claim 103 wherein said base station is operative to discriminate between said signal transmitted from each one of said tags using the unique pattern of one or more codes in one or more transmitted signal.

105. The method as set forth in claim 91 wherein said identifying characteristic is a different frequency for each signal transmitted from each respective one of said tags.

106. The method as set forth in claim 105 wherein said base station is operative to discriminate between said signal transmitted from each one of said tags using the frequency of each transmitted signal.

107. The method as set forth in claim 91 wherein said identifying characteristic is a different time slot for each signal transmitted from each respective one of said tags.

108. The method as set forth in claim 107 wherein said base station is operative to discriminate between said signal transmitted from each one of said tags using the time slot of each transmitted signal.

109. The method as set forth in claim 91 wherein said identifying characteristic is a key uniquely identifying each respective one of said tags placed in said signal transmitted from each respective one of said tags.

110. The method as set forth in claim 109 wherein each of said tags includes a memory, said key being stored in said memory.

111. The method as set forth in claim 110 wherein said memory is nonvolatile.

112. The method as set forth in claim 110 wherein said memory is flash memory.

113. The method as set forth in claim 110 wherein each of said tags further includes a tag transmitter, said key being applied to said tag transmitter in each of said tags, said tag transmitter in each of said tags being operative to transmit said signal from each of said tags.

114. The method as set forth in claim 113 wherein said signal transmitted from each of said tags is minimally said key unique to each of said tags.

115. The method as set forth in claim 91 wherein each of said tags is further operative to develop a timing pulse, said signal being transmitted from each of said tags in response to said timing pulse.

116. The method as set forth in claim 115 wherein each of said tags includes a tag transmitter and a clock counter to provide a binary count of a number of clock pulses applied thereto, said clock counter having a plurality of output bits, said timing pulse being developed in response to a selected one of said output bits transitioning from a first binary state to a second binary state, said tag transmitter transmitting said signal in response to said timing pulse.

117. The method as set forth in claim 116 wherein said timing pulse is developed in response to a logical combination of selected ones of said output bits transitioning from said first binary state to said second binary state.

118. The method as set forth in claim 116 wherein said selected one of said output bits is the same in each of said tags.

119. The method as set forth in claim 116 wherein said selected one of said output bits is different in each of said tags.

120. The method as set forth in claim 116 wherein said selected one of said output bits is the same in one group of said tags but different from said selected one of said output bits in another group of said tags.

121. The method as set forth in claim 116 wherein each of said tags further includes a clock to develop said clock pulses.

122. The method as set forth in claim 116 wherein said base station includes a clock to develop said clock pulses and a base station transmitter to which said clock pulses are applied and wherein each of said tags further includes a tag receiver, said base station transmitter transmitting said clock pulses, said tag receiver receiving said clock pulses and applying said clock pulses to said clock counter.

123. The method as set forth in claim 122 wherein said tag receiver further converts RF energy of the carrier of said clock pulses to DC power.

124. The method as set forth in claim 91 wherein for one of said tags with which said positive response has been associated, said base station is further operative to determine that a negative response is to be associated with said one of said tags in the event said signal ceases to be received from said one of said tags.

125. The method as set forth in claim 124 wherein said negative response is associated with said one of said tags upon expiration of a selected time duration from last receipt of said signal received from said one of said tags.

126. The method as set forth in claim 124 wherein said one of said tags is operative to transmit said signal there from with a preselected temporality, a selected time duration being commensurate with said temporality.

127. The method as set forth in claim 126 wherein each of said tags is operative to transmit periodically said signal, said selected time duration being commensurate with a periodicity of said signal.

128. The method as set forth in claim 124 wherein said base station includes a processor and a clock counter to which a plurality of clock pulses are applied, said clock counter having a reset input and a plurality of output bits at which a count of said clock pulses is developed, said processor applying a reset pulse to said reset input upon said processor setting a flag to indicate that said positive response has been associated with said one of said tags, said negative response to be associated with said one of said tags upon a selected one of said output bits transitioning from a first binary state to a second binary state.

129. The method as set forth in claim 128 wherein said processor removes said flag in response to said selected one of said output bits transitioning from said first binary state to said second binary state.

130. The method as set forth in claim 128 wherein said processor is further operative to develop a request to retransmit said signal wherein said request is to be transmitted to said one of said tags in response to said selected one of said output bits transitioning from said first binary state to said second binary state.

131. The method as set forth in claim 130 wherein said processor maintains said flag in the event a retransmitted signal is received from said one of said tags in response to said request such that said positive response continues to be associated with said one of said tags.

132. The method as set forth in claim 131 wherein said processor applies a reset pulse to said clock counter upon said retransmitted signal being received by said base station.

133. The method as set forth in claim 130 wherein said processor remove said flag in the event said retransmitted signal is not received by said base station in response to said request such that said negative response is associated with said one of said tags.

134. The method as set forth in claim 130 wherein said processor accessing said lookup table to read said key for said one of said tags to develop said request wherein said request includes said key.

135. A method for electronic article surveillance, the method comprising:

transmitting by a base station a sync pulse to a plurality of active RF tags attached to articles under surveillance;

responsive to the sync pulse, receiving from the plurality of RF tags a succession of radio transmissions of signals having unique identifying characteristics of said RF tags, wherein each signal is transmitted by each of said plurality of RF tags after a selected time delay from receipt of said sync pulse by said RF tags, wherein said time delay for each of said tags is selected such that said signal transmitted from each of said tags is received in succession at said base station;

knowledgeable of said identifying characteristics of said signals, discriminating between said signals transmitted from each of said RF tags, and

indicating that a positive response is associated with each of said tags from which said signal is received and a negative response is associated with each of said tags from which said signal is not received.

136. The method as set forth in claim 135 wherein said base station includes a base station transmitter and a clock counter to provide a binary count of a number of clock pulses applied thereto and wherein each of said tags includes a tag receiver and a tag transmitter, said clock counter having a plurality of output bits, said sync pulse being developed in response to a selected one of said output bits transitioning from a first binary state to a second binary state, said sync pulse being transmitted by said base station transmitter and received by said tag receiver, said tag receiver applying said sync pulse to said tag transmitter, said tag transmitter transmitting said signal in response to said sync pulse.

137. The method as set forth in claim 136 wherein said sync pulse is developed in response to a logical combination of selected ones of said output bits transitioning from said first binary state to said second binary state.

138. The method as set forth in claim 136 wherein said base station further includes a clock to develop said clock pulses.

139. The method as set forth in claim 135 wherein each of said tags includes a tag receiver, a clock counter to provide a binary count of a number of clock pulses applied thereto, said clock counter having a reset input and a plurality of output bits, said sync pulse being received by said tag receiver and said tag receiver applying said sync pulse to said reset input, a tag transmitter transmitting said signal in response to a timing pulse developed upon said selected one of said output bits changing state.

140. The method as set forth in claim 139 wherein said selected one of said output bits is different in each one of said tags.

141. A method for electronic article surveillance using a plurality of active RF tags attached to articles under surveillance, the method comprising:

obtaining a seed value from a memory of a RF tag of said plurality of RF tags;

executing a function that implements an algorithm for generating a data content from the obtained seed value, wherein data content for each of said RF tags is variant in accordance with said function; and

transmitting by said RF tag independently from other tags of said plurality of RF tags an unsolicited radio transmission of a signal containing said generated data content,

wherein the data content obtained from the radio transmission from said RF tag is used by a base station to verify said data content such that when verified said data content is valid and a positive response is associated with said RF tag and when not verified said data content is invalid and a negative response is associated with said RF tag.

142. The method as set forth in claim 141 wherein said data content is identical for two or more of said tags.

143. The method as set forth in claim 141 wherein said data content is different for two or more of said tags.

144. The method as set forth in claim 141 wherein said data content for each of said tags is a preselected bit string.

145. The method as set forth in claim 144 wherein said data content is a bit pattern of said preselected bit string, said base station recognizing said bit pattern to verify said data content.

146. The method as set forth in claim 141 wherein said data content for each of said tags is variant as a function of time.

147. The method as set forth in claim 141 wherein said data content for each one of said tags is variant as a function of a number of instances said signal is transmitted from a same one of said tags.

148. The method as set forth in claim 141 wherein said seed value is identical in each of said tags.

149. The method as set forth in claim 141 wherein said seed value is different in each of said tags.

150. The method as set forth in claim 141 wherein said seed value is an initialized bit string.

151. The method as set forth in claim 141 wherein said base station is further knowledgeable of said seed value stored in each of said tags to develop expected data content with which to verify said data content in said signal received from each of said tags.

152. The method as set forth in claim 151 wherein said base station is further operative to compare said expected data content to said data content in said signal received from each of said tags wherein said positive response is associated with each of said tags for which the comparison is positive and said negative response is associated with each of said tags for which the comparison is negative.

153. The method as set forth in claim 151 wherein each one of said tags includes a tag clock counter to which a succession of clock pulses is applied and having a plurality of output bits at which a count of said clock pulses is developed, a logic circuit to which each of said seed and at least one of said output bits of said count are applied to develop an output bit string applied to a transmitter, said transmitter being operative to transmit said signal wherein said output bit string is said data content in said signal.

154. The method as set forth in claim 153 wherein each of said tags further includes a register into which said output bit string is serially clocked and further wherein contents of said register is applied to said transmitter in response to a timing pulse.

155. The method as set forth in claim 154 wherein a current value of said at least one of said output bits of said clock counter is added to the contents of said register upon said timing pulse being developed such that said data content contains said at least one of said output bits and the contents of said register.

156. The method as set forth in claim 155 wherein a current value of said output bits is added to the contents of said register.

157. The method as set forth in claim 154 wherein said timing pulse is developed in response to a selected one of said output bits of said clock counter transitioning from a first binary state to a second binary state.

158. The method as set forth in claim 153 wherein each of said tags further includes a clock to develop said succession of clock pulses.

159. The method as set forth in claim 153 wherein said base station includes a processor, a lookup table containing said seed associated with each of said tags, a clock to develop said succession of clock pulses, a base station clock counter having a plurality of output bits at which a count of said clock pulses is developed and a transmitter operative to transmit said clock pulses to each of said tags, each of said tags further including a receiver to receive said clock pulses and to apply said clock pulses to said tag clock counter, said base station clock counter developing a value at least one of said output bits of said base station clock counter in lockstep with said at least one of said output bits of said tag clock counter, said processor developing expected data content from each of said seed in said lookup table associated with said one of said tags and said at least one of said output bits of said base station clock counter in accordance with said algorithm as implemented by said logic circuit, said processor verifying said data content in said signal received from each of said tags to said expected data content developed for each of said tags.

160. The method as set forth in claim 159 wherein said processor is further operative to develop a sync pulse to reset each of said base station clock counter and said tag clock counter in each of said tags, each of said tags being responsive to said sync pulse to reset said counter.

161. The method as set forth in claim 160 wherein said base station further includes a transmitter to transmit said sync pulse to each of said tags and wherein each of said tags further includes a receiver operative to receive said sync pulse and to apply said sync pulse to said counter.

162. The method as set forth in claim 141 wherein each respective one of said tags includes an instance counter having a plurality of output bits at which a count of a number of instances of said signal has been transmitted from said respective one of said tags, a logic circuit to which each of said seed and said count are applied and operative to develop an output bit string, and a transmitter to which said output bit string is applied, said transmitter being operative to transmit said signal.

163. The method as set forth in claim 162 wherein each of said tags further includes a register into which said output bit string is serially clocked and further wherein contents of said register is applied to said transmitter in response to a timing pulse.

164. The method as set forth in claim 163 wherein said instance counter is incremented in response to said timing pulse.

165. The method as set forth in claim 163 wherein each respective one of said tags further includes a clock counter to which a succession of clock pulses is applied to develop a binary count of said clock pulses, said clock counter having a selected output bit, said timing pulse being developed in response to said selected output bit transitioning from a first binary state to a second binary state.

166. The method as set forth in claim 165 wherein each of said tags further includes a clock to develop said succession of clock pulses.

167. The method as set forth in claim 165 wherein said base station includes a clock to develop said succession of clock pulses and a transmitter operative to transmit said clock pulses to each of said tags, each of said tags further including a receiver to receive said clock pulses and to apply said clock pulses to said clock counter.

168. The method as set forth in claim 162 wherein said base station is further operative to develop a sync pulse, each of said tags being responsive to said sync pulse to reset said instance counter.

169. The method as set forth in claim 168 wherein each of said tags further includes a receiver operative to receive said sync pulse and to apply said sync pulse to said instance counter.

170. The method as set forth in claim 141 wherein each of said tags includes:

a n-bit wide shift register having a plurality of cascaded gates, said seed being applied as a bit string to said shift register, each of said gates having a Q output and a Q output; and

a logic circuit having a plurality of inputs and an output, each of said inputs being connected to a selected one of said Q output and said Q output of a corresponding one of said gates, said data content of said signal being an output bit string developed at said output.

171. The method as set forth in claim 170 wherein each of said tags further includes a memory to store said seed.

172. The method as set forth in claim 170 wherein said seed is transmitted to each of said tags by said base station.

173. The method as set forth in claim 170 wherein a number, of said inputs is less than a number of said gates.

174. The method as set forth in claim 170 wherein each of said gates further has a D input, said D input being selectively connected to one of said Q output and said Q output of an immediately preceding one of said gates.

175. The method as set forth in claim 170 further comprising a standard gate to which said seed and an output bit of a selected one of said Q output and said Q output of a least significant one of said gates are applied.

176. The method as set forth in claim 170 wherein each of said tags further includes:

a buffer containing said output bit string from said output;

a counter containing a count of a selected one of clock pulses applied to said counter and each instance of said signal being transmitted from each respective one of said tags, said counter having a plurality of output bits; and

a second logic circuit operative to combine logically said output bit string in said buffer with at least one of said output bits of said counter whereby said data content for said signal for each respective one of said tags is developed.